NASA’s Planet-Hunter TESS Has Just Been Launched to Check Out the Near Exoplanet Neighborhood


This column was written by my colleague Elizabeth Tasker, now at the Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Sciences (ISAS).  Trained as an astrophysicist, she researches planet and galaxy formation and also writes on space science topics.  Her book, “The Planet Factory,” came out last year.

The TESS exoplanet hunter telescope launched today on a SpaceX Falcon 9 rocket at the Cape Canaveral Air Force Station in Cape Canaveral, Fla. The space telescope will survey almost the entire sky, staring at the brightest and closest stars in an effort to find any planets that might be orbiting them. (AP Photo/John Raoux)

On January 5, 2010, NASA issued  landmark press release : the Kepler Space Telescope had discovered its first five new extra-solar planets.

The previous twenty years had seen the discovery of just over 400 planets beyond the solar system. The majority of these new worlds were Jupiter-mass gas giants, many bunched up against their star on orbits far shorter than that of Mercury. We had learnt that our planetary system was not alone in the Galaxy, but small rocky worlds on temperate orbits might still have been rare.

Based on just six weeks of data, these first discoveries from Kepler were also hot Jupiters; the easiest planets to find due to their large size and swiftly repeating signature as they zipped around the star. But expectations were high that this would be just the beginning.

“We expected Jupiter-size planets in short orbits to be the first planets Kepler could detect,” said Jon Morse, director of the Astrophysics Division at NASA Headquarters at the time the discovery was announced. “It’s only a matter of time before more Kepler observations lead to smaller planets with longer period orbits, coming closer and closer to the discovery of the first Earth analog.”

Morse’s prediction was to prove absolutely right. Now at the end of its life, the Kepler Space Telescope has found 2,343 confirmed planets, 30 of which are smaller than twice the size of the Earth and in the so-called “Habitable Zone”, meaning they receive similar levels of insolation –the amount of solar radiation reaching a given area–to our own planet.

Yet, the question remains: were any of these indeed Earth analogs?

In just a few decades, thanks to Kepler, the Hubble Space Telescope and scores of astronomers at ground-based observatories, we have gone from suspecting the presence of exoplanets to knowing there are more exoplanets than stars in our galaxy. (NASA/Ames Research Station; Jessie Dotson and Wendy Stenzel)

It was a question that Kepler was not equipped to answer. Kepler identifies the presence of a planet by looking for the periodic dip in starlight as a planet passes across the star’s surface. This “transit technique” reveals the planet’s radius and its distance from the star, which provides an estimate of the insolation level but nothing about the planet surface conditions.

To distinguish between surfaces like those of Earth or Venus, a new generation of space telescopes is required.

These are the tasks before NASA’s long-awaited flagship James Webb Space Telescope (JWST) and  WFIRST  (if ultimately funded,)  Europe’s ARIEL mission and potentially what would be the 2030s flagship space telescope LUVOIR, if it is selected by NASA over three competitors. These telescopes will be able to probe exoplanet atmospheres and will have the capacity to measure the faint reflected light of the planets to study, via spectroscopy, their composition, geology and possibly biology.

But there is one big problem. While Kepler has found thousands of exoplanets, very few are suitable targets for these studies.

At the time of Kepler’s launch, we had no idea whether planet formation was common or anything about the distribution of planet sizes. Kepler therefore performed a planet census. By staring continuously at a small patch of the sky, Kepler waited out the time needed to see planets whose orbits took days, months and then years to complete.

From this, we discovered that planet formation takes place around the majority of stars, small planets are common and planets frequently get shoveled inwards onto short orbits close to the star. The cost of focusing on a small patch of sky is that many of the planets Kepler discovered were very distant. This is like staring into a forest; if you try to count 100 trees by looking in just one direction, many will be deep in the wood and far away from you.

Looping animated gif of the unique orbit TESS will fly. At 13.7 days, it is exactly half of the moon’s orbit, which lets the moon stabilize it. During the part of the orbit marked with blue, TESS will observe the sky, collecting science data. During the orange part, when TESS is closest to Earth, it will transmit that data to the ground. (NASA’s Goddard Space Flight Center)”

These distant planets are great for number counting, but they are too far away for their atmosphere or reflected light to be detected. In such cases, even enticing properties such as an orbit within the habitable zone have little meaning as follow-up studies that could probe signs of life are not possible.

Yet the census result that short-period planets were common allows for an entirely new type of mission. A survey to focus only on the bright, close stars whose planets would be near enough to detect their atmospheres with instruments such as the JWST. Prior to Kepler, we did not know such a telescope would find any planets. Now, we can be certain.

And that is why TESS was launched on Wednesday.

Standing for the Transiting Exoplanet Survey Satellite, TESS is a NASA mission to look for planets around bright stars less than 300 light years from Earth. All told, TESS will look at 200,000 stars spread over 85% of the sky in two years. For comparison, the field of view for Kepler had a sky coverage of just 0.25% and looked as deep as 3,000 light years into space.

