A Richness of Planets

I’ve been writing a lot lately about hatred and discrimination, about the small prejudices that keep humanity fractured and ignorant. It’s important to fight for reason and equality, but I think it’s equally important to remember why we’re fighting these prejudices, and keep in mind the greater things that we can accomplish if we overcome them. Consider, then, this column about the real meaning of the exoplanet revolution by Caleb Scharf, director of astrobiology at Columbia University.

The early, less sensitive planet-detecting methods were best suited to find “hot Jupiters“, gas giants that orbited their stars at extremely close distances. But our methods have grown more sensitive since then, making it possible to detect the medium-size worlds called “super-Earths“, and even exoplanets the size of the Earth or smaller. Despite the heartbreaking failure of NASA’s Kepler planet-finder satellite, the search continues, and we now know of almost 1000 confirmed exoplanets, with many more likely to be hiding in data yet to be analyzed.

I grant that we’re not yet ready to begin compiling the Encyclopedia Galactica. In most cases, everything we know about these planets is defined by a few numbers: the length of their orbits, their size, their average density, their surface temperatures. For a very few, we have spectrographic evidence for the composition of their atmospheres, hints of the presence of organic molecules; even, in one case, the signature of a raging global superstorm. But we don’t know what they look like. We don’t know whether they have rings or moons; we don’t know whether they have plate tectonics or magnetospheres; we don’t know whether they’re ocean worlds, ice worlds, desert worlds, or temperate worlds with continents and seas.

But the sheer size of the possibilities ought to set anyone’s imagination afire. The most common kind of stars in the galaxy are red dwarfs, smaller and cooler than our sun. There’s every indication that planets orbiting at the right distance from these stars could support life – and there are a lot of them:

The estimated number of Earth-sized planets orbiting around these stars at a distance that allows for the possibility of a temperate surface (capable of holding that biological elixir — liquid water) varies from study to study, but it’s coming in at about one per seven systems. Given the concentration of these small stars locally, there is a 95 per cent probability that one of these potentially temperate worlds sits within a mere 16 light years of Earth. There could be about 23 billion stars in our Milky Way galaxy, each harbouring Earth-sized planets with life-friendly temperatures on their surfaces.

It didn’t have to be this way. We could have found ourselves living in a universe where planets were spectacularly rare, where there was nothing between the stars but clouds of gas and dust. Our solar system could have been unique, the product of a one-in-a-trillion fluke of chance; the human species could have found itself isolated forever, like a castaway clinging to a lone piece of driftwood in an ocean with no islands. Or, we could have found that planets were common but habitable planets were the rarity; the Earth could have been a flourishing green-and-blue exception in a cosmos of boiling gas giants and frozen, airless lumps of rock.

But delusions of our uniqueness have been knocked down every time, and this is just the latest domino in that chain to fall. We have every reason to believe that terrestrial planets like the Earth aren’t the exception, but the rule. (And why not, when the explosion of a single star forges enough heavy elements to create 200,000 planets like ours?) Far from being a rarity, our world might merely be one in an unimaginably rich galactic community of billions like it. And where there are so many planets, how could we not expect that at least some of them harbor life of their own, possibly even minds like our own? Even if the evolution of intelligence is a rarity, we have billions of tumbles of the cosmic dice to work with.

Granted, even if the galaxy is overflowing with sentience, we’re separated by vast gulfs of time and space. Even if habitable planets are common, we’ll probably never jaunt between solar systems like a sailing ship stopping at different ports of call. Space is too big, and physics is too unforgiving. But even if we never have a working warp drive or a convenient wormhole network, it’s far from impossible that we could build robot messengers and surveyors, artificial intelligences that would make the trip to other planetary systems and report back, centuries or millennia later, on what they found.

It’s even conceivable – just barely – that we could build colony ships, multi-generational arks that would be sent on a one-way mission to a hospitable nearby star system. The resources required to construct such a ship would be enormous, and even beyond the technical challenges, the psychology of the people who signed up for the mission would be a major concern. But human beings have always been explorers, and there’s an unimaginable richness of planets waiting to be discovered. Who among us wouldn’t be tempted, even just a little, by the prospect?

Image credit: NASA, via Wikimedia Commons

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About Adam Lee

Adam Lee is an atheist writer and speaker living in New York City. His new novel, City of Light, is available in paperback and e-book. Read his full bio, or follow him on Twitter.

  • katiehippie

    I’m more than tempted. I would go.

  • Elizabeth

    The math might be off in this quotation from the Star Trek episode “Balance of Terror” written by Paul Schneider, but I like it anyway.

    “In this galaxy, there’s a mathematical probability of three million Earth-type planets. And in all of the universe, three million million galaxies like this. And in all of that… and perhaps more, only one of each of us.” – Dr. McCoy

  • Tommykey69

    it’s far from impossible that we could build robot messengers and surveyors, artificial intelligences that would make the trip to other planetary systems and report back

    I have recently thought that our first contact with intelligent beings would be precisely between our robotic probes and theirs.

  • Jason Koskey

    If there is anything to the “transhumanism” movement, space travel will become more feasible as human beings become less organic. Biological robots with a human brain at their core. (And plasma arm cannons, so long as we’re fantasizing.)

  • Loren Petrich

    It must be pointed out that the abundance of “hot Jupiters” was a big surprise. I don’t think that anyone expected lots of Jupiter-like planets to be orbiting at the Earth’s sort of distance or less.

