Astronomers have spotted a planet that has survived the massive ballooning of its parent star, providing the first "optimistic" evidence for the long-term survival of Earth.
The parent star, V 391 Pegasi, belongs to a rare class of red giant stars known as B-type subdwarfs that have prematurely expelled their outer shells of hydrogen. At one point, V 391 Pegasi was a star much like our own sun. As it evolved and grew old, its core ran out of hydrogen fuel. The star's core contracted and began burning helium instead, while its outer shell expanded by a factor of about 100.
Scientists think our sun will undergo the same expansion when it runs out of hydrogen fuel in about 5 billion years...
But for reasons that are still unclear, V 391 Pegasi expelled its outer envelope early, before the core even began fusing helium, exposing a compact, dense star that has not yet fully died. Only about 2 percent of stars that reach the red-giant phase are thought to undergo the same catastrophic mass loss that V 391 Pegasi did.
Even more unusual, V 391 Pegasi pulsates, dimming and brightening for several minutes at a time. By making precise observations of the timing of the pulses for seven years, Silvotti's team detected a giant gas planet in the system that was gravitationally tugging the star to and fro as seen from Earth.
Because very few red giants are expected to go through what V 391 Pegasi did, the new discovery will likely not have direct implications for whether Earth will or will not be engulfed by our sun, Silvotti said. It's almost certain that the two planets closest to our sun, Mercury and Venus, eventually will be vaporized, and that Mars will not, Silvotti said. But Earth is in the middle, so we don't know yet…
For sure this discovery will move other people to look for other similar systems, so in a few years we will have much stronger constraints for the models. At that point, it will be possible to do relatively good models for what happens to the planets in general in the red giant phase. So in the end we might know what will happen to Earth.
Kemo D. (a.k.a. no.7) www.beyondgenes.com