Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

  1. Dec 15, 2017 #21
    True, but I think the goal of fully characterizing planets would shift to image the nearby terrestrial planets in the next few decades. The Kepler habitable-zone planets are so far away that imaging their separation angles is impossible to achieve in the next 30 years. Perhaps transmission spectroscopy is possible with next-generation ground-based telescope or JWST, but nothing can be better than directly studying the spectroscopy of the planets. I think in the future even we have the capability of studing those planets, we would not spend much time on them.
     
    Last edited: Dec 15, 2017
  2. Dec 15, 2017 #22

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Sure, spectroscopy of a direct image of a nearby exoplanet is a much better use of ELT time.
     
  3. Dec 18, 2017 #23
    I tried to find the 8 orbital radii, or periods, by searching the Internet, but my skills were inadequate. I am curious about whether the 8 planets have orbital radii that satisfy something related to the Titus-Bode law.
     
  4. Dec 18, 2017 #24

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    The Wikipedia article has at least the periods. You can calculate the radii with Keplers’s law.
     
  5. Dec 19, 2017 #25

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    • The stellar mass is known with 10% uncertainty.
    • It doesn't matter if you are only interested in relative values. The Titus-Bode law doesn't care about absolute values.
    The absolute orbital periods are known with basically zero uncertainty, the relative orbital radii can be derived from that with essentially no uncertainty as well.

    Edit: This was an answer to a post that got deleted.
     
    Last edited: Dec 19, 2017
  6. Dec 19, 2017 #26
    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.

    Regards,
    Buzz
     
  7. 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.
     
  8. 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.
     
  9. Dec 26, 2017 #29

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    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.
     
  10. 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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: New Kepler results (8th planet around Kepler-90)
Loading...