Recent disvoveries suggest that the Milky Way hosts nomad planets adrift in space that may play a dynamic role in the universe. Titled "Nomads of the Galaxy," a recent study proposed an upper limit to the number of nomad planets that might exist in the galaxy: 100,000 for every star. And because the Milky Way is estimated to have 200 to 400 billion stars, that could put the number of nomad planets in the quadrillions.
"In the 20th century, many eminent scientists have entertained the speculation that life propagated either in a directed, random or malicious way throughout the galaxy," said Roger D. Blandford, A co-author of the recent study and director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University and the SLAC National Accelerator Laboratory.
"One thing that I think modern astronomy might add to that is clear evidence that many galaxies collide and spray material out into intergalactic space. So life can propagate between galaxies too, in principle."
I'm really curious about the exchange of planets between solar systems," said Louis E. Strigari, lead author of the study and research associate at KIPAC and the SLAC, " How often does it happen, and how far can a nomad planet travel? How many trips around our galaxy does it make? I think these are brand new, basic questions. And I think that's an exciting place to be."
"If you imagine the Earth as it is today becoming a nomad planet... life on Earth is not going to cease," said Dimitar D. Sasselov, Professor of Astronomy at Harvard University and the Harvard-Smithsonian Center for Astrophysics, and the Director of the Harvard Origins of Life Initiative. "That we know. It's not even speculation at this point. ...[Scientists] already have identified a large number of microbes and even two types of nematodes that survive entirely on the heat that comes from inside the Earth."
The image at the top of the page 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.
Journal reference: Monthly Notices of the Royal Astronomical Society
The Daily Galaxy via The Kavli Foundation