Still Seeking Earth 2.0

We’ve known about 55 Cancri e since 2004.

It may have lakes and rivers of lava. But that’s probably not what keeps its night side hot enough to melt copper.

Ross 128 b, discovered this year, is a bit more massive than Earth, warm enough for liquid water, and too hot. It’s not quite ‘Earth 2.0,’ but it may support life.


Changing Views of Mercury


(From USGS, used w/o permission.)
(Topographic map of Mercury, USGS (2016))

Scientists making the topographic map used data from MESSENGER, the first spacecraft to orbit Mercury. The other map is Eugène Michael Antoniadi’s, published in 1934; based on what’s visible from Earth.

Antoniadi and other astronomers were pretty sure that Mercury always kept one face pointed toward our sun.

It made sense for Mercury to be tidally locked on the sun, as Earth’s moon is with our planet. Observations seemed to back up that assumption.

We can only see Mercury during twilight, and then only when it’s far from the sun in our sky. Telescopes let astronomers see Mercury’s surface, but not clearly. Not through our still-sunlit atmosphere.

At best, astronomers observing Mercury saw the sunlit part of a tiny, low-contrast disk. Each time it seemed to be have the same indistinct markings.

If Mercury ‘day’ side was always sunlit, its center would the hottest spot in the Solar System; apart from the Sun. The night side would be colder than Pluto.

Like I said, it made sense.

Then astronomers tried calibrating the Arecibo radio telescope by aiming it at Mercury’s night side. That was in 1965. Mercury’s night side was emitting much more radio energy than they’d expected.

Their equipment was functioning properly, so the data wasn’t a technical glitch.

Still Learning

We didn’t have all the answers in 1965, and still don’t. But we were and are learning.

Over the previous few centuries we had learned that Newtonian physics matched observations better than Aristotle’s ideas.

Then, about a century back, better tech and more precise measurements showed that Newtonian physics wasn’t the whole picture. (October 6, 2017; August 25, 2017)

Scientists are rapidly learning about quantum mechanics, Schrödinger’s cat, and — more to the point — planets.

One explanation for Mercury’s warm night side was that it had an atmosphere. Winds could transferred heat. That seemed unlikely, at best. Mercury is too small and too close to our sun to keep much air.

Arecibo data made much more sense in models that had Mercury rotating once every 59 days. Roughly. Our world’s 24 hour days, that is.

Starting Points

That analysis explained Mercury’s comparatively warm night side.

Instead of having a 1/1 spin-orbit resonance, like Earth’s moon, Mercury’s spin-orbit resonance would be 3:2.

It would rotate on its axis three times for each two orbits.

That would explain why astronomers kept seeing the same side in sunlight. A 3:2 spin-orbit resonance would make Mercury’s rotation period, its day, almost exactly half its synodic period for observers on Earth.

A synodic period is the time it takes for something to be return to the same position relative to our sun, from our viewpoint. Our moon’s synodic period is about 28 days: the time between one full moon and the next.

Synodic periods and synods of bishops don’t have a lot in common.

A synod of bishops is an advisory group for the Pope. “Synod” is what happened when two Greek words got used in folks speaking Latin and then picked up by folks speaking English. And that’s another topic.

Mercury’s 58-day rotation period was confirmed when Mariner 10 flybys gave us the first somewhat-detailed views of its surface. We started getting a close-up look at the planet again in 2011, when MESSENGER settled into orbit around Mercury.

Some conclusions Eugenios Antoniadi and others arrived at weren’t accurate. Some were. Their observations, and trains of thought they started, gave other scientists starting points for more study.1

I think what we’re learning about exoplanets is a bit like what we knew about other worlds in the Solar System a few generations back. Some of today’s conclusions probably won’t match later observations. But we are learning what to look for, and how to look for it.


New Research: 55 Cancre e


(From NASA/JPL-Caltech, via Jet Propulsion Laboratory, used w/o permission.)
(An artist’s concept of 55 Cancri e with an atmosphere.)

Atmosphere, Not Lava Flows, for Exoplanet 55 Cancri e
Monica Young, Sky and Telescope (November 27, 2017)

Previous studies of 55 Cancri e haven’t been able to determine whether this super-Earth hosts an atmosphere. A new study settles the question.

“The exoplanet 55 Cancri e is a cipher. Astronomers have gone back and forth on its nature — waterworld, diamond world, or volcanic hellscape? Part of the riddle has been whether the planet is bare rock or has an atmosphere — previous studies have shown ambiguous results.

“Now, new research from Isabel Angelo and Renyu Hu (both at JPL-Caltech) published in the November 16th Astrophysical Journal (full text here) seems to have settled the question: 55 Cancri e probably does have an atmosphere and a substantial one at that….”

A key phrase here is “…seems to have settled….”

