Exoplanet Frontier

We wouldn’t expect to find life on 51 Eridani b, even if were the size of Earth and at the right distance from its star.

The planet is only a bit over 20,000,000 years old.

At that point in our home’s long story, the earliest critters wouldn’t appear for at least another several million years.

We’ve discovered thousands of new worlds so far, some a bit like Earth, most not; and many not like anything in our Solar System.

Scientists are starting to make sense of what’s being found, and discovering that we have a very great deal left to learn.

Worlds Circling Other Stars

Until around 1990, all known planets were in the Solar System.

We’d had several false alarms earlier, starting in the 19th century.

In 1855, for example, William Stephen Jacob published observations and analysis that he said showed a massive planet in the 70 Ophiuchi system.

Swarthmore College’s Peter van de Kamp did the same with Barnard’s Star in the mid-20th century.

We’ve learned quite a bit since then. It’s pretty much certain that Jacob’s and van de Kamp’s planets aren’t actually there.

That doesn’t mean there can’t be planets orbiting the stars. But they’d have to be a whole lot smaller than the ones folks like Jacob and van de Camp thought they’d found.

Then, in 1992, scientists confirmed that three exoplanets circled the pulsar PSR B1257+12. In 1995 we confirmed that a planet orbits 51 Pegasi, a main-sequence star. We’ve discovered thousands since then.

We’re not even close to thoroughly mapping planetary systems around nearby stars, let alone the rest of this galaxy.1

We are, however, starting to piece together enough to realize how much is left to learn.

1. 51 Eridani b Forecast: Partly Cloudy and Cooler

(From Rajan et al. 2017, via Sky and Telescope, used w/o permission.)
(“Images of 51 Eri b from GPI (top) and Keck (bottom).”
(Sky and Telescope))

A Partly Cloudy Exoplanet
AAS Nova, Sky and Telescope (June 22, 2017)

“Direct imaging of exoplanets was once only possible for the brightest of planets orbiting the dimmest of stars — but improving technology is turning this into an increasingly powerful technique. In a new study, direct-imaging observations of the Jupiter-like exoplanet 51 Eridani b provide tantalizing clues about its atmosphere.

Direct Imaging of 51 Eri b

“While transit detections remain the best way to discover large quantities of new exoplanets, direct imaging provides a unique advantage: you can measure the light from the exoplanet itself. With proper constraints on the host star, it therefore becomes possible to measure the spectrum of the planet’s atmosphere.

“One target for this technique is 51 Eri b, a Jupiter-like exoplanet located roughly 100 light-years away. This object was the first exoplanet directly imaged by the Gemini Planet Imager Exoplanet Survey, a project that used the Gemini Planet Imager (GPI) instrument in Chile to search for exoplanets around 600 young nearby stars….”

The planet is a lot like Jupiter, but not a twin. It’s about the same diameter, with twice the mass. Like Jupiter, there’s methane and water in its atmosphere.

It’s as far away from its sun as the Solar System’s outer planets are from ours: 13 Astronomical Units, give or take. Something orbiting our star at that distance would be between Jupiter’s and Saturn’s orbits.

51 Eridani b is hotter than the Solar System’s big planet: around 700 Kelvin, 427 Celsius, 800 Fahrenheit. Jupiter’s temperature is about 165 Kelvin where atmospheric pressure is the same as Earth’s. That’s 108 Celsius, 163 Fahrenheit.

The high temperature isn’t surprising. 51 Eridani is a young star, in the Beta Pictoris moving group.

Young Stars and Rogue Planets

The Beta Pictoris moving group is a set of young stars, more than a dozen; plus at least one ‘rogue planet,’ PSO J318.5-22.

Scientists figure the group’s stars formed between 20,000,000 and 26,000,000 years ago. For stars, that’s not a long time.

An early age estimate of around 10 or 12 million years was doubled as researchers made more exact observations of the group’s stars.

It’s the closest young group we’ve found, which makes important for scientists studying stellar and planetary system formation.

I wondered about the Sky and Telescope article’s discussion of 51 Eridani b’s “spectral type.” That’s a term I’d associated with a stellar classification system astronomers started developing in the mid-19th century.

Since a star’s spectral type is based on what sort of radiation it emits, applying the term to planets makes sense: particularly warmish ones glowing with noticeable infrared ‘light.’

While checking out 51 Eridani b’s “spectral type,” I learned that the star has a binary companion: GJ 3305 A and B, a slightly-mismatched pair of red dwarf stars.