Such a wide sweep means TESS cannot spend long staring at any one position. TESS will observe most of the sky for about 27 days, which is ample for detecting planets on ten day orbits, the most common orbital period found by Kepler. Over the ecliptic pole (90 degrees from the Sun’s position), TESS will observe somewhere between 27 and 351 days.  This region is where the JWST will be able to study planets throughout the year.

Image showing the planned viewing regions for the Transiting Exoplanet Survey Satellite mission. (Roland Vanderspek, Massachusetts Institute of Technology)

Bright and close by red dwarf stars, and the planets around them, are a prime target for TESS.  These stars are smaller and cooler than our sun, which makes it easier to spot the subtle dip in brightness from smaller planets. The cooler temperatures also mean that planets can orbit much closer to the star without roasting. A ten day orbit is still unlikely to be within the habitable zone, but orbits lasting between 20 – 40 days (which TESS will spot near the ecliptic poles) may receive similar insolation levels to the Earth.

A recent paper submitted to the Astrophysical Journal by Sarah Ballard, an exoplanet astronomer at MIT, estimated that TESS may find as many as 1000 planets orbiting red dwarfs and around 15 of these may be less than twice the size of the Earth and orbit within the habitable zone; ideal candidates for a JWST observation.

Previous predictions for TESS suggested the telescope will find a total (all orbits around all stars) of 500 planets less than twice the size of the Earth and 20,000 exoplanets over the first two years. Ballard’s new numbers for planets around red dwarfs are 1.5 times higher than previous predictions, so these totals look likely to be lower limits.

While future atmospheric studies with JWST are exciting, these observations will still be very challenging. Time on this multi-purpose telescope will also be limited and we have to wait until 2020 for the launch. However, the bright stars targeted by TESS are also perfect for a second type of planet hunting method: the radial velocity technique.

This second-most prolific planet-hunting technique looks for the slight shift in the wavelength of the light as the star wobbles due to the gravitational pull of the planet. As the star moves away from Earth, the light waves stretch and redden. The light shifts towards blue as the star wobbles back our way. The result is a measurement of the planet’s minimum mass. The true mass can be found if the inclination of the orbit is known, which can be measured if the planet is also seen to transit.

With both a transit measurement from TESS and a radial velocity measurement from another ground-based instrument such as HARPS, on Europe’s La Silla Telescope in Chile, the average density of the planet can be calculated.

The transit technique identifies planets by the tiny drop in starlight measured as a planet passes in front of the star.


The radial velocity technique identifies planets via the shift in the wavelength of the light of a star as it wobbles due to the presence of a planet.

The planet density can reveal whether a world is gaseous or rocky or heavy in volatiles such as water. This is a particularly interesting question for the “super Earths” that are one of the most common class of planet found by Kepler, but for which we have no solar system analog. While an average density can only be a crude estimate of the planet interior, it can potentially be measured for a large number of the planets found by TESS and is an extremely useful guide for narrowing down planet formation theories.

But before TESS can find these planets, it first has to get into a rather unusual orbit. From launch on the SpaceX Falcon 9, TESS will boost its orbit using solid rocket motors (ignitable cylinders of solid propellent) until it is able to get a kick from the Moon’s gravity. The need for the lunar push was why the launch window for TESS was a very brief 30 seconds.

After the lunar shove, TESS will enter a highly elliptical orbit around the Earth, circling our planet every 13.7 days. This means TESS will orbit the Earth twice in the time it takes the Moon to orbit once: a situation known as a 2:1 resonance.

Planets that orbit in very close packed systems are often seen to be in similar resonant orbits. For examples, the TRAPPIST-1  worlds are in resonance and within our own solar system, the Jovian moons of Io, Europa and Ganymede orbit Jupiter in a 4:2:1 resonance.

This common occurrence is because resonant orbits are very stable, due to the pull from the gravity of the neighboring planets or moons exactly cancelling out. It is exactly for this reason that such an orbit has been chosen for TESS. With the gravitational tugs from the Moon cancelling out over an orbit, TESS’s path around the Earth will remain stable for decades. This potentially allows the mission to continue far beyond its designated two year lifespan.

TESS will take about 60 days to reach its final orbit and power-on, initialize and test its instruments. Science operations are expected to begin properly 68 days after launch. The first full data release from TESS is planned for next January, but with science operations starting in the summer we may hear the first results from TESS in the second half of this year.

Unlike with Kepler, this will be the data that will let us get to know our neighborhood.


The Very Influential Natalie Batalha

Natalie Batalha, project scientist for the Kepler mission and a leader of NASA’s NExSS initiative on exoplanets, was just selected as one of Time Magazine’s 100 most influential people in the world. (NASA, TIME Magazine.)

