One of the most important developments in astronomy has been the unbelievably successful
launch, deployment and commencement of the science mission of the James Webb Space Telescope.
It could be said that the telescope is off and running, making multiple observations
per day working through it’s catalog of time booked on the telescope by science teams
around the world.
And while the telescope is primarily designed to probe the earliest stages of the universe
and look at the most distant objects we’ve ever seen, it also offers much promise in
the search for extraterrestrial life.
The first development here highlights the possibilities for exoplanet research in that
JWST has already directly imaged an exoplanet.
Taking direct images of exoplanets has been difficult and has only been accomplished in
a handful of cases before.
The reason is that most exoplanets are discovered through indirect means, either through the
planet transiting its star and blocking out light, or through gravitational wobbling induced
on the parent star.
Actually imaging an exoplanet is much more difficult for a variety of reasons ranging
from being too close to their star to resolve to being too dim or otherwise difficult to
see.
But in
the case of giant planets, it can be more easily done.
In this case it’s an exoplanet known as HIP 65426b, and is about 12 times more massive
than Jupiter.
It’s also a remarkably young planet, only having formed a few tens of millions of years
ago from our perspective.
It was a known exoplanet since its discovery in 2017, and orbits very distantly from its
parent star making it an ideal candidate for direct imaging while blocking out the light
from the star with a mask.
While this is a gas giant, and not a rocky planet, and not a candidate for a biosphere,
it shows well the astonishing capabilities of JWST.
But with biospheres, just how will the telescope search for them, and what might it find?
The answer to this lies in just how light behaves when it passes through a planet’s
atmosphere.
The telescope will use the transit method for this, so when an exoplanet passes in front
of its parent star from our perspective, it not only will block light, its atmosphere
will also change the characteristics of the star’s light and reveal information about
the planet’s atmospheric composition.
It’s useful to think about Earth and what observers elsewhere in the galaxy might see
when they point their telescopes here.
If they were observing from billions of light years away, which is a thought experiment
as it’s highly unlikely anyone at that distance could resolve earth, but if they could they
wouldn’t see a biosphere.
Early on in the history of life on this planet our biosphere was made up of the very simplest
microbial life.
As a result, any biosignature earth was giving off during the early days is not likely to
have been visible at great distance.
This means that worlds with very faint, very primitive biosignatures are unlikely to be
spotted.
But then came the great oxygenation event about 2.4 billion years ago.
This was the advent of photosynthesis, and earth’s atmospheric makeup being increasingly
oxygenated.
This Webb can see.
Oxygen is highly reactive, you can see this with rusting iron and how fast that can happen.
This makes it very useful for complex biology, though simple biology often finds it poisonous.
But the reactivity of oxygen yields a strong biosignature.
Since it likes to react, any free oxygen must be constantly replenished in an exoplanet’s
atmosphere, or have nothing to react with.
As a result if you see high oxygen levels on a rocky exoplanet, there has to be a source,
and the source for it here on earth is photosynthesizing life.
If JWST detects this across its decade long run, we will have our first candidates for
a biosignature, and just maybe we may know that at least plant life, whether algae or
otherwise, is common or rare in the universe.
In short, we may be able to say we’re not alone in the universe as far as life goes,
but the rest may be left to the imagination, such as carnivorous alien death plants that
prevent further evolution by eating anything that gets to that level.
But there may be more.
There is also a peculiar feature in the infrared spectrum that earth exhibits.
It’s called the vegetative red edge, where earth’s plants become highly reflective
in infrared light.
Due to their cell structure, they become almost mirror-like, and it’s conceivable that JWST
might detect this.
In this case, we could infer the presence of chlorophyll directly, and then hypothesize
that we’re seeing analoges of perhaps complex plants.
But this all works within the framework of a rocky planet like earth.
We know what earth life does, but we don’t know what alien life is like so it’s possible
that biosignatures might be picked up by JWST that we’re unfamiliar with and haven’t
even thought of yet.
But there’s one area of great interest that presents a wildcard.
Super earths.
With previous instruments super earth’s were discovered ranging from twice the mass
of earth to ten times the mass of earth, but short of ice giant sized planets like Uranus
or Neptune.
Super earths have turned out to be very common, so much so that it’s now seen as a little
weird that our solar system doesn’t have one, though there have been suggestions that
the hypothesized planet nine that may lurk in the outer solar system may be a super earth
ejected from the inner solar system early in our system’s history.
It’s been an open question just how big a super earth can be and support life without
being too big.
The first concern obviously is that it has to be placed in the right area of it’s star
system, within the habitable zone.
But the bigger the mass, the more atmosphere it can hold onto, so this means thick atmospheres
for larger super earths, which is probably a show stopper for life as we know it at some
point.
Another question is the presence of a magnetic field, which is a complete unknown how common
or rare those are in exoplanets.
All we can really say here is that Earth has one, but Venus and Mars not so much.
It’s also possible that super earths have very strong and robust magnetic fields, or
it’s some mixed bag where some do, some do not.
