How the James Webb Space Telescope will look for life around dead stars

When NASA’s James Webb Space Telescope launches next year, it may be able to find indications of life beyond our planet in an unexpected location — on planets which orbit dead stars called white dwarfs.

A recent study found an intact planet orbiting around a white dwarf, which surprised astronomers as in their death throes these stars usually destroy the planets around them when they swell before collapsing to form the white dwarf. But this planet somehow survived, giving a clue to a new type of location where we could search for habitable planets.

Rendering of a planet transiting a white dwarf star.
Rendering of a planet transiting a white dwarf star. Jack Madden, Carl Sagan Institute, Cornell University

“If rocky planets exist around white dwarfs, we could spot signs of life on them in the next few years,” Lisa Kaltenegger, one of the authors of the new study and associate professor of astronomy in the College of Arts and Sciences and director of the Carl Sagan Institute, said in a statement.

Her co-author Ryan MacDonald, also at the Carl Sagan Institute, agreed that planets orbiting white dwarf are a prime target for searches for life: “We know now that giant planets can exist around white dwarfs, and evidence stretches back over 100 years showing rocky material polluting light from white dwarfs. There are certainly small rocks in white dwarf systems,” he said. “It’s a logical leap to imagine a rocky planet like the Earth orbiting a white dwarf.”

To actually discover if there are habitable planets around these dead stars, researchers will make use of new tools like NASA’s upcoming James Web Space Telescope. This instrument is so sensitive it will be able to detect whether distant planets have an atmosphere, which is a key requirement for habitability, and even whether that atmosphere contains gases that could indicate life.

Rendering of a white dwarf star on the horizon of a mountainous planet.
Rendering of a white dwarf star on the horizon of a mountainous planet. Jack Madden, Carl Sagan Institute, Cornell University

“When observing Earth-like planets orbiting white dwarfs, the James Webb Space Telescope can detect water and carbon dioxide within a matter of hours,” MacDonald said. “Two days of observing time with this powerful telescope would allow the discovery of biosignature gases, such as ozone and methane.”

The telescope is set to launch in 2021, when it will be able to begin its search for habitable worlds. The recently discovered planet orbiting a white dwarf, WD 1856 b, is a gas giant like Jupiter and therefore couldn’t host life, but finding it has opened the door to a new range of possibilities of where life could be located.

“What if the death of the star is not the end for life?” Kaltenegger said. “Could life go on, even once our sun has died? Signs of life on planets orbiting white dwarfs would not only show the incredible tenacity of life, but perhaps also a glimpse into our future.”

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