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TESS: Concluding First Year of Observations

If it seemed amazing to me that 50 years had gone by since Apollo 11, it surprises me as well to realize that, on a much shorter scale, the Transiting Exoplanet Survey Satellite (TESS) has been at work for a full year. In a recent news release, NASA is calling this “the most comprehensive planet-hunting expedition ever undertaken,” presumably a nod to the mission’s broad sky coverage as opposed to the sharply confined field of view of the Kepler mission.

Whereas Kepler took a ‘long stare’ at its starfield in Cygnus and Lyra, TESS keeps alternating what it sees, looking at a 24-by-96 degree section of sky for 27 days at a time. Moreover, TESS scientists are homing in on stars much closer to our Solar System. While Kepler was looking along the Orion arm of the galaxy at stars generally between 600 and 3,000 light years out (more distant stars were too faint to observe transit lightcurves), TESS puts the emphasis on stars closer than 300 light years, though with a similar method of looking for transits. The mission will wind up studying 85 percent of the sky, an area 350 times greater than Kepler.

George Ricker, TESS principal investigator at MIT, is thinking the mission he leads has had an outstanding first year:

“The pace and productivity of TESS in its first year of operations has far exceeded our most optimistic hopes for the mission. In addition to finding a diverse set of exoplanets, TESS has discovered a treasure trove of astrophysical phenomena, including thousands of violently variable stellar objects.”

That last bit is a nod to the fact that even as TESS hunts exoplanets, beginning with the southern sky in July of 2018, it also has been on the lookout for supernovae and other deep sky objects within its line of sight. The exoplanet haul in the past year includes 21 planets, with 959 candidates still waiting for confirmation by ground-based telescopes (the candidate list will swell enormously as the voluminous data yet to be analyzed comes into play). Its first year concluded, TESS is now looking at the northern sky. Bear in mind that the sections of sky TESS looks at can overlap — some parts of the sky thus wind up being observed for almost a year.

This is helpful, because an area near the poles in its observational ‘sphere’ will be under constant observation, producing targets for follow-up with the James Webb Space Telescope. The video below is useful for illustrating the TESS sky-coverage technique. Have a look, while pondering the words of Padi Boyd, a TESS project scientist at NASA GSFC:

“Kepler discovered the amazing result that, on average, every star system has a planet or planets around it. TESS takes the next step. If planets are everywhere, let’s find those orbiting bright, nearby stars because they’ll be the ones we can now follow up with existing ground and space-based telescopes, and the next generation of instruments for decades to come.”

Among the early TESS catches:

  • HD 21749c, the first Earth-size planet the mission has found. The world orbits a K-class star with about 70 percent of the mass of the Sun, located 53 light years away in the constellation Reticulum, one of two planets identified in this system;
  • A number of multi-planet systems, like that around L98-59, which includes a planet (L98-59b) between the size of Earth and Mars, the smallest yet found by TESS. Here the host star is an M-dwarf about a third the mass of the Sun, 35 light years away in the constellation Volans;
  • Three exocomets identified in the Beta Pictoris system. A comet’s lightcurve differs significantly from that of a transiting planet because of the extended cometary tail. These discoveries demonstrate the ability of TESS to identify tiny objects around young, bright stars, and should lead to future exocomet detections that can supply information about planet formation;
  • Six supernovae occurring in other galaxies, among them ASASSN-18rn, ASASSN-18tb and ATLAS18tne, found before ground-based surveys could identify them.

Image: Astronomers have found clear observational evidence of exocomets around the bright star Beta Pictoris, located some 65 light-years from Earth. At just 20 million years old, Beta Pictoris is relatively young, meaning it’s still surrounded by a disk of gas and dust known as a protoplanetary disk, seen here in this artist’s concept. Credit: NASA/FUSE/Lynette Cook.

