Posted: Thu, Jul 10, 2003, 9:29 PM ET (0129 GMT)
Astronomers said Thursday that they have discovered what they believe is the oldest known planet, a gas giant that formed within a billion years of the Big Bang. The planet, about 2.5 times the mass of Jupiter, is approximately 12.7 billion years old and orbits a binary system of a white dwarf and a pulsar in the center of the globular cluster M4; the planet is as far from the binary as Uranus is from the Sun. The object was first discovered a decade ago, when astronomers found irregularities in pulses from the pulsar PSR B1620-26 that could not be fully explained by its white dwarf. They turned to Hubble images of the core of the cluster, and were able to identify the white dwarf and measure its color and temperature. Those findings allowed them to computer the mass of the star, and thus determine the mass and orbit of the third body, which they now believe to be a planet. Astronomers believe the planet formed around a Sunlike star 13 billion years ago, and about one billion years ago both the planet and star were captured by the pulsar as the passed through the center of the cluster. The discovery may reshape models of planetary formation, and suggests that terrestrial planets may have also existed early in the history of the universe.
