Astronomers have identified an exoplanet, designated LHS 1140b, that exhibits the most Earth-like conditions discovered to date, significantly increasing the potential for finding extraterrestrial life. The planet orbits a red dwarf star approximately 48 light-years from Earth, a relatively close distance in astronomical terms.
According to a study published in Science, LHS 1140b meets critical criteria for habitability: it is the right temperature to sustain liquid water on its surface, possesses an atmosphere to retain that water, and is shielded from excessive radiation. These factors position it as a prime candidate for astrobiological research and the search for life beyond our solar system.
Planetary scientist Collin Cherubim of the University of Chicago, lead author of the study, explained that the presence of liquid water and a protective atmosphere are essential for a world to be considered potentially living. "LHS 1140b has all three of these things," Cherubim stated, highlighting its significance for habitability studies.
LHS 1140b was initially discovered in 2017 using the transit method, where astronomers detect the slight dimming of a star as a planet passes in front of it. The planet's diameter can be determined by the amount of light blocked, while its orbital period is revealed by the frequency of these transits. The radial velocity method, which detects the wobble of a star caused by a planet's gravity, was also employed to determine the planet's mass.
The planet orbits a red dwarf star, which is smaller and cooler than our sun. To maintain liquid water, planets orbiting red dwarfs must be situated in a close, yet temperate, zone. LHS 1140b orbits its star at a distance of about 9 million miles, roughly one-tenth of Earth's distance from the sun, completing an orbit every 24.7 days. The planet is approximately 1.7 times Earth's diameter and 5.6 times its mass.
Further investigation confirmed the presence of an atmosphere. Cherubim's computer model predicted that LHS 1140b would have an atmosphere and leak helium. Observations using the transit method detected absorption markers in the starlight filtering through the planet's atmosphere, confirming a helium bleed. While this helium atmosphere differs from Earth's nitrogen- and oxygen-rich atmosphere, Cherubim's models suggest the presence of other gases, including carbon dioxide, carbon monoxide, and potentially small amounts of molecular oxygen, along with significant amounts of water.
An additional favorable factor is the nature of LHS 1140b's host star. Red dwarfs can be volatile, emitting high levels of X-rays and ultraviolet energy that could sterilize a planet. However, LHS 1140, the star orbited by LHS 1140b, is relatively quiet, bathing the planet in only about 10 times the X-ray energy Earth receives. This level is not considered a significant threat to life as we know it.
While the presence of life on LHS 1140b is not confirmed, the discovery represents a significant step forward in the search for habitable exoplanets. The vast number of planets in the universe, combined with the discovery of worlds like LHS 1140b possessing Earth-like conditions, bolsters the possibility that life could emerge elsewhere.