1 00:00:07,860 --> 00:00:11,100 Episode 168 // NEOs — Near Earth Objects 2 00:00:11,560 --> 00:00:15,000 What is a NEO? 3 00:00:15,560 --> 00:00:22,180 Near Earth Objects are really just that. These are celestial objects that come near to the Earth 4 00:00:22,180 --> 00:00:28,080 and there are broadly two classes: Near Earth Asteroids and Comets. 5 00:00:29,180 --> 00:00:32,800 Where do these objects come from? 6 00:00:33,320 --> 00:00:38,300 The Near Earth Asteroids, they mostly come from the asteroid main belt 7 00:00:38,300 --> 00:00:44,960 which is between Mars and Jupiter and it can happen that because of a collision 8 00:00:44,960 --> 00:00:51,860 or because of an interaction with one of the planets, one of them falls down from its orbit in the main belt 9 00:00:51,860 --> 00:00:56,980 to an orbit that brings it closer to the Sun and therefore closer to the Earth. 10 00:00:57,980 --> 00:01:01,820 How many NEOs are there? 11 00:01:02,680 --> 00:01:07,580 The Near Earth Objects, there are a few big ones, there are many more small ones 12 00:01:07,580 --> 00:01:11,240 and there are many many more very small ones. 13 00:01:11,240 --> 00:01:22,120 We know most of the big ones, big is one kilometre or more. For those that are 100 metres we know about 10 percent. 14 00:01:22,120 --> 00:01:33,940 For those that are 10 metres we know less than one percent of them. So that’s annoying, because an object that is 10 metres in diameter 15 00:01:33,940 --> 00:01:40,160 on impact with the Earth, would release about the same energy as a Hiroshima bomb. 16 00:01:40,160 --> 00:01:48,300 We are trying to characterise everything that is bigger than 20 or 50 or 100 metres 17 00:01:48,300 --> 00:01:53,640 where we are at 10 percent now, so we still need to find 90 percent. 18 00:01:53,640 --> 00:02:00,460 In terms of numbers, we know 10, 20 thousand of them and we are still missing 90 percent 19 00:02:00,460 --> 00:02:04,540 so there is a lot of work to find them and to track them. 20 00:02:06,020 --> 00:02:09,160 How can we search for them? 21 00:02:09,780 --> 00:02:14,600 To discover Near Earth Objects, you need a super wide-angle telescope 22 00:02:14,600 --> 00:02:21,960 and then you just scan the whole sky night after night in order to see everything that is moving. 23 00:02:21,960 --> 00:02:26,840 The asteroids are moving, and so we have computer programmes that will find them 24 00:02:26,840 --> 00:02:33,220 measure their position and from this position we can extrapolate the orbit and we refine the orbit 25 00:02:33,220 --> 00:02:39,280 until we have an orbit that is good enough that we will not lose the asteroid again. 26 00:02:41,040 --> 00:02:44,920 How often do impacts on Earth occur? 27 00:02:45,760 --> 00:02:50,720 We know from history, and also looking at the Moon that there are many impacts. 28 00:02:51,380 --> 00:02:58,000 On average a small one, which is like a few tens of metres, that happens every few years. 29 00:02:58,000 --> 00:03:03,840 Bigger ones are fortunately less frequent because there are fewer of these objects. 30 00:03:03,840 --> 00:03:09,840 Very big ones are even less frequent because there are very very few of them. 31 00:03:09,840 --> 00:03:19,420 So if you take a very big one, a 15 or 20 kilometre asteroid, hitting the Earth, last one was 65 million years ago. 32 00:03:19,420 --> 00:03:28,640 That was bad for the dinosaurs, and historically we see this kind of giant impact every 50 million years or so. 33 00:03:30,620 --> 00:03:35,540 What we can do to predict impacts and what role does ESO’s Very Large Telescope play? 34 00:03:36,260 --> 00:03:44,840 To predict an impact with a Near Earth Asteroid, a Near Earth Object, you need to know its orbit very precisely. 35 00:03:44,840 --> 00:03:51,880 And so to do that you need to measure the position of the object on the sky over and over and over. 36 00:03:51,880 --> 00:03:58,820 It’s difficult because many of these objects are small and they are not always near the Earth. 37 00:03:58,820 --> 00:04:01,560 They can be on the other side of the Solar System. 38 00:04:01,560 --> 00:04:06,040 The combination of their size and their distance makes them extremely faint 39 00:04:06,040 --> 00:04:13,560 which means that most of the time the telescope that discovered them, which is a 2-metre class telescope 40 00:04:13,560 --> 00:04:18,880 can observe them only for a few days and then they cannot see them anymore because they become too faint. 41 00:04:18,880 --> 00:04:24,420 That’s where the VLT, the 8-metre, big telescope, comes into play 42 00:04:24,420 --> 00:04:30,680 because with the collecting power of the huge mirror we can see much fainter asteroids. 43 00:04:31,820 --> 00:04:35,800 What is the VLT in particular used for? 44 00:04:36,300 --> 00:04:41,440 Using the VLT, we refine the orbit of the Near Earth Object 45 00:04:41,440 --> 00:04:48,780 the threatening ones that could have a collision, in order to make sure that the orbit is known 46 00:04:48,780 --> 00:04:56,020 well enough either to rule out a collision, that’s ideal, or to characterise a collision. 47 00:04:56,840 --> 00:05:00,560 Is there anything we can do to prevent NEO impacts? 48 00:05:01,560 --> 00:05:05,260 To protect ourselves from a Near Earth Object 49 00:05:05,260 --> 00:05:10,680 we must know them, and prepare in advance before a collision. 50 00:05:10,680 --> 00:05:17,560 So if we have enough time, 20 years or so, we can send a rocket and do something to the asteroid. 51 00:05:17,560 --> 00:05:24,320 That can be nuke it; you know — atomic bomb — either to try to destroy it or to push it. 52 00:05:24,320 --> 00:05:33,440 There are some more gentle ways. A cute way to do it is to spray paint the asteroid with bright white paint 53 00:05:33,440 --> 00:05:40,440 because that will change the way it reflects the sunlight and that can be sufficient to push it away from its orbit. 54 00:05:40,440 --> 00:05:48,360 Or you could also land a small rocket on the asteroid and let this small rocket push it. 55 00:05:48,360 --> 00:05:54,420 Or if it’s a very small asteroid you can go cast a net and grab it and pull it away. 56 00:05:56,220 --> 00:06:00,680 Transcribed by ESO; Translated by —