14 September 2011

Super-Earths and sexy aliens


"Exoplanets" -- planets outside our own solar system -- are now routinely being discovered, and as our instruments grow more sensitive, smaller and smaller planets are being detected. Indeed, some of the most recently-found exoplanets are almost as small as Earth, a few even being described as "Earth sized". Unfortunately MSM reports of these discoveries suffer from an odd and naïve misplacement of emphasis. A recent example:

Astronomers using a telescope in Chile have discovered 50 previously unknown exoplanets. The bumper haul of new worlds includes 16 "super-Earths" - planets with a greater mass than our own, but below those of gas giants such as Jupiter. One of these super-Earths orbits inside the habitable zone - the region around a star where conditions could be hospitable to life.

The news piece is illustrated with an artist's conception of a very Earthlike-looking world, and speculation about life occupies a good chunk of its length.

In these media reports, the prospect of life is always at the fore- front. It's understandable, in a way; we have more than enough lifeless rocks, big and small, in our own solar system, and these stories have to be made appealing to a public raised on a diet of science fiction rich with alien beings (usually scary or sexy or both) often by authors with little knowledge of either astronomy or evolution. One could easily conclude that the discovery of an abundance of verdant Earthlike worlds, complete with analogs of the Ewoks or the Na'vi or at least the Klingons, is just around the corner.

Er, not really.

First off, the term "super-Earth" just means a planet with a certain mass range, larger than Earth but smaller than the gas giants of our solar system. It says nothing about other characteristics we associate with Earth. Most of these planets are several times as massive as Earth, implying much higher gravity, a very different atmosphere, and other drastic differences.

The "habitability zone" (H-zone) means the range of distance from the local sun within which temperatures would allow liquid water to exist on a planet. Being in the H-zone doesn't mean a planet actually has liquid water, nor that conditions are otherwise at all suitable for life.

Nevertheless, it's clear that planets are a common phenomenon, and given the number of stars in our galaxy, there must be billions of planets in the H-zones of their local suns -- even billions of such planets which are similar in mass to Earth -- whether we happen to have spotted them yet or not. (There are, of course, also billions of other galaxies.) That doesn't mean that planets with complex life are likely to be common.

To start with, most stars are smaller and dimmer than our own Sun, meaning that the H-zone is closer in. A planet within the zone would likely be "tidally locked", with one side permanently facing the local sun and the other permanently facing away, as our own Moon is "tidally locked" to Earth. This would produce permanent extremes of heat and cold respectively on the two hemispheres, and the atmosphere would all freeze out on the cold side. Not very Earthlike.

Also, evolution takes time. Earth is 4.6 billion years old and life has existed for at least 3.6 billion years, yet organisms big enough to see have existed for probably less than 1 billion years. How common is it for a planet to stay within the H-zone for billions of years? Most stars exist in parts of the galaxy where stars are much closer together than in our own area; close encounters between stars, which would disrupt planetary orbits, must be frequent (by stellar-lifetime standards) events. Gas giants bigger or closer to the local sun than Jupiter (which seem to be common) would be even more disruptive to the orbits of smaller planets.

Then there are factors such as a planet's chemical composition, axial tilt, the make-up of its atmosphere (if any), the likelihood of a magnetic field strong enough to screen out cosmic rays, frequency of meteorite impacts releasing enough heat to sterilize the entire surface, etc., and, again, the probability of all these factors staying within life-friendly limits for billions of years. It's very likely that Earth is actually a freak case. Finally, there's the problem of the low probability of an initial appearance of life, even if conditions are perfect.

Remember, no matter how ordinary Earth seems to us, it is not necessarily typical. No matter how freakishly rare planets with complex life are, we must by definition be living on one of them.

However, we won't need to rely on such assessments for much longer. Soon, we'll be able to actually detect the presence of complex life -- if it exists at all -- by studying the composition of exoplanets' atmospheres. The clue will be free oxygen. Oxygen is very chemically reactive and would not remain in a planet's atmosphere for a long period of time unless some process is constantly replenishing it -- and the only plausible such process is photosynthesis. That is, the presence of a significant amount of free oxygen in an exoplanet's atmosphere would be pretty solid evidence of an ecosystem with something like Earthly plant life, which would mean other complex life could well be present too. I'm betting that we won't find any such cases -- but in a few years we'll actually know.