We’re extremely early in the analysis of TESS data, considering that an object must make three transits to be considered an exoplanet candidate, after which a number of additional checks remain to be made before the object is submitted to study by ground-based telescopes. When the dust settles, TESS is expected to land more than 20,000 exoplanets, dozens of them the size of Earth and up to 500 planets less than twice the size of Earth. Of the total haul, scientists anticipate that the observatory will find about 17,000 planets larger than Neptune.

“The team is currently focused on finding the best candidates to confirm by ground-based follow-up,” said Natalia Guerrero, who manages the team in charge of identifying exoplanet candidates at MIT. “But there are many more potential exoplanet candidates in the data yet to be analyzed, so we’re really just seeing the tip of the iceberg here. TESS has only scratched the surface.”


Comments on this entry are closed.

  • Robin Datta July 26, 2019, 15:25

    Planets aplenty, almost a surfeit sans habitation. With “habitability” constrained to our concepts. Such studies help build a framework in which speculation moves towards theorizing. But absent evidence or suggestion of biological life, continued accumulation of data serves to emphasize the rarity of life “as we know it”.

    • Andrew Palfreyman July 27, 2019, 14:21

      Yes indeed. We’ve gone from suspecting that we’re alone, to hoping the multiplicity of discovered exoplanets meant we’re embedded within a universe teeming with life, and now back to appreciating the extraordinary set of constraints it takes for life to emerge. I’m doubtful we’ll find intelligent life within 100 lightyears or more. I suspect the nearest exemplars may be thousands of lightyears distant.

      • Kolyo Dankov August 2, 2019, 4:02

        This is on the positive side of the spectrum. As a Biophysicist I know that We don’t know at all the chances of generating self replicating entities i.e. LIFE and the possibility that this chance is extremely small (something like 10^-16 is still on table). Bright minds in biochemistry are trying to replicate in laboratory experiments that may lead to life on early Earth, did some incredibly complex things, but still the chance of randomly making molecule of RNA to replicate look more like close to zero. I bet that IF the chance of making life is that small or even smaller, than closest intelligent life may be not 1000 light years but a 50 million light years or so. I am sure that life exist somewhere else (and I am pretty sure that some percentage of life maybe 0.001% transform into intelligent civilizations. Universe is that enormous that if Life can happen in theory (and it can, because it is here) than it should definitely exist somewhere in the vastness of space, but problem is where. We are no in Era of overestimating the chances of life – we all believe it should be on Mars, or on Europe, or maybe on Triton. We believe if there is water there should be life, but this may not be the case. If there is no considerable mechanism for panspermia, and there are lot of limitations to this mechanism of life transfer, than we may not see life in our entire galaxy at all. I prefer to be wrong of course, but why not prepare for the chance of rare life, instead of abundant life in the Universe?

        • Bruce D. Mayfield August 4, 2019, 17:58

          One comes across so much wildly optimistic writings about how common abiogenesis must be that it is a refreshing change to read well informed, realistic opinions to the contrary. Think for a least a moment though, what if even “simple” life is too complex to self assemble from scratch? What if the odds of this happening is absolutely zero? I can imagine that most reading this will reject this immediately, reasoning that life here on this planet proves that life can self assemble. This is however just a widely held assumption.

          I point this out because even if abiogenesis turns out to be totally impossible we still could have a universe that is “rife with life” if whatever put life here did so elsewhere as well.

          • Kolyo Dankov August 5, 2019, 9:30

            Not fully out of scope, but I doubt that’s the case. Also if “something” put Life in the Universe, this something or somebody should also emerge somehow – we again face abiogenesis earlier or later in the Universe evolution. I am fully 100% sure abiogenesis took place and have chance to happen greater than Zero!

            Of course the possibility that it happened early in the Universe evolution somewhere else and than the intelligent forms transfer life forms across the entire Universe is possible, but in my view very unlikely.

            These are the only two possible options I don’t see any other – abiogenesis here on Earth, or abiogenesis somewhere else and than the Inteligent life transferred life here 3.8-4 billion years ago. I don’t think panspermia is viable, because we all know now that chances of Interstellar asteroid transfer is very very small, even after Ouamoua appearance it is still rare enough to be able to transfer life in a global scale, but who knows.

