Pluto is eccentric.
It circles the sun in an elongated and tilted orbit. For about 20 percent of its 248-year journey around the sun, it is within the orbit of Neptune. At its farthest distance it is nearly 50 times the distance from Earth to the sun.
It is unique. Its biggest moon, Charon, is so close by that the two revolve around each other and are considered by some scientists to be a double planet. Pluto also holds clues to the formation of our solar system.
“This (Pluto) system has everything,” said Sykes. “The coolness factor that it’s a double planet, a lot of geology, ice caps, dark regions, an atmosphere.”
Sykes predicted in a paper published in the journal Science in 1987 that Pluto would have dark and light features because of differences in its surface temperature. Those predictions have been proven out in subsequent studies and he’s been increasingly thrilled by the improving New Horizons’ images. “It’s really cool to see it at this kind of resolution.”
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Physicist Renu Malhotra, a professor of orbital dynamics at the University of Arizona’s Lunar and Planetary Lab, was a graduate student in the 1980s when she began thinking that Pluto’s orbit held the clue to development of our solar system.
“There was this big puzzle about Pluto, this peculiar planet that didn’t fit in with the rest of the planetary system. It had a strange resonance with Neptune. It crossed Neptune’s orbit but avoided colliding with it and it was tilted, greatly tilted.”
She figured out how it happened and modeled it mathematically. In order to explain Pluto, she proposed that Saturn and Neptune, along with Pluto and the Kuiper Belt objects, had migrated outward from the sun, while Jupiter migrated in the opposite direction.
“This would be considered like a cuckoo theory for a while — to move something so big (Neptune) in order to explain something so small as Pluto’s orbit,” Malhotra said.
Astrophysicists and planetary scientists soon found reason to accept the theory. They discovered the Kuiper Belt and other objects with Pluto’s eccentric orbit. They discovered extra-solar planets — huge “hot Jupiters” orbiting close to their suns in regions where they could not possibly have formed.
“That also very quickly turned astronomers into believers of planets migrating,” she said in a recent interview. “Pluto is really responsible for turning our heads to the fact that planets migrate.”
Hers is the prevailing theory on formation of our solar system, though she recognizes now that it probably did not occur as smoothly and simply as her mathematical formulas show.
A closer look will help, she said. A better measurement of Pluto and its orbit will give future adjustments to the theory more certainty.
