NASA’s New Horizons has sent exciting waves in the astronomy world by revealing a side of Pluto never seen before. Latest images from the mission reveal the planet is not just an icy, inert wasteland at the edge of the solar system – in fact it is geologically active, with new glacier plains of nitrogen ice carving out new surface features and having regions of active magnetic activity.
“It’s very hard not to call an object with this level of complexity in its geology, and such complex seasons, a planet,” said Alan Stern, New Horizons principal investigator at Southwest Research Institute, during press conference about the Pluto probe’s latest update.
“Astronomers and planetary scientists differ on this question but that’s how science works – scientists make individual decisions and consensus is reached. I think we’re going through a period of transition at the moment.”
It has a large, hazy atmosphere extending 100 miles from the surface, and the New Horizons data has revealed a lot about its history.
On Friday’s briefing we heard that Pluto is almost perfectly spherical, which was unexpected considering what we think happened during its formation.
It’s likely that way back in its history, Pluto was hit by a massive object that tore away a huge chunk of its mass, which went on to form into the dwarf planet’s five moons.
But no remnant of that impact can be seen on the surface or in its current clean, spherical form.
That means that Pluto must have been spinning very rapidly after the impact, said William McKinnon, New Horizons co-investigator at Washington University, before reaching equilibrium with its relatively massive moon Charon.
Why was Pluto dethroned in the first place?
Pluto was dismissed from the list of planets in 2006 when astronomers decided it did not fit the specific definition of a planet.
“Pluto is dead,” said Caltech researcher Mike Brown, who spoke with reporters via a teleconference while monitoring the vote. The decision also means a Pluto-sized object that Brown discovered will not be called a planet.
“Pluto is not a planet,” Brown said. “There are finally, officially, eight planets in the solar system.”
The vote involved just 424 astronomers who remained for the last day of a meeting of the International Astronomical Union (IAU) in Prague.
“I’m embarassed for astornomy,” said Alan Stern, leader of NASA’s New Horizon’s mission to Pluto and a scientist at the Southwest Research Institute. “Less than 5 percent of the world’s astronomers voted.”
“This definition stinks, for technical reasons,” Stern told SPACE.com. He expects the astronomy community to overturn the decision. Other astronomers criticized the definition as ambiguous.
The decision establishes three main categories of objects in our solar system.
Planets: The eight worlds from Mercury to Neptune.
Dwarf Planets: Pluto and any other round object that “has not cleared the neighborhood around its orbit, and is not a satellite.”
Small Solar System Bodies: All other objects orbiting the Sun.
Pluto and its moon Charon, which would both have been planets under the initial definition proposed Aug. 16, now get demoted because they are part of a sea of other objects that occupy the same region of space. Earth and the other eight large planets have, on the other hand, cleared broad swaths of space of any other large objects.
“Pluto is a dwarf planet by the … definition and is recognized as the prototype of a new category of trans-Neptunian objects,” states the approved resolution.
Dwarf planets are not planets under the definition, however.
“There will be hundreds of dwarf planets,” Brown predicted. He has already found dozens that fit the category.