            • Bruce D. Mayfield August 5, 2019, 22:40

              I agree completely with your thinking about panspermia being non-viable Kolyo. But you also wrote of “only two possible options” with abiogenesis either here or somewhere else first. But there really is a third option, although in the present people are often ostracized for voicing it. It is that intelligent life is a, to repurpose a phrase, steady-state condition that predates the universe and has always existed. If intelligent life has always existed then there would be no need to find a way for life to have arisen unaided.

  • Ashley Baldwin July 26, 2019, 18:31

    With enough propellant to keep it going for over ten years, just the notorious steering reaction wheels of the satellite bus will determine its operational life time. Hopefully eight years to take it up to 2026 when it can hand on the transit spectroscopy baton to PLATO for atleast the same mission time again.

    So the Northen Hemiphere for a year , then what ? Numerous observation strategies mooted, but I’m hoping for an extension of ( atleast) another year for the same hemisphere in order to more accurately pin down planetary transit ephemerides ( thus allowing for additional non transiting discoveries via transit timing variations ) . Also to discover more longer period and potentially terrestrial exoplanets in overlapping observation fields extending up to two years. Just in time for JWST. To say nothing of all the related ( but just as important ) asteroseismological data obtained in parallel.

  • wdk July 26, 2019, 19:39

    Kind of a review question. It is noted above that Kepler looked at the Orion spiral arm of the Galaxy with a range of objects 600 to 3000 light years away – and TESS has started the examination of the local neighborhood. In retrospect, I wonder why that sequence of exploration occurred. A technological imperative? Once the notion exoplanet transit is grasped, the difficulty would appear (sic) to be a fixed gaze into a celestial quadrant and awaiting for a wavering of light at fixed pixels glued to a corresponding points in deep space.

    Is it that the later survey slews about the local region more and that posed a greater difficulty a decade back? Or other issues?

    • Bruce Daniel Mayfield July 27, 2019, 0:27

      The primary Kepler mission’s field of view was selected so that it could stare at a rich field (156,000 systems!) of stars at a similar distance from our galaxy’s center as our system. Back when this mission was planned there was no proof that planets were common, so it made sense to look first where there were a great number of stars with as many similarities as possible to the one and only normal star then known to possess planets.

      • Bruce Daniel Mayfield July 30, 2019, 8:49

        And as I should have added, to see a visual of how TESS’s sky coverage is working just watch the video clip Paul included in his report.

  • wdk July 27, 2019, 12:46

    Bruce Daniel Mayfield,

    Thank you! That puts things in perspective.

    In addition, you mention:
    “There was no proof that planets were common”.

    Amidst the relative wealth now, it’s easy to forget that element
    of the inquiry back then. From decades earlier I do remember
    the stellar astronomical community being skeptical about existence or
    formation of bodies unable to generate their own heat or light: minimum mass for sustained fusion seemed to match estimates of
    minimum mass for a collapsing aggregate of gas and dust.
    Subsequent expectations seemed very much influenced by the low hanging fruit provided by doppler measurements… Thus, we could
    well assume that planets existed and that they were jovian or more in mass and in regions hotter than Mercury’s…

    The variety of planetary “states” has come to be a big surprise too.

    In terms of something like the Drake equation, the question of what
    is allowed or unallowable and how frequently will continue to be fascinating.


  • Ron Smith July 29, 2019, 13:50

    I am confused about the strategy used by TESS. If it stares at one section of the sky for only 27 days, how is there any chance of it capturing repeated transits about any particular star, considering it take 365 days for our planet, and even Mercury takes 88 days between transits?

    • Bruce D Mayfield July 30, 2019, 0:58

      The vast majority of exoplanets found to date, and especially so by the transit method, are in short period orbits, a great many having “years” that are shorter than 27 of our days. But rest assured that TESS is bound to also find at least a few longer period planets too. This is because there is much overlapping sky coverage with each of the sections it surveys. The polar regions will in turns be getting nearly continuous coverage for about a full (Earth) year. So if the mission lasts ten years stars near Polaris for example will get almost 5 years of coverage!

