Astronomy

What planet is better than earth to infer solar system configuration?

What planet is better than earth to infer solar system configuration?

The mankind had to work some centuries to infer the real configuration of solar system, starting from greeks, Ptolemeus, until Copernicus, Galilei, Kepler, Newton etc. Is there any planet where we could better/faster determine the configuration?

(For example, having a moon is an advantage. Maybe having two moons(or none) or having a thinner atmosphere or being closer/farther to the sun may helped.)

The area of the question starts from inferring the form of the planet(round) until the discovery and orbits of all eight planets.

PS: The question ignores the fact that life is not possible on another planet. It is from pure astronomical viewpoint. On Neptune you have a different sky, so other questions/answers.


I will argue Mars.

  • A smaller diameter makes it easier to determine the round shape of the planet, and determine the diameter more exactly.
  • A thinner atmosphere and almost no clouds are better conditions for sky observation.
  • The small orbital radius of the Mars moons makes it easy to figure out the distance to them. (For example, Phobos is only in the sky about a third of the time seen from equator). Also, the fact that there are two of them makes two data points to discover Kepler's third law.
  • Closer vicinity of the asteroid belt calls for an earlier discovery of objects with an irregular orbit.
  • The Moon is a much closer example of something orbiting another object than Galileo's discovery of the Jovian moons. "Mars is the centre of the universe" disproved.

I think Mercury has some of the points that Mars has. Plus:
- a highly eccentric orbit, making it more obvious that planets have ellptical orbits,
- no moon, which is great to avoid falling into the pitfall of thinking about being at the center of the universe,
- a very long solar day (about 6 earth months or two mercurian years), leaving plenty of time to study planetary motions


Venus, I propose, because it (almost) doesn't rotate. The winning (aristotelian) argument for geocentrism before Galileo was the idea that everybody's' hats would fly off by the (ethereal) air drag if the Earth rotated any faster than a horse in gallop (let alone at Earth's crazy 465 m/s compared to Venus' 1.8 m/s). Long nights too, as previously said. And with Mercury still as an inner planet, the faces of which to give further Galilean clues.


I would propose Enceladus.

  • Enceladus has diameter smaller than even Mercury.
  • From the nearside of a tidally-locked moon, the parent planet, Saturn, would appear nearly stationary. Being stationary Saturn might be viewed as the “center of the universe” instead.
  • Being on a moon as oppose to the parent planet, with other moons orbiting along with your own, it would seem more apparent that the other celestial bodies did not orbit around your planet/moon.
  • If their were theories proposed that the Saturn was the center of the universe they may disproved by watching the other planets go around the Sun. Which would be easier to notice as a telescope wouldn't be required. Quite unlike the Galilean moons which require a telescope to see.

Ask Ethan: Would An Alien Civilization Classify Earth As An 'Interesting' Planet?

The ideal 'Earth 2.0' will be an Earth-sized, Earth-mass planet at a similar Earth-Sun distance from . [+] a star that's very much like our own. We have yet to find such a world, but are working hard to estimate how many such planets might be out there in our galaxy. With so much data at our disposal, it's puzzling how varied the different estimates are.

NASA Ames/JPL-Caltech/T. Pyle

All across the Universe, trillions of galaxies can be seen, with each one typically containing billions and billions of stars. Here on Earth, life not only arose, thrived, and became complex and differentiated, but intelligent, technologically advanced, and even spacefaring, to a degree. But these last advances — taking us into the space and information ages — are extremely recent, and space is enormous. If an alien civilization saw us, would we even appear interesting from their perspective? Tayte Taliaferro wants to know, asking:

I was thinking about the projection of light through space. My curtain was open and I saw the stars and something from a book popped into my head. It had said that the stars we see are basically reruns. The light is from so long ago, we don't even know if the star still exists or not.
[. ] Whatever signals we send out, or changes in our planet that might be observable to prove intelligent life lives here, would take billions of years to reach anything alive and capable of responding! What do you think?

I think these are great questions to ponder, and that science has an awful lot to say about what aliens would see by looking at Earth.

The orbits of the eight major planets vary in eccentricity and the difference between perihelion . [+] (closest approach) and aphelion (farthest distance) with respect to the Sun. There is no fundamental reason why some planets are more or less eccentric than one another it's simply a result of the initial conditions from which the Solar System formed. However, the odds of a transit are much greater for an inner planet like Mercury, which makes 4 such transits every Earth year and has nearly a 2% chance of a good alignment, than any of the outer planets, which take longer to transit and have much lower odds of a good-enough alignment.

In our Solar System, Earth is a rocky planet with a thin atmosphere that orbits our Sun in what we call the habitable zone: at a distance where liquid water, given an Earth-like atmosphere, can stably exist on the planet's surface. Mars and Venus may potentially lie in that region of space as well, but Venus is presently too hot and Mars is too cold (and with too thin of an atmosphere) for Earth-like life to thrive there.

At present, our two most prolific methods for finding planets outside of the Solar System are:

  1. the stellar wobble method, where an orbiting planet tugs on its parent star, causing it to oscillate along the viewer's line-of-sight, and enabling scientists to determine the planet's period and mass (up to the uncertainty of its orbital orientation), and
  2. the transit method, where an orbiting planet transits across the face of its parent star from the perspective of an external observer, periodically causing the parent star to dim as the planet's disk blocks a portion of the star's light.

The main transit (L) and the detection of the exoplanet dipping behind the parent star (R) of the . [+] Kepler exoplanet KOI-64. The main flux dip is how planetary transits are initially found the additional information helps scientist determine properties beyond merely radius and orbital period.

Lisa J. Esteves, Ernst J. W. De Mooij and Ray Jayawardhana, via http://arxiv.org/abs/1305.3271

If a sufficiently advanced alien civilization were examining Earth from a great distance, and we happened to be at the right orientation for our world to transit across the face of the Sun from their perspective, they'd have extraordinary reasons to be hopeful about finding out our world was inhabited.

It's true: light can only travel at some finite speed (the speed of light), meaning that even the nearest stars are only now receiving signals from our planet that were emitted years or decades ago. More distant stars within our galaxy see Earth as it was centuries or millennia ago, while observers in distant galaxies see us as we were millions or even billions of years ago. Still, signatures that our planet is inhabited could be found from even a few billion light-years away, as aliens could take a spectrum of Earth's atmosphere whenever a transit occurred.

This is an illustration of the different elements in NASA’s exoplanet program, including . [+] ground-based observatories, like the W. M. Keck Observatory, and space-based observatories, like Hubble, Spitzer, Kepler, Transiting Exoplanet Survey Satellite, James Webb Space Telescope, Wide Field Infrared Survey Telescope and future missions. The power of TESS and James Webb combined will reveal the most Moon-like exomoons to date, possibly even in their star's habitable zone, while ground-based 30 meter telescopes, WFIRST, and possibly a next-generation space-based observatory like LUVOIR or HabEx is required to truly find what humanity has been dreaming of for so long: an inhabited world outside of our Solar System.

As Earth passes in front of the Sun (or any planet passes in front of its parent star), the starlight that collides with:

  • the surface of Earth simply gets blocked, causing a flux dip announcing the planet's presence,
  • nothing at all, missing the planet entirely, simply streams freely from the star to the observer, making up the background light,
  • the atmosphere of Earth (but not the surface) will largely pass through, but the atoms and molecules present will absorb a fraction of that light.

