New planet discovered dangerously close to red giant star HD 102272

Thursday, November 20, 2008

This isn't quite as momentous a discovery as the announcement a few days ago of the first planets to be directly imaged around another star, but it's still interesting for the fact that the Sun itself will eventually be a red giant, and as we find planet after planet around all types of stars we'll be able to see an endless number of situations similar to the way our solar system used to be, and how it might end up. This one is now dangerously close to its host star:

Scientists already know that stars expand as they age and that they eventually may gobble up adjacent planets. In fact, scientists expect our own planet to be swallowed up by the Sun in about a billion years. But what scientists don't yet understand fully is how aging stars influence nearby planets before they are destroyed. The team's newly discovered planet is interesting because it is located closer to a red-giant star than any other known planet.

"When red-giant stars expand, they tend to eat up the nearby planets, " said Wolszczan. "Although the planet we discovered conceivably could be closer to the star without being harmed by it, there appears to be a zone of avoidance around such stars of about 0.6 astronomical units, which is a little more than half of the distance from the Earth to the Sun. It is important to find out why planets don't want to get any closer to stars, so one of our next steps is to try to figure out why this zone of avoidance exists and whether it occurs around all red-giant stars."
The other interesting part is how the habitability zone changes along with the star, which could turn places in our solar system into locations capable of supporting life for a while:
Wolszczan said that he is particularly interested in applying to our own solar system the knowledge he gains about the effects of aging stars on planets orbiting other stars. "Our own Sun one day will become a red giant and it is interesting to think about what will happen to the outer planets of our solar system as the Sun expands," he said. "For example, Europa, one of Jupiter's moons, is covered by ice, but if it were to exist closer to the Sun, it might become a warm ocean world that could possibly support life."
Jupiter has an orbit of 5.2 AU, and with the Sun as a red giant that would be 3.2 AU away from the surface on average which is still much farther away than the much colder Mars is (1.5 AU), but there's also heat generated by tidal flexing/acceleration to account for, and besides I'm sure Dr. Wolszczan knows exactly what he's talking about. All these discoveries are just fantastic.


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