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Nomad Planets: Our Galaxy Awash in Homeless Worlds?

This image is an artistic rendition of a nomad object wandering the interstellar medium. The object is intentionally blurry to represent uncertainty about whether or not 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

Bacteria-carrying planets may be wandering through space instead of orbiting a star.

That’s the news from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the SLAC National Accelerator Laboratory.

A research team is suggesting that a new class of celestial objects – “nomad planets” — will affect current theories of planet formation and could 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 Louis Strigari, leader of the team in a Stanford University statement that reported the result in a paper submitted to the Monthly Notices of the Royal Astronomical Society.

The research was supported by NASA, the National Science Foundation and the Royal Astronomical Society.

Searches over the past two decades have identified more than 500 planets outside our solar system, almost all of which orbit stars.

But last year, researchers detected about a dozen nomad planets, using a technique called gravitational microlensing. That technique looks for stars whose light is momentarily refocused by the gravity of passing planets.

Microbial seeds of life

The research produced evidence that roughly two nomads exist for every typical, so-called main-sequence star in our galaxy. The new study estimates that nomads may be up to 50,000 times more common than that.

That data had led researchers to suggest that there may be 100,000 times more “nomad planets” in the Milky Way than stars!

A good count, especially of the smaller objects, will have to wait for the next generation of big survey telescopes, especially 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.

A confirmation of the work could lend credence to another possibility: That as nomad planets roam their starry pastures, collisions could scatter their microbial flocks to seed life elsewhere.

“Few areas of science have excited as much popular and professional interest in recent times as the prevalence of life in the universe,” said Roger Blandford, research team member and KIPAC Director.

“What is wonderful,” Blandford added, “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.”

By Leonard David via Andy Freeberg, media relations manager at SLAC National Accelerator Laboratory.


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