Astronomy

Parent stars of our Sun - Where are its remains?

Parent stars of our Sun - Where are its remains?


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This is in a way related to this question.

Question is: Our star is third generation star, which is explained by existing Barium. That Barium was created by other stars. Now, those stars must have been Supernova. When they exploded, it was either a neutron star or a black hole. Where is that Neutron star or black hole?


We have no way of identifying where the Sun was born, what the surrounding environment was, or where the Sun's siblings are right now. This is easy to see from some bare numbers: the Sun's current orbital period around the Milky Way is some 250 million years, and it's been around for some 4.5 billion years, making for some 20 orbits around the galaxy since its birth. There's a lot of stellar-movement dynamics that can happen over those twenty orbits, and any siblings have long parted ways. Similarly, any stellar remnants that are close to us right now are close because we're passing by, not because we were born in their neighbourhood.

As such, whatever the source of the heavy elements in the solar system, it's several billions of years too late to figure out any individual sources.


That said, it is important to emphasize that there is no such unique source to begin with. As explained in the answer you linked to, there are plenty of such predecessors:

There are grains of material trapped inside meteorites that consist of solids that were already present in the pre-solar material. These are important because these grains were thought to have formed in individual stellar events and their isotopic compositions can be studied. These tell us that the Sun formed from material that has been inside many different stars of different types.

Moreover, if you want to place those predecessors, you are fighting against the internal mixing of the interstellar gas on a galactic scale:

Mixing in the interstellar medium is reasonably effective. The material spewed out from supernovae and stellar winds 5-12 billion years ago has had plenty of time to mix throughout the Galaxy before the Sun's birth. Turbulence and shear instabilities should distribute material on galactic length scales in a billion years or less.

This means that the Sun was not born out of the ashes of its neighbours. Instead, it was born out of the ashes of stars that might have died on the opposite side of the galaxy, several billion years before the Sun's birth, whose ashes then got thoroughly distributed by the mixing of the interstellar medium.


Parent stars of our Sun - Where are its remains? - Astronomy

We can now take a brief introductory tour of the universe as astronomers understand it today to get acquainted with the types of objects and distances you will encounter throughout the text. We begin at home with Earth, a nearly spherical planet about 13,000 kilometers in diameter (Figure 1). A space traveler entering our planetary system would easily distinguish Earth from the other planets in our solar system by the large amount of liquid water that covers some two thirds of its crust. If the traveler had equipment to receive radio or television signals, or came close enough to see the lights of our cities at night, she would soon find signs that this watery planet has sentient life.

Figure 1: Humanity’s Home Base. This image shows the Western hemisphere as viewed from space 35,400 kilometers (about 22,000 miles) above Earth. Data about the land surface from one satellite was combined with another satellite’s data about the clouds to create the image. (credit: modification of work by R. Stockli, A. Nelson, F. Hasler, NASA/ GSFC/ NOAA/ USGS)

Our nearest astronomical neighbor is Earth’s satellite, commonly called the Moon. Figure 2 shows Earth and the Moon drawn to scale on the same diagram. Notice how small we have to make these bodies to fit them on the page with the right scale. The Moon’s distance from Earth is about 30 times Earth’s diameter, or approximately 384,000 kilometers, and it takes about a month for the Moon to revolve around Earth. The Moon’s diameter is 3476 kilometers, about one fourth the size of Earth.

Figure 2: Earth and Moon, Drawn to Scale. This image shows Earth and the Moon shown to scale for both size and distance. (credit: modification of work by NASA)

Light (or radio waves) takes 1.3 seconds to travel between Earth and the Moon. If you’ve seen videos of the Apollo flights to the Moon, you may recall that there was a delay of about 3 seconds between the time Mission Control asked a question and the time the astronauts responded. This was not because the astronomers were thinking slowly, but rather because it took the radio waves almost 3 seconds to make the round trip.

Earth revolves around our star, the Sun, which is about 150 million kilometers away—approximately 400 times as far away from us as the Moon. We call the average Earth–Sun distance an astronomical unit (AU) because, in the early days of astronomy, it was the most important measuring standard. Light takes slightly more than 8 minutes to travel 1 astronomical unit, which means the latest news we receive from the Sun is always 8 minutes old. The diameter of the Sun is about 1.5 million kilometers Earth could fit comfortably inside one of the minor eruptions that occurs on the surface of our star. If the Sun were reduced to the size of a basketball, Earth would be a small apple seed about 30 meters from the ball.

It takes Earth 1 year (3 × 10 7 seconds) to go around the Sun at our distance to make it around, we must travel at approximately 110,000 kilometers per hour. (If you, like many students, still prefer miles to kilometers, you might find the following trick helpful. To convert kilometers to miles, just multiply kilometers by 0.6. Thus, 110,000 kilometers per hour becomes 66,000 miles per hour.) Because gravity holds us firmly to Earth and there is no resistance to Earth’s motion in the vacuum of space, we participate in this extremely fast-moving trip without being aware of it day to day.

Earth is only one of eight planets that revolve around the Sun. These planets, along with their moons and swarms of smaller bodies such as dwarf planets, make up the solar system (Figure 3). A planet is defined as a body of significant size that orbits a star and does not produce its own light. (If a large body consistently produces its own light, it is then called a star.) Later in the book this definition will be modified a bit, but it is perfectly fine for now as you begin your voyage.

Figure 3: Our Solar Family. The Sun, the planets, and some dwarf planets are shown with their sizes drawn to scale. The orbits of the planets are much more widely separated than shown in this drawing. Notice the size of Earth compared to the giant planets. (credit: modification of work by NASA)

We are able to see the nearby planets in our skies only because they reflect the light of our local star, the Sun. If the planets were much farther away, the tiny amount of light they reflect would usually not be visible to us. The planets we have so far discovered orbiting other stars were found from the pull their gravity exerts on their parent stars, or from the light they block from their stars when they pass in front of them. We can’t see most of these planets directly, although a few are now being imaged directly.

The Sun is our local star, and all the other stars are also enormous balls of glowing gas that generate vast amounts of energy by nuclear reactions deep within. We will discuss the processes that cause stars to shine in more detail later in the book. The other stars look faint only because they are so very far away. If we continue our basketball analogy, Proxima Centauri, the nearest star beyond the Sun, which is 4.3 light-years away, would be almost 7000 kilometers from the basketball.

When you look up at a star-filled sky on a clear night, all the stars visible to the unaided eye are part of a single collection of stars we call the Milky Way Galaxy, or simply the Galaxy. (When referring to the Milky Way, we capitalize Galaxy when talking about other galaxies of stars, we use lowercase galaxy.) The Sun is one of hundreds of billions of stars that make up the Galaxy its extent, as we will see, staggers the human imagination. Within a sphere 10 light-years in radius centered on the Sun, we find roughly ten stars. Within a sphere 100 light-years in radius, there are roughly 10,000 (10 4 ) stars—far too many to count or name—but we have still traversed only a tiny part of the Milky Way Galaxy. Within a 1000-light-year sphere, we find some ten million (10 7 ) stars within a sphere of 100,000 light-years, we finally encompass the entire Milky Way Galaxy.

