An exoplanet 111 light-years away may be a supersized version of Earth with conditions ripe for life.
According to Sci-News, the James Webb Space Telescope has detected carbon dioxide (CO2) and methane (CH4)—the "holy grail of potential biosignatures" astronomers seek on exoplanets—in the atmosphere of K2-18b.
This marks the first time an Earth-sized planet in the "habitable zone" of a star has been found to have an atmosphere indicative of possible life. The "habitable zone" is the area around a star where temperatures are neither too hot nor too cold for liquid water.
"This is the first temperate Earth-sized planet that we've found outside the solar system and now we know it has water," Angelo Tsiaras, an astronomer at University College London, told The Guardian.
The new study, led by astronomers at the University of Texas at Scarborough and the University of Montreal, Canada, draws on data from the European Southern Observatory (ESO). They also discovered for the first time that K2-18b has a neighboring planet, K2-18c. Both planets orbit the red dwarf star K2-18, 111 light-years from Earth in the constellation Leo.
Planet Profile
K2-18b orbits its host star every 22 days at a distance of 0.15 AU (astronomical units, where 1 AU is the distance between the Earth and the Sun). It has a companion, K2-18c, an exoplanet 7.5 times more massive than Earth, which is likely too hot for life.
Its distance from its parent star, a cooler star than our sun, gives K2-18b roughly 1.28 times the amount of sunlight as Earth, and an average temperature of -2° Celsius.
Another "golden nugget" of the discovery is the hint of dimethyl sulfide ((CH₃)₂S), which on Earth can only be produced by living organisms.
'False Alarm'
However, the new study argues that the dimethyl sulfide detection may be a false alarm.
Using computer models that accounted for the physical and chemical properties of dimethyl sulfide and K2-18b's hydrogen-dominated atmosphere, the researchers found that the James Webb data was unlikely to reflect the presence of this gas.
The signal for dimethyl sulfide overlaps strongly with that of methane. Tsai believes the current capabilities of the telescope do not allow to distinguish between the two.
Of course, methane is still a—albeit weaker—biosignature, and it is the dimethyl sulfide we need to see that can only be produced by living organisms.
Therefore, the new study dampens the excitement around the planet's habitability.
Nevertheless, there is hope for next year: the James Webb is expected to be equipped with an even more advanced infrared instrument sensitive enough to peer deeper into exoplanet atmospheres, including detecting dimethyl sulfide exclusively.
Summary
The James Webb Space Telescope has detected carbon dioxide and methane in the atmosphere of K2-18b, an exoplanet in the habitable zone of its star. This marks the first time such an Earth-sized planet has been found with an atmosphere indicative of potential life. However, a subsequent study suggests that the detection of dimethyl sulfide, a potential biosignature, may be a false alarm. Despite this, scientists remain optimistic as the James Webb is expected to be equipped with improved instrumentation in the future that could confirm the presence of this key molecule.