In a universe of seemingly infinite scale and countless wonders,
it’s curious that the thing we're most hunting for is ourselves;
to discover that we are not alone.
Just 40 light-years away, in the constellation of Aquarius,
lies a tiny, dim star: TRAPPIST-1.
It’s cold, ancient, and barely visible.
And yet, it hosts something extraordinary - not one, but seven Earth-sized planets.
It’s as if nature itself set up an experiment: can life exist around a star like this?
One by one, scientists have ruled out most of these worlds as being habitable.
Too hot. Too cold. No atmosphere. No chance.
But one world still holds promise: TRAPPIST-1e.
And now, thanks to data from the James Webb Space Telescope,
we may finally have a glimpse of its atmosphere.
What we’ve found… is astonishing.
Could this be the first true Earth-like planet beyond our Solar System?
Could TRAPPIST-1e host life?
I’m Alex McColgan and you’re watching Astrum.
Join me today as we travel to the TRAPPIST-1 star system
to explore the potential for life on its most promising planet.
We’ll look at new data from the James Webb Space Telescope that has pushed it to its limit,
revealing the likely composition of TRAPPIST-1e’s atmosphere
and whether it could support life.
That is, if the very star that offers the chance of life hasn’t also issued a death sentence.
TRAPPIST-1 is an M8 class red dwarf.
Only a little larger than Jupiter, it’s 1800 times less luminous than our Sun -
a difference that’s like comparing a candle to a college running track floodlight.
Although the star was first discovered in 1999, its full planetary lineup wasn’t
revealed until 2017, when it became the first - and only - planetary system to be discovered by
the TRAPPIST optical robotic telescope. This telescope is made up of two parts:
TRAPPIST South in the Chilean mountains, and TRAPPIST North in Morocco’s Atlas Mountains.
They use transit photometry, a technique that measures periodic changes in the brightness
of a star, to find orbiting planets. In other words, if a planet passes between us and the star,
then some of its light is blocked and so we detect a dip in the star’s apparent output.
By taking multiple observations, the telescopes were able to isolate the individual orbits of
multiple planets around TRAPPIST-1. Initially their data analysis only found the three innermost
planets. But further data from both of the TRAPPIST telescopes as well as the Spitzer
Infrared Space Telescope took this total to seven. And not only that, but they are all rocky, and
all, at least roughly, Earth-sized, making this the most Earth-like planets found around any star.
If you’d like to know more about all the individual planets around TRAPPIST-1,
I made a video about them - you can check it out at the link on screen.
But with such a small dim star at the centre,
is there really any hope that they could be habitable?
For any of these planets to receive enough light to support life,
the orbits need to be much closer than we are to our Sun. In the TRAPPIST-1 system,
the planets certainly are: in fact, all seven are incredibly close.
TRAPPIST-1e orbits at only 1/13 th of Mercury’s orbit, which means it could be tidally locked to
its host star, the same side of the planet facing the star at all times - just like we only ever see
one side of our own moon. This has significant implications for the habitability of the planet,
and we’ll dive into those later in the video. But more interestingly,
its orbital distance also means that it is right in the middle of the predicted habitable zone,
where it receives about 2/3rds of the energy that we do from our Sun,
and that is why scientists are so curious about this planet.
But it takes more than light for life to thrive,
TRAPPIST-1e would almost certainly need an atmosphere so that’s exactly
what scientists have been looking for… using our most powerful space-based telescope - James Webb.
The teams who were involved with developing James Webb were rewarded with guaranteed
observation time. One group, “The Deep Reconnaissance of Exoplanet Atmospheres
through Multi-instrument Spectroscopy” – that’s right,
The DREAMS team – immediately wanted to set James Webb’s sights on the TRAPPIST-1 system.
The James Webb telescope is uniquely sensitive and precise - so much so
that it can detect spectral signatures from the thin band of gas that makes
up the atmospheres of these planets, a whole 40 light years from our own.
It does this thanks to a technique called transmission spectroscopy.
As an exoplanet passes its mother star, James Webb not only measures the drop in brightness,
but also how the spectrum of light changes.
The telescope’s near-infrared spectrometer, or NIRSpec for short, measures the wavelengths of
infrared radiation closest to the visible spectrum. Molecular bonds absorb energy
in this range and different bonds, like this carbon-hydrogen bond in methane,
or this carbon-oxygen double bond in carbon dioxide, absorb different wavelengths. It
means that by measuring which wavelengths are absorbed as a planet transits its star, we can
first of all work out if there is an atmosphere and then if so, determine which gases are present.
