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NASA's Kepler Spots Its First Rocky Exoplanet
coondoggie writes "NASA today said its star-gazing satellite Kepler has identified its first rocky planet orbiting a sun similar to our own — 560 light years from our solar system. While not in an area of space considered habitable, the rocky planet known as Kepler-10b is never-the-less significant because it showcases the ability of Kepler to find and track such small exoplanetary movements. 'Kepler's ultra-precise photometer measures the tiny decrease in a star's brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star. Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet's surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.'"
Yes. Mostly. For this (transit photometry) method.
There are several methods of finding an extrasolar planet.
Briefly:
1) Pulsar variations: If a planet orbits a pulsar, the pulsar's timing will vary in a manner that can be detected by us, and we can use 3-D trig to figure out relevant parameters such as mass and radial distance.
2) Doppler shift of a star's emission lines: If a planet orbits a solar-type star, we can use the star's doppler shift of certain spectra to determine the various parameters of the body (or bodies) orbiting the star.
3) Gravitational microlensing: If two stars align just right to create a microlensing effect, the star further from us will show up as several images or as an Einstein ring, and its brightness will be amplified. If there's a planet orbiting the star that's closer to us, those mirror images or the ring will change with time, and they will be a bit brighter than without the planet.
4) Astrometry (measurements of the variation of a star's position relative to the "plane of the sky"): If there's a massive planet with an eccentric orbit, the star will orbit a barycenter that's outside of its mass, causing the star to move relative to the background.
5) Direct imaging: with certain techniques for processing stellar imagery, we can detect whether or not there's a planet reflecting some of that star's light to us.
6) Transit photometry: observing the star's brightness decrease as the planet eclipses the star. This works best for planets with a perfect orbital alignment with us, but we can still detect and work out minimum values for the relevant parameters.
7) Radio flux: Certain jovian-type planets can emit radio fluxes that differ significantly from most stars. These fluxes can be difficult, though not impossible, to detect from the interstellar noise.
There are more methods...
The Roche limit is defined as:
d = R ( 2 rhoM/rhom) ^ (1/3).
d is the orbital distance.
R is the primary (star in this case) radius.
rhoM is the primary's density.
rhom is the satellite's density.
If rhom > 2 rhoM, d is inside the radius of the primary.
The star in question is similar to ours, so I'll use our sun's density: 1.4 g/cm^3
The planet's density is 8.8 g/cm^3.
Therefore, the roche limit is within the star's radius and the planet will not be ripped apart.
This presumes a nearly circular orbit, which is good enough for this case.
But its a dry heat.
Have gnu, will travel.