1 00:00:03,279 --> 00:00:05,640 Speaker 1: Welcome to Stuff to Blow Your Mind, a production of 2 00:00:05,640 --> 00:00:10,920 Speaker 1: I Heart Radio. Hi, my name is Joe McCormick, and 3 00:00:11,039 --> 00:00:14,560 Speaker 1: this is the Artifact, a short form series from Stuff 4 00:00:14,600 --> 00:00:18,439 Speaker 1: to Blow Your Mind, focusing on particular objects, ideas, and 5 00:00:18,560 --> 00:00:24,440 Speaker 1: moments in time. One of the most powerful images from 6 00:00:24,440 --> 00:00:28,080 Speaker 1: the history of space exploration is notable not because it 7 00:00:28,200 --> 00:00:32,240 Speaker 1: captures the immensity of the great and far, but because 8 00:00:32,280 --> 00:00:34,720 Speaker 1: it shows us that, in the words of Carl Sagan, 9 00:00:35,240 --> 00:00:38,280 Speaker 1: on the scale of worlds, to say nothing of stars 10 00:00:38,360 --> 00:00:43,320 Speaker 1: or galaxies, humans are inconsequential, A thin film of life 11 00:00:43,440 --> 00:00:46,840 Speaker 1: on an obscure and solitary lump of rock and metal. 12 00:00:47,280 --> 00:00:51,040 Speaker 1: This image is the famous pale blue dot, a photograph 13 00:00:51,200 --> 00:00:54,480 Speaker 1: of Earth taken by the Voyager one space probe on 14 00:00:54,520 --> 00:00:59,160 Speaker 1: the fourteenth of February, when Voyager was about six point 15 00:00:59,240 --> 00:01:03,440 Speaker 1: four bill in kilometers away beyond the orbits of Neptune 16 00:01:03,440 --> 00:01:07,640 Speaker 1: and Pluto, rushing ever farther at more than sixty kilometers 17 00:01:07,680 --> 00:01:11,600 Speaker 1: per hour in a maneuver suggested by Carl Sagan and 18 00:01:11,760 --> 00:01:15,640 Speaker 1: executed by a team including Candy Hanson of NASA JPL 19 00:01:16,040 --> 00:01:19,760 Speaker 1: and Carolin Porco of the University of Arizona. The Voyager 20 00:01:19,800 --> 00:01:23,280 Speaker 1: probe turned its camera back toward the Solar system that 21 00:01:23,319 --> 00:01:27,319 Speaker 1: it was departing to capture final images of the local planets, 22 00:01:27,760 --> 00:01:31,680 Speaker 1: including Earth. That image of Earth, the pale blue dot, 23 00:01:32,200 --> 00:01:34,800 Speaker 1: is a humbling peak at our world from the vantage 24 00:01:34,800 --> 00:01:38,160 Speaker 1: point of the universe beyond. To call it a dot 25 00:01:38,400 --> 00:01:42,160 Speaker 1: is almost generous. It's more like a waning glimmer of 26 00:01:42,160 --> 00:01:45,520 Speaker 1: a dot, a speck that barely stands out from the 27 00:01:45,560 --> 00:01:49,840 Speaker 1: noise and could fall invisible under a passing shadow. Many 28 00:01:49,880 --> 00:01:52,160 Speaker 1: authors in the years since have written of the way 29 00:01:52,160 --> 00:01:56,720 Speaker 1: this photograph highlights the fragility and cosmic insignificance of our species. 30 00:01:57,520 --> 00:02:00,880 Speaker 1: Every human who has ever lived, and all the things 31 00:02:00,960 --> 00:02:04,920 Speaker 1: that they fought for, are contained within that dot. As 32 00:02:04,920 --> 00:02:09,600 Speaker 1: Sagan rites on a mode of dust suspended in a sunbeam, 33 00:02:09,639 --> 00:02:12,720 Speaker 1: but today I wanted to focus on one sometimes overlooked 34 00:02:12,760 --> 00:02:16,920 Speaker 1: aspect of the dot. Why is it pale blue? Sagan 35 00:02:17,000 --> 00:02:20,040 Speaker 1: himself had an answer for this. The color comes in 36 00:02:20,120 --> 00:02:23,840 Speaker 1: part from the oceans and in part from the sky. 37 00:02:24,040 --> 00:02:26,520 Speaker 1: When you look at water in a drinking glass, it 38 00:02:26,639 --> 00:02:30,160 Speaker 1: doesn't usually appear to have any color at all, But 39 00:02:30,280 --> 00:02:33,360 Speaker 1: this is only because of the tiny volume of the glass. 