Figure 4. Spiral Galaxy. This galaxy of billions of stars, called by its catalog number NGC 1073, is thought to be similar to our own Milky Way Galaxy. Here we see the giant wheel-shaped system with a bar of stars across its middle. (credit: NASA, ESA)

Our Galaxy looks like a giant disk with a small ball in the middle. If we could move outside our Galaxy and look down on the disk of the Milky Way from above, it would probably resemble the galaxy in Figure 4, with its spiral structure outlined by the blue light of hot adolescent stars.

The Sun is somewhat less than 30,000 light-years from the center of the Galaxy, in a location with nothing much to distinguish it. From our position inside the Milky Way Galaxy, we cannot see through to its far rim (at least not with ordinary light) because the space between the stars is not completely empty. It contains a sparse distribution of gas (mostly the simplest element, hydrogen) intermixed with tiny solid particles that we call interstellar dust. This gas and dust collect into enormous clouds in many places in the Galaxy, becoming the raw material for future generations of stars. Figure 5 shows an image of the disk of the Galaxy as seen from our vantage point.

Figure 5. Milky Way Galaxy. Because we are inside the Milky Way Galaxy, we see its disk in cross-section flung across the sky like a great milky white avenue of stars with dark “rifts” of dust. In this dramatic image, part of it is seen above Trona Pinnacles in the California desert. (credit: Ian Norman)

Typically, the interstellar material is so extremely sparse that the space between stars is a much better vacuum than anything we can produce in terrestrial laboratories. Yet, the dust in space, building up over thousands of light-years, can block the light of more distant stars. Like the distant buildings that disappear from our view on a smoggy day in Los Angeles, the more distant regions of the Milky Way cannot be seen behind the layers of interstellar smog. Luckily, astronomers have found that stars and raw material shine with various forms of light, some of which do penetrate the smog, and so we have been able to develop a pretty good map of the Galaxy.

Recent observations, however, have also revealed a rather surprising and disturbing fact. There appears to be more—much more—to the Galaxy than meets the eye (or the telescope). From various investigations, we have evidence that much of our Galaxy is made of material we cannot currently observe directly with our instruments. We therefore call this component of the Galaxy dark matter. We know the dark matter is there by the pull its gravity exerts on the stars and raw material we can observe, but what this dark matter is made of and how much of it exists remain a mystery. Furthermore, this dark matter is not confined to our Galaxy it appears to be an important part of other star groupings as well.

Figure 6: Star Cluster. This large star cluster is known by its catalog number, M9. It contains some 250,000 stars and is seen more clearly from space using the Hubble Space Telescope. It is located roughly 25,000 light-years away. (credit: NASA, ESA)

By the way, not all stars live by themselves, as the Sun does. Many are born in double or triple systems with two, three, or more stars revolving about each other. Because the stars influence each other in such close systems, multiple stars allow us to measure characteristics that we cannot discern from observing single stars. In a number of places, enough stars have formed together that we recognized them as star clusters (Figure 6). Some of the largest of the star clusters that astronomers have cataloged contain hundreds of thousands of stars and take up volumes of space hundreds of light-years across.

You may hear stars referred to as “eternal,” but in fact no star can last forever. Since the “business” of stars is making energy, and energy production requires some sort of fuel to be used up, eventually all stars run out of fuel. This news should not cause you to panic, though, because our Sun still has at least 5 or 6 billion years to go. Ultimately, the Sun and all stars will die, and it is in their death throes that some of the most intriguing and important processes of the universe are revealed. For example, we now know that many of the atoms in our bodies were once inside stars. These stars exploded at the ends of their lives, recycling their material back into the reservoir of the Galaxy. In this sense, all of us are literally made of recycled “star dust.”


STAGE 1: A Giant Gas Cloud

A star be g ins life as a giant cloud of gas which is generally an accumulation of dust, gas and plasma.

Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds. At these temperatures, gases become molecular meaning that atoms bind together. CO and H2 are the most common molecules in interstellar gas clouds.


What Are The Most Famous Stars?

While there are untold billions of celestial objects visible in the nighttime sky, some of them are better known than others. Most of these are stars that are visible to the naked eye and very bright compared to other stellar objects. For this reason, most of them have a long history of being observed and studied by human beings, and most likely occupy an important place in ancient folklore.

So without further ado, here is a sampling of some of the better-known stars in that are visible in the nighttime sky:

Polaris:
Also known as the North Star (as well as the Pole Star, Lodestar, and sometimes Guiding Star), Polaris is the 45th brightest star in the night sky. It is very close to the north celestial pole, which is why it has been used as a navigational tool in the northern hemisphere for centuries. Scientifically speaking, this star is known as Alpha Ursae Minoris because it is the alpha star in the constellation Ursa Minor (the Little Bear).

The Polaris star system, as seen within the Ursa Minor constellation and up close. Credit: NASA, ESA, N. Evans (Harvard-Smithsonian CfA), and H. Bond (STScI)

It’s more than 430 light-years away from Earth, but its luminosity (being a white supergiant) makes it highly visible to us here on Earth. What’s more, rather than being a single supergiant, Polaris is actually a trinary star system, comprised of a main star (alpha UMi Aa) and two smaller companions (alpha UMi B, alpha UMi Ab). These, along with its two distant components (alpha UMi C, alpha UMi D), make it a multistar system.

Interestingly enough, Polaris wasn’t always the north star. That’s because Earth’s axis wobbles over thousands of years and points in different directions. But until such time as Earth’s axis moves farther away from the “Polestar”, it remains our guide.

Because it is what is known as a Cepheid variable star – i.e. a star that pulsates radially, varying in both temperature and diameter to produce brightness changes – it’s distance to our Sun has been the subject of revision. Many scientific papers suggest that it may be up to 30% closer to our Solar System than previously expected – putting it in the vicinity of 238 light years away.

Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King

Sirius:
Also known as the Dog Star, because it’s the brightest star in Canis Major (the “Big Dog”), Sirius is also the brightest star in the night sky. The name “Sirius” is derived from the Ancient Greek “Seirios“, which translates to “glowing” or “scorcher”. Whereas it appears to be a single bright star to the naked eye, Sirius is actually a binary star system, consisting of a white main-sequence star named Sirius A, and a faint white dwarf companion named Sirius B.

The reason why it is so bright in the sky is due to a combination of its luminosity and distance – at 6.8 light years, it is one of Earth’s nearest neighbors. And in truth, it is actually getting closer. For the next 60,000 years or so, astronomers expect that it will continue to approach our Solar System at which point, it will begin to recede again.

In ancient Egypt, it was seen as a signal that the flooding of the Nile was close at hand. For the Greeks, the rising of Sirius in the night sky was a sign of the”dog days of summer”. To the Polynesians in the southern hemisphere, it marked the approach of winter and was an important star for navigation around the Pacific Ocean.

