White Dwarf Search May Yield Habitable Planets
April 25, 2013

James Webb Telescope To Hunt For Life Around Dying Stars

April Flowers for redOrbit.com - Your Universe Online

A dead star, known as a white dwarf, will eventually cool down and fade away because it has no energy source. A new study led by Professor Dan Maoz of Tel Aviv University's School of Physics and Astronomy suggests that white dwarfs can still support habitable planets.

The team, which includes Prof. Avi Loeb, Director of Harvard University's Institute for Theory and Computation and a Sackler Professor by Special Appointment at TAU, has demonstrated that it should be possible to detect biomarkers surrounding these habitable planets — including methane and oxygen — that indicate the presence of life using advanced technology that will become available in the next decade.

The study, published in the Monthly Notices of the Royal Astronomical Society, uses a "simulated spectrum" to demonstrate that the James Webb Space Telescope (JWST) will be capable of detecting oxygen and water in the atmosphere of Earth-like planets orbiting a white dwarf star. The JWST, set to be launched by NASA in 2018, will only need a few hours of observation time - making the determination much easier than it would be for an Earth-like planet orbiting a sun-like star.

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

Observations of white dwarfs have revealed an abundance of heavy elements on the surface, suggesting rocky planets orbit a significant fraction of them. A survey of 500 of the closest white dwarfs could spot one or more habitable planets, the researchers estimate.

The team has shown that such planets orbiting white dwarfs will be easier to spot than the same planets orbiting normal stars because of the unique characteristics of this type of star. As an orbiting planet crosses in front of the star, dimming the star's observable light, the atmosphere can be detected and analyzed. Elements in the planet's atmosphere will absorb some of the background starlight shining through, leaving chemical clues to their presence that can be detected by JWST.

When an Earth-like planet orbits a normal star, "the difficulty lies in the extreme faintness of the signal, which is hidden in the glare of the 'parent' star," Prof. Maoz said. "The novelty of our idea is that, if the parent star is a white dwarf, whose size is comparable to that of an Earth-sized planet, that glare is greatly reduced, and we can now realistically contemplate seeing the oxygen biomarker."

The research team created the "synthetic spectrum" to estimate the kind of data the JWST will be capable of seeing. This spectrum replicates that of an inhabited planet similar to Earth orbiting a white dwarf. The spectrum allowed them to demonstrate that JWST should be able to pick up signs of oxygen and water on such a planet.

Oxygen biomarkers would be the most critical sign of the presence of life on an exoplanet. For example, Earth's atmosphere is 21 percent oxygen, which is entirely produced by our planet's plant life as a result of photosynthesis. Without plants, an atmosphere would be completely devoid of oxygen.

JWST is designed to look into the infrared region of the light spectrum where such biomarkers are prominent, making it an ideal instrument for hunting out signs of life on exoplanets. JWST will also be able to analyze the atmosphere of Earth-like planets without weeding out the similar signatures of Earth's own atmosphere because it will be space-based and not ground-based.

The study was made possible by the Harvard TAU Astronomy Initiative.