This is an update in my continuing coverage of the Trappist
-1 system, a fascinating solar system that could host up to 7 roughly
earth-sized planets where the conditions could be right for liquid water, and
thus hold the potential for life. See my other videos on this channel for more
back story.
When I was a kid sitting in grade school science classes in
the 1980's, I remember two scientific consensuses that stick in my mind to this
day. One was that even though we had never seen one, or indeed any evidence of
one, exoplanets outside our solar system almost certainly existed. There was no
reason why they shouldn't, all you need to form them is a sufficient amount of
solid material around a star to coalesce into planets. And that clearly
happened here, so unless rocks and dust were rare in the universe it was a good
bet that it happened elsewhere.
That consensus turned out to be correct, in 1992 the
existence of an exoplanet was confirmed and since those days we have discovered
evidence of well over 3000 planets not located in our solar system scattered
among a wide variety of stars in our galaxy.
The other consensus that I remember was that, at the time,
there wasn't any particular reason to think that Earth was rare. Indeed, blue
jewel worlds like our own could populate the universe to such an extent that
there could be untold thousands of civilizations in our galaxy alone allowing
for science fiction universes like Star Trek where the discovery and contact of
such civilizations was a routine, and often unpleasant and tricky, occurrence.
After all, if exoplanets turned out to be common, then why
not? What would be so special about Earth? On its face, would seem like only serendipity
favored it. After all, it just happens to be a certain size located at a
certain distance from its star. And out of the vast multitude of stars in our
galaxy alone, surely there would be many analogues of earth that took advantage
of that same kind of luck. But that consensus has changed.
We know now that many things have come together to make our
planet the way it is. Atmospheric composition, orbital stability, the presence
of a moon to help keep earth rotating on its axis, the stability of the sun,
are just a few of the many factors that make this planet an abode where complex
life could evolve. Earth is probably not common at all, in fact it now seems
likely that it is an extremely rare kind of world that we won't encounter much
as we explore our universe.
And that leads us to Trappist - 1. This is a star system
full of could be's. We see evidence of at least seven worlds that appear to be
of a similar size to earth. More, they cluster in close to their dim, small red
dwarf sun in such a way that, at least a portion of them, might, depending on
the specific conditions present on those worlds, be able to support liquid
water. Where there is liquid water, there is the possibility of life as we know
it. Again, after all, we know that happened here.
A new climate model, which is no doubt one of many to come,
may give us a picture of what these worlds might be like and suggest which
planet astronomers should take a look at first. Also, models like this, and
models of what the spectra of the planets might be like, are important because
as scientists collect the data on these worlds in future years they can then
compare them to the models and see which ones fit best.
According to the new model by Eric Wolf of the University
of Colorado
Wolf modeled a variety of possible atmospheres for these three
candidate worlds. To do this, he assumed that water, in whatever form, was
freely available in the system. This is a reasonable assumption, the planets
are modeled to have formed farther out from the star where ices are likely to have
been present and then the planets migrated closer after formation. From there,
he modified a model originally intended to study Earth's climate to produce the
most complex model of the Trappist - 1 system we so far have.
Now, modeling planetary climates is a tricky business. Earth
especially. As a result, more models are needed for a consensus to be arrived
at as to what's going on with these planets. But in Wolf's model out of the
three most likely candidates, only Trappist - 1e made the grade for liquid
water. Planet d is too close to the star, if it had liquid water, it would
simply boil off into a thick water vapor atmosphere. That should cause a
runaway greenhouse effect producing a planet perhaps similar to Venus.
Planet f has the opposite problem. It's too far from the
star and any water on its surface would be frozen solid. Wolf found no
combination of atmospheric gases which could keep it warm enough, even carbon
dioxide would freeze out according to the model. Not so with Planet e, liquid
water was predicted to be possible there. But would that planet be earth-like?
Not likely.
The planets at Trappist - 1 are probably tidally locked,
given their proximity to their star. This means that Trappist -1e would always
present the same face towards its star, much like the moon is similarly tidally
locked with earth and always shows us the same face. This would create an
eyeball-like world where you would have liquid water at the point on the planet
that received the most light from the star. The rest would be ice. How much of
the planet is conducive to liquid water is unknown, it would depend on if the
sunlight is striking an ocean or a dryer continental landscape, the content of
the atmosphere and so on, but perhaps around 20 percent of the surface could be
earthlike in temperature.
But, as we're seeing with our own solar system, earth-like
worlds are not the exclusive domain of liquid water. There are a variety of
conditions, such as those of Enceladus or Europa, that could allow for
subsurface liquid water. While it will be a long time before we know if such
things are possible in the Trappist - 1 system, we at least know that the
possibility for one potentially habitable planet more in the grain of earth is
on the table.
Thanks for listening! I am futurist and science fiction
author John Michael Godier currently with an upcoming book, it's called
Supermind and asks if our universe is really a computer simulation and be sure
to check out my other books at your favorite online book retailer and subscribe
to my channel for regular, in-depth explorations into the interesting, weird
and unknown aspects of this amazing universe in which we live.
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