Astronomy

New method for exoplanet detection?

New method for exoplanet detection?

Could it be possible to detect exoplanets that have an abundance of iridescent minerals by analyzing their star's spectra over time as the angle in observation would lead to changes in absorbed wavelengths?


Detecting Exoplanets

Astronomers have discovered exoplanets using a number of different methods:


Radial Velocity Method

The vast majority of exoplanets were discovered through the gravity force they exert on their parent star. In other words they make their stars 'wobble' about as the star-planet system circles around a common centre-of-mass.

If we look along the plane of the planet's orbit we see the wobble as movement of the star towards and away from us. If we are looking down on the system from above, as in the animation, then we see the wobble as an astrometric shift, i.e. the star does a small circle in the sky when compared to other nearby stars which are fixed in position.

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However, astronomers find it much easier to spot motion toward and away from us, the star's radial velocity, by observing its spectrum. Current technology allows us to detect radial velocities of just 1 metre per second - a fast walking pace. Jupiter causes the Sun to wobble by up to 12.5 metres per second, so it is no surprise that astronomers are now finding Jupiter-like planets.


Transit Method

Animation showing the light dip
as a planet transits its parent star
Credit: NJIT

Another method of finding exoplanets is simple enough that we can do it with the Liverpool Telescope. The method works by looking for regular dips in the brightness of a star as a large planet passes, or transits, in front of it

For close-orbiting giant planets, this dip in brightness can be as much as 2% of the original brightness and occurs every few days. In the wobble animation (above), the planet is orbiting at right-angles to us. As a result, there would be no chance of it passing in front of the star, but we now know of dozens of cases where transits do occur.

In fact, given the millions of stars in our galaxy, the chances are that many more are inclined such that a planet will block out a fraction of the parent star's light at some point. It is thought that around 1% of stars might have a transiting planet, although it is difficult to catch one in the act.


Direct Imaging Method

Image of planet around GQ Lupi
Credit: ESO

This technique aims to get an actual image of the planet as illuminated by the light from its parent star. This is more difficult than it may seem.

The star can be thousands of times brighter than the planet, such that the planet image is lost in the glare. Imagine trying to spot a candle in a searchlight. Also, the vast distances involved mean that telescopes find it hard to resolve (or separate) the star and planet, especially if they are close-orbiting planets.

Astronomers have developed instrumentation that reduces the contrast between the planet and star, such as using a "coronagraph" - a physical mask to block out light from the star. They also use techniques that reduce the effects of atmospheric turbulence, like using a space-based platform.

The image here was taken in 2005 and shows a planet (b) orbiting the star GQ Lupi (A) at a distance of twenty times the orbital distance of Jupiter.


New method to detect oxygen on exoplanets developed by researchers

Even before its launch in 2021, researchers have discovered a new way to use NASA's James Webb Space Telescope (JWST) to look for signs of oxygen on distant exoplanets, according to a new study.

The research notes that by looking for signals of oxygen molecules colliding in the atmospheres of these distant planets, scientists could "distinguish between living and nonliving planets," a statement accompanying the study reads.

"Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb," said Thomas Fauchez of NASA's Goddard Space Flight Center, in the statement. "This oxygen signal is known since the early 1980s from Earth's atmospheric studies but has never been studied for exoplanet research."

Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. Crescents are other planets in the system, and the red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger. (Credit: (NASA/GSFC/Friedlander-Griswold))

Using the JWST, researchers will look for light patterns in a planet's atmosphere when the oxygen molecules collide, they block some of the infrared light spectrum seen by the telescope, indicating their presence.

If researchers were to detect colliding oxygen molecules using the JWST, it's possible these planets could contain organisms that use photosynthesis to convert sunlight into energy. It's also possible that the oxygen may be on a planet that has no life at all, which is why the new technique is important, according to UC Riverside astrobiologist Edward Schwieterman.

