Quartet of giant planets puzzles astronomers - space - 08 December 2010 - New Scientist

Quartet of giant planets puzzles astronomers - space - 08 December 2010 - New Scientist: "The discovery of a fourth giant world around the star HR 8799 is straining the two leading theories of how planets form.

Planets are thought to coalesce from a dusty disc around a young star. One model, called core accretion, says that giant planets form when the dust gathers into a rocky core, which then draws in gas to form a massive atmosphere. Another, called disc instability, says that these planets collapse suddenly from sections of the disc.

HR 8799's four planets, each five to 13 times Jupiter's mass, are too far apart to be explained easily by either model, say Christian Marois of the Herzberg Institute of Astrophysics in Victoria, British Columbia, Canada, and colleagues."