One Planet, But Many Different Earths

Facebooktwittergoogle_plusredditpinterestlinkedinmail
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. Others are now thought to have occurred much further back in time. They varied in duration and extent but during a full-on snowball event, life could only survive in ice-free refuges, or where sunlight managed to penetrate through the ice to allow photosynthesis.

Lyons is the principal investigator for one of the newer science teams selected to join the NASA Astrobiology Institute (NAI), an interdisciplinary group hat calls itself “Alternative Earths.”

Consisting of 23 scientists from 14 institutions, its self-described mission is to address and answer these questions: How has Earth remained persistently inhabited through most of its highly changeable history?  How has the presence of very different kinds of lifeforms been manifested in the atmosphere, and simultaneously been captured in what would become the rock record? And how might this approach to early Earth help in the search for life beyond Earth?

“The idea that early Earth can help us understand other planets and moons, especially in our solar system, is certainly not new,” Lyons said.  “Scientists have studied possible Mars analogues and extreme life for years.  But we’re taking it to the next level with exoplanets, and pushing hard on the many ways that conditions on early Earth can help us study exoplanet atmospheres and habitability.”

The importance of this work was apparent at a recent workshop on biosignatures held by NASA’s initiative, the Nexus for Exoplanet System Science (NExSS.)  As Earth scientists, Lyons and his group are expert at finding proxy records in ancient rocks that hold information important to exoplanet scientists (among others) want to know.

Those proxy fingerprints occur as elemental, molecular, and isotopic properties preserved in rocks that correspond to ancient characteristics in the ocean or atmosphere that can no longer be observed directly.

“We can’t measure the pH in ancient oceans, and we can’t measure the composition of ancient atmospheres,” Lyons said.  “So what we have to do is go to the chemistry of ocean and land deposits formed at the same time and look for the chemical fingerprints locked away and preserved.”

At the exoplanet biosignatures workshop, Lyons was struck by how eager exoplanet modelers were to learn about the proxy chemicals they could profitably put in their models for clues about how distant planet atmospheres might form and behave.  It’s clear that no single element or compound will be a silver bullet for understanding whether there’s life on an exoplanet, but a variety of proxy results together can begin to tell an important story.

chromium
The element chromium and its isotopes have become important proxies for the measurement of oxygen levels in the atmosphere of early Earth and have led to some revised theories about when those concentrations jumped.  Understanding the potential makeup of early Earth’s atmosphere and oceans is a pathway to understanding exoplanets.

“We told them about the range of things they should be modeling and, wow, they were interested.  I was thinking at the time that ‘you guys really need us — and vice versa.'”

Some of the researchers most intrigued by potentially new geochemical proxies from the University of Washington’s Virtual Planetary Laboratory,  They’ve been a pioneer in modeling how different atmospheric, geological, stellar and other factors characterize particular kinds of planets and solar systems and their possibilities for life.

In keeping with the growing connection between exoplanet and Earth science, Lyons just brought one of the VPL top modellers, Edward Schwieterman, to UC Riverside for a postdoc as part of the Alternative Earths project.

Among his initial projects will take the new data being generated by the Alternative Earths team about the atmosphere and oceans of early Earth, and model what would happen on a planet with that kind of atmosphere if it was orbiting a very different type of star from our own.

“It’s a direct use of early Earth research on exoplanet studies, and is exactly the kind of work we plan to do be doing,” Lyons said. “Eddie is the perfect bridge between the lessons learned from early Earth and their implications for exoplanets.”

Banded iron formations Karijini National Park, Western Australia. The layers of reddish iron show the presence of oxygen, which bonded with the iron to form a rust-like iron oxide. These formations date most commonly from the period of 2.4 to 1.9 billion years ago, after the Great Oxidation Event.
Banded iron formations at Karijini National Park, Western Australia. The layers of reddish iron point to an early ocean poor in oxygen and rich in dissolved iron. These formations date most commonly from the periods just before and right after the Great Oxidation Event, which spanned from about 2.4 to 2.0 billion years ago. Their distributions over times and their chemical properties are key proxies for the tempo and fabric of the earliest permanent oxygenation of Earth’s atmosphere.

Lyons, along with colleagues Christopher Reinhard of Georgia Tech and Noah Planavsky of Yale and other members of their Alternative Earths team, are especially focused on an effort to understand Earth’s atmosphere—as tracked in the rock record—over the eons and especially the levels of oxygen present.

The concentration of oxygen in the atmosphere is now about about 21 percent and, by some estimates, reached as high as 35 percent within the past 500 million years.

In comparison, early Earth had but trace amounts of oxygen for two billion years before what is called the Great Oxidation Event—when marine O2-producing photosynthesis outpaced reactions that consumed O2 and allowed for the beginnings of its permanent accumulation in the atmosphere.  Estimated to have occurred 2.4 billion years ago, it began (or was part of) an oxidizing process that led to ever more complex life forms over the following one to two billion years.

Timothy Lyons, distinguished professor of geobiochemistry at the University of California, Riverside. He is also the principal investigator of a National Astrobiology Institute project xxx.
Timothy Lyons, distinguished professor of biogeochemistry at the University of California, Riverside. He is also the principal investigator of a National Astrobiology Institute project “Alternative Earths:  Explaining Persistent Inhabitation on a Dynamic Early Earth.

There is a spirited scientific debate underway now about whether that “Great Oxidation Event” triggered permanently high levels of oxygen in the atmosphere and the oceans, or whether it began an up and down process through which the presence of oxygen was quite unstable and still well below current levels until relatively recent times.

