Planets coalesce from the placental cloud of gas and dust that surrounds a newborn star. Over time, gravity gathers the gas and dust into ever larger clumps. Dust grains form pebble-size bodies, which stick together to make objects as big as boulders. These bodies, called planetesimals, may grow large enough to form planets as massive as Jupiter.
New observations by Aki Roberge of Johns Hopkins University in Baltimore and her colleagues suggest that a mere stripling of a star, which might be as young as 300,000 years, already has planetesimals. If confirmed, the star, known as 51 Ophiuchi, may rank as the youngest star known to have initiated the planet-forming process. Roberge cautions, however, that the star's age is not well determined.
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