Climate Stability and a Hike along a Triassic Coral Reef

The breathtaking white-gray peaks in the Italian Alps. Photo by D. Apai

The breathtaking white-gray peaks in the Italian Alps.

After two hours of hike up on a rocky trail in the Italian Alps, finally I stand at an elevation just above 2,500 meters, staring at a breathtaking and unique mountain range, the Dolomites, that holds an exciting clue to the habitability of our planet.

One of the many streams along an Alpine trail.

One of the many streams along an Alpine trail. Photo by D. Apai

With gigantic sharp white-gray peaks emerging from the lush green of Alpine meadows, these mountains rise where the African continental plate has been slamming violently into the European plate for millions of years, forcing rocks up thousands of meters  — and giving birth to the geologically young Alps.

In a trip zig-zagging Europe — visiting observatories, universities, and workshops — I stopped briefly in South Tirol for a few hikes. The most picturesque of them took me up to the Three Peaks of Lavaredo (or Tre Cime di Lavaredo), three 3,000m-high peaks, one of the gems of the Alps. Dotted by rifugi (mostly little huts, but at the easier trails often with nice cafes) the trails are popular among both tourists and locals. They offer an incredible view ascending towards the peaks, before joining an old network of high-altitude Alpine hiking trails, many of which take a week to complete.

Alpine flowers in the Dolomites. Photo by D. Apai

Alpine flowers in the Dolomites. Photo by D. Apai

The Dolomites are a unique mountain range within the Alps: their composition and history is different from any other in the Alps. They also hold an exciting clue to the process that keeps our planet habitable. Named after a relatively rare form and unusually stable form of carbonate rocks, dolomite, the mountain range’s unique color and composition was noted long ago and, for some time, posed one of the mysteries of geology. Now we know that the majestic dolomite layers in the Dolomite mountains are — amazingly — the work of tiny organisms: it is a very thick layer of ancient coral reefs. During part of the Triassic period (about 255-199 million years ago) the region was part of a shallow sea, which was slowly pulled deeper and deeper. But corals, only capable of living in the upper photic zone of the sea (where enough light is present for photosynthesis), kept on building their reefs higher and higher, managing to always keep the top layer of the coral reef close to the sea surface. With the sea floor sinking and the coral reef growing higher, these tiny animals constructed one of the giant carbonate deposits of the Triassic period.

As most geological periods, the Triassic also did not end well: in fact, it ended with the Triassic-Jurassic mass extinction, one of the greatest extinctions known, which eradicated about 50% of the known marine species. This extinction — occuring just before the Pangea super-continent began to break apart — paved the way for dinosaurs to become the dominant land animals in the Jurassic period that followed. The giant coral reefs of the Dolomites sank further and were covered by sedimentary layers and laid in depth for the next two hundred million years.

The Tre Cimes are a striking triple peaks in the Dolomites.

The Tre Cimes are a striking triple peaks in the Dolomites. Photo by D. Apai

Only recently, when the African continental plate collided again with the European plate, were the ancient coral reefs forced to resurface again. Together with other Triassic layers these rocks — once a seafloor — were now pushed up thousands of meters to become the dramatic high peaks of the new-born Alps. Once exposed to snow, ice, rain, and wind, the layers began to rapidly erode, creating the picturesque formations I was able to see today.

But the Dolomites’s story also holds a clue to why we are here: amazingly, the process that formed them and destroys part of a grander process them keeps Earth habitable. The mean temperature of Earth and its local and seasonal variations — its climate — is relatively stable: although major global changes occurred in the past and will probably occur in the future, Earth’s mean temperature mostly remained close to the current temperature and has seen much smaller changes than Mars and Venus have.

The key long-term stabilizing mechanism that keeps Earth’s climate in the habitable range (allowing liquid water on its surface) is the carbon cycle: it is the journey of carbon through the atmosphere, the ocean, the rocks, and the volcanoes of our planet. It is a journey that may take hundreds of million of years for a given carbon atom to complete, providing a slow connection between key reservoirs of carbon in Earth: CO2 in the atmosphere and carbonate rocks in the lithosphere. What makes this journey a feedback cycle is that it is both sensitive to the temperature and able to regulate it: The amount of CO2 — a powerful greenhouse gas — in the atmosphere directly impacts Earth’s temperature: the more CO2 is in the air, the more of Earth’s own emission is captured by it and re-radiated back to Earth, just like a blanket would provide additional heating to our planet (by slowing its cooling) — just as glass windows do in a greenhouse. However, the higher the temperature, the higher the humidity in the air and the more condensation occurs — and the more it rains, the more CO2 is washed out from the atmosphere forming acidic rain. The rain then interacts with silicate-rocks and forms carbonate rocks in the silicate weathering process — or, in a planet that is so filled with life as ours, tiny organisms can grab the carbon-dioxide dissolved in the ocean to build shells or coral reefs. As the Dolomites also show, vast amounts of carbon dioxide can be captured (over long periods of time) in rocks. Slowly, the carbonate rocks will be eroded and carried by rivers to the oceans, deposited to the ocean floor and, eventually, subducted along the oceanic/continental plate boundaries. There, many kilometers deep, the carbonate rocks will be exposed to very high pressures and temperatures, converting the carbonate rocks back to the silicates and expelling CO2 and water — these gases will then find their ways to the surface through explosive volcanoes near the plate subduction boundaries.

