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The evidence for Planet Nine comes in the form of a strange clumping of other objects around the edges of the solar system called trans-Neptunian objects (TNOs). The most distant of those frigid rocks all have similar orbits, oblong and tilted in the same ways, which might indicate that something big out there is affecting their movements. If it does exist, Planet Nine is probably between five and 10 times the mass of Earth, and 400 to 800 times as far from the sun.

Its existence has been hotly debated ever since it was first seriously proposed in the early 2010s, and observational hunts for it have turned up nothing so far – but they haven’t ruled it out either. One of the theoretical issues with the planet’s existence is that we don’t know how it could have gotten there. There’s never been enough material in the outer solar system to form such a huge world, so if it was born within our solar system along with the rest of the planets, it must have formed closer to the sun and then moved outwards.

A new model of the early solar system has finally explained in detail how that could have happened: early in the sun’s history, when the planets weren’t yet settled into their current orbits, most researchers believe that they jostled around quite a bit. The gravitational effects of this jostling could have thrown a young Planet Nine out of the solar system. But if it happened early enough, when our star was still close with the others that formed in its same cluster, those sibling stars could have saved this strange world, nudging it back towards the sun until it ended up in a far-flung – but still stable, gravitationally bound – orbit. With things as they are in our solar system, if that planetary jostling happened early enough, the odds of this scenario could be as high as 40 per cent.

That’s good news for Planet Nine, but there’s another fresh wrinkle in the story. A separate group of researchers has found what appears to be a new dwarf planet in the outer solar system among the TNOs. It is only about a third of the diameter of Pluto, and it’s about 90 times as far from the sun as Earth is. Called 2017 OF201 (not quite as catchy as Planet Nine), this little world poses a problem for the hypothetical huge one out there. Its orbit does not match the clustered paths of the other TNOs. And models suggest that if Planet Nine is out there, it should have ejected 2017 OF201 from the solar system – much in the same manner as it may have been banished to the edges itself.

Ultimately, we probably won’t know for sure until we either spot Planet Nine or find a whole lot more TNOs to analyse. The odds of both are about to increase dramatically, though, when the brand new Vera C. Rubin Observatory in Chile begins building its extraordinarily detailed sky map.

Credit: KPNO/NOIRLab/NSF/AURA/P. Marenfeld

Results from the Dark Energy Spectroscopic Instrument (DESI) suggest that dark energy, a mysterious force in the universe, is changing over time. This would completely re-write our understanding of the cosmos - but now other physicists are challenging this view. Read more

After two decades of debate, research confirms that an odd binary star system has an equally odd planetary companion. Read more

The failure of SpaceX’s ninth Starship launch has raised fresh concerns about the future of the rocket, but is there any alternative to Elon Musk’s approach to space? Read more

Abell S1063 is so massive that the light from distant galaxies bends around it, allowing it to act as a magnifying glass to the early universe. Read more

Credit: Schmidt et al./NJIT/NSO/AURA/NSF 

This GIF is made of some of the most detailed images of the sun ever taken. This one in particular shows coronal rain, which happens when hot plasma in the sun’s outermost region – its corona – cools down and falls deeper into the star. Detailed observations of coronal rain and other processes in the corona are crucial to our understanding of the sun, because the corona is way hotter than the surface of our star and we don’t know why. Videos like these help us understand the processes that are happening there, which slowly brings us closer to understanding the corona more generally. Read more

In a newsletter a couple of months ago, I wrote that right after the big bang, the universe was a roiling soup of hot plasma. Berwyn wrote in to ask where all that hot plasma came from, which is a great question. It’s a tough one to answer, but I’ll do my best.

I’ll start by saying that all of this is fairly speculative – there’s no way for us to create the high-energy conditions that existed in the very first moments after the big bang, so we can’t really test any of this experimentally. The best we can do is work from what physicists call first principles, which are what others might call laws of nature, to figure out what should have happened.

If we want to go all the way back to the beginning, before the big bang and before the space-time we know and love, that’s so speculative that it tends towards science fiction – we can talk about multiverses, or cyclical models of the universe that are born and die over and over again, or some sort of grand creator, but there is little if any evidence for any of those. Some hypotheses, like cyclic cosmology, do present the opportunity to gather evidence, but we haven’t found any yet.

So instead, let’s go just a little bit later, after the formation of space-time. By its very nature, space-time is made of fields seething with energy. Thanks to quantum fluctuations, this energy isn’t static; it has peaks and valleys, and sometimes those peaks are strong enough to become particles that pop into existence and then dissipate. But while most of those particles disappear, not all of them do, and in most models of the early universe, those quantum fluctuations sticking around are what formed the first particles.

That does bring up another question, though. When a particle of matter is formed, another corresponding particle of antimatter arises too. In theory, those two particles should annihilate, leaving us with an empty universe. Clearly the universe isn’t empty, so something caused it to produce more matter than antimatter. We don’t know why that is yet, despite many physicists working on it, so unfortunately I’m answering your question with another question, but it’s a fun one!

Credit: Arkitek Scientific

The two pillars of modern physics – gravity and quantum mechanics – seem incompatible. If we could determine whether gravity is quantum, like all the other known forces, it would go a long way towards healing this rift at the heart of physics, but the experiments required to do so have long been thought to be impractical at best and impossible at worst. Now, physicists have finally figured out how to start searching in earnest for signs of quantum gravity: a quest that could turn our understanding of the very fabric of space-time upside down. Read more

Thank you for reading! If you have any comments, questions or wild hypotheticals about space, let me know by emailing me at launchpad@newscientist.com and I’ll try to answer them in an upcoming newsletter. Next month, I’ll be in the Arctic with New Scientist Discovery Tours – we’ve got a lot of really cool trips coming up, and you can check them out here – so you’ll be hearing from a guest writer in the next Launchpad. I’ll be back in your inboxes at the beginning of August!

And remember… if we included dwarf planets in our list of planets in the solar system, there could be anywhere from 13 (including only the five official dwarf planets) to 741 (including known objects that could be dwarf planets) to more than 10,000 (based on estimates of what might be out there). Imagine trying to come up with a pneumonic device to remember 10,000 worlds – it’d be 20 pages long!

Leah Crane

Features Editor, New Scientist
Email me at launchpad@newscientist.com
Follow me @downhereonearth

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