Planet Nine's moons might help astronomers find our missing cosmic neighbour

Planet Nine's moons might help astronomers find our missing cosmic neighbour

The existence of Planet Nine, which has long been hypothesised to be lurking beyond Neptune, could explain the odd behaviour of some trans-Neptunian objects.

Astronomers believe they might finally be able to find our solar system’s elusive Planet Nine — which is most certainly not Pluto — if at all it exists.

The long-hypothesised ninth planet of our cosmic neighbourhood, first proposed by scientists in 2014, probably lurks out past Neptune in the Kuiper Belt and its existence — if confirmed — could explain the unusual orbits of many extreme trans-Neptunian objects (ETNOs), which will help locate it.

An ETNO is a trans-neptunian object —such as an asteroid, comet, dwarf planet or a moon — orbiting the Sun from well beyond 30 astronomical units, or over 30 times as far as the Earth does.

Man Ho Chan, a researcher for The Education University of Hong Kong, argues in a new paper submitted to the The Astrophysical Journal that since dwarf planets like Pluto have their own satellite systems, it’s very likely that an object as massive as the elusive Planet Nine — with an estimated mass between five and 10 times that of Earth — would have captured some satellites itself.

Planet Nine

So far, Planet Nine itself remains an enigma and might as well be a black hole for all we know.

Scientists believe it was ejected to the outer reaches of the solar system after wandering too close to either Saturn or Jupiter. Now orbiting the Sun at 400-800 AU, it takes between 10,000 and 20,000 years to complete one full orbit — according to NASA — and has no observable light signatures that could be detected by astronomers.

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But if this speculative “Planet 9” exists, the luminosity (or the lack of it) won’t matter as its gravitational effect on other objects would conclusively smoke it out even from the murky fringes.

While it's reasonable to suspect that the satellites would be harder to stumble upon given their size, a phenomenon called "tidal heating" would help find Planet Nine, according to a preprint of the study.

Tidal heating occurs when the gravitational tug-of-war between two celestial objects, like Jupiter and its moon IO, distorts the body being pulled harder, with the resultant friction giving off heat.

"This provides a new indirect way for examining the Planet Nine hypothesis and revealing the basic properties of Planet Nine," said Chan.

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