Far away in the fringes of the Solar System are a bunch of dark, icy “detached objects” that aren’t behaving as they should.
Their strange orbits could even be linked to the extinction of the dinosaurs.
Take “The Goblin,” also called 2015 TG387. Found during Halloween in 2015, it’s an “extreme” dwarf planet or sednoid—possibly a big ball of ice—that measures 186 miles across. It can get to about 2,300 times further from the Sun than the Earth—something astronomers call an astronomical unit (au)—but it’s currently only 78 au from the Sun in the constellation of Pisces.
“The Goblin” doesn’t orbit the Sun as it should. Nor do the two other sednoids we know of.
Sedna and Biden are slightly bigger, but no less mysterious dark, icy worlds. While everything else in the Solar System orbit the Sun on a relatively flat plane, these mysterious “detached objects” have highly elliptical orbits that tilt and buckle. They also largely cluster in just one segment of the Solar System.
Why? Could it be the influence of a hypothetical giant “Planet Nine” or “Planet X” that scatters objects in its wake? Or do we need a new tweak to the theory of gravity that governs planetary motion?
Scientists at the University of Colorado Boulder think they may have solved one of the biggest mysteries about these far away worlds.
What do we know about Biden, Sedna And ‘The Goblin?’
These are the coldest and most distant known objects in the Solar System (excepting 2018 VG18, also called “Farout”) and as cold as -400°F/-240°C.
Biden (now in Taurus)
A pink mini-planet nicknamed Biden—also known as 2012 VP113—was discovered in 2014. It’s 370 miles across and at its closest it gets to 50 au, and at its furthest, 150 au. It takes 4,136 years to complete one orbit of the Sun. It’s nicknamed Biden because Joe Biden was vice president (VP) of the US when it was discovered.
Sedna (now in Taurus)
Discovered in 2004 and named after the Inuit goddess of the sea, Sedna (also known as 90377 Sedna) is 800 miles wide—twice the size of Biden. It gets to within 76 au of the Sun, and to 937 au away from it during its 11,400-year orbit.
‘The Goblin’ (now in Pisces)
Around 186 miles across, it’s 80 au from the Sun on average, “The Gobins” —also called 2015 TG387 and 541132 Leleākūhonua—gets as far as a whopping 2,300 au from the Sun during its 35,760-year orbit. That’s much further than either Biden or Sedna, but “The Goblin” is much smaller. It was found in 2015.
Both Sedna and “The Goblin” were only discovered because, luckily, they happen to getting closer to the Sun at the moment.
What region of the Solar System do they hang out in?
It’s the region way beyond Pluto called the inner Oort Cloud. The Oort Cloud is best thought of as a bubble around the Solar System that comprises particles left over from its birth. It contains icy objects, including comets. The Kuiper Belt is different; that’s a disk around the Sun on roughly the same plane as the planets orbit. It’s home to Pluto and Arrokoth.
Sure, this region of the Solar System is very far away, but since we spend so much time thinking about planets orbiting other stars, we need some perspective here. “This region of space, which is so much closer to us than stars in our galaxy and other things that we can observe just fine, is just so unknown to us,” said Ann-Marie Madigan, an assistant professor in the Department of Astrophysical and Planetary Sciences (APS) at CU Boulder.
Why is the Oort Cloud so hard to study?
It’s a difficult place to study because it is just so dark. “Ordinarily, the only way to observe these objects is to have the Sun’s rays smack off their surface and come back to our telescopes on Earth,” said Madigan. “Because it’s so difficult to learn anything about it, there was this assumption that it was empty.”
However, this region of space is definitely not empty.
Why are the orbits of Sedna, Biden and ‘The Goblin’ so strange?
According to their paper published July 2, 2020 in the Astronomical Journal and last month in the Astronomical Journal Letters, the out-of-plane buckling of the likes of Sedna, Biden and “The Goblin” is perhaps down to something called “collective gravity.”
What is ‘collective gravity?’
In supercomputer simulations the icy objects began orbiting the Sun just like everything else does in the Solar System, but over time they began to pull and push on each other and their orbits grew wonkier—“collective gravity.”
Crucially, Madigan and graduate student Alexander Zderic discovered that this process happened naturally—a massive “Planet Nine” was not a factor. “Individually, all of the gravitational interactions between these small bodies are weak,” said Madigan. “But if you have enough of them, that becomes important.”
It’s the first time all the weird orbital anomalies that scientists have seen over the years have been reproduced.
How is this connected to the extinction of the dinosaurs?
The research may also provide clues about the extinction of the dinosaurs. As these bodies interact in the outer Solar System their orbits tighten and widen in a repeating cycle, which could be what shoots comets into the inner solar system—including in the direction of Earth. “While we’re not able to say that this pattern killed the dinosaurs, it’s tantalizing,” said Alexander Zderic, a graduate student in APS at CU Boulder, also co-authored the new research.
A problem with ‘collective gravity’
However, the theory of “collective gravity” does require the outer Solar System to have once contained a huge amount of stuff. Objects that added up to something on the order of 20 Earth masses, in fact. “That’s theoretically possible, but it’s definitely going to be bumping up against people’s beliefs,” said Madigan.
It’s hoped that the Vera C. Rubin Observatory in Chile, scheduled for first light in 2022, will help astronomers delve deeper into this mysterious region of the Solar System.
Wishing you clear skies and wide eyes.