Lyons and Reinhard are of the “boring billion” school, arguing that oxygen levels did not head continuously upwards after the Oxidation Event, but rather stayed relatively stable and still very low for most of a billion and half years after the Great Oxidation Event and continued to challenge O2-requiring life—for almost a third of Earth history.

This would be primarily an Earth science issue if not for the fact that oxygen — on its own and in conjunction with other compounds — is among the most prominent and promising biosignatures that exoplanet scientists are looking for.

Christopher Reinhard, Georgia Institute of technology. (Brad...
Christopher Reinhard of Georgia Institute of Technology and Alternative Earths project. (Ben Brumfield/Georgia Tech.)

In fact, not that long ago, it was widely accepted that a discovery of oxygen and/or ozone in the atmosphere of a planet pretty much proved, or at least strongly suggested, the presence of some sort of biology on the planet below.  That view has been modified of late by the identification of ways that free oxygen can be formed abiotically (without the presence of photosynthesis and life), potentially producing false positives for potential life.

While the field is a long way from an active search for direct, in situ fingerprints of life on exoplanets light years away, oxygen and its relationship with other atmospheric gases remains a lodestar in thinking about what biosignatures to search for. The technology is already in place for characterizing the compositions of very distant atmospheres.

And this is where, for Lyons, Reinhard and others, things get both interesting and complicated.

For more than a billion years before the Great Oxidation Event Earth demonstrably supported life.  It consisted mostly of anaerobic microbes that did just fine without oxygen, but in many cases needed and produced methane, an organic compound with one carbon atom and four hydrogens.

So if an exoplanet scientist from a distant world were to search for life on Earth during that period via the detection of oxygen only, they would entirely miss the presence of an already long history of life.  Searching for a potentially large-scale presence of methane might have been more productive, though that is a source of rigorous debate as well.

 

An image of a rock with fossilized stromatolites, tiny layered structures from 3.7 billion years ago that are remnants from a community of microbes. Found in a newly melted part of Greenland, Australian scientists reported in the journal Nature that the stromatolites lived on an ancient seafloor at a time when Earth's skies were orange and its oceans green. They describe the stromatolites as perhaps the oldest fossil found so far on Earth. (Allen Nutman/University of Wollongong)
An image of a rock with fossilized stromatolites, tiny layered structures from 3.7 billion years ago that are remnants from a community of microbes. Found in a part of Greenland new exposed by melting glaciers, Australian scientists reported in the journal Nature that the stromatolites lived on an ancient seafloor at a time when Earth’s skies may well have been orange and its oceans green. They describe the stromatolites as perhaps the oldest fossil found so far on Earth, although chemical suggestions of life may extend further back in time . (Allen Nutman/University of Wollongong)

Because both oxygen and methane can be formed without life, a current gold standard for detecting future biosignatures on exoplanets is the presence of the two together.  As a result of the way the two interact, they would remain in an atmosphere together only if both were being replenished on a substantial, on-going scale.  And as far as is now understood, the only way to do that is through biology.

Yet as described by Reinhard, the most current research suggest that oxygen and methane were probably never in the Earth’s atmosphere together at levels that would be detectable from afar.  There is some evidence that Earth’s atmosphere held a lot of methane in its early times, and there has been a lot of oxygen for the past 600 million years or so, but as one grew in concentration the other declined — and during the “boring billion” both were likely low.

“So we have a complicated situation here where using the best exoplanet biosignatures we have now, intelligent beings looking at Earth over the past 4.5 billion years would not find a convincing signature of life for most, or maybe all, of that time if they relied only on co-occurrence of oxygen and methane,” Reinhard said.  Yet there has been life for at least 3.7 billion years, and those beings studying Earth would have come up with a very false negative.

Lyons insists this is should not be a source of pessimism in the search for life on exoplanets, instead it is a “call to arms for new and more creative possibilities rather than the lowest hanging fruit.” It’s a challenge “to help us sharpen our thinking in a search that was never going to be easy.”

And the best test bed available for coming up with different answers, he said, may very well be the many different Earths that have come and gone on our planet.

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Out of the Stovepipes and Into the Galaxy

Facebooktwittergoogle_plusredditpinterestlinkedinmail

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.

The work that NExSS is doing is extremely relevant to this effort because we recognize that faced with the gargantuan task of discerning how innumerable planets beyond our solar system can be found, formed, characterized and understood — we have to do something different. The decisions we make and the effort we invest at this still very early stage will determine the future of planet discovery, and build the foundations for how we come to understand the planet system and its evolution.

We are likely the first of many generations of interdisciplinary exoplanetologists. To build a sturdy foundation for this approach, we will need to further break down the often restrictive scientific “stovepipes” that can keep necessary data known to scientists in one field from others who need it to understand their own data.  After the stovepipes have been dismantled (or at least modified), then comes the process of together building the exoplanetary chimney.

This is not an effort that can be successfully undertaken by individuals alone, or even already formed cross-disciplinary groups.

By its very nature, exoplanet science needs the insights and energy of the entire community of astrophysicists, heliophysicists, Earth scientists and planetary scientists interested in how their particular field of study fits in to the grand picture beginning to take shape.

Planets are endlessly complex and dynamic islands at the confluence of the physical, chemical and biological realms, and therefore our approach to making sense of them must be interdisciplinary, inclusive and epistemologically unique.