40 00:02:33,840 --> 00:02:37,880 Speaker 1: The deeper the water, the bluer it gets. According to Sagan, 41 00:02:38,000 --> 00:02:40,160 Speaker 1: by the time you have a column of water at 42 00:02:40,240 --> 00:02:43,520 Speaker 1: least ten meters in depth, almost all of the red 43 00:02:43,680 --> 00:02:47,360 Speaker 1: light that strikes it is absorbed, while blue frequencies of 44 00:02:47,440 --> 00:02:50,919 Speaker 1: light are scattered and reflected for us to see. Hence 45 00:02:50,960 --> 00:02:53,360 Speaker 1: the reason, or at least one of the major reasons, 46 00:02:53,400 --> 00:02:56,920 Speaker 1: that the oceans are blue. And at a different scale, 47 00:02:56,960 --> 00:02:59,440 Speaker 1: the same is true for the air in our atmosphere. 48 00:03:00,080 --> 00:03:02,560 Speaker 1: When you look at a blue sky, what are you 49 00:03:02,600 --> 00:03:07,040 Speaker 1: actually seeing? Assuming you're not looking directly toward the sun, 50 00:03:07,600 --> 00:03:11,920 Speaker 1: you're looking through a deep field of gas particles illuminated 51 00:03:11,960 --> 00:03:15,360 Speaker 1: by the sunlight. But since you're not looking toward the 52 00:03:15,400 --> 00:03:18,399 Speaker 1: sun the source of the light, the rays of light 53 00:03:18,480 --> 00:03:22,160 Speaker 1: hitting your eyes need to have been redirected somehow. The 54 00:03:22,240 --> 00:03:25,800 Speaker 1: light is bouncing off of something, and that something is 55 00:03:25,919 --> 00:03:29,320 Speaker 1: the air. Instead of allowing the sunlight to pass through 56 00:03:29,440 --> 00:03:33,560 Speaker 1: on a straight trajectory or reflecting it back like a mirror, 57 00:03:34,200 --> 00:03:38,320 Speaker 1: molecules of gas in the atmosphere scatter the light, meaning 58 00:03:38,360 --> 00:03:41,520 Speaker 1: they cause it to reflect in all different directions at once, 59 00:03:41,840 --> 00:03:44,600 Speaker 1: including down toward our eyes as we look up from 60 00:03:44,600 --> 00:03:47,760 Speaker 1: the ground, or out towards space as we peer back 61 00:03:47,840 --> 00:03:51,720 Speaker 1: with a camera. The particular gas molecules that make up 62 00:03:51,760 --> 00:03:55,360 Speaker 1: our atmosphere happen to scatter blue light from the sun 63 00:03:55,720 --> 00:03:59,040 Speaker 1: more than they scatter red light. Thus, a clear sky 64 00:03:59,200 --> 00:04:01,920 Speaker 1: on a sunny day a tends to reflect more blue 65 00:04:02,080 --> 00:04:05,720 Speaker 1: light in any given direction. This effect is known as 66 00:04:05,800 --> 00:04:10,240 Speaker 1: Rayleigh scattering. But the dominance of Rayleigh scattering and defining 67 00:04:10,280 --> 00:04:13,400 Speaker 1: the color of our atmosphere really does depend on what 68 00:04:13,560 --> 00:04:16,919 Speaker 1: kinds of molecules are present in the air, and the 69 00:04:16,960 --> 00:04:19,719 Speaker 1: color of the surface of the Earth depends on what's 70 00:04:19,760 --> 00:04:22,440 Speaker 1: there on the surface. Remember, our planet is covered in 71 00:04:22,480 --> 00:04:26,400 Speaker 1: blue oceans. But could a different atmosphere or a difference 72 00:04:26,440 --> 00:04:30,520 Speaker 1: in what's on the surface shade the dot and unfamiliar color. 73 00:04:35,200 --> 00:04:38,440 Speaker 1: The answer is yes, and in fact, some researchers suggest 74 00:04:38,520 --> 00:04:41,479 Speaker 1: that deep in Earth's past, the planet may well have 75 00:04:41,560 --> 00:04:44,640 Speaker 1: had a face that would be unrecognizable to us today. 