Astronomers find planet bigger than Earth
SF State scientists help discover planet that is similar to our own
November 15, 2007 9:33 AM
After an 18 year search, a league of planet hunting scientists from SF State and afar discovered a fifth planet in a multi-planetary system much like our own.
The new discovery is the fourth planet away from the star 55 Cancri, making it the 2nd largest planetary system after our solar system. The new planet has a 260-day orbit and is 45 times the mass of the earth. The first planet orbiting 55 Cancri was discovered in 1996, and there are only four other known planetary systems with three or more planets, said astronomy professor Debra Fischer.
“The three things that are interesting is the scale, the planets are in circular orbits – and that’s important because that means there’s almost a constant but seasonal temperature, and the new planet occupies the habitable zone,” said Fischer, who teaches a course on Astrobiology that examines the possibility of extraterrestrial life.
The discovery prompts the possibility that other unidentified planets in the habitable zone may sustain life, Fischer said.
“This planetary system looks like it’s packed with planets, I bet there are some planets between [the new planet and the outermost planet],” Fischer said. “They’re too small to detect, but that gives us the possibility that lots of planets fill the habitable zone, and that gives a lot of chances for biology life.”
The team has a rich history of inviting SF State students to participate in the planet search. Former SF State professor Geoffrey Marcy leads the team, which includes alumni astronomy professors Fischer and Chris McCarthy, as well as graduate student Howard Isaacson.
While the new planet exists in the habitable zone—the distance from the star where liquid water exists without vaporizing away or completely freezing—the planet is mostly made of gas and does not have a surface or liquid water—making it inhabitable, Fischer said.
“To be in the habitable zone is not enough,” she said. “You need to have a rocky surface to have oceans of water, and it’s important for carbon-based life. Since this [new planet] is not likely to have liquid water, it’s not going to be suitable for life as we know it.”
The astronomers find planets by using the Doppler effect to detect the star’s wobble, which is caused by the gravitational pull of the planet. They then measure the change in starlight as the star moves toward and away from earth, Isaacson said.
“If you measure the change of the starlight precisely enough, you can make a good guess how big the planet is that is causing the change,” Isaacson said.
The team uses the technique to detect the planets without actually seeing them.
“The way you see the planets is that you see the star wobbling,” McCarthy said. “We can’t actually see the planet. We only see the wobbles.”
The team usually spends several nights a month at UC’s Lick Observatory on Mount Hamilton in San Jose and the W.M. Keck Observatory on Mauna Kea in Hawaii, Fischer said. The team is scheduled to observe approximately 15 nights in November.
“We’re working during the day to set up the telescope,” said Fischer, who has been a part of the team since 1997 when she began managing the Lick Observatory Program. “Just before the sun sets, we’re pointing our telescope at the first star until the sun comes up, and then we have to quit. Then we sleep in the morning, analyze our data,and get ready for the next night.”
The team sends one or two people to the observatory, said McCarthy, who became involved in the planet search as a master’s student in 1993.
“We share the burden of doing all these runs,” McCarthy said.
While the team discovers new planets, they do not get to officially name them, Fischer said.
“There are [more than 200] planets that have been discovered, and every year we discover more than the year before - it’s very fast paced,” she said. “We talked about of course selling the naming rights for research funds, but we’re too busy finding them.”
After this groundbreaking finding, the planet hunt continues their quest on a tight calendar.
“I was scheduled twice at two different observatories over Thanksgiving,” Fischer said. “Isaacson will be [at Lick Observatory], and I’ll be at Keck observing in Hawaii. Nobody gets a holiday.”
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