# 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.

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”.

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.

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.

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

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.

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.

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 ( http://otherearths.org ).

# Extrasolar Storms Talk Video from HST 25 Symposium

My Extrasolar Storms talk, given at the Hubble 25 Symposium, is now available online – check it out if you like a mix of the Hubble Space Telescope, iron raindrops, gigantic storms, and methods to map extrasolar planets: http://tinyurl.com/pjjbyv4

# 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!

Astrobiology:

Cosmos
Carl 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.

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.

Exoplanets:

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.

Textbooks

Life in The Universe
3rd 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
Jonathan 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!

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.

# 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

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!

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

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.

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.

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.

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.

# Exoplanets in the UA Daily Wildcat

The University of Arizona’s Daily Wildcat has published a nice article by Zane Johnson on our work on rotational mapping of brown dwarfs and exoplanets. It was fun talking to Zane. Good luck with the new science desk at the Wildcat!

# How to Get Your Own Exoplanet?

If you have been reading about exoplanets, you know that they all have boring names, such as GJ 876b, 51 Peg b, or WASP-19b (not to speak about the likes of KOI-762.02). Up to a few days ago the official names of exoplanets had to be the catalog identifier of their host star plus a letter assigned in the order the planet was discovered in the given system. Yes, while most sci-fi writers used exotic names for their planets, astronomers shied away from anything more exciting than GJ 436b. These were the rules – even if you discovered a new planet, you could not give it a proper name!
But this has all changed with a new decision by the International Astronomical Union, the entity that represents astronomers worldwide.

The names of exoplanets are currently a combination of the host star name and a letter in the order the planet was discovered in a given system. The first planets are assigned ‘b’, the second ‘c’, etc.

To understand the changes let me tell you more about the background of naming celestial objects and, in particular, extrasolar planets.

Let’s start with stars. All bright stars on the sky have names, often derived from their Arabic names (such as Altair or Deneb). Nowadays these names
are often used by amateur astronomers, but professional astronomers tend to use a simpler scheme: in each constellation the brightest star is named Alpha, the second brightest is Beta, etc. leading to names like alpha Persei (the brightest star of the constellation Perseus). However, most stars that we study are too faint for this system – there are not enough letters in the Greek alphabet to name the 13,234th brightest star in Orion!. We now simply use an identifier from one of the all-sky catalogs of stars. These names look like HD 172555, which is the 172,555th star in the Henry-Draper Catalog, a list of stars and celestial positions compiled in 1924. Similarly, a name like GJ 436 is the 436th star in the catalog of nearby stars compiled by German astronomers Wilhelm Gliese and Hartmut Jahreiss. Because the catalogs have the coordinates of each star, astronomers do not need to know anymore in which constellation it belongs to.

Sounds simple, right? But as astronomers began to study in detail the stars in the catalogs, many of the apparently single stars turned out to be two stars orbiting around each other (more precisely: they really orbit around the center of mass of the system). Of course, once you spent 15 years cataloging around 200,000 stars and numbered them, you don’t want to renumber all of them just because the third star turned out to be a binary, right?

Instead, astronomers decided to make a logical change to the system: if a star turns out to be a binary star, we keep the catalog number, but call the two stellar components as A and B. Some systems even turned out to have four components, leading to letters A through D.

Then came planets and with their discovery another change was needed. You could envision to add numbers for each planet, but astronomers decided that the simplest solution is to use lower-case letters for the planets: GJ436 b, for example, is the first planet discovered around the 436th star of the Gliese-Jahreiss catalog. Why is not planet “a” the first planet? Astronomers thought that “a” could lead to confusion with the star itself, so the planets start from b.

This system was simple and worked well. But as the number of planets rapidly grew and they became frequent subjects of the news in all media, there was more and more pressure to introduce more interesting names. The interest was so high that many companies decided to sell planet names – just as some companies used to sell land on the moon.
Eventually, the IAU decided to allow the public to propose planet names.

This is a welcome decision: Allowing everyone to propose names for new worlds means sharing the excitement of discovery.

So, how do you name your own planet?

