In about 4.5 billion years, the Sun will enter its red giant phase, swallowing Mercury and Venus and rendering Earth uninhabitable. This radical transformation will push the habitable zone toward the outer reaches of the Solar System, potentially offering an unexpected opportunity for life.
Researchers at the Carl Sagan Institute at Cornell University have modeled the impact of this evolution on Europa, a moon of Jupiter. They predict that increased heat will cause its icy crust to sublimate, exposing its subsurface oceans to evaporation. This process would create a thin atmosphere of water vapor, particularly at northern and southern latitudes.
Illustration of NASA's Europa Clipper probe flying over the icy moon Europa. Launched on October 14, 2024, it will reach Europa in April 2030.
Credit: NASA/JPL-Caltech This atmosphere could persist for up to 200 million years, a narrow but significant window for the emergence or persistence of life. Conditions would be particularly favorable on the sides of Europa facing away from Jupiter, where water loss would be reduced.
This study, published in the
Monthly Notices of the Royal Astronomical Society, opens new perspectives on the resilience of life under extreme conditions. It also highlights the importance of exploring icy moons in the outer Solar System like Europa or Enceladus.
Scientists now plan to model other moons, such as Ganymede or Callisto, to assess their potential to host life during the Sun's red giant phase. This work could guide future space exploration missions.
What is a red giant star?
A red giant star is an advanced phase of stellar evolution, reached when the star has exhausted the hydrogen in its core. The core contracts while the outer layers expand, cool, and redden.
This expansion can engulf the closest planets, as the Sun will do with Mercury and Venus. The surface temperature drops, but the overall luminosity increases significantly.
Red giants are massive objects, often hundreds of times larger than their initial size. Their lifespan in this phase is relatively short on a cosmic scale, ranging from a few million to a few billion years.
This phase often precedes the formation of a planetary nebula and the transformation into a white dwarf, marking the end of the star's active life.