Some extrasolar planets are like Earth, almost. Many are unlike anything in the Solar System.
I’ll be looking at recently-discovered worlds; some almost familiar, others wonderfully unexpected. Also an informal ‘top 10 best exoplanets’ list.
- Imagined worlds
- In the news
- Faith, reason, and reality
Many folks, scientists included, thought we should look for a planet like Earth.
Two other worlds in the Solar System, Mars and Venus, seemed promising.
Both are inside our star’s habitable zone.
Venus is nearly as massive as Earth. Mars has ice caps, and seasonal changes that reminded Earth-based astronomers of our planet’s temperate zone summer-winter vegetation cycle.
We’d learned that much by the time Mariner 4 reached Mars. Scientists hadn’t taken Lowell’s “canals” seriously, but we were pretty confident about finding some sort of life on the red planet.1
That’s about 0.6% of sea level pressure here. It’s not a vacuum, but far from the Earth-like atmosphere 19th century observations suggested.
Hopes for finding life on Mars had gone from vegetation of some sort, to Lowell’s canal-building Martians, to variously-defined “simple” life, to ‘nothing there but craters and dust.’
We started getting a more complete picture of Mars after orbiters arrived. The planet isn’t nearly as Earth-like as we’d hoped, but the question of Martian life is still open.
We’re also learning that life isn’t nearly as finicky as we thought. I’ll get back to that.
Most figured the planet was nearly covered by clouds.
That was enough for science fiction writers and artists.
Pulp science fiction was in full bloom. Writers churned out stories about heroes and villains, exotic empires and mysterious wastelands. The genre’s science was more reality-based than realistic.
Artist Frank R. Paul imagined a tropical Venus with dinosaurs and “Munchkin villages.” (“Venus,” Tales of Future Past, David S. Zondy)
Edgar Rice Burroughs gave us rousing tales of Carson Napier’s adventures on Venus: called Amtor by its very-human natives. The adventures started when Napier made a wrong turn on his way to Mars and landed on Venus instead.
The Burroughs Amtor tales were filled with about as much stark scientific realism as his Barsoom adventures.
Maybe it’s because science started catching up with imagination sooner for Mars than for Venus.
We’d found carbon dioxide in Venusian atmosphere by 1940.
Rupert Wildt used that data, plus other factors, and said Venusian surface temperatures were above water’s boiling point. Flyby and orbital missions confirmed it. The planet’s surface is over 450 °Centigrade. That’s hot enough to melt solder.
If Venus supports life, it’s not ‘life as we know it.’ Its atmosphere has sulfuric acid the way Earth’s has water.
Life not-as-we-know-it on Venus is possible, but not likely. The planet’s atmosphere is out of chemical equilibrium.
So is Earth’s. Our home’s atmosphere is about 20% oxygen. It’s a very reactive element. Critters like us need it, plants produce it. Without life, Earth’s atmosphere wouldn’t have nearly that much oxygen.
Oxygen is a biosignature, evidence of life. Scientists think any sort of chemical imbalance may be a biosignature. But not necessarily proof of life.
Probes also found a fair amount of hydrogen sulfide and sulfur dioxide in the upper Venusian atmosphere. Those substances react with each other.
Carbonyl sulfide is present too. It’s not easy to make in the lab, but some critters on Earth produce the chemical. The same could be true on Venus. Or not.
Volcanic activity is another source of carbonyl sulfide on Earth. Maybe that’s where it comes from on Venus.
Another oddity is a chlorine-rich layer just under the Venusian cloud deck.
My guess is that something other than exotic biochemistry is happening on Venus. But I also suspect that Earth’s biochemistry is just one of many varieties. I’ll get back to that, too. Our sort of life chemistry is nucleic acid/protein (O) in water.
The more we learned about Mars, the less like Earth it seemed. But thinking terrestrial life could survive there seemed plausible until the 1950s.
(From Giovanni Schiaparelli, via Meyers Konversationslexikon/Wikimedia Commons, used w/o permission.)
(From Giovanni Schiaparelli, From NASA’s “On Mars: Exploration of the Red Planet. 1958-1978, via Wikimedia Commons, used w/o permission.)
