Three super-Earths orbit same star

Three new super-Earths have been spotted around the same star in a remarkable new discovery by planet-hunters announced today. The new worlds – all less than ten times the Earth’s mass – are orbiting a star 42 light-years away in the constellation of Pictor, the painter’s easel.

Most planets detected in alien solar systems have been so-called “hot Jupiters” because they are much more massive.

The three new planets are 4.2, 6.7, and 9.4 times the mass of the Earth and orbit their parent sun in 4.3, 9.6, and 20.4 days, respectively.

They were discovered using a starlight-analysing instrument called HARPS on a giant 3.6-metre telescope at Europe’s La Silla Observatory in Chile.

It is so powerful that it can detect the motion of a planet to a precision of one metre a second.

The star, labelled HD 40307, is similar to the Sun but slightly smaller. It is only visible in the southern hemisphere and never rises above the UK’s horizon. News of the discovery was broken today at an international conference of astronomers at Nantes, France.

The international team of discoverers said their find implies that one Sun-like star in three harbours similar planets. If planets are so common, it boosts the chances that life is also widespread in the universe.

The latest news comes hot on the heels of the discovery of the most Earthlike planet yet found around a brown or red dwarf. NASA’s Spitzer space telescope revealed earlier this year that rocky planets like Earth should be common in the galaxy.

Planet hunter Michel Mayor, of Geneva Observatory, said: “We have made very precise measurements of the velocity of the star HD 40307 over the last five years, which clearly reveal the presence of three planets.

“Does every single star harbour planets and, if yes, how many? We may not yet know the answer but we are making huge progress towards it.”

At the same conference, the team of astronomers announced the discovery of two other planetary systems, also with the HARPS spectrograph. In one, a super-Earth 7.5 times the Earth’s mass orbits a star called HD 181433 in 9.5 days. This star also hosts a Jupiter-like planet with a period close to 3 years.

The second system contains a 22 Earth-mass planet that takes four days to orbit its star and a Saturn-like planet with a three-year period as well. “Clearly these planets are only the tip of the iceberg,” says Mayor.

They are among a total of 45 possible new planets with less than 30-times the mass or “size” of the Earth and years, or orbital periods, lasting less than 50 days.

More than 270 planets have now been detected around other stars since the first was found orbiting 51 Pegasi in 1995.

Picture: An artist’s impression of the three super-Earths. (ESO).

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Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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