  • Laintal July 29, 2019, 19:40

    Yes I’m reading about this one now

  • Christopher Phoenix July 30, 2019, 16:36

    …like that around L98-59, which includes a planet (L98-59b) between the size of Earth and Mars, the smallest yet found by TESS.

    I knew it was just a matter of time, but it is very exciting that we have finally detected exoplanets smaller than Earth. I remember when the only exoplanets we could detect around main-sequence stars were those that are both massive and close to their stars, the “hot Jupiters”. Once we could detect terrestrial planets around Sun-like stars, the trend continued—they were all “super-Earths”, larger and more massive than the Earth. Then, as now, our catalog was skewed towards the easiest planets for us to detect.

    With TESS is detecting a wider range of smaller exoplanets, and looking around stars nearer to Earth than the distant stars Kepler examined, I anticipate that we will soon compile a list of the most promising rocky planets within a few hundred light-years. The targets for any future interstellar missions will be picked from that list.

    Once we have that list, we will finally be able to really work out the feasibility of launching interstellar missions at all. All our speculation on interstellar flights to date have had to rely on guesswork to specify what targets we should aim for, and often researchers optimistically picked nearby sun-like stars like Alpha Centauri or Tau Ceti. But it will make a big difference if the nearest potentially habitable exoplanets turn ou to be over a hundred light-years away, rather than as close as Tau Ceti. After all, while we could arguably gain plenty of knowledge from a close look at any star, even if it had no Earth-like planets (or no planets at all), there will be much less motivation to invest in such missions unless there are potentially habitable planets within reach.

  • Kolyo Dankov August 4, 2019, 10:20
    • Bruce D. Mayfield August 4, 2019, 11:34

      GJ 357 d has generated far more press coverage than most exoplanets get, even being covered by Fox and CBS in recent days.

      So what would it be like to stand on the frozen surface of this world? We don’t know its radius, but it’s been estimated at up to twice the size of Earth. Therefore, with a mass of 6.1 earths surface gravity would be 6.1/2^2 = 1.525 g at the least, cuz the radius is probably less than 2 earths. Better work out hard and eat your spinach before landing!

  • Ashley Baldwin August 9, 2019, 13:53

    Great news that given its first successful year TESS, has already been granted a minimum additional two years operations . Money well spent. Will be interesting to see what observation strategy is adopted. Revisit each hemisphere again to improve transit timing accuracy and discover longer period planets or go for something completely different ? Either way there will be three years worth of close by planetary targets for JWST to choose from once launched.

    • Bruce D. Mayfield August 9, 2019, 20:43

      IMHO it would be idiotic not to extend a perfectly working mission such as TESS. It should be utilized to obtain as much data as possible for as long as possible, of course.

      As to your question of how to use the extension, my two cents would be to revisit the hemispheres in hopes of finding longer period planets, so they can catch HZ planets of at least a few K or even G stars.

  • Michael Fidler August 10, 2019, 2:30

    Nautilus: A Revolutionary Space Telescope.



    “An outstanding, multi-disciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize 1,000 transiting exo-earth candidates. The Nautilus concept is based on an array of inflatable spacecraft carrying very large diameter (8.5m), very low-weight, multi-order diffractive optical elements (MODE lenses) as light-collecting elements. The mirrors typical to current space telescopes are replaced by MODE lenses with a 10 times lighter areal density that are 100 times less sensitive to misalignments, enabling light-weight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has a potential to greatly reduce fabrication and launch costs, and mission risks compared to the current space telescope paradigm through replicated components and identical, light-weight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths.”

    This is a good concept and is wise in it’s design because the telescope is becoming the one instrument. The normal set up is for a common telescope with many different instruments, by doing it this way the Nautilus can be made cheaply and have multiple units combined to make it larger and better adapted to it goal.

  • ljk September 26, 2019, 16:31