Last summer, as it sped through the Pluto system, the New Horizons spacecraft only had a few hours to pack its memory banks with as much data about the dwarf planetary system as possible. On October 25, the last few hundred bits of that data finally arrived in one of NASA's deep space radio dishes.
For posterity's sake, take a moment and remember that before the flyby—a mere 15 months ago—the dwarf planet was a pixellated blur. Planetary scientists had some ideas about Pluto's atmosphere, geology, and satellite system, well, pixellated works as an analogy for the clarity of those ideas. But now, hoo boy. New Horizons didn't just deliver a picture of Pluto's gigantic heart: The probe's flyby revealed the dwarf planet as one of the most dynamic and complex worlds in the solar system. What a time to be a planetary scientist.
New Horizons is equipped with seven different instruments—multi-spectral imagers, particle sniffers, dust collectors. Together, they collected 6.25 gigabytes of data. You could download (legally, of course) a movie that size in a few minutes. But New Horizons is 3 billion miles away. Bit by bit, the New Horizons ground team collected the flyby data over 469 days.
Alice Bowman, New Horizons' mission operations manager, was the point person for those transmissions. You might remember her as the person who received the "all's well" signal New Horizons sent on July 15, 2015 after it finished its historic fly by. "I would say July 15th was not the norm for us," she says. Instead of elated public check ins, Bowman's team was doing heavy logistical lifting for the priority scientific data.
"God forbid anything happen to that spacecraft, we wanted to have the highest value data on the ground as soon as we could," says Bowman. But doing so isn't just a matter of drag and dropping folders from your flash drive onto your laptop. Every bit of data on New Horizons' drives is indexed according to when it was collected. And that goes back to Newtonian physics. New Horizons' engineers had to calculate exactly how many seconds it would take for the probe to reach Pluto. And then instruct the computer with things like, "At 299,791,044 seconds after New Horizons has left Earth, roll 32 degrees, pitch 15 degrees, and yaw 256 degrees, and activate the Ralph imager for .25 seconds."
Bowman and her team had to start planning each of these downlinks 8 weeks in advance. And the process wasn't just figuring out which jigsawed piece of data to retrieve. "Then we run the command through software simulators, hardware simulators, and have the science and mission operations teams review the results of those simulations to make sure the commands do what we want," she says.
Bowman and her team also had to jostle with other missions, like Voyager, Cassini, and Stereo, for antenna time on NASA's 70-meter Deep Space Network antennas. "If we were able to get that time, we would get the data down and run operations software to make sure we got everything we requested," she says. If not, her team had to send a realtime request back to New Horizons. Sound fun? Repeat this process for over 500 chunks of data.
"New Horizons was just raining data every week for a year and a half," says Alan Stern, the mission's principal investigator. The images showed vast glaciers, mountains made of water ice, plains of frozen nitrogen, atmospheric haze layers, cryogenic volcanoes, and geologic evidence that Pluto has been tectonically active for 4.5 billion years. Plus surprises—like Charon's 600-mile minimum equatorial canyon—from each of Pluto's five satellites.
While Stern treats every byte of data like his own blood, a few downlinks hold special significance. First was that first, lovely, high resolution downlink from July 14, 2015. "After 26 years of working on this, it was just stunning to see what the world really looked like," he says. New Horizons took the second image towards the end of its fly by. "It's the true color image of Pluto's atmosphere, with a blue ring around it," he says. The only way to get that image was to be on the far side of the dwarf world, backlit by the sun. That one really nailed it for Stern: It was his equivalent of seeing the Apollo Earthrise picture.
Stern says his team has only turned about 80 percent of the New Horizons data into science. Completing the job might employ another generation of planetary scientists. Imagine: A 10-year-old kid inspired by last year's flyby could spend her post-doc solving Plutonian mysteries using New Horizons' data. "There are people who were born after Voyager who have earned a PhD and work on data from the 1980s," he says. NASA knows this. The agency recently sent out research proposals for more scientists to help the original New Horizons team analyze data.
And lest you think data analysis is the team's only chore, remember that they are still steering New Horizons towards its next target—a remote object in the Kuiper Belt known as 2014 MU69.
What's that? The last bit of Pluto data New Horizons sent home? "Some composition mapping data from the LEISA infrared mapping spectrometer aboard out Ralph instrument," says Stern. What does that mean? Wait and see. Or go get a degree in planetary science and find out for yourself.
