Dying Stars ‘Key to Finding Alien Life’

Dying stars are humanity's best bet at finding alien life in the near future, researchers have said.

Astronomers at the Harvard-Smithsonian Centre for Astrophysics (CfA) say life could be detected within the next 10 years on planets orbiting white dwarf stars.

Planets orbiting white dwarfs offer the best hope of finding extraterrestrials because scientists can detect oxygen in their atmosphere fairly easily.

In comparison, it is very hard to find oxygen on planets orbiting sun-like stars or red dwarfs.

Before a star turns into a white dwarf, it swells into a red giant and engulfs and destroys nearby planets.

The Cfa recently found that the closest habitable planet was orbiting a red dwarf. Although these types of stars are much smaller and fainter than the sun, it is much bigger than a white dwarf and its glare would overwhelm any signal from an orbiting planet's atmosphere.

Theorist Avi Loeb said: "In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs.

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf."

When a star such as our sun dies, it "puffs off" its outer layers and leaves behind a hot core - a white dwarf.

White dwarfs are about the same size as Earth and they slowly cool and fade over time - billions of yearsm which allows it to retain heat long enough to warm a nearby world.

Chemical fingerprint

A planet would have to be fairly close to a white dwarf for it to have liquid water on its surface and would circle the star about once every 10 hours.

If a planet did exist in the habitable zone, it would be fairly easy to find - if an Earth-like planet passed an Earth-sized star it would block a large fraction of its light. It is estimated that there are one or more potentially habitable planets orbiting the nearest 500 white dwarfs.

When the white dwarf shines light through the ring of air surrounding the planet, the atmosphere absorbs some of it, leaving a chemical fingerprint that would tell whether there is water vapour in the air.

Astronomers are specifically looking for oxygen. Earth's atmosphere regenerates itself by continually replenishing oxygen through photosynthesis.

If all life on Earth ended, the atmosphere would quickly become devoid of oxygen. Large quantities of oxygen on another planet would suggest ot contained life.

The James Webb Space Telescope (JWST), which will be launched before 2020, is engineered to detect gases on suspected life-bearing planets.

Loeb and Dan Maoz, of Tel Aviv University, replicated what JWST will see and found it could detect water and oxygen within a few hours.

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz.