New Horizons Arrives At Pluto: Everything Is a Surprise

NASA: “One of the final images taken before New Horizons made it’s closest approach to Pluto on 15 July 2015.”

At 7:49 a.m. EDT July 14th, the New Horizons spacecraft will make its closest approach to Pluto—a fly-by that takes it a mere 7,700-odd miles from the surface of the dwarf planet—ending a 3 billion-mile journey, that took 9.5 years to make. Until now, the most sophisticated ground-based telescopes, and even the orbiting Hubble Space Telescope, only revealed a fuzzy ball. Everything we will learn about Pluto will be new. Residing in the Kuiper Belt, beyond the orbit of the planets, Pluto is the largest in a class of trans-Neptunian objects, which followed a different evolutionary path than the eight bodies now considered as the Solar System’s planets. Although it had been proposed that this icy cold and dark world would be featureless, the opposite is being revealed.

Over the past week, as New Horizons came closer to Pluto, scientists could discern dark spots and dark features, indicating an active geological past; they noted that they were able to observe nitrogen escaping from the atmosphere of Pluto from farther away than they had expected, which could indicate the source is stronger, or the escape from Pluto is stronger; they discovered that there are methane and hydrogen in Pluto’s polar ice cap; and that the small body is actually larger than they had been able to see from a distance, through its atmosphere. These are observations and hints. The measurements from the suite of seven scientific instruments on board New Horizons, which will be delivered to Earth over the next year, should help provide some answers, and raise more questions.

Pluto and its largest moon, Charon, which is half the size of Pluto, are considered a two-planet system, as they rotate around a common center of gravity, “like a pair of figure skaters, clasping hands.” Charon is, itself, turning out to be a world with intriguing characteristics, including craters, a dark north polar region, and a chasm in its southern hemisphere that is longer and deeper than the Grand Canyon. Fourteen minutes after skimming above Pluto, New Horizons will zip past Charon, and then look back. Both Pluto and Charon will then be observed from the dark side, opposite the Sun-facing side, as New Horizons proceeds to farther reaches.

Although the Pluto fly-by will be just before 8 a.m., the spacecraft will not start sending data back to Earth immediately, but instead complete its scientific mission. Then it will interrupt its science observations for 15 minutes, and turn itself around to point its antenna toward Earth and send back engineering data. It takes 4.5 hours for transmissions from Pluto reach NASA’s Deep Space Network. All told, it will not be until nearly 9 p.m., that the scientists and engineers will find out if New Horizons is in good health and survived its Pluto encounter. They hope to start to have data coming back to Earth the day after the fly-by but it will be a trickle, due to the very low data rate by which it can transmit.