The star Gliese 667C is as intriguing as it is because it underlines in triplicate the ‘habitability’ question, which surfaces every time a planet is discovered in a zone around its star where liquid water could exist on the surface. This is the classic definition of ‘habitable zone,’ meaning not so much a place where humans could live — we have no knowledge of other conditions on these worlds, knowing little more than their minimum mass — but a place where a basic condition for life as we know it is possible.
I’m much in favor of considering exotic environments for life, and these would include venues ranging from the upper clouds of Venus to the depths of the icy gas giant satellites in our own system. But when we read about ‘habitable zones’ in most scientific papers, we’re usually falling back on the liquid water criterion because it’s hard enough to search for any kind of life on a distant world, much less a kind that we don’t even know exists. Liquid water is a starting point, a baseline in the search for life-supporting worlds, but it hardly means the hunt for life stops there.
My own speculations about systems like GJ 667C become purely imaginative. I notice how many systems we’re finding that have ‘super-Earths,’ a category of planet that doesn’t even appear in our own Solar System. I also note that small M-dwarfs can produce clusters of planets that, in the case of GJ 667C, are close enough that three can be squeezed into the habitable zone. Imagine a civilization emerging on one such world, with other possible life-bearing planets so tantalizingly close — what a boost that would give to the proponents of the local space program!
Image: This picture shows the sky around multiple star Gliese 667. The bright star at the centre is Gliese 667 A and B, the two main components of the system, which cannot be separated in this image. Gliese 667C, the third component, is visible as a bright star, very close and just under A and B, still in the glare of these brighter stars. The very subtle wobbles of Gliese 667C, measured with high precision spectrographs including HARPS, revealed it is surrounded by a full planetary system, with up to seven planets. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin.
Searching for Life’s Equations
In Are We Alone, a fine essay in Aeon Magazine, astrobiologist Caleb Scharf (Columbia University) places the exoplanet hunt in a cosmic context. We may be getting used to them now, but the early proliferation of ‘hot Jupiters’ and now ‘super-Earths’ was not an expected outcome at the beginning of exoplanet detection — for that matter, the pulsar planets found around PSR B1257+12 in 1991 certainly raised eyebrows as orbiting the remnant of a once massive star. Scharf points out, too, that 70 Virginis b and 16 Cygni Bb, discovered not long after the detection of planets around 51 Pegasi in 1995, were moving on highly elliptical orbits.
These wonderful finds — and news like GJ 667C delivered yesterday — keep reminding us that the old idea that our Solar System is somehow representative of what we’ll find elsewhere is deeply flawed. Says Scharf:
Many exoplanets… follow orbits that are far more elliptical than any followed by the major planets around our Sun. More puzzling still, the most frequent type of configuration, the one that has earned the moniker of ‘the default mode of planetary formation’, is that of closely packed worlds, on orbits that take mere days or weeks to loop around their stars. These compressed versions of our own system seem, for now, to be far more normal than our own. But if we’re not normal, what are we? That’s a question we can’t answer yet, because our census of stars and planets is still woefully incomplete.
Back to the habitability question. With the prospect of tens of billions of stars in our galaxy harbouring planets of Earth-size and into the super-Earth range, we live in a universe that gives us the chance to find out whether life is rare or common. Being in a habitable zone does not mean a planet sustains life, and it will be the job of our next-generation instruments to help us study planetary atmospheres so we can unlock the numbers on just what the odds are. Scharf speaks of an ‘equation for abiogenesis’ that we can search for throughout a galaxy that accommodates us by giving us a vast number of targets. We can thus take a measure of our own significance:
If we lived in a cosmos with only a few planets, we could never deduce the true probability of abiogenesis with any precision, even if they all harboured life — as imagined by earlier advocates of plurality. We might never be lucky enough to find one of these worlds within examining range, and all would be lost among the stellar fields of the Milky Way. The existence of billions of planets gives us a chance to write the equation, a chance to pin down the relationship between habitability and actual habitation.