I’d like to make a slight detour and talk not about the science of exoplanets and astrobiology, but rather a particular exoplanet scientist who I’ve had the pleasure to work with.

The scientist is Natalie Batalha, who has been lead scientist for NASA’s landmark Kepler Space Telescope mission since soon after it launched in 2009, has serves on numerous top NASA panels and boards, and who is one of the scientists who guides the direction of this Many Worlds column.

Last week, Batalha was named by TIME Magazine as one of the 100 most influential people in the world. This is a subjective (non-scientific) calculation for sure, but it nonetheless seems appropriate to me and to doubtless many others.

Batalha and the Kepler team have identified more than 2500 exoplanets in one small section of the distant sky, with several thousand more candidates awaiting confirmation.  Their work has once and for all nailed the fact that there are billions and billions of exoplanets out there.

“NASA is incredibly proud of Natalie,” said Paul Hertz, astrophysics division director at NASA headquarters, after the Time selection was announced.

“Her leadership on the Kepler mission and the study of exoplanets is helping to shape the quest to discover habitable exoplanets and search for life beyond the solar system. It’s wonderful to see her recognized for the influence she has had on the world – and on the way we see ourselves in the universe.”

And William Borucki, who had the initial idea for the Kepler mission and worked for decades to get it approved and then to manage it, had this to say about Batalha:

“She has made major contributions to the Kepler Mission throughout its development and operation. Natalie’s collaborative leadership style, and expert knowledge of the population of exoplanets in the galaxy, will provide guidance for the development of successor missions that will tell us more about the habitability of the planets orbiting nearby stars.”

Batalha has led the science mission of the Kepler Space Telescope since it launched in 2009. (NASA)

As a sign of the perceived importance of exoplanet research, two of the other TIME influential 100 are discoverers of specific new worlds.  They are Guillem Anglada-Escudé (who led a team that detected a planet orbiting Proxima Centauri) and Michael Gillon (whose team identified the potentially habitable planets around the Trappist-1 system.)

But Batalha, and no doubt the other two scientists, stress that they are part of a team and that the work they do is inherently collaborative. It absolutely requires that many others also do difficult jobs well.

For Batalha, working in that kind of environment is a natural fit with her personality and skills.  Having watched her at work many times, I can attest to her ability to be a strong leader with extremely high standards, while also being a kind of force for calm and inclusiveness.

We worked together quite a bit on the establishing and running of this column, which is part of the NASA Nexus for Exoplanet System Science (NExSS) initiative to encourage interdisciplinary thinking and collaboration in exoplanet science.

It was NASA’s astrobiology senior scientist Mary Voytek who set up the initiative and saw fit to start this column, and it was Batalha (along with several others) who helped guide and focus it in its early days.

I think back to her patience.  I was visiting her at NASA’s Ames Research Center in Silicon Valley and talking shop — meaning stars and planets and atmospheres and the like.  While I had done a lot of science reporting by that time, astronomy was not a strong point (yet.)

So in conversation she made a reference to stars on the Hertzsprung-Russell diagram and I must have had a somewhat blank look to me.  She asked if I was familiar with Hertzsprung-Russell and I had to confess that I was not.

Not missing a beat, she then went into an explanation of what is a basic feature of astronomy, and did it without a hint of impatience.  She just wanted me to know what the diagram was and what it meant, and pushed ahead with good cheer to bring me up to speed — as I’m sure she has done many other times with many people of different levels of exposure to the logic and complexities of her very complex work.

(Incidently, the Hertzsprung-Russell diagram plots each star on a graph measuring the star’s brightness against its temperature or color.)

I mention this because part of Batalha’s influence has to do with her ability to communicate with individuals and audiences from the lay to the most scientifically sophisticated.  Not surprisingly, she is often invited to be a speaker and I recommend catching her at the podium if you can.

By chance — or was it chance? — the three exoplanet scientists selected for the Time 100 were at Yuri Milner’s Breakthrough Discuss session Thursday when the news came out. On the left is Anglada-Escude, Batalha in the middle and Gillon on the right.

Batalha was born in Northern California with absolutely no intention of being a scientist.  Her idea of a scientist, in fact, was a guy in a white lab coat pouring chemicals into a beaker.

As a young woman, she was an undergrad at the University of California at Berkeley and planned on going into business.  But she had always been very good and advanced in math, and so she toyed with other paths.  Then, one day, astronaut Rhea Setton came to her sorority.  Setton had been a member of the same sorority and came to deliver a sorority pin she had taken up with during on a flight on the Space Shuttle.

“That visit changed my path,” Batalha told me.  “When I had that opportunity to see a woman astronaut, to see that working for NASA was a possibility, I decided to switch my major — from business to physics.”

After getting her BA in physics from UC Berkeley, she continued in the field and earned a PhD in astrophysics from  UC Santa Cruz. Batalha started her career as a stellar spectroscopist studying young, sun-like stars. Her studies took her to Brazil, Chile and, in 1995, Italy, where she was present at the scientific conference when the world learned of the first planet orbiting another star like our sun — 51 Pegasi b.