If we did find one or more such cases, it would actually be bad news. We would still be stuck with the Fermi paradox -- the total absence of any evidence for technological civilizations elsewhere in the universe. Remember, the universe is billions of years old. If technological civilizations are even somewhat abundant, some of them should be millions, or even hundreds of millions, of years older than we are. Consider how far human technology has advanced in the mere 400 years since real systematic science began, and how the pace of progress has steadily accelerated. A civilization a million years older than ours, anywhere in the galaxy, ought to be producing effects we could easily detect and identify. Since we don't see any such effects, such civilizations probably aren't out there.

If complex life is fantastically rare, Fermi's paradox would be instantly explained. But if it's common, we have a mystery. It might be that, for some reason, complex life almost never evolves high intelligence, but that doesn't seem very likely. Intelligence is too useful. We'd pretty much have to conclude that there's some unknown factor that always destroys technological civilizations before they get much more advanced than we are now -- and that we ourselves are therefore doomed. There is already something of a cottage industry of speculation along these lines, most of it scientifically-worthless venting of whatever form of cynicism about humanity happens to obsess a given writer.

But I don't think that's the case. Everything points to complex life, or even life in general, being freakishly rare.

One last point -- about those sexy aliens. Here's a photo of a female chimpanzee in estrus:


Recall that all life on Earth -- humans, apes, spiders, trees, mold, bacteria, everything -- descends from one common ancestor, whereas life on another planet would have a different origin and would have followed different evolutionary pathways. To a male chimpanzee, the image above would be the epitome of sexy, but frankly it doesn't do a thing for me, and if you're a typical human male, you feel the same. Now, not only is this a fellow Earthly animal, but of all the millions of animal species on Earth, it's the one most closely related to ourselves. Yet the standards of sexual attractiveness are obviously quite different. So, no, an organism that had evolved independently on a different planet would not look like Deanna Troi, or even like anything that the notoriously omnivorous Captain Kirk would give a second glance.

(Chimpanzee image found via PZ Myers, who makes a similar point.)

19 Comments:

Blogger okjimm said...

I like Holst's " The Planets" but boy and howdy are you over my head on this one. I new a sexy alien, once, but she moved back to Japan.

14 September, 2011 11:10  
Blogger Robert the Skeptic said...

Coincidentally I received an "e-skeptic" newsletter from the Skeptics Society talking about the search for extraterrestrial intelligence. Specifically, we should be cautious about letting the universe know we are home.

The article references Stephen Hawking, Carl Sagan and more recently, Jared Diamond who has made a living demonstrating that when more civilized cultures encounter less civilized cultures, disaster often results. Consider how European explorers exploited and destroyed new world cultures.

So perhaps like the alien encounters portrayed in Hollywood, they may indeed not be benevolent beings eager to share their advanced technology with us.

Maybe we should pull the plug on SETI before they notice us (says, tongue-in-cheek).

14 September, 2011 14:29  
Blogger Infidel753 said...

Okjimm: Many have suspected that the Japanese are from "elsewhere".

RtS: Another good point -- I've read what Diamond and Hawking have said about this, and they make sense. Any Australian Aborigine or American Indian could confirm that being discovered by a more advanced civilization can be quite unpleasant. I'm glad that, in fact, there's probably nobody out there.

14 September, 2011 19:10  
Blogger Shaw Kenawe said...

Hi Infidel753,

Hope you don't think it too forward of me to post a poem related to this subject--it combines the wishful hope for alien life, plus skepticism of a certain religion's claim:

THE FLYING HOUSE OF LORETO

I’ve always wanted to meet one of those gray, bug-eyed aliens,
the ones that get blamed for our missing time, for the little metal

beads found stuck up our noses, the sexual probings, egg implantations.
It never happens. I make myself available to them: walk the beach

at night far from buildings, lights, anything that might scare
them away. I think they avoid me. I’m too willing to cooperate,

say yes to the cc’s of blood, the clumps of follicles, yes to the speculum,
(as long as it’s body-temperature, space-age plastic). I’m wild to have them

take specimens to Coma Bernices with my name printed in Alien on each vial.
In Loreto, Italy, they say the Virgin’s house was transported on the backs

of angels from Nazareth to the Anconan coast. Why not?
I want my aliens; they have their flying house.

15 September, 2011 06:18  
Blogger Infidel753 said...

Interesting concept (though a lab monkey might say "be careful what you wish for").

for our missing time, for the little metal

beads found stuck up our noses, the sexual probings, egg implantations
.

