When the scientists of the New Horizons mission launched their probe nearly a decade ago, they had no idea what to expect when it reached Pluto. And the things it’s revealed in the days since it made its closest approach to the dwarf planet have exceeded astronomers’ expectations.
New Horizons is officially out of its nine-day close surveillance period—the time when it passed closest to Pluto and could collect the most important data about the distant icy rock. Now that its attention is less dominated by collecting science and more focused on sending it home, the real fun begins for the New Horizons mission scientists. On Friday, some of the team’s principals sat down to present some of the probe’s freshest downlinks, as well as let us all know that New Horizons fever would be winding down to a steady pulse—updates each Friday, rather than every time new data comes in.
Speaking of pulse, one of the first announcements today came from principal investigator Alan Stern, who showed some new information on Pluto’s massive heart-shaped plain. The area, now officially named Tombaugh Regio, happens to coincide with a region of frozen carbon monoxide. According to Will Grundy, New Horizons’ expert on ices, the layer is at least a centimeter thick. But he can’t say for sure whether it is being deposited from above, or upwelling from below.
Contours of frozen carbon monoxide show an increase in concentration towards the middle of the heart’s left lobe. NASA/JHAPL/SWRI
Weird ices aside, evidence continues to pile up for active geology on Pluto. At Friday’s press conference, team scientist Jeff Moore showed two close-up flyover animations of the surface. The first shows a mountainous region that the team has unofficially named Norgay Montes (after Tenzing Norgay, the Sherpa who summited Everest with Sir Edmund Hillary). Some of these mountains, says Moore, are up to two miles high.
The mountains are awesome, but Pluto’s surface is even more dynamic. Moore also showed off Sputnik Planum, “the frozen plains of Pluto”—part of that heart-shaped feature. Judging from the lack of impact craters on the plain, he estimates that this surface is less than 100 million years old, and is possibly still active. But activity isn’t restricted to the substrate. Pointing to the irregularly shaped icy blobs, Moore says they show the same patterns of a boiling pot of oatmeal. They could be signs of convection heating, driven by Pluto’s modest subsurface heat, or of contraction—cooling.
Features in Pluto’s Sputnik Planum show evidence of active geology, erosion, or both. NASA/JHAPL/SWRI
New Horizons’ team usually shies away from speculation, but Moore couldn’t help showing off some very compelling patterns on the plains in the northwest part of Tombaugh Regio.
Evidence of wind, or possibly even geysers. NASA/JHAPL/SWRI
“These dark smudges appear to be aligned, and may have been produced by winds on Pluto’s icy surface,” says Moore. And to his eye, the longer, lighter lines running perpendicular to the smudges add more weight to that interpretation. “On Earth and Mars, these are called wind streaks, caused by erosion or deposition on topographic obstacles,” he says. Then again, the black smudges could be evidence of geysers. But like everything Pluto—at least at this point—every bit of data is wide open to interpretation.
Above its icy surface, Pluto has an atmosphere made of methane and nitrogen. One of New Horizons’ key objectives was capturing the structure of the dwarf planet’s atmosphere, using the sun’s rays as it shone through the horizon while New Horizons was behind Pluto. “We see the atmosphere goes way far out,” says Randy Gladstone, one of the team’s atmosphere experts. So far, mission ops hasn’t downloaded enough data to fully characterize the atmosphere, but the readings so far are consistent with less turbulent weather.
Friday’s press briefing piles more data on this week’s earlier scientific revelations. This included new estimates of the shock wave that occurs as solar wind buffets Pluto’s leaking nitrogen atmosphere. And speaking of leaking nitrogen, the team estimates that 500 tons of the stuff is slipping into space every hour. “For comparison, the escaping atmosphere from Mars is about one ton per hour,” says Fran Bagenal, one of New Horizons’ atmospheric scientists. Which, over the course of Pluto’s existence, “adds up to a substantial mountain of ice removed through evaporation,” she says. There’s still no telling how Pluto is regenerating its nitrogen atmosphere, nor for how long it can continue to do so.
That question, and many others about Pluto’s atmosphere (and whether its biggest moon Charon might also have one) shouldn’t linger for long. Stern says New Horizons will devote much of the next month or so to sending home data collected by its plasma sensors. The downside is, opening up this bandwidth means shutting off the stream of gasp-inducing pictures.
Which is a shame. That means one of the last new pictures of the system everyone will see, for at least a little while, is a pixelated image of Nix, Pluto’s second (of five) moons. Great, but Nix, Styx, and Kerberos are like those guys in the Rolling Stones who are not Mick or Keith: We only care about them because of their proximity to Pluto and Charon.
But it was only in April that the best view of Pluto anyone had ever seen was more pixelated than Friday’s picture of Nix. Since then, so much data has already come in, it’s hard to imagine how little scientists knew barely more than a week ago. Of the 50 gigabits New Horizons collected during its nine-day flyby of Pluto, less than 2 percent has made it back to Earth.
“I’m a little biased, but I think the solar system saved the best for last,” said Alan Stern. Technically Alan, Neptune 1 is the last planet in the solar system but…ah, I see what you did there. Pluto might not be a full planet, but it is one hell of a world.
1 UPDATE 20:15 ET 07/17/15: This post has been updated to correct the last planet in the solar system.