GJ 3305 A and B orbit each other every 29.03 years, give or take six months. They’re small stars, spectral type M1.1; 0.67 and 0.44 times our sun’s mass plus or minus 0.05.

Big Planets, Small Stars

Maybe GJ 3305 A and B just happen to be in 51 Eridani’s vicinity.

There’s probably still debate on that point. Consensus seems to be that they’re gravitationally bound to 51 Eridani.

Their connection to 51 Eridani, if it exists, isn’t particularly firm.

Passing close, by cosmic standards, to another large star could send them off on their own.2

51 Eridani b’s spectra looks a lot like what comes from Spectral class T brown dwarfs.

That’s the current name for objects considerably more massive than Jupiter but not quite massive enough to be stars.

It’s probably not a brown dwarf, though. It’d be a very lightweight one, and its spectra is too “red.” Scientists who published the latest study say we’re probably looking at clouds in 51 Eridani b’s atmosphere.

Clouds in Earth’s atmosphere are usually made of water. 51 Eridani b’s atmosphere has water, but these clouds are probably dust: salt and sulfide, or maybe iron and silicate. What’s observed so far could be either.

That sort of could is what scientists expect to observe in atmospheres of ‘cold start’ or ‘warm start’ big planets as they cool off. This is a wonderful opportunity to see if those models match what’s in the real world.

Fine-Tuning the Nebular Hypothesis

Scientists figure planets start at least one of two or three ways.

The Sky and Telescope article says the cold-start scenario is where planets form slowly by accretion onto a solid core.

The hot-start scenario is faster, with hot stuff in the protoplanetary disk collapsing to form a gas giant.

Warm-start is, naturally enough, about halfway between hot and cold.3

They’re all variations of the nebular hypothesis.

The nebular hypotheses started looking good in my youth. Scientists still figure it’s the best explanation we’ve found for how planetary systems form.

What’s been changing is basically fine-tuning of the nebular hypothesis.

It’s sort of like what’s been happening with the Copernican model of the Solar System.

We still figure our sun is in the center of the Solar System. What’s been changing in the last 475 years is how much we know about the details. (April 14, 2017; March 24, 2017; December 9, 2016)

2. Unexpected New Worlds

(From NASA/Ames Research Center/Natalie Batalha/Wendy Stenzel, via Space.com, used w/o permission.)
(“The planets characterized by NASA’s Kepler mission (yellow dots) and other surveys split into several different broad planet types. Future exoplanet surveys will reveal small planets orbiting further from their stars in the corner marked ‘frontier’.”

NASA’s Kepler Space Telescope Finds Hundreds of New Exoplanets, Boosts Total to 4,034
Sarah Lewin, Space.com (June 19, 2017)

“NASA has unveiled the complete set of data from the first four years of the agency’s Kepler Space Telescope mission, which stared at a single patch of the sky in the search for alien planets. The result: Kepler has discovered 219 new candidates since NASA’s last data unveiling, including 10 near-Earth-size planet candidates in the so-called habitable zone around their stars where the conditions are just right for liquid water to exist on a planet’s surface — a key feature in the search for habitable worlds.

“The new discoveries boost Kepler’s total to 4,034 candidate planets during its mission, 2,335 of which were later confirmed by follow-up observations, NASA officials said in a statement. The 10 newfound potentially Earth-size worlds bring Kepler’s total up to 50 of that type of exoplanet, with more than 30 of those being confirmed, NASA officials said during a briefing today (June 19).

“The researchers also revealed a surprising divide between small, Earth-like planets and mini-Neptunes gleaned from the data….”

The Kepler telescope isn’t the only one being used to look for exoplanets. But I feel like I’m mentioning Kepler-this and Kepler-that quite often.

There’s at least two reasons for that.

First, I’m an American — which gives me a particular interest in America’s people, issues, and government activities. That includes NASA.

I’m also interested in other space agencies like KARI, JAXA, AEB, UNOOSA. But I don’t think exploration and other activities in space should be a government-only thing.

That’s why I’m glad to see more private-sector outfits like Excalibur Almaz, Planetary Resources, Blue Origin, and SpaceX.

I don’t mind folks finding practical reasons for space exploration. Maybe that’s because I’m an American. Knowing a bit about history helps. And that’s another topic.

Another reason for focusing on Kepler is that it’s been collecting a lot of data.4

My guess is that we haven’t run out of surprises among ‘Kepler’ planets: and will learn even more as we extend the search for new worlds past today’s “frontier.”