And it’s been particularly easy to get a read at TRAPPIST-1,
in fact the data we have is 10 times more sensitive than what we have on any other system.
Why? Counterintuitively, it’s because the star is relatively dim. The light a planet
obscures causes a bigger relative drop in apparent brightness of this star than the
same planet passing in front of a large bright star. A bigger difference is easier to measure.
Using these measurements, the team have already discounted TRAPPIST-1c and d from
having atmospheres. But results from observations of TRAPPIST-1e, a rocky planet around 0.9 times
the size of Earth, were so intriguing that scientists couldn’t ignore them - it looked
like this planet may, in fact, have an atmosphere. And that was more than enough evidence for the
DREAMS team to decide to use up all their guaranteed JWST time trying to find more.
So far they’ve seen four TRAPPIST-1e transits with James Webb. But what did they find?
Well, we can start by discounting a few possibilities. We now know that
TRAPPIST-1e does not have a primordial atmosphere - one a planet is born with.
These are usually dominated by light gases like helium and hydrogen, which haven’t been
detected. They were likely stripped away by the star’s radiation, early on in its life.
Nor does it seem to have a carbon dioxide dominant atmosphere like Venus, which is thick and dense.
An atmosphere like that of Mars, which is thin and sparse, is also unlikely
given the recent measurements. Believe it or not, all of this is good news as it’s
unlikely that any of these atmospheres could support life, well not as we know it anyway.
So what atmosphere does it have?
Well, here’s the big one: there could be an Earth-like atmosphere - one dominated
by a heavier gas such as nitrogen, with a strong greenhouse effect, from water,
carbon dioxide or methane. Such an atmosphere with a surface pressure of
around 1 bar - equivalent to Earth’s - may be able to sustain enough heat transfer to
the dark side of the planet to allow a global surface ocean, despite it being tidally locked.
Were this confirmed, that would make headlines the world over.
However, that might be too much to ask. The data instead slightly
favours the idea that TRAPPIST-1e is a cold planet without a global ocean.
Analysing the data correctly here is key. Being able to understand what we’re
seeing - and what it means - is the difference between
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But if you’re a scientist tasked with data analysis, don’t worry,
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Let's go back to TRAPPIST-1e. As I mentioned, there is an alternative
to an Earth-like atmosphere. High levels of methane instead create a reverse greenhouse
effect. TRAPPIST-1 has a surface temperature of about 2400K, much cooler than our Sun’s 5670K,
and more of the energy it outputs is shifted to the near infrared wavelengths. Atmospheric
methane can absorb that energy before it even reaches the surface of the planet,
then re-emit it into space, resulting in a cooler atmosphere. For the tidally-locked TRAPPIST-1e,
this would mean that liquid water may only exist on the surface of the planet that permanently
faces the star. No global ocean here. But that’s not necessarily bad news for life either…
such conditions could satisfy Darwin’s ‘warm little pond’ hypothesis of the Origin of Life.
And atmospheric modelling has backed this up. Simulations suggest that even if TRAPPIST-1e
has limited water, or if what water there is is locked on the dark side of the planet,
it could still have a stable atmosphere.
Although, this may lead to what’s known as “terminator habitability” - where life
could only find a home across a dynamic band in perpetual twilight that separates day from night.
But water on the surface isn’t the only option… we know TRAPPIST-1e is rocky,
but not much more than that. It may be an icy volcanic planet with a sub-surface ocean,
like we find on Europa and Enceladus in our own solar system. Life on Earth is believed
by some to have formed near deep-sea vents and the same process could happen on 1e.
No matter where on TRAPPIST-1e water may be, life is possible - there’s an
energy source and potentially an atmosphere that provides the building blocks for life.
But there is one issue. Although all these things are possible,
scientists can’t yet completely rule out the possibility that TRAPPIST-1e is a cold,
barren and airless marble with no atmosphere at all.
So, we need to talk about what could prevent a stable atmosphere from ever
forming. And in this case it’s the red dwarf star TRAPPIST-1 itself.
Imagine standing with me on TRAPPIST-1e, just for a second. Look up. The star above us would appear
more than 4 times as large as our Sun in the sky. The star would be a deep red-orange colour,
illuminating the sky as if it were in perpetual sunset. What a sight that would be. Now, red
dwarfs are extremely active and they produce more powerful flares than our Sun, and more often too..
