The James Webb Space Telescope (JWST), launched last December, has been
slowly powering up its instruments and unfurling its sunshield, and is now
in the process of aligning its mirrors in preparation for operation. Within
a few months, the most powerful space telescope ever built is going to set
its sights on the stars. Astronomers are hoping that what JWST sees will
change the way we understand our universe, just as the Hubble Space
Telescope did decades before.
One tantalizing capability that JWST offers that Hubble could not is the
opportunity to directly image planets orbiting distant stars, and maybe,
just maybe, detect signs of life.
The possibility of remotely detecting biosignatures has been a hot topic in
recent years. In our own solar system, the recent discovery of phosphine in
Venus' atmosphere sparked speculation that the chemical might be created by
a microbial lifeform. Similarly, remote sensing experts have proposed that
plant life—which uses photosynthesis for energy—could be detected in
infrared wavelengths, as chlorophyll absorbs visible light, but shows up
brightly in infrared, and would give planets covered in foliage a distinct
"red edge." A single-pixel photo of a distant planet just might contain
enough information to tell us if biological life is there, based on the
information stored in the wavelengths of light that reach the telescope
lens.
But what about intelligent life? Could JWST detect civilizations similar to
ours? How would we look for them? The best answers come from understanding
what humanity's presence on Earth looks like from outer space. We give off
waste heat (from industry and homes and so on) and artificial light at
night, but perhaps most significantly, we produce chemicals that fill our
atmosphere with compounds that wouldn't otherwise be present. These
artificial atmospheric constituents just might be the thing that gives us
away to a distant alien species scanning the galaxy with their own powerful
telescope.
A recent paper—available in preprint on ArXiv—examined the possibility of
using JWST to search for industrial pollutants in the atmospheres of
exoplanets. The paper focused specifically on chlorofluorocarbons (CFCs),
which, on Earth, are produced industrially as refrigerants and cleaning
agents. CFC's infamously created a massive hole in Earth's ozone layer in
the 1980s, before an international ban on their use in 1987 helped reduce
the level of CFCs back to less harmful levels. These "potent greenhouse
agents with long atmospheric residence times," if found elsewhere in the
galaxy, are almost certain to be the result of a civilization capable of
rampant industrialization.
In other words, some of humanity's worst byproducts—our pollution—may be the
very thing that makes us detectable. And it means that we may be able to
find other species capable of treating their own planet's atmosphere with
the same disregard.
There are some limitations to JWST's CFC finding capabilities. If a planet's
star is too bright, it will drown out the signal. The telescope will
therefore have the most success by looking at M-class stars, which are dim,
long-lived red dwarfs. A nearby example is TRAPPIST-1, a red dwarf 40
light-years away, with several Earth-sized planets orbiting within its
habitable zone. JWST would be able to see CFCs on TRAPPIST-1's planets,
because the dim star won't drown out the CFC signature in the same way that
a bright star, like our sun (a G-type star), would.
Conversely, a JWST-like telescope at TRAPPIST-1 wouldn't be able to see
Earth's CFCs: Our sun is just too bright.
Unfortunately, M-class stars are not usually conducive to life, because when
they are young, they are unstable, sending out powerful solar flares that
might just exterminate any nascent life on nearby planets. They do, however,
tend to calm down as they age, so it isn't an impossibility. It just means
that we should temper our expectations a bit.
Whatever we find, or don't find, out there, the fact that we are about to
have the capability to look at all is a game-changer. As the paper
concludes, "with the launch of JWST, humanity may be very close to an
important milestone in SETI [the Search for Extra-Terrestrial Intelligence],
one where we are capable of detecting from nearby stars not just powerful,
deliberate, transient, and highly directional transmissions like our own
(such as the Arecibo Message), but consistent, passive technosignatures of
the same strength as our own."
Reference:
Jacob Haqq-Misra, Ravi Kopparapu, Thomas J. Fauchez, Adam Frank, Jason T.
Wright, Manasvi Lingam. “Detectability of Chlorofluorocarbons in the
Atmospheres of Habitable M-dwarf Planets.” ArXiv preprint.
https://arxiv.org/abs/2202.05858
Tags:
Space & Astrophysics