"Oxygen is one of the most exciting molecules to detect because of its link with life, but we don't know if life is the only cause of oxygen in an atmosphere," Schwieterman said. "This technique will allow us to find oxygen in planets both living and dead."

If oxygen were present on an exoplanet that did not host life, it could be that it is outside of the "habitable zone," have a warmer-than-average atmosphere or it could have an abundance of water vapor from evaporating oceans, the researchers added.

"It is important to know whether and how much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not," Schwieterman added.

The study has been published in the scientific journal Nature Astronomy.

The JWST, the long-awaited successor to the Hubble Space Telescope, was finally assembled in August after two halves of the telescope were joined together in Redondo Beach, Calif.

The next steps for the telescope include engineers deploying the five-layer sunshield, which NASA said is "designed to keep Webb's mirrors and scientific instruments cold by blocking infrared light from the Earth, Moon and Sun." The space agency added that the deployment of the sunshield "is critical to mission success."

Following final testing, including environmental and deployment testing, the telescope will launch into space in 2021, taking over for the Hubble, which continues to make incredible discoveries since its launch into space in April 1990.


Scientists develop new method to detect oxygen on exoplanets

Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. Crescents are other planets in the system, and the red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger. Credit: NASA/GSFC/Friedlander-Griswold

Scientists have developed a new method for detecting oxygen in exoplanet atmospheres that may accelerate the search for life.

One possible indication of life, or biosignature, is the presence of oxygen in an exoplanet's atmosphere. Oxygen is generated by life on Earth when organisms such as plants, algae, and cyanobacteria use photosynthesis to convert sunlight into chemical energy.

UC Riverside helped develop the new technique, which will use NASA's James Webb Space Telescope to detect a strong signal that oxygen molecules produce when they collide. This signal could help scientists distinguish between living and nonliving planets.

Since exoplanets, which orbit stars other than our sun, are so far away, scientists cannot look for signs of life by visiting these distant worlds. Instead, they must use a cutting-edge telescope like Webb to see what's inside the atmospheres of exoplanets.

"Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb," said Thomas Fauchez of NASA's Goddard Space Flight Center and lead author of the study. "This oxygen signal is known since the early 1980s from Earth's atmospheric studies but has never been studied for exoplanet research."

UC Riverside astrobiologist Edward Schwieterman originally proposed a similar way of detecting high concentrations of oxygen from nonliving processes and was a member of the team that developed this technique. Their work was published today in the journal Nature Astronomy.

"Oxygen is one of the most exciting molecules to detect because of its link with life, but we don't know if life is the only cause of oxygen in an atmosphere," Schwieterman said. "This technique will allow us to find oxygen in planets both living and dead."

When oxygen molecules collide with each other, they block parts of the infrared light spectrum from being seen by a telescope. By examining patterns in that light, they can determine the composition of the planet's atmosphere.

Schwieterman helped the NASA team calculate how much light would be blocked by these oxygen collisions.

Intriguingly, some researchers propose oxygen can also make an exoplanet appear to host life when it does not, because it can accumulate in a planet's atmosphere without any life activity at all.

If an exoplanet is too close to its host star or receives too much star light, the atmosphere becomes very warm and saturated with water vapor from evaporating oceans. This water could then be broken down by strong ultraviolet radiation into atomic hydrogen and oxygen. Hydrogen, which is a light atom, escapes to space very easily, leaving the oxygen behind.

Over time, this process may cause entire oceans to be lost while building up a thick oxygen atmosphere—more even, than could be made by life. So, abundant oxygen in an exoplanet's atmosphere may not necessarily mean abundant life but may instead indicate a history of water loss.

Schwieterman cautions that astronomers are not yet sure how widespread this process may be on exoplanets.

"It is important to know whether and how much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not," he said.

Schwieterman is a visiting postdoctoral fellow at UCR who will soon start as assistant professor of astrobiology in the Department of Earth and Planetary Sciences.