About Kepler

By June 22, 2017, we’d found and confirmed 3,497 exoplanets. Don’t bother memorizing that number. It may have changed by the time you read this.

Quite a few of those planets were first spotted by Kepler.

Kepler’s observed 4,496 stars that might host exoplanets before May 11, 2013, a little over four years after launch.

Then the second of the telescope’s four reaction wheels failed. The telescope could hold steady with only three working, but not with two. Most of its equipment should keep working for years, but without stability the telescope wasn’t usable.

Ideally, technicians would repair the worn parts, or replace them. We could do that with the Hubble telescope, since it was in low Earth orbit — and the Shuttles were flying.

Kepler is orbiting the sun a little outside Earth’s orbit, for pretty much the same reasons observatories are built on mountaintops.

By 2013, it was 137,000,000 kilometers, 85,000,000 miles. Nobody’s developed spacecraft that carry folks that far, which I think is another reason for developing long-range vehicles.

For the time being, however, Kepler is well outside NASA’s service area. Scientists and engineers developed workarounds that let Kepler start its Second Light mission with slightly different goals.

Kepler’s found 391 more candidate exoplanets exoplanets so far.

Not quite 58% of Kepler’s ‘maybe’ planets have been shown to be the real thing.

That’s a little over 28% of the three-thousand-plus confirmed expolanets we’ve found to date. By any reasonable standard, I think that’s a significant contribution.

Being Human

My guess is that folks were wondering how things began long before we started developing information storage tech like pictograms and cuneiform.

That doesn’t bother me, since I accept being curious as part of being human. I’m also quite sure that using our brains doesn’t offend God. I’ll get back to that.

Nobody had wondered how the Solar System formed before 1500.

That’s mainly because up to that point we didn’t realize that Anaximander and Pythagoras were on the right track.

Aristotle had been much more persuasive, and had many overly-enthusiastic fans in Europe. (December 2, 2016 )

We didn’t have data to back up Copernican heliocentrism until well after the idea started giving some folks fits. (June 2, 2017; December 2, 2016)

René Descartes thought the sun and planets might have formed in a vortex. The same sort of folks Copernicus had called babblers didn’t like vortexes either. (April 28, 2017)

You can call more than one vortex vortices. Or you can sidestep the ‘how do I say it’ issue by calling them whirlpools, and that’s another topic.

Rightly or otherwise, Emanuel Swedenborg often gets credit for the first version of the nebular hypothesis. That was in 1734. About 15 years later, Georges-Louis Leclerc said maybe planets formed after a comet hit the sun.

Still Learning

Various folks pointed out that angular momentum and orbital mechanics made nebular and collision scenarious unlikely.

We’ve been learning that nebular and collision hypotheses were both not entirely wrong. They weren’t entirely right, either.

We’re pretty sure that planets and stars start as a sort of nebula, and that planets run into each other fairly often before settling into more-or-less stable orbits. (December 9, 2016)

James Jeans should, I think, get more credit for his work. He was wrong about quite a bit, but his 1917 tidal or near-miss idea made sense at the time.

My high school science textbooks included variations of his near-miss and tidal ideas.

The nebular hypothesis started looking a lot more likely after 1970. We had more data by then, plus work by folks like Otto Schmidt and Andrew Prentice. Getting Victor Safronov’s ideas about accretion disks translated helped.5

I would be astounded, and disappointed, if we now know everything there is to learn about this universe. But I suspect that the nebular hypothesis is a pretty good match to reality. It’ll do until we uncover something better.

Super-Earths, Mini-Neptunes, and More

(From NASA/Ames Research Center/JPL-Caltech/R. Hurt, via Space.com, used w/o permission.)
(“Researchers combining data from the Keck telescope in Hawaii and the Kepler space telescope found that there’s a sharp divide between super-Earths and mini-Neptunes.”

Scientists figured that planetary systems around other stars, if they existed, would be pretty much like the Solar System. It was a reasonable assumption.

I think it’s likely that we’ll find systems like ours, with rocky planets closer to the star than the big gassy ones. Eventually.

What we’re been finding so far is, I think, much more interesting than ‘more of the same.’

Upsilon Andromedae A’s planetary system is the closest thing to a Solar System analog we’ve spotted so far. One of its planets is close to Jupiter’s mass and about as far away from its star as Jupiter is.

The system isn’t a really close match to ours, though. Two of the three known inner planets, Samh and Majriti, have 10.25 and 13.98 times Jupiter’s mass.