Alpha Centauri System:
Also known as Rigel Kent or Toliman, Alpha Centauri is the brightest star in the southern constellation of Centaurus and the third brightest star in the night sky. It is also the closest star system to Earth, at just a shade over four light-years. But much like Sirius and Polaris, it is actually a multistar system, consisting of Alpha Centauri A, B, and Proxima Centauri (aka. Centauri C).

Artist’s impression of the planet around Alpha Centauri B. Credit: ESO

Based on their spectral classifications, Alpha Centauri A is a main sequence white dwarf with roughly 110% of the mass and 151.9% the luminosity of our Sun. Alpha Centauri B is an orange subgiant with 90.7% of the Sun’s mass and 44.5% of its luminosity. Proxima Centauri, the smallest of the three, is a red dwarf roughly 0.12 times the mass of our Sun, and which is the closest of the three to our Solar System.

English explorer Robert Hues was the first European to make a recorded mention of Alpha Centauri, which he did in his 1592 work Tractatus de Globis. In 1689, Jesuit priest and astronomer Jean Richaud confirmed the existence of a second star in the system. Proxima Centauri was discovered in 1915 by Scottish astronomer Robert Innes, Director of the Union Observatory in Johannesburg, South Africa.

In 2012, astronomers discovered an Earth-sized planet around Alpha Centauri B. Known as Alpha Centauri Bb, it’s close proximity to its parent star likely means that it is too hot to support life.

Betelgeuse:
Pronounced “Beetle-juice” (yes, the same as the 1988 Tim Burton movie), this bright red supergiant is roughly 65o light-year from Earth. Also known as Alpha Orionis, it is nevertheless easy to spot in the Orion constellation since it is one of the largest and most luminous stars in the night sky.

Betelgeuse, as seen by the Hubble Space Telescope, and in relation to the Orion constellation. Credit: NASA

The star’s name is derived from the Arabic name Ibt al-Jauza’ , which literally means “the hand of Orion”. In 1985, Margarita Karovska and colleagues from the Harvard–Smithsonian Center for Astrophysics, announced the discovery of two close companions orbiting Betelgeuse. While this remains unconfirmed, the existence of possible companions remains an intriguing possibility.

What excites astronomers about Betelgeuse is it will one day go supernova, which is sure to be a spectacular event that people on Earth will be able to see. However, the exact date of when that might happen remains unknown.

Rigel:
Also known as Beta Orionis, and located between 700 and 900 light years away, Rigel is the brightest star in the constellation Orion and the seventh brightest star in the night sky. Here too, what appears to be a blue supergiant is actually a multistar system. The primary star (Rigel A) is a blue-white supergiant that is 21 times more massive than our sun, and shines with approximately 120,000 times the luminosity.

Rigel B is itself a binary system, consisting of two main sequence blue-white subdwarf stars. Rigel B is the more massive of the pair, weighing in at 2.5 Solar masses versus Rigel C’s 1.9. Rigel has been recognized as being a binary since at least 1831 when German astronomer F.G.W. Struve first measured it. A fourth star in the system has been proposed, but it is generally considered that this is a misinterpretation of the main star’s variability.

Rigel A is a young star, being only 10 million years old. And given its size, it is expected to go supernova when it reaches the end of its life.

Vega:
Vega is another bright blue star that anchors the otherwise faint Lyra constellation (the Harp). Along with Deneb (from Cygnus) and Altair (from Aquila), it is a part of the Summer Triangle in the Northern hemisphere. It is also the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere (after Arcturus).

Characterized as a white dwarf star, Vega is roughly 2.1 times as massive as our Sun. Together with Arcturus and Sirius, it is one of the most luminous stars in the Sun’s neighborhood. It is a relatively close star at only 25 light-years from Earth.

Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was also one of the first stars whose distance was estimated through parallax measurements, and has served as the baseline for calibrating the photometric brightness scale. Vega’s extensive history of study has led it to be termed “arguably the next most important star in the sky after the Sun.”

Artist’s concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega. Credit: NASA/JPL/Caltech/T. Pyle (SSC)

Based on observations that showed excess emission of infrared radiation, Vega is believed to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk. For this reason, stars that display an infrared excess because of circumstellar dust are termed “Vega-like stars”.

Thousands of years ago, (ca. 12,000 BCE) Vega was used as the North Star is today, and will be so again around the year 13,727 CE.

Pleiades:
Also known as the “Seven Sisters”, Messier 45 or M45, Pleiades is actually an open star cluster located in the constellation of Taurus. At an average distance of 444 light years from our Sun, it is one of the nearest star clusters to Earth, and the most visible to the naked eye. Though the seven largest stars are the most apparent, the cluster actually consists of over 1,000 confirmed members (along with several unconfirmed binaries).

The core radius of the cluster is about 8 light years across, while it measures some 43 light years at the outer edges. It is dominated by young, hot blue stars, though brown dwarfs – which are just a fraction of the Sun’s mass – are believed to account for 25% of its member stars.

Pleiades, also known as M45, is a prominent open star cluster in the sky. Image Credit: Jamie Ball

The age of the cluster has been estimated at between 75 and 150 million years, and it is slowly moving in the direction of the “feet” of what is currently the constellation of Orion. The cluster has had several meanings for many different cultures here on Earth, which include representations in Biblical, ancient Greek, Asian, and traditional Native American folklore.

Antares:
Also known as Alpha Scorpii, Antares is a red supergiant and one of the largest and most luminous observable stars in the nighttime sky. It’s name – which is Greek for “rival to Mars” (aka. Ares) – refers to its reddish appearance, which resembles Mars in some respects. It’s location is also close to the ecliptic, the imaginary band in the sky where the planets, Moon and Sun move.

This supergiant is estimated to be 17 times more massive, 850 times larger in terms of diameter, and 10,000 times more luminous than our Sun. Hence why it can be seen with the naked eye, despite being approximately 550 light-years from Earth. The most recent estimates place its age at 12 million years.

A red supergiant, Antares is over 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Credit: NASA/Ivan Eder

Antares is the seventeenth brightest star that can be seen with the naked eye and the brightest star in the constellation Scorpius. Along with Aldebaran, Regulus, and Fomalhaut, Antares comprises the group known as the ‘Royal stars of Persia’ – four stars that the ancient Persians (circa. 3000 BCE) believed guarded the four districts of the heavens.

Canopus:
Also known as Alpha Carinae, this white giant is the brightest star in the southern constellation of Carina and the second brightest star in the nighttime sky. Located over 300 light-years away from Earth, this star is named after the mythological Canopus, the navigator for king Menelaus of Sparta in The Iliad.

Thought it was not visible to the ancient Greeks and Romans, the star was known to the ancient Egyptians, as well as the Navajo, Chinese and ancient Indo-Aryan people. In Vedic literature, Canopus is associated with Agastya, a revered sage who is believed to have lived during the 6th or 7th century BCE. To the Chinese, Canopus was known as the “Star of the Old Man”, and was charted by astronomer Yi Xing in 724 CE.

