In this article, Alycia Weinberger says, “The discovery of a disk around the planetary-mass companion to 2M1207 should be a bit of a relief to planet-formation theorists” because it casts doubt on the object being a planet. But wouldn’t our early solar system have been composed of at least two planets, Jupiter and Saturn, that had extensive disks around them before their satellites coalesced into moons?

Howard Zimmerman
New York, N.Y.

Researchers say that Jupiter and Saturn indeed had their own disks, but they think that 2M1207 formed as a star in its binary system because it’s relatively massive and is far from its partner .—R. Cowen