Scientists suggest watery planets around dead stars could host alien life

A recent study has highlighted the potential for life on watery planets orbiting dead stars, known as white dwarfs. These stellar remnants, which are the remains of stars that have exhausted their fuel, might be ideal locations for harboring life due to the presence of water.

The study suggests that scientists should look for the shadow of a planet transiting a shrunken white dwarf, which could still retain its water oceans for billions of years despite undergoing violent final stages. Juliette Becker, the lead author and an astronomy professor at the University of Wisconsin–Madison, explained that white dwarfs’ small and featureless nature makes it easier to analyze the atmosphere of a transiting terrestrial planet.

“White dwarfs are so small and featureless that if a terrestrial planet transited in front of them, you could characterize its atmosphere much better,” Becker said. “The planet’s atmosphere would have a much larger, clearer signal because a larger fraction of the light you’re seeing is passing through exactly what you want to study.”

However, for a planet to host alien life, it must first survive the tumultuous final days of its star. When stars like our Sun deplete their fuel, they undergo fusion reactions at their core, causing them to expand significantly.

“There are two phases during which the star expands to 100 times its normal radius, engulfing any planets within that radius,” Becker explained, referring to this as Destruction Phase No. 1.

If a water-bearing planet avoids being engulfed, it must then withstand the star’s mass loss and increased brightness. “The star’s increased brightness can drastically raise the surface temperatures of all planets in the system, potentially evaporating their oceans and causing significant water loss,” Becker added.

To retain a significant amount of water, an Earth-like planet would need to be positioned approximately 5 to 6 astronomical units away from its dying star. Over a billion years, the star would eventually shrink and cool. “Being far enough away to avoid losing surface water is crucial,” Becker said. “But the downside is that the water would likely be frozen, which isn’t ideal for life.”

Becker concluded that finding white dwarfs that are good candidates for hosting potentially habitable exoplanets could be worthwhile. “These theoretical techniques will help us identify the best targets, so we don’t waste time on less promising ones,” she explained.