They came 882 light years to hold a frat party?:-)

We'll have our own flying houses soon enough.

15 September, 2011 06:28  
Anonymous chris said...

A quite thought provoking piece. It is a bit crass to inject politics into this but I couldn't help but wonder whether it wouldn't be wise to expedite exploration of these H planets in order to have potential safe havens once the baggers are done destroying earth. We'd leave them here of course.

15 September, 2011 09:31  
Blogger mendip said...

Excellent entry - thanks! Has led me to cancel the correspondence course I was taking in Klingon... ;)

15 September, 2011 12:08  
Blogger Infidel753 said...

Chris: Hopefully we can get them to emigrate instead.

Mendip: Thanks. As best I can tell, that Klingon language seems to have been invented to sell sore-throat medications.

15 September, 2011 12:44  
Anonymous krissthesexyatheist said...

Are you sayin' that out in space somewhere, in all that vastness and, err, space...there are not hot green women for Captain "Sexist" Kirk to travelo where no man has gone before. cool that.

Astronomy, cosmology and anything thing space-y are, like, my weakest science subjects. I used to fall for the media's "we found a super erff" with life on it or whatever. now i know it is not what the average lay peep thinks (an identical earth that can have humans on it) and it probably means that there is water of some form on the planet.

As far as sexy aliens...that's me and i've got it covered. Awesome buddy,

Kriss

15 September, 2011 18:44  
Blogger Infidel753 said...

Nope, no hot green women, I'm afraid -- and I should have mentioned, for any ladies intrigued by that "sexual probings" stuff, they won't look like David Bowie in "The Man Who Fell to Earth" either. They'll probably look like that thing that's always chasing Sigourney Weaver around spaceships, and that's if we're lucky. I'm frankly not expecting more than pond scum, and not much of that.

"Super-Earth" = really, really big dead rock.

15 September, 2011 19:12  
Blogger Green Eagle said...

What amazing progress planetary astronomers have made in the last few years. Why, I predict that any year now they are going to discover the planet where cutting taxes on the rich makes things better for everyone.

16 September, 2011 12:59  
Blogger Infidel753 said...

I think that's one's in a whole other universe.....

16 September, 2011 13:03  
Anonymous nonnie9999 said...

the question is--what planet are rethuglicans from?

always informative, infidel. though i could have lived without that last pic. ;o)

16 September, 2011 23:04  
Blogger Infidel753 said...

I know.....us guys and our girlie pictures on our blogs.....

17 September, 2011 04:17  
Blogger Tim McGaha said...

Very nicely written. Free oxygen IS the key. There are only a handful of processes that create it, most of which are life-related, and unless continuously renewed it doesn't stay free for long.

As to the abundance of life ... Beats me. I think single-celled life may be quite common. But complex life might be very rare. The book "Rare Earths" by Ward and Brownlee goes into that argument in detail. It's worth reading.

17 September, 2011 06:22  
Blogger Infidel753 said...

TM: Thanks! I've read Rare Earth and found it to make a devastatingly convincing case. Since then I've never been able to swallow the idea of complex life being abundant. More recently, however, I realized that even the initial appearance of simple life might well be a very rare event, although of course this gets into areas where our knowledge is still very incomplete.

17 September, 2011 06:40  
Blogger Tommykey said...

A civilization a million years older than ours, anywhere in the galaxy, ought to be producing effects we could easily detect and identify.

Of course, you can't limit yourself to just this galaxy, as the universe is filled with billions. Though an intelligent civilization in a galaxy outside of our cluster might as well not exist due to the insurmountable distances.

What I look forward to, and hopefully it will happen in my lifetime, is a mission to Europa to see if there is life in the liquid water believed to be beneath the icy surface.

27 September, 2011 17:07  
Blogger Infidel753 said...

In fact, I would expect a civilization just a few centuries older than ours to have overrun the whole universe -- but I'm trying to be conservative.

A Europa mission would be fascinating, but very technically challenging considering how much ice a probe would have to dig through to reach liquid water. With good enough AI it could certainly be done, though.

27 September, 2011 18:44  
Anonymous Super Earth said...

Just so you guys in the world know, The Daily Mail is well known for it scaremongering here in the super earth and is often subject to ridicule. I am sure they will get around to blaming the whole thing on illegal information and Benefit cheats.

17 October, 2011 08:58  

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