Image of Canopus, as taken by crew members aboard the ISS. Credit: NASA

It is also referred to by its Arabic name Suhayl (Soheil in persian), which was given to it by Islamic scholars in the 7th Century CE. To the Bedouin people of the Negev and Sinai, it was also known as Suhayl, and used along with Polaris as the two principal stars for navigation at night.

It was not until 1592 that it was brought to the attention of European observers, once again by Robert Hues who recorded his observations of it alongside Achernar and Alpha Centauri in his Tractatus de Globis (1592).

As he noted of these three stars, “Now, therefore, there are but three Stars of the first magnitude that I could perceive in all those parts which are never seene here in England. The first of these is that bright Star in the sterne of Argo which they call Canobus. The second is in the end of Eridanus. The third is in the right foote of the Centaure.”

This star is commonly used for spacecraft to orient themselves in space, since it is so bright compared to the stars surrounding it.

Universe Today has articles on what is the North Star and types of stars. Here’s another article about the 10 brightest stars. Astronomy Cast has an episode on famous stars.


Planet 'reared' by four parent stars

This artist's conception shows the 30 Ari system, which includes four stars and a planet. The planet, a gas giant, orbits its primary star (yellow) in about a year's time. The primary star, called 30 Ari B, has a companion -- the small "red dwarf" star shown at upper left. This pair of stars is itself locked in a long-distance orbit with another pair of stars (upper right), known as 30 Ari A. Researchers using instruments at the Palomar Observatory near San Diego, Calif., recently discovered the red star at upper left, bringing the total number of known stars in the system from three to four. Credit: Image copyright: Karen Teramura, UH IfA

Growing up as a planet with more than one parent star has its challenges. Though the planets in our solar system circle just one star—our sun—other more distant planets, called exoplanets, can be reared in families with two or more stars. Researchers wanting to know more about the complex influences of multiple stars on planets have come up with two new case studies: a planet found to have three parents, and another with four.

The discoveries were made using instruments fitted to telescopes at the Palomar Observatory in San Diego: the Robo-AO adaptive optics system, developed by the Inter-University Center for Astronomy and Astrophysics in India and the California Institute of Technology in Pasadena, and the PALM-3000 adaptive optics system, developed by NASA's Jet Propulsion Laboratory in Pasadena, California, and Caltech.

This is only the second time a planet has been identified in a quadruple star system. While the planet was known before, it was thought to have only three stars, not four. The first four-star planet, KIC 4862625, was discovered in 2013 by citizen scientists using public data from NASA's Kepler mission.

The latest discovery suggests that planets in quadruple star systems might be less rare than once thought. In fact, recent research has shown that this type of star system, which usually consists of two pairs of twin stars slowly circling each other at great distances, is itself more common than previously believed.

"About four percent of solar-type stars are in quadruple systems, which is up from previous estimates because observational techniques are steadily improving," said co-author Andrei Tokovinin of the Cerro Tololo Inter-American Observatory in Chile.

The four stars and one planet of the 30 Ari system are illustrated in this diagram. This quadruple star system consists of two pairs of stars: 30 Ari B and 30 Ari A. A gas giant planet (red) orbits one of the stars in 30 Ari B about once a year. New observations led by NASA's Jet Propulsion Laboratory in Pasadena, California, identified the fourth star in the system (green) the three others stars and the planet were previously known. This is the second quadruple star system known to host a planet. The orbits shown are only approximations and are not as circular as they appear. Distances are not drawn to scale. Credit: NASA/JPL-Caltech

The newfound four-star planetary system, called 30 Ari, is located 136 light-years away in the constellation Aries. The system's gaseous planet is enormous, with 10 times the mass of Jupiter, and it orbits its primary star every 335 days. The primary star has a relatively close partner star, which the planet does not orbit. This pair, in turn, is locked in a long-distance orbit with another pair of stars about 1,670 astronomical units away (an astronomical unit is the distance between Earth and the sun). Astronomers think it's highly unlikely that this planet, or any moons that might circle it, could sustain life.

Were it possible to see the skies from this world, the four parent stars would look like one small sun and two very bright stars that would be visible in daylight. One of those stars, if viewed with a large enough telescope, would be revealed to be a binary system, or two stars orbiting each other.

In recent years, dozens of planets with two or three parent stars have been found, including those with "Tatooine" sunsets reminiscent of the Star Wars movies. Finding planets with multiple parents isn't too much of a surprise, considering that binary stars are more common in our galaxy than single stars.

"Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems," said Lewis Roberts of JPL, lead author of the new findings appearing in the journal Astronomical Journal. "It's amazing the way nature puts these things together."

Roberts and his colleagues want to understand the effects that multiple parent stars can have on their developing youthful planets. Evidence suggests that stellar companions can influence the fate of planets by changing the planets' orbits and even triggering some to grow more massive. For example, the "hot Jupiters"—planets around the mass of Jupiter that whip closely around their stars in just days—might be gently nudged closer to their primary parent star by the gravitational hand of a stellar companion.

In the new study, the researchers describe using the automated Robo-AO system on Palomar Observatory to scan the night skies, searching hundreds of stars each night for signs of stellar companions. They found two candidates hosting exoplanets: the four-star system 30 Ari, and a triple-star planetary system called HD 2638. The findings were confirmed using the higher-resolution PALM-3000 instrument, also at Palomar Observatory.

The new planet with a trio of stars is a hot Jupiter that circles its primary star tightly, completing one lap every three days. Scientists already knew this primary star was locked in a gravitational tango with another star, about 0.7 light-years away, or 44,000 astronomical units. That's relatively far apart for a pair of stellar companions. The latest discovery is of a third star in the system, which orbits the primary star from a distance of 28 astronomical units—close enough to have influenced the hot Jupiter's development and final orbit.

"This result strengthens the connection between multiple star systems and massive planets," said Roberts.

In the case of Ari 30, the discovery brought the number of known stars in the system from three to four. The fourth star lies at a distance of 23 astronomical units from the planet. While this stellar companion and its planet are closer to each other than those in the HD 2638 system, the newfound star does not appear to have impacted the orbit of the planet. The exact reason for this is uncertain, so the team is planning further observations to better understand the orbit of the star and its complicated family dynamics.


Habitable Planets:

The first exoplanet confirmed by Kepler to have an average orbital distance that placed it within its star’s habitable zone was Kepler-22b. This planet is located about 600 light-years from Earth in the constellation of Cygnus and was first observed on May 12th, 2009, and then confirmed on Dec 5th, 2011. Based on all the data obtained, scientists believe that this world is roughly 2.4 times the radius of Earth and either has oceans or a watery outer shell.

The discovery of exoplanets has also intensified interest in the search for extraterrestrial life, particularly for those that orbit in the host star’s habitable zone. Also known as the “goldilocks zone“, this is the region of the solar system where conditions are warm enough (but not too warm) so that it is possible for liquid water (and therefore life) to exist on the planet’s surface.

Prior to the deployment of Kepler, the vast majority of confirmed exoplanets fell into the category of Jupiter-sized or larger. However, over the course of its missions, Kepler managed to identify over 6000 potential candidates, many of them falling into the categories of Earth-size or “Super-Earth” size. Many of these are located in the habitable zone of their parent stars, and some even around Sun-like stars.

