The possibility of alien life on the icy planets and moons in our Solar System could be lower than previously thought, because any water on them will quickly vaporize, according to a new study in Nature Geoscience.
Scientists believe that Enceladus, Saturn’s sixth largest moon, and Europa, Jupiter’s smallest Galilean moon, are the most promising candidates in our search for extraterrestrial life, because of their icy exteriors.
As the Sun ages and gets hotter over time, the ice will melt and turn into water – a key ingredient needed to support life. But the paper published on Monday shows that those icy worlds will “transition directly to runaway greenhouse state, without passing through a habitable Earth-like state.”
Earth is unique, as it has been geologically active throughout its history. Volcanoes have emitted a steady stream of greenhouse gases such as carbon dioxide, sulfur dioxide, and hydrogen sulfide that trap heat from the Sun’s rays. It keeps Earth at the perfect temperature for liquid water to exist.
Other bodies such as Enceladus and Europa lack these processes, and with no help from greenhouse gases, the temperature is determined solely on the energy they receive from the Sun.
Researchers from Peking University in China, the University of Chicago and Cornell University in the US, and the University of Toronto in Canada developed climate models to simulate the evolution of the icy planets and moons.
They found that the solar energy – or stellar flux – needed to melt the ice is so high that they just transition from a “snowball state” to a “moist greenhouse state.”
“Our results suggest that an icy exoplanet at the equivalent distance of the modern Earth from the Sun would remain in a snowball state for a billion years or even longer until its received stellar flux evolves to become much higher than the insolation [exposure to the Sun’s rays] for the modern Earth,” the researchers warned.
“Following this, the planet would directly jump to a moist or runaway greenhouse state. Europa and Enceladus will have no habitable period. They will transit to a moist or runaway greenhouse state when the Sun becomes a red giant in 6-7 billion years." ®