NASA launches satellite ‘TESS’ in hunt for exoplanets

With the launch of NASA’s TESS satellite due this very day, this is a popular-level account of TESS and exoplanet hunting that I wrote for The Conversation (and which has been re-published by the BBC Focus Magazine). Actually this is my version, prior to their editing.

Previous generations have looked up at the stars in the night sky and wondered whether they are also orbited by planets; our generation is the first to find out the answer. We now know that nearly all stars have planets around them, and as our technology improves we keep finding more. NASA’s newest satellite, TESS (the Transiting Exoplanet Survey Satellite), scheduled for launch on Monday, will extend the hunt for small, rocky planets around nearby, bright stars.

NASA’s TESS planet hunter (artist’s impression)

We want to know how big such planets are, what orbits they are in, and how they formed and evolved. Do they have atmospheres, are they clear or cloudy, and what are they made of? It is conceivable that, over coming decades, we might find a planet that has a size and mass similar to Earth’s. If that planet also lies at the right distance from its star for water to be liquid, and has an atmosphere containing molecules such as free oxygen and has an atmosphere containing molecules such as free oxygen then we could even find biological activity. TESS is a major step towards that long-term goal.

Planets are so faint and tiny compared to their host stars that it is remarkable we can detect them at all, let alone study their atmospheres. TESS exploits the fact that, if the planet’s orbit is edge on to us, then it will “transit” across the face of the star, blocking a small fraction of the star’s light. TESS will monitor 200,000 bright stars in the solar neighbourhood, looking for tiny dips in their brightness that reveal a transiting planet.

During transit, the planet’s disc is surrounded by the thin smear of its atmosphere, back-lit by the bright star. That starlight will be absorbed at some wavelengths by molecules in the planet’s atmosphere, while at other wavelengths it shines straight through. By observing the starlight passing through the planet’s atmosphere and splitting it up into its spectrum, we can deduce what that atmosphere is made of.

The spectrum of starlight passing through a planet’s atmosphere can tell us what the atmosphere is made of. Credit: Christine Daniloff/MIT, Julien de Wit

Such observations are right at the limit of current capabilities, requiring the James Webb Space Telescope (JWST), the $8 billion successor to Hubble scheduled for launch in 2020. With a 6.5-m mirror, collecting much more light than Hubble, and with specially designed instruments, JWST has been built to study exoplanet atmospheres.

With JWST time being so valuable we first need to know which stars have the best transiting exoplanets to study, and that’s why we need TESS. Its predecessor spacecraft, Kepler, surveyed 150,000 stars in a patch of sky near the constellation Cygnus, and found over a thousand planets ranging from gaseous giants like Jupiter to rocky planets as small as Mercury. But Kepler covered only a small patch of sky, containing few bright stars, so most of the stars it looked at are faint, and that makes it hard to study their planets.

In contrast, ground-based surveys for transiting exoplanets have searched wider swathes of the sky looking at brighter stars. The most successful has been the UK-led Wide Angle Search for Planets, of which I am a member. Using an array of camera lenses, the WASP project has spent the last decade monitoring a million stars every clear night looking for transit dips. Nearly two hundred planets have been found, and indeed many of the transiting exoplanets so far chosen as JWST targets come from WASP.

But ground-based transit surveys have one big limitation: they look through Earth’s atmosphere, and that severely limits the data quality. They can detect brightness dips of 1 per cent, which is sufficient to find giant gaseous planets like our own Jupiter and Saturn, but smaller, rocky planets block out far less light. Our Earth would produce a dip of only 0.01 per cent if seen projected against our Sun.

The JWST is currently being readied for launch. Credit: NASA/Chris Gunn

TESS will combine the best of both, observing bright stars over the whole sky, but with the advantage of space-based photometric quality. It should find the small, rocky planets that Kepler proved are abundant, but transiting much brighter stars. That means they can be studied and characterised by JWST.

TESS will observe each region of sky for typically 30 days, meaning that it will be most sensitive to planets with short orbital periods that produce frequent transits. Planets in short-period orbits are close to their star. Therefore most of the planets that TESS finds will be highly irradiated and too hot for liquid water. But if found orbiting red-dwarf stars, which are intrinsically dim, even close-in planets can be in the habitable zone.

The dwarf star TRAPPIST-1 is a thousand times less luminous than our Sun, and is known to host seven short-period planets. TESS will look for such planets around other dwarf stars, and while TESS does so from space, the SPECULOOS survey will be attempting the same from the ground. All such finds will be prime targets for JWST.

Looking further ahead we then want to find rocky planets in the habitable zone of stars like our Sun. They will have longer-period orbits and so will be harder to find. That is the task of the ESA satellite PLATO, currently under development for launch in 2026. The race will then be on to find biomarker molecules in the atmosphere of an Earth-twin exoplanet.

13 thoughts on “NASA launches satellite ‘TESS’ in hunt for exoplanets

  1. Paul Braterman

    Reblogged this on Primate's Progress and commented:
    My own best bet for inteligent life elsewhere would be aroud a red dwarf. More of them, and far longer lifetimes. Our own Sun was nearly half way through its useful lifetime before earth had multicellular organisms.

  2. Rob

    Very interesting, Coel.

    It’s going to be fantastic getting the data that these new scopes will provide. I think it is very likely that in the first half of the current century we’ll know if life exists elsewhere. If we find biological activity on any of the thousands of planets discovered that will be one of mankind’s a BIG question answered.

  3. Phil Tanny

    More compelling evidence that scientists have no clue.

    $8 billion to detect incoming asteroids would have been a rational investment which I would have supported. $8 billion spent on collecting information which will be of no use to us, while we continue racing towards civilization collapse at an ever accelerating rate, is an act of irrational madness.

