Could the Hubble Telescope see planets around other stars?

Under certain circumstances and with the right instruments, yes it could. Planets can be detected by monitoring the frequencies of many spectral lines from the star to a Doppler speed precision of 30 feet per second. Planets could be detected by their reflected light by the Hubble Space telescope, because the optics and 'seeing' conditions on orbit are superior to anything on the ground looking up through the turbulent atmosphere. A Jupiter-sized planet orbiting a star three light years away at the distance of Jupiter from the Sun, will be seen about five arcseconds from the star. Only Hubble's perfect optics and no distortion will allow astronomers to search for faint objects within a few arc seconds from a nearby star.

In 2006, Astronomers using NASA's Hubble Space Telescope have taken the first visible-light snapshot of a planet orbiting another star. The images show the planet, named Fomalhaut b, as a tiny point source of light orbiting the nearby, bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Australis. An immense debris disk about 21.5 billion miles across surrounds the star. Fomalhaut b is orbiting 1.8 billion miles inside the disk's sharp inner edge.

This answer was updated in 2011. See my books: The Astronomy Cafe (1998) and Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011

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