random toons

Friday, September 14, 2007

Planet Survives its Star Becoming a Red Giant


When a star like our own Sun nears the end of its 10 billion year life, it expands up into a red giant, consuming any planets foolish enough to orbit closely. But what happens to the more distant planets?
Astronomers have discovered just such a planet, orbiting a red giant star. Perhaps this gives us hope for the fate of our own planet Earth, when the Sun expands too. Not so fast.

The planet is called V 391 Pegasi b, and before its parent star transformed into the red giant we see today, it orbited at roughly the same distance as the Earth. As the star expanded, its centre of gravity changed, and the planet's orbit spiraled outward, keeping pace with the changing star. Although the star now engulfs a distance comparable between the Sun and the Earth, the planet is now out past the orbit of Mars; takes 3.2 years to complete a full year.
We shouldn't take too much heart in this - this planet is larger than Jupiter, so a smaller planet like the Earth could still be vulnerable. As far as our planets are concerned, we expect Mercury and Venus to disappear in the Sun's envelope, whereas Mars should survive. The fate of the Earth is less clear because its position is really at the limit: it appears more likely that the Earth will not survive the red giant expansion of the sun either, but it is not for sure.

Finding this planet was incredibly laborious work. It took seven years of observations and calculations to confirm its existence. It also marks the first time that a new technique was used to discover planets. Traditionally, astronomers measure the change in a planet's velocity as it's yanked back and forth by the gravity of a large planet using a technique called spectroscopy, where the spectrum of its light shifts. In the case of V391 Pegasus b, the astronomers measured small variations in timing of light coming from the star to determine its velocity.