It had quite an impact.  Four years later, after a discussion with Kepler principal investigator Borucki at Ames about challenges that star spots present in distinguishing signals from transiting planets, she was hired to join the Kepler team.  She has been working on the Kepler mission ever since.

Asked how she would like to use her now publicly acknowledged “influence,” she returned to her work on the search for  habitable planets, and potentially life, beyond earth.

“We’ve seen that there’s such a keen public interest and an enormous scientific interest in terms of habitable worlds, and we have to keep that going,” she said. “This is a very hard problem to solve, and we need all hands on deck.”

She said the effort has to be interdisciplinary and international to succeed, and she pointed to the two other time 100 exoplanet hunters selected.  One is from Belgium and the other is working in the United Kingdom, but comes from Spain.

When the nominal Kepler mission formally winds down in September, she says she looks forward to more actively engaging with the exoplanet science Kepler has made possible.

The small planets identified by Kepler as one one year ago that are small and orbit in the region around their star where water can exist as a liquid. NASA Ames/N. Batalha and W. Stenzel

Batalha’s role in the NASA NExSS initiative offers a window into what makes her a leader — she excels at making things happen.

Voytek and Shawn Domogal-Goldman of Goddard founded and oversee the group.  They then chose Batalha two other leaders (Anthony Del Genio of the Goddard Institute for Space Studies and Dawn Gelino of NASA Exoplanet Science Institute ) to be the hands-on leaders of the 18 groups of scientists from a wide variety of American universities.

(Asked why she selected Batalha, Voytek replied, “TIME is recognizing what motivated us to select her as one of the leaders for….NExSS. Her scientific and leadership excellence.”)

This is the official NExSS task:  “Teams will help classify the diversity of worlds being discovered, understand the potential habitability of these worlds, and develop tools and technologies needed in the search for life beyond Earth. Scientists are developing ways to identify habitable environments on these worlds and search for biosignatures, or signs of life.  Central to the work of NExSS is understanding how biology interacts with the atmosphere, surface, oceans, and interior of a planet, and how these interactions are affected by the host star.”

She has encouraged and helped create the kinds of collaborations that these tasks have made essential, but also helped identify upcoming problems and opportunities for exoplanet research and has started working on ways to address them.  For instance, it became clear within the NExSS group and larger community  that many, if not most exoplanet researchers would not be able to effectively apply for time to use the James Webb Space Telescope (JWST) for several years after it launched in late 2018.

To be awarded time on the telescope, researchers have to write detailed descriptions of what they plan to do and how they will do it. But how the giant telescope will operate in space is not entirely know — especially as relates to exoplanets.  So it will be impossible for most researchers to make proposals and win time until JWST is already in space for at least two of its five years of operation.

Led by Batalha, exoplanet scientists are now hashing out a short list of JWST targets that the community as a whole can agree should be the top priorities scientifically and to allow researchers to learn better how JWST works.  As a result, they would be able to propose their own targets for research much more quickly  in those early years of JWST operations.   It’s the kind of community consensus building that Batalha is known for.

She also has an important roles in the NASA Astrophysics Advisory Committee and hopes to use the skills she developed working with Kepler on the upcoming Transiting Exoplanet Survey Satellite (TESS) mission.

Batalha preparing for the Science Walk in San Francisco on Earth Day.

A mother of four (including daughter Natasha, who is on her way to also becoming an accomplished astrophysicist), Batalha is active on Facebook sharing her activities, her often poetic thoughts, and her strong views about scientific and other issues of the day.

She was an active participant, for instance, in the National March for Science in San Francisco, posting photos and impressions along the way.  I think it’s fair to say her presence was noticed with appreciation by others.

And that returns us to what she considers to be some of her greatest potential “influence” — being an accomplished, high ranking and high profile NASA female scientist.

“I don’t have to stand up and say to young women ‘You can do this.’  You can just exist doing your work and you become a role model.  Like Rhea Setton did with me.”

And it is probably no coincidence that four other senior (and demanding) positions on the Kepler mission are filled by women — two of whom were students in classes taught some years ago by Natalie Batalha.




With the Main JWST Mirror Completed, Scientists Focus On How To Best and Most Fairly Use It Once In Space

Engineers conduct a white light inspection on NASA's James Webb Space Telescope in the clean room at NASA's Goddard Space Flight Center, Greenbelt, Maryland. Credits: NASA/Chris Gunn
Engineers conduct a white light inspection on NASA’s James Webb Space Telescope in the clean room at NASA’s Goddard Space Flight Center, Greenbelt, Maryland. (NASA/Chris Gunn)

Recent word that the giant mirror of the James Webb Space Telescope is essentially complete is a cause for celebration, a milestone in the long march toward launching what will be the most powerful astronomical instrument ever.  NASA Administrator Charlie Bolden made the announcement at the Goddard Space Flight Center, with senior project scientist John Mather declaring that “we’re opening up a whole new territory of astronomy.”

