1 00:00:02,040 --> 00:00:08,399 Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff, 2 00:00:08,480 --> 00:00:11,680 Speaker 1: Christian Sager Here. The Milky Way is thought to hold 3 00:00:11,760 --> 00:00:16,479 Speaker 1: at least a hundred billion planets. About seventeen billion of 4 00:00:16,520 --> 00:00:19,799 Speaker 1: those are roughly the size of Earth. And check this out. 5 00:00:20,160 --> 00:00:24,440 Speaker 1: One in every six of our galaxy stars have planets 6 00:00:24,480 --> 00:00:28,760 Speaker 1: revolving around them. As far as confirmed planets go, though, 7 00:00:29,200 --> 00:00:32,880 Speaker 1: as of this recording, NASA has confirmed nine hundred and 8 00:00:32,920 --> 00:00:37,360 Speaker 1: sixty two of those one hundred billion planets. We used 9 00:00:37,400 --> 00:00:39,720 Speaker 1: to think that they were rare, but since we launched 10 00:00:39,760 --> 00:00:43,480 Speaker 1: the Kepler Space Telescope, we're finding more planets every day, 11 00:00:43,680 --> 00:00:47,120 Speaker 1: especially ones with water on them. And what we've also 12 00:00:47,240 --> 00:00:50,320 Speaker 1: learned is that these planets don't need to be as 13 00:00:50,400 --> 00:00:54,320 Speaker 1: perfect as we once thought to sustain life here at home. 14 00:00:54,720 --> 00:00:58,080 Speaker 1: We've learned that life is a lot hardier and exists 15 00:00:58,160 --> 00:01:02,560 Speaker 1: in some extremely hard environments. All of this adds up 16 00:01:02,720 --> 00:01:05,560 Speaker 1: to a lot more evidence that we aren't alone in 17 00:01:05,600 --> 00:01:09,000 Speaker 1: the galaxy. While Earth is still the only planet that's 18 00:01:09,040 --> 00:01:12,880 Speaker 1: proven to support life, we're actively searching for other worlds 19 00:01:12,920 --> 00:01:16,120 Speaker 1: to join us. But to do that, first, we have 20 00:01:16,240 --> 00:01:21,360 Speaker 1: to define what life actually means. And not everyone agrees 21 00:01:21,400 --> 00:01:24,520 Speaker 1: on this topic, but let's try this one out. Life 22 00:01:24,520 --> 00:01:29,480 Speaker 1: requires an organized cellular structure that functions in a relatively 23 00:01:29,640 --> 00:01:35,120 Speaker 1: unchanging state. It's capable of reproduction, growing, taking in energy 24 00:01:35,160 --> 00:01:39,560 Speaker 1: from its environment, and responding to stimuli, and it can 25 00:01:39,600 --> 00:01:43,440 Speaker 1: adapt to the environment it lives in. Okay, and per 26 00:01:43,520 --> 00:01:49,280 Speaker 1: Darwinian evolution, we know that similar organisms produce similar organisms, 27 00:01:49,320 --> 00:01:54,120 Speaker 1: so for instance, a dog reproduces another dog, not a dandelion. 28 00:01:54,520 --> 00:01:57,520 Speaker 1: And while there's variation from one generation to the next, 29 00:01:58,000 --> 00:02:01,920 Speaker 1: some are more favorable than there's, leading to natural selection, 30 00:02:02,320 --> 00:02:06,120 Speaker 1: which leads us to how tough we've discovered life can 31 00:02:06,160 --> 00:02:10,200 Speaker 1: survive to be. Until around thirty years ago, we thought 32 00:02:10,280 --> 00:02:13,440 Speaker 1: all life on Earth needed energy from the sun and 33 00:02:13,520 --> 00:02:18,239 Speaker 1: couldn't survive in extreme temperatures. But we were so wrong. 34 00:02:18,800 --> 00:02:22,200 Speaker 1: When we explored hydrothermal vents on the ocean floor, we 35 00:02:22,280 --> 00:02:27,600 Speaker 1: discovered clams, crabs, and giant tube worms. The latter survived 36 00:02:27,600 --> 00:02:31,840 Speaker 1: through bacteria in their tissue that helped them derive energy 37 00:02:31,880 --> 00:02:36,240 Speaker 1: from the water, subsequently feeding the other animals. What this 38 00:02:36,360 --> 00:02:41,320 Speaker 1: potentially means is that life could exist in similar extreme 39 00:02:41,440 --> 00:02:46,880 Speaker 1: environments on other planets or moons. In other words, big 40 00:02:46,960 --> 00:02:51,320 Speaker 1: things have small beginnings. Now we're taking a huge leap 41 00:02:51,360 --> 00:02:54,480 Speaker 1: in the likelihood of alien life, and while people like 42 00:02:54,600 --> 00:02:58,600 Speaker 1: Frank Drake and Carl Sagan