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Featured I New Kepler results (8th planet around Kepler-90)

  1. Dec 19, 2017 #26

    Buzz Bloom

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    Hi @mfb:

    Thank you for your posts. I do not know why I was unable to spot the table of astronomical values in the Wikipedia article when I first looked at it. I suppose I can just call it another careless senior moment.

    I created a spreadsheet with the semi-major axis data from the table, and tried to fit it to a Titus-Bode type function, but that failed miserably. There are several possibilities I plan to investigate. These are based on an assumption that two neighboring planets with semi-major axes that are close to each other might be treated like our asteroid belt.

  2. Dec 26, 2017 #27
    Artificial Intelligence, NASA Data Used to Discover Exoplanet | NASA -- not only one for Kepler-90, but also one for Kepler-80. The latter now has 6 known planets, of which 5 are in a resonant chain. That has made it possible to estimate their masses with Transit Timing Variations (TTV"s).

    The names of the planets follow the usual convention for exoplanets: discovery order, and for same-time discovered, distance outward.
    Kepler-80: f, d, e, b, c, g
    Kepler-90: b, c, i, d, e, f, g, h

    I have estimated the prospects for finding the masses of the Kepler-90 planets, something that I have done with the help of a rather naive way of estimating planet masses: a power law between the Earth's size and an average of Uranus's and Neptune's sizes. With those masses, I have estimated the radial velocities that might be observed. It's 0.4 - 0.5 m/s for the innermost three, 0.9 - 1.2 m/s for the next three, and 3 and 25 m/s by using a hydrogen-helium composition for the outer two.

    Likewise, all of Kepler-80's planets except the outermost one should produce an observable radial velocity. Kepler-80's TTV masses give us composition estimates. The second planet is much like Mercury, 60% iron and 40% rock, with more iron if it has a big ocean. The third one can be fit by being entirely rock with 1% or 2% ocean by mass, though if it has an iron core, it will have a much deeper ocean. By comparison, the Earth's ocean is about 0.02% by mass. For the fourth and fifth ones, I find a composition like Uranus and Neptune, rock and water along with H and He.

    [1704.04290] Updated Masses for the TRAPPIST-1 Planets -- most of them likely have super oceans. So rocky planets with deep oceans may be common.
  3. Dec 26, 2017 #28
    I will now estimate the surface temperatures of these planets. I will use the numbers in HEC: Description of Methods used in the Catalog - Planetary Habitability Laboratory @ UPR Arecibo, scaled to 1 AU using the Stefan-Boltzmann law. I find -19 C or 254.15 K.

    As a check, I do the Solar System: Mercury: 408, Venus: 299, Earth: 254, Mars: 206, Ceres: 153, Jupiter: 111, Saturn: 82, Uranus: 58, Neptune: 46, all in K.

    For the Earth, that gives -19 C, which is colder than the actual +15 C. For Venus, that's 26 C, much colder than the actual value of 450 C. Atmospheric greenhouse effects fill in those gaps for both planets.

    For these exoplanets,
    Kepler-80: {1234, 846, 736, 636, 580, 436} K
    Kepler-90: {563, 537, 499, 390, 365, 353, 320, 293} K

    Like many other Kepler planets, most of these planets are very hot.
  4. Dec 26, 2017 #29


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    Well, Kepler is more likely to find planets in close orbits. Kepler-90 has an apparent magnitude of 14, that is not the best candidate for good RV measurements.

    Here is a HARPS measurement of Gliese 581 with an apparent magnitude of 10.5, many times brighter than Kepler-90. The individual measurements have an uncertainty of 2-3 m/s.
  5. Dec 27, 2017 #30
    Both Kepler-90 and Kepler-80 are too faint for radial velocity work. The TTV-derived masses for Kepler-80d, e b and c are based on the work of MacDonald et al (2016). One caveat about TTV-derived mass is that it might be perturbed by an undiscovered planet in the system. Thus, when MacDonald et al was analyzing the dynamics of Kepler-80, they did not include Kepler-80g. As what the discovery article said
    Kepler-80d might turn out to be an ocean world with steam envelop. We don't know. TTV-derived masses are notorious for changing by rather large amounts as new data become available.
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