Space may swarm with homeless planets

Our galaxy may be teeming with homeless planets, wandering through space rather than orbiting a star, according to media reports Monday. The galaxy could hold a tremendous number of “nomad planets”, many thousands existing for each main-sequence star in the galaxy, a research conducted by the Kavil Institute for Particle Astrophysics (KIPAC) said. KIPAC – a joint research institution of Stanford University and America’s SLAC National Accelerator Laboratory – predicted that there may be 100,000 times more of these wandering, homeless planets than stars in the Milky Way. For the past few years, gravitational microlensing (the refocusing of a star’s light by planets passing “in front” of them) has introduced new insights into planets that don’t seem to be bound to stars. "If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist," study leader Louis Strigari said in a statement to the Royal Astronomical Society. Most of the 500-odd exoplanets discovered in the past two decades orbit stars, but astronomers turned up a dozen nomad planets that don’t orbit stars last year. Some may have been expelled from the solar systems in which they formed; others may need to be explained with new theories of planetary formation. However, Strigari said that known values like the mass of the galaxy, which is estimated from its gravitational pull, indicate that it could be “teeming” with nomad planets. New instruments to be put into service during the 2020s, such as the ground-based Large Synoptic Survey Telescope and the space-based Wide-Field Infrared Survey Telescope, will provide related observations facilitating new estimates of the number of nomads, Strigari’s paper stated.