76 00:04:45,600 --> 00:04:49,080 Speaker 1: For example, in there was a paper published in the 77 00:04:49,120 --> 00:04:54,240 Speaker 1: journal Astrobiology by Arnie at All called the Pale Orange 78 00:04:54,400 --> 00:04:59,680 Speaker 1: Dot The Spectrum and Habitability of Hazy Archaean Earth. In 79 00:04:59,720 --> 00:05:03,000 Speaker 1: the course of exploring ways to search for habitable planets, 80 00:05:03,279 --> 00:05:06,400 Speaker 1: the authors of the study discuss evidence indicating that during 81 00:05:06,440 --> 00:05:09,919 Speaker 1: the Archaean eon. Roughly three point eight to two point 82 00:05:09,960 --> 00:05:13,560 Speaker 1: five billion years ago, the Earth was likely covered in 83 00:05:13,640 --> 00:05:18,200 Speaker 1: what the authors describe as a Titan like organic rich haze, 84 00:05:18,720 --> 00:05:22,840 Speaker 1: referring to Saturn's rocky moon Titan, which is surrounded by 85 00:05:22,880 --> 00:05:26,560 Speaker 1: a shroud of large molecules that can give its atmosphere, 86 00:05:26,880 --> 00:05:32,800 Speaker 1: especially at lower altitudes, a soft apricot glow. On Titan, 87 00:05:33,080 --> 00:05:35,280 Speaker 1: this smog is thought to be the result of chain 88 00:05:35,360 --> 00:05:39,400 Speaker 1: reactions beginning in the upper atmosphere, where methane and nitrogen 89 00:05:39,440 --> 00:05:43,920 Speaker 1: molecules are broken apart by UV radiation and bombardment by 90 00:05:44,000 --> 00:05:48,440 Speaker 1: high energy particles. These broken molecules in the atmosphere then 91 00:05:48,560 --> 00:05:54,760 Speaker 1: recombined to form large organic compounds, including polycyclic aromatic hydrocarbons 92 00:05:54,880 --> 00:05:57,440 Speaker 1: or p A h s, which are bigger than the 93 00:05:57,560 --> 00:06:01,120 Speaker 1: simple gas particles in our atmosphere and cause light to 94 00:06:01,160 --> 00:06:04,840 Speaker 1: absorb and scatter very differently, leading to clouds of mist 95 00:06:04,960 --> 00:06:08,839 Speaker 1: that look brownish orange at a distance. According to the 96 00:06:08,839 --> 00:06:12,039 Speaker 1: paper's lead author, Jotta Arney, despite the fact that we 97 00:06:12,120 --> 00:06:16,400 Speaker 1: often think of habitable earthlike exoplanets as pale blue dots 98 00:06:16,880 --> 00:06:20,000 Speaker 1: like we see in the Voyager one photo, during the 99 00:06:20,040 --> 00:06:24,120 Speaker 1: haze enveloped our Chaean period, Earth itself would likely have 100 00:06:24,279 --> 00:06:29,000 Speaker 1: been a pale orange dot more like Titan is today. 101 00:06:29,160 --> 00:06:32,440 Speaker 1: While the haze of Titan is caused by a biotic processes, 102 00:06:32,760 --> 00:06:35,200 Speaker 1: the orange haze of the early Earth would have been 103 00:06:35,200 --> 00:06:39,280 Speaker 1: dependent on methane that was largely a byproduct of life 104 00:06:39,880 --> 00:06:44,799 Speaker 1: microorganisms that release methane gas as they metabolize energy to survive, 105 00:06:45,560 --> 00:06:47,479 Speaker 1: and this can tell us something about how to look 106 00:06:47,520 --> 00:06:51,279 Speaker 1: for habitable planets and solar systems across the galaxy. The 107 00:06:51,360 --> 00:06:57,280 Speaker 1: author's right quote. Because methane producing metabolisms evolved early, and 108 00:06:57,480 --> 00:07:01,440 Speaker 1: Earth's atmosphere was antoxic for out a billion years after 109 00:07:01,520 --> 00:07:05,360 Speaker 1: the origin of life, pale orange dots may proliferate in 110 00:07:05,400 --> 00:07:09,520 Speaker 1: the galaxy if other habitable worlds evolve on similar paths 111 00:07:09,560 --> 00:07:12,360 Speaker 1: to Earth. And in fact, there are lots of ways 112 00:07:12,440 --> 