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Gizmodo
So far, the only examples of sentient life we’ve found are right here on our own planet. It’s not for lack of trying, though—we’ve sent out spacecraft deep into our solar system and, so far, still remain alone. What if the problem isn’t where we are looking, though, but when?
A forthcoming study in Journal of Cosmology and Astroparticle looks at the possibility that life as we know it may not require a star similar to our sun but could emerge on planets orbiting much smaller, weaker stars. If we do allow for the possibility of life around non-sunlike stars, then it turns out that the universe is likely to be much more habitable in the distant future than it is today.
“It’s natural for us to think that we are the most common form of life, simply because that’s the only one that we know of,” lead author of the paper, Harvard University’s Avi Loeb, told Gizmodo. “Therefore, people assumed that being next to star like the sun was the most likely place for life to emerge.”
If you throw out the assumption that we need a sun-like star, though, then there’s a whole new class of stars—smaller and less powerful than the sun, but far more common—that suddenly start to look like good candidates. They’re called low mass stars.
Although these stars throw out less light and heat than our powerful sun, they still emit enough to create potentially habitable zones that could support liquid water on close-orbiting rocky planets. Not only are these types of stars more common in the universe than sun-like stars, but they also have much considerably longer lifespans of more than 1,000 times that of the sun.
Using this information, Loeb calculated that it was much more likely for life to have emerged in the distant future around one of those low mass stars than to have emerged in our time on a sun-orbiting planet like Earth.
“If you allow low mass stars to have life, just like we find here on Earth, then the probability of life emerging in the future 10 trillion years from now is one thousand times bigger to find life,” noted Loeb.
And yet, we are not orbiting a low mass star, trillions of years in the future. We are here and now, orbiting our Sun—and this is the only place we’ve ever found sentient life. That suggests an intriguing explanation. Perhaps we are simply searching way too soon.
In other words, we may be alone in the universe right now. But that’s only because we showed up long before life really started to get going. If this hypothesis is the correct one, then the real explosion of life in the universe hasn’t yet happened—and likely won’t happen for trillions of years after us.
There’s also a second, alternate explanation that would account for all the facts. Perhaps there’s something about low mass stars which, even in zones that are technically habitable, suppresses life from ever forming.
“We still keep the notion that, perhaps, we are at the center of the biological universe, that we are really the only ones or special in that regard, or in terms of intelligence,” Loeb said. “If it turns out that we are rare and early on in the game then that would be really surprising to me because, so far, whenever we look we have found that we are not special and we are not the center of the universe.”
Figuring out which of these two possibilities are correct hinges on the question of whether low mass stars can indeed support life. We won’t necessarily have to wait several trillions of years to find out, though. Instead, Loeb suggests that the answers could be found in the next decade or so.
By sampling the atmospheres of planets around nearby low mass stars, researchers can search for biomarkers that would suggest whether these planets are capable of supporting life. If they keep finding atmospheres devoid of signs that they are capable of supporting life, then it’s likely that something about these low mass stars—perhaps their frequent solar flares or some other attribute—renders the planets orbiting them sterile.
If, however, they find that these planets do appear able to support life then it may be that the lack of other life in the universe is simply because we showed up too soon to see any of it.
By
GEORGE DVORSKYIt’s been over half a century since Frank Drake developed an equation to estimate the probability of finding intelligent life in our galaxy. We’ve learned a lot since then, prompting an astrophysicist from MIT to come up with her own take on the equation. Here’s how the new formula works — and how it could help in the search for alien life.
The new formula was devised by Sara Seager, a professor of planetary science and physics at the Massachusetts Institute of Technology. I contacted her to learn more about the new equation and why the time was right for a rethink.
Assessing the Probability of Intelligent Life
Back in 1961, Frank Drake proposed a probabilistic formula to help estimate the number of active, radio-capable extraterrestrial civilizations in the Milky Way Galaxy. It goes like this:
Where:
N is the number of civilizations in our galaxy with which we might hope to be able to communicate
R* is the average rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can potentially support life per star that has planets
fl is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space
People have plugged in a variety of values over the past 50 years — all of them purely speculative. Values for N have ranged anywhere from one (i.e. here's looking at you kid) up to the millions.
“The original Drake Equation just gave us the format with which to see what the different ingredients would be,” Seager told io9. “No one had ever quantitatively organized our thoughts before. That’s the revolutionary nature of the equation.”
But it can never give us a quantitative answer, she says, and we shouldn’t expect the equation to be a real equation in the sense that we can have precise definitions for each term.
“It’s a wonderful, amazing, innovative way for us to think about intelligent life — or the existence of intelligent life,” she says, “But there are just so many unknowns that can’t be quantified.”
But things have changed since 1951. Thanks to the Kepler Space Telescope, we now know that there's an absolute plethora of exoplanets out there. What’s more, they come in all sorts of shapes and sizes, they orbit a diverse array of stars, and they reside in solar systems that scarcely resemble our own. Our sense of the galaxy is changing dramatically with each new discovery — as is our sense of its potential to harbor life.
Given all this new information, Seager felt that the time was right to rethink the Drake Equation.
cont.
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HERE at io9
