Worlds collide in the Seven Sisters

New-born rocky planets have been detected in the Seven Sisters, the most famous star cluster in the sky. Astronomers have even recorded what look like collisions between the young worlds, similar to that which produced the Earth and the Moon.

Evidence for the latest batch of new planets comes from study of a star called HD 23514 in the cluster, which is also known as the Pleiades.

The star is a stellar teenager with an untidy room compared to our own Sun – it is 45 times younger and surrounded by dust.

Joseph Rhee, of the University of California, Los Angeles, used a heat-seeking camera called MICHELLE on the Gemini North Telescope on Hawaii to look at the warm dust.

He believes it was pulverized by catastrophic collisions in a young, evolving planetary system around the young star. They appear to be happening in a zone comparable to that between Mercury and Mars in our own solar system.

The new observations, by Dr Rhee and colleagues Inseok Song and Benjamin Zuckerman, indicate that rocky terrestrial planets, perhaps like the Earth, Mars or Venus, are forming or have recently formed. Their discovery will be announced in the Astrophysical Journal.

Dr Rhee said: “This is the first clear evidence for planet formation in the Pleiades, and the results we are presenting strongly suggest that terrestrial planets like those in our solar system are quite common.”

Despite their rocky nature, no one imagines that there could be any life on the planets of HD 23514 as the newly formed planets are still so young. Alien-hunters are looking instead at more mature solar systems such as 55 Cancri and Gliese 581.

The Pleiades can be seen with the naked eye during the evening at this time of the year, and were likened to “a swarm of fire-flies” by the poet Tennyson. Although six or seven can easily be spotted, the cluster actually contains around 1,400 stars.

• Talking of Gemini, the Royal Astronomical Society has expressed shock at a sudden decision by the Science and Technology Facilities Council to withdraw the UK from the Gemini Observatory.

The decision came despite the UK having been a key partner since the start of the project to install twin 8-metre telescopes in Hawaii and Chile to cover the entire sky. In a statement, the RAS Council said the decision to withdraw “appears to have been made without any consultation with the astronomical community.”

Our picture is an artist’s impression of a planetary collision around HD 23514 by Lynette Cook for Gemini Observatory.


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