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Trio of Super-Earths Discovered

Posted by CmdrTaco on from the no-they-don't-have-powers dept.

FiReaNGeL writes "A group of astronomers have now discovered a system of three super-Earths around a rather normal star, which is slightly less massive than our Sun, and is located 42 light-years away towards the southern Doradus and Pictor constellations. 'We have made very precise measurements of the velocity of the star HD 40307 over the last five years, which clearly reveal the presence of three planets.' The planets, having 4.2, 6.7, and 9.4 times the mass of the Earth, orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively. 'The perturbations induced by the planets are really tiny — the mass of the smallest planets is one hundred thousand times smaller than that of the star — and only the high sensitivity of HARPS made it possible to detect them' says co-author François Bouchy, from the Institut d'Astrophysique de Paris, France. Clearly these planets are only the tip of the iceberg."

7 of 178 comments (clear)

  1. Really short periods by Some+guy+named+Chris · · Score: 5, Interesting

    Why is it that most of the planets discovered have extremely short orbital periods compared to our own? Is it because those are the easiest types to detect, or is it because we are a cosmic oddity with our slow orbit around our star?

    Also, I wonder if one were on one of these planetary speedsters, would you be able to tell you were whizzing around your star so fast.

    1. Re:Really short periods by Anti_Climax · · Score: 5, Insightful

      A short orbital period and a higher mass mean a greater possibility we can see the star shifting back and forth as the planet revolves around it. As our instrumentation and measurements get more accurate and precise we should be able to reliably infer the presence of smaller planets with longer orbital periods.

      With how many large planets we're finding, it's pretty likely there are plenty of smaller earth like planets to be found when we gain the ability to do so.

      --
      Even people that believe in pre-destiny look both ways before crossing the street.
    2. Re:Really short periods by Glith · · Score: 5, Informative

      Because our primary method of detecting a planet right now involves looking at its gravitational effect on the star, and planets that have a lot of mass, are near to their star, and go quickly cause the greatest fluctuation in gravitational force.

    3. Re:Really short periods by Anonymous Coward · · Score: 5, Funny

      Whatever you do, don't try to answer this question by typing "really short periods" into Google. Trust me.

    4. Re:Really short periods by shma · · Score: 5, Informative

      As others have mentioned it is a selection bias. Part of this has to do with the detection method. What they do is look at spectral lines from the star to determine how fast it is moving as it 'orbits 'around the center of mass of the star-planet system (this is very close to the center of the star since the star is so massive, so it is more of a wobble than a straight orbit). The closer the planet is to the star, the larger the gravitational force, so the larger the velocity/ doppler shift. So it is easier to find planets with shorter periods. But even if we developed a new technique today that didn't depend on doppler shifts, we would still only find short period planets for the first few years. Why? Because you need to take measurements for at least a full period before you can determine with any accuracy that you're seeing a planet. So planets with 5yr or 10yr periods will not be confirmed right using any new technique, anyways.

      And to add to another point made below, it is possible to have a planet with an orbital period measured in days which we could comfortably live on. A white dwarf star would be cold enough to allow for normal temperatures, even at distances closer than Mercury.

      --
      I came here for a good argument
  2. 42 light-years away? by gmuslera · · Score: 5, Funny

    Space race just found a new meaning for its life, its universe, and everything.

  3. Re:So, time for a REALLY long-baseline telescope? by drerwk · · Score: 5, Informative

    Two problems with your suggestion. 1) Baseline is not the limit of any planet searches. 2) Planet searches are done with optical frequencies.
    You could put a radio telescope on the moon and do VLBI - but not an optical telescope.
    The most difficult part right now of detecting planets using Doppler shift is a fixed frequency standard to compare the stars spectrum against - they are measuring centimeter/second movements of the star. Baseline has nothing to do with the current limits. AFAIK, the only optical interferometer of any note is at Keck - and I don't even know if it has been used yet. See this article: http://optics.org/cws/article/research/33693