Although liftoff isn’t scheduled until two years from now, the mirror’s completion has led to an intensifying of the far less public but also essential task of determining how precisely the JWST will be used.

This is a major issue because the observatory will be far more complicated with many more moving parts for astronomers than the Hubble Space Telescope and other predecessors, and a significant amount of the learning about how to make observations can’t be done until JWST is already in space.

But more pressing still is the fact that “JW” (as it is now commonly called) will fly for a limited time, and as of now cannot be repaired or upgraded once in space because it will be too far away.

So while astronomers and the public have grown accustomed to long-lived observatories like the Hubble and Spitzer space telescopes — which have been revolutionizing astronomy for decades now — JW has a planned mission duration of just five years. Should the instruments continue working after that, the observatory will nonetheless run out of necessary fuel in 10 years.

Especially for exoplanet astronomers who often have to focus on a particular star and planet over a substantial time, this means they need to learn the JWST ropes fast or miss out on a scientific opportunity of a lifetime.

Natalie Batalha, a member of the JWST Science Advisory Committee and project scientist for the Kepler mission, said that the logic of  the traditional proposal cycles and proprietary periods “threatens to stall the release of potentially important technical information keeping data out of the public domain until the five year nominal mission is well underway.”

“Because of the finite lifetime of JWST, we have an urgency here that we didn’t have with Hubble,” she told me.

“The JWST Science Advisory Committee recognized the need to get data into the hands of community scientists as early as possible to take full advantage of this so valuable but limited opportunity.”

WST is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate JWST after launch.
JWST is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), and the development effort is being managed by the NASA Goddard Space Flight Center.  It is scheduled to launch in October, 2018 and be ready to begin observations after a six-month checkout. (ESA)

The issue is doubly important because the four instruments flying on JWST all operate in a variety of modes and at a broad range of wavelengths.  This makes understanding how to use the telescope and calibrate the data especially challenging.

To mitigate these problems, officials at the Space Telescope Science Institute (STScI) in Baltimore, which manages the JWST program, have agreed to set up an Early Release Science (ERS) program that will have no proprietary privileges and that will require researchers to share what they’ve learned with the community.

A limited but still significant 500 hours of JWST observation time will be given out of the Director’s Discretionary Time to the ERS.  Those hours will be split among the main science communities that will use JWST — those studying the very early cosmos, the dynamics of galaxy formation and stars, and the worlds of exoplanets and objects in our solar system.

“It is one of the first programs of its kind,” said Kevin Stevenson, an European Space Agency/Aura astronomer at STScI and the lead author of a recent white paper on transiting exoplanet science that could be done as part of the ERS the program.

It will probably be the first program of its kind, said Kevin Stevenson, an European Space Agency/Aura astronomer at STScI and the lead author of a recent white paper on the program.

ostdoc 2012 -- 2014, Sagan Fellow 2014 -- 2016 Now an ESA Astronomer at STScI
Kevin Stevenson, an ESA astronomer at the Space Telescope Science Institute, has played a leading role with the JWST Early Release Science program.

“As far as I know, an Early Release program like this has never been done before with other telescope programs,” he said.

Without the ERS program, researchers awarded JWST time in year 1 would have a proprietary period of 12 months after receiving their data, and they can use those results for Cycle (year) 2 proposals without anyone else having knowledge of how the telescope behaved for them.

“This creates a very unfair playing field for the rest of the community, which wouldn’t have that first year data until well into the second year — meaning they can make strong proposals only for (year) 3, when the nominal mission is half over.”

Under this Early Release Science program, the researchers have no proprietary rights to data and so must share everything promptly. “The goal is to do what’s good for the community and allow many researchers to have the information they need to make a strong case for JWST time,” Stevenson explained.

One consequence of the Early Release logic is that selected projects will most likely focus on easy to acquire, low-hanging fruit.  The ERS program will intentionally focus on providing essential and representative data for the community rather than aiming for scientific breakthroughs — although who ever knows where important surprises may be hiding.

While the Early Release program is important and novel, it remains quite small compared to standard calls for observing time that will also be in place.

Guaranteed time for researchers — who have often worked for years developing JW instruments– will account for about 1,500 hours during the first year of observing, and 5,500 hours will go to researchers whose proposals are selected by JWST peer review panels.

While these researchers will be under no obligation to share their data for those substantial periods, efforts are underway to encourage sharing of what they learn about the operations of the telescope and instruments in particular because of the relatively short time JWST will operate.

