Monday, November 17, 2008

First images of planets

From today's APOD, astronomers have finally imaged planets around other stars. See also this image from September showing the first image of a planet around another star.

Why is this important?

So far, hundreds of planets have been found orbiting other stars. Typically, they are found through detecting the gravitational pull they exert on their star, causing a small wobble in the motion of the star. But all that can be inferred from these discoveries is the existence of the planet, and a rough estimate of its mass.

Capturing light from another planet, and especially capturing a spectrum of that light, allows us to probe the chemical composition of its atmosphere.  Changes in the brightness or color of the planet over time allow us to infer its rotation rate. This will be how life will be discovered on other planets.  The discover article (pdf) shows a nice spectrum of this planet.

These planets were discovered now because they are particularly easy to find.  All the planets are very large (several Jupiter masses) and quite far from their host star.  The innermost planet (labelled d in the image) is at a Neptune's distance from its star.  These planets are thus quite different from the planets of our solar system, and we will need a new theory of planet formation to explain how they got out there.  We're still a long way off from seeing tiny Earth-mass planets orbiting close-in to their sun.

See movies here at the telescope home page to see how the image of the star was removed and then images taken over several years were added together to reduce noise.

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