NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto’s moon Charon just before closest approach on July 14, 2015. Charon’s striking reddish north polar region is informally named Mordor Macula.Credits: NASA/JHUAPL/SwRI
Where were you at 7:49 a.m. Eastern Time on July 14, 2015?
Three billion miles from Earth, NASA’s New Horizons spacecraft, moving at speeds that would get it from New York to Los Angeles in about four minutes, was pointing cameras, spectrometers, and other sensors at Pluto and its moons – distant worlds that humankind had never seen up close – recording hundreds of pictures and other data that would forever change our view of the outer solar system.
“New Horizons not only completed the era of first reconnaissance of the planets, the mission has intrigued and inspired. Who knew that Pluto would have a heart?” said NASA’s Director of Planetary Science Jim Green. “Even today, New Horizons captures our imagination, rekindles our curiosity, and reminds us of what’s possible.”
To say that New Horizons shook the foundation of planetary science is an understatement—discoveries already culled from the pictures and compositional and space environment readings have not only introduced us to the Pluto system, but hint at what awaits as scientists examine other worlds in the Kuiper Belt. New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, lists the mission’s most surprising and amazing findings from Pluto (so far):
- The complexity of Pluto and its satellites is far beyond what we expected.
- The degree of current activity on Pluto’s surface and the youth of some surfaces on Pluto are simply astounding.
- Pluto’s atmospheric hazes and lower-than-predicted atmospheric escape rate upended all of the pre-flyby models.
- Charon’s enormous equatorial extensional tectonic belt hints at the freezing of a former water ice ocean inside Charon in the distant past. Other evidence found by New Horizons indicates Pluto could well have an internal water-ice ocean today.
- All of Pluto’s moons that can be age-dated by surface craters have the same, ancient age—adding weight to the theory that they were formed together in a single collision between Pluto and another planet in the Kuiper Belt long ago.
- Charon’s dark, red polar cap is unprecedented in the solar system and may be the result of atmospheric gases that escaped Pluto and then accreted on Charon’s surface.
- Pluto’s vast 1,000-kilometer-wide heart-shaped nitrogen glacier (informally called Sputnik Planum) that New Horizons discovered is the largest known glacier in the solar system.
- Pluto shows evidence of vast changes in atmospheric pressure and, possibly, past presence of running or standing liquid volatiles on its surface – something only seen elsewhere on Earth, Mars and Saturn’s moon Titan in our solar system.
- The lack of additional Pluto satellites beyond what was discovered before New Horizons was unexpected.
- Pluto’s atmosphere is blue. Who knew?
“It’s strange to think that only a year ago, we still had no real idea of what the Pluto system was like,” said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “But it didn’t take long for us to realize Pluto was something special, and like nothing we ever could have expected. We’ve been astounded by the beauty and complexity of Pluto and its moons and we’re excited about the discoveries still to come.”
New Horizons is now nearly 300 million miles beyond Pluto, speeding to its next destination deeper into the Kuiper Belt, following NASA approval of an extended mission. About 80 percent of the data stored on the spacecraft’s recorders has been sent to Earth; transmission of the remainder will be complete by October.
“Our entire team is proud to have accomplished the first exploration of Pluto and the Kuiper Belt—something many of us had worked to achieve since the 1990s,” said Stern. “The data that New Horizons sent back about Pluto and its system of moons has revolutionized planetary science and inspired people of all ages across the world about space exploration. It’s been a real privilege to be able to do that, for which I’ll be forever indebted to our team and our nation.”