Astronomers have been in the news recently thanks to the exciting launch on Friday of the Kepler space telescope, which will search for Earth-like planets within our Galaxy. But you’re likely to see astronomy in the news throughout the year, since 2009 has been designated as the International Year of Astronomy by the United Nations. (more…)

Today in a press conference, three UCB astronomers announced the first image of an extrasolar planet. And it’s around Fomalhaut, a star we profiled in this week’s featured article by Danae Schulz, From Dust to Dawn: How Solar Systems Arise. (Well, the Berkeley astronomers tied for first. Another group today announced an image of three stars around HR 8799 in Pegasus.)

This is big news! We know of over 200 extrasolar planets (planets orbiting stars other than our Sun) already, but so far we’ve only detected them indirectly, either by the gravitational tug of the planet on its host star, or by the faint dimming of the host star as the planet crosses between us and it. These are the very first images of planets themselves. They might just look like dots, but they’re EXCITING dots.

The UC Berkeley astronomers who made the announcement are Paul Kalas, James Graham, and Eugene Chiang. They’ve been imaging Fomalhaut (pronounced FOO-mal-oh or FO-mal-hout, depending who you talk to) with the Hubble Space Telescope for a few years now, and the star is known to have a dusty debris disk around it. The inner edge of the ring is very abrupt, a phenomenon astronomers suspected could indicate the presence of a planet. Detecting a planet, however, required overcoming two challenges: how to see the planet in the glare of the central star, and how to tell a dot of light is actually a planet and not a background star.

Astronomers overcome the first obstacle by obscuring the central star with a coronagraph, a small disk that blocks out the star’s light and allows observers to take longer exposures that reveal the star’s surroundings.

The key to the second obstacle, differentiating between planets and background stars, is time. Stars have some velocity in space and move relative to one another. Their motion is slow enough that most stars appear to be fixed in the sky, but nearby stars like Fomalhaut (which is only 25 light years away) will move relative to the more distant background stars. Anything that is in orbit around Fomalhaut will move along with Fomalhaut—anything that isn’t, won’t.

The Berkeley team took an image of Fomalhaut’s dust ring in 2004 and again in 2006, both times with a coronagraph on the Hubble Space Telescope. As expected, most of the dots of light didn’t move in the same direction as Fomalhaut (indicating they’re background objects), but one little dot did. And it even progressed along a circular path centered on the star, just as astronomers would expect an orbiting planet to do. The UCB team thinks that the planet is orbiting at 25 astronomical units from Fomalhaut, and that it’s probably about three times the mass of Jupiter.

There will likely be plenty more direct observations of planets in the future, but this is the first, and it has astronomers pretty excited. Every time observers detect a planet by a new method, they take a great leap in learning about worlds other than our own. And to think, the extrasolar planets field didn’t even exist twenty years ago. It’s a brave new world out here.

Read more:
The UC Berkeley Press Release
The NASA Press Release
The New York Times (good graphic of the planet’s progress over time, and HR 8799)
From Dust to Dawn: How Solar Systems Arise