Exoplanet Discoveries, discussion of the latest finds |
Exoplanet Discoveries, discussion of the latest finds |
Guest_PhilCo126_* |
Apr 21 2009, 11:10 AM
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Guests |
Well-known exoplanet researcher Dr Michel Mayor ( discoverer of Peg 51b with Dr Didier Queloz in 1995 ) today announced the discovery of the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist:
http://www.eso.org/public/outreach/press-r...9/pr-15-09.html |
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Feb 22 2017, 06:16 PM
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Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
-------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
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Feb 22 2017, 06:57 PM
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Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
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Feb 22 2017, 08:06 PM
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
This is quite an interesting and – IMO – surprising discovery for the sheer number of planets packed so tightly together. Six of the planets have orbital periods between 1.51 and 12.35 days. Not surprisingly, there are small-integer ratios galore between orbital periods. In terms of the shortest period, the next four are 8:5, 8:3, 4:1, and 6:1.
In terms of bolometric luminosity, the second, third, and fourth ones get about the same thermal input as Venus, Earth, and Mars. There's no doubt that whatever one considers to be earthlike context in terms of that alone, at least one of these planets has it. And here's one of the interesting consequences: There are about 500 red dwarfs closer than this system. The probability of a transit for a single planet in the "habitable zone" of such stars is about 2.5%, which would mean 12.5 such systems. But if there are multiple planets per system, then the number of planets we can see transiting will be higher than ~12.5, perhaps double that. And that'll increase the bounty when the time comes that we can do serious follow-up science by examining spectra. A decade or so from now, we may have spectra for something like 20-50 sub-Neptune-sized planets in the HZ of red dwarfs. That's a nice future set of results to look forward to. |
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Feb 22 2017, 09:03 PM
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#5
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Not surprisingly, there are small-integer ratios galore between orbital periods. And, if the Jovian system is anything to go by, these resonances will be evolving over time with each planet experiencing different episodes of orbital forcing, eccentricity change and tidal heating. So once the orbital/thermal history of the Galilean moons has been definitively settled the dynamicists will then have this diabolically complex and even more crowded planetary system to chew over. Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits? |
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Feb 22 2017, 09:36 PM
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#6
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits? Maybe. The ecliptic is the plane of Earth's orbit, and 1° would put the Earth almost 4 Sun radii above/below the Sun's disk as seen from afar. But the other planets are all separate players, so perhaps some of them happen to transit as seen from Trappist 1. The farther out you go, the less likely. Also note that close-in planets tend to orbit close to the star's plane of rotation, whereas planets further out tend to orbit in planes that are closer to one another than to the star's rotation. These are the things we've learned from other planetary systems. So if I had to bet, I'd bet that none of the solar system's planets transit as seen from Trappist 1. (A couple of pages of trigonometry could provide the answer.) Roughly speaking, the probability of a planet orbiting a sunlike star at 1.0 AU transiting its star is 0.5%. Red dwarfs are smaller than the Sun but their, e.g., "habitable zone" is much closer in by an even larger factor, so planets orbiting red dwarfs and getting the same radiation as Earth have about a 2.5% probability of transiting. This – along with the intrinsic number of different types of stars – is why, when we get instruments that can detect the spectra of transiting HZ terrestrial planets, we should get a bonanza of red dwarf candidates vs. far fewer that orbit sunlike stars. As seen from another system, the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method. Earth and Saturn are the next runners-up. Detecting Mercury would require the Sun to exhibit very low noise. Mars is a distant sixth. We have yet to have any methods that have much chance of detecting Uranus/Neptune analogs, though with microlensing, it's a longshot. |
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Feb 22 2017, 10:52 PM
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#7
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method. So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles. |
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Feb 23 2017, 05:41 AM
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#8
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles. We don't know a lot about the outer systems of red dwarfs. In a case like this, the outer system may be empty, may have more terrestrial planets, or may have some bigger planets. Generally, red dwarfs have far fewer big planets than do solar-type stars, so it's quite plausible that there simply aren't any Jupiters. There are many unknowns in exoplanet frequency concerning the norms of system architecture. We know quite well what the inner systems look like in terms of planet frequency by type (size and orbital period), but we don't have a lot of firm evidence about the dependencies, i.e.., if there is a planet of type X, how likely is it that the system also has a planet of type Y? In fact, I think it's rather challenging even to describe systematically these sorts of dependencies. It's troublingly verbose even if we use bins and talk about systems with multiple planets (e.g., if we have a Super Earth orbiting between 30 and 45 days and a Neptune orbiting between 60 and 90 days, then what is the probability of each size of planet with a period between 120 and 240 days?). But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex. |
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Feb 23 2017, 05:24 PM
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#9
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Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex. Yeah, we have to be very very careful when we do datamining for correlations. I'm reading Standard Deviations by Gary Smith, and that's one of the big dangers to look out for when attempting to discuss data with many possible combinations. Even random data will have a few correlations if it's sliced and diced enough different ways. Experimental physics gets around this issue by doing calculations and flow development on a small subset of the data, and once a signal is detected, rerunning the analysis across the whole dataset. ObXKCD: https://xkcd.com/882/ -------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
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