Ultimately the best guess here is that only the smallest super earths, not much bigger
than twice the mass of earth could conceivably host life.
This would eliminate most super earths, but super earths again are very common so there
is still the possibility for habitable super earths.
And there are always earth analogues of a similar size to earth, which as we know represent
a very good class of planet for the possibility of life.
Smaller worlds however start to run into the problems of our own planets.
Mars was once habitable, and certainly had liquid water for a long period, but lost it
simply due to not being big enough to hold onto a thick earth-like atmosphere.
And, there is another aspect that’s recently come up that may alter the equation as to
whether a planet can harbor life.
It’s actually impacts, such as earth’s late heavy bombardment.
Recent work from NASA’s GRAIL spacecraft has shown that the moon actually has a really
porous surface, extending down at least 4 kilometers that’s on the order of 12 percent
empty space, and below that 4 percent.
That’s extremely porous, and quite surprising for the moon.
Models have shown that this is due to impacts, and is applicable to Earth, Mars and the moon.
Sustained impacts can apparently have long reaching effects on the overall porosity of
planets.
This means that earth’s crust as it originally was early in its history, was shattered, cracked
and pulverized very widely.
This may have an effect on life, providing cracks and voids for water and allowing for
microbial life to reproduce and spread, shielded to some degree from the massive impacts that
were going on during the late heavy bombardment.
This might explain why life on earth arose during that period, when it seems like the
environment should have been too harsh while under bombardment, and may also provide a
medium of water and volcanic glasses for RNA to arise, as recent work has shown how that
happens in such an environment.
It may well be that life on earth began underground.
And this is applicable to exoplanets because those conditions may be critical for abiogenesis,
and exoplanets that did not see as heavy of a bombardment may not have had the porosity
needed to life to easily get going.
But that brings us to another interesting aspect of JWST’s mission, its ability to
search for water.
The search for exoplanets with water has been progressing.
Recently an exoplanet known as Ross 508b was discovered orbiting just within the habitable
zone of its red dwarf parent star.
At just 37 light-years away, this super earth is really close, making it an excellent target
for study, and answering at least some of the questions of just how life-friendly red
dwarf star systems are.
While not a candidate for JWST due to the method of how it was discovered, this discovery
shows that our understanding of exoplanets and our ability to characterize them is increasing.
But there has also been a second discovery, and this one JWST can investigate further.
This exoplanet known as TOI-1452b is located in a binary star system made up of two red
dwarfs.
Discovered by the TESS satellite, this exoplanet is about 100 light-years away.
Importantly, this exoplanet transits in front of one of the red dwarfs, opening the way
for JWST to characterize its atmosphere.
And it’s actually turning out eerily earth-like.
This exoplanet has a diameter 1.67 times that of earth, but significantly more massive,
so is a super earth that orbits its host red dwarf every 11 days.
But there’s something strange.
Scientists working with the Canada-France-Hawaii telescope were able to determine the planet’s
bulk density.
The results were that something between 22 and 30 percent of the planet's mass seems
to be water.
Given its position within the habitable zone, this is likely to be liquid making this a
potential oceanic planet with a temperate climate.
This is by far the best candidate yet for an oceanic world, and a prime candidate for
JWST to search it’s atmosphere for biosignatures.
Indeed, if it were to come back that this planet has oxygen, then it would become a
serious question as to whether we’re looking at an algae planet.
But there are also pitfalls with observing exoplanets with JWST.
A method of confusing JWST’s exoplanet observations has been raised.
The uncertainty comes in with the possibility that any strange results JWST might come up
with, raises the possibility that the observation might be incorrect due to the presence of
two exoplanets in the same frame.
With two different planets confusing the spectrograph, it may yield confounding results in some observations.
As a result, this may make observations more difficult than what was envisioned.
But there may be ways around this kind of contamination, such as using multiple telescopes
to check results, or making observations over time to compare and determine if there is
contamination, and other methods.
So it’s not a show stopper per se, but rather something that will have to be taken into
account when interpreting exoplanet atmosphere data from JWST, and confirming observations
may become key.
In the end however, JWST promises many new exoplanet discoveries, and is already making
the observations.
Papers are already appearing on the JWST data, and it’s conceivable that we may not have
long to wait to see a candidate for a bio or technosignature.
On the other hand, if it keeps coming up blank, we’ll at least be able to start answering
the question as to whether life in the universe is common or rare, or may take forms we currently
can’t recognize or detect.
Interesting times ahead indeed.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently sensing a bit of
jealousy from The Hubble Space Telescope.
Well, not really, but you know it's there with JWST stealing its thunder after decades
as the top space telescope.
I guess we’ll know if unflattering Hubble images of JWST start coming down inexplicably
to be leaked to the public.
Very disturbing and be sure to check out my books at your favorite online book retailer
and subscribe to my channels to regular, in-depth explorations into the interesting, weird and
unknown aspects of this amazing universe in which we live.