(Giovanni Schiaparelli’s maps of Mars, 1877 (top) and 1877-1886. (bottom))
Someone noticed Martian polar ice caps in the 1600s: Giovanni Domenico Cassini or maybe someone else.
Other astronomers noticed Martian seasonal changes in the 1700s.
Astronomical tech kept improving. Mapping Mars started in the 1800s. Fr. Pietro Angelo Secchi, at the Vatican Observatory, drew some of the first color maps of Mars.
Fr. Secchi described “channels”on the Martian surface in 1858. “Channels” in Italian is “canali.” “Canali” aren’t necessarily artificial. I don’t know if Lowell would have seen “canals” on Mars without that “canali” as inspiration.
Giovanni Schiaparelli mapped an extensive canali network 1877. We still use many of his names for Martian features: like Hellas, Tharsis, and Chryse.
Channels, natural and otherwise, usually have water in them on Earth.
Assuming that water filled the Martian channels seemed reasonable. At first.
William Wallace Campbell’s 1894 spectral analysis showed no water in the Martian atmosphere. (December 16, 2016)
He was pretty sure they held water: and were canals, artificial channels. His “Mars” (1895), “Mars and Its Canals” (1906), and “Mars As the Abode of Life” (1908) said they were Martian engineering projects.
It makes a good story: citizens of dying world, uniting in a doomed struggle for survival.
“…On the earth the sea-bottoms still hold seas, on Mars they only nourish vegetation….
“…once fertile fields become deserts….
“…That it [a canal network] joins the surface from pole to pole and girdles it at the equator betrays a single purpose there at work. … Nations must have sunk their local patriotisms in a wider breadth of view and the planet be a unit to the general good….”
(“Mars as the abode of life,” Percival Lowell (1908))
From what I know of his work, it seems likely that he honestly believed he was seeing canals on Mars.
I also think he was mistaken.
We didn’t get a clear look at Mars until Mariner and other probes sent images from their flyby and orbital missions.
Astronomers had been viewing the planet from Earth’s surface, millions of miles away, through our turbulent atmosphere.2
The best human observer is still human. Sometimes we see things that aren’t there.
Arcimboldo’s odd paintings use pareidolia.
It’s what psychologists call our knack for unconsciously arranging jumbled data into something familiar.
Sometimes we see faces when we’re looking at a pile of books or a piece of chicken. (August 13, 2017)
That’s one reason the Catholic Church has procedures for evaluating reports of miracles. We’ve been dealing with astonishing stories for millennia.
Some folks who report them honestly believe they witnessed a miracle, or think they might have. Some want others to think they did. A few saw something extraordinary happening. And that’s yet again another topic.
“A ‘Pale Green Dot’: Why Proxima Centauri b May Have a Shiny Tint”
Nola Taylor Redd, Space.com (October 9, 2017)
“A world orbiting the sun’s closest stellar neighbor may have a shiny green tint to it — and not necessarily because it’s covered in leafy plants.
“Researchers have found a way to characterize potential auroras on the nearby exoplanet Proxima Centauri b and found that, if the planet sports oxygen in its atmosphere, the auroras may give the atmosphere a greenish cast…..”
Proxima Centauri is a red dwarf. We didn’t know red dwarf stars existed until astronomers started using telescopes.
I haven’t confirmed this, but I think Robert Innes was first to spot one, in 1915.
Since then we’ve learned that the part of our galaxy we can see has more red dwarfs than stars like our sun.
Many are flare stars. We’re not entirely sure, but scientists think those red dwarfs have flares like our sun’s; and as powerful.
Harlow Shapley said Proxima Centauri was a flare star in 1951. Scientists looking through photographic plates taken since its discovery. Shapley was right.
Our star’s flares didn’t affect us much, apart from lighting up northern skies, until we started stringing telegraph lines.3 We eventually connected sparking telegraph equipment and aurora with solar ‘weather.’
Some planets circling red dwarfs are like Earth. They’re about the same mass and diameter.
That very strongly suggests they’re made of rock and metal, like the Solar System’s inner worlds. Some even have atmospheres. We think the odds of finding life on one of those planets is pretty good. Or not.
On the one hand, some would be about the right temperature. Red dwarfs last much longer than stars like ours, so life could have plenty of time to develop.
