Looking for extraterrestrial life is still a science in search of a subject, but it’s getting increasingly difficult to argue that there couldn’t be critters out there.
Today I’ll be talking about the search for life in the universe, a possibly-habitable planet circling the next star over, and a planet that couldn’t possibly be habitable.
Make that not habitable by life as we know it. Life using fluorine and carbon as we do hydrogen and carbon, with sulfur as a water-substitute — is a topic for another post.
- Looking for Alien Life
- Proxima Centauri b
- Gliese 1132 b: Still Worth Studying
I don’t ‘believe in’ space aliens, not in the sense that I believe space-alien emissaries of niceness will come to solve all our problems: sort of like Klaatu, in “The Day the Earth Stood Still,” who stopped just short of walking on water.
The title character in “The Thing from Another World” acted like an invader. But the Thing’s bad attitude may have come from being shot after the humans blew up his ship, and that’s another topic.
Me? I’m firmly convinced that there’s life elsewhere in the universe, or that life exists only on Earth. We don’t know — yet.
Either way, it’s not my decision: and I’m certainly not going to tell the Almighty whether or not we should have neighbors. That’s up to God:
Finding any sort of life, like the alien equivalent of bacteria, would be a huge discovery; but the ‘jackpot’ would be finding neighbors, folks like us, but not human.
If we meet during the next few centuries, I think the odds are that they’ll be finding us. Either way, I’m pretty sure that reactions would be mixed; and that’s yet another topic.
“…Frankly, if you think about it, any creatures on other planets, subject to the same laws of chemistry and physics as us, made of the same kinds of atoms, with an awareness and a will recognizably like ours would be at the very least our cousins in the cosmos. They would be so similar to us in all the essentials that I don’t think you’d even have the right to call them aliens.”
(“Brother Astronomer;” Chapter Three, Would You Baptize an Extraterrestrial? — Brother Guy Consolmagno (2000))
“Where should we look for alien life?”
Paul Rincon, BBC News (August 25, 2016)
“Astronomers have discovered a small planet around Proxima Centauri, the closest star to the Sun. But how do astronomers decide whether a planet is hospitable to life?
“In the science fiction film Interstellar, astronauts leave a dying Earth in search of a hospitable planet for the human race to settle.
“But the first two worlds on their shortlist – deemed ‘potentially habitable’ from a distance – turn out to be nightmarishly hostile on closer inspection. The crew’s first stop is an ocean planet lashed by 1km-high tidal waves, while the second is a deep-frozen world choked by toxic ammonia.
“While Christopher Nolan’s movie is fantasy, it draws on a real-life aspect of the work done by astronomers who study exoplanets – worlds beyond our Solar System.
“The search for planets capable of supporting life could answer an age-old question: are we alone in the Universe? But what do astronomers mean when they refer to distant worlds as potentially habitable, or Earth-like?…”
“…they describe this ecological disaster on Earth. I like the fact they are talking about that and raising consciousness. It’s clear that it’s climate change and we screwed up the Earth…That’s a good theme. But the specific things they say about it—they say there’s this blight [attacking all crops] that’s building up the nitrogen [in the atmosphere] and that’s going to draw down the oxygen. Anybody who knows about planetary atmosphere is going to sit there at that point and go, ‘That’s a bunch of BS.’…”
(“What’s Wrong With the Science of ‘Interstellar’?,” Mother Jones (November 12, 2014))
That started me thinking of other ‘we’re all gonna die’ scenarios that could be good enough for movies.
They could have had Earth’s magnetic field failing: sort of like “The Core,” only slightly more reality-based.
Headlines like “Earth’s magnetic field ‘could flip in the space of 100 years’, scientists warn” would have made that scenario more “relevant” in the months following “Interstellar’s” release.
It’s true, by the way: Earth’s magnetic field is weakening a whole lot faster than scientists expected. Our planet’s north and south magnetic poles will switch places “soon” — on the geologic time scale.
Sometimes the magnetic poles stay put for much longer, sometimes they’re downright twitchy. The Laschamp event, 41,400 years back — give or take a few thousand years — lasted centuries, not millennia.
If it went out entirely, and stayed that way, we’d have trouble. Besides letting us use compasses for navigation, Earth’s magnetic field keeps the solar wind from blowing bits of the upper atmosphere away, and keeps many charged particles from reaching the ground.
We think Mars lost most of its air that way, although there’s more to it than that. Venus, with no magnetic field to speak of, is closer to our sun than either Mars or Earth and has a massively dense atmosphere.
Earth’s current ice age was in progress at the time, and had been for over two million years. We’d been around, too, and didn’t know about Beryllium-10, magnetic fields, or geomagnetic reversals, until quite recently.
