NASA’s New Horizons spacecraft phoned home Tuesday night, reporting that it had made it to Pluto and beyond after crossing the solar system for 9
“We have a healthy spacecraft. We’ve recorded data in the Pluto system. And we’re outbound from Pluto,” Alice Bowman, the mission operations manager, announced to her thrilled colleagues in the control room at the Johns Hopkins University Applied Physics Laboratory, the home of New Horizons. In a nearby auditorium, hundreds of people who had been watching the video feed stood and gave the team a standing ovation.
On its approach to Pluto, the spacecraft obtained the most arresting image yet of the dwarf planet. Pluto is not a bland and featureless ball of ice, but rather a complex, variegated, mottled world with broad snowfields, structures that look like cliffs or fault lines, and a strikingly bright heart-shaped area that could be the eroded remnant of a giant impact crater.
Cheers erupted at 7:50 a.m. Tuesday as a countdown clock ticked to zero, signifying the spacecraft’s closest approach to Pluto’s surface, about 7,750 miles.
Instantly the “My Other Vehicle Is On Its Way to Pluto” bumper stickers on the team members’ cars became obsolete.
“Pluto has now been explored!” exulted Alan Stern, the mission’s principal investigator.
The members of the New Horizons team then spent the rest of the day waiting for the crucial signal that their spacecraft was intact. Traveling at more than 31,000 miles per hour, New Horizons could potentially have been disabled by a collision with debris, or perhaps in some way overloaded or discombobulated by its frenetic schedule of observations of Pluto and its five moons.
New Horizons crossed the face of Pluto in just three minutes and continued on its way through the realm of small ice-worlds in the outer solar system, destined ultimately for interstellar space.
The New Horizons spacecraft hadn’t been heard from since 11:17 p.m. Monday, when it ceased to transmit any information about its location or operations. That was all part of the plan, because New Horizons had so many duties to perform. The seven instruments on board were programmed to conduct a dizzying series of observations of Pluto and its moons.
Pluto is three billion miles from Earth, and so even at the speed of light it takes 4.5 hours for instructions to cross that distance. As a result, the spacecraft is flying autonomously, following a program loaded onto the main computer last Monday.
That “encounter load” called for 433 separate scientific observations over nine days and requiring roughly 600 spacecraft maneuvers. The New Horizons team chose to remain in the dark during the encounter so that the spacecraft could focus entirely on Pluto and its moons and thereby maximize its science yield.
The newest photo of Pluto, obtained by New Horizons on Monday and made public Tuesday morning, thrilled the hundreds of people who showed up at APL for the encounter celebration. The most prominent feature is the “heart,” a bright, twin-lobed region with boundaries so sharp it appears to have been stamped onto the surface.
In fact that may not be far off, because one hypothesis that scientists said they’re discussing is that at least part of the heart — the left lobe — is the remnant of a huge impact long ago. It’s possible that region is a depression filled with nitrogen snow, said team member Carey Lisse.
Stern said there are indications of tectonic activity — perhaps even recently. Asked if the images show that there’s snow on Pluto, Stern said, “It sure looks that way.”
Project scientist Hal Weaver said there is a small bright spot that might be the tip of a mountain covered with snow. He said it looks “almost like a lighthouse.” Weaver cited a number of spots that bring to mind Almond Joy candy bars. “It looks like there are these great mounds — like the mounds with almonds on top,” Weaver said.
Linear features on the surface “could be scarps, or faults,” said New Horizons team member and planetary scientist Cathy Olkin.
But Stern cautioned that it’s too soon to reach any conclusions about things like mountains, faults, canyons or other kinds of dramatic topography. The next batch of images should be 10 times as detailed. For the best assessment of topography, scientists need stereoscopic imagery that remains stored on the spacecraft and will take time to download to Earth, Stern said.
That said, scientists uniformly rejoiced in the color variations and diversity of features. Pluto is not a simple and smooth snowball, which was one possibility before New Horizons got close enough to learn otherwise, NASA associate administrator for science John Grunsfeld noted in a news briefing.
“The speculation varied from, we would see a cloud-enshrouded nitrogen haze, and there’d be no features at all, and we’d zip by and go, ‘Oh, well, that was fun’ . . . or we might have seen something that looks like an ancient, monolithic, crater-laden body,” he said. Instead, Pluto turned out to be complicated and intriguing. “Nature always comes up with these surprises,” he said.
The team had been aiming at a keyhole in space about 7,800 miles from Pluto’s surface and at a certain point in time when lighting conditions would be optimal for imagery. In recent days, the team knew that New Horizons was running about 72 seconds ahead of what would be the perfect flight schedule, but that was still well within the 100-second margin of error for excellent scientific returns.
“I have to pinch myself,” said Bowman, who managed one hour of sleep in her office Monday night. “Look what we accomplished. It’s truly amazing humankind can go out and explore these worlds, and see Pluto revealed just before our eyes. It’s just fantastic.”
All the New Horizons team members were on hand for the morning celebration. Who was back at Mission Operations? A closed-circuit feed briefly cut to the control room and provided the answer: a lone worker vacuuming the carpet. The audience erupted in laughter.
No one at APL on Tuesday seemed to care that astronomers in 2006 officially demoted Pluto to the status of “dwarf planet.” The new images seemed to render that entire discussion moot.
Stern has pointed out that new measurements show Pluto to be slightly larger than previously estimated, and a wee bit larger than Eris, another dwarf planet in the outer solar system.
Among those on hand Tuesday were the children of Clyde Tombaugh, the astronomer who discovered Pluto in 1930. Some of his ashes are on board New Horizons.
Rachel Feltman and Robert Gebelhoff contributed to this report.