On the other hand, many red dwarfs are flare stars. Stellar flares affect Earth, but not enough to bother life here.
Flares on red dwarfs are about as powerful as Sol’s. They’d have about the same effect on planets as far from the stars as Earth is from ours.
But a red dwarf’s habitable zone is tiny compared to the Solar System’s. A planet at the right distance to host life would almost certainly be tidally locked, with one face always facing its sun.
‘Sunlight’ would be twice as bright during a flare.
That might not make a big difference, but the radiation would. At this point we’re not sure if an Earth-like planet’s magnetic field could be strong enough to protect its atmosphere and any critters living there.4
Prospects for finding life on Proxima Centauri b look slim. Probably.
On the ‘up’ side, the planet’s aurora should be at least 100 times brighter that Earth’s. That’s bright enough to register on our instruments, here in the Solar System.
In a way, we’re now at the point we were three centuries back, when astronomers could see ice caps on Mars.
“The Closest Star System to Earth Could Be Concealing a Dark, Long-Kept Secret”
Interstellar theft is a thing.
Peter Dockrill, Science Alert (October 9, 2017)
“The nearest star system to our own could hold our best chance of finding a habitable, Earth-like exoplanet – but it may also be concealing a dark, long-kept secret.
“Alpha Centauri, located just 4.37 light-years from our own Solar System, is the closest thing we have to a neighbour in the galaxy, but it looks like one of its three stars could be a victim of theft on an interstellar scale….”
Don’t let expressions like “theft on an interstellar scale” fool you. There’s solid science going on here.
Our Solar System’s planetary orbits are pretty stable, and have been for the last several billion years, most likely.
Scientists are pretty sure that orbits of Mercury, Venus, and Earth are stable.
Fairly stable, that is. Venus and Mercury almost certainly won’t collide during the next few billion years.
We’re nearly certain that the Solar System wasn’t nearly that stable at first.
What we’re learning about this universe makes a lot more sense if we assume that gravity and inertia have worked pretty much the same way for the last few billion years.
We think moon- and planet-size objects changed orbits fairly often when the Solar System was new. Sometimes they collided. That may be how we got our moon. (June 30, 2017; December 9, 2016; September 9, 2016)
Making the same assumptions about reality and physical laws let astronomers make sense of what they observe in our part of this galaxy.
The ‘interstellar theft’ paper published last month may or may not be on the right track. I think the idea looks plausible. Whether or not it’s accurate? That’s something we’ll be closer to knowing when scientists analyze more data.
Intellectual rotgut like the recent Nibiru predictions is something else.6
I suspect it’s a high-proof mix of fermented tabloid science, my culture’s folklore and superstitions — with a dash of Bible verses. (September 29, 2017)
“The 10 best exoplanets we’ve discovered so far, ranked”
Patrick Daniels, Digital Trends (October 1, 2017)
“Are you tired of the same old scenery? Do you look up at the sky and think, ‘Man I’m tired of all this blue!’ ? Has your wanderlust exhausted Earth’s options?…”
Gliese 3942b: Super-Earth Found Orbiting Nearby Star”
Natali Anderson, Sci-News (September 25, 2017)
“Designated Gliese 3942b, the newfound alien world is about 7.1 times as massive as the Earth….”
An Atmosphere of Heavy Metals”
Javier Barbuzano, Sky and Telescope (September 18, 2017)
“Researchers have found strong evidence of titanium oxide in the atmosphere of a hot giant planet, adding new insights to the complex motions of these planets’ extreme atmospheres.
“Astronomers might have observed one of the molecules that govern the atmospheric structure of a hot Jupiter….”
Puffed-Up Hot Jupiter Is Surprisingly Dark”
Javier Barbuzano, Sky and Telescope (September 21, 2017)
“Researchers have found that a football-shaped, ultra-hot gas giant that’s being devoured by its host star is also one of the least reflective exoplanets ever found.
“Imagine a football-shaped planet covered in a fresh layer of asphalt and you might get close to what WASP-12b, a hot Jupiter 900 light-years away, would look like to a hypothetical space traveler. Add a faint red glow like that of a smoldering iron and you’re probably dead on….”
We didn’t start finding planets circling other stars until recently. But folks have wondered about other worlds for a very long time.
