Kepler Mission |
Kepler Mission |
Sep 24 2005, 04:23 PM
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#1
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Member Group: Members Posts: 147 Joined: 3-July 04 From: Chicago, IL Member No.: 91 |
This NASA Discovery mission is to be launched in June 2008 and will search for Earth-size and smaller planets. Launch was originally scheduled in 2007 but delayed by 8 months due to "funding constraints".
Here's the official web site: http://www.kepler.arc.nasa.gov/ |
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Apr 27 2009, 05:02 PM
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#2
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Member Group: Members Posts: 544 Joined: 17-November 05 From: Oklahoma Member No.: 557 |
As I mentioned earlier, any moon of Tres-2 would have to be within about half a lunar distance of the planet to be stable. Say about 130,000 mile radius (forgive my english units here) for the orbit. My back of the envelop calculations, using Wiki values, showed a hill sphere of about a lunar distance. Over the long haul, only orbits about half the size of a hill sphere are truly stable, even if the orbit is retrograde.
Earth has a hill sphere of about four lunar distances, so the moon could effectively orbit to twice its distance (or four times for a geologically brief period). You could also keep the moon at its current distance, move the earth to half its current distance to the sun (not recommended), and still have a stable earth-moon system. The most massive moon in our solar system is Ganymede. The mass ratio of Tres-2 : Ganymede is about 16,000 : 1. If we put Ganymede in orbit around Tres-2 at 130,000 miles, the center of mass of the system is offset from the center of mass of the planet by 8 miles. At 50 miles/sec orbital speed of the planet about the star, the difference in transit timings at greatest elongation amount to about plus or minus 0.15 seconds from the expected. Over a fifteen minute integration of photometry, you get about a 0.02 per cent lightening or darkening over what you would expect during that interval. The moon, by the way, would preceed or follow the planet by about 40 minutes at greatest elongation. I welcome any efforts to check (and correct) my math here. |
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