Washington: Thousands of rogue alien planets
may be rambling through space in our Milky Way galaxy instead
of being locked in orbit around a star, says a new study.
According to researchers at the Kavli Institute for
Particle Astrophysics and Cosmology (KIPAC), an independent
laboratory of Stanford University, these "nomad planets" could
be surprisingly common in our bustling galaxy.
And they predict that there may be 100,000 times more of
these wandering, homeless planets than stars in the Milky Way.
If this is the case, these intriguing cosmic bodies would
belong to a whole new class of alien worlds, shaking up
existing theories of planet formation, and may also raise new
and tantalizing questions in the search for life beyond Earth,
the researchers said.
"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 was
quoted as saying.
And while nomad planets cannot benefit from the heat
given off from their parent stars, these worlds could generate
heat from tectonic activity or internal radioactive decay, the
For now, characteristics of these foreign objects are
still unknown; they could be icy bodies, similar to other
objects found in the outer solar system, rocky like asteroids,
or gas giants similar to the most massive planets in our solar
Over the past several decades, astronomers have keenly
hunted for planets outside our solar system. So far, the
search has turned up more than 700 of these exoplanets.
Almost all of these newfound worlds orbit stars, but last
year, scientists found about a dozen planets with no
discernible host star.
The researchers, who detailed the study in the Monthly
Notices of the Royal Astronomical Society, used a technique
called gravitational microlensing to detect these homeless and
free-flying planets. The method examines the effects of a
massive object passing in front of a star.
Based on initial estimates, approximately two free-flying
planets exist for every "normal" star in our galaxy, but the
results of the new study produced even more staggering
findings: nomad planets may be up to 50,000 times more common
The researchers are hopeful that follow-up observations
using next generation telescopes, particularly of the smaller
objects, will yield more detailed results. If the estimated
number of these nomad planets is correct, the results could
lead to exciting prospects about the origin and abundance of
life in our Milky Way galaxy, they said.
For instance, as these homeless planets mosey through
space, collisions could break apart pieces of these rogue
worlds and fling bacterial life onto other celestial bodies,
the researchers said.
"Few areas of science have excited as much popular and
professional interest in recent times as the prevalence of
life in the universe," co-author Roger Blandford, director of
"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."