Tag: exoplanet

A New Way to Find Signals of Habitable Exoplanets?

Scientists propose a new and more indirect way of determining whether an exoplanet has a good, bad or unknowable chance of being habitable.  (NASA’s Goddard Space Flight Center/Mary Pat Hrybyk)

The search for biosignatures in the atmospheres of distant exoplanets is extremely difficult and time-consuming work.  The telescopes that can potentially take the measurements required are few and more will come only slowly.  And for the current and next generation of observatories, staring at a single exoplanet long enough to get a measurement of the compounds in its atmosphere will be a time-consuming and expensive process — and thus a relatively infrequent one.

As a way to potentially improve the chances of finding habitable conditions on those exoplanets that are observed, a new approach has been proposed by a group of NASA scientists.

The novel technique takes advantage of the frequent stellar storms emanating from cool, young dwarf stars. These storms throw huge clouds of stellar material and radiation into space – traveling near the speed of light — and the high energy particles then interact with exoplanet atmospheres and produce chemical biosignatures that can be detected.

The study, titled “Atmospheric Beacons of Life from Exoplanets Around G and K Stars“, recently appeared in Nature Scientific Reports

“We’re in search of molecules formed from fundamental prerequisites to life — specifically molecular nitrogen, which is 78 percent of our atmosphere,” said Airapetian, who is a solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and at American University in Washington, D.C. “These are basic molecules that are biologically friendly and have strong infrared emitting power, increasing our chance of detecting them.”

The thin gauzy rim of the planet in foreground is an illustration of its atmosphere. (NASA’s Goddard Space Flight Center)

So this technique, called a search for  “Beacons of Life,” would not detect signs of life per se, but would detect secondary or tertiary signals that would, in effect, tell observers to “look here.”

The scientific logic is as follows:

When high-energy particles from a stellar storm reach an exoplanet, they break the nitrogen, oxygen and water molecules that may be in the atmosphere into their individual components.

Water molecules become hydroxyl — one atom each of oxygen and hydrogen, bound together. This sparks a cascade of chemical reactions that ultimately produce what the scientists call the atmospheric beacons of hydroxyl, more molecular oxygen, and nitric oxide.… Read more

Getting Real About the Oxygen Biosignature

Oxygen, which makes up about 21 percent of the Earth atmosphere, has been embraced as the best biosignature for life on faraway exoplanets. New research shows that detecting distant life via the oxygen biosignature is not so straight-forward, though it probably remains the best show we have. (NASA)

 

I remember the first time I heard about the atmospheres of distant exoplanets and how could and would let us know whether life was present below.

The key was oxygen or its light-modified form, ozone.  Because both oxygen and ozone molecules bond so quickly with other molecules — think rust or iron oxide on Mars, silicon dioxide in the Earth’s crust — it was said that oxygen could only be present in large and detectable quantities if there was a steady and massive source of free oxygen on the planet.

On Earth, this of course is the work of photosynthesizers such as planets, algae and cyanobacteria, which produce oxygen as a byproduct.  No other abiotic, or non-biological, ways were known at the time to produce substantial amounts of atmospheric oxygen, so it seemed that an oxygen signal from afar would be a pretty sure sign of life.

But with the fast growth of the field of exoplanet atmospheres and the very real possibility of having technology available in the years ahead that could measure the components of those atmospheres, scientists have been busy modelling exoplanet formations, chemistry and their atmospheres.

One important goal has been to search for non-biological ways to produce large enough amounts of atmospheric oxygen that might fool us into thinking that life has been found below.

And in recent years, scientists have succeeded in poking holes in the atmospheric oxygen-means-life scenario.

Oxygen bonds quickly with many other molecules. That means has to be resupplied regularly to be present as O2 in an atmosphere . On Earth, O is mostly a product of biology, but elsewhere it might be result of non-biological processes. Here is an image of oxygen bubbles in water.

Especially researchers at the University of Washington’s Virtual Planetary Laboratory (VPL) have come up with numerous ways that exoplanets atmospheres can be filled (and constantly refilled) with oxygen that was never part of plant or algal or bacteria photo-chemistry.

In other words, they found potential false positives for atmospheric oxygen as a biosignature, to the dismay of many exoplanet scientists.