Transit data are rich with information. By measuring the depth of the dip in brightness and knowing the size of the star, scientists can determine the size or radius of the planet. The orbital period of the planet can be determined by measuring the elapsed time between transits. Once the orbital period is known, Kepler's Third Law of Planetary Motion can be applied to determine the average distance of the planet from its stars. Credit: NASA Ames
Transit data are rich with information. By measuring the depth of the dip in brightness and knowing the size of the star, scientists can determine the size or radius of the planet. The orbital period of the planet can be determined by measuring the elapsed time between transits. The JWST instruments will add substantially to this kind of information by allowing for more expanded and precise readings of the atmospheres of transiting planets.  (NASA Ames Research Center)

JWST was conceived and largely designed before the detection of the first exoplanet in 1996 and as a result many of the  observatory’s goals and capabilities lie elsewhere.  Still, some modifications have been made to the original plans, and new insights into how exoplanet researchers can use the telescope and its instruments have led to great excitement and anticipation.

While the Hubble mostly observes in optical wavelengths with some infrared, JWST is primarily an infrared telescope and will be able to detect radiation emitted at much longer wavelengths.

In practical terms for exoplanet exploration, that means the instruments are expected to detect important compounds from methane to ammonia, sulfur dioxide and onward to larger carbon-based molecules, all of which have been challenging to identify so far.  Using the fact that infrared radiation contains and transmits heat energy, the telescope should be able to see through the thick hazes and clouds that surround many exoplanets so its instruments can characterize the atmospheres and planets below based on thermal emissions.

Some researchers are convinced that JWST will be able to directly image some larger exoplanets — meaning that it will be able to collect and read the spectra of the atmospheres whether the planets are transiting or not.

Sasha Hinkley, an astrophysicist and expert in infrared instrumentation at the University of Exeter, said he is convinced JWST direct imaging of exoplanets is feasible and indicated he will  propose an Early Release observation with that in mind (they’re due next August.)  With direct imaging, he said, JWST could not only identify important compounds, but could also quite possibly identify “weather” on exoplanets.

“JW is just so versatile, and has so many bells and whistles,” he said.  “This will allow for breakthrough science, but will also take valuable time to master.  I think the community would really benefit if some of the early learning involved direct imaging.”

Stevenson has a somewhat different perspective.  The white paper he authored was based on a workshop for scientists eager to work with JWST, and the recommendation in the paper was to focus on transits of large and well-defined planets, and most preferably the gas giant planet WASP-62b.

Rendering of gas giant planet, WASP-62b
Rendering of gas giant planet, WASP-62b.  It has been put forward as a good candidate to observe under the JWST Early Release Science program.


But all involved agree that research communities should put forward a small number of proposals with broad community input for the Early Release Science Program.  This is in keeping with the goals of NASA’s Nexus for Exoplanet System Science, or NExSS, a research coordination network established to catalyze interdisciplinary and community collaboration. NExSS recently initiated a working group to draft a small number of ERS proposals to do transiting exoplanet science.

The STScI has also addressed the question of the observatory’s relatively short lifetime by commissioning development of a number of simulators to help guide scientists as they decide which planets and stars to explore, and in which observing modes to do it.  These tools use known exoplanet and host star characteristics, combined with the most current knowledge of how the JWST instruments behave, to help simulate what the observations will look like through the eyes of JWST.

Substantial effort by STScI is being put into the simulators, the main one called the JWST Exposure Time Calculator (Pandeia) and the exoplanet equivalent (PandExo).  Natasha Batalha, a graduate student at the Pennsylvania State University, has led the exoplanet simulator effort out of the Goddard Space Flight Center.

“PandExo will help researchers decide which JWST observing modes are best suited for the science they want to carry out. It will also help them to pin down exactly how many transits they need to observe to attain their desired level of precision, ” she said. “All of this information will be a crucial part of each researcher’s observing proposal.”

This ability is important when proposing observations of large planets but even more so with the smaller ones — the super Earths and sub-Neptunes.  Because those planets will require many more transit measurements, Batalha said it’s crucial to determine how much observing time is needed to get a handle on whether the proposals are feasible.

NASA sent astronauts to fix or upgrade the Hubble Space Station five times since it launched in 1993. As of now, it looks like JWST will be too far away to ever be serviced should something go wrong. This 2009 shows astronauts John Grunsfeld, left, and Andew Feustel working on the HST during the first of five STS-125 spacewalks. (NASA)
NASA sent astronauts to fix or upgrade the Hubble Space Station five times since it launched in 1993. As of now, it looks like JWST will be too far away to ever be serviced should something go wrong. This 2009 shows astronauts John Grunsfeld, left, and Andew Feustel working on the HST during the first of five STS-125 spacewalks. (NASA)

It is because JWST is primarily an infrared telescope that it will be sent to an area about one million miles away, the second Sun-Earth Lagrange Point.  That’s a gravitationally stable location where the observatory’s sunshade will always face the sun, and consequently defect most of the heat energy coming its way. This is essential since the telescope needs temperatures around -370 Fahrenheit to operate properly.