Majriti’s orbit is a bit eccentric, but inside Upsilon Andromedae A’s habitable zone.

If planets that size can have rocky moons — there’s debate about that — one of Majriti’s moons could be habitable.

My guess is that the climate would be somewhat extreme.

But habitable doesn’t mean idyllic. I’m among the humans who ended up living in central Minnesota, and that’s another topic.

There’s another Jupiter-analog planet orbiting HIP 11915. Maybe there are rocky planets closer to that star, maybe not.

An interesting — to me, your experience may vary — detail is that there’s a distinct break between terrestrial planets and the smaller gassy planets.

It looks like if a growing planet gets beyond a specific mass, it’ll keep enough gasses to become a mini-Neptune. Below that mass, it’ll lose the ‘extra’ gas as it heats up.

Still Seeking Another Earth

We’re starting to find planets with about Earth’s mass in other systems.

We’re also finding planets that aren’t like anything in the Solar System. Based on their mass, orbits, and other data, scientists have been sorting them into categories.

Some hot Jupiters may be losing their atmosphere rapidly enough to become chthonian planets before the star runs out of fuel. Then again, maybe not.

COROT-7b, Kepler-78b, and Kepler-10b, may be lava planets: terrestrial planets so close to their sun that they’re covered by molten rock.

Terrestrial doesn’t mean ‘just like Earth.’ In this context it means the planets are mostly rock and metal, like Mercury, Venus, Earth, and Mars.

Gliese 1214 b, Kepler-22b, and many of the worlds circling Kepler-11, may be ocean planets: worlds with a rocky core and far more water than Earth. That doesn’t necessarily make them habitable, but Kepler-22b might be.

Kepler-438b, is the closest to an Earth-analog that we’ve found so far.

That world orbits a red dwarf a bit more than 470 light-years out in the general direction of Sheliak. It’s more massive than Earth, and gets more sunlight. Or would that be starlight? Kepler-438b isn’t quite quite an ‘Earth twin.’ Cousin, maybe.

Faith Embraces All Truth, or Should

I don’t know why so many folks assume that religion is against science, and that science threatens faith.

Folks who don’t think God exists sometimes say that since the universe follows rational physical laws, a rational Creator can’t exist. I’m over-simplifying the point, a lot.

The ‘knowable physical laws exist, so God doesn’t’ attitude makes sense, almost. As much as many political campaigns, anyway.

What makes considerably less sense to me is why loudly-Christian folks agree.

Much of the sound and fury focuses on evolution, so leftovers from 19th century English politics are probably a factor. (October 28, 2016)

There was almost certainly more going on in the days of Konstantin Pobedonostsev and the Belle Époque. From what folks like Nietzsche said, I get the impression that what passed for Christianity back then didn’t much resemble my faith. (March 31, 2017)

Some still doesn’t, sadly. (March 31, 2017)

Even if I felt like ignoring reality and reason, I couldn’t. Not if I’m going to act like being a Catholic matters.

Faith, we’re told, means embracing “the whole truth that God has revealed,” including what we find in this universe; and using our brains. (“Fides et Ratio;” “Gaudium et Spes,” 36; Catechism of the Catholic Church, 3132, 142150, 159, 319)

I’m not sure why so many Christians, some of them Catholics, insist that evolution mustn’t be real. Some of them seem equally devoted to the notion that this universe is no more than a few thousand years old.

That does not, I think, help correct the notion that Christianity’s worldview is by its nature more a little myopic.

“A millennium before Europeans were willing to divest themselves of the Biblical idea that the world was a few thousand years old, the Mayans were thinking of millions and the Hindus billions.”
(“Cosmos,” p. 213-214, Carl Sagan, via Wikiquote)

God Thinks Big

Narrow-gauge versions of Christianity may have encouraged some folks around my age to start taking Hindi beliefs seriously, back in the 1960s.

I sympathize, a bit, with those who decided that Christianity couldn’t be right.

I don’t agree with them, but can see their point.

Most of us had grown up in a world where scientists were taken seriously.

Those of us who were paying attention realized that we lived in a universe that’s vast on a literally cosmic scale.

Meanwhile, vehemently-Christian types were attacking what they called Satanic threats. Like evolution, commies, the Catholic Church, and rock music.

Many of them insisted that Christianity depended on unyielding allegiance to the King James Bible and declaring October 23, 4004 BC, as the day of creation.

Hindu beliefs didn’t seem nearly as goofy.