The absorbed light will excite the atoms or molecules they collide with, which can result in either an absorption or emission feature showing up in the atmospheric spectrum. We've already used this technique to discover atoms like hydrogen and helium — and even molecules like water — in the atmospheres of planets beyond our own Solar System.

When a planet transits in front of its parent star, some of the light is not only blocked, but if an . [+] atmosphere is present, filters through it, creating absorption or emission lines that a sophisticated-enough observatory could detect. If there are organic molecules or large amounts of molecular oxygen, we might be able to find that, too. at some point in the future. It's important that we consider not only the signatures of life we know of, but of possible life that we don't find here on Earth.

If an alien civilization were capable of observing our planet at any point over the past 2-to-2.5 billion years, they'd discover a planet whose atmosphere was made mostly out of nitrogen gas, but with a very large-and-substantial fraction of molecular oxygen as well. Water vapor and argon gas would make up about 1% of the atmosphere each, and then there'd be trace amounts of carbon dioxide, methane, ozone, and a few other notable compounds.

This combination of gases would be a "smoking gun" for life if we found it on a world other than our own. We know of a few inorganic pathways to arrive at substantial amounts of oxygen on a planet, but reaching a level of 5% or more seems to be extremely disfavored without life. The presence of oxygen in a primarily nitrogen atmosphere is even more favorable for life, and so if Earth transited across the face of the Sun for an alien civilization, we'd be a tremendously interesting world, even during the era of the dinosaurs.

Although the exact ratios of the different atmospheric components of Earth throughout its entire . [+] history are unknown, there were large amounts of methane present in the atmosphere prior to 2.5 billion years ago and virtually no oxygen. With the arrival of oxygen, the methane was destroyed, and the planet's greatest ice age began. However, these atmospheric changes were driven by biological processes the detection of a biologically altered atmosphere could be our first hint of alien life beyond the Solar System.

Victor Ponce / San Diego State University

That's a solid way to search for potentially inhabited worlds, but it only works for planets that are serendipitously aligned with their parent star from the viewpoint of an external, distant observer. It's how future observatories, like the James Webb Space Telescope or the 30-meter ground-based telescopes currently under construction, plan to search the nearest transiting worlds to Earth for potential biosignatures.

However, we're certain to miss most of the inhabited worlds if the transit technique is the only one we use. If the alignment is off by even a tiny amount — a fraction of a degree for a planet like Earth — the transit simply won't occur, and we'll have no way of probing its atmospheric contents. But all hope isn't lost, because there's another technique that doesn't rely on a lucky alignment, and could be brought within our reach with foreseeable improvements in technology: direct imaging.

This visible-light image from the Hubble shows the newly discovered planet, Fomalhaut b, orbiting . [+] its parent star. This is the first time a planet was ever observed beyond the solar system using visible light. However, it will take a further advance in direct imaging to reveal an exomoon, or advanced signatures that can be attributed to intelligent aliens.

NASA, ESA, P. Kalas, J. Graham, E. Chiang, and E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center, Greenbelt, Md.), M. Fitzgerald (Lawrence Livermore National Laboratory, Livermore, Calif.), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory, Pasadena, Calif.)

Owing to the power of the Hubble Space Telescope (and later, ground-based adaptive optics), we've already taken our first direct images of exoplanets, and have even witnessed them actively orbiting their parent stars. By utilizing instruments such as a coronagraph or a starshade, we can block the light of the parent star the potentially inhabited planet orbits, imaging only the planet of interest instead.

From just a single pixel, if we're willing to wait and observe the distant world over large amounts of time, we could not only tell whether it's inhabited or not, but additionally we could look for some of the most striking features we find on Earth. By taking a direct image of a planet and quantifying the various wavelengths of light that arrive at different times, there's a very long list of properties we could learn.

The Starshade concept could enable direct exoplanet imaging as early as the 2020s. This concept . [+] drawing illustrates a telescope using a star shade, enabling us to image the planets that orbit a star while blocking the star's light to better than one part in 10 billion.

NASA and Northrop Grumman

From short-period changes and recurrent spectroscopic signatures, we could determine what the orbital period of the planet is.

From the colors of the planet, we could determine how much of the world is covered in water versus land versus ice, and detect the presence of clouds if they exist.

Over the course of a year (where the planet makes a full revolution around its parent star), we could determine:

  • its orbital properties (from the phases),
  • whether the land masses turn green and brown and green again with the passing of seasons (from photometric observations),
  • and, with advanced enough technology, we could even determine if there's artificial lighting of any type unexpectedly illuminating the planet's night side.

This composite image of the Earth at night shows the effects of artificial lighting on how our . [+] planet appears along the portion that isn't illuminated by sunlight. This image was constructed based on 1994 and 1995 data, and the intervening 25 years have seen approximately a twofold increase in the amount of light humans create at night on Earth. We have conquered the night, but only at a great environmental cost. With an advanced enough telescope, an alien civilization could detect these artificial lights, and infer that Earth is inhabited by intelligent 'aliens.'

Craig Mayhew and Robert Simmon, NASA GSFC data from Marc Imhoff/NASA GSFC & Christopher Elvidge/NOAA NGDC

For an observer located less than 100 light-years away, that artificial lighting would be visible to a telescope large enough and optimized to view this type of faint light. It's an amazing feat of technology that human beings have conquered the darkness of night through artificial lighting, but there's a cost: the loss of the natural darkness that plants, animals, and other living creatures have adapted to over billions of years of evolution.

However, there's a benefit we don't often consider: the fact that we've modified the natural appearance of our planet means that a sufficiently intelligent alien species observing us could infer the existence of a planet-altering species. It's not a slam dunk, but such a signature is a strong hint that the planet isn't only inhabited, but inhabited by an intelligent, technologically advanced species.

Left, an image of Earth from the DSCOVR-EPIC camera. Right, the same image degraded to a resolution . [+] of 3 x 3 pixels, similar to what researchers will see in future exoplanet observations.

Without a second example of life in the Universe, we can only speculate on what the odds of life arising on a potentially habitable planet are. There could be billions of other worlds in the galaxy with life on them right now, or Earth could be the only one. There could be complex life that sustains itself for hundreds of millions or even billions of years on a plethora of planets in the Milky Way, or Earth could be it.

And finally, there could be thousands of spacefaring alien species in our galaxy, or human beings might be the most advanced creatures in the entire visible Universe. Until we find a second example of life to know that we aren't alone, all we can do is speculate and impose limits on what isn't out there.

There are four known exoplanets orbiting the star HR 8799, all of which are more massive than the . [+] planet Jupiter. These planets were all detected by direct imaging taken over a period of seven years, with the periods of these worlds ranging from decades to centuries. As in our Solar System, the inner planets revolve around their star more rapidly, and the outer planets revolve more slowly, as predicted by the law of gravity. With the next generation of telescopes like JWST, GMT, and the ELT, we may be able to measure Earth-like or super-Earth-like planets around the nearest stars to us.

Jason Wang / Christian Marois

The same signals that we're seeking from other civilizations — atmospheric signatures, surface features that evolve in a particular way, satellites and spacecraft, even deliberate and information-rich signals like FM radio waves — make our own civilization detectable by equally (or more) advanced extraterrestrials. From even a great distance away, an inhabited Earth would be identifiable, but an Earth inhabited by technologically advanced beings is only detectable to those civilizations close enough to see us in our recently achieved state.

Even though the majority of galaxies in the Universe are many billions of light-years away, there are millions upon millions of stars located within just a few hundred light-years of Earth. That means millions of planets, millions of chances at life, and even millions of possibilities for intelligent aliens. If even one such nearby world turns out to be inhabited, even the great cosmic distances won't keep us from finding out about them, just as they'll be more than capable of finding out about us, too.