“Ice age” is a lot simpler to say than “Quaternary glaciation,” which is what scientists call most recent of the five known glaciations during Earth’s history, and that’s yet again another topic.
Before cyanobacteria came along, 2,400,000,000 years back — roughly, scientists are still working on the exact timeline — there wasn’t much of any oxygen at all.
Oxygen would have combined with methane, forming carbon dioxide and water: good for us, since we’re not suited to breathing methane; but carbon dioxide and water vapor don’t retain heat as well as methane does.
The ice eventually melted, today’s sort of critters got started 541,000,000 to 485,400,000 years back — that’s phyla of animals, a phylum being the taxonomic rank below kingdom and above class, and aren’t you glad there won’t be a test on this?
The Cambrian critters in that illustration don’t look quite like today’s animals: hardly surprising, since it’s been a half-billion years since they were around.
Earth’s atmospheric oxygen supply peaked during the Carboniferous. That was 358,900,000 to 298,900,000 years ago, and Earth’s atmosphere hasn’t been 35% oxygen since.
Besides, I’m missing the main point of that BBC article: where should we be looking for extraterrestrial life?
“…’When we say “potentially habitable” exoplanets, that’s a term that refers to measurable qualities of a planet that are necessary for habitable conditions,’ says Prof Abel Méndez, from the University of Puerto Rico (UPR) at Arecibo.
“These are, then, promising targets where nothing is guaranteed. But two criteria dominate popular discussions of planetary habitability: first, whether it is within Earth’s general size range (and therefore has a chance of being rocky) and, second, whether it resides in what’s known as the habitable – or Goldilocks – zone.
“This is the range of distances around a host star where there’s just enough starlight to keep water in liquid form on a planet’s surface. Too close to the star, and the heat will cause water to boil off; too far away and any water will freeze.
“These are useful rules of thumb, but a host of factors influence how hospitable planets are. And some are excluded from the conversation because of limitations in technology….”
(Paul Rincon, BBC News)
This BBC News article assumes that life will live on or near the surface of a planet like Earth, which is a reasonable assumption; and that it’ll be ‘life as we know it:’ critters made of nucleic acid/protein in water.
There’s been serious discussions of life in Europa’s subsurface ocean, and other ‘biochemistries,’ but that’ll wait for another post.
Paul Rincon’s article also gets into how we have been finding planets circling other stars: and why so many seem to be around red dwarf stars.
The ‘wobble method,’ Dopper spectroscopy for folks who like the technical name, measures how fast the planet’s star moves towards and away from us as star and planet rotate around their center of gravity.
Measuring it is easier when the planet is heavy and the star small, which is one reason that so many of the first exoplanets spotted were so big.
Transit photometry, the method illustrated in that ‘brightness/light curve’ picture, measures how much a star’s light dims as a planet crosses in front. That method works better with smaller stars, too.
The good news about looking for habitable worlds around red dwarf stars is that there are a great many more of these smaller stars than ones like our comparatively bright sun.
The not-so-good news is that a red dwarf’s habitable zone is really small, which I think makes the number of ‘Goldilocks zone’ planets circling red dwarfs rather remarkable.
On the other hand, red dwarf stars last a really time, far longer than ours will, so life around a red dwarf’s planet would have a very long time to develop.
“Red dwarf” is a bit of a misnomer, as I said in an earlier post. Even a very cool red dwarf like TRAPPIST-1 has a surface temperature below 2,700 K/2,430 °C/4,400 °F: very roughly the temperature and color of a ‘warm’ LED or incandescent bulb. (July 29, 2016)
I put an unnecessarily-long link list of resources, mostly in Wikipedia, near the end of this post.3
“Neighbouring star Proxima Centauri has Earth-sized planet”
Jonathan Amos, BBC News (August 24, 2016)
“The nearest habitable world beyond our Solar System might be right on our doorstep – astronomically speaking.
“Scientists say their investigations of the closest star, Proxima Centauri, show it to have an Earth-sized planet orbiting about it.
“What is more, this rocky globe is moving in a zone that would make liquid water on its surface a possibility.
“Proxima is 40 trillion km away and would take a spacecraft using current technology thousands of years to reach….”
One of the many things we don’t know about Proxima Centauri b yet is its orbital inclination: how much its orbit around Proxima Centauri is tipped from our viewpoint.
If we’re ‘seeing’ it edge-on, or nearly so, Proxima Centauri b’s mass is only 1.27 times Earth’s. If it’s made of the same stuff as Earth, it’ll be at least 1.1 times as wide as our planet.
That’s the least possible value for its mass and size, but 90% of the possible orientations give it a mass less than 3 times Earth’s.
There’s a good chance Proxima Centauri b is what scientists call a super-Earth, a planet with more mass than Earth’s, but substantially less than the Solar System’s ice giants Uranus and Neptune.
