Star’s Fourth World Stumps Astronomers

If three’s a crowd, a new planet recently discovered orbiting a sunlike star is really cluttering up its neighborhood.

The new planet is the fourth Jupiter-like world to be found around the young star HR 8799, astronomers announced today. The same team had previously found the other three planets in 2008, when they took a direct picture of the star system.

Of the more than 500 planets discovered to date outside our solar system, most have been found via indirect methods, such as looking for planets’ gravitational tugs on their host stars or for dips in starlight when planets pass in front of their hosts.

The new planet was also found in a direct image of the HR 8799 system. But based on the masses of the planets and their distances from the star, the fourth world challenges current theories of planet formation, according to the study authors.

“This is the first multiplanet system directly imaged so far, so it’s quite a feat,” said lead study author Christian Marois, an astronomer at the Herzberg Institute of Astrophysics in Canada.

“But we are now stuck with four planets [and] we cannot explain their formation and their current locations by any of our models.”



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