'Rogue Moons' May Be as Common as Stars, Cornell Scientist Discovers

Wednesday, 21 March 2018 - 10:24AM
Weird Science
Moon
Wednesday, 21 March 2018 - 10:24AM
'Rogue Moons' May Be as Common as Stars, Cornell Scientist Discovers
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Image credit: YouTube
Gravity is a fun thing.

Heavy things pull towards each other throughout the universe, and this can often have unusual results. When a moon gets caught in between the pull from two different planets, it can end up being thrown out of orbit and launched across space; a process that's known as "planet-planet scattering."

A new paper studying the journey of rogue moons across the known universe has revealed some fascinating information about these nomadic lunar bodies. Without a planet to cling to, some of these moons can get up to some very unusual antics.

According to scientists from Cornell University, rogue moons often end up in "eccentric" orbits around their suns, effectively becoming dwarf planets in their own right. They can end up in elliptical orbits, find their way to new homes around completely unrelated planets, or crash down onto the surface of any world in their path.

Alternatively, rogue moons could simply spin off into the abyss, traveling in the empty blackness of space on an endless journey as free-floating bodies.

It seems that this phenomenon is actually incredibly common—lead scientist Yu-Cian Hong claims that the number of rogue moons "may exceed the number of free-floating planets in the universe and could even be as numerous as stars."



This isn't too outrageous of a claim—most stars in the universe have their own series of planets, and many planets have moons of some form, there are a lot of moons out there. If even a small number of these moons are subjected to the push and pull of planet-planet scattering, the numbers are still going to mount up quickly.

It's natural to wonder what it might be like to stand upon one of these moons as it travels unrestricted through space. Without light and heat from a star, this environment would be very dark and entirely hostile to anyone unlucky enough to be caught up on the ride, but as our own moon is similarly no place for unaided breathing, it's hard to imagine that a rogue moon would be any more disastrous of a place to play golf.

Many of the moons that are subjected to planet-planet scattering don't entirely survive the process—these gravitational forces are strong and powerful, and even a large lunar body can be ripped apart. This new research suggests that the moons that are most likely to endure these forces and go rogue are ones that orbit close to large planets, thereby keeping them safe from the more wrenching pangs of gravitational struggle when another planet draws too close.

Of course, it's hard to be clear on exactly what's going on with rogue moons. In the big, dark universe, it's difficult to spot any structures that don't give off an easily identifiable glow. Thus, we can count the stars, but we can rarely get a good glimpse at either rogue moons or rogue planets (which also occur, sometimes very close to home).

The scientists involved with this research are enthusiastic that NASA's upcoming WFIRST satellite telescope will be able to give us a better glimpse at rogue moons once it is sent into orbit. We'd just better hope that the entire project isn't canceled, or else we'll never learn more about all the weird stuff these rogue moons get up to.
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