And according to a study conducted by NASA’s Ames Research Center, analysis of the Kepler mission data indicated that about 24% of M-class stars may harbor potentially habitable, Earth-size planets (i.e. those that are smaller than 1.6 times the radius of Earth’s). Based upon the number of M-class stars in the galaxy, that alone represents about 10 billion potentially habitable, Earth-like worlds.

Meanwhile, analyses of the K2 phase suggest that about one-quarter of the larger stars surveyed may also have an Earth-size planet orbiting within their habitable zones. Taken together, the stars observed by Kepler make up about 70% of those found within the Milky Way. So one can estimate that there are literally tens of billions of potentially habitable planets in our galaxy alone.


Astronomers discover exoplanet where it rains sunscreen

By Keith A. Spencer
Published October 29, 2017 7:30PM (EDT)

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If you're going to Kepler 13Ab, don't worry about forgetting your sunscreen.

Scientists at Penn State University, using observational data from the Hubble Space Telescope's Wide Field Camera 3, studied the gaseous planet's atmosphere and observed that the atmosphere "snows" titanium oxide — which is a close relative of the UV-blocking component of the strongest sunscreens, and what temporarily stains human skin white when copiously applied.

If you've ever used serious day-at-the-beach grade sunscreen, the kind that lasts all day without rubbing off, you're almost certainly using either zinc oxide or titanium dioxide sunscreen. Just as polished metals like brass and aluminum tend to be shiny and reflective, metal oxides like zinc oxide and titanium dioxide are similar and can be used to reflect back the sun's harmful rays — like having a liquid metal sheath over your skin. (The nonprofit watchdog group Environmental Working Group actually recommends titanium dioxide sunscreen as one of the safest.) What scientists detected in Kepler 13Ab's atmosphere was technically titanium oxide, as opposed to the sunscreen-component titanium dioxide, mainly because the temperature under which the atoms fused yielded a slightly different molecule with one less oxygen atom.

Still, you would need a lot of sunscreen to avoid getting a sunburn on Kepler 13Ab. That's because it orbits quite close to its parent star — far closer than Mercury orbits our sun — and also because its parent star, Kepler 13A, is much, much hotter and larger than our sun. As such, the sun-facing side of Kepler 13Ab is a toasty 5,000 Fahrenheit, beyond the point at which most metals turn to liquid.

Kepler 13Ab is part of a class of planets known as "hot Jupiters" — gaseous worlds the size of Jupiter or larger, yet which orbit their sun(s) much closer than Jupiter does ours, yielding scorching-hot gaseous planets. A large number of discovered exoplanets are of the hot Jupiter variety this is because larger exoplanets are easier to detect than smaller Earth-sized ones, and also because planets orbiting closer to their parent stars tend to be easier to detect due to the nature of the observational methods generally used to hunt exoplanets.

Besides being scorching and having metal oxide snowfall, Kepler 13Ab has the added unpleasantry of being tidally locked in its orbit around its parent star. "Tidal locking" refers to a phenomenon where a planet or moon's rotation matches its revolution — in other words, Kepler 13Ab only spins on its axis once in the time that it orbits its star, meaning that the same side of the planet always faces its sun, and the opposite side is always dark. Earth readers may recall that our moon is in tidal lock with Earth hence, we only see one face of the moon from our perspective.

"The sunscreen snowfall happens only on the planet's permanent nighttime side," notes the press release from the Penn State scientists. "Any visitors to this exoplanet would need to bottle up some of that sunscreen, because they won't find it on the sizzling-hot daytime side." The scientists describe the process by which the titanium oxide snowfall happens as such:

. powerful winds on Kepler-13Ab carry the titanium oxide gas around, condensing it into crystalline flakes that form clouds. Kepler-13Ab's strong surface gravity -- six times greater than Jupiter's -- then pulls the titanium oxide snow out of the upper atmosphere and traps it in the lower atmosphere on the nighttime side of the planet.

Many exoplanets (that's the technical term for planets orbiting stars besides our own) that have been discovered so far have been tidally locked with their parent star it is relatively common in the solar system. It is unclear whether life could form on a tidally-locked planet, mainly because the temperature differential is vast and weather patterns are so different studying planets in tidal lock helps give scientists insight into habitability and properties of such worlds.

Keith A. Spencer

Keith A. Spencer is a senior editor for Salon. He manages Salon's science, tech, economy and health coverage. His book, "A People's History of Silicon Valley: How the Tech Industry Exploits Workers, Erodes Privacy and Undermines Democracy," was released in 2018. Follow him on Twitter at @keithspencer, or on Facebook here.

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Red Dwarfs May Be Unfit Parent Stars

Red dwarf stars are the smallest true stars dancing around in our Galaxy, as well as the most abundant. Because of their small size--by star standards, that is--they can "live" for trillions of years on the hydrogen-burning main-sequence, and the Universe itself is "only" about 13.8 billion years old. For these reasons, many astronomers have suggested that most of the exoplanets in our Milky Way Galaxy circle "tiny" red dwarf stars--making these planetary systems prime targets in the hunt for life on other, distant worlds. However, a team of astronomers announced in June 2014 that life in the Universe may be rarer than previously believed, because their study found that harsh space weather might tear the atmosphere off any rocky world circling within a red dwarf's life-friendly habitable zone. The team of astronomers announced their discovery during a press conference at the 2014 summer meeting of the American Astronomical Society (AAS) held in Boston, Massachusetts.

"A red dwarf planet faces an extreme space environment, in addition to other stresses like tidal locking," commented Dr. Ofer Cohen to the press on June 2, 2014. Dr. Cohen is of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts.

Our own planet is protected from violent solar eruptions and space weather by its magnetic field, which essentially works like the shields of the Starship Enterprise of Star Trek. Earth's magnetic field serves to deflect approaching--and potentially destructive--blasts of energy. Our planet is also protected by its distance from the Sun, since it circles it at a comfortable 93 million miles!

Because a red dwarf's habitable zone is much further in towards its seething star than the Earth's distance from the Sun, any planet circling it would be subjected to more powerful and destructive space weather originating from its fiery stellar parent. The habitable zone of a star is that comfortable "Goldilocks" distance where the temperature is not too hot, not too cold, but just right for water to exist on its surface in a life-sustaining liquid state. Where liquid water exists, the potential for life as we know it, also exists.

Relatively small red dwarf stars compose the vast majority of stellar inhabitants of our large, majestic, barred-spiral Galaxy, the Milky Way--which sparkles with the fires of at least 100 billion stars. There are approximately 100 red dwarf systems dwelling within 25 light-years of Earth. These tiny stars are very faint, and because they emit such a comparatively puny amount of radiation, they can lurk in interstellar space quite secretively, well-hidden in our Galaxy, where they cannot be easily detected by the prying eyes of curious astronomers.