The research received funding from Goddard's Sellers Exoplanet Environments Collaboration, which is funded in part by the NASA Planetary Science Division's Internal Scientist Funding Model. This project has also received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.

Webb will be the world's premier space science observatory when it launches in 2021. It will allow scientists to solve mysteries in our solar system, look to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.


Scientists develop new method to detect oxygen on exoplanets

Scientists have developed a new method for detecting oxygen in exoplanet atmospheres that may accelerate the search for life.

One possible indication of life, or biosignature, is the presence of oxygen in an exoplanet’s atmosphere. Oxygen is generated by life on Earth when organisms such as plants, algae, and cyanobacteria use photosynthesis to convert sunlight into chemical energy.

UC Riverside helped develop the new technique, which will use NASA’s James Webb Space Telescope to detect a strong signal that oxygen molecules produce when they collide. This signal could help scientists distinguish between living and nonliving planets.

Since exoplanets, which orbit stars other than our sun, are so far away, scientists cannot look for signs of life by visiting these distant worlds. Instead, they must use a cutting-edge telescope like Webb to see what’s inside the atmospheres of exoplanets.

“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb,” said Thomas Fauchez of NASA’s Goddard Space Flight Center and lead author of the study. “This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.”

UC Riverside astrobiologist Edward Schwieterman originally proposed a similar way of detecting high concentrations of oxygen from nonliving processes and was a member of the team that developed this technique. Their work was published today in the journal Nature Astronomy.

“Oxygen is one of the most exciting molecules to detect because of its link with life, but we don’t know if life is the only cause of oxygen in an atmosphere,” Schwieterman said. “This technique will allow us to find oxygen in planets both living and dead.”

When oxygen molecules collide with each other, they block parts of the infrared light spectrum from being seen by a telescope. By examining patterns in that light, they can determine the composition of the planet’s atmosphere. Schwieterman helped the NASA team calculate how much light would be blocked by these oxygen collisions.

Intriguingly, some researchers propose oxygen can also make an exoplanet appear to host life when it does not, because it can accumulate in a planet’s atmosphere without any life activity at all.

If an exoplanet is too close to its host star or receives too much star light, the atmosphere becomes very warm and saturated with water vapor from evaporating oceans. This water could then be broken down by strong ultraviolet radiation into atomic hydrogen and oxygen. Hydrogen, which is a light atom, escapes to space very easily, leaving the oxygen behind.

Over time, this process may cause entire oceans to be lost while building up a thick oxygen atmosphere — more even, than could be made by life. So, abundant oxygen in an exoplanet’s atmosphere may not necessarily mean abundant life but may instead indicate a history of water loss. Schwieterman cautions that astronomers are not yet sure how widespread this process may be on exoplanets.

“It is important to know whether and how much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not,” he said.

Schwieterman is a visiting postdoctoral fellow at UCR who will soon start as assistant professor of astrobiology in the Department of Earth and Planetary Sciences.

The research received funding from Goddard’s Sellers Exoplanet Environments Collaboration, which is funded in part by the NASA Planetary Science Division’s Internal Scientist Funding Model. This project has also received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.

Webb will be the world’s premier space science observatory when it launches in 2021. It will allow scientists to solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

Bill Steigerwald and Nancy Jones of NASA Goddard Space Flight Center made significant contributions to this article.


New Method May Expedite Search for Exoplanets with Atmospheres

By: Kate S. Petersen December 2, 2019 0

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A team of astronomers propose screening exoplanets by their temperatures to determine whether they host an atmosphere — and are worth following up.

Artist’s impression of a cool, red star surrounded by planets.
NASA / JPL-Caltech

Since the first confirmed discovery of an exoplanet in 1992, astronomers have scoured the skies for one that could support life as we know it: a planet that is rocky, has liquid water, and possesses an atmosphere. But their ability to investigate the 4,093 exoplanets confirmed so far is limited by available observational technology.

