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  1. #1
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    Sep 2020
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    Is TESS finding fewer planet candidates than expected

    Hi,

    I've been watching the TESS mission closely as I did the successful Kepler mission.

    Before TESS launched, I remember reading several articles and published papers that modeled the expected number planet candidates TESS was to find (and the size distribution).

    The numbers were in the 10,000 to 20,000 range with dozens of Earth sized planets and many hundreds less than 2x the diameter of earth. Here is one example from NASA:

    https://exoplanets.nasa.gov/tess/

    "Astronomers predict that TESS will discover dozens of Earth-sized planets and up to 500 planets less than twice the size of Earth. In addition to Earth-sized planets, TESS is expected to find some 20,000 exoplanets in its two-year prime mission. TESS will find upwards of 17,000 planets larger than Neptune."

    However, TESS has completed it's full 2-year initial run and, although the data is still be processed with more candidates to be picked from the data, the tally is much lower at 2,174 as of Sept 1, 2020. This is only about 11% of the expected number.

    What am I missing? Three possibilities:

    1) The bulk of the data analysis not begun or perhaps they have significantly delayed the release of the results. (Even the first year's data, downloaded over a year ago, should have produced close to 10,000 planets)
    2) The expectation of 20,000 exoplanets is from possible extended missions with many more years of orbits?
    3) Or, as I fear, they just didn't find as many as expected in this initial 2 year run. (But I don't see any discussions of the reasons: Technical issues, solar atmospheres too noisy, or simply fewer planets than originally expected out there?)

    Any insights from TESS followers?

    Regards,

    Steven Miller

  2. #2
    Part of the problem could be getting processor time or what in old days would be called grad students to go thru the data. Or by chance TESS wasn't pointing in the right area at the right time to catch anything, or there is nothing there.
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    You can not be afraid of the wind, Enterprise: Broken Bow.
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  3. #3
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    Quote Originally Posted by The Backroad Astronomer View Post
    Part of the problem could be getting processor time or what in old days would be called grad students to go thru the data. Or by chance TESS wasn't pointing in the right area at the right time to catch anything, or there is nothing there.

    Plus TESS was looking candidates for other researchers to verify, PLATO from the ESA will launch in 2024 will be looking exo-earths as well.
    Thanks for responding. It appears you made three points that I'll address based on my best understanding:

    1) Part of the problem could be getting processor time or what in old days would be called grad students to go thru the data

    I don't know the specifics of TESS data processing bandwidth but I doubt this is the issue as they've been planning for years for this mission and data processing wasn't a big issue limiting Kepler result releases when computers were an order of magnitude slower. Also, we're talking about planet candidates, not confirmed planets (TESS has only 67 confirmed) and I know this is where the real work begins, but "candidates" can largely be identified without followup.

    2) Or by chance TESS wasn't pointing in the right area at the right time to catch anything, or there is nothing there.

    If you talk about any one star or a very small set, this is true, you could get unlucky with your sampling statistically speaking, but TESS is looking at 200,000 stars, so the law of averages plays out here. Statistically, it's HIGHLY improbable to flip a coin 200,000 times and have the result be highly biased one way or another (i.e. It will be close to 50% as expected, not only a fraction of the expected value as with the TESS data)


    3) Plus TESS was looking candidates for other researchers to verify, PLATO from the ESA will launch in 2024 will be looking exo-earths as well.

    Yes, and I'm only talking about candidates, the expected number was around 10,000 (I think there were ranges of estimates from as low as about 5,000 to over 20,000 with NASA quoting 20,000). I agree there will be years of follow-up to confirm, but I wasn't talking confirmed planets, just the initial candidates.

    Thanks again for replying,

    Steven

  4. #4
    Plus TESS was looking candidates for other researchers to verify, PLATO from the ESA will launch in 2024 will be looking exo-earths as well.
    From the wilderness into the cosmos.
    You can not be afraid of the wind, Enterprise: Broken Bow.
    https://davidsuniverse.wordpress.com/

  5. #5
    Join Date
    Sep 2020
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    Repost to correct forum: Is TESS finding fewer planet candidates than expected ?

    Hi,

    My apologies, but I think I originally posted this to the wrong forum (Here is a slightly clarified version):

    I've been watching the TESS mission closely as I did the successful Kepler mission.

    Before TESS launched, I remember reading several articles and published papers that modeled the expected number planet candidates TESS was to find (and the size distribution).

    Most or the original estimates I recall reading were in the 10,000 to 20,000 candidates range (there were some more recent modified estimates as low as ~5000) with dozens of Earth sized planets and many hundreds less than 2x the diameter of earth. Here is one statement that is currently posted from NASA:

    https://exoplanets.nasa.gov/tess/

    "Astronomers predict that TESS will discover dozens of Earth-sized planets and up to 500 planets less than twice the size of Earth. In addition to Earth-sized planets, TESS is expected to find some 20,000 exoplanets in its two-year prime mission. TESS will find upwards of 17,000 planets larger than Neptune."

    However, TESS has completed its full 2-year primary mission and, although the data is still be processed with more candidates to be picked from the data, the tally is much lower at 2,174 as of Sept 1, 2020. This is only about 10-20% of the expected number.

    What am I missing? Three possibilities:

    1) The bulk of the data analysis has not begun or perhaps they have significantly delayed the release of the results. (Even the first year's data, downloaded over a year ago, should have produced close to 10,000 candidates)
    2) The expectation of 20,000 exoplanets is from possible extended missions with many more years of orbits (yet NASA was explicit in stating "its two year prime mission).
    3) Or, as I fear, they just didn't find as many as expected in this initial 2 year run. (But I don't see any discussions of the reasons: Technical issues, solar atmospheres too noisy, or simply fewer planets than originally expected out there?)

    Just for clarification, I'm talking planet candidates and I understand it takes years of followup to sort through them and determine which are actual planets.

    Any insights from TESS followers?

    Regards,

    Steven Miller

  6. #6
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    Threads merged and moved.

    Steven Miller,

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  7. #7
    Hey Steven Miller, this paper shows what the astronomers do to verify if an exoplanet is an exoplanet.
    https://arxiv.org/pdf/2010.15905.pdf
    Basically they make sure that some other star is not causing the changing in brightness is not due to a binary star that has not been observed, or instrument error, and check by several techniques of the planets are planets.
    From the wilderness into the cosmos.
    You can not be afraid of the wind, Enterprise: Broken Bow.
    https://davidsuniverse.wordpress.com/

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