Cancer Posted February 3, 2011 Author Report Share Posted February 3, 2011 Re: Exoplanet detection news ... Aaaaand in this morning's paper is a mention of the Kepler-11 system, which was published yesterday in Nature. A more-or-less Sun-like star ("Teff = 5,680 ± 100 K, surface gravity g of log[g (cm s−2)] = 4.3 ± 0.2, metallicity of [Fe/H] = 0.0 ± 0.1 dex, and an projected stellar equatorial rotation of vsini = 0.4 ± 0.5 km s−1. Combining these measurements with stellar evolutionary tracks ... yields estimates of the star’s mass, 0.95 ± 0.10 M⊙, and radius, 1.1 ± 0.1 R⊙, where the subscript ⊙ signifies solar values.") with six planets now known to be orbiting it. (For reference, the Sun has Teff = 5780 K, log g = 4.44 in the same system of units, [Fe/H] = 0 by definition, and an equatorial rotation speed of a hair less than 2.0 km/s.) The planets' masses range from 2.3 to 13.5 times Earth (the outermost planet doesn't have a mass estimate yet); the two innermost ones have densities of 3.1 and 2.3 grams per cc (= metric tons per cubic meter). The others are less than 1. For comparison, Uranus is 14.5 Earth masses; but in our Solar System, only the larger moons of the giant planets have densities in that range, and those have large amounts of ice. These guys can't have ice. Before these planets might have been labeled "super-Earths" but the low densities make them rather different from the terrestrial planets we know. All their orbits are smaller <= 0.462 AU. Only one of them has an orbital size (and period) larger than Mercury's. So they are all pretty close to the star and therefore pretty warm, probably Venus-like surface temperatures in the simplest possible models (there is no direct information about this in the available data). Interesting was another comment in the paper that the Kepler mission has 1200+ candidate planets now. That seems to have been just a press conference, without the hard data I want to find. Quote Link to comment Share on other sites More sharing options...
austenandrews Posted February 3, 2011 Report Share Posted February 3, 2011 Re: Exoplanet detection news Before these planets might have been labeled "super-Earths" but the low densities make them rather different from the terrestrial planets we know. Are there any prominent theories as to what these things might look like up close? Quote Link to comment Share on other sites More sharing options...
Cancer Posted February 3, 2011 Author Report Share Posted February 3, 2011 Re: Exoplanet detection news Not that I've heard. Figure 5 from that Nature paper puts these planets on a graph of radius versus mass with curves for various compositions. Planet b is spang on a curve for something that is 50% water by mass (the rest is a metal/rock core and atmosphere) but the temperature (about 900 K) is much too high to be anything familiar. Probably something gas-giant-ish is the best guess, but we have no good analogs of these guys in our Solar System. Quote Link to comment Share on other sites More sharing options...
megaplayboy Posted February 3, 2011 Report Share Posted February 3, 2011 Re: Exoplanet detection news We probably need to get to about 10,000 detected Earth-size planets in the habitable zones of stars, before a real significant chance of discovering ET life is sufficient to justify fast unmanned sublight probes/explorers sent to everything within 100-200 LY of us. Even then, it may take millenia for us to colonize something outside our own solar system. I guess we could find an uninhabitable planet and cannibalize resources to build a large orbital colony there, though. Quote Link to comment Share on other sites More sharing options...
Cancer Posted February 3, 2011 Author Report Share Posted February 3, 2011 Re: Exoplanet detection news Their press conference said 1235 candidate planets and 54 Habitable Zone candidates. Unfortunately, that's the only numbers available, and those are almost devoid of context. There is the key quoted comment, "Five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars." Quote Link to comment Share on other sites More sharing options...
McCoy Posted February 3, 2011 Report Share Posted February 3, 2011 Re: Exoplanet detection news Their press conference said 1235 candidate planets and 54 Habitable Zone candidates. Unfortunately' date=' that's the only numbers available, and those are almost devoid of context. There is the key quoted comment, "Five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars."[/quote'] To clairify, "near Earth-size" in this context is 10 Earth-masses or less? Quote Link to comment Share on other sites More sharing options...
Escafarc Posted February 4, 2011 Report Share Posted February 4, 2011 Re: Exoplanet detection news To clairify' date=' "near Earth-size" in this context is 10 Earth-masses or less?[/quote'] Well I guess obesity is a growing problem everywhere. Quote Link to comment Share on other sites More sharing options...
Cancer Posted February 4, 2011 Author Report Share Posted February 4, 2011 Re: Exoplanet detection news To clairify' date=' "near Earth-size" in this context is 10 Earth-masses or less?[/quote'] I don't know. Literally the only information here is the sentence I quoted. If I had to guess, "near Earth-size" here refers to planetary diameter. Kepler is an instrument that looks for eclipses made by planets blundering in front of stars, so the thing that comes out of its raw data is an estimate of the duration and depth of eclipses, both of which depend on planetary diameter. But that is a guess on my part. I've been rooting around for other more detailed information and come up empty so far. Quote Link to comment Share on other sites More sharing options...
megaplayboy Posted February 4, 2011 Report Share Posted February 4, 2011 Re: Exoplanet detection news Anyone know how many exo-planets have been detected within, say, 20 to 200 light years? I think that would be the practical range, where an advanced probe moving at 1 to 10% of lightspeed could be sent to probe/explore them. Quote Link to comment Share on other sites More sharing options...
Cancer Posted February 4, 2011 Author Report Share Posted February 4, 2011 Re: Exoplanet detection news My guess is that just about anything with a Greek letter designation or an HD or HIP or GJ number will most likely be within 100 parsecs (326 light-years). There are some on-line tools for playing with published exoplanet data, most notably http://exoplanets.org/table/ . Just applying a parallax filter, only 82 of 427 have parallaxes smaller than 10 milliarcseconds (which is a fancy way of saying: further than 100 parsecs). Most of the early searches focussed on bright stars, which necessarily are nearby ones. Quote Link to comment Share on other sites More sharing options...
Cancer Posted February 15, 2011 Author Report Share Posted February 15, 2011 Re: Exoplanet detection news I missed this when it came out a couple of months ago, but HIP 13044 was found to have a planet as well. This made for some hoopla. HIP 13044 is a metal-poor star, which probably, but not quite certainly, means it is quite old: probably around 10 Gyr or perhaps a bit more. The metallicity value (-2.09, which means its iron content is about 1/120 that of the Sun) isn't quite bulletproof from my point of view but it's almost certainly in the right ball park. If that metallicity is right, it is the lowest known metallicity for a planet-hosting star. The star is vehemently suspected of originating in a galaxy that has since been destroyed and incorporated into our own, so it got announced as "a planet of extragalactic origin". There's clearly lots of those stars that have been annexed into our Galaxy, so IMO the only thing unusual about this is that the evidence for said origin is clear. The star is also a "horizontal branch" star, which means it is between red giant stages. It has been a red giant star before, and will be again. That means any close-in planets that were in the system have been consumed already. There are a few other red giant stars known to have planets, though. The combination of metal-poor, old, and post-main-sequence is extreme in all senses, and more or less takes any hard limits away from where one might think one could find a planet. The only exception to that is ... you won't find a planet in space that used to be inside the star. For stars that used to be red giants, any planets that were within ~1 AU of the star got consumed during the red giant phase. Quote Link to comment Share on other sites More sharing options...
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