On Aug. 24, 2006, nine years ago today, the International Astronomical Union demoted Pluto from a planet to a dwarf planet — a move that sparked protests and split the space-science community.
Some in the community, including leading Pluto researchers, are still upset at the decision.
“It’s bulls—,”Alan Stern, the lead scientist behind NASA’s New Horizons mission to Pluto, told Tech Insider in July (and said we could quote him on that).
The problem, Stern said, is that the reclassification largely stemmed from the opinions of astronomers, not planetary scientists. His beef here is that astronomers study a large variety of celestial objects and cosmic phenomena, while planetary scientists focus solely on planets, moons, and planetary systems.
“Why would you listen to an astronomer about a planet?” Stern said.
He compared it to going to a podiatrist for brain surgery.
“Even though they’re both doctors, they have different expertise,” Stern said. “You really should listen to planetary scientists that know something about this subject. When we look at an object like Pluto, we don’t know what else to call it.”
That’s because Pluto meets the main criteria for planethood: It is rounded by its own gravity.
But there’s more than that, Stern said.
On July 14 of this year — after a nearly 10-year, 3-billion-mile journey — New Horizons finally flew past Pluto and returned our first close up look at the dwarf planet.
We are learning from the New Horizons data that Pluto is unexpectedly complex.
It has more moons than the entirety of the inner solar system. It possesses close to a million times the amount of atmosphere that Mercury has.
The surface has water-ice mountains that could rival the Rocky Mountains here on Earth. Its frozen plains are lined with ridges that scientists think are caused by some kind of ongoing geological process.
“We were just dumbfounded by what a wonderland it is scientifically,” Stern said.
A nonplanet shouldn’t be so active.
“[Pluto] qualifies in every respect,” he said. Astronomers — not planetary scientists — “made up a definition, which is actually bogus.”
Of course there are other criteria for planet status, and there’s plenty of room for argument. Pluto is far smaller than any of our solar system’s other planets; in fact, it’s about one-quarter of a per cent as massive as the Earth.
Pluto also doesn’t orbit the sun on the same plane that the planets do. Its elliptical path even crosses in front of Neptune’s orbit during its 248-year-long revolution around the sun:
But, as astronomy professor and self-professed “Pluto-killer” Mike Brown told Tech Insider, Pluto doesn’t have to be a planet to be interesting.
And interesting it definitely is. We are learning a ton about the dwarf planet as New Horizons continues to beam back more data over the next 15 months.
It’s possible this new info will change people’s minds about its classification.