Because the loss of CO2 from the atmosphere is temperature sensitive (higher temperature leads to more rain and more carbonate formation) but the source of the CO2 is temperature insensitive (volcanoes do not care about the surface temperatures), the whole cycle forms a net negative feedback cycle: higher temperatures will result in cooling and lower temperatures will result in warming. The negative cycle means that it is stabilizing the temperature of Earth: because the carbonate reservoirs are vast, the effect is powerful; but because it takes hundreds of millions of years to transport carbonate rocks to subduction zones via plate tectonics, the cycle is also very small. While it has kept Earth habitable on long timescales (~100 Myr), the cycle can’t work well on short timescales (<10-30 Myr).

How would this apply to other Earth-like planets? While on present-day Earth the carbonate formation is dominantly through organic processes (various shell-forming marine organisms are happy to make use of the CO2 dissolved in the ocean), in the early Earth and, presumably, in other Earth-like planets with little or no life the same process can occur inorganically, but somewhat slower, in silicate rock weathering.

Therefore, as long as the overall composition of other Earth-like planets are the similar to ours, we would expect them to sport a carbon cycle (either organic or inorganic), also providing a stable climate for them — as long as the planets remain within the temperature range where the carbon cycle can work.

This means that carbonate deposits should be common even beyond the Solar System — and, just perhaps, a few in the Galaxy will also match the majestic beauty of the Dolomites.

The Dolomites mountain range preserves a thick layer of Triassic coral reefs.

Daniel Apai at the Dolomites mountain range, that preserves a thick layer of Triassic coral reefs.

Building Planetary Systems

Mikayla Mace is a UA journalism graduate student who is writing a nice series of article on our Earths in Other Solar Systems work. She has just posted a piece on our Genesis Database, the mother of all planet formation simulations, featuring Gijs Mulders and Fred Ciesla. The Genesis Database will help us understand how habitable earth-like planets can form and around which stars are they more likely to exist:

Building Planetary Systems: The Genesis Database

Not the ocean planet you were told about: By weight Earth has only very little water, below a percent.

Not the ocean planet you were told about: By weight Earth has only very little water, below a percent.

The Future of Exoplanet Research

By Daniel Apai
Includes interview with Nick Siegler and Shawn Domagal-Goldman

Over the weekend, at the Hilton on the San Diego Bay, a small group met to speak about the present and future of NASA’s Exoplanet Exploration program. To someone not in the field of exoplanets the talks and debates may have resembled science fiction: giant space telescopes, rockets and spacewalks, hyper-precise measurements of stellar motion, search for alien life, exploration of volcanism on exoplanets, laser-combs, starshades, and other Earths across the Galaxy were just a few of the topics that were debated. The memorable images included cows illuminated by lasers in a Nevada desert. It was a fun meeting and a timely one, too.

EXOPAG Meeting San Diego

The field of exoplanets is hotter than ever: we learned that planets are literally everywhere and that planets with sizes similar to Earth are the most common among the known planets. Many of the stars (probably 1 in 4) harbor about-earth-sized planets with stellar heating similar to Earth. Not only did we learn about the frequency of the planets, but also about their properties. New missions and instruments are being built and planned, conferences and school galore, and amazing discoveries are made almost weakly. The enthusiasm is palpable in the field; yet. we know that reaching our grand goal of finding extraterrestrial life is going to be anything but easy.

We can only find life if it produces a signature that is detectable from vast – literally astronomical – distances. Seen from space humans, trees, elephants, or even whales are undetectable and unremarkable, yet Earth would reveal its secret to an outside observer through the surprising abundance of a highly reactive gas, molecular oxygen. Oxygen is and has been produced by  advanced photosynthetic organisms, first in the ocean and then on land. About 2.3 billion years ago oxygen has saturated the planet’s surface and rapidly accumulated in vast amounts in our atmosphere, From that point on Earth’s atmosphere became a glowing indicator of life for the entire Galaxy – at least, for civilizations that are slightly better in building telescopes than we are.

So, starting from the only example we have, NASA’s Exoplanet Exploration program is aiming to build a telescope that will look for oxygen or other similarly odd gases in other earth-like planets atmospheres as possible signatures of life.

