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Trio of Super-Earths Discovered
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."
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.
---they can't be very Earth-like. "Super-Mercury" would be more like it.
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One of the ways we detect planets (not sure about the HARPS) is the measurement of the wiggle the parent star makes. The more massive the planet and/or the faster it orbits, the easier it is to detect the wiggle. Basically, the star will move either side to side or back forth from our vantage point (depending on the orientation of the orbit compared to our position), and this slight movement is used to calculate the mass, speed, etc of the orbiting planets. If the planet is orbiting side to side from our veiw point, we measure the speed the star moves side to side. For back and forth, we measure the slight doppler shift in light as it moves towards and away from us. Since closer planets tend to orbit faster, most of the planets we've discovered so far are large, close, fast-moving ones.
Again, this is only one way this is done, and I'm not sure about this particular planet. I can't make heads or tails of the HARPS link in any case.
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> I think it just means its relatively solid, ie: non-gasious, plus they may deem it to be
> in the proper "zone" to become an earth-like planet (not too close, not too far)
With orbital periods of less than three weeks around a sun-like star they are going to be hotter than Mercury: far too hot for life.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
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.
Anything orbiting a star in 4.3 DAYS is extremely close to the star, and could not possibly anything more than a cinder, probably at near rock melting temperatures.
Mercury has an orbital period of 88 days for comparison.
Sig Battery depleted. Reverting to safe mode.
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.
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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