New Horizons at Pluto: Flyby, Computer Reset and Ice Volcano

New Horizons flew past Pluto in July 2015, passing within 8,000 miles of the dwarf planet and returning the first close images of its surface. Even later, 35 to 40 percent of the flyby data was still on the spacecraft, unseen by any human.

The Pluto Underground

Pluto was three billion miles away and smaller than Earth's moon. The best Hubble image was a fuzzy ball about six pixels by six pixels. A group of young scientists and graduate students, nicknamed the Pluto Underground, wanted to fly a spacecraft there. Dr. Alan Stern led them. Ralph McNutt, then a physics professor at MIT, was among them. The plan was to fly within 8,000 miles of the surface, almost 30 times closer than the moon is to Earth, and photograph the terrain. It faced resistance because NASA could do quicker missions closer to home. In 2003 the group convinced NASA and the New Horizons mission was born.

Pluto orbits in the Kuiper Belt, a region of leftover objects from the formation of the solar system, and is the largest of them. Pluto was described as a four and a half billion-year-old fossil that could hold clues to how Earth formed.

Built for speed

Pluto is 33 times as far from the Sun as Earth. To arrive within ten years of launch, the spacecraft had to leave Earth at more than 30,000 miles per hour. It was the size of a small piano and weighed about 1,000 pounds. It carried fuel only for minor course corrections, so it could not slow down and enter orbit. It would fly past once.

The launch was described as picture-perfect. In February 2007 a gravity assist from Jupiter increased its speed by 20 percent and cut three years off the trip.

Contact lost ten days out

About nine and a half years after launch and ten days from the flyby, Alan Stern called with the news: "We've lost communication with the spacecraft." Alice Bowman, the mission operations manager, led the recovery. The team found that the main computer had been overworked and had reset, and six months of programming were lost. Over three days they uploaded command codes to the spacecraft, with four hours to spare before the flyby sequence was due to start on July 7th.

Flyby day

The night before closest approach, the spacecraft sent home a handful of images that were the highest resolution ever obtained of Pluto. The team counted down to the closest approach at 7.49 am. At 9 pm they gathered to learn whether the spacecraft had survived, searched for a frequency, and locked onto telemetry. The result: a healthy spacecraft that had recorded data for the Pluto system.

What the images showed

• Mountains of water ice, many about 10,000 feet tall.
• Chasms much bigger than the Grand Canyon.
• Glacier flows of molecular nitrogen ice.

Alan Stern concluded that Pluto is geologically alive after four and a half billion years. That upended theories that predicted small planets would cool and die early.

In January 2016 NASA released an image of what appears to be a giant ice volcano with almost no craters on its flanks and a summit depression that is the caldera. Scientists said nothing like it had been seen elsewhere in the solar system. An active volcano would mean a source of heat, and the team believes the heat could be warming an ocean of water beneath the surface.

Looking back toward the sun after the flyby, the spacecraft saw Pluto's blue atmosphere. The nitrogen atmosphere should have dissipated into space billions of years ago, so something is replenishing it. Volcanic activity was raised as one possible source.

The team still had over a year's worth of data to download.