In a perhaps unusual consensus, the exoplanet community is united behind the most important goal, surveying nearby exo-earths for biosignatures. Few other approaches to detecting extraterrestrial life seem feasible. Although the goal is clear, possible approaches and ideas are plenty: the abundance of proposed approaches stems from the fact that no telescope that exists today (or at least, accessible to astronomers) is capable enough to directly search for biosignatures in known exo-earths. Building one that will be up for the job is not going to be easy: in fact, right now, we do not know how good exactly that telescope would need to be, what capabilities it would have to have — and we don’t know how we would build it.

Guided by the vision of finding extraterrestrial life, astronomers, astrobiologists, technologists, engineers, project managers are all working together to come up with concrete plans for such telescopes. Our goal is to create at least two different designs for life-finding telescopes by 2019. The year is important, because in 2020 the astronomical community will issue a major report, the Decadal Survey. This study will set the strategy for NASA for 2020s and beyond and will determine whether planning and construction of such a telescope can begin in a few years or we need to wait another decade.

What the best telescope design is will depend on what questions we want to answer and on the properties of planets, too: our meeting in San Diego explored these issues as well as the technology development needed to build a telescope more ambitious than anything very built. For example, one possible telescope design would use a “starshade” – a giant (think fifty meters or hundred and fifty feet) flower-petal-shaped mask. The strange mask would fly tens of thousands of miles in front of the telescope and could, if positioned precisely, cancel out the light of the host star completely, revealing the faint planets. However, nothing like this has ever been flown in space or used in ground – so a Northrop-Grumman team of engineers is testing this idea in the night in a dark Nevada desert, shining bright a light to a telescope from miles away and covering the light with a small starshade mask in between. One night however, a cow, perhaps intrigued by the strange glowing flower in the desert, wandered into the light beam and photo-bombed the experiment, thus becoming part of the history of space exploration.

The San Diego meeting was exciting and fun: a lot of progress has been made recently, but much more needs to be done in the next three years to finalize plans for a space telescope that can look for life on other Earths

At the meeting I also grabbed the opportunity to interview two experts who approach this question from different angles: Dr. Nick Siegler, who is the Chief Technology of NASA’s Exoplanet Exploration Program; and Dr. Shawn Domagal-Goldman, astrobiologist and biosignature-expert at the NASA Goddard Space Flight Center.

Several important studies of space telescope design and science questions will be carried out over the next year or two, pushing our technology and understanding toward the long-term goal. It will be exciting to see how this group of smart people figures out solutions to problems that were thought to be impossible to solve, and how it will overcome unexpected barriers, such as curious cows.

Launching Toward Other Earths – EOS Updates from the PI

News and updates on NASA’s Earths in Other Systems Project from PI Daniel Apai. May 10, 2015.

NASA's new Nexus for Exoplanet System Science program offers an ambitious, novel approach to study and understand habitable exoplanetary systems.

NASA’s new Nexus for Exoplanet System Science program offers an ambitious, novel approach to study and understand habitable exoplanetary systems.

Sunday early morning with a coffee in my hand, sitting next to giant blooming Saguaro cacti and citrus trees in Tucson with the spectacular Catalina mountains in the background. Two tiny hummingbirds angrily hover around each other in the air, in a surreal, high-speed aerial fight over the nectar drops in our bottlebrush flowers. A rare, quiet moment to reflect on the launch of our Earths in Other Systems project and the five years ahead of us in this exciting endeavor.


Morning Coffee with Saguaros and Catalina Mnts

After almost two years in planning and preparation, our Project EOS has finally began: an exciting meeting at NASA HQ has launched NASA’s new Nexus for Exoplanet System Science program (which is funding EOS), we published the first paper with EOS results and investigators, the first postdoctoral researchers and a program coordinator are joining our project in May, our website is also online, and we began preparations for transforming a group of offices at the Steward Observatory of The University of Arizona into the EOS “Headquarters”.

EOS Overview

Our EOS team studies the formation of planets capable for sustaining life through three closely connected questions.

