[00:00] We may have lost two planets. And no, I don't&nbsp; mean astrophysicists have another disagreement&nbsp;&nbsp; about what we're allowed to call a planet. I mean&nbsp; the result of a recent study which found that the&nbsp;&nbsp;
[00:12] solar system used to have six giant planets, not&nbsp; four, but we lost two of them billions of years&nbsp;&nbsp; ago. That's relatable. I mean, who hasn't lost&nbsp; a planet or two? But seriously, what the hell&nbsp;&nbsp;
[00:25] happened there? I have a brief summary. The solar&nbsp; system was not born as the neat diagram you find in&nbsp;&nbsp; school books with the planets all in place. It&nbsp; formed from a huge cloud of gas and dust. The&nbsp;&nbsp;
[00:37] cloud contracted under the pole of its own gravity&nbsp; and began to spin. The center became so dense and&nbsp;&nbsp; hot that nuclear fusion ignited it. That became&nbsp; our Sun. The leftover material formed a flat&nbsp;&nbsp; disc around the young Sun. Inside that disc,&nbsp; tiny grains began to stick together and slowly&nbsp;&nbsp;
[00:54] built larger and larger objects which became&nbsp; the planets and their moons. So far so clear.&nbsp;&nbsp; The devil is in the details. And it's the details&nbsp; that the authors of the new paper have now put&nbsp;&nbsp;
[01:06] together and compared with evidence. What we do&nbsp; know is that in the early solar system, it was so&nbsp;&nbsp; hot close to the Sun that only rock could clump&nbsp; and form planets. That's why the inner planets,&nbsp;&nbsp;
[01:20] Mercury, Venus, Earth, and Mars are small and&nbsp; rocky. Further out, it was cold enough for ice to&nbsp;&nbsp; also clump. That gave the young planets out there&nbsp; much more building material. Jupiter and Saturn&nbsp;&nbsp;
[01:32] grew quickly and became massive enough to pull in&nbsp; huge amounts of gas. Uranus and Neptune also grew&nbsp;&nbsp; large, but not large enough to collect as much gas&nbsp; before the disc disappeared. These four planets&nbsp;&nbsp;
[01:45] are called 'gas giants', and they're fascinating. If&nbsp; Jupiter were hollow, about 1,000 Earths could fit&nbsp;&nbsp; inside. Saturn has such a low density that it'll&nbsp; float in water if you could find a bathtub to fit&nbsp;&nbsp;
[02:00] it in. But here's the thing. If physicists try to&nbsp; reproduce the formation of our solar system on a&nbsp;&nbsp; computer, it doesn't work if there are only these&nbsp; planets. The way that they do this is to start&nbsp;&nbsp; with the initial distribution of matter and let&nbsp; it form a solar system. Then they keep only cases&nbsp;&nbsp;
[02:17] which result in something that looks similar&nbsp; to what we in fact observe. The thing is now&nbsp;&nbsp; that to match our observations, they need at least&nbsp; one but better two large extra planets otherwise,&nbsp;&nbsp;
[02:30] the solar system does not come out correctly.&nbsp; The idea is not entirely new. The biggest hint&nbsp;&nbsp; that something dramatic must have happened in the&nbsp; young solar system is Uranus because its axis is&nbsp;&nbsp;
[02:43] tilted a lot to the side and is not aligned with&nbsp; the overall axis of the solar system. This doesn't&nbsp;&nbsp; naturally come about during the formation of the&nbsp; solar system. It seems that something hit Uranus,
[02:55] hard. The new paper now looked at Uranus's moons&nbsp; and finds that these fit the picture as well. The&nbsp;&nbsp; moons also orbit around the tilted axis. And these&nbsp; moons, especially one by the name of Miranda,&nbsp;&nbsp;
[03:09] have more rise than one would expect. The&nbsp; authors now say this all fits together like this:&nbsp;&nbsp; The early solar system had not four, but&nbsp; probably six of these ice giants. They were&nbsp;&nbsp;
[03:21] much closer together than the ice giants are&nbsp; now. If these giant planets are close together,&nbsp;&nbsp; this makes their orbits very unstable. Solar&nbsp; systems are naturally chaotic and in a case like&nbsp;&nbsp;
[03:33] this, the chaos sets in very quickly. So, two of&nbsp; the giant planets didn't stay on regular orbits,&nbsp;&nbsp; but instead began to wander around and one of them&nbsp; hit Uranus and tilted its axis. In the aftermath,&nbsp;&nbsp;
[03:45] Uranus's moons got shaken out of their orbit and&nbsp; collided, which created multiple smaller moons,&nbsp;&nbsp; which then put on extra ice. The two extra planets&nbsp; eventually ended up on a path that took them out&nbsp;&nbsp;
[03:57] of the solar system entirely. This would have&nbsp; happened billions of years ago, so they'd be far&nbsp;&nbsp; away from us now. They may still exist somewhere,&nbsp; but by now they'd be wandering between the stars,&nbsp;&nbsp;
[04:09] cold and dark, alone, and probably not subscribed&nbsp; to my channel. I give this paper a 3 out of&nbsp;10 on the bullshit meter. Not because of the&nbsp; paper, but because of the general difficulty&nbsp;&nbsp;
[04:22] of the subject. We're trying to patch together&nbsp; what happened in the distant past from what we&nbsp;&nbsp; see today. So all the evidence we can ever have&nbsp; is indirect. The problem is not so different from&nbsp;&nbsp;
[04:34] trying to understand the origin of life, but it's&nbsp; more dominated by physics. So I think it's more&nbsp;&nbsp; doable. I couldn't think of a closing joke, so I&nbsp; asked Chad GPT. And here's what he came up with.&nbsp;&nbsp;
[04:48] Six ice giants close together. This is not a solar&nbsp; system. This is a physics department after the&nbsp;&nbsp; coffee machine breaks. If you want to stay safe&nbsp; on the internet, I can really recommend NordVPN,&nbsp;&nbsp;
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