The March 2021 launch of NASA’s highly anticipated James Webb Space Telescope (JWST) is expected to change the game, allowing astronomers to make a more detailed look at the cosmos than ever before. Exoplanet observation time on JWST will be limited, as scientists with diverse interests compete for access. Hoping to make the most expeditious use of the new satellite, a team of researchers published a series of papers in the Astrophysical Journal, which together outline a new way to quickly detect atmospheres on rocky exoplanets, just by using daytime temperatures readings.

This artist’s impression shows one of the middle planets in the TRAPPIST-1 system, with the glare of the host star illuminating the rocky surface. Seven Earth-size planets orbit this ultracool dwarf star 40 light-years from Earth, but whether they host habitable atmospheres remains up for debate.
ESO / N. Bartmann / spaceengine.org

When a planet has an atmosphere, daytime heat from its star is redistributed throughout the planet by atmospheric winds, reducing overall daytime temperatures. This limits how hot the day side can get. If the telescope detects a day side that's cooler than that limit, “this is an indication for an atmosphere,” says Daniel Koll (MIT), a lead author on one of the papers. “It's not a solid detection—it's an inference. But the good thing is, an inference is very cheap. You can make it fast.” Koll says the method will allow researchers to scan exoplanets quickly and then double back for more information if they find one with a potential atmosphere.

Astronomers measure exoplanet daytime temperatures indirectly during the exoplanet’s secondary eclipse, when the exoplanet moves behind its star with respect to Earth. During the eclipse, the heat signal from the planet is obstructed, so astronomers measure the heat coming from just the star. When the planet moves back into view, it will add its heat to the signal. Astronomers subtract the star’s heat signature from the star-planet heat signature to calculate the planet’s daytime temperature.

If an exoplanet orbits its host star at an angle nearly perfectly edge on to Earth's line of sight, the planet will transit the star once per orbit. It will also pass behind its star each orbit, an event called a "secondary eclipse."

The proposed technique would complement spectroscopy, which can be used to detect atmospheres, but takes a long time. The new method can be used to sift through targets two to three times faster than spectroscopy would allow, says Eliza Kempton (University of Maryland), a coauthor on the papers.

“This whole set of papers is very much aiming to push the outside of the envelope of what we're able to observe today,” says Ian Crossfield (MIT), who was not involved in the studies.

The new technique is designed to evaluate exoplanets orbiting M-dwarf stars, which are redder, smaller, and dimmer than yellow stars like our Sun. Because they are smaller, they don’t outshine exoplanets to the degree brighter stars do, which makes the secondary eclipse more practical to observe.

The new technique is limited to evaluating exoplanets inside the inner edge of the so-called habitable zone — those that are probably too hot to support liquid water, and thus life. These hot planets, close to the star, are also thought to be most vulnerable to atmospheric stripping due to the duration and intensity of radiation produced by M dwarfs when they are young. However, Koll notes that if these hot planets have atmospheres that survived the star’s violent youth, then it’s likely cooler, farther-out planets would also retain their atmospheres.

Until JWST is in orbit, and we have another 1½ years to wait for that, the team’s technique will remain untested. But if it’s successful, Kempton says, their results will help direct the next steps in exoplanet exploration.

“If we find that these planets all lack atmospheres, then we should cancel our plans to search for life on M-dwarf planets and instead focus our efforts on building larger, next-generation telescopes that could image Earth-like planets orbiting stars more similar to the Sun,” she says.

“However, if we do find that the M-dwarf planets have atmospheres, then it's full speed ahead to characterizing those atmospheres and beginning the search for signs of life.”


