One of the final images taken before New Horizons made its closest approach to Pluto on 14 July 2015. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

It’s over three billion miles away from Earth. We’ve only known about it since 1930. Pluto is an icy rock about a fifth the size of Earth. We called it a planet until 2006, but now we say it’s a dwarf planet. Scientists decided that it’s not a planet like Venus or Jupiter because it’s just one of many objects in the Kuiper Belt. That’s a ring of icy rocks on the edge of our solar system.

But just because it’s not quite a planet like Venus and Jupiter, that doesn’t mean we don’t want to learn more about it. It’s so far away that it’s hard to see with even the most powerful telescopes. To get a better look, we sent a small spacecraft named New Horizons to visit Pluto. It left Earth on January 19, 2006.

New Horizons is the fastest spacecraft ever launched. It left Earth travelling 31,000 miles per hour. That’s really fast. But because Pluto is so far away, it still took nine and half years to make it there.

 It flew right by Pluto on July 14, 2015. For 22 hours, it took lots of pictures and measurements of this icy world. While it collected information, we couldn’t talk to the spacecraft.

New Horizons has a radio antenna, cameras, and other tools. It uses the antenna to send messages to Earth. But New Horizons couldn’t point its cameras at Pluto and keep its antenna pointed toward Earth. This meant it couldn’t photograph Pluto and send messages to Earth at the same time. Scientists chose to get as many pictures of Pluto as possible, even if that meant we couldn’t get messages from New Horizons for a while.

After the flyby, the mission team reconnected with the New Horizons spacecraft. They wanted to make sure everything went as planned. New Horizons sent a message to Earth saying it was OK. Because the spacecraft was so far away, the message took 4 hours and 25 minutes to reach us.

When we heard from New Horizons on July 14, 2015, it was just past 9 p.m. Eastern Daylight Time. Everyone was overjoyed. We sent a probe to Pluto, we took pictures, and the spacecraft worked just right.

For months to come, New Horizons will keep sending back the information it collected near Pluto. It takes a long time to get data from so far away. We’ll learn about Pluto’s surface, temperature, atmosphere, and moons—especially its largest moon, Charon. That’s not bad for a spacecraft the size of a baby grand piano!

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