The speed of light may be a limiting factor, but with enough time, the impact of human beings will be visible to any being residing in any one of more than 60 billion galaxies. It might not make for the fastest conversation, but finding even one instance of alien life beyond Earth would change our conception of existence forever. I can't wait for us to find out!


Earth Might Have Hairy Dark Matter

Dense filaments of dark matter particles, called "hairs," are sprouting from Earth, according to a new study based on computer simulations.

The solar system might be a lot hairier than we thought.

A new study publishing this week in the Astrophysical Journal by Gary Prézeau of NASA's Jet Propulsion Laboratory, Pasadena, California, proposes the existence of long filaments of dark matter, or "hairs."

Dark matter is an invisible, mysterious substance that makes up about 27 percent of all matter and energy in the universe. The regular matter, which makes up everything we can see around us, is only 5 percent of the universe. The rest is dark energy, a strange phenomenon associated with the acceleration of our expanding universe.

Neither dark matter nor dark energy has ever been directly detected, although many experiments are trying to unlock the mysteries of dark matter, whether from deep underground or in space.

Based on many observations of its gravitational pull in action, scientists are certain that dark matter exists, and have measured how much of it there is in the universe to an accuracy of better than one percent. The leading theory is that dark matter is "cold," meaning it doesn't move around much, and it is "dark" insofar as it doesn't produce or interact with light.

Galaxies, which contain stars made of ordinary matter, form because of fluctuations in the density of dark matter. Gravity acts as the glue that holds both the ordinary and dark matter together in galaxies.

According to calculations done in the 1990s and simulations performed in the last decade, dark matter forms "fine-grained streams" of particles that move at the same velocity and orbit galaxies such as ours.

"A stream can be much larger than the solar system itself, and there are many different streams crisscrossing our galactic neighborhood," Prézeau said.

Prézeau likens the formation of fine-grained streams of dark matter to mixing chocolate and vanilla ice cream. Swirl a scoop of each together a few times and you get a mixed pattern, but you can still see the individual colors.

"When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity," Prézeau said.

But what happens when one of these streams approaches a planet such as Earth? Prézeau used computer simulations to find out.

His analysis finds that when a dark matter stream goes through a planet, the stream particles focus into an ultra-dense filament, or "hair," of dark matter. In fact, there should be many such hairs sprouting from Earth.

A stream of ordinary matter would not go through Earth and out the other side. But from the point of view of dark matter, Earth is no obstacle. According to Prézeau's simulations, Earth's gravity would focus and bend the stream of dark matter particles into a narrow, dense hair.

Hairs emerging from planets have both "roots," the densest concentration of dark matter particles in the hair, and "tips," where the hair ends. When particles of a dark matter stream pass through Earth's core, they focus at the "root" of a hair, where the density of the particles is about a billion times more than average. The root of such a hair should be around 600,000 miles (1 million kilometers) away from the surface, or twice as far as the moon. The stream particles that graze Earth's surface will form the tip of the hair, about twice as far from Earth as the hair's root.

"If we could pinpoint the location of the root of these hairs, we could potentially send a probe there and get a bonanza of data about dark matter," Prézeau said.

A stream passing through Jupiter's core would produce even denser roots: almost 1 trillion times denser than the original stream, according to Prézeau's simulations.

"Dark matter has eluded all attempts at direct detection for over 30 years. The roots of dark matter hairs would be an attractive place to look, given how dense they are thought to be," said Charles Lawrence, chief scientist for JPL's astronomy, physics and technology directorate.

Another fascinating finding from these computer simulations is that the changes in density found inside our planet - from the inner core, to the outer core, to the mantle to the crust - would be reflected in the hairs. The hairs would have "kinks" in them that correspond to the transitions between the different layers of Earth.

Theoretically, if it were possible to obtain this information, scientists could use hairs of cold dark matter to map out the layers of any planetary body, and even infer the depths of oceans on icy moons.

Further study is needed to support these findings and unlock the mysteries of the nature of dark matter.


Does intelligent life exist on other planets? Technosignatures may hold new clues

Scientists have discovered more than 4,000 planets outside our solar system. In the search for intelligent life, astrophysicists including the University of Rochester's Adam Frank are seeking the physical and chemical signatures that would indicate advanced technology. Credit: NASA/JPL-Caltech

In 1995 a pair of scientists discovered a planet outside our solar system orbiting a solar-type star. Since that finding—which won the scientists a portion of the 2019 Nobel Prize in Physics—researches have discovered more than 4,000 exoplanets, including some Earth-like planets that may have the potential to harbor life.

In order to detect if planets are harboring life, however, scientists must first determine what features indicate that life is (or once was) present.

Over the last decade, astronomers have expended great effort trying to find what traces of simple forms of life—known as "biosignatures"—might exist elsewhere in the universe. But what if an alien planet hosted intelligent life that built a technological civilization? Could there be "technosignatures" that a civilization on another world would create that could be seen from Earth? And, could these technosignatures be even easier to detect than biosignatures?

Adam Frank, a professor of physics and astronomy at the University of Rochester, has received a grant from NASA that will enable him to begin to answer these questions. The grant will fund his study of technosignatures—detectable signs of past or present technology used on other planets. This is the first NASA non-radio technosignature grant ever awarded and represents an exciting new direction for the search for extraterrestrial intelligence (SETI). The grant will allow Frank, along with collaborators Jacob-Haqq Misra from the international nonprofit organization Blue Marble Space, Manasvi Lingam from the Florida Institute of Technology, Avi Loeb from Harvard University, and Jason Wright from Pennsylvania State University, to produce the first entries in an online technosignature library.

"SETI has always faced the challenge of figuring out where to look," Frank says. "Which stars do you point your telescope at and look for signals? Now we know where to look. We have thousands of exoplanets including planets in the habitable zone where life can form. The game has changed."

The nature of the search has changed as well. A civilization, by nature, will need to find a way to produce energy, and, Frank says, "there are only so many forms of energy in the universe. Aliens are not magic."

Although life may take many forms, it will always be based in the same physical and chemical principles that underlie the universe. The same connection holds for building a civilization any technology that an alien civilization uses is going to be based on physics and chemistry. That means researchers can use what they've learned in Earth-bound labs to guide their thinking about what may have happened elsewhere in the universe.

"My hope is that, using this grant, we will quantify new ways to probe signs of alien technological civilizations that are similar or much more advanced to our own," says Loeb, the Frank B. Baird, Jr., Professor of Science at Harvard.

The researchers will begin the project by looking at two possible technosignatures that might indicate technological activity on another planet:

  • Solar panels. Stars are one of the most powerful energy generators in the universe. On Earth, we harness energy from our star, the sun, so "using solar energy would be a pretty natural thing for other civilizations to do," Frank says. If a civilization uses a lot of solar panels, the light that is reflected from the planet would have a certain spectral signature—a measurement of the wavelengths of light that are reflected or absorbed—indicating the presence of those solar collectors. The researchers will determine the spectral signatures of large-scale planetary solar energy collection.
  • Pollutants. "We have come a long way toward understanding how we might detect life on other worlds from the gases present in those worlds' atmospheres," says Wright, a professor of astronomy and astrophysics at Penn State. On Earth, we are able to detect chemicals in our atmosphere by the light the chemicals absorb. Some examples of these chemicals include methane, oxygen, and artificial gases such as the chloroflourocarbons (CFCs) we once used as refrigerants. Biosignature studies focus on chemicals like methane, which simple life will produce. Frank and his colleagues will catalogue the signatures of chemicals, such as CFCs, that indicate the presence of an industrial civilization.