So the excitement of finds like the planets around GJ 667C isn’t that we have yet more evidence that clement places for life can exist in the cosmos. It’s that we have another target — at 22 light years a relatively close one — that we’ll eventually be able to use as we make the crucial call on life’s equations. In the coming century, a discovery in either direction, that life is a rarity or is as common as, well, planets in the habitable zone, will have profound implications for philosophy as well as practical action. It will guide our intentions as we develop the technologies to reach other stars
The prime factor determining whether ANY of these planets are habitable is: How EXTENDED are heir atmospheres(especially if they contain a lot of hydrogen,as the Kepler 11 system appears to have)? My own BELIEF is that there is very little hydrogen, due to the proximity of the AB primaries th Gliese 667C! there is an EXCELLENT WAY o TEST this belief! The proximity of the AB primaries should “deplane” the GL667C system, increasing the possibility of at least one of the planets TRANSITING! The MOST spacecraft should be able to detect a transit if the transiting planet DOES have an extensive hydrogen atmosphere!
The more information and details that filter in about exoplanet existence and potential habitability, the more this seems to be the ultimate Big Data problem/opportunity. One could reasonably hope that the technology for extracting ever more information from the photons reaching us from distant planets and their atmospheres will continue to improve, by orders of magnitude, allowing us to enhance and refine those “abiogenesis equations” to the point where our predictive abilities re: habitability become more and more statistical certainties.
One could envision reaching a state where we’re not only able to rapidly assess habitability, but also able to identify presence of life, “type” of life, civilization, technology level, etc.
Then, of course, we reach the point where we’re able to realize the *true* value of Big Data: “Which of these identified civilizations would be most interested in buying our sh*t?” ;-)
It would be an interesting challenge, certainly. One question would be how difficult it would be to bring the astronauts back: with the Moon, a fairly small rocket was needed to get back from the surface. Imagine if Venus were an Earthlike, habitable planet: while you could certainly benefit from a nice atmosphere for parachuting down to the surface, assembling a Saturn V and the associated launch facility is difficult enough on Earth, let alone on an alien planet!
And that’s before you start considering what it would take to get around the Gliese 667 system, with its super-Earth planets and high orbital velocities.
Good point — I can imagine these astronauts grumbling about all the work. How about on a “super-earth” with 2-4x the gravity here? Ugh.
Without some breakthrough propulsion device, it almost sounds “easier” to install a space elevator rather than deliver or construct a heavy lift vehicle in-situ.
Or, have some really capable nanobots that can fabricate a heavy lift ship for you while you explore. Either way, it will take a huge advancement in tech if you want to get back out of the gravity well.
Planets in such closely-packed orbits probably exchange bolide-impact debris more readily than Mars and Earth do, with shorter transit times, too.
So, assuming even marginal habitability, if there’s life on any one of them, there will very likely be life on all of them.
I wonder what a native of such a solar system would think were the chances of life or civilisation appearing in a sparse, cold, almost empty system such as ours? We might come as an equally big surprise to them.
How reliable are our current estimates about how common different types of planets and solar system configurations are? When we found mostly Hot Jupiters, we knew the numbers were biased by our very detection methods. Detecting planets the size of Earth and smaller is still much harder than detecting Super Earths, thus it is my assumption that we still cannot really trust our current statistics on frequency of occurrence for different planet types.
In summary the typical star has long been known to be a class M red dwarf. Based on the peak of the Kepler results distribution, the typical planet is in the Neptune or dwarf-Neptune (a more accurate term than “super-Earth” in my opinion) classes. There are probably at least as many habitable zone Neptune + dwarf-Neptune planets as there are class M red dwarf stars, more than 10^11 in the Milky Way. So what does this imply re: SETI and the Fermi paradox?
The surprising answer is very little. Big volatile rich worlds are most likely to have world oceans and very thick atmospheres with deep gravity wells. Their whale and giant squid analogs (maybe plus living zeppelin and flying manta ray analogs?) might get very intelligent, but they won’t be building any radio transmitters or rockets, ever. Could such beings ever be contacted? There are a couple of very interesting affirmative opinions in the SF literature. Are
“Star Maker” by Olaf Stapledon and “Up the Walls of the World” by James Tiptree Jr. really just escapist fantasies for entertainment purposes only? Or are they revelations from exceptional persons who knew far more about the cosmos and our place in it than they let on?
The first interstellar explorers will be machines. We may send humans later as colonists, but machines both intelligent and otherwise will be the ones who reach those alien worlds. They will be more efficient than humans in just about every task and they won’t need to be brought back to Earth or this Sol system.