In contrast, the Hubble is in low-Earth orbit, about 375 miles away from home.  The difference in locations explains why the Hubble has been serviced by astronauts five times, while current plans discount the possibility ever having humans fly to JWST to fix or upgrade it.  NASA doesn’t now have the capability to send astronauts there, and if it did the mission would be enormously expensive.

So the astronomy community is left with this reality:  The most powerful and potentially important telescope ever developed will have a relatively short working lifetime, as major space observatories go.  And that’s why planning now for how it will be used during that window of time is so pressing.




Out Of The Darkness

Simulation of the "Dark Ages," a period between 380,000 years and 4 million years after the Big Bang. The universe was made up primarily of hydrogen in a neutral state, which did not easily connect with any other particles. NASA/WMAP
Simulation of the “Dark Ages” of the universe, a period predicted by theorists to have lasted as long as several hundred million years after the Big Bang.  The first hydrogen atoms in the universe had not yet coalesced into stars and galaxies. (NASA/WMAP)

Before there were planets in our solar system, there was a star that would become our sun.  Before there was a sun, there were older stars and exoplanets throughout the galaxies.

Before there were galaxies with stars and exoplanets, there were galaxies with stars and no planets.  Before there were galaxies without planets, there were massive singular stars.

And before that, there was darkness for more than 100 million years after the Big Bang — a cosmos without much, or at times any, light.

So how did the lights get turned on, setting the stage for all that followed?  Scientists have many theories but so far only limited data.

In the coming years, that is likely to change substantially.

First, the James Webb Space Telescope, scheduled to launch in 2018, will be able to look back at distant galaxies and stars that existed in small or limited numbers during the so called Dark Ages.  They gradually became more prevalent and then suddenly (in astronomical terms) became common.  Called the epoch of cosmic “reionization,” this period is an essential turning point in the evolution of the cosmos.

Less well known but also about to begin pioneering work into how and when the lights came on will be an international consortium led by a team at the University of California, Berkeley. Unlike the space-based JWST,  this effort will use an array of radio telescopes under construction in the South African desert.  The currently small array will expand quickly now thanks in large part to a $9.6 million grant recently announced from the National Science Foundation.

Named the Hydrogen Epoch of Reionization Array (HERA), the project will focus especially on the billion-year process that changed the fundamental particle physics of the universe to allow stars, galaxies and their light burst out like spring flowers after a long winter.  But unlike the JWST, which will be able to observe faint and very early individual galaxies and stars, HERA will be exploring the early universe as a near whole.


Before stars and galaxies became common, the universe went through a long period of darkness and semi-darkness, but ended with the Epoch of Reionization. (S.G. Dorgovski & Digital Media Center, Caltech.)
Before stars and galaxies became common, the universe went through a long period of darkness and semi-darkness, but ended with the “Epoch of Reionization.” (S.G. Djorgovski & Digital Media Center, Caltech)

Aaron Parsons, an associate professor at Berkeley and principal investigator of the HERA project, said his team is now ready to grow their proof-of-concept array to a full-fledged observatory with 270 radio telescopes, with science that just might give some solid answers about how the lights came on.

Parsons said they see their effort as a continuation of the earlier pioneering work that identified and mapped the cosmic microwave background radiatio that was produced by another cosmos-changing event some 380,000 years after the Big Bang.

“We have learned a ton about the cosmology of our universe from studies of the cosmic microwave background, but those experiments are observing just the thin shell of light that was emitted from a bunch of protons and electrons that finally combined into neutral hydrogen 380,000 years after the Big Bang,” Parsons said.

“We know from these experiments that the universe started out neutral {at that point}, and we know that it ended ionized, and we are trying to map out how it transitioned between those two.”

Aaron Parsons, associate professor of astronomy at the University of California, Berkeley, and the principal investigator of the HERA prject.
Aaron Parsons, associate professor of astronomy at the University of California, Berkeley, and the principal investigator of the HERA prject.

More specifically, here is what cosmologists and astrophysicists theorize or know happened:

The Big Bang produced a scorching cauldron of  particles that had electrical charge.  That condition ended with the ‘recombination” event that joined protons and neutrons together to form atomic hydrogen, and as a result produced the cosmic microwave background radiation.

What followed was 100 million or more years of abject darkness because the atomic hydrogen was neutral and unable to do much of anything.  Some relatively few stars appeared in those Dark Ages, when enough gas clumped together and set off a star-forming gravitational collapse.

Those stars, and later dwarf galaxies, emitted photons which had the effect of splitting (or ionizing) the hydrogen that surrounded them — creating bubbles of charged hydrogen (and some helium) in a vast ocean of neutral hydrogen.

Much remains unknown about how and when the population of stars and galaxies grew over the ensuing hundreds of millions of years during this epoch of reionization.  But a time came, an estimated one billion years after the Big Bang, when the islands of split hydrogen turned into a universe of split hydrogen. That made widescale star and galaxy formation possible.

