TESS Finds First Nearby Super-Earth (and it may be Habitable)
The Transiting Exoplanet Survey Satellite (TESS) has found its first super-Earth near our solar system. This world, GJ 357 d, also orbits within the habitable zone of the star, where temperatures are neither too hot, nor too cold, for water to pool on its surface, potentially filling oceans.
The star around which this world (and at least two others) orbit, GJ 357, is an M-type star, one-third the size and mass of our Sun, and 40 percent cooler. This system is found just 31 light years from Earth, in the direction of the constellation Hydra.
“This is exciting, as this is humanity’s first nearby super-Earth that could harbor life — uncovered with help from TESS, our small, mighty mission with a huge reach,” Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University stated.
Astronomers utilizing NASA’s TESS space observatory noticed periodic dimming in light coming from GJ 357. The effect, first seen in February 2019, repeated once every 3.9 days. This finding led to the discovery of three worlds, the outer most of which which may be habitable.
“In a way, these planets were hiding in measurements made at numerous observatories over many years. It took TESS to point us to an interesting star where we could uncover them,” said Rafael Luque, a doctoral student at the Institute of Astrophysics of the Canary Islands (IAC) on Tenerife.
Getting to Know the Neighbors
The innermost of the trio of exoplanets, GJ 357 b, is just 22 percent larger than the Earth. However, an orbit just nine percent of the distance between the Sun and Mercury heat this world to unbearable temperatures. Even without an atmosphere to raise temperatures, this world would have a surface temperature of 254 degrees Celsius (490 Fahrenheit) — as hot as a broiler! It was this “hot Earth” that triggered the attention of astronomers in February.
The middle planet of the system, GJ 357 c, orbits is stellar parent once every 9.1 days, at a distance just twice that of its broiler-hot sibling. Even at this distance from its sun, temperatures without an atmosphere would hover around 127 C (260 F) — too hot for life as we know it.
If GJ 357 d were composed mostly of rock, the world would be around twice the size of our home world. This super-Earth has a mass more than six times greater than our home world, and it orbits its sun once every 55.7 days. The amount of sunlight it would receive from its parent star would be comparable to the amount of light received from the Sun by Mars. Without an atmosphere, this planet would have a temperature of -53 C (-64 F).
“GJ 357 d is located within the outer edge of its star’s habitable zone… If the planet has a dense atmosphere, which will take future studies to determine, it could trap enough heat to warm the planet and allow liquid water on its surface,” Diana Kossakowski of the Max Planck Institute for Astronomy in Heidelberg, Germany, stated.
“A time will come when men will stretch out their eyes. They should see planets like our Earth.”
― Christopher Wren, Scientist, 1632–1723
Eyes on the Prize
Only the innermost planet, GJ 357 b, was found through the transit method, as that world passed between its sun and our line-of-sight. The two outer planets were discovered from the gravitational tug they have on their companion star. This is known as the radial velocity method of detecting exoplanets.
“However, only eleven M dwarf planet systems have been detected with both the transit as well as the radial velocity method, which allows us to derive their density from their measured radius and mass,” researchers describe in a journal article published in Astronomy & Astrophysics.
Will this be on the TESS?
The TESS spacecraft was designed to survey the sky, searching for planets passing between their sun and our solar system, revealing their location. Since its launch in April 2018, TESS has discovered 24 confirmed planets, as well as 993 candidate worlds, awaiting further study. During its planned two-year mission, TESS is expected to find 20,000 worlds orbiting other stars to add to the 4,000 exoplanets already known to astronomers.
Data from TESS was matched with observations obtained by other instruments since 1998, confirming the finding.
Astronomers hope to study any atmosphere of the worlds within the GJ 357 system, using the upcoming Extremely Large Telescopes (ELT’s) and the James Webb Space Telescope, due for launch in March 2021. This research could reveal signs of life, even primitive lifeforms, on that not-so-distant world.
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