Biogeochemistry postdoc Andrew Rushby arrived at Ames last month and will remain for two years, with some of his time dedicated to the NExSS program.
Biogeochemistry postdoc Andrew Rushby arrived at Ames last month and will remain for two years, with some of his time dedicated to the NExSS program.

I’ve always thought, naively perhaps, of the search for exoplanets and for other life in the universe as a proxy search for our own place.

With our telescopes we peer ever outward, trying to find other worlds like our own to give meaning to that which we know best – this planet and its biosphere. It’s the next inevitably tumultuous battle in the long and sustained campaign for a greater perspective on ourselves, one that began when we first looked up at the night sky and wondered if what was out there was anything like what was down here.

It’s difficult, of course, to see how far you’ve already traveled on a journey of unknown length. But his field has come so far already and made so many strides in the last twenty years that analogies to its pace of discovery are difficult to come by.

As for me, I come from a biogeochemical background and was schooled at the University of East Anglia the UK. I spent my PhD years building models to investigate how the planetary evolution of Earth and Earth-like planets may affect their long-term habitability.  But I have also dedicated much time to telling just about anyone who would listen just how very cool exoplanets are. I hope to continue this work too.

Artist illustration of an exoplanet and a debris disc orbiting their host star. (NASA)
Artist illustration of an exoplanet and a debris disc orbiting their host star. (NASA)

During my exoplanet talks in the UK – at meetings, science cafes, outreach events, at the pub and online through my blog — I can honestly say I’ve never encountered anyone who didn’t find this science fascinating. Whatever my own speaking skills may be,  I know that it’s not difficult to enthuse people about the idea of exotic planets, alien life, and space missions. It’s almost cheating. There’s an optimism inherent in the field – one that says we can learn about these distant, shrouded and endlessly complex planetary systems through our own hard work, cleverness and technology. I think it’s an optimism that people relate to.

I hope therefore to make some small contribution to this effort through my time with NExSS by helping to build and maintain future and current collaborations among our existing members, growing our network, helping with our upcoming meetings and workshops, and facilitating communication from the network and its members.

I look forward to both embracing the differences, and identifying the similarities, between my training in the UK and the research culture here in USA. I think other countries would benefit greatly from the ‘NExSS approach’, and I look forward to welcoming the input of international colleagues in making NExSS a truly global enterprise. Many countries may be looking to NExSS’s example: let’s lead the way in showing the world how best to find and understand other worlds.

The 3-day in-person workshop will be coordinated with pre-workshop online activities to summarize the state of the science of exoplanet biosignatures. This review will provide background for the in-person workshop, which will focus on advancing the science of biosignatures, and understanding the technological needs and capabilities for their detection. This information will be exchanged with the Science Technology Definition Teams (STDTs) of upcoming planet-observing missions.
The 3-day in-person workshop will be coordinated with pre-workshop online activities to summarize the state of the science of exoplanet biosignatures. This review will provide background for the in-person workshop, which will focus on advancing the science of biosignatures, and understanding the technological needs and capabilities for their detection. This information will be exchanged with the Science Technology Definition Teams (STDTs) of upcoming planet-observing missions.

In addition to on-going PI collaborations,  NExSS has some exciting plans for the year ahead, as well as some tasks with significant and formal purposes.

First is the NExSS Exoplanet Biosignatures Workshop Without Walls in Seattle in July, which will have 30-35 on-site participants and an opportunity for many more to participate online.  Insights and conclusions from the Biosignatures Workshop will be exchanged with NASA’s Science Technology Definition Teams (STDTs) for upcoming planet-observing missions.

In addition, summary reports from the workshop will be circulated to the community for feedback. These reports will then be filed with a dedicated Exoplanet Biosignatures Study Analysis Group (SAG 16) of the Exoplanet Exploration Program Analysis Group (ExoPAG).

A heliophysics-based workshop (title and details tbc) will also be held in November, with title and details to be announced.

The second Face-to-Face meeting of all 17 NExSS PIs and associated team members, Co-leads, and NASA HQ representatives will be held at NASA Headquarters and the Carnegie Institution for Science in May. The two-day event offers an opportunity to discuss what worked and what didn’t work so well during the first year of NExSS, to hopefully come up with new collaborations, and to look ahead to the future of the network.

Over the next two years, the initiative will also continue to engage with the wider exoplanet community through workshops, meetings, and outreach activities in order to grow the network organically while ensuring inclusivity and representation from all of areas of this multidisciplinary field.

Per unitatem ad astra! (Through unity, to the stars!)

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Breaking Down Exoplanet Stovepipes

Facebooktwittergoogle_plusredditpinterestlinkedinmail
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 collabortions, 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. (Softpedia)

 

One collaboration resulted in a “White Paper” on how laboratory work today can prepare researchers to better understand future exoplanet measurements coming from new generation missions. Led by NExSS member Jonathan Fortney of the University of Clalfornia, Santa Cruz, it was the result of discussions at the first NExSS meeting in Washington, and was expanded by others from the broader community.

Another NExSS collaboration between Steven Desch of Arizona State University and Jason Wright of Penn State led to a proposal to NASA to study a planet being pulled apart by the gravitational force a white dwarf star.  The interior of the disintegrating planet could potentially be analyzed as its parts scatter.

Leaders of NExSS say that other collaborations and proposals are in the works but are not ready for public discussion yet.

In addition, NExSS — along with the NASA Astrobiology Institute (NAI) and the National Science Foundation (NSF) — sponsored an unusual workshop this winter at Arizona State University focused on a novel way to looking at whether an exoplanet might support life.  Astrophysicists and geoscientists (some paertr of NExSS teams; some not) spent three days discussing and debating how the field might gather and use information about the formation, evolution and insides of exoplanets to determine whether they might be habitable.