Joy said on June 27, 2013 at 5:10 (in quotes):
“In summary the typical star has long been known to be a class M red dwarf. Based on the peak of the Kepler results distribution, the typical planet is in the Neptune or dwarf-Neptune (a more accurate term than “super-Earth” in my opinion) classes. There are probably at least as many habitable zone Neptune + dwarf-Neptune planets as there are class M red dwarf stars, more than 10^11 in the Milky Way. So what does this imply re: SETI and the Fermi paradox?”
I do not know how many exoplanets around M class stars might develop their own intelligent life, but I can imagine them being used for exploration and resource purposes by nonnative advanced ETI, especially because of their long stellar lives (good place for Dyson Shells and Matroishka/Jupiter Brains). How many of these kinds would be conducting SETI/METI is another matter.
“The surprising answer is very little. Big volatile rich worlds are most likely to have world oceans and very thick atmospheres with deep gravity wells. Their whale and giant squid analogs (maybe plus living zeppelin and flying manta ray analogs?) might get very intelligent, but they won’t be building any radio transmitters or rockets, ever. Could such beings ever be contacted? There are a couple of very interesting affirmative opinions in the SF literature.”
Has anyone beyond the SF literature ever tried to figure out if aquatic or aerial intelligences could become technological and how? I would not want to dismiss the possibility just because our cetaceans and squid don’t have cities and starships (that we know of…). Remember until 1995 we thought most solar systems would look similar to ours, with little rocky planets up front and big gassy ones in the back.
“Are “Star Maker” by Olaf Stapledon and “Up the Walls of the World” by James Tiptree Jr. really just escapist fantasies for entertainment purposes only? Or are they revelations from exceptional persons who knew far more about the cosmos and our place in it than they let on?”
Interesting comment from Wikipedia on Tiptree’s novel:
“In November 2006 astronomers discovered a polar vortex on Saturn very similar to the one described by Alice Sheldon in this novel.”
Related article I wrote for Centauri Dreams about potential life forms living among the clouds of Jupiter:
https://centauri-dreams.org/?p=6308
The Sagan and Salpeter paper notes that the twin Voyager cameras would be just poweful enough to image floaters in the Jovian atmosphere should they exist. Has anyone ever sifted through those images and the ones from Galileo and Cassini of Jupiter itself for such beings? Think of it as a novel SETI project.
And speaking of Jupiter, those long brown lines on Europa: I am willing to bet they are composed of organic material, perhaps even organisms themselves. So let us land there and find out. Cheaper and easier than drilling to the subsurface ocean.
On the other hand, the high orbital velocities mean higher ejection velocities are needed to get between the planets. The higher planetary masses suggest that impact velocities should be higher too. Transfer of material via bolide impacts is likely to be a far more violent process (and therefore more potentially-destructive to any organisms that might be hitching a ride) between the planets of Gliese 667C than between Mars and Earth.
Also perhaps somewhat relevant to this discussion, see this news release and the associated poster presentation (pdf) regarding impact transfer between the planets of Gliese 581.
You were discussing rotation periods. Has anybody worked out the parameters for unusual orbital periods?
A planet might have a 3:2 orbital resonance, or 9:17. The day might be much longer than a year. Could the rotation period be a thousand, or a million years? Our day varies slightly; how much variation is likely? Is rotation on 2 or 3 axes of rotation unlikely? The axes wouldn’t have to be perpendicular.
These planets are so close together that a hypothetical journey between them, at the right time, could be almost as “easy” as traveling from the earth to the moon!
Though a surface gravity of 1.5g or more would make things more difficult.
Sorry, maybe that last bit about axes not being perpendicular doesn’t make sense–I was thinking of something like a precession of equinoxes. Ours is almost 27,000 years; what if another planet’s precession period is 27 years? Would that situation not last long?
Discovery! More Planets Found Orbiting in a Star Cluster
by Elizabeth Howell on June 26, 2013
Could star clusters also host planets? Or do they have to wait for the little guys until the stars evolve and move further apart? Well, astronomers have actually just found planets — yes, two planets — orbiting Sun-like stars in a cluster 3,000 light-years from Earth.
These are the third and fourth star cluster planets yet discovered, but the first found “transiting” or passing across the face of their stars as seen from Earth. (The others were found through detecting gravitational wobbles in the star.)
This is no small feat for a planet to survive. In a telescope, a star cluster might look pretty benign, but up close it’s pretty darn harsh. A press release about the discovery used a lot of words like “strong radiation”, “harsh stellar winds” and “stripping planet-forming materials” in a description of what NGC 6811 would feel like.