In part because she and her own team were involved in some of these oxygen false-positive papers, VPL director Victoria Meadows set out to review, analyze and come to some conclusions about what had become the oxygen-biosignature problem.… Read more

Coming to Terms With Biosignatures

Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely. That includes the question of whether they might support life — an aspect of exoplanet science that is getting new attention. This is artist Ron Miller’s impression of an exoplanet.

Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely. That includes the question of whether they might support life — an aspect of exoplanet science that is getting new attention. This is artist Ron Miller’s impression of an exoplanet.

The search for life beyond our solar system has focused largely on the detection of an ever-increasing number of exoplanets, determinations of whether the planets are in a habitable zone, and what the atmospheres of those planets might look like.  It is a sign of how far the field has progressed that scientists are now turning with renewed energy to the question of what might, and what might not, constitute a sign that a planet actually harbors life.

The field of “remote biosignatures” is still in its early stages, but a NASA-sponsored workshop underway in Seattle has brought together dozens of researchers from diverse fields to dig aggressively into the science and ultimately convey its conclusions back to the exoplanet community and then to the agency.

While a similar NASA-sponsored biosignatures workshop put together a report in 2002, much has changed since then in terms of understanding the substantial complexities and possibilities of the endeavor.  There is also a new sense of urgency based on the observing capabilities of some of the space and ground telescopes scheduled to begin operations in the next decade, and the related need to know with greater specificity what to look for.

“The astrobiology community has been thinking a lot more about what it means to be a biosignature,” said Shawn Domogal-Goldman of the Goddard Space Flight Center, one of the conveners of the meeting.  Some of the reason why is to give advice to those scientists and engineers putting together space telescope missions, but some is the pressing need to maintain scientific rigor for the good of one of humankind’s greatest challenges.

“We don’t want to spend 20 years of our lives and billions in taxpayer money working for a mission to find evidence of life, and learn too late that our colleagues don’t accept our conclusions,” he told me.  “So we’re bringing them all together now so we can all learn from each other about what would be, and what would not be, a real biosignature.”

 

How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A). By subtracting A from B, we get the planet counterpart, and from this the “chemical fingerprints” of the planet atmosphere can be revealed. Credits: NASA/JPL-Caltech.

How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A).

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Rocky, Close and Potentially Habitable Planets Around a Dwarf Star

This artist’s impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. (M. Kornmesser/ESO)

This artist’s impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. (M. Kornmesser/ESO)

Forty light-years away is no small distance. But an announcement of the discovery of two planets at that separation that have been determined to be rocky and Earth-sized adds a significant new twist to the ever-growing collection of relatively close-by exoplanets that just might be habitable.

The two planets in the TRAPPIST-1 system orbit what is known as a red dwarf star, a type of star that is typically much cooler than the sun, emitting radiation in the infrared rather than the visible spectrum.  While there has been much debate about whether an exoplanet around a dwarf can be deemed habitable, especially since they are all believed to be tidally locked and so only one side faces the star, a consensus appears to be growing that dwarf stars could host habitable planets.

The two new rocky exoplanets were detected using the Hubble Space Telescope and were deemed most likely rocky by the compact sizes of their atmospheres — which were not large and diffuse hydrogen/helium envelopes (like that of the Jupiter) but instead more tightly packed, more like the atmospheres of Earth, Venus, and Mars.  It was the first time scientists have been able to search for and at least partially characterize of atmospheres around a temperate, Earth-sized planet.

Having determined that the planets are rocky, principal investigator Julien de Wit of M.I.T’s Department of Earth, Atmospheric and Planetary Sciences, said the goal now is to characterize their atmospheres.

“Now the question is, what kind of atmosphere do they have?” de Wit said. “The plausible scenarios include something like Venus, where the atmosphere is dominated by carbon dioxide, or an Earth-like atmosphere with heavy clouds, or even something like Mars with a depleted atmosphere. The next step is tomtry to disentangle all these possible scenarios that exist for these terrestrial planets.”