Project EOS is an ambitious, exceptionally large-scale research project that combines different disciplines and research techniques to understand how Earth-like planets form. While we now know that Earth-sized planets that receive similar amount of energy from their host stars as Earth does are common in the Galaxy, we do not know how similar these worlds are to Earths: do they only have the same size, but very different compositions, or are many of these worlds truly Earth-like, each carrying in it a potential for rich and complex living systems to emerge? Consider Venus, Earth’s “evil twin”:  81% as massive as Earth and orbiting at 72% of the Earth-Sun distance, it is a world that — seen from hundreds of lightyears — could appear misleading similar to Earth. Yet, through differences in its formation and evolution Venus has become a world with a surface and atmosphere astonishingly different from Earth: entirely devoid of water, lacking plate tectonics and its ability to bury CO2 and stabilize its, Venus’s thick CO2 atmosphere traps the incoming solar radiation and heats up to about 740 K (464 C). Or consider the opposite extreme: NASA’s Kepler mission has found a new type of planets, super-Earths, to be very common in the Galaxy. Many of these super-earths may have very low densities, an evidence that they must have lot of water and light, extended atmospheres. And a “lot of water” here means hundreds or thousands of Earth oceans’s worth of water, completely covering the silicate mantle of the planets, most likely in hundreds of km-thick high-pressure water ice layers, below thick liquid oceans or high-pressure steam atmospheres. These “water worlds” may be just inhospitable to life as the hot, acidic, bone-dry desert Venus has evolved into.

View from the hellish surface of Venus from the Soviet Venera probes.

View from the hellish surface of Venus from the Soviet Venera probes.

How many of the planets in the solar neighborhood are truly Earth-like — moderately rich in volatiles and organics — is an essential question to answer if we want to carry out a meaningful search for extraterrestrial life: for surveying nearby Earths for signatures of life is going to be one of the most complex and challenging endeavors in science yet.

In Project EOS twenty-five of the best experts from five disciplines will work together over the next five years to understand how the composition and volatile and organics budget of newly formed Earth-sized planets is set. In a fascinating set of projects we will look at the smallest scales and back in time, probing the mineralogy and composition of micron-sized grains in ancient meteorites using the most sophisticated microscopic techniques, to explore the history of volatiles and organics in planetary building blocks at the time when the Solar System was young. We will also use optical, radio, and infrared telescopes to study young stars and, around them, planetary systems in formation to piece together the incredible story of a dusty disk rapidly transforming itself into a planetary system that may support life. In search of new knowledge our team will travel to most continents on Earth and will use telescopes in the Sonoran Desert, the Chilean Atacama Desert and on Hawaii’s Mauna Kea; the Hubble and Spitzer Space Telescopes. We will also build powerful computer models for the planet formation process and use these to inspect the details and fill out the gaps; we will  compare the predictions of these models to the properties of exoplanetary systems: planetary orbits, masses, densities, atmospheric compositions. If we succeed, what we learn here will guide our and NASA’s search for life beyond Earth.

I am fortunate enough to work with a team of truly outstanding scientists from the diverse fields, all working toward a shared goal. Over the next five years, our team will also be joined by a dynamic group of young students and postdoctoral researchers: the team at its largest will include over forty researchers. But we will reach an and involve much larger groups: Our results will find their way to the courses we teach and we will also build up a team of Other Earths Ambassadors – citizen scientists excited by the search for life on other planets and eager to contribute.

We will share the excitement and news from the EOS project through blog updates, public talks, Twitter and Facebook posts; join us and follow the blog and twitter feeds and you will learn about our science results, discoveries, travels, and about exploring other worlds, directly from the front line.

Twitter: @EOSNExSS, @danielapai

NExSS Kick-off Meeting at NASA HQ

Two weeks ago NASA has announced its new Nexus for Exoplanet System Science, which may prove to be a major change in the way NASA will fund exoplanet science in the future. Our UA-led team was part of the first selection and I, the principal investigator of our project, joined the program’s two-day kick-off meeting at NASA HQ. The meeting was exciting, inspiring, and challenging at the same time. There have been several press releases and articles about the program in various online and printed media; what follows is my own personal perspective on the meeting.
Introduction to VPL by Victoria MeadowsView from 17th Floor in Crystal City

Questions, Problems, & Puzzles

NASA has invited the principal investigators and key members of 16 NASA-funded teams working on topics related to exoplanet habitability, as well as the directors of the new initiative to discuss and debate the best format and goals for the new program. The teams were selected from regular proposal  submissions to different NASA programs through the usual peer-review process, but invited to NExSS in addition to their selection to carry out the research they proposed.

The motivation for launching NExSS, as I understand, comes from the rapidly growing importance of extrasolar planet habitability research within many different NASA programs. The recent restructuring of NASA research grant programs (XRP, Habitable Worlds, etc.) further emphasized planetary habitability studies across many programs, which led to different aspects of habitability funded through different channels, without a good way to coordinate research between the programs. In addition, planetary  habitability-related proposals accounted for a very large fraction of the major proposals that responded to the latest opportunity to join the NASA Astrobiology Institute.

NExSS is a new approach to study extrasolar planets: the program’s idea is to combine various studies of planetary habitability funded through existing NASA programs into a new framework – one in which the teams collaborate and have influence over the broader, longer-term research directions.