Red dwarfs are, therefore, the coolest, tiniest, and most common type of star. Estimates of their abundance range from 70% of all the stellar denizens of a spiral galaxy to more than 90% of all stars dwelling in elliptical galaxies. Usually, the median figure quoted is that red dwarfs account for 73% of all the stars dancing around in our Milky Way. Because of their relatively feeble energy output, these faint stars are never visible with the unaided human eye from Earth. The closest red dwarf to our Star, the Sun is Proxima Centauri, and it is a glittering member of a triple system of sister stars. Proxima Centauri (which is also the Sun's nearest stellar neighbor), is much too dim to be viewed from Earth with the naked eye--as is the closest solitary red dwarf named Barnard's star.

In recent years, astrobiologists and astronomers have been considering the possibility of life dwelling on alien worlds circling these tiny and very dim stars. A red dwarf sports the relatively small mass of only about one-tenth to one-half that of our Sun, and determining how their various characteristics affect the potential habitability of the planets that circle them may reveal to scientists the frequency of extraterrestrial life and intelligence.

Because red dwarf planets orbit so close to their parent stars, they are subjected to powerful tidal heating--which is certainly a major impediment to the evolution of delicate living things within these systems. Other tidal effects also make the development of life in such planetary systems difficult. For example, there are extreme temperature variations that result from the fact that one side of habitable zone red dwarf planets permanently face the star--while the other side is perpetually turned away. There are also non-tidal impediments to the evolution of tender living creatures on red dwarf worlds, such as small circumstellar habitable zones resulting from small light output. Other non-tidal impediments include extreme stellar variation, as well as spectral energy distributions that are shifted to the infrared part of the electromagnetic spectrum relative to our Sun.

However, many scientists have considered that several factors actually increase the chances for life to evolve on red dwarf worlds. For example, vigorous cloud formation on the star-facing side of a tidally locked alien world may lessen overall thermal flux, thus reducing equilibrium temperature variations between the two sides of the exoplanet. Furthermore, the sheer abundance of these faint little stars increases the number of potentially habitable alien worlds that may be circling them. As of 2013, scientists calculated that approximately 60 billion red dwarf worlds inhabit our Galaxy.

On our own planet Earth, the discovery of a vast and diverse array of bizarre creatures, collectively termed extremophiles, has encouraged some exobiologists to speculate that these cool and very abundant little stars may be the most likely alien worlds to finally discover extraterrestrial life. Extremophiles are organisms that can thrive under conditions that human beings find hostile--such as extremely hot environments, extremely cold environments, extremely acidic environments, and extremely dry environments.

Unfit To Be Parent Stars?

Earlier studies have focused on the impact of stellar flares that are violently hurled out by red dwarfs in the direction of a close-in, unfortunate exoplanet. However, the new study that was announced in June 2014 at the AAS summer meeting, instead examines the effect of persistent gusts of fierce stellar wind. The team of astronomers used a supercomputer model created at the University of Michigan to represent a trio of known red dwarf worlds orbiting a simulated, middle-aged star.

The team found than even a magnetic field, like that of our own planet, would not necessarily be able to protect a habitable zone alien world from its seething red dwarf star's persistent bombardment. Although there were intervals when the unfortunate planet's magnetic shield functioned effectively, it spent far too much time with weak shields than strong shields.

"The space environment of close-in exoplanets is much more extreme than what the Earth faces," study co-author Dr. Jeremy Drake told the press on June 2, 2014. Dr. Drake, of CfA, is a study co-author. "The ultimate consequence is that any planet potentially would have its atmosphere stripped over time," he continued to explain.

The ferocious and extreme space weather could also create breathtaking Northern Lights, or aurorae. The aurora lighting a red dwarf world's sky could be a whopping 100,000 times more powerful than those seen on Earth--and they could extend from the poles halfway to the equator.

"If Earth were orbiting a red dwarf, then people in Boston would get to see the Northern Lights every night. On the other hand, we'd also be in constant darkness because of tidal locking, and blasted by hurricane-force winds because of the dayside-nightside temperature contrast. I don't think even hardy New Englanders want to face that kind of weather," Dr. Cohen commented to the press on June 2, 2014.

Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.


The Nearest Sun-Like Star May Be As Miraculous As Our Own!

In the great cosmic ocean, there's only one planet that we know -- for certain -- has the right conditions and history to result in intelligent life: our own.

Image credit: NASA, from the Space Shuttle, for Sun-Earth Day 2008.

Life -- or even intelligent life -- may be possible in environments vastly different than our own: around different classes of stars, at different temperatures, and even with different molecules and/or chemical elements.

But we know for certain that it's definitely possible with the conditions we have here on Earth, given our Sun with its properties and its distance from us.

Image credit: F. Espenak of http://astropixels.com/, from this past August, 2012.

Our Sun is the only star in its system, has the temperature and luminosity properties of a G-type star, and the Earth is located at just the right distance that liquid water -- existing for long periods of time -- is prevalent on our world's surface.

You might be curious, looking up at the night sky, what the nearest star to us is that is also a G-type star, and the only star in its Solar System. To find it, just look in the constellation of Cetus, and find this clearly visible naked-eye star.

Image credit: Wikipedia user Till Credner's own work: via AlltheSky.com.

Tau Ceti is the 20th closest star system to us, only 12 light years distant. (That's less than a third the length of Han Solo's famous Kessel Run!) It's the same class as our Sun -- nearly the same temperature -- with 78% of our Sun's mass, and a corresponding smaller radius. It's also less active and less variable than our own Sun, and slightly "yellower" due to the slightly lower temperature.

Viewed from the same distance, the Sun and Tau Ceti would appear slightly different from one another, with the Sun on the left and Tau Ceti on the right.

Image credit: PaintShopPro illustration by contributor R.J. Hall.

For a long time, we didn't know whether Tau Ceti had any possibly habitable planets around it, or -- for that matter -- any planets at all! It's true, of course, that we've found thousands of planets around thousands of stars, and we now believe that the vast majority of stars do have planets around them.

Image credit: NASA / Kepler Mission / Kepler Science Team.

But that doesn't mean that we can look at any star we choose and know whether there are planets around it or not. The way we've found most of these planets is by the transit method, where we look at the variability in the amount of light coming from a distant star. If there's a planet (or multiple planets) that pass in between that star and our line-of-sight, it will block a small amount of that light during that planetary transit.

And over time (or, I should say, over many orbits), we can observe multiple transits by the same extra-solar planet, allowing us to determine how many planets there are in that star system that transit their parent star, as well as to measure the radius and semimajor axes of those worlds.

Image credit: NASA / Kepler Mission.

Even though this is likely to soon become the most prolific method of detecting extra-solar planets, it also has a fatal flaw which makes it unsuitable for detecting most of the planets around most of the stars out there.

Think about it for a second. The Sun is a pretty big object: it's slightly over one million kilometers (1.38 million, to be precise) in diameter, or about 109 times the diameter of the Earth. But it's really, really far away from the Earth, at an average distance of 150 million kilometers. We don't usually draw the Earth, Sun and Moon to scale when we talk about them, and there's a good reason for it: the distances between them are tremendous compared to the actual sizes of these objects. If we drew it to scale, it would look like this.