Artist's impression of the two planets in the Trappist-1 solar system. These worlds have sizes, temperatures and potentially atmospheres similar to those of Venus and Earth. Some believe they may be the best targets found so far for the search for life outside the solar system. They are the first planets ever discovered around such a tiny and dim star. (Nasa/ESA/STScI)

Artist’s impression of the two planets in the Trappist-1 solar system. These worlds have sizes, temperatures and potentially atmospheres similar to those of Venus and Earth. Some believe they may be the best targets found so far for the search for life outside the solar system. They are the first planets ever discovered around such a tiny and dim star. (Nasa/ESA/STScI)

 

Host stars with exoplanets that are (very relatively) close to us are highly valued because they are potentially easier to observe and characterize.… Read more

Out of the Stovepipes and Into the Galaxy

This “Many Worlds” post is written by Andrew Rushby, a postdoctoral fellow from the United Kingdom who recently began working with NASA’s NExSS initiative. The column will hopefully serve to both introduce this new NExSS colleague and to let him share his thoughts about the initiative and what lies ahead.

NExSS encourages a "systems science" approach to understanding exoplanets, and especially whether they might be habitable. Systems science is inherently interdisciplinary, and so fields such as earth science and planetary science (and many more) provide needed insights into how exoplanets might be explored. (NASA)

NExSS encourages a “systems science” approach to understanding exoplanets, and especially whether they might be habitable. Systems science is inherently interdisciplinary, and so fields such as earth science and planetary science (and many more) provide needed insights into how exoplanets might be explored. (NASA)

I’m most excited to join NExSS at its one year anniversary, and hope that I can help the network as it advances into, and works to fashion, the exoplanetary future.

Coming in from the outside, the progress I already see in terms of bringing researchers together to work on interdisciplinary exoplanet science is impressive. But more generally, I see this as a significant juncture in the fast-expanding study of these distant worlds, with NExSS and its members poised to facilitate a potentially revolution in how we look at planets in this solar system and beyond.

The ‘systems science’ approach to understanding exoplanets is, I believe, the right framework for advancing our understanding.  Earth scientists and biogeochemists have been using systems science for some time now to build, test, and improve theories for how the Earth functions as an interconnected system of physical, chemical and biological components — all operating over eons in a complex and tangled evolutionary web that we are only now unraveling.

It is this method that allows us to better understand the respective roles of the atmosphere, ocean, biosphere, and geosphere in influencing the past and present climate of this planet. It allows us to clearly see the damage we are causing to these systems through the release of industry and transport-created greenhouse gases, and offers opportunities for mitigation. We know the systems science approach works for the Earth, and the time to make it work for exoplanets is now.

But as Marc pointed out in his previous post about the first year of NExSS, the opportunity to leverage this method for comparative planetology is a relatively new one. We just haven’t had the data for building exoplanet systems models and making  testable hypotheses.

Understanding a planetary system like this artist's view of an ocean world, scientists have learned, takes an interdisciplinary approach.

Understanding a planetary system like this artist’s view of an ocean world, scientists have learned, takes an interdisciplinary approach.

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Breaking Down Exoplanet Stovepipes

he search for life beyond our solar system requires unprecedented cooperation across scientific disciplines. NASA's NExSS collaboration includes those who study Earth as a life-bearing planet (lower right), those researching the diversity of solar system planets (left), and those on the new frontier, discovering worlds orbiting other stars in the galaxy (upper right). Credits: NASA

The search for life beyond our solar system requires unprecedented cooperation across scientific disciplines. NASA’s NExSS collaboration includes those who study Earth as a life-bearing planet (lower right), those researching the diversity of solar system planets (left), and those on the new frontier, discovering worlds orbiting other stars in the galaxy (upper right). (NASA)

That fields of science can benefit greatly from cross-fertilization with other disciplines is hardly a new idea.  We have, after all, long-standing formal disciplines such as biogeochemistry — a mash-up of many fields that has the potential to tell us more about the natural environment than any single approach.  Astrobiology in another field that inherently needs expertise and inputs from a myriad of disciplines, and the NASA Astrobiology Institute was founded (in 1998) to make sure that happened.

Until fairly recently, the world of exoplanet study was not especially interdisciplinary.  Astronomers and astrophysicists searched for distant planets and when they succeeded came away with some measures of planetary masses, their orbits, and sometimes their densities.  It was only in recent years, with the advent of a serious search for exoplanets with the potential to support life,  that it became apparent that chemists (astrochemists, that is), planetary and stellar scientists,  cloud specialists, geoscientists and more were needed at the table.