A few centuries ago we learned that Aristarchus of Samos was right. The stars are other suns. More about that near the end of this post.
During the 19th century, a few folks said they’d spotted planets circling other stars.
Most astronomers didn’t take the claims seriously. It wasn’t that they “believed in” a lack of extrasolar planets.
Scientists didn’t “believe in” a planet circling Barnard’s star, either.
But Peter van de Kamp had pretty good evidence for a roughly Jupiter-mass planet orbiting the red dwarf.
That was in 1963.
It took a decade of painstaking work to show that it probably isn’t there. Follow-up observations with much better tech haven’t found anything.
Scientists are pretty sure the star doesn’t host any Jupiter-size planets in close orbits. Smaller worlds and planets in wide orbits are possible, but haven’t been detected.
We have, however, found more than three thousand other exoplanets, with more being confirmed as scientists work through growing databases.7
We’re also learning that the Solar System’s planets are a small sample of worlds we’ll find.
TRAPPIST-1 is 39.5 light-years away. It’s close, but not the nearest planetary system. I’m reasonably sure we’ll send probes to Proxima Centauri and Epsilon Eridani first.
Patrick Daniels put his ’10 best’ list in reverse order, with #1 coming last.
I enjoyed his lighthearted look at some of the darkest, hottest, and strangest worlds we’ve found so far.
I doubt some of his names, like “The Dracula Planet” for TrES-2B, will get the IAU stamp of approval.
That’s the International Astronomical Union. It’s a professional outfit of PhD-plus astronomers. One of their functions is giving their official stamp of approval to names for astronomical objects and features.
I’ll acknowledge that it’s nice having somewhat-consistent names for all the worlds we’re finding. It’s arguably easier than remembering that the Charles V comet and Great Comet of 1556 are the same comet: C/1556 D1. (December 11, 2016)
Happily, the IAU doesn’t seem particularly pompous. Not yet.
Here’s the Patrick Daniels ‘top 10,’ with my not-as-colorful descriptions:
- TrES-2b — The Dracula Planet
Kepler-1b, a hot Jupiter, darkest known exoplanet
- Kepler-36c/b — That’s no moon!
Two planets in very small orbits
- OGLE-2005-BLG-390 — Love the snow? This one is nicknamed ‘Hoth’
About five times Earth’s mass, coldest known exoplanet
- PSR B1257+12 system — A light show to die for
A pulsar named Lich with three known planets: Draugr, Poltergeist and Phobetor
- 55 Cancri e — An intergalactic prospector’s dream
Eight times Earth’s mass, probably a ‘carbon planet’
- Kepler-16b — Where your shadow will never be lonely
Saturn-mass planet orbiting a binary star
- Wasp 12 b — A crumbling planet being eaten by its sun
A ‘hot Jupiter’ orbiting a sun-like star
- Kepler-452b — Earth’s bigger, older cousin
“Earth 2.0,” almost
- Proxima B — Only a hop, skip, and four light years away
A nearby terrestrial planet
- Trappist-1 System — A fistfull of Earths
Seven terrestrial planets
(Source: Patrick Daniels, Digital Trends, Wikipedia)
Gliese 3942b, WASP-19b and WASP-12b aren’t like any planets in the Solar System.
Gliese 3942b is a super-earth: a rocky world like Earth, but much more massive. We’ve found quite a few. Some might support life. Probably not Gliese 3942b, not life as we know it. It’s a hot world. Scientists figure lead wouldn’t melt on its surface: it would boil, fast.
WASP-19b and WASP-12b are hot Jupiters. We’re finding a fair number of these, too.
I think they’re more of a surprise than the super-earths. Jupiter and other big outer planets in the Solar System are just that: outer planets.
Models for planetary system development generally assumed that the Solar System was typical. It seemed reasonable.
We expected other systems to have comparatively small, rocky worlds close to the star, big hydrogen-rich planets out where it’s nice and cool.
That’s not what we’re finding.
Scientists could have assumed that they were wrong about everything and chucked the idea of understanding physical laws.
The notion that nothing makes sense, including the universe, may be fashionable. But most scientists still figure physical laws exist. That means we can learn how things work.
Instead of giving up, scientists took another look at how planets form. I talked about orbital dynamics earlier.
