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How should we think about the discovery of what appears to be an Earth-like planet orbiting another star? Cynics might say “What, again?”—for there have been several earlier candidates among these “exoplanet” surveys for an Earth 2.0. But the interest in this one, called Kepler 452b and orbiting the star Kepler 452 1,400 light years away in our Milky Way galaxy, is justified. It is surely the most Earth-like yet: rocky and only about five times the mass of the Earth, and comfortably within the orbital region of its parent star known as the habitable zone, where temperatures should be right for liquid water to exist. Given the similarity of Kepler 452b to our own sun, there’s good reason to think that the formation of planets around it would have involved a similar apportioning of chemical ingredients, including water.
Kepler 452b was found by NASA’s Kepler spacecraft, which is dedicated to searching for planets around other stars. Given that it is now possible to detect water in the atmospheres of at least some exoplanets, we can expect to know more before too long about, if not Kepler 452b itself, then other worlds like it.
Does this mean the new exoplanet is likely to harbour life? That’s harder to say. Some researchers, such as geologist Peter Ward and astronomer Donald Brownlee, think that life on Earth is made possible by a remarkable concurrence of circumstances that render our environment stable and hospitable, such as the seasonality of climate caused by the tilt of the Earth’s rotation axis, a large moon to create tides (and thus fecund tidal pools), and the presence nearby of a giant planet (Jupiter) that sweeps up all the local cosmic debris that would otherwise keep raining down on our planet with catastrophic consequences. Even given those conveniences, did the appearance of life entail an incredibly unlikely sequence of chemical processes that gave rise to the first proto-organisms? Or is that result almost inevitable once the right ingredients—rock, water, carbon dioxide and a source of energy such as undersea volcanic activity—are present, making the galaxy what biochemist Nick Lane calls in his book The Vital Question a “cosmic culture dish?”
All of this is speculation right now, although Lane has done a splendid service in working out the details of a plausible route to life that doesn’t involve the chance formation of replicating molecular systems in some prebiotic soup of raw materials. Another, more abstract line of argument suggests that, again given the raw chemical ingredients and an energy source to set them reacting, the appearance of organisation (a sine qua non of living systems) is virtually a law of nature. For what it’s worth, I’m with these “probabilists."
I also think Richard Dawkins is right to suggest that if life appears in the cosmos, it is highly likely to evolve by Darwinian natural selection, albeit partly for reasons he did not adduce: it is looking increasingly probable that the property of “evolvability” is a fundamental, though still imperfectly understood, feature of how information is organised in complex systems. I’m not even convinced that all this can only take place in water, rather than some other liquid solvent, although the issues around this are more subtle than is often acknowledged.
One objection to this assertion of the frequent occurrence of life on other worlds is the famous Fermi paradox: if aliens abound, where are they all? (The SETI Institute in California, which searches the skies for broadcast signs of intelligent life, is already training its sights on Kepler 452b.) But this issue is more an illustration of physicist Enrico Fermi’s incisive mind than it is a fundamental problem for believing in life on other planets. For one thing, there is no reason to think that life must always evolve to the complexity of humans (who are in any event by most measures no more complex than apes or whales). But even if it did, it seems an absurdly solipsistic idea that we can extrapolate from the fleeting status and motivations of 20th-century Homo sapiens to deduce anything at all about the fate and goals of intelligent life on other worlds.
The real significance of the discovery of Kepler 452b, at least at this point, is not that it tells us anything new about life elsewhere—it was surely only a matter of time, given the rate of exoplanet discovery, that we found a place like this, and it’s likely that our galaxy contains hordes of them. Rather, it could be a catalyst for getting serious about trying to answer at least a few of these long-standing but still woolly questions about what it takes for life to appear. We can now feel confident that they are questions genuinely worth asking.
How should we think about the discovery of what appears to be an Earth-like planet orbiting another star? Cynics might say “What, again?”—for there have been several earlier candidates among these “exoplanet” surveys for an Earth 2.0. But the interest in this one, called Kepler 452b and orbiting the star Kepler 452 1,400 light years away in our Milky Way galaxy, is justified. It is surely the most Earth-like yet: rocky and only about five times the mass of the Earth, and comfortably within the orbital region of its parent star known as the habitable zone, where temperatures should be right for liquid water to exist. Given the similarity of Kepler 452b to our own sun, there’s good reason to think that the formation of planets around it would have involved a similar apportioning of chemical ingredients, including water.
Kepler 452b was found by NASA’s Kepler spacecraft, which is dedicated to searching for planets around other stars. Given that it is now possible to detect water in the atmospheres of at least some exoplanets, we can expect to know more before too long about, if not Kepler 452b itself, then other worlds like it.
Does this mean the new exoplanet is likely to harbour life? That’s harder to say. Some researchers, such as geologist Peter Ward and astronomer Donald Brownlee, think that life on Earth is made possible by a remarkable concurrence of circumstances that render our environment stable and hospitable, such as the seasonality of climate caused by the tilt of the Earth’s rotation axis, a large moon to create tides (and thus fecund tidal pools), and the presence nearby of a giant planet (Jupiter) that sweeps up all the local cosmic debris that would otherwise keep raining down on our planet with catastrophic consequences. Even given those conveniences, did the appearance of life entail an incredibly unlikely sequence of chemical processes that gave rise to the first proto-organisms? Or is that result almost inevitable once the right ingredients—rock, water, carbon dioxide and a source of energy such as undersea volcanic activity—are present, making the galaxy what biochemist Nick Lane calls in his book The Vital Question a “cosmic culture dish?”
All of this is speculation right now, although Lane has done a splendid service in working out the details of a plausible route to life that doesn’t involve the chance formation of replicating molecular systems in some prebiotic soup of raw materials. Another, more abstract line of argument suggests that, again given the raw chemical ingredients and an energy source to set them reacting, the appearance of organisation (a sine qua non of living systems) is virtually a law of nature. For what it’s worth, I’m with these “probabilists."
I also think Richard Dawkins is right to suggest that if life appears in the cosmos, it is highly likely to evolve by Darwinian natural selection, albeit partly for reasons he did not adduce: it is looking increasingly probable that the property of “evolvability” is a fundamental, though still imperfectly understood, feature of how information is organised in complex systems. I’m not even convinced that all this can only take place in water, rather than some other liquid solvent, although the issues around this are more subtle than is often acknowledged.
One objection to this assertion of the frequent occurrence of life on other worlds is the famous Fermi paradox: if aliens abound, where are they all? (The SETI Institute in California, which searches the skies for broadcast signs of intelligent life, is already training its sights on Kepler 452b.) But this issue is more an illustration of physicist Enrico Fermi’s incisive mind than it is a fundamental problem for believing in life on other planets. For one thing, there is no reason to think that life must always evolve to the complexity of humans (who are in any event by most measures no more complex than apes or whales). But even if it did, it seems an absurdly solipsistic idea that we can extrapolate from the fleeting status and motivations of 20th-century Homo sapiens to deduce anything at all about the fate and goals of intelligent life on other worlds.
The real significance of the discovery of Kepler 452b, at least at this point, is not that it tells us anything new about life elsewhere—it was surely only a matter of time, given the rate of exoplanet discovery, that we found a place like this, and it’s likely that our galaxy contains hordes of them. Rather, it could be a catalyst for getting serious about trying to answer at least a few of these long-standing but still woolly questions about what it takes for life to appear. We can now feel confident that they are questions genuinely worth asking.
