Physical Characteristics
PSR B1620-26 b orbits a pair of stars. One, the pulsar, is a neutron star spinning at 100 revolutions per second. The second is a white dwarf with a mass of 0.34 solar masses. These stars orbit each other at a distance of 1 AU about once every six months. As the first planet found in the system, the planet's designation is PSR B1620-26 b. The planet has a mass of 2.5 times that of Jupiter, and orbits at a distance of 23 AU (3,400 million km), a little larger than the distance between Uranus and the Sun. Each orbit of the planet takes about 100 years.
The triple system is just outside the core of the globular cluster Messier 4. The age of the cluster has been estimated to be about 12.7 billion years, and because all stars in a cluster form at about the same time, and planets form together with their host stars, it is likely that PSR B1620-26 b is also about 12.7 billion years old. This is much older than any other known planet, and nearly three times as old as Earth.
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