    But such planets could have Earth-sized moons. Imagine a “hot Jupiter” in the habitable zone with more than one Earthlike moon.

    On the downside, we don’t know for sure how much water that habitable-zone Earthlike planets tend to have. Hardly any at all? They would then be desert planets. Much more than the Earth? They would be covered by deep super oceans.

  • http://www.patheos.com/blogs/daylightatheism Adam Lee

    As the fellow who creates the (endlessly fascinating) World Dream Bank site points out, Earth very nearly has too much water. If it wasn’t for our very active plate tectonics building up rugged continental topography, we’d be surprisingly close to being an ocean planet.

  • Phasespace

    For the most part, we can assume that planets in the habitable zone will have significant amounts of water, not necessarily oceans, but a lot of water just the same.

    The reason this assumption is safe is because water is one of the more abundant molecules, is easily formed, and once formed, it takes quite a bit of UV radiation to break it apart.

    I would also argue that an earth-sized moon of a Jupiter-sized planet in the habitable zone is pretty much guaranteed to have enough water to form oceans. The reason is that a Jupiter sized planet is going capture enough comets to spread a *lot* of water around its satellites.

  • Katatonic

    The Mars One project is seeking colonists for their expedition; these volunteers will not be returning to earth. I am old enough that living to the end of my (possibly VERY short) life in space or on Mars doesn’t dismay me. Will I apply? /hollowlaugh I am in no way qualified and doubt my ability to learn the necessary skills to contribute meaningfully to their goals (apart from donating cash).

  • Bdole

    Given the possibility that sentient creatures could have evolved at any time – even millions of years ago on another planet, it’s surprising we haven’t already encountered aliens with godlike technological prowess.
    What do we do if we reach a planet teeming with primitive life forms? The ethical question might be asked: Could our tramping around prevent another intelligent species from arising?

  • Joe

    There is a good chance that planets the size of Earth or larger would have plate tectonics which would in turn build up similar rugged topography. There is evidence that Mars is…or WAS tectonically active and it is much smaller than Earth. There have been moons that have shown tectonics as well. I think it’s likely that plate tectonics are common. If they are common, then such planets would also generally have strong magnetic fields as well to protect them from solar wind.

  • Joe

    I’ve heard this before as well. Take a look at how humans have evolved socially and ethically. We’re far from perfect, but we are learning more and more that the ethical path is the path that does not interfere or disturb nature. It’s better to observe from afar than to destroy an environment. I think likewise it may be the norm that a civilization which has reached the technological level of interstellar travel has evolved ethics that would prevent them from interfering in our progress…kind of an observe from afar type of thing. Some assume aliens may be violent or destructive, and it’s possible, but I tend to believe that they would be much more likely to be the exact opposite. In fact it may be an evolutionary imperative … a species that evolves the intelligence to maniuplate its’ environment but does not quickly evolve the social and ethical standards of conservation & acceptance may be a species that is likely to destroy itself or its’ environment(and thus itself) before it reaches the stage of interstellar flight.

  • GCT

    Why should we assume that non-interference is better ethically?

  • David Simon

    That’s a false dichotomy. There’s plenty of space on the scale between destruction and being completely hands-off.

  • http://www.patheos.com/blogs/daylightatheism Adam Lee

    I very much hope this is true – I like to think that any inherently violent species would destroy itself before it ever reached the step of colonizing the cosmos. On the other hand, I’m minded that war and conflict have often driven rapid technological progress in humanity.

  • Loren Petrich

    Let’s work out some numbers. The average depth of the Earth’s oceans is about 4.3 km (2.7 mi, 14,000 ft), and if the oceans uniformly covered all of the Earth’s surface, they’d have a depth of 3 km (2 mi, 10,000 ft).

    The average height of the continents is about 840 m (0.5 mi, 2800 ft), so one more kilometer of ocean, and much more of the Earth would be covered by ocean. However, above-water land has a lot of erosion, so if there was more ocean, there may still be a lot of above-water land.

    The highest place by gravitational potential is the peak of Mt. Everest, at 8.85 km (5.5 mi, 29,000 ft) above sea level. It was produced by two continental plates colliding, so it’s a tectonic feature. So it would take 14 km (9 mi, 45,000 ft) of ocean to drown it.

    The highest place above nearby terrain is the peak of Mauna Loa. Its base is 5 km (3 km, 16,000 ft) below sea level and its peak 4.17 km (2.59 mi, 14,000 ft) above sea level, for a total of 9.2 km (5.7 mi, 30,000 ft). In the absence of plate tectonics, one would get giant volcanoes, like this one and what Mars has.

    Source: Earth’s Surface

  • http://eternalbookshelf.wordpress.com/ Ani J. Sharmin

    The vastness of space is such a wonderful and awe-inspiring thing to contemplate. It would be extremely tempting to go on such a voyage, far way, to another world. One could be cynical and say that humanity will just bring our worst characteristics with us to other worlds … but we’ll bring our best characteristics with us, too.

  • Jon Jermey

    Far more likely than a ‘multigenerational ark’ is the following scenario: onboard computers on an uncrewed vessel detect a likely planet; the ship lands and carries out further tests. If these are all passed then the ship’s robots get busy making more robots and assembling mechanical placentas. Early-stage human embryos are taken out of storage, mutated if necessary in ways that will help them survive on the planet, then grown to birth weight, after which they are cared for by robots until they reach adulthood. We’re talking about thousand-year journeys here; another generation or so at the other end isn’t going to make a lot of difference.