Although many people at NASA have been involved in and contributed to launching NExSS, Mary Voytek, senior scientist for astrobiology, is the chief architect of the new program and program officers Christina Richey and Doug Hudgins, among others, also played important roles. Shawn Domagal-Goldman has also provided important input and advice for the new program.

Our meeting began with short talks at a NASA HQ auditorium, which included welcomes by Jim Green and Paul Hertz, the directors of the NASA Planetary Sciences and Astrophysics divisions. They expressed excitement about exoplanet research, emphasized the need for studying planets as “systems” and they strongly endorsed connecting research projects in different disciplines that address exoplanet habitability. Their enthusiastic support of NExSS was a clear demonstration of how strongly NASA is supporting the new interdisciplinary research coordination network.

We were also welcome by the three new co-directors of NExSS, Dawn Gelino, Natalie Batalha, and Anthony Del Genio, who work on various aspects of exoplanet research.

Next, lightning talks by the leads of each of the 16 teams introduced the scope of the teams; the single-slide presentations gave the first insights into the surprising breadth of NExSS. The NExSS teams have been selected from a set of projects submitted and selected for regular NASA programs (e.g., XRP, Habitable Worlds, Astrobiology, Heliophysics), so the sixteen teams brought very different expertise and perspectives to the table.

The projects also covered a broad spectrum in size, ranging from a few 1-2 investigator grants through a number of medium-sized teams to a few really large teams with multi-million dollar grants. These latter programs are our University of Arizona-led Earths in Other Solar Systems team (PI: Apai), the Arizona State University-led team (PI: Desch), a team led by NASA Goddard Institute for Space Sciences (PI: Del Genio), a team led by Berkeley (PI: Graham), and the one at Hammond University (PI: Moore). NASA’s press release and the team websites provide more information about the teams; I will instead focus on the kick-off meeting.


Working hard on putting the puzzle pieces together at the NASA NExSS Kick-Off meeting.

In contrast to the more usual top-down approach, our group’s first task is to brainstorm on its own purpose and definition. This has been an unusual responsibility; most committees are tasked to chart a course to reach a specific goal on a well-defined timescale. Defining our own goals and purpose is much more challenging; however, it also gave us the valuable opportunity to brainstorm and debate on the importance and achievability of different science goals over various timescales.

NASA has contracted a small company, KnowInnovate, to facilitate the creative process; this small team — two brothers — helped us move forward in the complex debate. Indeed, it has proven challenging for our team to converge on a set of well-defined goals in its first meeting; but by the end of the meeting we did identify our next steps and, I believe, made progress forward in surveying the questions, problems, and goals for the field.

Questions, Questions, Questions

Questions, Questions, Questions

The 2-day discussion resulted in covering most vertical surfaces of the meeting room with neon-colored sticky post-it notes, each with a question, problem, goal, or idea relevant for exoplanet studies. Arranged thematically, by importance, or by timescale, these stickies captured well the complexity and the heavily connected nature of next decade’s exoplanet research.

There discussion was productive and interesting; the number of questions and problems identified, and their complexity, is daunting, to say the least. Questions ranged from the impact of stellar hosts on the habitable planets through the importance of the formation and evolution of planetary systems to the unknowns of planetary interiors and life’s impact on the planet.DistantEarths-1029

Nevertheless, in a process that built on large quantities of coffee, snacks, and post-it notes, we identified some short-term steps and topics of immediate interests. These included establishing working groups on topics relevant for many questions (missing experimental data, cloud physics and chemistry), plans for workshops/conferences to connect to the community, blog-type snippets on new exoplanet research papers, just to name a few.DistantEarths-1028

It has been exciting to see a launch of a new program and one the exoplanet community can so actively shape. From my perspective, the NExSS group’s most important goal is interfacing and connecting: both within the group – in which we had a great start – and also with the broader community. The NExSS Executive Council will gradually change as PIs rotate in and out of the group over the next years, but I am very hopeful that the group will maintain its collaborative spirit as we put together the pieces of this exciting, but complex extrasolar puzzle.

You can follow our team’s work and results on Twitter (@EOSNExSS) or by subscribing to email announcements on our website ( ).

The Best Astrobiology and Exoplanet Books

I am often asked to recommend books on astrobiology, habitable exoplanets, and extraterrestrial life.

There are many great books in these exciting fields, but there are a number of stand-outs that I highly recommend. Below is a gradually growing list of my favorite ones.

Is your favorite book missing? Add other book suggestions in the comments below!


CosmosCarl Sagan
A classic 1980 book by Carl Sagan. Although missing some of the new developments, this book remains an excellent treatise on life in the universe (and Earth).

