We're about to get our closest ever look at Pluto.
After nearly a decade hurtling across 3 billion miles of space, NASA's New Horizons probe has sped past the dwarf planet just 7,800 miles from the surface, snapping pictures and capturing data all the way.
New Horizons left Earth in 2006 at a speed of 36,000 miles per hour on a mission to study Pluto and its moons. As it has neared the dwarf planet, the probe has been sending back increasingly clearer images of its target, and got as close as possible at around 11.50am GMT Tuesday -- that's 12.50pm UK time, 4.50am Pacific time or 9.50pm Australian time.
Having flown by Pluto, New Horizons is continuing past the dwarf planet. Scientists on Earth have sent a radio pulse from three massive satellite dishes, carefully timed to arrive when the probe is on the other side of Pluto. By comparing the pulse received after it's passed by Pluto with the pulse sent out from Earth, scientists hope to learn more about the dwarf planet's atmosphere.
Update at 6:30 p.m. PT: The craft has been out of touch with NASA -- by design -- since this morning. This evening, right on schedule, mission control began receiving data from the craft.
While it's too far away to watch in real time, you can keep up with the mission at NASA's website, on the official NASA Instagram or New Horizons Twitter feeds, or via the free Pluto Safari app (Android | iOS).
Photos taken during the flyby will be beamed back to Earth and are expected to reach us around 15 hours after the probe passes Pluto.
"Pluto was discovered just 85 years ago by a farmer's son from Kansas [Clyde Tombaugh], inspired by a visionary from Boston, using a telescope in Flagstaff, Arizona," John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington, said Tuesday in a statement. "Today, science takes a great leap observing the Pluto system up close and flying into a new frontier that will help us better understand the origins of the solar system."
Grunsfeld certainly isn't alone in acknowledging the significance of the achievement.
"After nearly 15 years of planning, building, and flying the New Horizons spacecraft across the solar system, we've reached our goal," said project manager Glen Fountain at the Johns Hopkins University Applied Physical Laboratory in Laurel, Maryland, which designed, built and operates New Horizons for NASA. "The bounty of what we've collected is about to unfold."
Previously, the best image we had was a composite of images from the Hubble telescope. We didn't even know how big Pluto was. That led to debate over whether it was actually a planet. In 2006, Pluto was demoted from a full planet to a dwarf planet -- because if Pluto remained a planet, lots of similar-sized bodies on the edge of the solar system would have to be considered as planets too.
Disappointed Pluto fans can at least take heart that the Long Range Reconnaissance Imager (LORRI) aboard New Horizons has now revealed that at 1,473 miles in diameter, Pluto is larger than previously thought.
Update, 5pm UK: NASA quotes added.