New method for exoplanet detection? - Astronomy

Additional methods include:

  • Astrometry - precise measurements of a star path along the celestial sphere
  • Microlensing - the act of altering a path of light by the result of an unseen massive object (like a planet)
  • Optical and Infrared Interferometry - by combing the light from two or more telescopes, resolution is greatly increased

The rule of professional detection is increased spectrometer sensitivity and improved resolution. For spectrometer sensitivity:

An Echelle type spectrometer - like the image above - is the preferred style. There are five methods used to increase a spectrometers sensitivity:

  • Increase the number of grooves cut into a diffraction grating
  • Improved fiber optic quality
  • Extending the focal length of the light inside the spectrometer
  • Improved resolution of the CCD camera
  • Introduce Iodine gas through which light must pass prior to entering the slit of the spectrometer

The last method has been used the pioneering gurus of exoplanet detection Geoff Marcy and Paul Butler. By introducing iodine gas, the overall spectrum is enhanced and provides an iodine line on the spectra to act as a ruler for helping to increase accuracy in measurements.

The improved spectrometer is designed to increase sensitivity of detecting the "wobble" of a star:

and also to determine of an atmosphere is present on the unseen planet (a spectra of a star is known, so any added spectra will be assumed to be a part of the planets atmosphere).

This wobbling will affect the stars path along the sky. By using precise Astrometric measurements, the net effect can be determined by comparing the predicted path of the star with the actual path.

Microlensing if fairly new, but light from the star should be affected by a transiting planet:

Interferometry is the method of determining phase changes in an electro-magnetic signal. These changes are overlapped to cancel out any ambient noise so only the desired signal is enhanced. Radio Interferometry has been used for some time, and essentially is used to create a much larger, virtual disk that can detect larger wavelengths. Optical Interferometry is much more challenging since the wavelengths are much smaller. Unlike radio Interferometry where the distortions of the atmosphere result in phased distortion, more precise measure of small wavelengths are possible - but the sources of these short wavelengths are often very dim so optical interferometer components must include very large telescopes.

Take a look at the Additional Resource section to get up to date information direct from the pioneers in the field.


Scientists develop new method to detect oxygen on exoplanets

Scientists have developed a new method for detecting oxygen in exoplanet atmospheres that may accelerate the search for life.

One possible indication of life, or biosignature, is the presence of oxygen in an exoplanet’s atmosphere. Oxygen is generated by life on Earth when organisms such as plants, algae, and cyanobacteria use photosynthesis to convert sunlight into chemical energy.

UC Riverside helped develop the new technique, which will use NASA’s James Webb Space Telescope to detect a strong signal that oxygen molecules produce when they collide. This signal could help scientists distinguish between living and nonliving planets.

Since exoplanets, which orbit stars other than our sun, are so far away, scientists cannot look for signs of life by visiting these distant worlds. Instead, they must use a cutting-edge telescope like Webb to see what’s inside the atmospheres of exoplanets.

“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb,” said Thomas Fauchez of NASA’s Goddard Space Flight Center and lead author of the study. “This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.”

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UC Riverside astrobiologist Edward Schwieterman originally proposed a similar way of detecting high concentrations of oxygen from nonliving processes and was a member of the team that developed this technique. Their work was published today in the journal Nature Astronomy.

“Oxygen is one of the most exciting molecules to detect because of its link with life, but we don’t know if life is the only cause of oxygen in an atmosphere,” Schwieterman said. “This technique will allow us to find oxygen in planets both living and dead.”

When oxygen molecules collide with each other, they block parts of the infrared light spectrum from being seen by a telescope. By examining patterns in that light, they can determine the composition of the planet’s atmosphere.

Schwieterman helped the NASA team calculate how much light would be blocked by these oxygen collisions.

Intriguingly, some researchers propose oxygen can also make an exoplanet appear to host life when it does not, because it can accumulate in a planet’s atmosphere without any life activity at all.

If an exoplanet is too close to its host star or receives too much star light, the atmosphere becomes very warm and saturated with water vapor from evaporating oceans. This water could then be broken down by strong ultraviolet radiation into atomic hydrogen and oxygen. Hydrogen, which is a light atom, escapes to space very easily, leaving the oxygen behind.

