Is it time to restore Pluto back to the planet club?
A new effort to restore Pluto to the so-called Planet club is underway.
As reported at astronomy.com
“Rather than focusing on “external” factors such as whether a body has cleared its orbit (the portion of the IAU criteria that Pluto failed in 2006), the new geophysical definition instead brings to the forefront the intrinsic properties of the body itself. It takes into account the fact that many of the solar system’s worlds are physically complex and geologically active, from Ceres’ ice volcano to Pluto’s slushy heart.”
In essence, rather than focusing on the orbit, this proposed new definition suggests we focus on the object itself. Questions like. Is it round? Is is complex on the surface? Is it active? Unfortunately this approach may suffer the same fate as many others, in that this new definition is too open. It would result in over 100 new ‘planets’ in our solar system alone. Even our Moon would now be a planet. As such, maybe this new definition is doomed to failure.
So, adopt this new approach of Pluto-as-a-planet, at the cost of labeling 100 other objects as planets? Or leave things as they are?
Pluto is now King of the distant dwarf planets, but are there other larger planets out there?
The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Moreover, when viewed in three-dimensions, they are all tilted nearly identically away from the plane of the solar system. Such an orbital alignment can only be maintained by some outside force. In a new paper, Batygin and Brown show that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration.
The part of science I like best is that the more we learn, the more questions we have. Pluto provides a perfect example of this. Initially a planet, although lonesome. Then it found its kin, a set of dwarf planets. And now, when we actually see it, it looks more Earthly than we could have imagined. Large, frosty glaciers, seemingly draining watery residue from icy mountains. A distinct, hazy atmosphere, layered and complex. Active landscapes. This is absolutely not the dead cold planet we teach about. This enigma is alive.
In the photo, the New Horizon’s spacecraft is looking back at Pluto, with the Sun setting through the mist. The glaciers slowly drain moisture from icy mountains that tower over smooth, lowland basins. Overhead, the sky is filled with haze – lots and lots of it, carved into multiple layers. The image, “reminds me of the Transantarctic Mountains along the Ross Ice Sheet, because of the tall mountains looming over a flat open expanse of ever-changing ice,” says New Horizons team member Simon Porter of the Southwest Research Institute.
But there the similarity to Earth ends. Pluto’s mountains cannot be made by plate tectonics. Pluto’s glaciers are made from nitrogen, not water ice. Pluto has something analogous to Earth’s hydrological cycle, where water evaporates from the oceans, rains or snows back down, and returns to the seas by rivers and glaciers. But Pluto’s chemistry and temperature are different, perhaps dominated by soft nitrogen ice, and also featuring methane and carbon monoxide ices. This is not Earth-like. It is not reminiscent of Mars or Venus. This is not a planet.
To use the word ‘planet ‘ to describe this land is doing it a disservice. It is so much more than that. This, is an enigma.