Like NASA’s planet-hunting Kepler Space Telescope, the technique would only work for white dwarf systems that are aligned relative to the observatory’s line of sight so that orbiting planets pass in front of, or transit, their parent stars.
While the star is eclipsed, some light will pass through the planet’s atmosphere -- if it has one -- and leave telltale chemical fingerprints that can be detected by instruments in a telescope.
“If we happen to be situated so that we can see an eclipse, then the planet would block a substantial fraction of the light from the white dwarf. Then we can basically use the light that is passing through the atmosphere to figure out what the atmosphere is made of,” Loeb said.
Of key interest would be detections of oxygen, which on Earth is a clear sign of life from photosynthesis by plants.
“The only reason we have oxygen in the atmosphere right now is because of life,” Loeb said. “If you remove life from Earth, then within 1 million years or so, the oxygen will be completely depleted. It will make all kinds of molecules of oxidized metals, for example, and it will be consumed from the atmosphere.”
Scans of exoplanets’ atmospheres also could find water vapor and other potential biomarkers.
While there is not yet any direct evidence of planets circling white dwarfs, astronomers believe they exist. Previous studies have shown that as many as 30 percent of white dwarf stars have heavy elements on their surfaces, presumably from rocky bodies that broke up relatively soon after the white dwarf formed.
A planet could find a stable orbit in white dwarfs’ habitable zone, one that would have it circle its parent star in just 10 hours.
“I’m not saying that we definitely know that such planets are there, but it’s quite plausible that the system after a while cleans itself up and for over a billion years or more, it may have stable Earth-mass planets,” Loeb said.
“It sounds like a reasonable extrapolation for what we’ve seen,” added astronomer Marc Kuchner, with the Exoplanets and Stellar Astrophysics Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Md.
“There’s no reason to think you wouldn’t find one now and then," Kuchner told Discovery News.
The research will be published in an upcoming edition of the Monthly Notices of the Royal Astronomical Society and is available online via the arXiv preprint service.