The information will be gathered in an online library of technosignatures that astrophysicists will be able to use as a comparative tool when gathering data.

"Our job is to say, 'this wavelength band is where you might see certain types of pollutants, this wavelength band is where you would see sunlight reflected off solar panels," Frank says. "This way astronomers observing a distant exoplanet will know where and what to look for if they're searching for technosignatures."

The work is a continuation of Frank's previous research on theoretical astrophysics and SETI, including developing a mathematical model to illustrate how a technologically advanced population and its planet might develop or collapse together classifying hypothetical "exo-civilizations" based on their ability to harness energy and a thought experiment asking if a previous, long-extinct technological civilization on Earth would still be detectable today.


The Biggest Problem In Science Isn’t Groupthink

Some 500 years ago, there was one scientific phenomenon that was, without controversy, extremely well-understood: the motion of the celestial objects in the sky. The Sun rose in the east and set in the west with a regular, 24 hour period. Its path in the sky rose higher and the days grew longer until the summer solstice, while its path was the lowest and shortest on the winter solstice. The stars exhibited that same 24 hour period, as though the heavenly canopy rotated throughout the night. The Moon migrated night-to-night relative to the other objects by about 12° as it changed its phases, while the planets wandered according to the geocentric rules of Ptolemy and others.

We often ask ourselves, “how was this possible?” How did this geocentric picture of the Universe go largely unchallenged for well over 1,000 years? There’s this common narrative that certain dogma, like the Earth being stationary and the center of the Universe, could not be challenged. But the truth is far more complex: the reason the geocentric model held sway for so long wasn’t because of the problem of groupthink, but rather because the evidence fit it so well: far better than the alternatives. The biggest enemy of progress isn’t groupthink at all, but the successes of the leading theory that’s already been established. Here’s the story behind it.

Although it isn’t well known, the idea of a heliocentric Universe goes back at least more than 2,000 years. Archimedes, writing in the 3rd century BCE, published a book called The Sand Reckoner, where he begins contemplating the Universe beyond Earth. Although he isn’t quite convinced by it, he recounts the (now lost) work of his contemporary, Aristarchus of Samos, who argued the following:

“His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.”

The work of Aristarchus was recognized as having great importance for two reasons that have nothing to do with heliocentrism, but nonetheless represented huge advances in the early science of astronomy.

Why do the heavens appear to rotate? This was an enormous question of the time. When you look at the Sun, it appears to move through the sky in an arc each day, where that arc is a fraction of a 360° circle: about 15° each hour. The stars also move the same way, where the entire night sky seems to rotate about the Earth’s north or south pole (depending on your hemisphere) at that exact same rate. The planets and Moon do nearly the same thing, just with the tiny, extra addition of their nightly motion relative to the background of stars.

The issue is that there are two ways to account for this:

  1. The Earth is stationary, and the heavens (and everything in them) rotate about the Earth with a rotational period of 360° every 24 hours. In addition, the Moon and planets have a slight, extra motion.
  2. The stars and other heavenly bodies are all stationary, while the Earth rotates about its axis, with a rotational period of 360° every 24 hours.

If all we saw were the objects in the sky, either one of these explanations could fit the data perfectly well.

And yet, practically everyone in the ancient, classical, and medieval world went with the first explanation and not the second. Was this a case of dogmatic groupthink?

Hardly. There were two major objections that were raised to the scenario of a rotating Earth, and neither one was successfully addressed until the Renaissance.

The first objection is that if you dropped a ball on a rotating Earth, it wouldn’t fall straight down from the perspective of someone standing on the Earth, but rather would fall straight down while the person on Earth moved relative to the falling ball. This was an objection that persisted through the time of Galileo, and was only resolved with an understanding of relative motion and the independent evolution of horizontal and vertical components for projectile motion. Today, many of these properties are known as Galilean relativity.

The second objection was even more severe, though. If the Earth rotated about its axis every 24 hours, then your position in space would differ by the diameter of Earth — about 12,700 km (7,900 miles) — from the start of the night to the end of the night. That difference in position should result in what we know astronomically as parallax: the shifting of closer objects relative to the more distant ones.

And yet, no matter how acute your vision was, nobody had ever observed a parallax for any of the stars in the sky. If they were at different distances and the Earth was rotating, we’d expect to see the closest ones shift position from the beginning of the night to the end of the night. Despite that prediction, no parallax was ever observed for more than 1000 years.

With no evidence for the rotating Earth here at Earth’s surface, and no evidence for parallax (and hence, a rotating Earth) among the stars in the heavens, the explanation of the rotating Earth was disfavored, while the explanation of a stationary Earth and a rotating sky — or a “celestial sphere” beyond Earth’s sky — was chosen as the favored explanation.

The Earth does rotate, but we didn’t have the tools or the precision to make quantitative predictions for what we’d expect to see. It turns out that the Earth does rotate, but the key experiment that allowed us to see it on Earth, the Foucault pendulum, wasn’t developed until the 19th century. Similarly, the first parallax wasn’t seen until the 19th century either, owing to the fact that the distance to the stars is enormous, and it takes the Earth migrating by millions of kilometers over weeks and months, not thousands of kilometers over a few hours, for our telescopes to detect it.

The problem was that we didn’t have the evidence at hand to tell these two predictions apart, and that we conflated “absence of evidence” with “evidence of absence.” We couldn’t detect a parallax among the stars, which we expected for a rotating Earth, so we concluded that the Earth wasn’t rotating. We couldn’t detect an aberration in the motion of falling objects, so we concluded that the Earth wasn’t rotating. We must always keep in mind, in science, that the effect we’re looking for might be present just below the threshold of where we’re capable of measuring.

Still, Aristarchus was able to make important advances. He was able to set his heliocentric ideas aside, instead using light and geometry within a geocentric framework to concoct the first method for measuring the distances to the Sun and the Moon, and hence to also estimate their sizes. Although his values were way off — mostly due to “observing” a dubious effect now known to be beyond the limits of human vision — his methods were sound, and modern data can accurately leverage Aristarchus’s methods to calculate the distances to and sizes of the Sun and Moon.

In the 16th century, Copernicus revived interest in Aristarchus’s heliocentric ideas, noting that the most puzzling aspect of planetary motion, the periodic “retrograde” motion of the planets, could be equally well-explained from two perspectives.

  1. Planets could orbit according to the geocentric model: where planets moved in a small circle that orbited along a large circle around the Earth, causing them to physically move “backwards” at occasional points in their orbit.
  2. Or planets could orbit according to the heliocentric model: where every planet orbited the Sun in a circle, and when an inner (faster-moving) planet overtook an outer (slower-moving) one, the observed planet appeared to change direction temporarily.

Why do the planets appear to make retrograde paths? This was the key question. Here we had two potential explanations with vastly different perspectives, yet both were capable of producing the phenomenon that was observed. On the one hand, we had the old, prevailing, geocentric model, which accurately and precisely explained what we saw. On the other hand, we had the new, upstart (or resurrected, depending on your perspective), heliocentric model, which could also explain what we saw.

Unfortunately, the geocentric predictions were more accurate — with fewer and smaller observational discrepancies — than the heliocentric model. Copernicus could not sufficiently reproduce the motions of the planets as well as the geocentric model, no matter how he chose his circular orbits. In fact, Copernicus even started adding in epicycles to the heliocentric model to try and improve the orbital fits. Even with this ad hoc fix, his heliocentric model, although it generated a renewed interest in the problem, did not perform as well as the geocentric model in practice.

