It was back in 1980, and I still remember being blown away by it all -- the melding of science with animation and gorgeous music, and Carl Sagan's lyrical, almost poetic way of expressing his enduring love for astronomy. My friends and I always waited excitedly for the next episode to air, and the day afterward spent an inordinate amount of time chatting about what we'd learned.
One of the episodes that resonated the most strongly with me was entitled "Encyclopedia Galactica." Sagan predicted a day when we'd know so much about the universe that we'd have an encyclopedia of alien planets, each page of which would be accompanied by a list of their physical characteristics -- and types of life forms. He was unequivocal in his belief that we were not alone in the universe, and that in fact life would turn out to be common. Not, perhaps, "life as we know it, Jim" -- and much of it almost certainly pre-technological -- but life, he thought, would turn out to be pretty much everywhere we looked.
In the forty-five years since it aired, our detecting equipment has gotten better and better, but we're still up against the Fermi Paradox -- that famous quip from physicist Enrico Fermi who, when told that life was likely to be common in the universe, said, "Then where is everybody?" Long-time readers of Skeptophilia may recall that a few years ago I did a deeper dive into the Fermi Paradox and the infamous "three f's," but the fact remains that despite getting better and better at astronomy and astrophysics, we still have no incontrovertible evidence of extraterrestrial life (intelligent or otherwise).
But extrasolar planets? Those are kind of a dime a dozen. As of this month, there have been a bit over six thousand exoplanets conclusively identified, and some of them have challenged our models of what planets can be. (I took a look at a few of the weirder ones in a post earlier this year.) So even if we don't yet have aliens in our back yard, there's been a lot of really cool information discovered -- three examples of which have just come out in the past couple of weeks.
No Andorians yet, more's the pity.
The first is about the TRAPPIST-1 system, which was one of the first multi-planet systems discovered. Not only that, it has four planets in the "Goldilocks zone" -- the region around the host star that is "just right" for having temperatures where water could be in its liquid state. (This doesn't mean there is water; just that if other factors were favorable, there could be liquid water.) Not only that, but we lucked out that TRAPPIST-1 is fairly close (a little over forty light years away, in the constellation of Aquarius), and that its planets' orbits are aligned so that from our perspective, they cross in front of their host star, allowing astrophysicists to use the transits to take a stab at the composition of their atmospheres.
The outstanding YouTuber Dr. Becky Smethurst did a wonderful video explaining how this all works (and why the planet TRAPPIST-1d probably doesn't have an atmosphere), but a capsule summary is that when the planet passes in front of the star, its light passes through the planet's atmosphere (if it has one), and any gases present absorb and scatter characteristic frequencies of light. Compared to the unobstructed spectrum of the star, those frequencies are then missing (or at least diminished in intensity), and from that information astrophysicists can deduce what might be present in the atmosphere.
Well, the other three planets in the habitable zone -- TRAPPIST-1b, c, and d -- have pretty conclusively been shown to lack an atmosphere. So it all hinges on 1e, the farthest one out, and a study at the University of Bristol, using data from the James Webb Space Telescope, has said that it cannot rule out the presence of an atmosphere on that one. Not a ringing endorsement, that, but at least not a categorical no -- so we'll keep our eyes on TRAPPIST-1e and hope future studies will give us good news.
The other two stories are about "rogue exoplanets" -- planets out there floating in space that don't (or at least, don't now) orbit a star. Whether they formed that way, or started out in a stellar system and then were ejected gravitationally, is unknown (and may well be different in different cases). These, for obvious reasons, are considered poor candidates for life, but they still are pretty amazing -- and the fact that we know about them at all is a tribute to our vastly improved ability to detect objects out there in interstellar space.
The first one, CHA-1107-7626, is currently accreting material like mad -- something not seen before in an exoplanet, rogue or otherwise. It is estimated to be between five and ten times the mass of Jupiter, so on the verge of being a "brown dwarf" -- a superplanet that has sufficient mass and pressure to fuse deuterium but not hydrogen. They emit more energy than they absorb, but don't quite have enough for the nuclear furnace to turn on in a big way.
But if CHA-1107-7626 keeps going the way its going, it may get there. It's hoovering up an estimated Jupiter's worth of material every ten million years or so, which is the largest accretion rate of any planet-sized object ever observed. So what we might be witnessing is the very earliest stages of the formation of a new star.
The final study is about the rogue exoplanet SIMP-0136, which came out of Trinity College Dublin and again uses data from JWST. But this exoplanet is bizarre for two different reasons -- it has vast storms of what amounts to liquid droplets of sand... and it has auroras.
Once again, I'm staggered by the fact that we could detect this from so far away. The temperature of the surface of the planet is around 1,500 C -- hotter than my kiln at full throttle -- and it has three hundred kilometer per hour winds that blow around bits of molten silica. But most peculiar of all, the planet's atmosphere shows the characteristic polar light flashes we see down here as auroras.
What's weirdest about that is that -- at least on Earth -- auroras are caused by solar activity, and this planet isn't orbiting a star. The way they form down here is that the solar wind ionizes gases in the upper atmosphere, and when those ions grab electrons, and the electrons descend back to the ground level, they emit characteristic frequencies of light (the same ones, not coincidentally, that are swiped by gases in the atmospheres of planets during transits). Red for monoatomic oxygen, green for diatomic oxygen, blue for molecular nitrogen, and so on.
What is ionizing the gases on SIMP-0136? Astrophysicists aren't sure. Sandstorms here on Earth can certainly cause static electrical discharges (what we laypeople refer to as "bigass lightning bolts"), so it's possible we're seeing the light emitted from interactions between the molten silica and whatever gases make up the planet's atmosphere. But it's too soon to be sure.
So even if we haven't yet discovered Skithra or Slitheen or Sontarans or whatnot, we're still adding some pretty amazing things to our Encyclopedia Galactica. Carl Sagan, as usual, was prescient. As he put it, "Somewhere, something incredible is waiting to be known."
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