00:07:15,400 Speaker 1: that the surface of planet Earth probably has changed and 113 00:07:15,480 --> 00:07:19,080 Speaker 1: will change colors over the eons. Not all of these 114 00:07:19,160 --> 00:07:21,760 Speaker 1: changes will make a major difference in how the planet 115 00:07:21,800 --> 00:07:24,720 Speaker 1: looks from the vantage point of deep space, but they 116 00:07:24,760 --> 00:07:29,840 Speaker 1: are strange and wonderful to imagine. Nonetheless, According to paper 117 00:07:29,880 --> 00:07:33,720 Speaker 1: in the Astrophysical Journal by San Roma, at all about 118 00:07:33,800 --> 00:07:36,880 Speaker 1: three billion years ago, one of the most widespread life 119 00:07:36,920 --> 00:07:39,640 Speaker 1: forms on planet Earth would have been a class of 120 00:07:39,640 --> 00:07:45,000 Speaker 1: photosynthetic purple bacteria, which, depending on their distribution and a 121 00:07:45,080 --> 00:07:48,640 Speaker 1: number of other factors, could have influenced how Earth looked 122 00:07:48,680 --> 00:07:52,680 Speaker 1: from space. As it stands today, that ecological niche is 123 00:07:52,760 --> 00:07:56,280 Speaker 1: dominated by organisms more clustered around the green part of 124 00:07:56,280 --> 00:07:59,880 Speaker 1: the spectrum like plants. In fact, if it's life in 125 00:08:00,080 --> 00:08:03,400 Speaker 1: particular you're concentrating on, it could be hard to argue 126 00:08:03,400 --> 00:08:06,160 Speaker 1: against the characterization of Earth today as a kind of 127 00:08:06,320 --> 00:08:10,000 Speaker 1: green dot if you evacuate the water out of all 128 00:08:10,080 --> 00:08:14,360 Speaker 1: living organisms and count only the solid carbon content. By 129 00:08:14,400 --> 00:08:17,840 Speaker 1: some estimates, plants make up about eighty percent of all 130 00:08:17,960 --> 00:08:22,600 Speaker 1: the biomass on planet Earth. Despite all of our technology 131 00:08:22,760 --> 00:08:26,160 Speaker 1: and progress and powers of self reflection, in many ways, 132 00:08:26,240 --> 00:08:30,560 Speaker 1: this ball still belongs to the photosynthesizers. These ideas about 133 00:08:30,560 --> 00:08:32,880 Speaker 1: the shifting colors of the dot bring me back to 134 00:08:32,960 --> 00:08:37,079 Speaker 1: Carl Sagan's writings and the Voyager One photo. Sagan wrote 135 00:08:37,120 --> 00:08:39,800 Speaker 1: that it has been said that astronomy is a humbling 136 00:08:39,880 --> 00:08:44,120 Speaker 1: and character building experience. There is perhaps no better demonstration 137 00:08:44,200 --> 00:08:47,880 Speaker 1: of the folly of human conceits than this distant image 138 00:08:48,040 --> 00:08:51,000 Speaker 1: of our tiny world. What people often notice about the 139 00:08:51,040 --> 00:08:53,160 Speaker 1: pale blue dot is that it's so tiny in the 140 00:08:53,240 --> 00:08:57,520 Speaker 1: grand structure of space. That's true, but even its pale 141 00:08:57,559 --> 00:09:00,920 Speaker 1: blueness might well be tiny in the grands structure of time. 142 00:09:04,640 --> 00:09:07,840 Speaker 1: Tune into new editions of the artifact every Wednesday, hosted 143 00:09:07,880 --> 00:09:11,280 Speaker 1: either by Robert or myself. As always, You can email 144 00:09:11,360 --> 00:09:22,840 Speaker 1: us at contact at stuff to Blow your Mind dot com. 145 00:09:22,960 --> 00:09:24,760 Speaker 1: Stuff to Blow Your Mind is a production of I 146 00:09:24,880 --> 00:09:27,840 Speaker 1: Heart Radio. For more podcasts my heart Radio, visit the 147 00:09:27,840 --> 00:09:30,640 Speaker 1: i heart Radio app, Apple Podcasts, or wherever you listen 148 00:09:30,720 --> 00:09:31,600 Speaker 1: to your favorite shows.