Dying Stars Reveal the Clue to Extraterrestrial Life: Earth-like Planets Unmasked

Dying stars may hold the clues to extraterrestrial life, and scientists predict that if such life exists, we may be able to detect it within the next decade. The new research comes from a theoretical study of Earth-like planets orbiting white dwarf stars.

The new study, which has been accepted for publication in the Monthly Notices of the Royal Astronomical Society, found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star.

When a star like the sun dies, it leaves behind a hot core called a white dwarf. About the size of Earth, this core then cools and fades over time, but usually retains heat long enough to warm a nearby world for billions of years. Since these white dwarfs are much fainter than our sun, a planet would have to be much closer in order to possess liquid water on its surface--it would have to circle a white dwarf about once every 10 hours at a distance of a mere million miles.

Yet the conditions for this occurring are time sensitive. Before a star becomes a white dwarf, it swells into a red giant, engulfing and destroying nearby planets. This means that an Earth-like planet would have to arrive in a habitable zone after the star became a white dwarf.

Current findings, though, are encouraging. A survey of the 500 closest white dwarfs found that there were one or more habitable Earth-like planets. Since white dwarfs have an abundance of heavy metals on their surface, they could form second generation worlds from leftover dust and gas.

How do scientists plan to find these stars? The best way to do so is with a transit search, which is essentially looking for a star that dims slightly as an orbiting planet crosses in front of it. An Earth-like planet would be able to block a large fraction of a white dwarf's light and thus create an obvious signal. In contrast, studying brighter stars makes it harder to pick out Earth-like planets. We can also examine the atmosphere of these planets when a white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk. In addition, NASA's James Webb Space Telescope (JWST) is scheduled for launch by the end of this decade, and should give scientists the opportunity to find out what gases exist on alien worlds. This could allow researchers to find a world that possesses an abundance of oxygen, like our own Earth.

Even so, a habitable planet is unlikely to be found any time soon--even if scientists do predict a mere decade. Researchers will have to wait for JWST to launch, and keep watching the stars for the signals of an Earth-like planet.