Tag: biosignatures

Joining the Microscope and the Telescope in the Search for Life Beyond Earth

 

Niki Parenteau of NASA’s Ames Research Center is a microbiologist working in the field of exoplanet and Mars biosignatures. She adds a laboratory biology approach to a field generally known for its astronomers, astrophysicists and planetary scientists. (Marisa Mayer, Stanford University.)

 

The world of biology is filled with labs where living creatures are cultured and studied, where the dynamics of life are explored and analyzed to learn about behavior, reproduction, structure, growth and so much more.

In the field of astrobiology, however, you don’t see much lab biology — especially when it comes to the search for life beyond Earth.  The field is now largely focused on understanding the conditions under which life could exist elsewhere, modeling what chemicals would be present in the atmosphere of an exoplanet with life, or how life might begin as an organized organism from a theoretical perspective.

Yes, astrobiology includes and learns from the study of extreme forms of life on Earth, from evolutionary biology, from the research into the origins of life.

But the actual bread and butter of biologists — working with lifeforms in a lab or in the environment — plays a back seat to modeling and simulations that rely on computers rather than actual life.

Niki Parenteau with her custom-designed LED array, can reproduce the spectral features of different simulated stellar and atmospheric conditions to test on primitive microbes. (Marc Kaufman)

There are certainly exceptions, and one of the most interesting is the work of Mary “Niki” Parenteau at NASA’s Ames Research Center in the San Francisco Bay area.

A microbiologist by training, she has been active for over five years now in the field of exoplanet biosignatures — trying to determine what astronomers could and should look for in the search for extraterrestrial life.

Working in her lab with actual live bacteria in laboratory flasks, test tubes and tanks, she is conducting traditional biological experiments that have everything to do with astrobiology.

She takes primitive bacteria known to have existed in some form on the early Earth, and she blasts them with the radiation that would have hit the planet at the time to see under what conditions the organisms can survive.  She has designed ingenious experiments using different forms of ultraviolet light and a LED array that simulate the broad range of radiations that would come from different types of stars as well.

What makes this all so intriguing is that her work uses, and then moves forward, cutting edge modeling from astronomers and astrobiologists regarding thick photochemical hazes understood to have engulfed the early Earth — making the planet significantly colder but also possibly providing some protection from deadly ultraviolet radiation.… Read more

False Positives, False Negatives; The World of Distant Biosignatures Attracts and Confounds

This artist’s illustration shows two Earth-sized planets, TRAPPIST-1b and TRAPPIST-1c, passing in front of their parent red dwarf star, which is much smaller and cooler than our sun. NASA’s Hubble Space Telescope looked for signs of atmospheres around these planets. (NASA/ESA/STScI/J. de Wit, MIT)

What observations, or groups of observations, would tell exoplanet scientists that life might be present on a particular distant planet?

The most often discussed biosignature is oxygen, the product of life on Earth.  But while oxygen remains central to the search for biosignatures afar, there are some serious problems with relying on that molecule.

It can, for one, be produced without biology, although on Earth biology is the major source.  Conditions on other planets, however, might be different, producing lots of oxygen without life.

And then there’s the troubling reality that for most of the time there has been life on Earth, there would not have been enough oxygen produced to register as a biosignature.  So oxygen brings with it the danger of both a false positive and a false negative.

Wading through the long list of potential other biosignatures is rather like walking along a very wet path and having your boots regularly pulled off as they get captured by the mud.  Many possibilities can be put forward, but all seem to contain absolutely confounding problems.

With this reality in mind, a group of several dozen very interdisciplinary scientists came together more than a year ago in an effort to catalogue the many possible biosignatures that have been put forward and then to describe the pros and the cons of each.

“We believe this kind of effort is essential and needs to be done now,” said Edward Schwieterman, an astronomy and astrobiology researcher at the University of California, Riverside (UCR).

“Not because we have the technology now to identify these possible biosignatures light years away, but because the space and ground-based telescopes of the future need to be designed so they can identify them. ”

“It’s part of what may turn out to be a very long road to learning whether or not we are alone in the universe”.

 

Artistic representations of some of the exoplanets detected so far with the greatest potential to support liquid surface water, based on their size and orbit.  All of them are larger than Earth and their composition and habitability remains unclear. They are ranked here from closest to farthest from Earth. 

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Putting Together a Community Strategy To Search for Extraterrestrial Life

I regret that the formatting of this column was askew earlier; I hope it didn’t make reading too difficult.  But now those problems are fixed.

The scientific search underway for life beyond Earth requires input from many disciplines and fields. Strategies forward have to hear and take in what scientists in those many fields have to say. (NASA)

Behind the front page space science discoveries that tell us about the intricacies and wonders of our world are generally years of technical and intellectual development, years of planning and refining, years of problem-defining and problem-solving.  And before all this, there also years of brainstorming, analysis and strategizing about which science goals should have the highest priorities and which might be most attainable.

That latter process is underway now in regarding the search for life in the solar system and beyond, with numerous teams of scientists tackling specific areas of interest and concern and turning their group discussions into white papers.  In this case, the white papers will then go on to the National Academy of Sciences for a blue-ribbon panel review and ultimately recommendations on which subjects are exciting and mature enough for inclusion in a decadal survey and possible funding.

This is a generally little-known part of the process that results in discoveries, but scientists certainly understand how they are essential.  That’s why hundreds of scientists contribute their ideas and time — often unpaid — to help put together these foundational documents.

With its call for extraterrestrial habitability white papers, the NAS got more than 20 diverse and often deeply thought out offerings.  The papers will be studied now by an ad hoc, blue ribbon committee of scientists selected by the NAS, which will have the first of two public meetings in Irvine, Calif. on Jan. 16-18.

Shawn Domagal-Goldman, a leader of many NASA study projects and a astrobiologist at NASA’s Goddard Space Fight Center. (NASA)

Then their recommendations go up further to the decadal survey teams that will set formal NASA priorities for the field of astronomy and astrophysics and planetary science.  This community-based process that has worked well for many scientific disciplines since they began in the late 1950s.

I’m particularly familiar with two of these white paper processes — one produced at the Earth-Life Science Institute (ELSI) in Tokyo and the other with NASA’s Nexus for Exoplanet System Science (NExSS.)  What they have to say is most interesting.Read more

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

One Planet, But Many Different Earths

Artist conception of early Earth. (NASA/JPL-Caltech)

Artist conception of early Earth. (NASA/JPL-Caltech)

We all know that life has not been found so far on any planet beyond Earth — at least not yet.  This lack of discovery of extraterrestrial life has long been used as a knock on the field of astrobiology and has sometimes been put forward as a measure of Earth’s uniqueness.

But the more recent explosion in exoplanet discoveries and the next-stage efforts to characterize their atmospheres and determine their habitability has led to rethinking about how to understand the lessons of life of Earth.

Because when seen from the perspective of scientists working to understand what might constitute an exoplanet that can sustain life,  Earth is a frequent model but hardly a stationary or singular one.  Rather, our 4.5 billion year history — and especially the almost four billion years when life is believed to have been present  — tells many different stories.

For example, our atmosphere is now oxygen-rich, but for billions of years had very little of that compound most associated with complex life.  And yet life existed.

The same with temperature.  Earth went through snowball or slushball periods when most of the planet’s surface was frozen over.  Hardly a good candidate for life, and yet the planet remained habitable and inhabited.

And in its early days, Earth had a very weak magnetic field and was receiving only 70 to 80 percent as much energy from the sun as it does today.  Yet it supported life.

“It’s often said that there’s an N of one in terms of life detected in the universe,” that there is but one example, said Timothy Lyons, a biogeochemist and distinguished professor at University of California, Riverside.

“But when you look at the conditions on Earth over billion of years, it’s pretty clear that the planet had very different kinds of atmospheres and oceans, very different climate regimes, very different luminosity coming from the sun.  Yet we know there was life under all those very different conditions.

“It’s one planet, but it’s silly to think of it as one planetary regime. Each of our past chapters is a potential exoplanet.”

 

A rendering of the theorized "Snowball Earth" period when, for millions of years, the Earth was entirely or largely covered by ice, stretching from the poles to the tropics. This freezing happened over 650 million years ago in the Pre-Cambrian, though it's now thought that there may have been more than one of these global glaciations. They varied in duration and extent but during a full-on snowball event, life could only cling on in ice-free refuges, or where sunlight managed to penetrate through the ice to allow photosynthesis.

A particularly extreme phase of our planet’s history is called  the “Snowball Earth” period.  During these episodes, the Earth’s surface was entirely or largely covered by ice for millions of years, stretching from the poles to the tropics. One such freezing happened over 700 to 800 million years ago in the Pre-Cambrian, around the time that animals appeared.

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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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