Universities were the first to create more wide-ranging exoplanet centers and studies, and by now there are a number of active sites here and abroad.  NASA formally weighed in one year ago with the creation of the Nexus for Exoplanet System Science (NExSS) — an initiative which brought together 17 university and research center teams with the goal of supercharging exoplanet studies, or at least to see if a formal, national network could produce otherwise unlikely collaborations and science.

That network is virtual, unpaid, and comes with no promises to the scientists.  Still, NASA leaders point to it as an important experiment, and some interesting collaborations, proposals and workshops have come out of it.

“A year is a very short time to judge an effort like this,” said Douglas Hudgins, program scientist for NASA’s Exoplanet Exploration Program, and one of the NASA people who helped NExSS come into being.

“Our attitude was to pull together a group of people, do our best to give them tool to work well together, let them have some time to get to know each other, and see what happens.  One year down the road, though, I think NExSS is developing and good ideas are coming out of it.”

 

Illustration of what a sunset might look like on a moon orbiting Kepler 47c and its two suns. (Softpedia)

Illustration of what a sunset might look like on a moon orbiting Kepler 47c and its two suns.

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Storming the One-Meter-Per-Second Barrier

Kitt Peak National Observatory mountain top at Dusk looking north. Visible in the picture are the NOAO 4-meter Mayall, the Steward Observatory 90-inch, the University of Arizona Lunar and Planetary Laboratory Spacewatch Telescopes, LOTIS, 0.4-meter Visitor Center Telescope, Case Western Reserve University Observatory and the SARA Observatory. Credit: P. Marenfeld (NOAO/AURA/NSF)

The Kitt Peak National Observatory, on the Tohono O’odham reservation outside Tucson, will be home to a next-generation spectrometer and related system which will allow astronomers to detect much smaller exoplanets through the radial velocity method.  P. Marenfeld (NOAO/AURA/NSF)

When the first exoplanet was identified via the radial velocity method, the Swiss team was able to detect a wobble in the star 51 Pegasi at a rate of 50 meters per second.   The wobble is the star’s movement back and forth caused by the gravitational pull of the planet, and in that first case it was dramatic — the effects of a giant Jupiter-sized planet orbiting extremely close to the star.

Many of the early exoplanet discoveries were of similarly large planets close to their host stars, but it wasn’t because there are so many of them in the cosmos.  Rather, it was a function of the capabilities of the spectrographs and other instruments used to view the star.  They were pioneering breakthroughs, but they didn’t have the precision needed to measure wobbles other than the large, dramatic ones caused by a close-in, huge planet.

That was the mid 1990s, and radial velocity astronomers have worked tirelessly since to “beat down” that 50 meters per second number.  And twenty years later, radial velocity astronomers using far more precise instruments and more refined techniques have succeeded substantially:  1 meter per second of wobble is now achieved for the quietest stars.  That has vastly improved their ability to find smaller exoplanets further from their stars and is a major achievement.  But it has nonetheless been a major frustration for astronomers because to detect terrestrial exoplanets in the Earth-sized range, they have to get much more precise  — in the range of tens of centimeters per second.

A number of efforts to build systems that can get that low are underway, most notably the ESPRESSO spectrograph scheduled to begin work on the High Accuracy Radial Vlocity Planet Searcher (HARPS) in Chile next year. Then earlier this month an ambitious NASA-National Science Foundation project was awarded to Penn State University to join the race.  The next-generation spectrograph is scheduled to be finished in 2019 and installed at the Kitt Peak National Observatory in Arizona, and its stated goal is to reach the 20 to 30 centimeters per second range.

Suvrath Mahadevan, an assistant professor at Penn State, is principal investigator for the project.  It is called NEID, which means ‘to see’ in the language of the Tohono O’odham, on whose land the Kitt Peak observatory is located.… Read more

Hunting for Exoplanets Via TESS

 

The TESS satellite, which will launch in 2017, will use four cameras to search for exoplanets around bright nearby stars. MIT

The TESS satellite, which will launch in 2017, will use four cameras to search for exoplanets around bright nearby stars. MIT initially proposed the mission, and it was approved in 2013.  (MIT)

Seven years ago this month the Kepler spacecraft launched into space – the first NASA mission dedicated to searching for planets around distant stars. The goal was to conduct a census of these exoplanets, to learn whether planets are common or rare. And in particular, to understand whether planets like Earth are common or rare.