The reason it took so long to supersede the geocentric model of the Universe, close to 2000 years, is because of how successful the model was at describing what we observed. The positions of the heavenly bodies could be modeled exquisitely using the geocentric model, in a way that the heliocentric model could not reproduce. It was only with the 17th century work of Johannes Kepler — who tossed out the Copernican assumption that planetary orbits must be reliant on circles — that led to the heliocentric model finally overtaking the geocentric one.

  • What was most remarkable about Kepler’s achievement wasn’t:
  • that he used ellipses instead of circles,
  • that he overcame the dogma or groupthink of his day,
  • or that he actually put forth laws of planetary motion, instead of just a model.

Instead, Kepler’s heliocentrism, with elliptical orbits, was so remarkable because, for the first time, an idea had come along that described the Universe, including the motion of the planets, better and more comprehensively than the previous (geocentric) model could.

In particular, the (highly eccentric) orbit of Mars, which was previously the biggest point of trouble for Ptolemy’s model, was an unequivocal success for Kepler’s ellipses. Under even the most stringent of conditions, where the geocentric model had its greatest departures from what was predicted, the heliocentric model had its greatest successes. That’s often the test case: look where the prevailing theory has the greatest difficulty, and try to find a new theory that not only succeeds where the prior one fails, but succeeds in every instance where the prior one also succeeds.

Kepler’s laws paved the way for Newton’s law of universal gravitation, and his rules apply equally well to the moons of the Solar System’s planets and to the exoplanetary systems we have in the 21st century. One can complain about the fact that it took some

1800 years from Aristarchus until heliocentrism finally superseded our geocentric past, but the truth is that it until Kepler, there was no heliocentric model that matched the data and observations as well as Ptolemy’s model did.

The only reason this scientific revolution occurred at all is because there were “cracks” in the theory: where observations and predictions failed to align. Whenever this occurs, that’s where the opportunity for a new revolution may arise, but even that is not guaranteed. Are dark matter and dark energy real, or is this an opportunity for a revolution? Do the different measurements for the expansion rate of the Universe signal a problem with our techniques, or are they an early indication of potential new physics? What about non-zero neutrino masses? Or the muon’s g-2 experiment?

It’s important to explore even the most wild possibilities, but to always ground ourselves in the observations and measurements we can make. If we ever want to go beyond our current understanding, any alternative theory has to not only reproduce all of our present-day successes, but to succeed where our current theories cannot. That’s why scientists are often so resistant to new ideas: not because of groupthink, dogma, or inertia, but because most new ideas never clear those epic hurdles. Whenever the data clearly indicates that one alternative is superior to all the others, a scientific revolution is inevitably sure to follow.


A mysterious Mars-sized planet may be hiding at the edge of our solar system

A mysterious celestial body may be lurking in the frozen, far-flung reaches of the solar system, scientists say.

This is not the proposed "Planet Nine," an enormous body that Caltech scientists believe could be tugging at the orbits of the solar system's most distant inhabitants. And it's not Pluto. (Sorry Pluto, you still don't count.)

Instead, University of Arizona astronomers Kat Volk and Renu Malhotra say it's a Mars-sized body in the Kuiper belt, a swarm of small icy objects that extends beyond the orbit of Pluto. If both the Arizona and Caltech researchers are right, then these proposed bodies could bring the total number of planets in our solar system to 10.

Volk and Malhotra haven't seen their new planet, but they say they can sense its presence. In a new paper due to be published in the Astronomical Journal, they describe an odd distortion in the orbits of objects in the outer part of the Kuiper belt, ones that are between 50 and 80 AU away (AU stands for astronomical unit, or the distance from the sun to Earth, about 92 million miles).

Though most of the nearer bodies in the solar system circle the sun in the same plane, largely thanks to Jupiter's steadying heft, these far away Kuiper belt objects (KBOs) orbit at all kinds of wonky angles.

That in itself wouldn't raise too many questions. But when Volk and Malhotra analyzed these orbits in search of the average plane, they found that it was offset by about 8 degrees.

"It's significant," Volk said. "And the most likely explanation is this object on the outer solar system."

If there is a planet out there with roughly the same mass as Mars, its gravity could pull on the orbits of small KBOs, dragging them out of the "invariable plane" that Earth, Jupiter and the rest of the planets inhabit.

The Caltech researchers used similar logic to infer the presence of Planet Nine, arguing that this "massive perturber" is responsible for peculiarities in the point at which KBOs are closest to the sun.

"It's the same idea of indirectly detecting a planet by its effects," Volk said.

For their study, Volk and Malhotra examined the orbits of about 600 KBOs. Scientists know of roughly 2,000 KBOs right now, but they believe there may be as many 100,000 of significant size.

"It would be useful to have more Kuiper belt objects to make sure this is a real signal," Volk acknowledged. But even so, their analysis suggests there's only a 1 to 2 percent chance that the results are a result of a fluke in the data.

Alessandro Morbidelli at the Côte d'Azur Observatory in Nice, France, told New Scientist he found it hard to believe that astronomers could have missed something as big as a planet so nearby. (The Caltech scientists' "Planet Nine" is said to be 10 times as distant, which explains why it's been so hard to track down.)

"I am dubious that a planet so close and so bright would have remained unnoticed," Morbidelli said.


Image Is Believed to Be the First Of a Planet Beyond Solar System

After deciphering digitized pictures made by the Hubble Space Telescope last August, astronomers have reconstructed what they believe to be the first image ever captured of a planet outside our solar system.

The putative planet, scorching hot and estimated to be several times as large as Jupiter, lies in the constellation Taurus about 450 light-years from Earth -- comparatively close in astronomical terms.

At a news conference yesterday at the headquarters of the National Aeronautics and Space Administration in Washington, the discovery team presented an image showing two stars circling each other. A third object was visible, much smaller and dimmer than the double-star system, but apparently linked to it by a luminous trail.

Although as many as eight possible extrasolar planetary systems have been detected since 1995, neither space-based nor ground-based telescopes have revealed images of any planets. The existence of extrasolar planets has been inferred mainly from the gravitational wobbling induced in their parent stars. In a few cases, including that of the star Beta Pictoris, circumstellar dust and rubble disks have been imaged, and planets are believed to be forming in these disks, but no planets were seen directly.

Dr. Susan Tereby, the founder of the Extrasolar Research Corp. in Pasadena, Calif., and the leader of the discovery team, said yesterday that the planet, called TMR-1C, has apparently been expelled from its binary-star system and is hurtling outward at about 12 miles per second. It appears, she said, that this very young but very large planet was created at about the same time as the two sunlike stars it orbited. Its orbit was unstable, however, and it was subjected to a gravitational ''slingshot'' that expelled it from its star system when it approached one of its parent stars too closely. (Spacecraft are sometimes steered into courses that closely pass planets so that they can receive similar gravitational boosts.)

Planet TMR-1C seems destined to be a rogue planet, detached from any star and drifting forever outward. Its fate may be shared by many similar bodies drifting aimlessly through space, astronomers said yesterday.

Astronomers agreed that TMR-1C is not a likely host for life in any form. But its discovery and other evidence suggest that planetary systems are probably very common and that some of them almost certainly contain Earthlike planets where life could arise -- or could already exist.

