This news seemed so major that I bumped things to get it on my blog within a week of it coming out.
https://www.nytimes.com/2025/04/16/science/astronomy-exoplanets-habitable-k218b.html
Astronomers Detect a Possible Signature of Life on a Distant Planet
Further studies are needed to determine whether K2-18b, which orbits a star 120 light-years away, is inhabited, or even habitable.
The search for life beyond Earth has led scientists to
explore many suggestive mysteries, from plumes
of methane on Mars to clouds
of phosphine gas on Venus. But as far as we can tell, Earth’s inhabitants
remain alone in the cosmos.
Now a team of researchers is offering what it contends is
the strongest indication yet of extraterrestrial life, not in our solar system
but on a massive planet, known as K2-18b, that orbits a star 120 light-years
from Earth. A repeated analysis of the exoplanet’s atmosphere suggests an
abundance of a molecule that on Earth has only one known source: living
organisms such as marine algae.
“It is in no one’s interest to claim prematurely that we
have detected life,” said Nikku Madhusudhan, an astronomer at the University of
Cambridge and an author of the new study, at a news conference on Tuesday. Still, he
said, the best explanation for his group’s observations is that K2-18b is
covered with a warm ocean, brimming with life.
“This is a revolutionary moment,” Dr. Madhusudhan said.
“It’s the first time humanity has seen potential biosignatures on a habitable
planet.”
The study was published Wednesday in the Astrophysical
Journal Letters. Other researchers called it an exciting, thought-provoking
first step to making sense of what’s on K2-18b. But they were reluctant to draw
grand conclusions.
“It’s not nothing,” said Stephen Schmidt, a planetary
scientist at Johns Hopkins University. “It’s a hint. But we cannot conclude
it’s habitable yet.”
If there is extraterrestrial life on K2-18b, or anywhere
else, its discovery will arrive at a frustratingly slow pace. “Unless we see
E.T. waving at us, it’s not going to be a smoking gun,” said Christopher Glein,
a planetary scientist at the Southwest Research Institute in San Antonio.
Astronomers discovered K2-18b in 2015, using data from the
Kepler Space Telescope. It was a type of planet commonly found outside our
solar system, but one without any analog near Earth that scientists could study
closely for clues.
These planets, known as sub-Neptunes, are much bigger than
the rocky planets in our inner solar system, but smaller than Neptune and other
gas-dominated planets of the outer solar system.
In 2021, Dr. Madhusudhan and his colleagues proposed that
sub-Neptunes were covered with warm oceans of water and wrapped in atmospheres
containing hydrogen, methane and other carbon compounds. To describe these
strange planets, they coined a new term, “Hycean,” from a combination of the
words “hydrogen” and “ocean.”
The launch of the
James Webb Space Telescope in December 2021 allowed astronomers a
closer look at sub-Neptunes and other distant planets.
As an exoplanet passes in front of its host star, its
atmosphere, if it has one, is illuminated. Its gases change the color of the
starlight that reaches the Webb telescope. By analyzing these changing
wavelengths, scientists can infer the chemical composition of the atmosphere.
While inspecting K2-18b, Dr. Madhusudhan and his colleagues
discovered it had many of the molecules they had predicted a Hycean planet
would possess. In 2023, they reported they had also detected faint hints of another molecule, and one of huge
potential importance: dimethyl sulfide, which is made of sulfur, carbon, and
hydrogen.
On Earth, the only known source of dimethyl sulfide is life.
In the ocean, for instance, certain forms of algae produce the compound, which
wafts into the air and adds to the sea’s distinctive odor. Long before the Webb
telescope was launched, astrobiologists had wondered whether dimethyl sulfide
might serve as a sign of life on other planets.
Last year, Dr. Madhusudhan and his colleagues got a second
chance to look for dimethyl sulfide. As K2-18b orbited in front of its star,
they used a different instrument on the Webb telescope to analyze the starlight
passing through the planet’s atmosphere. This time they saw an even stronger
signal of dimethyl sulfide, along with a similar molecule called dimethyl
disulfide.
“It is a shock 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 revisited their readings, the
signal stayed strong. They concluded that K2-18b may in fact harbor a
tremendous supply of dimethyl sulfide in its atmosphere, thousands of times
higher than the level found on Earth. This would suggest that its Hycean seas
are brimming with life.
Other researchers emphasized that much research remained to
be done. One question yet to be resolved is whether K2-18b is in fact a
habitable, Hycean world as Dr. Madhusudhan’s team claims.
In a paper posted online Sunday, Dr. Glein and his
colleagues argued that K2-18b could instead be a massive hunk of rock with a
magma ocean and a thick, scorching hydrogen atmosphere — hardly conducive to
life as we know it.
Scientists will also need to run laboratory experiments to
make sense of the new study — to recreate the possible conditions on
sub-Neptunes, for instance, to see whether dimethyl sulfide behaves there as it
does on Earth.
“It’s important to remember that we’re just starting to
understand the nature of these exotic worlds,” said Matthew Nixon, a planetary
scientist at the University of Maryland who was not involved in the new study.
Researchers want to wait to see what the Webb telescope
finds as it continues to examine K2-18b; provocative early findings sometimes
fade in the light of additional data. NASA has been designing and building more
powerful space telescopes that will look
specifically for signs of habitability on planets orbiting other stars,
including K2-18b. Even if it takes years to decipher what’s happening on
K2-18b, it could be worth it, scientists said.
“I’m not screaming, ‘aliens!’” said Nikole Lewis, an
exoplanetary scientist at Cornell University. “But I always reserve my right to
scream ‘aliens!’”
But Joshua Krissansen-Totton, an astrobiologist at the
University of Washington, said he worried that American astrobiologists may not
be able to follow up on the latest results on K2-18b.
The Trump administration is reportedly planning to cut NASA’s science budget in half,
eliminating future space telescope and other astrobiology projects. If that
happens, Dr. Krissansen-Totton said, “the search for life elsewhere would
basically stop.”
A correction was made on
April 17, 2025
:
An earlier version of this article misstated the name of
a scientific journal. It is Astrophysical Journal Letters, not Astrophysics
Journal. The article also misstated the year and manner in which the planet
K2-18b was discovered; it was 2015 using data from the Kepler Space Telescope,
not 2017 using ground-based telescopes in Chile.
When we learn of a mistake, we acknowledge it with a
correction. If you spot an error, please let us know at nytnews@nytimes.com.Learn
more
Carl
Zimmer covers news about science for The Times and writes
the Origins column.
A version of this article appears in print on April 19,
2025, Section A, Page 16 of the New York edition with the
headline: Astronomers Detect a Possible Signature of Life on a Distant
Planet.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