Rare Earth
Peter Ward and Don Brownlee

This is a classic book which provides an interesting overview of many key factors and problems that have made it difficult for complex life to evolve on Earth. Many of these factors apply to all habitable planets making, in the view of the authors, complex life extremely rare.
The “Rare Earth” hypothesis splits astrobiologists and it will take decades — if not centuries — until we will be able to decide if Ward and Brownlee are right. Nevertheless, the book provides a highly readable and interesting narrative of many exciting problems related to the development of simple and complex life.

Peter Ward is a Professor of Geosciences at the University of Washington, has led one of the NASA Astrobiology Institute nodes and an author of 16 popular science books.

Don Brownlee is a Professor of Astronomy at the University of Washington and the Principal Investigator of NASA’s Stardust mission.

Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life
Peter Ward

How to Find a Habitable PlanetKasting How to Find a Habitable Planet
James Kasting
Princeton University Press, 2010

James Kasting is one of the pioneers of planetary habitability studies and in this book he provides an insider’s view on what makes a planet habitable and how can we find planets suitable for life.

The 5th Miracle: The Search for the Origin and Meaning of Life
Paul Davies
Touchstone, 2000

Paul Davies’s book provides an exciting exploration of the possible origins of life, including the principles of biological systems.

Crowded Universe
Alan Boss
Basic Books, 2009

Alan Boss’s book offers an enjoyable insider’s view on the birth of the exoplanet field: from the first radial velocity discoveries until the launch of the Kepler mission, Alan gives a diary-like summary of the major new exoplanet discoveries and results, including the controversies, debates, and the impact of politics and space policies on the science of exoplanets.

Alan P. Boss is an astrophysicist at the Carnegie Institution for Science’s Department of Terrestrial magnetism and an expert on extrasolar planets and the formation of planetary systems.

Biology / Paleontology

Life on a young planet
Andrew Knoll
Princeton University Press, 2003

The book provides an interesting, in-depth, but very readable discussion of research on the earliest life on Earth and especially on microfossils. While the book does not focus on extraterrestrial life, the history of life on Earth is an absolutely fundamental part of astrobiology and this is a great introduction to it.


Distant Wanderers
Bruce Dorminey
Copernicus Books, 2002

A somewhat older, but excellent book on the beginning of the era of exoplanet discovery and characterization. The book includes great interviews with many of the prominent scientists in the field and provides a great introduction to the initial discoveries of extrasolar planets.

Strange New Worlds
Ray Jayawardhana

This book provides an exciting narrative of exoplanet exploration and discoveries, with clear explanation oft he techniques and peppered with anecdotes from the field.


Life in The Universe
Benneth Shostak Life In the Universe3rd Edition
J. Benneth, S. Shostak

A best-selling introduction to astrobiology, mainly aimed at non-science majors. This richly illustrated and entertaining textbook provides a well-balanced overview of how concepts from astronomy, planetary sciences, geosciences, and biology can be combined to search for life in and beyond the Solar System.

How to Build a Habitable Planet: The Story of Earth from the Big Bang to Humankind
Charles Langmuir and Wally Broecker

Princeton University Press, 2012

This well-written book follows Earth’s formation and evolution, including the overview of biological evolution. The book provides an interesting, geoscience perspective on these topics, which complements well most other books that approach the topic more from an astrophysics/planetary sciences perspective. Well suited for undergraduate courses.

Earth: Evolution of a Habitable World
Lunine Evolution of a HabitablePlanetJonathan Lunine
Cambridge University Press, 2013

An excellent undergraduate introduction to the formation and evolution of Earth and to the processes that made and keep our planet habitable.

See my review of the this book in Meteoritics & Planetary Sciences.

On to A New Year and New Exoplanets!

Grand Canyon Panorama

The 2014 year has brought much excitement in the field of extrasolar planets and 2015 is set to be at least as exciting as the past year: new powerful adaptive optics systems are searching the northern and southern skies for new exoplanets and Kepler2 should start bringing a large number of new planet candidates!

Just after Christmas my family took a break and visited the Grand Canyon, just a few hours drive from Tucson. I took the pictures from the South Rim’s Mather Point. Amazing to think how, in just about 5-10 million years, the apparently small Colorado river eroded away one vertical mile of rocks deposited over 1.8 billion years!

Back to the field, the first week of January also brings along the largest US meeting of professional astronomers, the winter meeting of the American Astronomical Society. This year astronomers are gathering in Seattle and we can take for certain that during the course of the next week there will be exciting announcements every day.

The large AAS meeting will be preceded by the open meeting of the NASA Exoplanet Analysis Group, where many in our field gather to review progress in exoplanet research and plan the next steps. The meeting will be broadcasted live, so you can watch it even if you are not in Seattle!

I wish everyone an exciting new year!

In just 5-10 million year the Colorado river eroded one vertical mile of mostly sedimentary rocks deposited over nearly two billion years.

In just 5-10 million year the Colorado river eroded one vertical mile of mostly sedimentary rocks deposited over nearly two billion years.