Many astronomers study primordial stars and galaxies to learn about this still mysterious process, but the HERA project will analyze instead how those earliest celestial objects changed the nature of intergalactic space.  And that essentially means capturing tiny changes in the vast universe of uncharged hydrogen during and after the Dark Ages, since hydrogen was most of what was present.

As Parsons explained it, the changes within hydrogen atoms they are looking for were weak and occurred only infrequently — perhaps once in 10 million years for a single atom of hydrogen.  “But there’s an awful lot of hydrogen out there, and that allows the weakness to be an advantage.  That means we can see through clouds, can see deep into the hydrogen clouds,” and that allows for observing on a much longer time scale.

The goal of the HERA project is, most broadly, to trace those minute changes in hydrogen from about 100 million years after the Big Bang to one billion years after, when the epoch of reionization culminated with a conclusive turning on of the universe.

An artist rendering of the "bubbles" of ionized atoms theorized to have surrounded the earliest stars. As Parsons explained: "The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today." Illustration from Scientific AmericanAn artist rendering of the "bubbles" of ionized atoms that surrounded the earliest stars. As Parsons explained: "The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today." Illustration from Scientific American
An artist rendering of the “bubbles” of ionized atoms theorized to have surrounded the earliest stars. As Parsons explained: “The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today.” (Illustration from Scientific American)

The HERA array currently has 19 radio telescopes, will grow to 37 soon, and to 270 in 2018.  The team hopes to some day expand to 350 telescopes.  Each is a of radio dish looking fixedly upwards and measuring primordial radiation.  It was originally emitted at a wavelength of 21 centimeters, a  key spectral tracer for the neutral hydrogen atom.  The photons have been been stretched by a factor of 10 or more since it was emitted some 13 billion years ago, making the detections more easily measured.

The signal is nonetheless weak and has been difficult to measure. Previous experiments, such as the UC Berkeley-led Precision Array Probing the Epoch of Reionization (PAPER) in South Africa and the Murchison Widefield Array (MWA) in Australia, have not been sufficiently powerful and sensitive.  But HERA is much more powerful and hopes are high.

The researchers will be looking for the boundaries between those bubbles of ionized hydrogen around early stars — which are invisible to HERA — and the surrounding neutral or atomic hydrogen being measured.  By tuning the receiver to different wavelengths, they can map the bubble boundaries at different distances to follow the the evolution of the bubbles over time.

HERA is being constructed at the Karoo desert site where PAPER was deployed.  Joining the Berkeley team will be scientists from England, South Africa, Italy, MIT, the National Radio Astronomical Observatory, the University of Washington, Arizona State University and others.

HERA was recently granted the status of a precursor telescope for the Square Kilometer Array (SKA), an ambitious project to build a vast collection of radio dishes around Africa and Australia — thereby creating the largest astronomical observatory of all time.  HERA is located close by one of the South African SKA sites.

The HERA present:


The HERA telescope as built so far. (The HERA team)
The HERA telescope as built so far. (The HERA team)

The HERA future:

An artist rendering of the HERA telescope when it has grown to 220 dishes, scheduled to occur in 2018. (The HERA team)
An artist rendering of the HERA telescope when it has grown to 220 dishes, scheduled to occur in 2018. (The HERA team)

“Many Worlds” generally focuses on exoplanet science, so perhaps you’re wondering why you’re reading about the early universe, reionization and a radio telescope that will attempt to unravel its mysteries.  One reason is simply that the subject is most intriguing, but also it speaks to two important aspects of exoplanet science.

The first is cosmic evolution, the many phenomena and processes that have led to a universe that features billions of planets and at least one (and most likely more) that hosts life.

The Dark Ages and epoch of reionization set the stage for a far more active universe, including supernova that explode and in the process produce otherwise absent carbon, oxygen, phosophrus and many of the elements needed for planets and for life are formed.  Clearly, knowing more about how the stars, galaxies and interstellar medium evolved allows for deeper understandings of the history and characteristics of exoplanets.

But there is a technical connection between HERA and exoplanets as well.  The array may well be quite useful in detecting certain important types of exoplanets — those with magnetic fields.

Parsons explained that when a host star emits a strong coronal mass ejection,  the flare often comes into contact with orbiting exoplanets.  Scientists know from studying Jupiter, which has an ionosphere and thus a magnetic field, that when the CME hits that field a radio pulse or burst is registered.

“In principle this could happen with lots of planets,” Parsons said.  “A host star is active, sends out a big flare, it interacts with the magnetic field around a planet, and we could measure it.

“Potentially, we could detect planets this way, but more unique is that we can identify planets with magnetic fields.  It’s not clear what role magnetic fields have in making life possible, but the Earth does have a strong magnetic field that protects us.  That’s probably not an accident, and so it would be very valuable to identify planets with magnetic fields.”

So it’s possible that the effort to understand the epoch of reionization just might help uncover a trove of habitable planets.