The latest study makes sense. The new analysis of data from NASA’s Spitzer Space Telescope confirms that 55 Cancri e’s hot spot is eastwards of the spot where 55 Cancri is straight overhead. Something is transferring heat.

Someone suggested that maybe constant flow in massive lava lakes and rivers account for the easterly shift. That might be happening, but lava wouldn’t flow fast enough to account for what’s observed. A “substantial atmosphere” would.

The scientists who published this study, Isabel Angelo and Renyu Hu, say 55 Cancri e’s surface pressure would be around 1.4 bar. A bar is 100 kilopascals, a little under Earth’s current sea level air pressure.

They may be right. Their analysis seems like a much better fit with what we know about 55 Cancri e than the ‘lava rivers’ scenario. But I won’t be surprised if we learn that something else accounts for what’s been observed so far.

We’ll know more after more analysis of data we’ve collected, and better technology lets us get a better look. My guess is that there will still be surprises, even after the first probes reach 55 Cancri e.

A Quick Look at 55 Cancri

55 Cancri is a double star, about 41 light-years away. It’s visible, barely, in our sky: for someone with good eyesight and very dark skies.

The five planets we’ve found there so far orbit 55 Cancri A, a star that’s a little smaller and cooler than ours.

55 Cancri B is a red dwarf, a thousand times further from 55 Cancri A than Earth is from our sun.

Technically, I should be calling 55 Cancri e “55 Cancri Ae.” But just about every resource I found says “55 Cancri e,” so that’s what I’ll do, too.

55 Cancri f is just inside the star’s habitable zone. It’s at least half as massive as Saturn, so it’s probably a gas giant. It might have a moon that’s roughly Earth-size, though.2

That wouldn’t be why folks sent a radio message toward the system in 2003. We didn’t know about it then.


Ross 128 b: Not Quite Earth 2.0?


(From ESO / M. Kornmesser , via BBC News, used w/o permission.)
(“Artwork: Ross 128 b might be a target in the search for extra-terrestrial life”
(BBC News))

Nearby planet is ‘excellent’ target in search for life
Paul Rincon, BBC News (November 15, 2017)

Astronomers have found a cool, Earth-sized planet that’s relatively close to our Solar System.

“The properties of this newly discovered planet – called Ross 128 b – make it a prime target in the search for life elsewhere in the cosmos.

“At just 11 light-years away, it’s the second closest exoplanet of its kind to Earth.

“But the closest one, known as Proxima b, looks to be less hospitable for life….”

Scientists have had quite a few opinions about habitable planets and red dwarf stars.

I don’t know who first studied of red dwarfs and habitability. Other than science fiction authors, who had varying degrees of concern regarding facts and plausibility.

We knew an Earth-like planet orbiting a red dwarf would have to be very close to its sun to have liquid water.

A red dwarf planetary system with life on a planet like ours would have to be on a scale more like Jupiter and its moons than the Solar System.

That made life around red dwarfs seem unlikely. Red dwarfs are less massive than our star, but they’re significantly more massive than Jupiter. Expecting their planets to have big orbits made sense.

Then we started finding lots of planets orbiting very close to red dwarfs.

Many were a great deal more massive than Earth, but early detection methods wouldn’t pick up Earth-mass worlds.

Scientists started thinking maybe life could exist with a red dwarf sun.

Or maybe not.

We were also learning that some, but not all, red dwarfs apparently have flares as strong as our star’s. Since an Earth-like planet orbiting a flaring red dwarf star would be very close to its sun, it might not be ‘habitable’ by our standards when its sun flared

Radiation wouldn’t be the only problem.

Some simulations showed that being that close to a flaring star might blow part or all of the planet’s atmosphere away. On the other hand, maybe Earth-like planets with sturdy magnetic fields would keep their air. Other simulations suggested that was true.

Ross 128 doesn’t flare, not that we’ve noticed, so it was and is on ‘might be life here’ lists. Except those kept by scientists who had other reasons for not expecting life on a red dwarf’s planets.

Weather and climate on a planet somewhat like ours, where it’s always ‘day’ on one side and ‘night’ on the other, would be — different. Just how different is yet another topic.

Even if we find life on Ross 128 b, I don’t see it as ‘Earth 2.0.’ Surface gravity would be higher than we like, for one thing. But it’s among the best bets we’ve found in our search for life outside the Solar System.

What We Know, and Don’t Know


(From ESO, IAU and Sky & Telescope; used w/o permission.)
(Ross 128 is at 11h 47m, +00° 48′, near Beta Virginis in our sky. It’s in that faint red circle.)

We’ve known about Ross 128 since the 1920s. It was unremarkable except for being among the nearer stars.

We don’t know much about Ross 128 b, apart from its mass and orbit.

It’s about 1.35 times as massive as Earth, with a year that’s roughly 9.9 days long. Our days, that is. Its orbit is a bit more eccentric than Earth has today, but not nearly as much as Mercury’s. Thinking it’s got a 1/1 spin-orbit resonance seems reasonable.

