https://archive.is/ApwLm

New observations fail to confirm signs of life
in the atmosphere of the distant planet K2-18b.
They also raise questions about what it will
take to detect biology light-years away.

In April, a team of scientists based at the
University of Cambridge claimed that a planet
orbiting a distant star bore a possible
signature of life. The announcement kicked up
a fierce debate among astronomers, with many
skeptics arguing that the evidence was too
ambiguous.

Now a NASA-led team has made a new set of
observations of the planet known as K2-18b,
which lies 124 light-years from Earth. They
have provided a clearer picture of the planet
— confirming the presence of water, perhaps
even as a liquid ocean.

But the new observations have failed to confirm
evidence for life. In the original study, the
Cambridge team claimed that K2-18b appeared to
have a gas in its atmosphere that on Earth is
produced only by living things. The NASA study
did not find strong evidence for that gas.

What’s more, the NASA team argues that even if
the gas was on K2-18b, it might have formed
through mere chemistry. What once seemed like
a promising clue of life — a biosignature —
might be a mirage.

“A key takeaway is that biosignatures are going
to be hard, no matter what kind of planet we
are talking about,” said Jacob Bean, an
astronomer at Cornell University, who was not
involved in the study.
...

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