Let’s assume — optimistically — that we’re seeing Proxima Centauri b’s orbit edge-on, which would mean that it’s mass is 1.27 times Earth’s, or 1.27 x 5.97237 ×1024 kilograms = 7.5849099 ×1024 kg.
That’s 7,584,909,900,000,000,000,000,000 kilograms, which helps explain why folks use exponential notation so often when dealing with big numbers.
I like comparisons, so here’s Venus, Earth, and Proxima Centauri b:
- Venus mass: 4.8675×1024 kg
- Earth mass: 5.97237 ×1024 kg
(1.227 x Venus)
- Minimum Proxima Centauri b mass: 7.5849099 ×1024 kg
(1.27 x Earth)
That doesn’t prove much, apart from the newfound planet being roughly as close to Earth’s mass as Venus, only bigger.
Proxima Centauri b’s equilibrium temperature is 234 K; or -39 °Centigrade, -38 °Fahrenheit. That’s a bit cooler than Earth’s roughly 260 K, 8.33 °Fahrenheit, but not by much.
Earth’s surface is, on average, warmer than that because we’ve got an atmosphere, and that isn’t another topic, since a big question is whether life can exist on Proxima Centauri b.
The answer depends partly on the planet’s star.
Proxima Centauri is small, cool, and dim compared to our star: with about an eighth of the Sun’s mass; roughly 3,042 K at the surface, compared to our star’s 5,772 K; and about 0.0015 times as bright.
Since most of the energy coming from its sun is down in the infrared, Proxima Centauri b gets very roughly as much heat as Earth, but only a fraction of the visible light. ‘High noon’ wouldn’t be particularly bright.
Proxima Centauri is what astronomers call a “red dwarf,” but like I said earlier — standing on Proxima Centauri b’s surface, what we’d chiefly notice is that it looks bigger than our Sun. The color is a bit ‘warmer’ than we’re used to here, but it would not look like a stop light.
Orbiting as close to its sun as it does, Proxima Centauri b may be tidally locked, with one side always facing the star: as Earth’s moon always has one side facing us.
Or it might have a more complex spin-orbit resonance, like Mercury. This may or may not affect habitability.
The bad news, as far as hoping for habitability goes, is that Proxima Centauri is a flare star. Stars like that “can undergo unpredictable dramatic increases in brightness for a few minutes.” (Wikipedia)
Bright light would be the least of life’s problems on Proxima Centauri b. Orbiting as close to its star as it does, the planet gets something like 400 times as much x-ray radiation as Earth does.
A thick atmosphere and strong magnetic field might keep x-ray levels at the surface at safe levels for life. Or maybe life on a planet like that could be fine in the ocean, but not on land.
If there is life on Proxima Centauri b, it’ll have plenty of time to grow. At the rate the star’s burning fuel, it’s good for about another four trillion years: almost 300 times the current age of the universe.
- “Proxima Centauri b: Have we just found Earth’s cousin right on our doorstep?”
Franck Marchis, The Planetary Society (August 24, 2016)
- “Planet Found in Habitable Zone Around Nearest Star”
ESO press release (August 24, 2016)
- “A terrestrial planet candidate in a temperate orbit around Proxima Centauri”
Guillem Anglada-Escudé, Pedro J. Amado, John Barnes, Zaira M. Berdiñas, R. Paul Butler, Gavin A. L. Coleman, Ignacio de la Cueva, Stefan Dreizler, Michael Endl, Benjamin Giesers, Sandra V. Jeffers, James S. Jenkins, Hugh R. A. Jones, Marcin Kiraga, Martin Kurster, Marıa J. López-González, Christopher J. Marvin, Nicolas Morales, Julien Morin, Richard P. Nelson, Jose L. Ortiz, Aviv Ofir, Sijme-Jan Paardekooper, Ansgar Reiners, Eloy Rodrıguez, Cristina Rodrıguez-Lopez, Luis F. Sarmiento, John P. Strachan, Yiannis Tsapras, Mikko Tuomi, Mathias Zechmeister; Nature (July 13, 2016)
- “Equilibrium Temperatures of Planets”
Michael Strauss, Writeup 3/Planetary Thermodynamics (September 27, 2009)
(From CfA/Dana Berry/Skyworks Digital, via Phys.org, used w/o permission.)
(“This artist’s conception shows the rocky exoplanet GJ 1132b, located 39 light-years from Earth. New research shows that it might possess a thin, oxygen atmosphere – but no life due to its extreme heat.”
“Venus-like exoplanet might have oxygen atmosphere, but not life”
Harvard-Smithsonian Center for Astrophysics, Phys.org (August 18, 2016)
“The distant planet GJ 1132b intrigued astronomers when it was discovered last year. Located just 39 light-years from Earth, it might have an atmosphere despite being baked to a temperature of around 450 degrees Fahrenheit. But would that atmosphere be thick and soupy or thin and wispy? New research suggests the latter is much more likely.
