Galaxy Could Be Teeming With 'Nomad Planets'
February 24, 2012

Galaxy Could Be Teeming With ‘Nomad Planets’

Researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) suggest in a new study that the heavens could be teeming with “nomad planets,” wandering through space instead of orbiting around host stars.

In fact, say the researchers, there could be 100,000 times more of these planets in the Milky Way alone than there are stars. And if observations confirm this estimate, it could affect the current theories of planet formation and change our understanding of the origin and abundance of life.

“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,” said study leader Louis Strigari.

Using gravitational microlensing, the KIPAC team have so far discovered a few nomad planets in our galaxy. Astronomers have hypothesized that there could be around twice as many nomads as there are stars in the Milky Way, but the research team believe that number should be multiplied by 50,000.

To come up with the number, they took into account the known gravitational pull of our Milky Way, the amount of matter available to make such objects and how that matter might be distributed.  There is room for error, however, as there is still great uncertainty as to how nomad planets form. Some were most likely ejected from solar systems, but research indicates not all could have formed this way.

The KIPAC team, hoping to find the answer to that riddle, plan to employ the space-based Wide-Field Infrared Survey Telescope and the ground-based Large Synoptic Survey Telescope, both set to begin operation in the early 2020s.

If indeed there are that many nomads wandering about, there is a real possibility that they could be spreading the seeds of life through collisions, say the researchers.

“Few areas of science have excited as much popular and professional interest in recent times as the prevalence of life in the universe,” says KIPAC director Roger Blandford. “What is wonderful is that we can now start to address this question quantitatively by seeking more of these erstwhile planets and asteroids wandering through interstellar space, and then speculate about hitchhiking bugs.”

Researchers note that although nomad planets do not have a star to warm them, they may be able to generate heat through internal radioactive decay and tectonic activity. Their paper was submitted to the Monthly Notices of the Royal Astronomical Society.

Additional authors of the paper included KIPAC member Matteo Barnabè and affiliate KIPAC member Philip Marshall of Oxford University. The research was supported by NASA, the National Science Foundation and the Royal Astronomical Society.

KIPAC is a joint institute of Stanford University and the SLAC National Accelerator Laboratory.


Image Caption: This image is an artistic rendition of a nomad object wandering the interstellar medium. The object is intentionally blurry to represent uncertainty about whether it has an atmosphere. A nomadic object may be an icy body akin to an object found in the outer solar system, a more rocky material akin to asteroid or even a gas giant similar in composition to the most massive solar system planets and exoplanets. Credit: Greg Stewart / SLAC National Accelerator Laboratory


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