NASA’s New Horizons has literally revolutionized our understanding of Pluto and its moons and has cast a light on the potential variety of objects that we might discover at the edge of the Solar System.
It has been two years since the flyby of Pluto and the next target is still 15 months away, so this seems like an ideal time to assess the impact of the mission on planetary science. In a Nature Astronomy review, Dr Catherine Olkin and colleagues cover what we know about Pluto, its moon Charon and the many mysteries that still surround the system.
"It’s a good time for a review article as it was less than a year ago that we got all the data down from the spacecraft and there have been so many interesting questions that came up from New Horizons that take time to dig in and really understand," Dr Olkin, of the Southwest Research Institute, told IFLScience.
The paper explains just how ignorant we were of the former planet before July 2015. Scientists knew that Pluto was redder than Charon and about twice as big, but there were huge uncertainties on either's actual size and the composition of their surfaces. Some of the best pictures were collected by Hubble in 1994, and while they produced interesting data, weren’t as eye-catching as New Horizons' turn out to be. Hubble is also responsible for the discovery of its four smaller satellites, Nix and Hydra in 2005, Kerberos in 2011, and Styx in 2012.
Months before New Horizons actually arrived at its primary target, it began seeing a more complex surface than had been predicted or expected, and as the months turned into days, scientists saw that both Pluto and Charon were quite complex. The flyby then showed that Pluto was not just complex but active.
The most intriguing feature of Pluto both in the public imagination and for the planetary scientists working on it is its heart, officially named Tombaugh Regio, and especially its western lobe known as the Sputnik Planitia. The region is suspected to have formed in an ancient impact basin and the interaction with Charon (the heart is on the side that never faces the moon) could help keep it active. Some astronomers have suggested that an ocean might even lay beneath the ice.
But it's not all about Pluto, for the researchers. Its large moon, Charon, is equally as exciting. The two objects are tidally locked, both showing the same face to each other. It's also interesting that Charon doesn't orbit Pluto but they both orbit a common center of mass, outside the dwarf planet. Like a cosmic dance between the two objects. And that's not the only interaction between the two. They also share materials, which causes the moon's red spot.
"One thing that was amazing was seeing the red pole on Charon. Usually, when we think of poles in planets like the Earth or Mars, we think of bright ice caps but Charon had this pole that was clearly different from things that we have seen before," Dr Olkin, who is also the Deputy Project Scientist for New Horizons, explained.
"We now understand that this reddish material probably accumulates from methane molecules that escape from Pluto and they would bounce around Charon and then stick at the poles and get cold trapped during the long winter and be transformed by radiolysis into these longer hydrocarbon chains, these tholins."
There are studies for new missions to Pluto (although nothing has been approved yet) but we should soon be able to monitor what’s happening with the dwarf planet a bit more regularly. The James Webb Space Telescope will launch next year and it should be sensitive enough to study Pluto’s surface ice.
"If money weren’t an issue I would love to go back and actually send a rover. It would be amazing to rover across the surface of Pluto and sample these different regions," concluded Dr Olkin.
New Horizons is currently en route to encounter another object, MU69. The flyby is scheduled for January 1, 2019.