Science & Technology

Nearby ‘Super-Earth’ could harbour life

Only 31 light-years away from Earth, the exoplanet GJ 357 d catches light from its host star GJ 357, in this artistic rendering. (
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A ‘Super-Earth’ discovered by NASA’s TESS mission, closer to Earth than any other yet found, could potentially host life.

NASA’s Transiting Exoplanet Survey Satellite (TESS), a mission designed to comb the heavens for exoplanets, has discovered its first potentially habitable world outside of our own solar system – and an international team of astronomers has characterized the super-Earth, about 31 light-years away.

The team led by Lisa Kaltenegger, associate professor of astronomy and director of Cornell’s Carl Sagan Institute, models the conditions under which the planet — discovered in early 2019 — could sustain life. The findings are detailed in a paper published in the journal The Astrophysical Journal Letters.

Kaltenegger says: “This is exciting, as this is humanity’s first nearby super-Earth that could harbour life – uncovered with help from TESS, our small, mighty mission with a huge reach.

“If GJ 357 d were to show signs of life, it would be at the top of everyone’s travel list – and we could answer a 1,000-year-old question on whether we are alone in the cosmos.”

In addition to the question of supporting life, as this super-Earth exoplanet is more massive than our own blue planet, it will provide insight into Earth’s heavyweight planetary cousins, says Kaltenegger.

She adds: “With a thick atmosphere, the planet GJ 357 d could maintain liquid water on its surface like Earth and we could pick out signs of life with upcoming telescopes soon to be online.”

Tour the GJ 357 system, located 31 light-years away in the constellation Hydra. Astronomers confirming a planet candidate identified by NASA’s Transiting Exoplanet Survey Satellite subsequently found two additional worlds orbiting the star. (NASA)

Astronomers from the Institute of Astrophysics of the Canary Islands and the University of La Laguna, both of Spain, announced the discovery of the system July 31st in the journal Astronomy & Astrophysics.

They showed that the distant solar system – with a diminutive M-type dwarf sun, about one-third the size of our own sun – harbours three planets, with one of those in that system’s habitable zone: GJ 357 d.

Last February, the TESS satellite observed that the dwarf sun GJ 357 dimmed very slightly every 3.9 days, evidence of a transiting planet moving across the star’s face. That planet was GJ 357 b, a so-called “hot Earth” about 22% larger than Earth, according to the NASA Goddard Space Flight Center, which guides TESS.

Follow up observations from the ground led to the discovery of two more exoplanetary siblings: GJ 357 c and GJ 357 d. The international team of scientists collected Earth-based telescopic data going back two decades – to reveal the newly found exoplanets’ tiny gravitational tugs on its host star, NASA says.

Exoplanet GJ 357 c sizzles at 260 degrees Fahrenheit and has at least 3.4 times Earth’s mass. However, the system’s outermost known sibling planet – GJ 357 d, a super-Earth – could provide conditions just like on Earth and orbits the dwarf star every 55.7 days at a distance about 20% of Earth’s distance from the Sun.

It is not yet known if this planet transits its sun.

Kaltenegger, doctoral candidate Jack Madden and undergraduate student Zifan Lin simulated light fingerprints, climates and remotely detectable spectra for the planet, which could range from a rocky composition to a water world.

Madden explains how investigating new discoveries provide an opportunity to test theories and models: “We built the first models of what this new world could be like.

“Just knowing that liquid water can exist on the surface of this planet motivates scientists to find ways of detecting signs of life.”

Featured image caption and credit: Only 31 light-years away from Earth, the exoplanet GJ 357 d catches light from its host star GJ 357, in this artistic rendering. Jack Madden/Cornell University

Original research: https://iopscience.iop.org/article/10.3847/2041-8213/ab2769

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