Thursday, July 30, 2009

Planets from Hell - Upsilon Andromedae

Until 1995 the idea of finding other planets was pure science fiction. Now astronomers have found more than 100 planets orbiting other stars. Some ten times the size of Jupiter, others with a magnetic field stronger than anything here on earth, and some are so close to their star they are literarily evaporating.
The astronomers were still no closer to answer one of the biggest questions of all, is there another planet like earth. “For me it would be the most exciting discovery of all,” said Geoff Marcy, “because why are we doing this? Why should anybody care if there are planets around other stars? Well ultimately we humans care about the earth and we would like to know if there are other solar systems that harbour earth like planets.The astronomers needed to find another solar system like our own where small rocky planets had a chance of survival. In California a colleague of Geoff Marcy and Paul Butler is planet hunter Deborah Fisher, her driving ambition is to find a solar system like our own. She is convinced that we are on the verge of discovering a planet where humans could survive. “Now we begin a new era I think of finding systems that are much more like our own.” Said Deborah Fisher “And I think that it is the first one hundred planet discoveries that have been made in the last 5 years probably don’t represent the planet discoveries that are going to be made in the next five years.”Fisher monitors her stars from the Lick Observatory just south of San Francisco on Mount Hamilton. Says Fisher “ When I go up and I see the telescope domes the think that always strikes me is that these are monuments to mankind’s curiosity to find out who we are and what is our place in the Universe.” She comes here to look for evidence of multiple planets orbiting a single star. “I always feel very lucky,” says Fisher “to be the first one sometimes to sit down and look at the data and see there is a planet there and have one more piece of the puzzle.” After years of searching her dedication was about to pay off.

One of the stars Fisher had been monitoring was Upsilon Andromedae. As she analyzed the faint starlight, Fisher’s equipment registered that the star was wobbling, but in an unusual way. She calculated that there must be more than one planet out there. But even two planets couldn’t explain the complex motion. The star was moving in a way no one had ever seen before. Deborah Fisher had discovered that the star Upsilon Andromedae was being pulled in different directions by the gravitational force of several planets. For the planet hunters, it was the breakthrough they had all been waiting for. “When we realized that there were three planets in the solar system and not two it was astonishing. My first view was that I was wrong, that I’ve done something wrong and I would look foolish when this news came out and as I became more confident in fact this was the correct description, the correct model for this. It was very profoundly moving.”
But her hopes to find a planetary system like our own had been shattered. There were indeed three planets but they were all gas giants. This planetary system was as hostile as anything the astronomers had seen before. Like 51Peg, Upsilon Andromedae had a close orbiting hot planet but it also had two other gas giants that swung out through wild eccentric orbits. “That has some pretty amazing implications”, said Fisher, “because a planet in an eccentric orbit is going to spend most of the time far away from the star in sort of the cold regions and then it will dive quickly around the star where it’s very hot.”Following Fisher’s discovery other eccentric planetary systems soon followed but there still no chance to finding an earth like planet. When a gas giant swings close to the parent star, its gravity would force any rocky planet out of the system.The astronomers knew that an earth like planet could only survive if the gas giants were like our own in circular orbit hundreds of millions of miles away from their star. It was a quest that would require to watch their favourite stars for years on end.
Console Tutorial #2greg posted in Uncategorized on November 21st, 2005The star Upsilon Andromedae lies roughly 40 light years away in the constellation Andromeda, and it is visible to the naked eye if you know where to look. The star is roughly 2.5 billion years old (about half the age of our Solar System), and is about 30% more massive (and roughly twice as luminous) as the Sun. Because of Upsilon Andromedae’s relative brightness and proximity, and because it is fairly similar to the Sun, it was among the original group of 50-odd stars surveyed for planets by Marcy and Butler with the radial velocity technique. It was also one of the first stars found to be accompanied by an extrasolar planet (see Butler et al. 1997, Three New 51-Peg Type Planets, Astrophysical Journal Letters, 474, 115-118).

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