First 'Super Earth' Planet Found

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First 'Super Earth'

Planet Found

By Stephen Battersby

NewScientist.com

8-26-4

 

A new kind of planet has been discovered in a star system 50 light

years away. It is the smallest world to be found outside our Solar

System, and probably the first rocky planet found so far, astronomers

revealed on Wednesday.

 

The planet orbits the star mu Arae, which has been monitored by a

European team of astronomers using an instrument called HARPS (High

Accuracy Radial velocity Planet Searcher), attached to the 3.6-metre

telescope at La Silla observatory in Chile.

 

HARPS measures the frequency of light from the star, so precisely

that it can pick up slight doppler shifts caused by motion of the

star's surface. It is sensitive to velocity changes as small as 1

metre per second.

 

The team's original aim was to catalogue stellar pulsations in order

to work out the internal structure of the star, but they noticed a

regular oscillation that had to have another source - the star was

being wobbled by the gravity of a planet.

 

The new planet orbits about 13 million kilometres from mu Arae, with

a year lasting only 9.5 Earth days, and it has about 14 times the

mass of Earth. That gives it about the same mass as Uranus, the

smallest giant planet in our Solar System.

 

Ice or gas

 

However, team member Nuno Santos of Lisbon University, Portugal, does

not think the new planet is a gas giant. Being so close to its star

means it probably never had a chance to gather an envelope of ice or

gas. Instead, it is probably a rocky world, like Earth - just a lot

bigger. "It's some kind of super Earth," says Santos.

 

HARPS could spot smaller worlds too. "I think we can go below 10

Earth masses; it's only a question of time," Santos told New

Scientist. But detecting true twins of the Earth will probably

require a completely different method, because a star's own

pulsations would obscure the gravitational wobble from such small

planets.

 

The newly discovered planet must be extremely hot. Its star, mu Arae,

is similar to the Sun, but the planet orbits at less than a tenth of

Earth's distance, so it gets a hundred times as much heat and light.

 

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