Over time, this process may cause entire oceans to be lost while building up a thick oxygen atmosphere—more even, than could be made by life. So, abundant oxygen in an exoplanet’s atmosphere may not necessarily mean abundant life but may instead indicate a history of water loss.

Schwieterman cautions that astronomers are not yet sure how widespread this process may be on exoplanets.

“It is important to know whether and how much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not,” he said.

Schwieterman is a visiting postdoctoral fellow at UCR who will soon start as assistant professor of astrobiology in the Department of Earth and Planetary Sciences.

The research received funding from Goddard’s Sellers Exoplanet Environments Collaboration, which is funded in part by the NASA Planetary Science Division’s Internal Scientist Funding Model. This project has also received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.

Webb will be the world’s premier space science observatory when it launches in 2021. It will allow scientists to solve mysteries in our solar system, look to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

Provided by: University of California – Riverside

More information: Thomas J. Fauchez et la. Sensitive probing of exoplanetary oxygen via mid-infrared collisional absorption. Nature Astronomy (2020). DOI: 10.1038/s41550-019-0977-7

Image: Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. Crescents are other planets in the system, and the red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger.
Credit: NASA/GSFC/Friedlander-Griswold


Cornell postdoc detects possible exoplanet radio emission

By monitoring the cosmos with a radio telescope array, an international team of scientists has detected radio bursts emanating from the constellation Boötes – that could be the first radio emission collected from a planet beyond our solar system.

The team, led by Cornell postdoctoral researcher Jake D. Turner, Philippe Zarka of the Observatoire de Paris - Paris Sciences et Lettres University and Jean-Mathias Griessmeier of the Université d’Orléans will publish their findings in the forthcoming research section of Astronomy & Astrophysics, on Dec. 16.

“We present one of the first hints of detecting an exoplanet in the radio realm,” Turner said. “The signal is from the Tau Boötes system, which contains a binary star and an exoplanet. We make the case for an emission by the planet itself. From the strength and polarization of the radio signal and the planet’s magnetic field, it is compatible with theoretical predictions.”

Among the co-authors is Turner’s postdoctoral advisor Ray Jayawardhana, the Harold Tanner Dean of the College of Arts and Sciences, and a professor of astronomy.

“If confirmed through follow-up observations,” Jayawardhana said, “this radio detection opens up a new window on exoplanets, giving us a novel way to examine alien worlds that are tens of light-years away.”

Using the Low Frequency Array (LOFAR), a radio telescope in the Netherlands, Turner and his colleagues uncovered emission bursts from a star-system hosting a so-called hot Jupiter, a gaseous giant planet that is very close to its own sun. The group also observed other potential exoplanetary radio-emission candidates in the 55 Cancri (in the constellation Cancer) and Upsilon Andromedae systems. Only the Tau Boötes exoplanet system – about 51 light-years away – exhibited a significant radio signature, a unique potential window on the planet’s magnetic field.

Observing an exoplanet’s magnetic field helps astronomers decipher a planet’s interior and atmospheric properties, as well as the physics of star-planet interactions, said Turner, a member of Cornell’s Carl Sagan Institute.

Earth’s magnetic field protects it from solar wind dangers, keeping the planet habitable. “The magnetic field of Earth-like exoplanets may contribute to their possible habitability,” Turner said, “by shielding their own atmospheres from solar wind and cosmic rays, and protecting the planet from atmospheric loss.”

Two years ago, Turner and his colleagues examined the radio emission signature of Jupiter and scaled those emissions to mimic the possible signatures from a distant Jupiter-like exoplanet. Those results became the template for searching radio emission from exoplanets 40 to 100 light-years away.

After poring over nearly 100-hours of radio observations, the researchers were able to find the expected hot Jupiter signature in Tau Boötes. “We learned from our own Jupiter what this kind of detection looks like. We went searching for it and we found it,” Turner said.

The signature, though, is weak. “There remains some uncertainty that the detected radio signal is from the planet. The need for follow-up observations is critical,” he said.

