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Back in 2014, an international team of astronomers was taking pictures of distant galaxies, when they noticed a dot moving across their images. Could it be Planet Nine?

Hosted by: Caitlin Hofmeister
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CITATIONS✓&object_id=2014+UZ224, ,
More sources:✓&object_id=2014+UZ224,

Deep Fields calculation based on: Angular area of the Hubble eXtreme Deep Field was about 4.6 square arcminutes (, assuming that I can just treat the “Distance” stats more or less like the sides of a rectangle); Angular area of a sphere is 148,510,660 square arcminutes (; Hubble eXtreme Deep Field was a 2-million-second exposure ( Putting that all together gives about two million years for the whole sky (*(2+million+seconds)+in+years )

The research paper: ,, (all the same paper)

Other source:,
[SciShow intro plays]

Caitlin: Astronomers are always finding new objects in our solar system. And few regions produce more discoveries than the Kuiper Belt, the distant band of rocky, icy objects beyond the orbit of Neptune. And this is where scientists reported last week that they may have discovered an important new addition to the solar system. Back in 2014, an international team of astronomers was taking pictures of distant galaxies, when they noticed a dot moving across their images.

Stars and galaxies don’t dart around the sky very quickly, so they knew the new object had to be here in our solar system. But since it was only in a couple of images, the team couldn’t figure out what it was -- or even what its orbit looked like. All they could do was name this mysterious object.

So they did: They called it 2014 UZ224. After seeing it a few more times over the past couple of years and mapping its orbit, they think that UZ224 is currently about fourteen billion kilometers from the Sun. That’s around ninety times farther from the Sun than Earth is, and about two and a half times farther than our old friend Pluto.

Which means -- I hate to be the one break it to you -- that this new object can’t be Planet Nine, the hypothesized ninth major planet in the solar system. Mathematical models put Planet Nine about a thousand times farther away, and with a completely different orbit. So, if it’s not Number Nine... then what is it? Well, the astronomers say the newly found object fulfills at least three of the four criteria that would qualify it as a dwarf planet.

Specifically, it orbits a star, it doesn’t orbit another planet, and it hasn’t cleared out its orbit -- meaning there are other objects in its orbital path. But the fourth thing an object needs to be a dwarf planet is to be large enough that its own gravity pulled it into a sphere. And this is the one astronomers aren’t sure about yet.

2014 UZ224 is really far away, so it’s really hard to know anything about its size and shape. Astronomers think it’s probably big enough to be spherical, but we’ll have to wait until they’re done analyzing new infrared images before they’re sure. Until then, all we can do is tell Pluto, Ceres, Eris, Makemake, Haumea, and the as-yet-unnamed 2007 OR10 that there might be a new dwarf planet in the neighborhood.

Well, new to us, at least. Probably not to them. And you know what else we’ve been underestimating for a really long time? The number of galaxies in the observable universe.

Based on images of deep space, astronomers have generally figured that there are around two hundred billion galaxies out there. But a new study suggests that there are about ten times more than that! So instead of two hundred billion galaxies, there could be as many as two trillion. But, how could we have been so far off?

Well, counting galaxies is... hard. Most of them are really dim and far away. We can only see them with super-long-exposure images of tiny patches of the sky -- like those amazing pictures that you’ve probably seen before, called Hubble Deep Fields, where all but the very brightest dots are entire galaxies. But these images can only show us so much, because a lot of the sky is blocked by the Milky Way. And even if it weren’t, taking Deep Fields of the entire sky would take about two million years. And nobody has time for that.

Now, astronomers had originally used Deep Fields to come up with the estimate of two hundred billion galaxies. But they knew that figure was really low, because some galaxies are just too dim to show up in those pictures. And for other galaxies, the light they emit is being stretched out by the expansion of the universe, so the telescope can’t detect it anymore. These challenges led a team of British and Dutch astronomers to take a different approach.

Instead of just counting up the galaxies in each Deep Field image, they mapped out how far away they all are. This allowed them to create a mathematical model of how the universe developed as it expanded, including how many galaxies there should’ve been at every stage. And when they ran the model, they realized the original estimate was off by way more than anyone thought.

But how did they get from a measly two hundred billion galaxies to two trillion? Most of the new additions, they say, are small galaxies that formed just a billion or so years after the Big Bang. Since then, these small, early galaxies have merged over and over to form larger galaxies like our Milky Way. For a long time, astronomers thought these distant, ancient galaxies should be out there, observable in the Deep Field images.

But they hadn’t found enough of them to account for all of the large galaxies we see today. Now, thanks to this new study, we know just how many galaxies those Deep Fields were missing. And that there really were enough little galaxies in the early universe to make up the ones we see today. The pieces finally fit together! Don’t you love it when that happens?

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