More images of exoplanet show it orbiting its star

Contributed by
Mar 3, 2011

Although well over 500 planets orbiting other stars are known to exist -- and we know of many, many more awaiting confirmation -- direct images of the planets are very rare. That's because stars are billions of times brighter than planets, and the planets tend to huddle so closely to their stars that their feeble light gets overwhelmed.

But it's possible, and we have several images of such exoplanets. One of them is Beta Pictoris b, a super-Jupiter orbiting the star Beta Pic (as we in the know call it) about as far out as Saturn orbits the Sun. Its existence was confirmed in 2009, but it was also seen in earlier images in 2003 and 2008. The motion of the planet from one side of the star was obvious, and now observations from March 2010 again show it has moved as it orbits the star:

Pretty cool! These infrared images from the Very Large Telescope all have the starlight removed to show the faint planet (the faint rings and other blobs are optical effects and can be ignored). The upper left picture is from 2003; the upper right from 2009, with the planet's position in 2003 labeled; and the bottom is the new image from 2010 with both previous positions marked. The orbit of Saturn (tilted to the same inclination as Beta Pic b) is shown for comparison. You can see the planet moved a wee bit between 2009 and 2010, just as predicted.

Besides helping nail down the planet's orbit, the new observations allow astronomers to find that the mass of the planet is between 7 and 11 times that of Jupiter, and the temperature probably between 1100 and 1700°C (2000 to 3100° F). The star is more massive and hotter than the Sun, which is one reason why the planet can be so hot even that far out. The other is that system is actually very young as well, being only about 12 million years old -- compare that to our solar system, which is 4.6 billion years old! So the planet is still glowing with the leftover heat of its formation. In fact, the temperature measurements are critical, because scientists who study the way planets form predict how hot planets will be at different times in their life ... and this planet is hotter than some computer models predict. Observations like this help theoretical astronomers figure out which models are correct, and which still need work.

But even aside from all that, this image is still pretty amazing. That planet is 630 trillion km (390 trillion miles) from Earth -- that's 630,000,000,000,000 kilometers! And there it is.

Think about that. In 1992 we didn't even know if planets outside our solar system existed. Then we discovered some weird ones, and just three years later the first planet orbiting a sun-like star was found. And now, just 16 years later, we've directly seen more than a half dozen of them!


Image credit: M. Bonnefoy et al., published in Astronomy & Astrophysics, 2011, vol. 528, L15