“Harvard astronomer Laura Schaefer (Harvard-Smithsonian Center for Astrophysics, or CfA) and her colleagues examined the question of what would happen to GJ 1132b over time if it began with a steamy, water-rich atmosphere.
“Orbiting so close to its star, at a distance of just 1.4 million miles, the planet is flooded with ultraviolet or UV light. UV light breaks apart water molecules into hydrogen and oxygen, both of which then can be lost into space. However, since hydrogen is lighter it escapes more readily, while oxygen lingers behind.
” ‘On cooler planets, oxygen could be a sign of alien life and habitability. But on a hot planet like GJ 1132b, it’s a sign of the exact opposite – a planet that’s being baked and sterilized,’ said Schaefer….”
Wikipedia’s page on this planet hasn’t been updated as I write this, Thursday evening, September 1. Before Proxima Centaur b’s discovery, it was the nearest known rocky/Earth-like exoplanet:
“…It has been called ‘one of the most important planets ever discovered beyond the Solar System’: Gliese 1132 b is three times closer to Earth than any other known rocky exoplanet and telescopes should be able to determine the composition of its atmosphere, the speed of its winds and the color of its sunsets….”
(Gliese 1132 b, Wikipedia)
Gliese 1132 b is still an important subject of study, particularly since it may help us understand how Venus got to be the way it is now.
Many scientists think Venus started with about as much water as Earth.
Schaefer’s team thinks that Gliese 1132 b started out with quite a bit of water, like Venus and Earth; but may still be in the process of losing that water. If that’s the case, they think some of the planet’s water is still there, as water vapor.
If that’s the case, Gliese 1132 b’s water is in the process of being lost to space; but what’s left is acting as a sort of blanket, insulating the planet and keeping a ‘magma ocean’ on its surface molten.
That magma would react with oxygen in the atmosphere, but the team figures only around 10% of the oxygen would combine with the molten rock.
If that’s the case, and it’s a lot of “ifs,” some of the oxygen may be staying in Gliese 1132 b’s atmosphere; which may be detectable from here.
A process like what’s probably happening now on Gliese 1132 b is what scientists think turned Venus from a somewhat Earth-like world into the hotter-than-an-oven place it is today.
- Planet GJ 1132 b
The Extrasolar Planet Encyclopaedia
- “Predictions of the atmospheric composition of GJ 1132b”
Laura Schaefer, Robin Wordsworth, Zachory Berta-Thompson, Dimitar Sasselov; The Astrophysical Journal (Submitted July 16, 2016)
- “New exoplanet in our neighborhood”
Jennifer Chu, MIT News Office (November 11, 2015)
- “Faith, the Universe, and Wisdom”
(August 28, 2016)
Ancient Mountains, Grasshoppers, and Baron Kelvin
The Last Few Billion Years, Briefly
- Earth Overshoot Day and Pollinators”
(August 12, 2016)
Ehrlich, Yeats, and Me
God’s Property, Our Responsibility
- “Studying Thousands of New Worlds”
(July 29, 2016)
Not My Decision
- “Earth’s Wandering Poles, A Comet, a Wobbling Moon”
(October 24, 2014)
Here’s what got me started that time:
- “Earth’s magnetic field ‘could flip in the space of 100 years’, scientists warn”
Rob Waugh, Metro.co.uk (October 21, 2014)
- “The Laschamp geomagnetic excursion featured in nitrate record from EPICA-Dome C ice core”
R. Traversi, S. Becagli, S. Poluianov, M. Severi, S. K. Solanki, I. G. Usoskin, R. Udisti1; Scientific Reports, via PubMed Central® (PMC), U.S. National Institutes of Health’s National Library of Medicine (January 28, 2016)
Even more, mostly about atmospheres, magnetic fields, and Solar wind:
- “THEMIS measures how solar wind interacts with Earth’s magnetic field”
Christine Gabrielse, UCLA Institute for Planets and Exoplanets (December 6, 2011)
- “Geomagnetic Reversals: Rates, Timescales, Preferred Paths, Statistical Models and Simulations”
Catherine Constable, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography (September 30, 2001)
- “What’s Wrong With the Science of ‘Interstellar’?”
David Corn’s interview of Astrobiologist David Grinspoon, Mother Jones (November 12, 2014)
- “Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes”
Robert Frei, Claudio Gaucher, Simon W. Poulton, Don E. Canfield; NATURE, via SAO/NASA ADS Astronomy Abstract Service/Harvard (2009)
- “Atmospheric oxygen over Phanerozoic time”
Robert A. Berner, Proceedings of the National Academy of Sciences of the United States of America (September 1999)