    1. Coel Post author

      Compared to the $4 or $5 trillion spent on various wars in the last decade or so it’s not that significant on a “civilisation” scale, and many people are interested in the science JWST will do.

  4. Phil Tanny

    The expenditure demonstrates that science culture doesn’t yet understand that all science research everywhere depends upon a single thing, that we avoid using nuclear weapons. If we fail at that one thing, all science research everywhere is a pointless waste of time as whatever is learned will be swept away in the collapse of civilization.

    Thus, if we were to use reason, instead of true believer wishful thinking blind dogmas left over from the past, the most rational action for scientists to take in protecting and advancing the future of science would be to focus like a laser on this single point of failure.

    Once the nukes threat was removed, the next rational step for scientists to take would be to examine and challenge the “more is better” relationship with knowledge which created nuclear weapons, and which will continue to generate threats of that scale unless that paradigm is edited to something more in line with the reality of the 21st century. It’s the simplest thing, a “more is better” relationship with knowledge is no more rational than a “more is better” relationship with food, or anything else.

    Here’s what scientists can do to address the nuke threat. Go out on strike. A series of escalating strikes by scientists can convey to the public who funds them that scientists are actually rational creatures as claimed, and that they will decline to give us more powers until such time as we demonstrate that we can responsibly manage the powers they’ve already given us.

    Let’s spend the $8 billion dollars on helping scientists feed their families while they are out on strike.

    So, here we see the welcome end of all the excuses the science clergy offers regarding how they can’t possibly do anything about the nuclear weapons which they themselves created.

    Once all of the above is accomplished, once civilization is made secure, once the future of science is safeguarded, then by all means, that would be a good time to learn more about exo-planets.

  5. Phil Tanny

    A more limited version of a global scientist strike would be for scientists to refuse to do the kind of optional but popular research represented by the TESS satellite. This would allow scientists to make a strong statement regarding the dangers of an out of control knowledge explosion without negatively affecting the public in any meaningful way. Limited strikes of this nature would likely be more productive as a first step than strikes which interrupted services which are desperately desired by the public, such as cancer research as example.

    This is a way in which the TESS satellite project and exo-planet research could be put to immediate use in addressing important human needs on this planet. Such optional projects could be delayed in such a public manner as to convey information which is far more important than what kind of atmosphere is on some planet we have no prospect of visiting any time soon.

    Such limited science strikes would be in compliance with the “more is better” relationship with knowledge which science culture is built upon. They would just represent a more intelligent understanding of “more is better” knowledge than the current TESS project, which is limited to developing only useless knowledge.

    1. Coel Post author

      A more limited version of a global scientist strike would be for scientists to refuse to do the kind of optional but popular research represented by the TESS satellite.

      Few people would care, especially not the politicians. As it is, scientists have to do a lot of lobbying to get funding for this sort of mission. Politicians would readily spend the money on all the other things they get asked to spend money on. Refusing to participate in exoplanet science would be just about the least effective way of protesting about nuclear weapons that one could imagine.

  6. Phil

    Not a lot of people would care about scientists declining to work on TESS, that’s true. That’s why I suggested it as a place to start, as it would make some news and open the conversation, without immediately alienating the public.

    As more projects closer to the average person’s interest were included in the strike over time more and more people would begin to care, which is all that’s needed to interest the politicians. The pressure would be gradually racketed up over time until it started to sink in that intellectual elites in general, and scientists in particular, were not going to give the public more and more and more power until such time as the public demonstrated it could successfully manage the power which has already been delivered.

    This is extremely simple common sense logic which the average man in the street routinely uses with their teenage children. So if they try just a little bit harder, even scientists should be able to grasp it.

    1. Coel Post author

      That’s why I suggested it as a place to start, as it would make some news and open the conversation, without immediately alienating the public.

      And of course no-one has ever discussed nuclear weapons before. Where have you been? Few topics have been discussed more than nuclear weapons since their invention.

      This is extremely simple common sense logic which the average man in the street routinely uses with their teenage children. So if they try just a little bit harder, even scientists should be able to grasp it.

      Ah yes, the nasty sneering that is your usual style.

  7. Phil

    As demonstrated by Coel’s responses, and in fairness the reaction of most people, a suggestion that scientists elect to strike rather than work on TESS will often be perceived as an attack on science. Let’s go ahead and debunk this misperception by use of an example.

    Imagine that I have a “more is better” relationship with food and that this philosophy is now endangering my life. I’ve gotten so fat that I could drop dead from a heart attack at any moment.

    You wouldn’t be attacking me if you made the suggestion that I edit my “more is better” relationship with food to another perspective which is more healthy and rational. In my addiction I might perceive it as an attack, that’s true. But it would not be an attack, but rather a well intended attempt to save my life.

    You can’t suggest “less is better” as an alternative because that too is just another simplistic formula which would endanger me. So what you would have to do is help me arrive at a more sophisticated and intelligent relationship with food than either of these simplistic formulas.

    There’s a good chance I would resist your efforts to help me develop a more intelligent relationship with food, because simplistic formulas are easy, they require no thinking. And after all I would say, I’ve been “more is better” eating for years, and here I still am, so what’s the problem? That is, there’s a good chance I would wait until the day AFTER the heart attack before I began to understand what you’re suggesting.

    But of course by then, I just might very well be dead, which would end any opportunity for me to correct my course. This is exactly the outcome you were trying to help me avoid, but because I insisted on being a stubborn mule headed true believer dolt clinging desperately to formulas of the past, I didn’t hear you, and had to pay the price for not hearing.

    Oh well, game over, no more tasty meals for me.


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