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New Horizons probe
An artist’s conception shows the New Horizons spacecraft beaming data back to Earth. (Credit: NASA / JHUAPL / SwRI)

More than 15 months after NASA’s New Horizons spacecraft flew past Pluto, the last bit of data captured during the flyby has finally been transmitted back to Earth.

NASA said the final transmission was a digital segment of an observation sequence captured by New Horizons’ Ralph/LEISA imager, focusing on Pluto and its biggest moon, Charon. The readings were stored up on July 14, 2015, as the piano-sized probe zoomed past Pluto about 3 billion miles from Earth. Since then, New Horizons’ distance from Earth has grown to 3.4 billion miles.

The downlink took place at 2:48 a.m. PT Tuesday via NASA’s Deep Space Network station in Canberra, Australia. In all, more than 50 gigabits of data relating to Pluto and its moons have been transmitted back to Earth.

Why did it take so long to send back an amount of data that would basically fit on a thumb drive? It’s because New Horizons’ power system was optimized to store loads of observations on its two onboard recorders, and then carefully send the data back via a radio transmitter at an average speed of roughly 2,000 bits per second. That’s about as fast as the old-style modems used back in the 1980s.

Mission operations manager Alice Bowman of Johns Hopkins University’s Applied Physics Laboratory compared the data set to a “pot of gold.”

She said the team will conduct a final data-verification review before commanding the spacecraft to erase the data on its recorders. That will clear out space for new data to be recorded during New Horizons’ extended mission, including observations farther out in the Kuiper Belt, the broad ring of icy material that lies beyond Neptune’s orbit.

The highlight of the extended mission is expected to be a close encounter on Jan. 1, 2019, with a small Kuiper Belt object known as 2014 MU69.

Meanwhile, the task of analyzing the data sent back from the Pluto system continues.

“The Pluto system data that New Horizons collected has amazed us over and over again with the beauty and complexity of Pluto and its system of moons,” principal investigator Alan Stern, a planetary scientist at Southwest Research Institute, said today in a news release.

“There’s a great deal of work ahead for us to understand the 400-plus scientific observations that have all been sent to Earth. And that’s exactly what we’re going to do — after all, who knows when the next data from a spacecraft visiting Pluto will be sent?”

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