Image credit: The old Rapt in Awe blog / Driftway Observatory, http://www.giveyoujoy.net/awe/.

If you can't see the Earth, that's because it'd be just about a twentieth of one pixel in the image above! If you were at a random location in the sky, you'd have under a 1% chance of being able to detect Earth via this transit method only very fortuitously located worlds would have a shot.

But there is another, older method that could have a shot even if you weren't favorably aligned: Doppler Spectroscopy.

Image credit: Wikipedia User Zhatt.

The key to this method is that, while it's a very good approximation in our Solar System that the Sun remains fixed at the center while the planets orbit it in ellipses, a more accurate picture is that each of the planets also exert a gravitational pull on the Sun while they orbit it. This means -- as it moves towards and away from us -- the light from it will be blue-and-redshifted (respectively) in a periodic fashion.

Image credit: Wikimedia Commons user Reyk original work.

This works best if the planet does transit the star, but it also allows, in principle, for the detection of any planet in a system that's not exactly "face-on" to our line-of-sight. Because we know how gravitation works, when we observe a star "wobbling" (or moving forwards and backwards, periodically) with respect to our line-of-sight, we can infer the mass of every planet that causes this radial motion.

As long, that is, as we can find a signal that exceeds the noise of our measurements.

Image credit: The Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org, maintained by Dr. Jason Wright, Dr. Geoff Marcy, and the California Planet Survey consortium.

For small-mass planets, the effect is tiny, and so Earth-sized planets have been very difficult to detect using this method unless they're extremely close to their parent star.

But a newly discovered technique may have just doubled the sensitivity of this method, severely reducing the noise of this radial velocity technique. And our nearest Sun-like star system, Tau Ceti, is the first beneficiary!

Image credit: J. Pinfield / RoPACS network / University of Hertfordshire.

Five candidate planets have been discovered around this lone G-star just 12 light years away, using this new technique. It took 14 years of observational data, and many detailed spectroscopic measurements of this star, to build up enough orbits of the inner planets to find these worlds. Although the announcement is still tentative and the discovery unconfirmed, this is very exciting. According to the Australian Broadcasting Company:

Tau Ceti was selected to calibrate the new technique because it's a very stable star, which after 14 years of study, showed no signs of a planetary system.

"Because it's so close, bright and similar to the Sun, it's a particularly valuable target for study," says [Dr. Jonti] Horner.

Once all the noise had been accounted for using the new modelling techniques, astronomers detected a signal indicating the presence of a planetary system.

Oh, and did I mention, one of those planets is about the same distance from Tau Ceti as Venus is from the Sun, putting it squarely in Tau Ceti's habitable zone!

Image credit: Wikipedia user Chewie, derived from Ignacio javier igjav's work.

No one expected there to be planets around this star, much less a rocky world in the habitable zone it was pure serendipity that this star, selected for its stability and proximity to develop a noise-reducing technique for doppler spectroscopy, happened to have an interesting rocky, inner solar system.

And if these planets do get confirmed, and turn out to be real? The proximity and stability of Tau Ceti means that it will likely not be long before we measure the atmospheres of these worlds!

Image credit: Exoplanetary spectrum around HR 8799, via ESO / M. Janson.

There's still plenty of work to be done and plenty of caution to be exercised, but you have every reason to get excited about the future of planet hunting in general and the worlds around Tau Ceti in particular! If confirmed, this would be the closest-ever potentially habitable world to our own! Follow all the news on Exoplanets here you won't regret it!

So get to work on those starships, Mr. Musk and Mr. Branson there's too much to explore and discover to remain confined to Earth!

More like this

great post. curious though how they can determine this is a 'rocky' world, at least observationally? are they just theorizing based on similarities to our own G star?, assuming inner rocky worlds? composition of Tauu Ceti, that sort of thing?

The combination of mass, metallicity and temperature. If you have a world that's less than about 4 times the mass of Earth closer than the "ice-line" of the Solar System in question, it's going to be a rocky world.

There are grey areas farther out and at higher masses, but the one in the habitable zone -- if it's confirmed to exist -- can safely be called a rocky world.

Ethan, is it possible to do a back-of-the-envelope calculation of how well the James Webb telescope would be able to resolve the planet in the habitable zone, given its size and distance--would we able able to see continents, in the case of an extremely earth-like planet, for example?

I tried to work it out myself, but something is clearly wrong - maybe you can tell me what. The angle subtended by a planet roughly the diamter of the earth (10^7 m) at a distance of roughly 12 light years (10^17 m) is approximated by 10^-10 radians or 0.00002 arcseconds. The JWST information page tells me the smallest "pixel" is 0.0034 arcsecond -- which means this hypothetical planet would be 1/100th of a pixel. (That information is here: http://www.jwst.nasa.gov/faq_solarsystem.html#angularresolution )
But this doesn't take into account how long you observe for, so I obviously don't know what the JWST statement about resolution means. Do you know how to do this Ethan?

Assuming we confirm an Earth like planet, would we be able to figure out its orbit well enough to send a probe?

Question two: Can we get a probe sent off today that can get there before. oh, say. humanity splits into the Eloi and the Morlocks?

I'd like to add that long time ago, there was a discovery of a huge dust disk surrounding Tau Ceti using infrared observations. The dust accounts for roughly 120 times the mass of the dust surrounding our solar system and it was much closer to the star. If there is a planet in the inner system and if there is likely no Jupiter type asteroid collector further out, the inner planets would be bombarded from asteroids very often. So dont keep your hopes to high to find life on these planets, it might exist but it is likely to be under heavy bombardment from the heavens. Their world might be described as hell on exo-earth -)

Semmel, your point is taken, but consider an alternative analysis. We know of the existence of the dust belt at Tau-Ceti, but it may well be fine dust, rather than large rocks. If that is the case, then Tau-Ceti Beta, or whatever we choose to name the "habitable" planet may well be heavily seeded with amino-acid bearing micrometeorites, and probably has spectacular views of shooting stars on any given night. Also, Tau-Ceti being a lower mass star than Sol, it will have a much longer life span. I don't know if we've estimated it's age, but conceivably, life may have had a longer time to develop there, and with a richer pool of materials to start.
I won't be holding my breath, but it would be pretty cool to find out, one way or the other.

"But this doesn’t take into account how long you observe for, so I obviously don’t know what the JWST statement about resolution means. Do you know how to do this Ethan?"

Observation time only gives you the chance to intercept more photons, affecting how dim an object you can observe.

The maximum resolution of a telescope is going to be constant based on the size of the primary divided by the wavelength of light you're observing -- makes sense if you think about it, right? Then you use the field of view of the telescope to convert that into angular resolution.

However toying with the range of 0.6 to 28 um, a primary 6.5m, and a field of view of 2.2 arcmin gave me much higher numbers. And that's when I went "doi!" and remembered that there's a CCD responsible for actually turning the collected photons into data, and indeed it's with respect to this detector that the minimum 'pixel' size figure you quoted applies.