have speculated how many civilizations 43 00:02:58,600 --> 00:03:02,000 Speaker 1: could evolve out there, we still don't know the basics 44 00:03:02,040 --> 00:03:07,040 Speaker 1: of what extraterrestrials require to exist. Yes, we can work 45 00:03:07,080 --> 00:03:10,440 Speaker 1: from variable traits were familiar with from natural selection, but 46 00:03:10,919 --> 00:03:15,000 Speaker 1: would they be bilaterally symmetrical like humans or more like 47 00:03:15,120 --> 00:03:20,000 Speaker 1: bacteria or viruses. Scientists in the field of astrobiology have 48 00:03:20,120 --> 00:03:23,680 Speaker 1: drawn a few guidelines to how aliens might work. They'd 49 00:03:23,680 --> 00:03:27,040 Speaker 1: be governed by the laws of physics and chemistry. Their 50 00:03:27,080 --> 00:03:33,239 Speaker 1: bodies would also require solvency, temperature, pressure, and energy. In addition, 51 00:03:33,440 --> 00:03:38,240 Speaker 1: they would probably be comprised of complex molecules, including informational 52 00:03:38,280 --> 00:03:43,880 Speaker 1: molecules like DNA that carry their genetic information. So, armed 53 00:03:43,880 --> 00:03:47,880 Speaker 1: with these assumptions about alien biology, to next find alien life, 54 00:03:48,160 --> 00:03:51,280 Speaker 1: we've got to go planet hunting. Traditionally, we've looked for 55 00:03:51,360 --> 00:03:54,960 Speaker 1: something like Earth, rocky, watery, and orbiting a star and 56 00:03:55,000 --> 00:03:57,920 Speaker 1: what is called the gold Delock zone because it's not 57 00:03:58,040 --> 00:04:00,480 Speaker 1: too hot and it's not too cold. It's got to 58 00:04:00,520 --> 00:04:05,119 Speaker 1: be just right. But we've discovered three things about planets 59 00:04:05,120 --> 00:04:08,640 Speaker 1: that make it much more likely that there's life out there. First, 60 00:04:08,680 --> 00:04:11,240 Speaker 1: of all, water is not as rare as we thought. 61 00:04:11,360 --> 00:04:15,800 Speaker 1: Take Mars, for example, scientists found water there inn or 62 00:04:16,200 --> 00:04:21,400 Speaker 1: Jupiter's moon. Europa it's a freezing atmosphere, less mess bombarded 63 00:04:21,440 --> 00:04:24,599 Speaker 1: by radiation. But we also think it has a deep 64 00:04:24,760 --> 00:04:28,760 Speaker 1: ocean under its icy exterior that could have hydrothermal vents 65 00:04:28,920 --> 00:04:32,880 Speaker 1: similar to the ones on Earth, spewing chemicals and nurturing 66 00:04:33,000 --> 00:04:36,200 Speaker 1: strange marine life. If we stick with the assumption that 67 00:04:36,279 --> 00:04:39,839 Speaker 1: water is essential to life, then the necessary materials are 68 00:04:39,960 --> 00:04:44,200 Speaker 1: all over the galaxy, and Europa could also prove the 69 00:04:44,320 --> 00:04:47,240 Speaker 1: second thing we know about the possibility of planetary life 70 00:04:47,560 --> 00:04:50,719 Speaker 1: that life is way more flexible than we originally thought. 71 00:04:51,160 --> 00:04:55,159 Speaker 1: We found strains of bacteria surviving under miles of ice 72 00:04:55,279 --> 00:04:59,839 Speaker 1: in Antarctica for thousands of years. Could similar microbes be 73 00:05:00,000 --> 00:05:03,920 Speaker 1: on Europa or somewhere outside our solar system. If that's 74 00:05:03,960 --> 00:05:06,520 Speaker 1: the case, then do we discard the notion of that 75 00:05:06,720 --> 00:05:11,120 Speaker 1: Goldilocks habitable zone near the Sun. And the third thing 76 00:05:11,160 --> 00:05:14,000 Speaker 1: we now know about planets is what we said at 77 00:05:14,040 --> 00:05:17,600 Speaker 1: the top of the episode. There are billions of them. 78 00:05:17,800 --> 00:05:20,520 Speaker 1: By measuring the light coming from each star and then 79 00:05:20,560 --> 00:05:23,320 Speaker 1: waiting for it to temporarily dim, we pose it that 80 00:05:23,360 --> 00:05:26,680 Speaker 1: there's a planet there eclipsing the star's view. Now, how 81 00:05:26,680 --> 00:05:29,920 Speaker 1: do we see this? Well? With the Kepler Telescope spacecraft 82 00:05:30,000 --> 00:05:33,720 Speaker 1: launched in two thousand nine, Kepler orbits our Sun using 83 00:05:33,760 --> 00:05:37,720 Speaker 1: a photometer light meter to monitor more than a