I don’t think we’ve got all the answers. I’m quite sure we don’t. But we’re solving some puzzles, finding intriguing new ones in the process.
Mesopotamian cosmology was closely tied to their religious beliefs.
Ancient Greeks had their religions, too.
Their philosophers considered theological issues. They also discussed the sort of realities we call “scientific.”
Some said we lived in a universe of nested spheres, with Earth in the center. Some figured Earth goes around our sun.
Philosophers came up with pretty good reasons for thinking their ideas were right.
With their technology, they couldn’t go much beyond making compelling arguments.
After we developed telescopes, and improved on the original designs, we realized that some of the ideas matched reality better than others.
We’ve learned that Aristarchus was right. The stars are other suns.
Aristotle said Earth is at the center of the universe, and is fundamentally different from the sun, planets, and stars.
Aristotle was a very smart man, and had good logic backing up his cosmology.
Folks like Ptolemy had tweaked it a bit, trying to make it fit observations. They did a pretty good job.
European scholars rediscovered Aristotle, starting around 1100. Many were huge fans of the Greek philosopher when speculation about other worlds was on the table.
Most academics of the 12th century figured Aristotle’s geocentric universe was on the right track.
Some Aristotelians said other worlds couldn’t exist: because Aristotle said so.
It was an inopportune time to declare unyielding allegiance to revolutionary ideas. Or refurbished old ideas in revolutionary wrapping, for that matter.
That got Giordano Bruno killed.
Copernicus had the good sense to say his heliocentric model was theory. He realized that “there will be babblers.”
Quite a few non-babbling folks, including a cardinal and a bishop, urged him to publish. (April 28, 2017)
Galileo insisted that folks accept his heliocentric ideas as incontrovertible fact.
Galileo was right, pretty much. But it would be centuries before astronomical tech let scientists find evidence backing up Copernican math. Almost.
Copernicus wasn’t spot-on accurate, but his heliocentric model matched reality better than Aristotle’s physics. (June 2, 2017)
Presenting Giordano Bruno as a heroic scientist, martyred by despotic forces of superstition and oppression, seems to have started in the 19th century. There’s a little truth to it.
As far as I can tell, Bruno was executed because he said his theology must be true. His personality apparently alienated folks, too.
I think killing someone for insisting on pantheism or pandeism is wrong. But I don’t think that makes him a martyr of science.8
“Faith and reason are like two wings on which the human spirit rises to the contemplation of truth; and God has placed in the human heart a desire to know the truth—in a word, to know himself—so that, by knowing and loving God, men and women may also come to the fullness of truth about themselves (cf. Ex 33:18; Ps 27:8–9; 63:2–3; Jn 14:8; 1 Jn 3:2)….”
(“Fides et Ratio,” Pope Saint John Paul II (September 14, 1998))
If you’ve seen my ‘science’ posts before, you know why I think science is a good idea, and think faith and reason should get along.
Some folks apparently believe that religion and science are at war, that someone can either be reasonable or Christian. Or at least think faith might be unreasonable.
I don’t see it that way. I’m a Catholic.
Someone doesn’t have to be a scientist to be a Catholic. That’s just as well for me, since my academic training is mostly in history and literature.
Being curious, thinking, and studying the universe, is part of being human. The order and beauty we notice in the process is one way we can learn about God. (Catechism, 31–32, 35–36, 301, 303–306, 311, 319, 1704, 2293–2296)
I’ve known Catholics whose devotion to ignoring what we’re learning about God’s creation is as fervent as the most rabid ‘creation science’ fundamentalist’s.
Happily, I realize that what they believe isn’t what the Church has been saying. And that’s yet another topic.
But I don’t think he or any scientist thought Martian princesses would look like Dejah Thoris of Helium. Or even that their society must include princesses.
If we have neighbors who aren’t from Earth we may eventually meet some who look almost exactly like humanity’s current model: at a distance and in dim light.
I think fictional aliens like Frank R. Paul’s “man from Venus” are slightly more plausible. Not in detail, but in not being too obviously human-like.
Even there, Paul’s aliens often had our body plan. Right down to being upright bipeds.
Maybe that is the only possible shape for creatures with bodies and free will.
I strongly suspect God is more inventive than pulp science fiction artists. But I won’t say that we must have neighbors: or that we can’t.
