Our Solar System Lost Two Planets!

[00:00] We may have lost two planets. And no, I don't  mean astrophysicists have another disagreement   about what we're allowed to call a planet. I mean  the result of a recent study which found that the  

[00:12] solar system used to have six giant planets, not  four, but we lost two of them billions of years   ago. That's relatable. I mean, who hasn't lost  a planet or two? But seriously, what the hell  

[00:25] happened there? I have a brief summary. The solar  system was not born as the neat diagram you find in   school books with the planets all in place. It  formed from a huge cloud of gas and dust. The  

[00:37] cloud contracted under the pole of its own gravity  and began to spin. The center became so dense and   hot that nuclear fusion ignited it. That became  our Sun. The leftover material formed a flat   disc around the young Sun. Inside that disc,  tiny grains began to stick together and slowly  

[00:54] built larger and larger objects which became  the planets and their moons. So far so clear.   The devil is in the details. And it's the details  that the authors of the new paper have now put  

[01:06] together and compared with evidence. What we do  know is that in the early solar system, it was so   hot close to the Sun that only rock could clump  and form planets. That's why the inner planets,  

[01:20] Mercury, Venus, Earth, and Mars are small and  rocky. Further out, it was cold enough for ice to   also clump. That gave the young planets out there  much more building material. Jupiter and Saturn  

[01:32] grew quickly and became massive enough to pull in  huge amounts of gas. Uranus and Neptune also grew   large, but not large enough to collect as much gas  before the disc disappeared. These four planets  

[01:45] are called 'gas giants', and they're fascinating. If  Jupiter were hollow, about 1,000 Earths could fit   inside. Saturn has such a low density that it'll  float in water if you could find a bathtub to fit  

[02:00] it in. But here's the thing. If physicists try to  reproduce the formation of our solar system on a   computer, it doesn't work if there are only these  planets. The way that they do this is to start   with the initial distribution of matter and let  it form a solar system. Then they keep only cases  

[02:17] which result in something that looks similar  to what we in fact observe. The thing is now   that to match our observations, they need at least  one but better two large extra planets otherwise,  

[02:30] the solar system does not come out correctly.  The idea is not entirely new. The biggest hint   that something dramatic must have happened in the  young solar system is Uranus because its axis is  

[02:43] tilted a lot to the side and is not aligned with  the overall axis of the solar system. This doesn't   naturally come about during the formation of the  solar system. It seems that something hit Uranus,

[02:55] hard. The new paper now looked at Uranus's moons  and finds that these fit the picture as well. The   moons also orbit around the tilted axis. And these  moons, especially one by the name of Miranda,  

[03:09] have more rise than one would expect. The  authors now say this all fits together like this:   The early solar system had not four, but  probably six of these ice giants. They were  

[03:21] much closer together than the ice giants are  now. If these giant planets are close together,   this makes their orbits very unstable. Solar  systems are naturally chaotic and in a case like  

[03:33] this, the chaos sets in very quickly. So, two of  the giant planets didn't stay on regular orbits,   but instead began to wander around and one of them  hit Uranus and tilted its axis. In the aftermath,  

[03:45] Uranus's moons got shaken out of their orbit and  collided, which created multiple smaller moons,   which then put on extra ice. The two extra planets  eventually ended up on a path that took them out  

[03:57] of the solar system entirely. This would have  happened billions of years ago, so they'd be far   away from us now. They may still exist somewhere,  but by now they'd be wandering between the stars,  

[04:09] cold and dark, alone, and probably not subscribed  to my channel. I give this paper a 3 out of 10 on the bullshit meter. Not because of the  paper, but because of the general difficulty  

[04:22] of the subject. We're trying to patch together  what happened in the distant past from what we   see today. So all the evidence we can ever have  is indirect. The problem is not so different from  

[04:34] trying to understand the origin of life, but it's  more dominated by physics. So I think it's more   doable. I couldn't think of a closing joke, so I  asked Chad GPT. And here's what he came up with.  

[04:48] Six ice giants close together. This is not a solar  system. This is a physics department after the   coffee machine breaks. If you want to stay safe  on the internet, I can really recommend NordVPN,  

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