hundred 84 00:05:37,760 --> 00:05:41,320 Speaker 1: and fifty thousand stars, looking for any changes in their 85 00:05:41,320 --> 00:05:44,919 Speaker 1: brightness to identify an eclipse. That's where we get the 86 00:05:44,920 --> 00:05:49,799 Speaker 1: potential number of seventeen billion planets from Scientists then compare 87 00:05:49,880 --> 00:05:55,159 Speaker 1: Kepler's findings with spectroscopic data from ground based observatories to 88 00:05:55,240 --> 00:06:00,320 Speaker 1: confirm planetary candidates. And soon there will be two new 89 00:06:00,400 --> 00:06:05,839 Speaker 1: space instruments to bolster Kepler's findings. The Transiting Exoplanet Survey 90 00:06:05,880 --> 00:06:11,760 Speaker 1: Satellite or TESTS will launch in scanning for nearby exoplanets, 91 00:06:11,760 --> 00:06:15,599 Speaker 1: and the James Web Telescope, scheduled to launch in eighteen, 92 00:06:16,040 --> 00:06:20,159 Speaker 1: is so powerful it could analyze these planets atmospheres for 93 00:06:20,320 --> 00:06:25,000 Speaker 1: signs of life. Kepler's already discovered several planets with inhabitable 94 00:06:25,000 --> 00:06:28,960 Speaker 1: Goldilocks zones, but they're not at all like Earth. Instead 95 00:06:29,040 --> 00:06:32,360 Speaker 1: of water and rocks, they seem to be small cores 96 00:06:32,400 --> 00:06:36,559 Speaker 1: surrounded by atmospheres of hydrogen and helium, which doesn't sound 97 00:06:36,640 --> 00:06:39,400 Speaker 1: life supporting at all. But don't forget there are still 98 00:06:39,560 --> 00:06:42,479 Speaker 1: several ways life could exist on planets we used to 99 00:06:42,520 --> 00:06:47,520 Speaker 1: consider inhabitable. There could be life deep under a planets subsurface, 100 00:06:47,600 --> 00:06:51,279 Speaker 1: like the bacteria in Antarctica or the nematode worms discovered 101 00:06:51,279 --> 00:06:55,559 Speaker 1: three point six kilometers below South Africa's deepest gold wine. 102 00:06:55,960 --> 00:06:59,840 Speaker 1: Or what if a planet had shifting habitable zones attributing 103 00:06:59,880 --> 00:07:03,960 Speaker 1: to a wobbling planet. Moving clouds could reflect radiation back 104 00:07:04,000 --> 00:07:07,120 Speaker 1: into space, or temperatures could rise and fall dramatically, but 105 00:07:07,240 --> 00:07:11,760 Speaker 1: at certain latitudes heat would dissipate, allowing for liquid water 106 00:07:11,880 --> 00:07:16,120 Speaker 1: to resist boiling. It's hard to know if photosynthetic life 107 00:07:16,160 --> 00:07:20,680 Speaker 1: could survive such drastic changes, but maybe it's possible. I mean, 108 00:07:20,880 --> 00:07:23,480 Speaker 1: then diesel survived on such a planet in the Chronicles 109 00:07:23,520 --> 00:07:26,600 Speaker 1: of Riddicks, so you know, I'd say anything's possible. Even 110 00:07:26,720 --> 00:07:30,600 Speaker 1: moons orbiting exoplanets could be habitable if they were large 111 00:07:30,680 --> 00:07:34,200 Speaker 1: enough to hold onto an atmosphere. For instance, even if 112 00:07:34,200 --> 00:07:37,400 Speaker 1: a planet within a habitable zone didn't have the right 113 00:07:37,400 --> 00:07:42,400 Speaker 1: composition for life, its moon might have rocky, watery settings 114 00:07:42,440 --> 00:07:44,800 Speaker 1: like Earth kind of like end or in the Return 115 00:07:44,840 --> 00:07:47,080 Speaker 1: of the Jetta, you know, the one with the Ewoks. 116 00:07:47,520 --> 00:07:51,440 Speaker 1: As we've seen, the previously established rules for life sustaining 117 00:07:51,480 --> 00:07:55,640 Speaker 1: planets are diminishing as we gather more and more information 118 00:07:55,720 --> 00:07:59,280 Speaker 1: about the universe. However, this brings up the Fermi paradox, 119 00:07:59,480 --> 00:08:03,960 Speaker 1: established by Enrico Fermi in nineteen fifty. If alien life 120 00:08:04,240 --> 00:08:08,520 Speaker 1: or even civilizations exist in the Milky Way Galaxy, why 121 00:08:08,560 --> 00:08:16,360 Speaker 1: haven't we detected them yet? Check out the Brainstuff channel 122 00:08:16,360 --> 00:08:18,480 Speaker 1: on YouTube, and for more on this and thousands of 123 00:08:18,520 --> 00:08:33,000 Speaker 1: other topics, visit how stuff works dot com.