Full article here:
http://www.universetoday.com/103151/discovery-more-planets-found-orbiting-in-a-star-cluster/
Anyone else think of the Isaac Asimov SF story “Nightfall” when reading about exoworlds inside a globular star cluster:
http://www.astro.sunysb.edu/fwalter/AST389/TEXTS/Nightfall.htm
Finding life on another planet or moon in the solar system would go a long way toward improving the predictions for life on exoplanets, especially if we were able to sample them and determine if they originated with Earth life (or the other way around). It’s a shame we are spending such a small fraction of the world GDP on going there.
Considering these opinions makes me think that machines may like the environment of star cluster planets . Or else water world creatures that withstand hard radiation by living undersea or in aquarium starships or iceships, fragments of their ‘Callistian’ homeworlds.
A race of intelligent giant squids might arise on an iceworld, harness geo thermal power and totally hollow out and reform the 20 mile deep mantel of sea ice until they discover tbe surface. Eureka! Then they launch probes from their low grav moon world. Or ice podlets of their offspring to colonize other geysers or cryro volcanic moons.
Sometimes correct statements can mislead worse than incorrect ones. Andy wrote
“Transfer of material via bolide impacts is likely to be a far more violent process (and therefore more potentially-destructive to any organisms that might be hitching a ride) between the planets of Gliese 667C than between Mars and Earth.”
This doesn’t address the most poignant find in from studying possible lithopanspermia in our own system. Even though the energy to throw a rock or organism from our planet is many times that needed to vaporise it into plasma, meteorite impacts lift much of that material from ‘spall zones’. The heating is so low in these, that most of it is due to air friction. We may suppose that superEarths have dense atmospheres, but that is just an educated guess.
Those articles you referenced looked interesting, but that critical first one was not published yet, my guess is that it assumed the following. Lithoparspermia only delivered viable organisms, on those extremely rare passages of rocks (as proposed between Earth and Mars) that took only a few hundred years. Considering the potential for perturbations in that Gliese 667 system, my guess is that their would be plenty of transfers that happen in just a few thousand years, and that may turn out to be good enough.
I don’t think its over yet Andy.
@Rob Henry: if you want to talk about misleading, your statement is a perfect example as you completely neglect the second impact, i.e. the one that delivers the material to the destination planet. These are going to be characterised by high impact velocities as well for the same reason that the initial impact does.
Yes Andy, the problem of the reentry of these is far more complex, but here’s the rub. Its results vary dramatically according to meteorite size, tensile strength, and thermal conductivity. The composition and density of the receptive atmosphere should also be important. Once again I am finding it amazing that often the interior of these rocks shows only mild heating, and don’t see why that miracle couldn’t be extended to dissipate twice the heat.
If your opinion reflects a study to which you have reference of how results vary for all classes of meteorites according to the variable of re-entry velocity, I would love to see it.
I’m back cause IT’S BAAAAAAAAK! Remember the FIRST exoplanet EVEN CONSIDERED to be habitable? THAT’S RIGHT! Gliese 581C!!! WELL: If recent calculaions moeling CLOUD COVER on tidally locked planets are CORRECT (BY THE WAY: Where is the BLOG on this INCREDIBLY IMPORTANT RESEARCH? Ive been waiting for a couple of days to see it on CD, because this could POTENTIALLY change EVERYTHING), GL581C just barely makes it in( but only if it has a CIRCULAR orbit, as Voight et al propose, instead of the swiss team’s eccentric orbit! NOW: Back to GL667C!
If 667Ch DOES exist, we would have the first EARTH SIZED(ie NOT super earth) in the red dwarf habitable zone. There are also DOZENS of KOI status Kepler candidates that would squeeze in, too!
A Cosmic Map of the Exoplanets [Interactive]
An interactive graphic charts the location and distance to 861 known exoplanets, highlighting those that might hold life
By Michael Moyer | June 18, 2013 | 4
http://www.scientificamerican.com/article.cfm?id=exoplanets-cosmic-map-extraterrestrial-life
Astronomers Search for Signs of Life in the Skies of Distant Exoplanets [Preview]
The galaxy is teeming with planets. Scientists are straining to peer into their atmospheres to seek signs of extraterrestrial life
By Michael D. Lemonick
Full article here:
http://www.scientificamerican.com/article.cfm?id=astronomers-search-for-signs-life-in-skies-distant-exoplanets