Grenoble and Planet Hunting with Adaptive Optics

In July I spent four exciting days at the Institut de Planetologie et d’Astrophysique de Grenoble (IPAG). Set in a picturesque green valley in the Alps where the rivers Drac and Ilsere merge, this scenic little town in Southern France is well-known for planet hunters.

A charming little town in the French Alps, a European center of adaptive optics development.  Image source:

A charming little town in the French Alps, a European center of adaptive optics development. Image source

The Grenoble group I visited is one of the world leaders in direct imaging of extrasolar planets: over the past decades Jean-Luc Beuzit and his group have developed more and more sophisticated instruments to enhance the sharpness of the images that can be obtained with the largest telescopes. Anne-Marie Lagrange and her group have used these adaptive optics systems to painstakingly search nearby stars (typically within a distance of 250 lightyears) for exoplanets. The group’s outstanding work has led to several exciting and now-classic discoveries: 2MASS1207b, AB Pictoris b, or the planet in the spectacular Beta Pictoris system, a project on which we worked together. During my stay in Grenoble I also enjoyed a memorable dinner hosted by Anne-Marie’s very friendly research group – everyone pinched in in the preparations and soon we enjoyed an amazing set of French dishes. Cheese, red wine, and exoplanets – what a pleasant way to spend an evening!

Planet around a Brown Dwarf?
Anne-Marie and her group made their discoveries with the European Very Large Telescope, a system of four 8m telescopes based at the Paranal Observatory in the Chilean Atacama desert. This telescope and its NACO instrument has discovered more directly imaged exoplanetary systems and planetary mass objects than any other telescope in the world.

Why do we need adaptive optics systems to image planets?

There are three factors that make it extremely difficult – really, almost impossible – to directly image planets around other stars:
1) Planets are inherently faint: unlike stars, planets have no stable internal heat sources apart from the decay of some radioactive isotopes. Therefore, planets are much cooler than stars – and being also much smaller, planets are typically ten million to a billion times fainter than their host stars. This means that the images must be very sensitive to detect them: very large telescopes must be used that can collect a lot of light.

2) By definition, each planet must orbit a star – and because stars are very distant, the planets appear to be extremely close to their host stars, which are always much brighter. Because of the large contrast between the star and its planets, we can only directly image planets that appear the farthest from their stars: those that are on very long orbits. For comparison, a planet at 5.4 AU separation (5.4 times the Earth-Sun separation or 1 times the Sun-Jupiter separation) will appear 5.4/10 = 0.54 arc second from its host star, the equivalent of the apparent size of a penny seen from about 5 miles. The great brightness difference between the star and its planet and the fact that they appear very close mean that an image showing exoplanets must have an extremely high contrast. And, in practice, the highest-contrast images are those that are taken with the highest quality and best-designed telescopes with near-perfect optics.

3) All ground-based telescopes must observe through the terrestrial atmosphere. As we are used to look through the atmosphere at first this may not seem to be a real problem, but it is: Just imagine trying to read time from a wall clock of a swimming pool from underwater – all you see are blurry images. Similarly, images taken even from the highest mountains are blurred by the turbulence of our atmosphere. Although observatories are built at sites that typically have clear skies and relatively calm air layers, the only ways to get truly sharp images is go above the atmosphere (think Hubble Space Telescope) or to build highly complicated adaptive optics systems that correct for the atmospheric turbulence (and even most imperfections of the telescope itself).

The astronomer slang for Adaptive Optics is AO. Although ten years ago astronomical AO systems were still a novelty, nowadays most major telescopes have them. But only the most powerful are capable of providing the image quality needed to hunt for planets.

The most capable systems can correct for changes in the atmosphere and telescope several hundred to a thousand times a second, providing incredibly sharp and stable images.

SPHERE AO system in Grenoble

SPHERE AO system in Grenoble

Perhaps the coolest thing I have seen in Grenoble was perhaps also the least exciting-looking. Tucked in a very large ground-floor laboratory was a room-sized pile of instrument boxes, all connected, and covered with green plastic covers and attached to large tubes and a thick string of cables. The tubes were blowing cold air under the covers to cool what is arguably the most complex adaptive optics system in the world: SPHERE. This highly complex instrument belongs to the next level in adaptive optics design: an Extreme AO system. Extreme AO systems (often called ExAOs) have been in the making for over a decade now with the first experimental one operating at the Palomar 5m telescope (Project 1640). The driver behind ExAO systems is to direct image extrasolar planets: to find them and to study their atmospheres. The European community has been building SPHERE for over 11 years, while the US astronomers have been working on their own ExAO system, the Gemini Planet Imager. Both systems are technological marvels – they are incredibly capable and will soon allow our telescopes to see and study dozens and dozens of new extrasolar planets. Both systems will likely deliver first science early next year and with that a friendly competition will begin for finding new worlds – and will bring us exciting new images and many surprising discoveries.

