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Planet Gliese 876

Quote:
Smallest extrasolar planet found
The planet was discovered using the "wobble" technique

Astronomers have detected the smallest extrasolar planet yet: a world about seven and a half times as massive as Earth, orbiting a star much like ours.

All of the 150 or so exoplanets found orbiting normal stars are larger than Uranus, itself 15 times Earth's mass.

The new find may be the first rocky world found around a star like our Sun.

The newly discovered "super-Earth" orbits the star Gliese 876, located 15 light-years away in the direction of the constellation Aquarius.

Over 2,000 years ago, the Greek philosophers Aristotle and Epicurus argued about whether there were other Earth-like planets
Geoffrey Marcy, UC Berkeley
This star also has two larger, Jupiter-size planets orbiting it.

The new planet whips around the star in a mere two days, and is so close to the star's surface that its temperature probably tops 200-400C 400-750F) - oven-like temperatures, far too hot for life as we know it.

The planet was discovered using the familiar "wobble technique": the planet's gravitational tug on its parent star produces changes in the star's velocity. This can be picked up in the light spectrum emitted by the star.

The nature of that signal can reveal details such as the mass and orbital period of the planet.

"We keep pushing the limits of what we can detect, and we're getting closer and closer to finding Earths," said team member Steven Vogt, professor of astronomy and astrophysics at the University of California, Santa Cruz.

Indirect evidence

The researchers have measured a minimum mass for the planet of 5.9 Earth masses. It orbits Gliese 876 with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 3.2 million km (2 million miles).

Though the team has no direct proof the planet is rocky, its low mass precludes it from holding on to gas in the way that Jupiter does.

Three other supposed rocky planets have been reported, but they orbit a pulsar, the corpse of an exploded star.

"This planet answers an ancient question," said team leader Geoffrey Marcy, professor of astronomy at the University of California, Berkeley.

"Over 2,000 years ago, the Greek philosophers Aristotle and Epicurus argued about whether there were other Earth-like planets. Now, for the first time, we have evidence for a rocky planet around a normal star."

Professor Marcy, Dr Vogt, Dr Paul Butler of the Carnegie Institution of Washington, and other team members carried out the study at the Keck Observatory in Hawaii.

They have submitted a scientific paper to the Astrophysical Journal.

AND some more news on it....

Quote:
A planet that may be Earth-like — but too hot for life as we know it — has been discovered orbiting a nearby star.

The discovery of the planet, with an estimated radius about twice that of Earth, was announced Monday at the National Science Foundation.

“This is the smallest extrasolar planet yet detected and the first of a new class of rocky terrestrial planets,” Paul Butler of the Carnegie Institution in Washington said in a statement. “It’s like Earth’s bigger cousin.”

Geoffrey Marcy, professor of astronomy at the University of California, Berkeley, added: “Over 2,000 years ago, the Greek philosophers Aristotle and Epicurus argued about whether there were other Earth-like planets. Now, for the first time, we have evidence for a rocky planet around a normal star.”

Though the researchers have no direct proof that the new planet is rocky, its mass means it is not a giant gas planet like Jupiter, they said. They estimated the planet’s mass as 5.9 to 7.5 times that of Earth.

It is orbiting a star called Gliese 876, 15 light years from Earth, with an orbit time of just 1.94 Earth days. They estimated the surface temperature on the new planet at between 400 degrees and 750 degrees Fahrenheit.

Gliese 876 is a small, red star with about one-third the mass of the sun. The researchers said this is the smallest star around which planets have been discovered. In addition to the newly found planet the star has two large gas planets around it.

Butler said the researchers think that the most probable composition of the planet is similar to inner planets of this solar system — a nickel/iron rock.

Gregory Laughlin of the Lick Observatory at the University of California, Santa Cruz, said a planet of this mass could have enough gravity to hold onto an atmosphere. “It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer.”

Three other extrasolar planets believed to be of rocky composition have been reported, but they orbit a pulsar rather than a normal type of star.

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