More exoplanets found by TESS

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Worlds without end: In confirming a candidate exoplanet previously discovered by TESS, astronomers have detected two more exoplanets orbiting the same star.

The transits TESS observed belong to GJ 357 b, a planet about 22% larger than Earth. It orbits 11 times closer to its star than Mercury does our Sun. This gives it an equilibrium temperature — calculated without accounting for the additional warming effects of a possible atmosphere — of around 490 degrees Fahrenheit (254 degrees Celsius). “We describe GJ 357 b as a ‘hot Earth,’” explains co-author Enric Pallé, an astrophysicist at the IAC and Luque’s doctoral supervisor. “Although it cannot host life, it is noteworthy as the third-nearest transiting exoplanet known to date and one of the best rocky planets we have for measuring the composition of any atmosphere it may possess.”

But while researchers were looking at ground-based data to confirm the existence of the hot Earth, they uncovered two additional worlds. The farthest-known planet, named GJ 357 d, is especially intriguing. “GJ 357 d is located within the outer edge of its star’s habitable zone, where it receives about the same amount of stellar energy from its star as Mars does from the Sun,” said co-author Diana Kossakowski at the Max Planck Institute for Astronomy in Heidelberg, Germany. “If the planet has a dense atmosphere, which will take future studies to determine, it could trap enough heat to warm the planet and allow liquid water on its surface.”

Without an atmosphere, it has an equilibrium temperature of -64 F (-53 C), which would make the planet seem more glacial than habitable. The planet weighs at least 6.1 times Earth’s mass, and orbits the star every 55.7 days at a range about 20% of Earth’s distance from the Sun. The planet’s size and composition are unknown, but a rocky world with this mass would range from about one to two times Earth’s size.

Even through TESS monitored the star for about a month, Luque’s team predicts any transit would have occurred outside the TESS observing window.

I think the results from TESS are soon going to overwhelm the general press. I myself had to check and make sure this story was about different exoplanets than the previous exoplanet discovery story from two days ago.

What is most interesting about these new exoplanets is their mass and size. TESS appears so far to be finding a lot of superEarths, something that Kepler did not do.



  • mike shupp

    Hmmm… Looking here at NASA’s Exoplanet Survey Archive
    and I see these tables

    Counts by Radius

    R ≤ 1.25 R_Earth 400
    1.25 < R ≤ 2 R_Earth 842
    2 < R ≤ 6 R_Earth 1305
    6 < R ≤ 15 R_Earth 418
    15 R_Earth < R 156

    Counts by Mass

    M ≤ 3 M_Earth 28
    3 < M ≤ 10 M_Earth 122
    10 < M ≤ 30 M_Earth 88
    30 < M ≤ 100 M_Earth 82
    100 < M ≤ 300 M_Earth 196
    300 M_Earth < M 337

    I don't know how you define "superearths" but surely some of these would qualify. This is just for the confirmed planetary candidates in the original Kepler ("K1") mission. Counting both K1 and K2 possibilities, there have been about 2700 planets observed and confirmed, at least to the extent that they were mentioned in published scientific papers. There are another 3000 possible exoplanets in the Kepler data, observed but not yet confirmed. Analysis continues.

    Meanwhile, for the newer satellite …..

    Confirmed Planets Discovered by TESS 24
    TESS Project Candidates 993
    Candidates Yet To Be Confirmed 679

    Lots of contenders which didn't make it last round ("false positives") — about one out of three in the TESS data. What I find interesting is not the number of superearths observed by TESS but the possible planets smaller than Earth; for comparison, none of the Kepler exoplanets were reported as smaller or less massive than Earth.

    Note that these are conservative estimates, based on watching transits of targeted stars by these planets and guesstimating how much light they blocked. I.e., Earth, the star being observed, and the possible planets have to be more or less in a line for this to work. Planets too far from their suns to be noticed in the relatively short period they are under observation (virtually everything beyond Mars in our solar system, I’d gather) won’t be counted. Similarly, planets which orbit in a plane at an angle to the line between Earth and the star may not be observed (we might count these as exoPlutos). And it’s a nice question whether some planet-sized bodies might be concealed within extensive asteroid belts (exoJunos ? superCereses?) Also, there must be a zillion exoplanets the size of Mercury or smaller which simply aren’t big enough to register on our current instruments.

    Plenty of planets yet to be see, in short.

  • Scott M.

    Awesome, in the original sense of the word. When I was a kid we knew of nine planets and that was all. We had one or two fuzzy images of things that might have been accretion discs around other stars, but nothing more.

    It’ll be interesting to see if the statistics shift as our imaging technology improves to the point where we don’t need to rely on transits to detect exoplanets.

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