The worst recorded geomagnetic storm ever to hit earth was the Carrington Event in 1859, a greater
than 1-in-100 year event. TRAPPIST-1 is believed to release a flare this powerful more than once
every two days. You’d likely be able to watch solar flares arcing out into space in real time.
And they carry huge amounts of energy towards a planet, enough that over
time any atmosphere could be stripped away, making life as we know it all but impossible.
That’s assuming that the atmosphere was ever allowed to form at all. Red Dwarfs
are stupendously long lived. TRAPPIST-1 is expected to exist for 10 trillion more years.
That is 700 times the current age of the universe. By comparison,
our Sun likely has only 5 Billion years left before it becomes a red giant. You might think
given the stability and lifespan of a red dwarf, there would be plenty of time for
life to find a way. But because of their long lives, their chaotic and energetic
‘teenage’ years before red dwarf stars settle down are correspondingly longer.
It’s during these formative years that some planets begin to produce their own atmosphere,
slowly replacing their primordial hydrogen-helium atmosphere,
with one comprised of heavier molecular gases, such as carbon dioxide, nitrogen and methane.
These chemicals are released from inside the planet through volcanic activity. The problem is,
if the aggressive atmosphere-stripping phase of a star lasts too long, then an Earth sized
planet might not have enough resources within its interior to fully generate a stable,
life-supporting secondary atmosphere. The unfortunate reality is that if a
planet’s atmosphere isn’t established before 5 billion years, it may never generate one,
condemning the planet to a death sentence before it was ever allowed to live.
I know, it’s actually sounding rather hopeless for TRAPPIST-1e,
and I bet you’re wondering “How is this one of the most promising planets?!”
But we don’t yet know one way or the other, whether an atmosphere has survived or not…
we’ve already seen there are hints of its existence. And although the star's violent
outbursts may be 1e’s downfall, they may also be completely necessary for life to begin.
UV radiation from flares may be essential to create RNA building blocks; molecules that
are central to the metabolism of every life form ever found. And now that TRAPPIST-1 is
in its calmer main-sequence phase, with lower UV and X-Ray irradiation than in its juvenile past,
there is a chance of a stable, habitable atmosphere existing on TRAPPIST-1e.
And that atmosphere could have protection from the continuing flares with its own magnetic field,
just like the Earth does. The Earth’s magnetic field exists because its outer core is a moving
mass of molten iron and nickel. There is a good chance that TRAPPIST-1e has a similar system.
In fact, TRAPPIST-1e’s close orbit to the red dwarf could actually help
maintain its magnetic field. If TRAPPIST-1e’s orbit is eccentric,
this would cause repeated compression and relaxation of the planet's shape. This
process creates internal friction that could heat the interior as much as 0.18 watts per
metre squared. That’s roughly 24 times the tidal heating flux generated in the Earth.
We see a similar process in Jupiter’s moon Io. Io is tidally locked with an eccentric orbit, and
gets stretched and squashed by the gravitational interactions with the other Jovian moons,
pumping it full of energy and making it the most volcanically active body in the solar system.
So where does this leave us? Well we may have an Earth-sized, volcanically active,
rocky planet with the building blocks for life, its own atmosphere and magnetic field,
orbiting in the habitable zone of a relatively calm red dwarf. Or it could be a cold dead world.
So, let us know in the comments which scenario you think will eventually be confirmed!
We might not get an answer until the proposed Habitable Worlds Observatory - a telescope
designed to look for life around stars like our own - which launches in 2041,
but until then, James Webb’s observations are our best bet.
The fact we are able to measure the light absorbed by a thin gaseous layer around a
rocky planet, orbiting a dim red dwarf star 40 light years away is pretty incredible!
And scientists haven’t given up hope.
They’ve learned from the first sets of James Webb data and modified their technique to achieve more
precise measurements. With another fifteen transit observations planned before December,
they expect to be able to confirm the presence or absence of carbon dioxide,
and a secondary atmosphere. A key step in the search for life on 1e.
Perhaps TRAPPIST-1e and its neighbours will turn out to have a unique inhospitable
atmosphere, or perhaps one that could theoretically support life. Or maybe,
just maybe, we’ll find one just like home.
It’s exciting to find so much potential for life relatively nearby, even in the
midst of an extreme environment. But whatever the atmosphere turns out to be on TRAPPIST-1e,
with the recent discovery of formations on Mars that are thought to have been
impossible to form without life, I find it hard to shake the feeling that the
discovery of extra terrestrial life feels inevitable. The only question is - when?