One participant was Shawn Domogal-Goldman, a research space scientist at the Goddard Space Flight Center and a leader of the NExSS group.  He’s an expert in ancient earth as well the astrophysics of exoplanets, and his view is that the Earth provides 4.5 billion years of physical, chemical, climatic and biological dynamics  that need to be mined for useful insights about exoplanets.

When the workshop was over he said: “For me, and I think for others, we’ll look back at this meeting years from now and say to ourselves, ‘We were there at the beginning of something big.”

NExSS has two more workshops coming up, one on “Biosignatures” July 27 t0 29 in Seattle and another on stellar-exoplanet interactions in November.  Reflecting the broad reach of NExSS, the biosignatures program has additional sponsors include the NASA Astrobiology Institute (NAI), NASA’s Exoplanet Exploration Program (ExEP), and international partners, including the European Astrobiology Network Association (EANA) and Japan’s Earth-Life Science Institute (ELSI).

SA (2001) By looking for signs of life like we have on earth, we focus on trying to find the presence of oxygen, ozone, water, carbon dioxide, methane and nitrous oxide; indicating plant or bacterial life. Looking at the figure above, we can see how complex Earth’s spectra is compared to Mars or Venus. This is because of various factors that balance and control the elements needed for life as a whole. In the same way, we’re hoping to find life that strongly interacts with its atmosphere on a global scale.
By looking for signs of life, scientists focus on the potential presence of oxygen, ozone, water, carbon dioxide, methane and nitrous oxide, which could indicate plant or bacterial life. The figure above shows how complex Earth’s spectra is compared to Mars or Venus. This is a reflection of the intricate balance and control of elements needed to support life. The upcoming NExSS workshop will focus on what we know, and need to know, about what future missions and observations should be looking for in terms of exoplanet biosignatures. (ESA)

The initial idea for NExSS came from Mary Voytek, senior scientist for astrobiology in NASA’s Planetary Sciences Division.  Interdisciplinary collaboration and solutions are baked into the DNA of astrobiology, so it is not surprising that an interdisciplinary approach to exoplanets would come from that direction.  In addition, as the study of exoplanets increasingly becomes a search for possible life or biosignatures on those planets, it falls very much into the realm of astrobiology.

Mary Voytek, NASA senior scientist for astrobiology, xxxx.
Mary Voytek, NASA senior scientist for astrobiology, who initially proposed the idea that became the NExSS initiative.

Hudgins said that while this dynamic is well understood at NASA headquarters, the structure of the agency does not necessarily reflect the convergence.  Exoplanet studies are funded through the Division of Astrophysics while astrobiology is in the Planetary Sciences Division.

NExSS is a beginning effort to bring the overlapping fields closer together within the agency,  and more may be on the way.  Said Hudgins:  “We could very well see some evolution in how NASA approaches the problem, with more bridges between astrobiology and exoplanets.”

NExSS is led by Natalie Batalha of NASA’s Ames Research Center in Moffett Field, California; Dawn Gelino with NExScI, the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena; and Anthony Del Genio of NASA’s Goddard Institute for Space Studies in New York City.

All three see NExSS as an experiment and work in progress, with some promising accomplishments already.  And some clear challenges.

NASA's NExSS initiative seeks to bring together scientists from varied backgrounds to address questions of exoplanet research. The initiative consists of 17 teams that had applied for NASA grants under a variety of different programs, but organizers are looking to bring other scientists into the process as well. (NASA)
NASA’s NExSS initiative seeks to bring together scientists from varied backgrounds to address questions of exoplanet research. The initiative consists of 17 teams that had applied for NASA grants under a variety of different programs, but organizers are looking to bring other scientists into the process as well. (NASA)

 

Del Genio, for instance, described the complex dynamics involved in having a team like his own — climate modelers who have spent years understanding the workings of our planet — determine how their expertise can be useful in better understanding exoplanets.

These are some of his thoughts:

“This sounds great, but in practice it is very difficult to do for a number of reasons.  First, all the disciplines speak different languages. Jargon from one field has to be learned by people in another field, and unlike when I travel to Europe with a Berlitz phrase book, there is no Earth-to-Astrophysics translation guide to consult.

Tony del Genio, a veteran research scientists at NASA's Goddard Institute for Space Studies in Manhattan.
Tony Del Genio, a veteran research scientists at NASA’s Goddard Institute for Space Studies in Manhattan.

“Second, we don’t appreciate what the important questions are in each others’ fields, what the limitations of each field are, etc.  We have been trying to address these roadblocks in the first year by having roughly monthly webinars where different people present research that their team is doing.  But there are 17 teams, so this takes a while to do, and we are only part way through having all the teams present.

“Third, NExSS is a combination of teams that proposed to different NASA programs for funding, and we are a combination of big and small teams.  We are also a combination of teams in areas whose science is more mature, and teams in areas whose science is not yet very mature (and maybe if you asked all of us you’d get 10 different opinions on whose science is mature and whose isn’t).

What’s more, he wrote, he sees an inevitable imbalance between the astrophysics teams — which have been thinking about exoplanets for a long time — and teams from other disciplines that have mature models and theories for their own work but are now applying those tools to think about exoplanets for the first time.

But he sees these issues as challenges rather than show-stoppers, and expects to see important — and unpredictable — progress during the three-year life of the initiative.