Understandably, the IAU wants to proceed carefully and wants to avoid names that are controversial (xkcd collected an interesting set of possibilities). So, there is a somewhat complex submission and approval process, but the key points are that you need to identify a suitable name and gather enough support. The name should be, of course, not offensive and should not aim to lead to any financial or political advantages. The next step is to convince a large number of people to support the proposal and then submit it to the IAU for approval. The process is overall very similar to that used to name minor planets in the Solar System.

With this opportunity open, we will surely see interesting and original planet names popping up in large numbers!

# The Wildest Clouds in The Universe

Flying on a Delta MD90 jet on my way back from Munich, Germany to Tucson among gorgeous towering clouds glowing in exotic shades of yellow, orange, and purple. Amazing view – especially interesting is the all the different clouds we see are made of water.

How would clouds on exotic other planets look?

Clouds seen from a jet on planet Earth – somewhere about Texas.

Earth is special (in the Solar System, but not in the Galaxy) that it hosts three phases of water simultaneously: liquid, gas, and solid (ice). This allows some fun physics to take place and lead to the hydrological cycle we all know. In the terrestrial atmosphere most water clouds form as the rising moist air cools down and water condensates to condensation nuclei and forms droplets; this process forms the low clouds (~1-2 km). Higher up in the atmosphere, where temperatures are very low, ice crystals will form clouds (>6km).

But we don’t need to go far to find exotic clouds: Earth’s hostile twin, Venus, has a thick carbon dioxide atmosphere (with a crushing surface pressure as high as 900 meters underwater on Earth!). As Venus has lost all of its water in the past, it does not have water clouds – but still has very thick clouds. And these clouds are made of hot droplets of sulphuric acid ($H_2SO_4$)! The cloud layer is so thick that no sunlight reaches the surface directly. The thick yellowish cloud layer has blocked the views of surface from the early space probes.

This Cassini image of Titan shows the formation of clouds close to the south pole as the winter begins. The overall yellow color of Titan is given by a thick organic haze.

Or think about the amazing Titan, Saturn’s large icy moon (larger than planet Mercury!). Titan is the only moon in the Solar System that has a significant atmosphere – in fact its atmospheric pressure is higher than that of Earth. But the surface temperature of Titan is so cold (only ~93 K) that it allows the three phases of methane on its surface. The Cassini orbiter, which keeps on returning amazing high-quality images from the Saturnian system, has photographed the formation and evolution of clouds in Titan’s atmosphere. The clouds of Titan are not well understood and remain an exciting field of research.

These planetary bodies are not exceptions: in fact, every Solar System planet that has an atmosphere has clouds, too. Depending on the temperature and the pressure (often called the “P-T profile”) and the composition of their atmospheres Solar System planets have different clouds. The very thin atmosphere of Mars allows the formation of tenuous water ice and carbon-dioxide clouds; Jupiter and Saturn sport clouds made of ammonia ($NH_3$), ammoniahydrosulfide ($NH4SH$), and water; while the upper atmospheres of the even colder ice giants Uranus and Neptune also have methane ($CH_4$) and $SH_2$ clouds.

This Voyager image from 1989 shows the great dark spot and surrounding whiter clouds on Neptune. Neptune’s upper atmosphere is about 70 K and at these low temperatures most clouds are composed of methane.
Image Source.

This bonanza of clouds raises the question: which are the craziest, most exotic clouds in the universe?
This is a difficult one, of course, as there are many candidates. My favorites are probably the clouds in hot super-Jupiters and brown dwarfs (see post on Substellar zoo). These gaseous planets and brown dwarfs have no solid surfaces but have extremely high pressures in their interiors. In their uppermost atmospheres, the layers visible to us, temperatures can exceed 1,800 K. In this class of objects iron can exist in two phases: in the hotter layer deeper down as gas and in the slightly cooler, lower pressure upper layers it will form droplets. Just as water droplets form massive clouds on Earth that can pour down heavy rain, hot super-Jupiters will have iron clouds that will drive heavy rain of hot molten iron droplets… Gives a whole new perspective on bad weather!

Back on the airplane, somewhere above New Mexico I miss another opportunity to get free pretzels, but still recall the beauty of our simple water clouds.