Again, I’m a Catholic. The 1277 rules were rescinded, but the principle still applies. God’s God, I’m not, and neither is any expert. Not even Aristotle.
We’ve found critters on Earth’s ocean floor, clustered around hydrothermal vents. They’re thriving at temperatures that would kill us, even if we had enough oxygen.
Even critters living in conditions we find comfortable don’t all look like us. Insects, for example, have their skeletons on the outside.
Terrestrial life hasn’t always been as it is now.
Body plans for some Cambrian critters are like today’s models. Others, like the — thing — with five eyes and one tentacle: not so much.
Maybe animal-analogs invariably shift from mostly-sessile to the more mobile mode we’re used to. Or maybe not.
People, self-willed creatures with bodies, might be as incurably social and noisy as we are. Maybe that’s inextricably linked to intelligence.
It’s not up to me. This is God’s creation. God decides how it works. Part of our job is learning about it.
Terrestrial organisms share a common biochemistry, although details vary. Some bacteria are photosynthetic but not green, for example. Oxygen is toxic to some.
I don’t think there must be life on Venus because something’s maintaining a chemical imbalance in the atmosphere. But scientists aren’t ruling it out.
All terrestrial life uses water as a solvent. Some scientists think life not-as-we-know-it could use sulfuric acid instead.
Hydrogen sulfide is another possible water-substitute, and fairly common on Jupiter’s moon Io.9
We don’t know if any of the hypothetical life chemistries scientists are finding actually exist. But scientists have mathematical models saying they could.
It’s good to see other scientists following up on Boston University’s Isaac Asimov’s ’60s alternative biochemistries speculations:
- Fluorosilicone in fluorosilicone
- Fluorocarbon in sulfur
- Nucleic acid/protein (O) in water
- Nucleic acid/protein (N) in ammonia
- Lipid in methane
- Lipid in hydrogen
(“View from a Height” Isaac Asimov (1963), Lancer Books (p. 63))
We’re third from the top in that list, nucleic acid/protein (O) in water.
We could find nothing but life that’s biochemically like Earth’s.
But I wouldn’t count on it.
We’ve learned that other planets in the Solar System, even the ones a bit like Earth, aren’t quite like Earth.
We’ve learned that some worlds circling other stars are a bit like the Solar System’s. Others are not.
We’ve learned that Earth and this universe do not follow Aristotelian physics.
We may find life throughout this galaxy. Or not. Either way, I think we’ll keep learning that there’s more to learn.
And that’s still another topic:
- “Labor Day SETI”
(September 8, 2017)
- “Exoplanet Frontier”
(June 30, 2017)
- “Looking for Life: Enceladus and Gliese 1132 b”
(April 21, 2017)
- “TRAPPIST-1: Water? Life??”
(March 3, 2017)
- “Proxima Centauri b, Looking for Life”
(September 2, 2016)
- “Mars as the abode of life”
Percival Lowell (1908) via Internet Archive
- A Solar Flare Effect
Magnetic Field, Space Weather Services, Australian Government Bureau of Meteorology
- “Transient Weakening of Earth’s Magnetic Shield Probed by a Cosmic Ray Burst”
P. K. Mohanty, K. P. Arunbabu, T. Aziz, S. R. Dugad, S. K. Gupta, B. Hariharan, P. Jagadeesan, A. Jain, S. D. Morris, B. S. Rao, Y. Hayashi, S. Kawakami, A. Oshima, S. Shibata, S. Raha, P. Subramanian, H. Kojima; abstract; Physical Review Letters (October 20, 2016)
- “The Pale Green Dot: A Method to Characterize Proxima Centauri b Using Exo-Aurorae”
Rodrigo Luger, Jacob Lustig-Yaeger, David P. Fleming, Matt A. Tilley, Eric Agol, Victoria S. Meadows, Russell Deitrick, Rory Barnes; Abstract; The Astrophysical Journal (March 3, 2017)
- Formation and evolution of the Solar System
- Stability of the Solar System
- Planet Nine
- Nibiru cataclysm
- “Was Proxima captured by alpha Centauri A and B?”
F. Feng H. R. A. Jones; Abstract; Monthly Notices of the Royal Astronomical Society (October 5, 2017)