Natalie Batalie said that she became involved with NExSS because “I wanted to help expedite the search for life on exoplanets.”

Natalie Batalha, project scientist for the Kepler mission and a leader of the NExSS initiative.
Natalie Batalha, project scientist for the Kepler mission and a leader of the NExSS initiative.

“Reaching this goal requires interdisciplinary thinking that’s been difficult to achieve given the divisional boundaries within NASA’s science mission directorate.  NExSS is an experiment to see if cooperation between the divisions can lead to cross-fertilization of ideas and a deeper understanding of planetary habitability.”

She said that in the last year, scientists working on planetary habitability both inside and outside of NExSS — and funded by different science divisions within NASA — have had numerous NExSS-sponsored opportunities to interact, learn from each other and begin collaborations.

The Fortney et al “White Paper” on experimental data gaps, for example, was conceived during one of these gatherings, as was the need for a biosignatures analysis group to support NASA’s Science & Technology Definition Teams studying the possible flagship missions of the future.

Dawn Gelino sees NExSS as an opportunity to speed the pace of addressing and answering open questions in the exoplanet field.  “As a community, we’re making progress towards answering some of them faster than others,” she wrote to me.

 Dawn Gelino, NExScI Science Affairs senior scientist and a leader of the NExSS initiative.
Dawn Gelino, NExScI Science Affairs senior scientist and a leader of the NExSS initiative.

“NExSS gives us an opportunity to look at all of these questions from many points of view.  Suddenly, a problem that a team of researchers has been stuck on has the potential to be solved quickly by learning from those in other disciplines who have dealt with similar problems. ”

Gelino said that NExSS is also working with various NASA study and analysis groups, the teams that come together to take on complicated questions and can later guide and sometimes define some of the science of a NASA mission. The discussion and conclusions from the upcoming Seattle biosignatures workshop, for instance, will be taken up by NASA’s Exoplanet Program Analysis Group (ExoPAG).

As a result, Gelino said, “NExSS scientists can share the knowledge gained from their interactions with earth scientists, heliophysicists, and planetary scientists, which broadens the knowledge of the community as a whole.”

In full disclosure, Many Worlds is funded by NExSS but represents only the views of the writer.

Facebooktwittergoogle_plusredditpinterestlinkedinmail

The Search for Exoplanet Life Goes Broad and Deep

Facebooktwittergoogle_plusredditpinterestlinkedinmail
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.

Twenty years after the detection of the first extra-solar planet around a star, the time seemed ripe for this coming together — especially if the organizing goal of the whole exoplanet endeavor is to search for signs of life beyond Earth.

 

Our vast body of knowledge about the formation, processes and evolution of Earth will become increasingly important in the exoplanet field as new generations of instruments make different and more precise kinds of measurements possible. Using Earth dynamics as a guide, those measurements will be made into models of what might be occurring on the exoplanets. The artist rendering of exoplanet Upsilon Andromedea g by Ron Howard.
Our vast body of knowledge about the formation, processes and evolution of Earth will become increasingly important in the exoplanet field as new generations of instruments make different and more precise kinds of measurements possible. Using Earth dynamics as a guide, those measurements will be made into models of what might be occurring on the exoplanets. The artist rendering of exoplanet Upsilon Andromedae g is by Ron Howard, Black Cat Studios.

Ariel Anbar, a biogeochemist at ASU, was one of the leaders of the meeting and the call for a broader exoplanet effort.

“The astronomical community has been pushing hard to make very difficult measurement, but they really haven’t been thinking much about the planetary context of what they’re finding.  And for geoscience, our people haven’t thought much about astronomical observations because they are so focused on Earth.”

“But this makes little sense because exoplanets open up a huge new field for geoscientists, and the astronomers absolutely need them to make the calls on what many of the measurements of the future actually mean.”

What’s more, the knowledge of researchers familiar with the dynamics of Earth will be essential when planet hunters and planet characterizers put together their wish lists for what kind of instruments are included in future telescopes and spectrographs.  For instance, a deep knowledge would be useful of the Earth’s carbon cycle, or what makes for a stable planetary climate, or what minerals and chemistry a habitable planet probably needs.

And then there are all the false positives and false negatives that could come with detections (or non-detections) of possible signatures of life.  The search for life beyond Earth has already had two highly-public and controversial seeming detections of extraterrestrial life — first by the Viking landers in the 1970s and the Mars meteorite ALH84001 in the mid 1990s.  The two are now considered inconclusive at best, and discredited at worst.

The risk of a similar, and even more complex, confusing and ultimately controversial, discovery of signs of life on an exoplanet are great.  The Arizona State workshop debated this issue at length.

President’s Professor at ASU’s School of Earth and Space Exploration and Department of Chemistry and Biochemistry.
Ariel Anbar, President’s Professor at ASU’s School of Earth and Space Exploration and School of Molecular Sciences. He hopes that the drive to understand exoplanets will push his field to develop a missing general theory for the evolution of Earth and Earth-like planets.

What they came away with was the understanding that while one or two measured biosignatures from a distant planet would be enormously exciting, a deeper understanding of the planet’s atmosphere, interior, chemical makeup and relationship to its host star are pretty much required to make a firm conclusion about biological vs non-biological origins.  (Here is a link to an introductory and cautionary tale to the workshop by another of its organizers, astrophysicist Steven Desch.)

