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Kepler Mission
Syrinx
post Dec 20 2011, 10:35 PM
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QUOTE
On Dec. 20, 2011, astronomers announced the discovery an alien solar system 950 light-years from Earth that is chock full of planets, including the first two extrasolar worlds ever confirmed to be the size of our own Earth or smaller.


Awesome news.

Kepler began recording scientific data in April 2009 I think? If so, we passed 25 months this past May. We should expect the data for Earth-size planets in Earth-distance orbits to start rolling through the pipeline about now. 25 months of Kepler observation would be the minimum, and 36 months would be the maximum.

I would expect a flood of really exciting announcements this time next year, after the northern hemisphere observation season has ended. It's been a long 2.5 years but we are almost there!
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brellis
post Dec 21 2011, 12:12 AM
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It will take a long time to detect an earth-ish planet inside the several-year orbit of a Jupiter. I hope Kepler stays online long enough to find some good candidates!
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belleraphon1
post Dec 21 2011, 01:46 PM
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Journal publications are here:

Two Earth-sized planets orbiting Kepler-20
http://arxiv.org/ftp/arxiv/papers/1112/1112.4550.pdf


Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
http://arxiv.org/PS_cache/arxiv/pdf/1112/1112.4514v1.pdf

Nutty system....

Craig
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Marz
post Dec 21 2011, 04:21 PM
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QUOTE (belleraphon1 @ Dec 21 2011, 07:46 AM) *
Nutty system....

Craig


Should we treat Kepler-20 as a freakish exception? If so, here's my wild guess at how it formed: flyby/merger with another star that resulted in lots of ejections, some additions, and inward migration of the survivors to stable orbits? I'll leave the math as an exercise to the reader. tongue.gif

The astromers didn't toss this out as an idea, and instead suggested its time to rehash planterary formation models. This makes me think they want to include this black sheep into the family. Come here 20-c, let have a group hug.

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brellis
post Dec 21 2011, 06:05 PM
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In that context, there could be an earth-ish planet in a verrrrrrry long comet-like orbit around its adopted star, that experiences habitable temperatures every 20k yrs or so.
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Greg Hullender
post Dec 21 2011, 06:32 PM
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Very briefly every 20k years. I've always been amazed at the "hang time" long elliptical orbits have. Objects in such orbits essentially spend all their time near apastron. I think the Russians use this for their communications satellites.

--Greg
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mchan
post Dec 22 2011, 04:00 AM
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The Kepler-20 orbits are not that elliptical (e<0.6). Objects in highly elliptical orbits would be even harder to detect with transits near periapsis being very short, and transits for most of the orbit being too long to track unless the period is really short, e.g. an object in an star-grazing Aten asteroid-like orbit.

(The Russian comsat orbit [Molniya after the comsat name] is pretty specialized. The period is 12 hours and the inclination at 63.4 deg is such that the argument of the periapsis is not perturbed by Earth's oblateness. 11 of the 12 hours is over the northern hemisphere, and the ground track and the antenna tracking repeats daily. US also uses this type orbit for data relay to users north of about 70 deg N where GEO satellites would be close to if not below the horizon.)
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brellis
post Dec 26 2011, 06:13 AM
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How many of the 150,000 stars in the Kepler survey are expected to spin edge-on to our perspective and thus potentially have planetary systems that can provide transits that register on Kepler's survey?

What are the chances of a system like Fomalhaut's existing in the survey slice? Do we already know of any stars or planetary systems spinning or orbiting at an angle similar to Fomalhaut's within Kepler's survey area?

I've poked around a bit, can't find answers. Anyone know where to look?
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Astro0
post Dec 26 2011, 07:29 AM
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Google came up with these:

Perhaps not a perfect answer but in the Kepler press kit it says: For a planet in an Earth-size orbit, the chance of it being aligned to produce a transit is less than 1%.

There's a very good spreadsheet and other information on the Planetquest website which gives a complete (as can be) list of exoplanets and their locations. Haven't conducted my own survey but you may be able to check the answer here. (Excel file: 350kb)
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brellis
post Dec 26 2011, 02:06 PM
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Thanks Astro! The PlanetQuest spreadsheet is a great, concise list. Thinking of Fomalhaut b, spotted in two HST pics in its 872-year orbit - if that system were aligned for transit observation, the transit itself might take months or years! blink.gif
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dilo
post Dec 26 2011, 05:43 PM
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QUOTE (Astro0 @ Dec 26 2011, 08:29 AM) *
...For a planet in an Earth-size orbit, the chance of it being aligned to produce a transit is less than 1%

Not difficult to compute: Sun diameter is slightly below 1% of Earth orbit radius, so the tilt angle allowing for transit (observed from an "infinite distance") is almost 0,01 radians; assuming random orbit tilt distribution, transit-observing probability will be this angle divided by 3.14 or 0.3%...

PS: hey, last Brellis post was the 1000th of this thread!


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I always think before posting! - Marco -
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Greg Hullender
post Dec 26 2011, 09:49 PM
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QUOTE (brellis @ Dec 25 2011, 11:13 PM) *
What are the chances of a system like Fomalhaut's existing in the survey slice?

Let's see. Radius of Fomalhaut is about 1.27e+6 km and the semimajor axis of Fomalhaut-b's orbit is about 1.72e+10 km. Taking the ratio and the arctan, I figure the half-angle to be about 74 microradians. Multiply by 2 and divide by pi (not 2 pi) I get a probability of 4.72e-5. Out of 150,000 stars, I'd figure one chance in 7--assuming every star actually had such a planet. Of course we'd have to watch for 1,000 years to witness such a transit.

At 115 from Fomalhaut (twice solar mass) it ought to have sqrt(2/115) Earth's velocity, or about 4 kps. I figure an equatorial transit should last just under four days.

As always, someone should check these figures before planning their own mission. :-)

--Greg
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Vultur
post Dec 26 2011, 11:16 PM
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"First two extrasolar worlds ever confirmed to be the size of our own Earth or smaller?"

What happened to the planets of PSR B1257+12? I think it has one confirmed small planet about 2% of Earth's mass... (Maybe the intent is 'first two extrasolar planets around a main-sequence star ever confirmed to be, etc.'?)
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Explorer1
post Dec 27 2011, 12:06 AM
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Yes, pulsar planets are generally excluded from these sorts of announcements, (and not without reason, too)!
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Greg Hullender
post Dec 27 2011, 04:25 PM
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Planet of PSR B1257+12 D is estimated at 0.0004 of Earth's mass.

http://en.wikipedia.org/wiki/PSR_B1257%2B12_D

That makes it less than 3x the mass of Ceres! I'm amazed they can measure anything that small. Given that, it surprises me that there are only five or six pulsar planets--and four of them are around the same pulsar. Is it just that no one is looking?

--Greg
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