Interestingly some folks say that a day of Brahma, the Hindi creator, endures for about 4,320,000 years.6

That’s a few powers of ten short of Earth’s age, as measured by radioactive decay rates: 4,540,000,000 years, give or take 50,000,000. But it’s a dang sight closer match to reality than the few thousand held to be ‘Biblical’ by loyal disciples of Ussher.

What impresses me, some days, is how many folks didn’t see Christianity as a quaint residue from the 17th or 19th century.

‘Biblical’ Ideas: Including Wisdom 11:22

As a Catholic, and a Christian, I have no problem with thinking that God’s creation is vast. We’ve known that for millennia.

3 Terrible and awesome are you, stronger than the ancient mountains.”
(Psalms 76:5)

“He sits enthroned above the vault of the earth, and its inhabitants are like grasshoppers; He stretches out the heavens like a veil, spreads them out like a tent to dwell in.”
(Isaiah 40:22)

3 Raise your eyes to the heavens, and look at the earth below; Though the heavens grow thin like smoke, the earth wears out like a garment and its inhabitants die like flies, My salvation shall remain forever and my justice shall never be dismayed.”
(Isaiah 51:6)

4 Indeed, before you the whole universe is as a grain from a balance, or a drop of morning dew come down upon the earth.”
(Wisdom 11:22)

As I’ve said before, all that’s been changing is how much we know about how vast it is.

I don’t mind:

1 Exoplanets:

2 Youthful stars and a rogue planet:

3 Learning how planets form:

4 The Kepler observatory:

5 Science, planetary systems, and accepting reality:

6 Senses of scale:

About Brian H. Gill

I'm a sixty-something married guy with six kids, four surviving, in a small central Minnesota town. I mostly write and make digital art. I'm only interested in three things: that which exists within the universe; that which exists beyond; and that which might exist.
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6 Responses to Exoplanet Frontier

  1. robertkurland says:

    this is a fine article You should publish it as an ebook. That being said, there are some more “anthropic coincidences” required before a planet can sustain mammalian type life (and you’re probably aware of them)–among others, tilt of the axis, proportion of water to land, orbit eccentricity, rotational frequency, and,very important, a large satellite to shield from asteroid impact.

    • Thank you for the encouragement – and recommendation. I know very little about ebook publishing, and use that media (those media?) very little: and so would involve a steep learning curve. Good idea, though.

      About “anthropic coincidences:” thanks for bringing that up, and the examples of what all is involved in evaluating habitability. I’ve been interested in watching scientists start admitting an interest in such topics – – – and how the discussion is proceeding.

      I’ve shared my strictly-amateur views occasionally. You may – or may not – find them interesting. I’d suggest checking out the exobiology and extraterrestrial-intelligence tags in the Tag Cloud ( http://brendans-island.com/catholic-citizen/#tag_cloud-2 )

      At this point, we don’t know whether there’s life anywhere except Earth, and what’s been carried elsewhere on spacecraft. If there *is* life elsewhere, my guess is that we’ll have some surprises.

      I think these bits may be good examples of my views and speculations. Then again, maybe not. 😉

      “TRAPPIST-1: Water? Life??” Life as We Know It: and Otherwise, Maybe

      “SETI: What If?” Speculation and Mr. Chuckles

      “New Worlds: The Search Continues” More Speculation

      • robertkurland says:

        Thanks for the links. There’s lots of software (some of it free, or inexpensive) around that makes it easy to do ebooks. Email me at drbob_k@icloud.com and I’ll give you a list. Also I can send you the chapter in my ebook on the Anthropic Coincidences.

        • Thank you! Noted, for future reference. I’m nowhere near having material ready, and so will defer/delay making the request. It’s good to know there are resources available.

  2. This is all far beyond my intelligence. However … E book (or paperback) publishing.

    It is easier than one thinks. First prepare you book in MS Word. Ideally with little if any drawings, pictures etc … as these add to costs. Hand over the script to Amazon. They cost it in paperback (and E Book) and tell you the minimum price they will print it and desptach it to buyers. You agree, or add a bit more to the price for profit. You retain all Copyright. They print it and make it available on their websites world-wide. You’ll need to tell people that the book exists – i.e. do your own marketing.

    If you’re ever interested we can discuss details off-line.

    God bless.

    • Wow. Thank you. That is a great deal less technical and more straightforward than what I was finding, a few years (several years?) back. I may discuss this with you – – – when I am much closer to having something print-ready. Or whatever the digital analog of that would be.

Thanks for taking time to comment!