And so the issues under debate were:  Does a planet need plate tectonics to be able to support life?  (Yes on Earth, perhaps elsewhere.) Would the detection of oxygen in an exoplanet atmosphere signify the presence of life? (Possibly, but not definitively.)  Does the chemical and mineral composition of a planet determine its ability to support life? (As far as we can tell, yes.)  Does photosynthesis inevitably lead to an oxygen atmosphere?  (It’s complicated.)

All these issues and many more serve to make the case that exoplanet science and Earth or planetary science need each other.

This is by no means an entirely new message — the Virtual Planetary Laboratory at the University of Washington has taken the approach for a decade from the standpoint of astronomy and the New Earths team of the NAI from a geological standing point.   But still, its urgency and proposed reach was  quite unusual.

It is also a reflection of both the success and direction of exoplanet science, because scientists have — or will have in the years ahead — the instruments and knowledge to learn more about an exoplanet than its location.  The James Webb Space Telescope is expected to provide much advanced ability to read the chemical compositions exoplanet atmospheres, as will a new generation of mammoth ground-based telescopes under construction and (scientists in the field fervently hope) a NASA flagship mission for the 2030s that would be able to directly image exoplanets with great precision.

But really, it’s when more and better measurements come in that the hard work begins.

Transmission spectrum of exoplanet MIT
Information about the make-up of exoplanets comes largely by studying the transmission spectra produced as the planet crosses in front of its star.  The spectra can identify some of the elements and compounds present around the exoplanet. Christine Naniloff/MIT, Julien De Wit.

 

Astrophysicist Steve Desch, for instance,  believes it is highly important to know what Earth-sized planets are like without life.  Starting with a biologically dead exoplanet in the Earth-sized ballpark, it would be possible to get a far better idea of the signatures of a similar planet with life.  But that’s a line of thinking that Earth scientists and geochemists are not, he said, used to addressing.  He felt the ASU workshop provided some consciousness-raising about the kinds of issues that are important to the exoplanet community, and to the Earth scientist, too.

Scientists from the geoscience side see similar limitations in the thinking of exoplanet astronomers.  Christy Till, a geologist and volcano specialist at ASU, said that at the close of the three-day workshop, she wasn’t at all sure that exoplanet scientists have been aware of just how complex the issue of “habitability” will be.

“Our field has learned over the decades that the solid interior of a planet is a big control on whether that planet can be habitable — along with the presence of volcanoes, the cycling elements like carbon and iron, and a relatively stable climate.  These issues were not widely discussed in terms of exoplanets, so I think we can help move the research further.”

Till is relatively new to thinking about exoplanets, brought into the field by the indisciplinary ASU (and NExSS/NAI) approach. But she said it has been most exciting to have the potential usefulness of her kind of knowledge expand on such a galactic scale.

Although the amount of detailed information about exoplanets is very limited, Till (and others) said what is and will be available can be used to create predictive models.  Absent the models that researchers can start building now, future information coming in could easily be misunderstood or simply missed.

ASU geologist and assistant professor Christy Till, a relatively new and enthusiastic member of the exoplanet community. (Abigail Wiebel)
ASU geologist and assistant professor Christy Till, a relatively new and enthusiastic member of the exoplanet community. (Abigail Wiebel)

While the usefulness of geosciences is being largely embraced in the exoplanet field, there are clear caveats.  If Earth becomes the model for what is needed for life in the cosmos, then is the field falling into a new version of the misguided Earth-centric view that long dominated astronomy and cosmology?

With that concern in mind, astronomer Drake Deming of the Harvard-Smithsonian Center for Astrophysics made the case for collecting potential biosignatures of all kinds.  Since we don’t know how potential life on another planet might have formed, we also may well be unaware of what kind of signatures it would put out.  ASU geochemist Everett Shock was similarly wary of relying too heavily on the Earth model when trying to understand planets that may seem similar but are inevitably different.

And Ariel Anbar felt challenged by his more complete realization post-workshop that the exoplanets available to study for the foreseeable feature will not be Earth-sized, but will be “Super-Earths” with radii up to 1.5 times as great as that of our planet.  A proponent of much greater exoplanet-geoscience collaboration, he said the Earth science community has a big job ahead figuring out how the processes and dynamics understood on Earth would actually apply on these significantly larger relatives.

One participant at the workshop pretty much personifies the interdisciplinary bridge under construction , and he was encouraged by the extensive back-and-forth between the space scientists and the Earth scientists.

Shawn Domogal-Goldman, a research space scientist at the Goddard Space Flight Center and a leader of the NExSS group, is an expert in ancient earth as well the astrophysics of exoplanet detection and characterizing.  His view is that the Earth provides 4.5 billion years of physical, chemical, climatic and biological dynamics  that need to be mined for useful insights about exoplanets.

“For me, and I think for others, we’ll look back at this meeting years from now and say to ourselves, ‘We were there at the beginning of something big.'”

 

 

 

 

 

 

 

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Shredding Exoplanets, And The Mysteries They May Unravel

Facebooktwittergoogle_plusredditpinterestlinkedinmail
In this artist’s conception, a tiny rocky object vaporizes as it orbits a white dwarf star. Astronomers have detected the first planetary object transiting a white dwarf using data from the K2 mission. Slowly the object will disintegrate, leaving a dusting of metals on the surface of the star. (NASA)
In this artist’s conception, a small planet or planetesimal vaporizes as it orbits close to a white dwarf star. The detection of several of these disintegrating planets around a variety of stars has led some astronomers to propose intensive study of their ensuing dust clouds as a surprising new way to learn about the interiors of  exoplanet.  (NASA)

One of the seemingly quixotic goals of exoplanet scientists is to understand the chemical and geo-chemical compositions of the interiors of the distant planets they are finding.   Learning whether a planet is largely made up of silicon or magnesium or iron-based compounds is essential to some day determining how and where specific exoplanets were formed in their solar systems, which ones might have the compounds and minerals believed to be necessary for  life, and ultimately which might actually be hosting life.

