Can life survive a star's death? Webb telescope can reveal the answer


Date:
September 16, 2020
Source:
Cornell University
Summary:
When stars like our sun die, all that remains is an exposed core --
a white dwarf. A planet orbiting a white dwarf presents a promising
opportunity to determine if life can survive the death of its star,
according to researchers.



FULL STORY ==========================================================================
When stars like our sun die, all that remains is an exposed core --
a white dwarf. A planet orbiting a white dwarf presents a promising
opportunity to determine if life can survive the death of its star,
according to Cornell University researchers.


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In a study published in the Astrophysical Journal Letters, they show how
NASA's upcoming James Webb Space Telescope could find signatures of life
on Earth-like planets orbiting white dwarfs.

A planet orbiting a small star produces strong atmospheric signals when
it passes in front, or "transits," its host star. White dwarfs push
this to the extreme: They are 100 times smaller than our sun, almost as
small as Earth, affording astronomers a rare opportunity to characterize
rocky planets.

"If rocky planets exist around white dwarfs, we could spot signs of
life on them in the next few years," said corresponding author Lisa Kaltenegger, associate professor of astronomy in the College of Arts
and Sciences and director of the Carl Sagan Institute.

Co-lead author Ryan MacDonald, a research associate at the institute,
said the James Webb Space Telescope, scheduled to launch in October 2021,
is uniquely placed to find signatures of life on rocky exoplanets.

"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 discovery of the first transiting giant planet orbiting a white dwarf (WD 1856+534b), announced in a separate paper --
led by co-author Andrew Vanderburg, assistant professor at the University
of Wisconsin, Madison - - proves the existence of planets around white
dwarfs. Kaltenegger is a co- author on this paper, as well.



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This planet is a gas giant and therefore not able to sustain life. But
its existence suggests that smaller rocky planets, which could sustain
life, could also exist in the habitable zones of white dwarfs.

"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," MacDonald said. "It's a logical leap to imagine a rocky
planet like the Earth orbiting a white dwarf." The researchers combined state-of-the-art analysis techniques routinely used to detect gases in
giant exoplanet atmospheres with the Hubble Space Telescope with model atmospheres of white dwarf planets from previous Cornell research.

NASA's Transiting Exoplanet Survey Satellite is now looking for such
rocky planets around white dwarfs. If and when one of these worlds is
found, Kaltenegger and her team have developed the models and tools to
identify signs of life in the planet's atmosphere. The Webb telescope
could soon begin this search.

The implications of finding signatures of life on a planet orbiting a
white dwarf are profound, Kaltenegger said. Most stars, including our sun,
will one day end up as white dwarfs.

"What if the death of the star is not the end for life?" she 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."

========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Kate Blackwood.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lisa Kaltenegger, Ryan J. MacDonald, Thea Kozakis, Nikole K. Lewis,
Eric
E. Mamajek, Jonathan C. McDowell, Andrew Vanderburg. The White Dwarf
Opportunity: Robust Detections of Molecules in Earth-like Exoplanet
Atmospheres with the James Webb Space Telescope. The Astrophysical
Journal, 2020; 901 (1): L1 DOI: 10.3847/2041-8213/aba9d3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113604.htm

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