It seems that there could be lots of planets out there that could be carrying life in Enceladus-like oceans that are frozen over on their surface, and whose life could be seeded on Earth-like planets as they careen through space. Such a scenario is another plausible mechanism for the panspermia theory of the origins of life in this solar system.
Since these planets appear to be relatively common, the seeds of life scattered throughout the galaxy could be relatively common as well. A good smack as it careens through another solar system's "Kuiper belt" and now there are lots of meteors floating around that could seed life on a hospitable inner planet.
In recent years, computers have become powerful enough to simulate the formation and evolution of planetary systems over many billions of years.
One of the surprises to come out this work is that planets are regularly kicked out of these systems by slingshot effects. By some calculations, this fate may still await planets in our own Solar System.
One interesting question is whether these so-called "rogue planets" could ever support life in the cold dark reaches of interstellar space.
Today, Dorian Abbot and Eric Switzer at the University of Chicago give us an answer. The generally accepted criteria for life is the presence of liquid water. They calculate that an Earth-like rogue planet could support liquid oceans if the water were heated from below by the planet's core and insulated from above by a thick layer of ice.
Their reasoning is straightforward. They define an Earth-like planet to have dimensions within an order of magnitude of Earth's and having a similar composition. They then calculate the heat flux from the core and suggest that the thickness of the ice above would reach a steady state in about a million years. That's much shorter than the lifetime of a hot core...