Moons orbiting starless “rogue” planets could stay warm enough to host liquid water for billions of years, a new study suggests, potentially creating long-lived habitats for life in deep space.
Using computer models, the researchers found that the temperatures on an Earth-sized moon orbiting a Jupiter-like rogue planet could stay warm enough to support liquid water on its surface for up to 4.3 billion years—almost as long as the earth has existed.
“The cradle of life does not necessarily require a sun,” said the study’s lead author David Dahlbüdding, a researcher at Ludwig Maximilian University in Munich, Germany. statement.
The article continues below
The new study focuses on natural satellites of exoplanetsknown as exomoonsespecially those orbiting free-floating rogue planets. Astronomers have yet to confirm the existence of an exomoon beyond doubt, however assembly circumstantial proof suggesting that the first discovery may not be far off.
Rogue planets are byproducts of chaotic young planetary systems, where close gravitational encounters can throw worlds out of orbit around their host star and into interstellar space. Recently research suggesting that these nomadic planets have a significant probability of retaining their moons even after being ejected. However, the violent process can dramatically reshape the orbits of these moons, stretching them into elongated orbits around their planets.
As a moon moves closer and further from its planet along such elliptical paths, the planet’s gravity repeatedly squeezes and bends its interior. In our own solar system, this process drives the intense volcanic activity of Jupiter’s moon Io and helps prevent subsurface oceans from freezing on icy moons such as Europe and Saturn’s Enceladus.
The process, known as tidal heating, generates internal heat through friction and, according to the new study, may be strong enough to keep liquid water oceans from freezing even in the cold of interstellar space.
Whether that heat can remain on the surface depends to a large extent on the moon’s atmosphere, the researchers say. Previous studies suggested that carbon dioxide could provide enough greenhouse heating to keep such moons habitable for up to 1.6 billion years. In the extreme cold of interstellar space, however, carbon dioxide can condense, causing the atmosphere to collapse and allowing heat to escape, the new study notes.
However, hydrogen behaves differently in thick, high-pressure conditions, the study claims. The team’s simulations show that when hydrogen molecules collide, they can briefly absorb heat that would otherwise radiate into space. This means that a dense hydrogen atmosphere acts as an insulating blanket, and captures the heat far more effectively.
The results, published in February in the journal Monthly Notices of the Royal Astronomical Society, shows that under these conditions some exomoons can remain hot enough for liquid water – and therefore be potentially habitable for life as we know it – for up to 4.3 billion years.
The findings could “significantly expand the range of possible environments that could harbor life,” the statement said, suggesting that “life can arise and persist even in the darkest regions of the galaxy.”