Studying exoplanet interiors is a daunting challenge for sure, maybe even more difficult in principle than understanding the compositions of exoplanet atmospheres.  After all, there’s still a lot we don’t know about the make-up of planet interiors in our own solar system.

An intriguing pathway, however, has been proposed based on the recent discovery of exoplanets in the process of being shredded.  Generally orbiting very close to their suns, they appear to be disintegrating due to intense radiation and the forces of gravity.

And the result of their coming apart is that their interiors, or at least the dust clouds from their crusts and mantles, may well be on display and potentially measurable.

“We know very little for sure about these disintegrating planets, but they certainly seem to offer a real opportunity,” said Jason Wright, an astrophysicist at Pennsylvania State University with a specialty in stellar astrophysics.  No intensive study of the dusty innards of a distant, falling-apart exoplanet has been done so far,  he said, but in theory at least it seems to be possible.

Artist’s impression of disintegrating exoplanet KIC 12255 (C.U Keller, Leiden University)
Artist’s impression of disintegrating exoplanet KIC 12557548, the first of its kind ever detected. (C.U Keller, Leiden University)

And if successful, the approach could prove broadly useful since astronomers have already found at least four of disintegrating planets and predict that there are many more out there.  The prediction is based on, among other things, the relative speed with which the planets fall apart.  Since the disintegration has been determined to take only tens of thousands to a million years (a very short time in astronomical terms) then scientists conclude that the shreddings must be pretty common  –based on the number already caught in the act.

Saul Rappaport, professor emeritus of physics at MIT, led the team that first identified a disintegrating planet around KIC 12557548, using data from transit light curves collected by the Kepler Space Telescope.  The transits clearly did not indicate the usual small but detectable blockage by a solid body planet,  but were nonetheless intriguing because they were showing that something interesting was crossing (or occulting) the star and trailing an orbiting object.

Rappaport said he was definitely not searching for a dust trail from a disintegrating planet.

“Nobody had suggested that and we weren’t looking for it,” he said. “It took us completely by surprise.  Actually, after we found it, we spent many weeks trying to model it as a collection of solid bodies or something other than a disintegrating planet.  But ultimately we had to face up to what it is – occultation by dust emanating from a planet.”

Four years after his first paper was published, Rappaport said he is now 99 percent certain that KIC 12557548 is a close-in planet slowly disintegrating via the emission of dusty materials, as are three other similar objects subsequently detected.

Rappaport said that speaking generally, measurements of the size of the dust particles coming from those decaying planets would provide very valuable information to scientists, as would any insights into their chemical composition.  But he said that good data will be challenging to collect and equally difficult to interpret.

When an Earth-size planet passes in front of a star, it creates a symmetric dip in the star's light that's shaped like the red curve here. But astronomers detected the strange-looking, blue dip in light from the white dwarf 1145+017. The team suspects the signal comes from a tiny disintegrating planet or asteroid and its comet-like dusty tail. The black dots are measurements recorded by the Kepler spacecraft during its K2 mission. CfA / A. Vanderburg - See more at: http://www.skyandtelescope.com/astronomy-news/white-dwarf-eats-planet2610201523/#sthash.p9521Fxi.dpuf
When an Earth-size planet passes in front of a star, it creates a symmetric dip in the star’s light that’s shaped like the red curve here. But astronomers detected the strange-looking, blue dip in light from the white dwarf 1145+017. The team suspects the signal comes from a tiny disintegrating planet or asteroid and its comet-like dusty tail. (CfA /A. Vanderburg)

Unrelated to Rappaport’s work, Wright and a Penn State team, although with from the Arizona State University astrophysicist Steve Desch and others, have just sent a proposal into NASA to fund  disintegrating exoplanet research using ground-based telescopes and the Hubble Space Telescope.

The collaboration originated at a meeting of the Nexus for Exoplanet Systems Science (NExSS), a five-year NASA initiative to bring together exoplanet scientists from a variety of disciplines with the goal of having them work together across disciplines.  Organized by Mary Voytek, NASA’s senior scientist for astrobiology, it aims to bring the highly interdisciplinary model of astrobiology to the field of characterizing exoplanets.

“This is a project that really calls for, in fact requires, an interdisciplinary approach,” Desch said.  “This is where astronomy and astrophysics meet planetary science and geology, and that should be a very fruitful place.”

Is a measure of the interdisciplinary effort, their team also includes Casey Lisse at the Johns Hopkins University Applied Physics Laboratory.  He’s a comet scientist with a specialty in planet formation and astromineralogy.

Jason Wright, associate professor at Penn State University, initiated the collaboration to use disintegrating planets as a pathway to understanding exoplanet interiors. (Gudmundur Stefansson)
Jason Wright, associate professor at Penn State University, initiated the collaboration to use disintegrating planets as a pathway to understanding exoplanet interiors. (Gudmundur Stefansson)

Wright and Desch want to focus on the unusual transit signals from five stars — three M dwarf identified by Kepler, one a burned-out but super-dense white dwarf and other made famous last fall when a substantial and currently impossible-to-explain dust cloud was detected nearby it.  All the known explanations to explain it were deemed inadequate, which led to (last option) suggestions that perhaps it was an alien “megastructure” or Dyson swarm built by intelligent beings.