Ut’ll be warmer than Earth, but probably not too warm to support our sort of life. If it’s got an atmosphere like ours. Scientists haven’t measured Ross 128 b’s diameter directly.

We’ve been learning a great deal about planets outside the Solar System, enough to get a reasonable idea of what we can expect.

Some are familiar: small, rocky worlds like Earth and Mercury.

Others are pretty good matches for the Solar System’s outer worlds. And quite a few aren’t like anything we’d seen before. (June 30, 2017)

A planet with Ross 128 b’s mass is almost certainly like the Solar System’s inner planets, mostly rock and metal. It’s massive enough to keep an atmosphere.

But we won’t know if it does or not until slightly better tech gets finished. Telescopes like ESO’s Extremely Large Telescope and NASA’s James Webb Space Telescope will let scientist study Ross 128’s atmosphere. If it has one.3 (June 2, 2017)

The May 12, 2017, Arecibo signal

On May 12 of this year scientists at Arecibo detected broadband signals coming from Ross 128’s location in our sky.

They were unusual, apparently not random: very likely not a natural phenomenon.

I’d love to be writing about efforts to translate our first message from another civilization. That’s almost certainly not what the Arecibo observatory detected.

Ross 128 is very close to our ecliptic, and in the same plane as geosynchronous satellites. It looks like the signal was from one of humanity’s orbiting devices.

The May 12 signal wasn’t our first false alarm. I’m quite sure it won’t be our last. (December 16, 2016; September 16, 2016)


“Ludicrous,” “Absurd,” and Starshot’s Microprobes

Our first interstellar missions will most likely be to places like Proxima Centauri b and Luyten b.

Their stars are both fairly close. “Close” compared to most, that is.

We’re no more able to build interstellar probes today than folks in Antoniadi’s day could send robotic spaceships to Mercury.

But I suspect we’re no more than a few decades from launching the interstellar equivalent of the Pioneer and Luna probes. Maybe a century.

Not everyone thinks so, apparently. A recent headline dismissed Stephen Hawking’s Breakthrough Starshot initiative as “ludicrous.”

Starshot’s proposed nanocraft and a steerable ground-based gigawatt laser aren’t off-the-shelf tech. But the headline reminded me of a New York Times op-ed dismissing Goddard’s research as “absurd.” Less than five decades later, Apollo 11 reached Earth’s moon. (June 9, 2017)

I talked about Starshot’s plans earlier this year. (March 3, 2017)

Something like Starshot’s microprobes could reach Proxima Centauri b in two or three decades. We can make equipment that stays operational that long: the Voyager spacecraft, for example. Doing the same with microprobes seems challenging, not impossible

At about 41 light-years, it’d take a bit upwards of two centuries for probes using Starshot’s technology to arrive at the 55 Cancri planetary system. My guess is that we’ll develop something faster before we start planning missions lasting that long.

Admiring God’s Work: Or Not

I’ll skip my usual explanation for why I don’t fear knowledge, and think learning about God’s creation is a good idea. (November 24, 2017; March 26, 2017)

About extraterrestrial life, I think we may find life elsewhere in this universe, or not.

Either way, it’s not up to me. Part of my job is admiring God’s work: not telling the Almighty what should and should not be real. (September 29, 2017; December 2, 2016)

“Our God is in heaven; whatever God wills is done.”
(Psalms 115:3)

I’m also quite sure that we’ll eventually meet folks whose ancestors come from another world. Or at least find evidence that they exist. Or that we won’t. Again, it’s not up to me. (January 29, 2017; December 23, 2016)

I see SETI, the Search for ExtraTerrestrial Intellignece, as a reasonable branch of science. Some assumptions folks make about how SETI should work, not so much.4

Pulp Science Fiction and SETI

We knew enough about Mercury in the 1930s to realize that insect-monkey people couldn’t live there.

But folks creating pulp science fiction had few restraints other than their fervid imaginations and publication deadlines.

I enjoy some of those rip-roaring tales of derring-do. But they’re much more fiction than science.

I strongly suspect that if SETI succeeds, we’ll learn that our neighbors are a great deal more “alien” than that 1930s “Life on Mercury” illustration.

I don’t think anyone seriously thinks that people who aren’t human will look like Barsoomians or the “aliens” in most 1950s movies.

On the other hand, many SETI projects assume that non-human folks use technology we developed during the last century, and are as intensely social as we are.

I’ll grant that we’re more likely to find folks with our chatty dispositions.

But expecting a civilization whose ancestors may have used radio waves for communication when we were working the bugs out of stone tools? I’ve talked about that before, and probably will again. (December 16, 2016)

More; mostly how I see science, faith, and being human:


1 Mercury, from Antoniadi to MESSENGER:

2 Rocky worlds:

3 Ross 128 b:

4 Serious SETI:

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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