Turner and his team have already begun a campaign using multiple radio telescopes to follow up on the signal from Tau Boötes.

In addition to Turner, Jayawardhana, Griessmeier and Zarka, the co-authors are Laurent Lamy and Baptiste Cecconi of the Observatoire de Paris, France Joseph Lazio from NASA’s Jet Propulsion Laboratory J. Emilio Enriquez and Imke de Pater from the University of California, Berkeley Julien N. Girard from Rhodes University, Grahamstown, South Africa and Jonathan D. Nichols from the University of Leicester, United Kingdom.

Turner, who laid the groundwork for this research while earning his doctorate at the University of Virginia, received funding from the National Science Foundation.


Detecting biomarkers on faraway exoplanets

Biomarkers have never been spotted in the atmosphere of an exoplanet, but a new generation of telescopes may be sensitive enough to detect them. Image credit: ESO/L. Calçada

On Earth, life leaves tell-tale signals in the atmosphere. Photosynthesis is ultimately responsible for the high oxygen levels and the thick ozone layer. Microbes emit methane and nitrous oxide into the atmosphere, and seaweeds emit chloromethane gas. These chemicals, when present in sufficient quantities, are indicators of life and are known as atmospheric biomarkers. Detecting them in the atmosphere of an exoplanet should, in theory, be a means of discovering whether life exists on any alien worlds.

While biomarkers have never been spotted in observations of an exoplanet, because their signal is so faint, the new generation of telescopes being planned today, such as the European Extremely Large Telescope, may be sensitive enough to detect them. New research presented to the European Planetary Science Congress at UCL by Lee Grenfell (DLR) aims to explore how such biomarkers might be detected in future.

“The main aim of our work is to assess the possible range of biomarker signals that might be detected by future telescopes,” Grenfell explains. “To do this, we developed computer models of exoplanets which simulate the abundances of different biomarkers and the way they affect the light shining through a planet’s atmosphere.”

Chemicals in a planet’s atmosphere affect light that passes through it, leaving characteristic chemical fingerprints in the star’s spectrum. Using this technique, astronomers have already deduced a wealth of information about the conditions present in (large, hot) exoplanets. Biomarkers would be detected in much the same way, but here the signal is expected to be so weak that scientists will need a solid understanding based on theoretical models before they can hope to decipher the actual data.

“In our simulations, we modelled an exoplanet similar to the Earth, which we then placed in different orbits around stars, calculating how the biomarker signals respond to differing conditions,” Grenfell explains. “We focused on red-dwarf stars, which are smaller and fainter than our Sun, since we expect any biomarker signals from planets orbiting such stars to be easier to detect.”

For detections of the biomarker ozone, the team confirms that there appears to be a ‘Goldilocks’ effect when it comes to the amount of ultraviolet radiation from the star to which the planet is exposed. With weak UV radiation, less ozone is produced in the atmosphere and its detection is challenging. Too much UV leads to increased heating in the middle atmosphere that weakens the vertical gradient and destroys the signal. At intermediate UV, the conditions are ‘just right’ for detecting ozone.

“We find that variations in the UV emissions of red-dwarf stars have a potentially large impact on atmospheric biosignatures in simulations of Earth-like exoplanets. Our work emphasizes the need for future missions to characterise the UV emissions of this type of star,” said Grenfell.

There are other limitations on using this method to detect signs of life. For example, it is assuming that any life-bearing planets would be identical to Earth, which is not guaranteed. Moreover, scientists will have to be certain that apparent biomarker signals they find truly arose from life, and not from other, non-living processes. Finally, dim red dwarf stars may not be the most suitable for the onset and maintenance of life. Nevertheless, this technique is an extremely promising one for detecting potential signs of life on alien worlds.

Grenfell concludes: “For the first time we are reaching a point where serious scientific debate can be applied to address the age-old question: are we alone?”

This research has been submitted to the journal Planetary & Space Science (2013) “Planetary Evolution and Life” Special Issue.