Assuming an "ideal' detector, the JWST optical system could in theory resolve objects as small as 1.22E-5 arcseconds at 0.6 um, or enough to make earth at that distance about 2 pixels in size.

Monty, that seems about right for the resolution. You can read about diffraction limited systems (which JWST will be) at http://en.wikipedia.org/wiki/Rayleigh_criterion#Explanation. Increasing the exposure length doesn't help, it's limited by basic wave mechanics.

On top of that, there are contrast issues with seeing a very dim object next to a very bright object, you need a coronograph or inteferometer that blocks out the light from the star. Plus, JWST will not measure in the visible spectrum, it's designed to see stuff far away that's red-shifted into the infrared.

CB, I think you're off on your calculations:
theta = arcsin(1.22*lambda/D) = 6.5e-6 degrees at 600nm = 4e-4 arcseconds.

whoops,
6.5e-6 degrees = 4e-4 arcminutes = 2e-2 arcseconds.

I'm not sure how exactly that corresponds to the spec Monty mentioned of 3.2e-3 arcseconds, but it's reasonable that the detector has 10 times the resolution of the optics.

Yes, you're right, I was off in the weeds.

Ok, so if the calculations above were close enough and there's really much less than one pixel to be devoted to the hypothetical planet, doesn't that mean JWST won't be able to detect such a planet after all?
I had gotten the impression that we'd be able to resolve planets enough to get spectral data from their atmosphere, but if an Earth 12 light-years away is not gettable, that's a bit disappointing.

Don't worry, uncleMonty, we would still be able to see it. There's a difference between detection and resolution -- the star's image would only illuminate a fraction of one pixel on the detector, but that just means that the detector won't be receiving as much light energy as it would if the pixel were fully illuminated. (A real-world analogy: you can't resolve stars with your unaided eye, but you can see them!)

We might be able to get a rough idea of the appearance of a planet of tau Ceti by watching the variations in brightness and color as it rotates. Before we were able to resolve Pluto we had a vague idea of some of its surface features using this method.

But I have bad news and good news about those planets. The bad news is that those "earthlike" planets may be much larger than the estimates cited in the press releases. What we can measure is m•sin(i), where i is the inclination of the orbit to our line of sight. So the estimates of two to six Earth masses are lower limits. Alas, there's evidence that we're viewing tau Ceti nearly pole-on, and the planetary system may be almost face-on from our viewpoint so sin(i) may be much less than 1 and the true masses may be several times greater -- Neptunes instead of Earths.

The good news is that there seems to be plenty of room in the tau Ceti system for at least one smaller planet in a stable orbit between e and f, smack in the middle of the habitable zone . which really is what we'd prefer. Planet e (the "earthlike" one" is about 0.5 AU from tau Ceti, and it would be kind of warm. The ideal location would be about 0.7 AUs from the star. And the orbit of a planet at that distance would be stable, and if the planet is the size and mass of Earth we wouldn't be able to detect it yet. In fact, the authors of the discovery paper make this point themselves, in Figure 16 and page 15 of the paper. Analysis of Kepler data indicates that low-eccentricity planetary systems tend to be "packed" -- if a planet can occupy a stable orbit, then there often will turn out to be one there when additional data comes in. So the possibility is still open for one or even two truly earthlike planets among the "hot Neptunes."

Yeah, the statements about resolution were regarding your original question, UncleMonty, about whether we'd be able to see continents. The answer is: Not even close.

That's a different question than whether or not it'd be possible to do spectroscopy on the light we do get from the planet. It's a very tricky thing to do, but possible.

CB, tickling the spectral data out of a star when the planet is in gibbous phase may reveal changes in the data that reveal surface features. There is a recent paper on this. [An asterochromograph gives accurate color variations, but it is only a prototype of my concotion. ]

Considering the wonderful graphics used, I would like to mention that the Sun is not a physically yellow appearing star, if seen from space at a comfortable attenuation. It is, as Newton called sunlght, "perfectly white". The yellow is a result of black and white spectral line studes by great folks like Fr. Secchi and, especially, Ms. Cannon, who's gargantuan work gave us our classification system (OBAFGKM)

So the possibility is still open for one or even two truly earthlike planets among the “hot Neptunes.”

. But how do you get a rocky planet between two gas giants?

I am glued to this topic with not auite so acute knowlege of the math. I do believe that unless we can advance dramatically with the new telescopes being launched, but also learn how to use a fraction of the energy we currently use in all we do, and dramatically advance our propulsion methods, it's all for nothing. Mankind must live in more than one location to survive, of that I'm sure.

It's all about propulsion.
Without a quantum leap, (no pun intended), in propulsion technology, finding an earth-like planet will result only in fanciful dreams and (im)possibilities.
Humans are not going there.
The fastest man-made object is traveling through space at 18 miles per second -- 75,000 years to the nearest star, (Alpha Centauri), at only 2.2 light years.
Even at near-light speed, a 12 year journey for humans, (to Tau Ceti for example), is fantastically impossible -- by a factor of perhaps a thousand.
Interstellar space is a dangerous nasty place -- even for humans in suspended animation.
Wormholes, if discovered, are suicidal folly.
I'm not particularly religious, but if God(s) placed mankind on planet earth insuring that humans will not leave it, (s)he/they could hardly have done a better job.
Humans are not going to these places -- ever.
Hopefully, our children or theirs will finally realize just how badly humans are abusing our precious home -- and find the ways to nurture it.
We, and our descendants, are here to stay.

We thankful are that sun and moon
Were placed so very high.
That no tempestuous hand might reach
To tear them from the sky.
Were it not so, we soon should find
That some reforming ass
Would straight propose to snuff them out,
And light the world with Gas.
Men might as well project a voyage to the Moon as attempt to employ steam navigation against the stormy North Atlantic Ocean!
Should man succeed in building a machine small enough to fly and large enough to carry himself, then in attempting to build a still larger machine he will find himself limited by the strength of his materials in the same manner and for the same reasons that nature has.

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Mythology

The ancient Greeks linked the constellation of Aquarius with Ganymede, the cup bearer to the gods. In the Greek mythos, Ganymede was a good-looking young man who was the object of Zeus’ affection.

He was brought to Mount Olympus to serve as cupbearer to the gods and was thus granted eternal youth in exchange. The constellation of Aquarius has several meanings and associations in other cultures as well.

The Babylonian astronomers identified the constellation of Aquarius as representing the god Ea, which was often depicted with an overflowing vessel.

Astrology

In astrology, Aquarius is the 11 th sign in the Zodiac and it represents those born between January 20, and February 18. As of 2002, the Sun appears in the constellation of Aquarius from 16 February to 11 March.

In tropical astrology, the Sun is considered to be in the sign Aquarius from 20 January to 19 February, and in sidereal astrology, from 15 February to 14 March.

Aquarius is also associated with the Age of Aquarius, a concept popular in the 1960s counterculture. Despite this prominence, the Age of Aquarius will not dawn until the year 2597, as an astrological age does not begin until the Sun is in a particular constellation on the vernal equinox.