Dr. Edward J. Weiler, an astronomer and director of a NASA program that seeks to explore the origin of the universe, called the tentative discovery of an extrasolar planet ''preliminary but compelling.''

''Twenty years ago, when we were discussing goals for the Hubble Space Telescope we put the discovery of an extrasolar planet at the top of our list,'' Dr. Weiler said. ''Until five years ago we had no proof of the existence of such planets, but then we began to infer their presence indirectly. Now, it seems, we may have actually captured an image of one.''

The astronomers who participated in the meeting yesterday said a very small chance existed that the object in the picture was not a planet but was merely a background star almost directly behind the binary-star system called TMR-1.

To rule out this possibility, Dr. Tereby said, her group must wait until the constellation Taurus rises in the sky in August. Then the astronomers will begin measuring the outward movement of the planet and will analyze its light spectrum with the big Keck II telescope in Hawaii.

She hypothesized that the 130-billion-mile-long luminous filament connecting the binary-star system with the supposed planet is a trail left by the planet since its ejection from the star system. She called it a ''light tunnel'' similar in principle to an optical fiber, carrying light through a dark and dusty medium.

Dr. Alan P. Boss, an astronomer with the Carnegie Institution of Washington, who participated in the meeting yesterday, published a paper in the journal Science a year ago that suggested that under some circumstances, giant planets might form very rapidly (in several hundred thousand years) in the protoplanetary disks surrounding infant stars. Traditionally, most astronomers had believed that it would take about 10 million years for a planet like Jupiter to condense from the disk. But he said the apparent expulsion of TMR-1C from its parent stars lends weight to a mechanism he proposed last year for the formation of at least some planetary systems.

Because the parent star system and planet TMR-1C appear to be young, the traditional notion that giant planets must form slowly appeared to have been ruled out in this case, he said. A plausible alternative is that the motions of the two stars in the system propelled particles making up the protoplanetary disk into unstable orbits, resulting in widespread collisions and the rapid clumping together of matter. This could have led to the rapid creation of a large planet at about the same time its parent stars were born.

In another landmark in astronomy, the European Southern Observatory announced that on Monday night its Very Large Telescope opened its first eye on the sky. The observatory, being completed on a hilltop in Chile, will consist of huge telescopes, four of them about 27 feet in diameter. By the end of the century, all of them will be able to be combined into one instrument of immense light-gathering power.

The first of these monster telescopes underwent 'ɿirst light'' this week, and its operators said it performed even better than planned. Its angular resolution, or ability to distinguish between very closely separated objects, 'ɾven at this early stage is unequaled by any large ground-based telescope,'' the observatory announced. On Wednesday the European astronomical consortium released a series of breathtaking images made by the telescope on its first night of operation.

For much of the 21st century, astronomers said, the Very Large Telescope is expected to remain the largest in the world.


What planet is better than earth to infer solar system configuration? - Astronomy

Kepler Telescope Found New Planets Better Than Earth
Feb 21, 2021
The Kepler Telescope was built for one purpose to look at a certain patch in the Milky Way in search of exoplanets.
The exoplanet hunter observed over hundreds of thousands of stars and discovered thousands of exoplanets during its lifetime.
Crash Course on Our Solar System & Beyond

Solar System Scope - New Version
New Version - Full Screen

SSS is Flash based 3D model of Planets of Solar System and the Night Sky.

The Model consists of 3 main Views (Heliocentric, Geocentric and Panaromatic), including:
&bull Precise Positions of all Celestial Objects according to NASA Calculations
&bull Schematic Distances and Sizes for better understanding of Planet Surfaces and Motions
&bull a unique feature to Drag Planets through their Orbits
&bull a lot of interesting Settings which allow you to Observe particular Motions and Events
&bull Distance Calculator to measure distances between Planets even while in motion
&bull Earth Observatory set-up with which you can watch Celestial Happenings on your Night Sky

SSS mean Astronomy for Everybody

Kids play with Planets while Discovering Universe. Our youngest regular visitors are only 7-8 years old. Many Teachers use our model as a practical Source of Education and with SSS they are able to show and simply explain happenings in our Solar System. But anyone can benefit from SSS: it brings Knowledge, Fun and Visual Experience.

Rare event to occur in Solar System July 19, 2018 - Several days..
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June 18, 2017: Looking ahead down the superhighway in the sky I couldn't help but notice something very interesting about to unfold as I approached the July 2018 timeframe. Something very unique was revealed to me. Pretty rare actually.

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Stage 9 - Enterprise-D Borg Encounter and more

Stage 9 - Virtual Enterprise-D Tour v0.09

US Space & Rocket Center - Huntsville, Alabama

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Later this year a 3D printer will be heading to the space station. This was a partnership between a commercial company called Made in Space and NASA's Marshall Space Flight Center. Bill Hubscher spoke with Mike Snyder of Made in Space and Niki Werkheiser from Marshall to find out more about working with small businesses on projects like this and the opportunities in the future. The 3-D printer represents the first step toward realizing a suite of capabilities for in-space manufacturing.

A look at Elon and SpaceX's plan to travel to a eventually colonize mars.







NASA ISS Live Stream - Earth From Space | ISS Live Feed: ISS Tracker + Live Chat
Started streaming on Aug 31, 2019

NASA Announces Big Exoplanet Discovery (Feb. 22, 2017)

Crew Demo-1 Mission | Rendezvous, Docking, and Hatch Opening
Published on Apr 8, 2019
At 2:49 a.m. EST on March 2, SpaceX launched Crew Dragon&rsquos first demonstration mission from Launch Complex 39A (LC-39A) at NASA&rsquos Kennedy Space Center in Florida. The intent of this test flight without crew on board the spacecraft was to demonstrate SpaceX&rsquos capabilities to safely and reliably fly astronauts to and from the International Space Station as part of NASA&rsquos Commercial Crew Program.

CRS-18 Mission
Streamed live on Jul 25, 2019
At 6:01 p.m. EDT, or 22:01 UTC, on Thursday, July 25, SpaceX launched its eighteenth Commercial Resupply Services mission (CRS-18) from Space Launch Complex 40 (SLC-40) at Cape Canaveral Air Force Station, Florida. Dragon separated from Falcon 9&rsquos second stage about nine minutes after liftoff.

Published on Jan 22, 2020

Hubble Space Telescope - Space Documentary 2015 marks the 25th anniversary year of the launch of the Hubble Space Telescope, an event that has propelled us into the Golden Age of Astronomy and brought us closer than ever to answering the most perplexing questions &ndash what are the origins of the universe? And are there other worlds like our own, rich with life?

Published on Feb 20, 2016
The James Webb SpaceTelescope will launch October 2018

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Juno is a NASA space probe orbiting the planet Jupiter. It was built by Lockheed Martin and is operated by NASA's Jet Propulsion Laboratory.

Thanks to Audible for sponsoring today's video. Get your free 30 day trial, one free audiobook, and 2 audible originals here! http://www.audible.com/jaredowen OR text "jaredowen" to 500 500

Published on Apr 10, 2019

A black hole is a cosmic abyss with gravity of such intensity that nothing, not even light, escapes it. Now, for the first time, a team of astronomers has released an image of the space anomaly, which is created when a star collapses. Professor Brian Greene of Columbia University and the World Science Festival provides context and talks to Judy Woodruff about this scientific breakthrough.

Published on Apr 10, 2019

In April 2017, scientists used a global network of telescopes to see and capture the first-ever picture of a black hole, according to an announcement by researchers at the National Science Foundation Wednesday morning. They captured an image of the supermassive black hole and its shadow at the center of a galaxy known as M87.

