LAUREL, Md. — The first set of images and other data collected by NASA’s New Horizons spacecraft during its July 14 flyby of Pluto, returned to Earth July 15, are already causing project scientists to reassess their understanding of the dwarf planet and its moons.
“I am completely surprised,” said Alan Stern, principal investigator for the New Horizons mission, during a July 15 briefing at the Applied Physics Laboratory to discuss the first set of flyby data that the spacecraft transmitted back to Earth earlier today. “I don’t think any one of us could have imagined that it was this good.”
The data returned to Earth during a communications pass that started shortly before 6 a.m. Eastern time July 15 included high-resolution images of portions of both Pluto and its largest moon, Charon, as well as images of a smaller moon, Hydra. The data also included spectra of part of Pluto.
Of particular interest was an image of Charon, whose surface scientists previously thought to be heavily cratered and thus very old. Instead, the images showed what deputy project scientist Cathy Olkin called a series of “troughs and cliffs” running across the surface for nearly 1,000 kilometers, which she interpreted as signs of more recent geologic activity.
The images also showed a canyon estimated to be as deep as 10 kilometers. “Charon just blew our socks off when we got the new image today,” she said. “We’ve just been thrilled.”
A high resolution image of one region of Pluto showed no impact craters, leading John Spencer, a member of the science team, to conclude that the region is relatively young geologically: less than 100 million years old. The image also showed mountains about 3,300 meters high, which scientists speculate are made of water ice.
The signs of geological activity on both Pluto and Charon suggest that the two worlds have some kind of internal heating source. Spencer said that, unlike other icy bodies in the outer solar system that get energy from tidal heating as they orbit giant planets, another mechanism must be at work here. That could be either heat from radioactive decay in their interiors, or heat liberated as a subsurface ocean freezes out.
“We’ve settled the fact that these very small planets can be very active after a long time,” Stern said. “It’s going to send a lot of geophysicists back to the drawing boards, trying to understand how exactly you do that.”
The images returned early July 15 represent only a small fraction of the data the spacecraft collected when is passed by Pluto and its moons a day earlier, coming within 12,500 kilometers of the surface of Pluto. “Frankly, we’re just skimming the top of it,” Stern said.
Scientists were hesitant to speculate in any detail on the images and spectra they presented at the briefing, given the limited time they had to analyze the data and because much more data will be coming back to Earth in the days and weeks to come. “Speculating now would be especially embarrassing we could be proven wrong very quickly,” Spencer said.
The spacecraft survived the flyby, including a communications blackout lasting nearly 22 hours so it could maximize the data it collected on closest approach, and remains in good condition. “Every indication is that the spacecraft is in great shape,” said Chris Hersman, New Horizons mission systems engineer, in a briefing here earlier July 15.
NASA is planning another briefing July 17 to discuss additional data retuned by the spacecraft. That will also give the science team more time to digest the initial batch of images. “Today is probably our biggest challenge,” Stern said, given the limited time they had to analyze the data before the briefing and the lack of sleep they got after the successful flyby July 14. “This is really hot off the press.”