Wright was part of the group trying to explain the vast cloud around the star — KIC 8462852 or “Tabby’s star,” named after Yale University post-doc and co-founder Tabetha Boyajian) and now suspects that a disintegrating planet could be a source (though he says that Desch was the first to make the case.)

KIC 8462852, informally known as Tabby’s Star, is a magnitude +11.7 F-type main-sequence star located in the constellation Cygnus approximately 1,480 light-years from Earth. Data from NASA’s Kepler space telescope shows that the star displays aperiodic dimming of 20 percent and more. KIC 8462852 is shown here in infrared (2MASS survey, left) and ultraviolet (GALEX). Image credit: IPAC/NASA (infrared); STScI/NASA (ultraviolet).
KIC 8462852, informally known as Tabby’s Star, is a magnitude +11.7 F-type main-sequence star located in the constellation Cygnus approximately 1,480 light-years from Earth. Data from NASA’s Kepler space telescope shows that the star displays unexplained periodic dimming of 20 percent and more. KIC 8462852 is shown here in infrared (2MASS survey, left) and ultraviolet (GALEX) IPAC/NASA (infrared); STScI/NASA (ultraviolet)

The object that orbits a white dwarf star at a distance about the same as between Earth and the moon.  When its discovery was announced last year by Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, he said that something unique had been found:  “We’re watching a solar system get destroyed.”

The planet (or planetesimal) orbits its white dwarf, WD 1145+017, once every 4.5 hours. This orbital period places it extremely close to the super-dense star, and that speeds the shredding and evaporating of the planet. But makes it a theoretically easier target to observe.  Each time it orbits is a potentially detectable transit to be captured and studied.

White dwarf stars have also served as an earlier destination for those looking for information about potential insides of planets, but via a more indirect approach.  Because of their greatly heightened gravity, white dwarfs have surfaces covered only with light elements of helium and hydrogen. For years, researchers have found evidence that some white dwarf atmospheres are polluted with traces of heavier elements such as calcium, silicon, magnesium and iron. Scientists have long suspected that the source of this pollution has been asteroids or, what was then theoretical, a small planet being torn apart.

Steven Desch, an astrophysicist at ASU, sees a frequent gap between the work of astronomers and planetary scientists, and hopes to help bridge it.
Steve Desch, a theoretical astrophysicist at ASU, sees a frequent gap between in the exoplanet work of astronomers and of planetary scientists, and hopes to help bridge it. (ASU News)

Another prime target for disintegrating-planet research is the first one identified,  KIC 12557548 b.  Because it is so small — no bigger than Mercury — it’s an object that would never be detected by telescopes looking for transits across a star.  It is, after all, 1500 light years away.  But the dust cloud is much bigger and blocks as much as 1 percent of the light from the star every time it orbits.  To compare, our Jupiter would block about the same amount of the sun’s light in a similar scenario seen from afar.

The team leaders said that while their goal is to collect data that will help them understand the grain size and chemical composition of the dusty planetary remains, they also aim to refine the observing and spectrographic techniques for future observations — most especially on the James Webb Space Telescope.

The JWST, which launches in 2018, will have the capacity to collect information about the disintegrating planets that current instruments cannot.  But time on the telescope will be very costly and competitive, so Wright said the team will be doing the groundwork needed to make disintegrating planets an appealing subject for research.

“A lot of the observational technique has to be invented,” said Wright.  “JWST will be prime time for new science, but before that we need a lot of ground-based pre-study to make the case.”

The proposal also calls for extensive modeling of the dynamics of how dust grains would be released under the pressure of intense gravity and radiation pressure.

Coincidentally, a paper that models exoplanetary interiors authored by Li Zeng of the Harvard-Smithsonian Center for Astrophysics (CfA) and others, has been accepted for publication by The Astrophysical Journal.

Making sure it first could reproduce the Preliminary Reference Earth Model (PREM) — the standard model for Earth’s interior — Zeng and his team modified their planetary interior code to predict the structure of exoplanets with different masses and compositions, and applied it to six known rocky exoplanets with well-measured masses and radii.

They found that the other planets, despite their different masses and presumably different chemical makeup, nevertheless all appear to have a iron/nickel cores containing about 30% of the planet’s mass, very similar to the 32% of the Earth’s mass found in the Earth’s core. The remainder of each planet would be mantle and crust, just as with Earth.

The model, however, does not add new information about the observed make-up of exoplanet interiors.  That’s where the disintegration of close-in exoplanets just might come in.

In this Chandra image of ngc6388, researchers have found evidence that a white dwarf star may have ripped apart a planet as it came too close. When a star reaches its white dwarf stage, nearly all of the material from the star is packed inside a radius one hundredth that of the original star. Using several telescopes, including NASA’s Chandra X-ray Observatory, researchers have found evidence that a white dwarf star – the dense core of a star like the Sun that has run out of nuclear fuel – may have ripped apart a planet as it came too close. ( NASA)
In this Chandra image of globular cluster NGC 6388, researchers have found evidence that another white dwarf star may have ripped apart a planet as it came too close. When a star runs out of nuclear fuel and reaches its white dwarf stage, nearly all of its material from the star is packed inside a radius one hundredth that of the original star. The images was made with from images taken by several telescopes, including NASA’s Chandra X-ray Observatory. (NASA)
Facebooktwittergoogle_plusredditpinterestlinkedinmail