Saturn’s Super Storm

If you live in the US, you will remember the great February snowstorm of 2010 – which entered history as “Snowmageddon” – that covered the East Coast in thick snow and paralyzed cities and airports. It was one of the largest winter storms in recent history.

Yet, the same year in the outer solar system another storm developed that dwarfed Snowmageddon – in fact, it dwarfed all storms combined on our planet. This much larger, much colder, and arguable much more mysterious storm has developed in the atmosphere of Saturn.

This was not the first such storm on Saturn: roughly every Saturnian year (29.3 Earth years) a dramatic mega-storm develops. These storms have been observed three times by now, always occurring on the northern hemisphere on Saturn during its summer.

Saturn's 2010-2011 Great Storm as seen by Cassini's ISS camera. Once in about every Saturnian year (~30 years) a giant storm system develops which, in a few weeks, engulfs the northern hemisphere.

Saturn’s 2010-2011 Great Storm as seen by Cassini’s ISS camera. Once in about every Saturnian year (~30 years) a giant storm system develops which, in a few weeks, engulfs the northern hemisphere.

Although the mysterious storms have been seen before, what was different this time was that a spacecraft was present in the saturnian system. Cassini got a first row seat to observe the megastore develop, engulf the northern hemisphere and eventually dissolve, after several months.

The 2010-2011 Storm is the first one observed by a spacecraft in the saturnian system.

The 2010-2011 Storm is the first one observed by a spacecraft in the saturnian system.

Cassini‘s amazing images of the gigantic storm have been published before, but the nature of the storm remained unexplained. Now, in a a University of Wisconsin team led by Lawrence Sromovsky presents a detailed analysis of the storm. The group has worked on trying to figure out the composition of the material dredged up by the storm.

To understand this monster storm let me tell you a bit about Saturn itself. Saturn is a very cold world — at least its upper atmosphere which is visible to us. At 1 bar (the same pressure as at sea level on Earth) Saturn’s atmosphere is only 134 K. Saturn has as much mass as 95 Earths would have – and this massive, cold planet rotates fully around every 10.7 hours!

Like the Solar System’s other gas giant, Jupiter, Saturn is mostly made up of hydrogen and helium, the most common elements in the universe. Most of Saturn’s hydrogen is in its molecular form (H_2), concentrated to the upper layers of the atmospheres (down to about 2 million bars!). Below these immense pressures hydrogen is thought to be compressed to its metallic form, in which electrons are stripped from individual hydrogen atoms and can wander freely among the protons, like they would in “regular” metals.

Based on observations of the previous storms decades ago it was suspected that the storms may dredge up gas that is of different composition than the molecular hydrogen that dominates Saturn’s upper atmosphere. However, lacking detailed observations the actual components could not be identified. This time was different: Cassini’s VIMS (Visible and Infrared Mapping Spectrometer) obtained spectra of the storm head and its vicinity. Sromovsky and colleagues compared the spectra of the gas from the storm’s head to the “ambient” spectra to figure out what components does the storm carry with it.

An infrared color composite image of Saturn's Giant Storm obtained by Cassini's VIMS instrument. The instrument also obtained spectra at the locations 1-6, which are used to explore the composition of the material dredge up by the storm. Locations 1 and 2 are in the storm head, while the other points sample Saturn's atmosphere outside the storm. From Sromovsky et al. 2013.

An infrared color composite image of Saturn’s Giant Storm obtained by Cassini’s VIMS instrument. The instrument also obtained spectra at the locations 1-6, which are used to explore the composition of the material dredge up by the storm. Locations 1 and 2 are in the storm head, while the other points sample Saturn’s atmosphere outside the storm. From Sromovsky et al. 2013.

Comparison of the in- and out-of-storm spectra showed a prominent difference at 3 micron: Sromovsky and his team use sophisticated atmospheric models to try to figure out what causes the difference in the spectra. They conclude that this feature must be caused by small particles present in the storm, but not found otherwise in Saturn’s upper atmosphere. The detailed analysis of the spectra suggests that Sromovsky’s team has observed ice particles, made of a mixture of water and ammonia (which gives urine its smell). Water ice has never been seen in Saturn’s atmosphere previously and thought to exist in Saturn at depths of 200 km and below!

So, how large is Saturn’s Super Storm? It has emerged from a depth of at least 200 km and covered at least 7 degrees latitude when it was first seen in the atmosphere. And that 7 degrees at mid-latitude Saturn corresponds to about 1 Earth radius – making this a monster storm compared to Snowmageddon, which only covered part of the US and did not even smell that bad.