Published on Jun 12, 2015

New Horizons is the first mission to the Kuiper Belt, a gigantic zone of icy bodies and mysterious small objects orbiting beyond Neptune. This region also is known as the &ldquothird&rdquo zone of our solar system, beyond the inner rocky planets and outer gas giants. Johns Hopkins University Applied Physics Laboratory (APL) in Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA&rsquos Science Mission Directorate in Washington. The Year of Pluto - NASA New Horizons is a one hour documentary which takes on the hard science and gives us answers to how the mission came about and why it matters. Interviews with Dr. James Green, John Spencer, Fran Bagenal, Mark Showalter and others share how New Horizons will answer many questions. New Horizons is part of the New Frontiers Program, managed by NASA&rsquos Marshall Space Flight Center in Huntsville, Alabama.

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On 12 November, the European Space Agency&rsquos Rosetta mission will try to land a probe on a comet, more than 500 million kilometres from Earth. Nature Video explains how the landing will unfold, and why the mission is so ambitious.

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www.dailymail.co.uk
It was a worrying end to an extraordinary day.
At the European Space Agency&rsquos mission control, a faint radio signal came back from the Philae lander at 4pm &ndash proof that it had finally reached the surface of the comet 67P/Churyumov-Gerasimenko after a decade-long chase through space.
Dr Stephan Ulamec, who ran the audacious landing programme, said early tests suggested the craft had bounced softly before turning and settling again.
He said: &lsquoIt touched down and was re-bouncing. So maybe today, we didn&rsquot just land, we landed twice.&rsquo
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It was not clear if its three ice screws had deployed either.
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Pandora is the idyllic blue world featured in the movie Avatar. Its location is a real place: Alpha Centauri, the nearest star to our Sun and the most likely destination for our first journey beyond the solar system.

This image shows particle jets erupting from a supermassive black hole in the nearby galaxy of Centaurus A. The image was created by merging X-ray data (blue) from NASA&rsquos Chandra X-ray Observatory with microwave (orange) and visible images which reveals the jets and radio-emitting lobes emanating from Centaurus A&rsquos central black hole.

Learning How To Navigate Eyes on the Solar System

Eyes on the Solar System
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Twinkle, twinkle: How astronomers investigate alien planets

Do you believe in aliens? More than one in two people in the UK, Germany and the US believe there is intelligent life out there in the universe, meaning that – whether your belief is rooted in crop circles, statistics or gut feeling – ‘you are not alone’.

100 years ago the hunt for alien life was limited to speculations about Mars and the moon. Nowadays we can look further afield, to planets which orbit stars outside our own solar system: exoplanets.

Unquestionably, the game-changer in the field of exoplanets was the Kepler space telescope. Johnannes Kepler (1571-1630) was a mathematician, astrologer, and astronomer. He used observations of the planets in our solar system to develop his famous laws of planetary motion. Kepler also worked on optics and invented an improved version of Galileo’s astronomical telescope – a refracting type or a Keplerian telescope.

vector punch/Shutterstock.com

Launched in 2009, armed with a photometer as its only scientific instrument, the Kepler space telescope began surveying one field of view in the sky. Kepler discovered more exoplanets during its mission than all other discovery methods combined.

Of particular interest to Kepler were discoveries of Earth-like planets. These ‘rocky’ planets have a similar size to Earth, and are within the ‘habitable zone’, usually defined as having a temperature in which liquid water could reside on the planet’s surface.

Unquestionably, the game-changer in the field of exoplanets was the Kepler space telescope.

Twinkle twinkle – spotting exoplanets
Directly viewing exoplanets is not quite so easy. The Kepler space telescope used photometric data to infer the existence of an exoplanet. This method is known as the transit method. It involves observing a star (or groups of stars) over time and monitoring their brightness very precisely. If an orbiting planet passes directly in front of – that is, it transits – a star, the light level will dip slightly and then return to normal. This will happen repeatedly, once for every orbit of the exoplanet. This is by no means the only way exoplanets can be detected. Another method, ‘direct imaging’ looks at the thermal emissions of young, large planets. The radial velocity method can identify exoplanet-hosting stars from the ‘wobble’ as their planets orbit them. Finally, gravitational microlensing observes the lensing effect of gravity when a solar system passes directly behind another (unrelated) star.

None of these other methods, however, have discovered as many exoplanets as transit photometry. Over its years of service, the Kepler space telescope observed a staggering 530,506 stars every 30 minutes for four years and detected over 4,000 exoplanets. After two of its three reaction wheels failed in 2014, an ingenious proposal to repurpose Kepler as ‘K2’ led to an adaptation of spacecraft balance by using sunlight with precise positioning using thruster fuel.

Standing below the Gemini telescope 8m mirror, Howell examines his high-resolution imaging instrument mounted to the telescope.

The K2 programme, with Dr Steve Howell as lead scientist, gave new life to Kepler until it retired in 2018 when the telescope finally ran out of fuel. K2 discovered many new exoplanets and extended the search for four additional years. The data collected by these missions is expected to continue revealing new exoplanets for several more years.

The need for exoplanet follow-up
A new wave of exoplanet space telescope missions is well underway, including NASA’s Transiting Exoplanet Survey Satellite (TESS). TESS searches for transit signals across the whole sky, and is expected to lead to several thousand more exoplanet discoveries. PLATO will also look for transits deeper in space than Kepler could. In addition, the James Webb Space Telescope and the Nancy Grace Roman Space Telescope will join the European Space Agency’s CHEOPS, collecting information to help characterise existing exoplanets in the search for life.

For each transit signal and new exoplanet discovered, it is important to perform detailed follow-up observations of the host stars. This crucial work has become Dr Steve Howell’s domain.

Gemini North Telescope, one of a pair of giant observatories (one in each hemisphere), providing full sky coverage.

Every star which shows a transit signature yields an exoplanet candidate, with the measured starlight viewed over time implying that a planet is regularly orbiting that star. The intrinsic brightness of the star is used as an indication of the star’s size the amount the brightness dips is used to determine the relative size of the planet.

However, there are several reasons why the data might not give the full story. Especially problematic is the existence of binary star systems. This two star system affects the brightness readings in the photometric data, and leads to incorrect estimates of planetary size, density, and therefore possibilities of habitability.

Doing the ground work
Dr Howell’s research focuses in – quite literally – on exoplanet candidates which may orbit one star in a binary star system. This work involves ground-based observational research, using a method called high-resolution speckle imaging.

The need for this type of follow-up research was identified even before Kepler was launched. Howell has spent the last decade studying what he refers to as ‘transit-like’ events. That is, since some of the exoplanet discoveries by transit observations may be false, the exoplanets remain candidates until scrutinised in more detail.

Mauna Kea (Hawai’i) is the site of many major telescopes, including Gemini-North. Its viewing conditions are the finest of any Earth-based observatory.

Exoplanet transit searches from space telescopes such as Kepler or TESS, which gather information for many stars at once but over a broad area of the sky, have relatively low spatial resolution. Each pixel of their cameras may contain multiple stars, making it hard to identify which star is responsible for the observed transit-like regular dip in brightness.

To solve this problem, and to validate and characterise the exoplanets and their host stars, high spatial resolution images are required. Speckle imaging is a technique used by ground-based telescopes to remove the distortions caused by disturbances in the Earth’s atmosphere. By re-constructing an image from many short exposures with specialised software, very high-resolution images can be produced with the ability to see deep into the alien solar system.