With the discovery and confirmation of over 1,000 exoplanets (and thousands more exoplanet candidates that have not yet been confirmed), Kepler has taught us that planets are indeed common, and scientists have been able to make new inferences about how planetary systems form and evolve. But the planets found by Kepler are almost exclusively around distant, faint stars, and the observations needed to further study and characterize these planets are challenging. Enter TESS.

The Transiting Exoplanet Survey Satellite (TESS) is a NASA Explorer mission designed to search for new exoplanets around bright, nearby stars. The method that TESS will use is identical to that used by Kepler – it looks for planets that transit in front of their host star. Imagine that you’re looking at a star, and that star has planets around it.

If the orbit of the planet is aligned correctly, then once per “year” of the planet (i.e. once per orbit), the planet will pass in front of the star. As the planet moves in front of the star, it blocks a small fraction of the light, so the star appears to get slightly fainter. As the planet moves out of transit, the star returns to normal brightness. We can see an example of this in our own solar system on May 9, 2016, as Mercury passes in front of the Sun.

Tranit

A small dip in the amount of light emanating from a star tells astronomers that a planet may well be crossing in front of it.

We can learn a lot from observing the transits of a planet. First, we can learn the size of a planet – the bigger the planet, the more light it will block, and the larger the “dip” in the brightness of the host star. Second, we can learn how long the planet’s year is – since it only passes in front of the star once per orbit, the time between transits is the planet’s year.… Read more

The Search for Exoplanet Life Goes Broad and Deep

The scientific lessons learned over the centuries about the geological, chemical and later biological dynamics of Earth are beginning to enter the discussion of exoplanets, and especially which might be conducive to life. This is an artist's view of the young Earth under bombardment by asteroids, one of many periods with conditions likely to have parallels in other solar systems. (NASA's Goddard Space Flight Center Conceptual Image Lab)

The scientific lessons learned over the centuries about the geological, chemical and later biological dynamics of Earth are beginning to enter the discussion of exoplanets, and especially which might be conducive to life. This is an artist’s view of the young Earth under bombardment by asteroids, one of many periods with conditions likely to have parallels in other solar systems. (NASA’s Goddard Space Flight Center Conceptual Image Lab)

I had the good fortune several years ago to spend many hours in meetings of the science teams for the Curiosity rover, listening in on discussions about what new results beamed back from Mars might mean about the planet’s formation, it’s early history, how it gained and lost an atmosphere, whether it was a place where live could begin and survive.  (A resounding ‘yes” to that last one.)

At the time, the lead of the science team was a geologist, Caltech’s John Grotzinger, and many people in the room had backgrounds in related fields like geochemistry and mineralogy, as well as climate modelers and specialists in atmospheres.  There were also planetary scientists, astrobiologists and space engineers, of course, but the geosciences loomed large, as they have for all Mars landing missions.

Until very recently, exoplanet research did not have much of that kind interdisciplinary reach, and certainly has not included many scientists who focus on the likes of vulcanism, plate tectonics and the effects of stars on planets.  Exoplanets has been largely the realm of astronomers and astrophysicists, with a sprinkling again of astrobiologists.

But as the field matures, as detecting exoplanets and inferring their orbits and size becomes an essential but by no means the sole focus of researchers, the range of scientific players in the room is starting to broaden.  It’s a process still in its early stages, but exoplanet breakthroughs already achieved, and the many more predicted for the future, are making it essential to bring in some new kinds of expertise.

A meeting reflecting and encouraging this reality was held last week at Arizona State University and brought together several dozen specialists in the geo-sciences with a similar number specializing in astronomy and exoplanet detection.  Sponsored by NASA’s Nexus for Exoplanet Systems Science (NExSS), NASA Astrobiology Institute (NAI) and the National Science Foundation,  it was a conscious effort to bring more scientists expert in the dynamics and evolution of our planet into the field of exoplanet study, while also introducing astronomers to the chemical and geological imperatives of the distant planets they are studying.… Read more

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