This is Exoplanet Radio.
I'm Tony Darnell.
In recent years, scientists have made great
strides in the search for extraterrestrial
life.
They have discovered thousands of exoplanets,
and some of them are located in the habitable
zone of their star, which means that
liquid water could exist on their surface and is
essential for life as we know it.
The search for life, however, is a little
more involved than finding planets, measuring
their location and distance around the star,
and figuring out their location within a habitable
zone.
Astronomers need more information to learn if life may be there.
The first thing we need to know is whether or
not the planet has an atmosphere, and thanks
to the Webb Space Telescope, we are starting
to get a handle on that data point with every
observation it makes using its onboard near-infrared spectrometer.
Once astronomers detect an atmosphere, the real fun begins - finding biosignatures.
Biosignatures are indicators of the presence
of life, traces left behind by living organisms.
These indicators can be chemical, biological, or physical.
An example of a physical biosignature would
be things like fossils, and since that requires
that we have a physical presence on the
planet, we can't see those from here, not even with
JWST, then we are left with chemical and biological indicators.
The best examples of biosignatures that we
can detect from so far away are atmospheric
gases and organic molecules.
Certain gases, such as oxygen and methane, can be produced by biological processes.
However, they can also be produced by non-biological means.
For example, oxygen can be produced by
photosynthesis, but it can also be produced by geological activity.
The presence of atmospheric gases in a
planet's atmosphere could be a sign of life, but it
is important to consider other evidence as well, like organic compounds.
Organic molecules are the building blocks of life.
They include amino acids, lipids, carbohydrates, and nucleic acids.
Organic molecules can be detected in the
atmospheres of exoplanets using a technique
called transit spectroscopy.
Spectroscopy involves splitting light into its component wavelengths.
Organic molecules absorb light at specific
wavelengths, so by looking for dips in the
spectrum of an exoplanet, scientists can
identify the presence of organic molecules.
JWST is currently the best instrument we
have that can detect biosignatures in this way.
It looks at absorbed starlight that has
passed through the exoplanet's atmosphere to see
what elements were absorbed.
Just recently, it reported the possibility
of the organic molecule dimethylsulfide in
the planet K2-18b, a compound that on Earth
is produced primarily by phytoplankton, which
are microscopic organisms that live in the ocean.
Dimethylsulfide can also be produced by
some other biological processes, but it is not
known to be produced by anything other than life.
Dimethylsulfide is a gas, so it can be detected in
the atmospheres of exoplanets using spectroscopy.
It is also relatively stable in the
atmosphere, so it can accumulate to detectable levels.
All this makes dimethylsulfide an ideal biosignature gas.
It's important to note that the detection
of a single biosignature is not definitive
evidence of life.
However, the presence of multiple biosignatures
in the same place would be very strong evidence.
Additionally, if a biosignature is detected
in a place where it is unlikely to be produced
by non-biological processes, such as, say,
in a Martian meteorite, then it is more likely
to be a sign of life.
The James Webb Space Telescope and the future
Habitable Worlds Observatory are two powerful
tools that we have to search for life on other planets.
Imagine the day when we discover signs of life beyond Earth.
It would be a watershed moment in human
history, one that would change our understanding of
our place in the universe forever.
Exoplanet Radio is produced by Deep
Astronomy. The music is by Geodesium and available at
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