Ultra-high resolution
As a result of Howell’s research into ultra-high spatial resolution images, three new instruments have been built. These are installed at some of the largest ground-based telescopes in the world. Essentially, Howell and his team produce the highest-resolution images yet achieved.

Typical ground-based image of a star field, showing a bright red star near the centre. A high-resolution image of this star (inset) reveals that it is really a close binary pair. Steve B. Howell

So far, the team has observed over 1,000 exoplanet hosting stars from Kepler and K2, and more than 500 from TESS. This has resulted in 65 published papers in the last year and a half alone. One of the most important learning points from this work is the value of community understanding of the host star or stars in an exoplanet-hosting system.

A new wave of exoplanet telescope missions is well underway, including Nasa’s Transiting Exoplanet Survey Satellite (TESS) which searches for transit signals across the whole sky.

Two stars are better than one (for planet formation)
Recent research led by Howell on TESS exoplanet stars finds that almost half of all exoplanet-hosting stars are actually part of a binary or multiple star system. This has important implications for the way we interpret the transit signals. For example, ‘contamination’ light from the second star can reduce the dip in brightness when the exoplanet transits its host star.

The exoplanet will then be predicted to be smaller than it really is, meaning the planet is incorrectly characterised. What may look Earth-like from TESS data may actually more likely be an Neptune-like ice giant!

Recent research from Howell’s team also details an interesting discrepancy between binary star pairs with and without exoplanets. This was discovered in a survey of 186 exoplanet host stars from the TESS mission.

Artist’s concept of five relatively small exoplanets discovered by Kepler, all of which orbit in the habitable zone of their host star. Kepler-186f is the most Earth-like planet Kepler discovered (NASA).NASA

Stellar work
The most up-to-date estimates suggest pairs of stars in binary systems are, on average, 40 astronomical units from each other (the distance between our Sun and the planet Pluto). These estimates are based on observations of binary stars without regard to exoplanets. Howell’s survey of TESS data – looking specifically at 45 binary systems with exoplanets, provides a different result.

Exoplanet-hosting binaries are more likely to orbit further from each other, typically around 100 astronomical units apart, and fall into a narrow range of possible inter-stellar distances.

Given that planets and their stars tend to be formed at the same time, Howell’s discovery changes our understanding of planetary formation. His work suggests that many planets were formed under the same conditions which lead to binary star formation, a very different mechanism than our own single-star solar system.

This isn’t the only big discovery made through speckle imaging. Howell and his team also use their research to answer important questions about the exoplanets themselves. Which star in the binary is the one hosting the planet? If two stars appear very close in space, are they really close, or do they just line up well with the view from Earth? Which planets are the best candidates for further investigation by telescopes that can perform spectroscopy to determine the composition of the exoplanet’s atmosphere and search for signatures of life?

High-resolution speckle imaging gives us new ways of understanding the increasing number of candidate exoplanets and their environments, including identifying those which might be best-suited to harbour life.

Personal Response

Can you briefly detail the part speckle imaging has to play amongst the ‘new generation’ of space telescopes like the James Webb and Nancy Grace Roman space telescopes?

One of the most fundamental questions of humanity is, Are we alone? Since humans looked up at the lights in the night sky the question of where we came from and who else is out there has been a fundamental driving force for exploration and discovery.

Speckle imaging and the research it enables is one aspect of the larger picture that someday will lead to the discovery of life on an alien world. My current work provides detailed information on many exoplanets and the stars which they orbit in order to help all of us in astronomy produce a list of the best exoplanets to observe in the future. These exoplanets will provide the greatest opportunity for science to discover signatures that life exists elsewhere in the Galaxy.


Venus, Not Earth, May Have Been Our Solar System’s Best Chance At Life

“It was the Venus I had prayed to, it was my prayer, though I had no such words. They filled my eyes with tears and my heart with inexpressible joy.”
-
Ursula Le Guin

If we were to wind the clock back some 4.5 billion years ago, to the early days of our Solar System, we would have seen a young, G-class star with four rocky worlds interior to our asteroid belt. Like many of the star systems the Kepler spacecraft has discovered, this type of configuration is relatively common there are billions upon billions of chances in our galaxy alone that began just like ours did. But the young worlds in our newborn Solar System were very different from how they are today, and so was the Sun, for that matter.

Venus’ atmosphere was very thin at the beginning, comparable to the thickness of Earth’s atmosphere today. Earth, on the other hand, was very different, with lots of methane, ammonia, water vapor, hydrogen and virtually no oxygen at all. And the Sun was so faint compared to what it is now: less than 80% as luminous as it is today. With all that in mind, perhaps — if we rewound the Solar System to the very beginning and started it again — the ingredients for life would come together on Venus far more easily than on Earth? And perhaps early Venus was teeming with life, while things on Earth were barely getting started?

Things didn’t need to turn out the way they did, even given the initial conditions the Solar System began with. And perhaps that makes it worth reconsidering an assumption we make: perhaps the habitable zone shouldn’t be defined by the location in the Solar System where an Earth-sized planet with an Earth-like atmosphere would have the right pressure-and-temperature combinations for liquid water on its surface? Perhaps, instead, we should consider the possibility that, just as a nudge in the wrong direction could have rendered early Earth either an inferno or a frozen wasteland, perhaps a nudge in the right direction would have led to life thriving on Venus or Mars . In other words, perhaps what we think of as the “habitable zone” of a star is actually much broader — and more variable — than we’ve thought up to this point.

This is exactly what Adrian Lenardic and collaborators consider in their latest article, published in the journal Astrobiology. What they explore is the possibility that if you began the Solar System anew with only very slight, perhaps imperceptible changes in the initial conditions, perhaps Venus, Earth or even Mars (or all three) might emerge with life thriving on them. The similar size and composition of Venus and Earth, their likely similar early histories coupled with their vastly different outcomes was once thought of as an inevitability. But as more planets are discovered and characterized, we may find out that the truth is vastly different from those expectations.

“[I]f you could run the experiment again, would it turn out like this solar system or not? For a long time, it was a purely philosophical question. Now that we’re observing solar systems and other planets around other stars, we can ask that as a scientific question. If we find a[n exo]planet sitting where Venus is that actually has signs of life, we’ll know that what we see in our solar system is not universal,” Lenardic said. As the next generations of exoplanet missions go from the planning stages to construction to operation, signs of life — to go from potentially habitable to inhabited — could become a reality. Plans to directly image rocky alien exoplanets or to view the starlight filtering through the atmosphere could reveal worlds with oceans, continents, seasonal changes, or, perhaps most tellingly, oxygen-rich atmospheres.

Yet even an absence of oxygen might not be a dealbreaker. After all, Earth had life for billions of years before our atmosphere became oxygen-rich, and it’s even possible that plate tectonics may not have become active on our world 2-to-3 billion years ago. “There are things that are on the horizon that, when I was a student, it was crazy to even think about,” Lenardic continued. “Our paper is in many ways about imagining, within the laws of physics, chemistry and biology, how things could be over a range of planets, not just the ones we currently have access to. Given that we will have access to more observations, it seems to me we should not limit our imagination as it leads to alternate hypothesis.”

Just as a planet’s location, pressure, temperature, composition, magnetic and geologic properties and more may influence whether it has life on its surface or not, that life may feed back onto the planet itself, perhaps altering its course in ways we do not yet understand. As we move from the realm of speculation into the era of data-rich information about alien worlds, we may find that life is far more common — and inhabited worlds are far more diverse — than we’ve ever considered before.