“The Strongest Indication Yet of Extraterrestrial Life”
The for life Earth has scientists to many , from plumes of methane on Mars to clouds of phosphine gas on Venus. But as far as we can tell, Earth’s alone in the .
Now a team of is offering what it is the strongest indication yet of life, not in our system but on a massive planet, known as K2-18b, that orbits a star 120 -years from Earth. A analysis of the atmosphere an of a molecule that on Earth has only one known : living such as marine algae.
“It is in no one’s to that we have detected life,” said Nikku Madhusudhan, an astronomer at the University of and an of the new study, at a news conference on Tuesday. Still, he said, the best for his ’s observations is that K2-18b is covered with a warm , with life.
“This is a moment,” Dr. Madhusudhan said. “It’s the first time has seen potential on a habitable planet.”
The study was published Wednesday in the Astrophysical Journal Letters. Other called it an exciting, -provoking first step to making of what’s on K2-18b. But they were to draw grand .
“It’s not nothing,” said Stephen Schmidt, a planetary scientist at Johns Hopkins University. “It’s a . But we cannot conclude it’s yet.”
If there is extraterrestrial life on K2-18b, or anywhere else, its will arrive at a slow pace. “Unless we see E.T. at us, it’s not going to be a ,” said Christopher Glein, a planetary scientist at the Southwest Research Institute in San Antonio.
astronomers discovered K2-18b in 2017, while -based telescopes in . It was a type of planet outside our system, but one without any near Earth that scientists could study closely for .
These planets, known as , are much bigger than the rocky planets in our inner system, but smaller than Neptune and other gas-dominated planets of the system.
In 2021, Dr. Madhusudhan and his colleagues that sub-Neptunes were covered with warm of water and in atmospheres hydrogen, methane and other . To these strange planets, they a new term, “Hycean,” from a of the words “hydrogen” and “.”
The launch of the James Webb Space Telescope in December 2021 allowed astronomers a closer at sub-Neptunes and other planets.
As an passes in front its star, its atmosphere, if it has one, is illuminated. Its gases change the color of the starlight that reaches the Webb telescope. By these changing , scientists can the chemical of the atmosphere.
While K2-18b, Dr. Madhusudhan and his colleagues discovered it had many of the molecules they had a Hycean planet would possess. In 2023, they reported they had also detected of another molecule, and one of huge potential : dimethyl sulfide, which is made of sulfur, , and hydrogen.
On Earth, the only known of dimethyl sulfide is life. In the , for , forms of algae the compound, which into the air and to the sea’s distinctive odor. Long before the Webb telescope was launched, had whether dimethyl sulfide might as a of life on other planets.
Last year, Dr. Madhusudhan and his colleagues got a second to for dimethyl sulfide. As K2-18b orbited in front of its star, they a different on the Webb telescope to the starlight passing the planet’s atmosphere. This time they saw an stronger signal of dimethyl sulfide, along with a molecule called dimethyl disulfide.
“It is a to the system,” Dr. Madhusudhan said. “We spent an enormous amount of time just trying to get rid of the signal.”
No matter how the scientists their readings, the signal stayed strong. They concluded that K2-18b may in fact a of dimethyl sulfide in its atmosphere, thousands of times higher than the on Earth. This would that its Hycean seas are with life.
Other emphasized that much to be done. One question yet to be is whether K2-18b is in fact a habitable, Hycean world as Dr. Madhusudhan’s team .
In a paper online Sunday, Dr. Glein and his colleagues argued that K2-18b could instead be a massive hunk of with a magma and a thick, hydrogen atmosphere — hardly to life as we know it.
Scientists will also need to run to make of the new study — to recreate the possible on sub-Neptunes, for , to see whether dimethyl sulfide there as it does on Earth.
“It’s important to remember that we’re just starting to the of these worlds,” said Matthew Nixon, a planetary scientist at the University of Maryland who was not in the new study.
Researchers want to wait to see what the Webb telescope finds as it to K2-18b; early findings sometimes fade in the of data. NASA has been and building more space telescopes that will specifically for of on planets orbiting other stars, K2-18b. Even if it takes years to what’s on K2-18b, it could be it, scientists said.
“I’m not , ‘aliens!’” said Nikole Lewis, an scientist at Cornell University. “But I always my right to ‘aliens!’”