Here in the inner solar system, we live in the land of rocky objects and cratered planets. While the largest concentration of rocky objects are gathered up in the Asteroid Belt, the entire inner solar system has swarming rocky objects of various sizes.
At the most basic level an asteroid is just something that doesn’t have ices on its surface that are causing it to grow a tail when temperatures rise and reflect lots of light when it’s fully frozen.
As we move out past Mars and into the asteroid belt, temperatures drop, and we transition from objects like Vesta that formed in wet conditions to objects like Ceres that formed in icy conditions. We start to see moons like Europa that are shelled in ice, and small icy objects that have names like Centaurs and Kuiper Belt Objects and trans-neptunian objects and Sedianoids. These small bodies are generally icy and would be called comets if they flew into the inner solar system. There is no hard and fast dividing line between an asteroid and an icy object, and technically, all these tiny things in the inner and outer solar system are minor planets and small bodies.
And our solar system is capable of weird identity changing feats. The orbits of Centaurs can evolve through interactions with Jupiter and the other large planets, and these large chunks of ice can get flung our way and turned into comets. Comets can lose their volatiles and get coated in material and start to look like asteroids. And objects, including planets, can even get flung out of our Solar System through interactions with each other and with passing stars.
Beyond our Solar System there are perhaps more rogue planets than there are stars.
And for every planet, there is likely a population of small bodies making their way through space.
As telescopes get better, teams put more and more effort into mapping out what exists in our outer solar system. We keep expecting or at least hoping to find planet Nine that explains why so many objects are in weirdly elliptical orbits pointed in vaguely the same direction.
But what if we instead found a bunch of objects in not aligned orbits, and the need for a planet Nine just went away?
Back in May, we told you about the unconfirmed discovery of an object in the IRAS and AKARI survey that appears to be potentially planet sized and several hundred astronomical units from the Sun.
Now, another team has found another object in the outer Solar System. This time it appears smaller – just a few hundred km across, and it’s orbit carries it from as close as about 66 AU to as far as about 438 AU away. This highly elliptical orbit makes this a Sednoid object, like the category namesake, Sedna.
Cataloged as 2023 KQ14 and nicknamed Ammonite, it’s totally not aligned with previously found outer worlds. It’s existence seems to indicate, a planet nine isn’t necessary to explain the previously seen weird orbits – rather we need to just look in that other direction a whole lot more and see if there is missing stuff waiting to be found that will fill in the gaps.
Ammonite was found using the Subaru Telescope on Mauna Kea and this work was published Nature Astronomy by a team led by Ting-Tung Chen.
Meanwhile, across the volcano at the Canada France Hawaii Telescope, another team was also looking for – and also finding – outer solar system objects. The LiDO survey found a new object, catalogued as 2020 VN40 , that orbits the sun once for every 10 orbits of Neptune. This is the first time anything has been found in a 10:1 resonance, and this is a pretty wild orbit. It comes in to 38.26 AU from the Sun, and then flies all the way out to more than 240 AU away. This is always farther out than Neptune, but it is close enough to Neptune’s 30AU orbit for Neptune’s gravity to play a major role.
According to project researcher Kat Volk, “This discovery helps expand our picture of how the orbits of distant objects are influenced by Neptune. It is the most distant confirmed object in an orbital resonance with Neptune, and the observed distribution of resonant objects provides vital clues to how Neptune and the other giant planets rearranged themselves after their formation.”
This work appears in the Planetary Science Journal with lead author Rosemary Pike, and this work was funded by NASA, the National Science Foundation, and the National Research Council of Canada.