1 00:00:00,000 --> 00:00:05,940 Taking advantage of the total lunar eclipse of January 2019, astronomers, using NASA’s 2 00:00:05,940 --> 00:00:11,150 Hubble Space Telescope, have detected ozone in Earth’s atmosphere. 3 00:00:11,150 --> 00:00:16,500 In this observation, Hubble did not look at Earth directly. Instead, astronomers used 4 00:00:16,500 --> 00:00:21,670 the Moon as a mirror to reflect sunlight that passed through Earth’s atmosphere. 5 00:00:21,670 --> 00:00:26,320 This method serves as a proxy for how they will observe planets around other stars in 6 00:00:26,320 --> 00:00:29,410 search for worlds similar to our own. 7 00:00:29,410 --> 00:00:34,060 Though numerous ground-based observations of this kind have been done previously, this 8 00:00:34,060 --> 00:00:38,290 is the first time ultraviolet light passing through Earth’s atmosphere was observed 9 00:00:38,290 --> 00:00:41,660 from space. The measurements from this experiment detected the 10 00:00:41,660 --> 00:00:45,020 strong spectral fingerprint of ozone. 11 00:00:45,020 --> 00:00:50,100 On Earth, photosynthesis over billions of years is responsible for our planet’s high 12 00:00:50,100 --> 00:00:55,830 oxygen levels and thick ozone layer. That’s one reason why scientists think ozone or oxygen 13 00:00:55,830 --> 00:00:58,820 could be a sign of life on another planet. 14 00:00:58,820 --> 00:01:04,500 But finding ozone on distant worlds isn’t an easy task. Ultraviolet observations like 15 00:01:04,500 --> 00:01:09,240 this can best be conducted from space telescopes, above the limiting effects of looking through 16 00:01:09,240 --> 00:01:15,030 Earth’s skies, because ozone blocks most ultraviolet light from beyond the atmosphere. 17 00:01:15,030 --> 00:01:20,740 One of NASA’s major goals is to identify habitable and inhabited planets. But how would 18 00:01:20,740 --> 00:01:24,350 we know whether a distant planet has ozone or not? 19 00:01:24,350 --> 00:01:28,780 The atmospheres of some extrasolar planets can be probed if that distant world passes 20 00:01:28,780 --> 00:01:34,440 across the face of its parent star, called a transit. During a transit, starlight filters 21 00:01:34,440 --> 00:01:37,070 through the backlit exoplanet’s atmosphere. 22 00:01:37,070 --> 00:01:40,340 Chemicals in the atmosphere leave their telltale signature 23 00:01:40,340 --> 00:01:43,060 by filtering out certain colors of starlight. 24 00:01:43,060 --> 00:01:47,280 Astronomers have used Hubble to observe the atmospheres of several gas giant planets that 25 00:01:47,280 --> 00:01:52,390 transit their stars. But terrestrial planets are much smaller objects and their atmosphere 26 00:01:52,390 --> 00:01:54,680 thinner, like the skin on an apple. 27 00:01:54,680 --> 00:01:59,080 Therefore, teasing out these signatures is much more difficult. 28 00:01:59,080 --> 00:02:03,660 To prepare for future studies with larger telescopes, astronomers used Hubble to conduct 29 00:02:03,660 --> 00:02:10,120 experiments on a much closer and only known inhabited terrestrial planet: Earth! Our planet’s 30 00:02:10,120 --> 00:02:14,740 perfect alignment with the Sun and Moon during a total lunar eclipse mimics the geometry 31 00:02:14,740 --> 00:02:18,040 of a transiting terrestrial planet with its star. 32 00:02:18,040 --> 00:02:22,560 But the observations were also challenging because the Moon is very bright, and its surface 33 00:02:22,560 --> 00:02:27,420 is not a perfect reflector because it is mottled with bright and dark areas. 34 00:02:27,420 --> 00:02:32,260 The Moon is also so close to Earth that it appears to move very quickly in the sky, making 35 00:02:32,260 --> 00:02:35,660 it harder for Hubble to stay pointed at the same location. 36 00:02:35,660 --> 00:02:41,219 However, in spite of the challenges, the experiment was an incredible success, and Hubble is supporting 37 00:02:41,219 --> 00:02:46,620 the ongoing quest to find planets that are similar to our own, and perhaps, one day, 38 00:02:46,620 --> 00:02:49,280 find signs of life on other worlds. 39 00:02:49,280 --> 00:02:59,280 [ BEAUTIFUL MUSIC ]