White dwarfs could be fertile ground for other Earths

March 31, 2011
White Dwarf

Habitable exoplanets near white dwarfs can be surveyed using 1-meter ground telescopes (credit: NASA/European Space Agency)

University of Washington associate professor of astronomy Eric Agol has proposed that potentially habitable planets orbiting white dwarfs could be much easier to find than other exoplanets located so far.

White dwarfs, cooling stars believed to be in the final stage of life, typically have about 60 percent of the mass of the sun, but by volume they are only about the size of Earth. Though born hot, they eventually become cooler than the sun and emit just a fraction of its energy, so the habitable zones for their planets are significantly closer than Earth is to the sun.

“If a planet is close enough to the star, it could have a stable temperature long enough to have liquid water at the surface – if it has water at all – and that’s a big factor for habitability,” Agol said.

So he has proposed a survey of the 20,000 white dwarfs closest to Earth. Using a 1-meter ground telescope, one star could be surveyed in 32 hours of observation, he said. If there is no telltale dimming of light from the star in that time, it means no planet orbiting closely enough to be habitable is passing in front of the star. The work could be carried out by a network of telescopes making successive observations of a white dwarf as it progresses through the sky.

Finding an Earth-like planet around a white dwarf could provide a meaningful place to look for life, and would be a potential lifeboat for humanity if Earth, for some reason, becomes uninhabitable, said Agol.

Ref.: Eric Agol, “Transit surveys for earths in the habitable zones of white dwarfs,” The Astrophysical Journal, March 29, 2011.