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New rocky exoplanet discovered is the closest to Earth

  1. Aug 1, 2015 #1
    Say hello to HD 219134b - a rocky exoplanet recently discovered using HARPS-North instrument on the Italian 3.6-meter Galileo National Telescope in the Canary Islands, who's existence has been confirmed by NASA's Sptizer Space Telescope.

    At a distance of 21 light years, it is the closest confirmed rocky exoplanet we know of. The transiting planet itself cannot be seen by telescopes, but it so happens that it can be seen transiting it's star (lucky us, right?), because the light that reaches us from the star is dimmed around the area where the planet is present, from which the planet's size was deduced (it's mass was worked out using a "radial velocity" method) . It's about 1.6 times as large and 4.5 times as massive as Earth with an orbital period of just 3 days. It's 6 g/cm^3 density classifies it as a rocky planet.

    Experts say that the planet is too close to its parent star (a K type main sequence star) to support life, but it is expected to be an object of considerable scientific interest in the near future.

    Three other planets in the system have also been discovered which are 2.7 times, 9 times, and 62 times as massive as the Earth, with orbital periods of 7 days, 47 days, and 1190 days respectively. The densities of these planet are yet to be determined as they have not been observed to transit till now.

    Any thoughts on this?
  2. jcsd
  3. Aug 1, 2015 #2


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    A pair of planets with a 3 day and 7 day orbital periods? Interesting.
  4. Aug 1, 2015 #3
    I bet summer vacations aren't fun there :rolleyes:
  5. Aug 1, 2015 #4


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    Probably need SPF 1,000,000.
  6. Aug 1, 2015 #5


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    What - That close to the star , if it was a gaseous planet would have been a real surprise.o0)
  7. Aug 1, 2015 #6
    Exactly. Plus it's parent star is less massive than the Sun, so that only means it's closer to the star than it would be if it were orbiting the Sun with the same time period.

    I bet it has a lot of orbital precession at those orbital distances.
  8. Aug 2, 2015 #7
    It is rather misleading. The keywords are "confirmed" and "transiting." There is also some doubt as to whether or not HD 219134b is "rocky." The closest "rocky" exoplanet to Earth is actually Alpha Centauri Bb, at a distance of 4.336 light years, but does not "transit" its star and its existence is still disputed and therefore not "confirmed." There are also several other "confirmed" exoplanets that are much closer than 21 light years, but they are too large to be considered "rocky" and they do not "transit" their parent star.

    Furthermore, the mass and density are calculated based upon the radius of the exoplanet using Weiss & Marcy (2014):

    "Because the solar system planets appear to satisfy a linear relation between density and radius, we choose a linear fit to planet density vs. radius. We find:"

    ρp = 2.43 + 3.39 ( Rp / R ) = 7.854 g/cm3

    "For exoplanets satisfying 1.5 ≤ Rp / R < 4, we calculate an empirical fit to their masses and radii, yielding:"

    Mp / M = 2.69 ( Rp / R )0.93 = 4.165 M

    See also Most 1.6 Earth-Radius Planets are not Rocky.
    Last edited: Aug 2, 2015
  9. Aug 2, 2015 #8
    I actually gathered most of my information from here: http://www.space.com/30112-closest-rocky-alien-planet-found.html

    I know that closer planets have been announced many times, but then again their existence isn't confirmed yet.
  10. Aug 2, 2015 #9
    Space.com got their information from JPL/NASA (NASA's Spitzer Confirms Closest Rocky Exoplanet) and the Spitzer press release (NASA's Spitzer Confirms Closest Rocky Exoplanet). I find that Space.com very accurately reflects the information obtained from JPL/NASA and other sources, and I use them quite often.

    However, when it concerns exoplanets, information can vary considerably depending on the source used. For example, the NASA Exoplanet Archive maintained by Cal Tech has 1,879 confirmed exoplanets as of July 23, 2015. Yet The Extrasolar Planets Encyclopaedia maintained by the EU "Exoplanet TEAM" from Françoise Roques Observatoire de Paris, France has 1,942 confirmed exoplanets as of August 1, 2015, and The Exoplanet Data Explorer maintained by the California Planet Survey consortium has 1,593 confirmed exoplanets.

    JPL/NASA, on the other hand, tends to be all over the place when it concerns their own data. For example, from the JPL/NASA and Spitzer press release I mentioned above:

    [emphasis added]

    Yet, according to their own database the closest known "confirmed" exoplanet is Alpha Centauri Bb at a distance of 4.403 light years (1.35 parsecs). Other astronomers, however, have questioned the existence of Alpha Centauri Bb due to the methodology used (doppler spectroscopy) to determine its presence. If we used only NASA's Exoplanet Archive, then Alpha Centauri Bb is "confirmed" with a radius of 1.13 ± 0.09 R, with a calculated density of 3.831 g/cm3 and a calculated mass of 1.002 M. That would make Alpha Centauri Bb the closest "confirmed," "rocky" exoplanet to Earth according to JPL/NASA. However, it was not detected "transiting" its parent star.

    So the discrepancy is not the fault of Space.com, but rather JPL/NASA publishing conflicting information.

    See also http://www.nature.com/nature/journal/v491/n7423/full/nature11572.html - Nature 491, 207–211 (08 November 2012) doi:10.1038/nature11572 (free reprint [PDF])
    Last edited by a moderator: May 7, 2017
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