Will Europa Become Habitable When the Sun Becomes a Red Giant? – Universe Today

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By Carolyn Collins Petersen May 27, 2025

People always want to know what will happen to Earth when the Sun eventually swells up as a red giant. For one thing, the expanding Sun will turn the inner planets into cinders. It will almost certainly spell the end of life on our planet. Mars might become more temperate and hospitable to life. In addition, it could well be a boon for the gas giant Jupiter and its moons. That's because the habitable zone of the Solar System will move outward from where it is now, to a spot encompassing the Jovian system and forcing changes on all of those worlds.

Take Europa, for example. It's an icy world today and will stay that way for a long time. However, when the Sun enters the red giant phase of its evolution in about 12 billion years, researchers estimate that Europa could develop and maintain a tenuous water vapor atmosphere. Whether or not it could support life is an open question. The fact that Europa could be affected by the "warmth" of the habitable zone means that there will be more possible places in the Solar System where life could develop (if only for a short time).

Graphic representation of the migration of the Solar System's habitable zone as the Sun evolves through the red giant phase. Courtesy NASA.

In a larger context, studying the effect of the Sun's red giant phase on worlds like Europa gives astronomers and planetary scientists a look at what happens to habitable zones, as well as the planets and moons that survive the death of their stars. Interestingly, well over 90 percent of all observed exoplanets orbit stars that will end up as white dwarfs, just as the Sun will. Understanding how these worlds will evolve during the red giant and white dwarf phases is important. It also sheds light on the evolution of our own Solar System.

What Happens When a Star Dies

In general, the evolutionary tale of a star like the Sun gets complicated as it ages. Currently it's on the main sequence - that is, the hydrogen-burning phase. That will go on for five or so billion years. Eventually, the hydrogen fuel in the core runs out, and the Sun will begin to fuse heavier elements (helium, etc.). That, in turn, will trigger the expansion of the outer envelope (atmosphere), and the Sun morphs into a red giant. Once the Sun enters that "bloating" phase, it will engulf the nearest worlds. Mercury and Venus will definitely disappear in the Sun's flames, but the jury is still out as to exactly what will happen to Earth. However, our home planet is not likely to remain a comfortable, habitable world. Planets and moons farther away (Mars and beyond) won't be affected the same way, and the scenario is different for each of those worlds. Eventually, the remnants of the Sun's atmospheric envelope will float away to space. The solar core will shrink down to become a white dwarf.

The Helix Nebula is a planetary nebula surrounding a white dwarf star. Our Sun could look like this in a several billion years. Courtesy NASA/ESA/STScI.

Larger, more massive stars go through more catastrophic deaths in the form of supernovae (for example), and their corpses become neutron stars or black holes. Any planets they have are probably destroyed in the original explosion, along with the habitable zones around the stars.

It makes sense to study how planetary systems evolve, along with their stars, particularly sun-like ones that move through the red giant phase and end up as white dwarfs. Seeing how our system does it is crucial, especially as astronomers try to understand the fate of exoplanets around similar-type stars. In particular, white dwarf planetary systems offer an interesting population of potentially habitable planets (and moons) that can be studied by our current (and upcoming) space-based observatories. It turns out that some white dwarfs have water-rich material orbiting them. Luckily, they take a long time to fade away and have stable futures that are about as long as the Universe exists. This means their remaining exoplanets (if they exist) are good targets for observations.

What Happens to Jupiter and Europa?

Astronomers want to examine the many factors that affect a planet's ability to survive its star's red giant phase. These include the changing variability of a parent star like the Sun as it evolves, changes to planetary bodies and their orbits, and the influence of the changing stellar wind on the planets and their moons. These comprise a fairly complex set of factors. A recent paper (see below) models and examines two scenarios: the first is when the system enters the red giant branch habitable zone in about 12 billion years at a distance of 2 astronomical units (AU) from the expanding Sun (currently it's at 5.2 AU from the unexpanded Sun). The second is at about 12.5 billion years, and Jupiter is only 0.8 AU from the expanding Sun. The models look at what happens to both Jupiter and Europa as the evolutionary process continues.

As we all know, Europa's an ice world with a subsurface liquid ocean. Since it will likely remain tidally locked to Jupiter as the Sun evolves, that gravitationally bound relationship will also affect this tiny moon. Among other things, when the Jovian system starts to experience the expanding solar atmosphere, Jupiter's upper cloud decks will likely become bright water clouds. That changing albedo will also affect Europa. It's also possible that Jupiter will "puff up", which could pose a threat to its inner moons. However, its strong gravity might keep it from doing that, and the moons could still be in safe orbits.

Under the influence of a brighter Jupiter, the expanding solar atmosphere and resulting stellar winds, Europa's surface ices will sublimate. This is similar to the way carbon dioxide ice (dry ice) sizzles away in sunlight. Much of the sublimated ice vapor will be lost to space, but some of it will remain bound to Europa for a couple of hundred thousand years before being lost completely. Whether or not there is any life there now, it may well be that Europa could be habitable during that time. One big question is whether or not it's long enough for life to arise and flourish.

Implications for Exoplanets and Exomoons

If that is Europa's fate, then it's likely that other exoplanets or exomoons around sun-like stars could follow the same evolutionary path as their stars die. Expanding exploration of those worlds already affected by their red giant or white dwarf stars could show how our own Solar System will be affected some 10 to 12 billion years from now. Currently available observatories, in addition to upcoming missions (such as the Roman telescope), could open up new chances to study these exoworlds. Those observations may also provide a pathway to understand whether or not life on those worlds could persist, even as the parent stars age out and die.