Sen—It's the moment we've been waiting for since January 19, 2006. When New Horizons lifted off from Cape Canaveral, bound for Pluto, it was the beginning of a long wait for a scientific payoff. Nine years later, New Horizons has finally, formally begun the scientific mission, delivering its first image data from the mission's Pluto approach phase.
The photos contain both Pluto and Charon, each touching just a couple of pixels. These early photos won't tell scientists much about the nature of the two frigid worlds; they're more immediately useful to the spacecraft navigators, who will measure Pluto and Charon's position with respect to background stars to fine-tune New Horizons' trajectory, preparing to adjust the spacecraft's course on March 10. But these photos signify the moment that New Horizons began to gather the data set that will revolutionize our understanding of Pluto, Charon, and the rest of the Kuiper belt.
The two images in this animation are the first two photos of New Horizons' scientific observations of Pluto. They were taken January 25 and 27, 2015, from a distance of more than 200 million kilometers. Although it appears that Pluto and Charon are half-full, their apparent shape is a result of a camera artifact. Their true, round shapes will not be revealed until New Horizons gets closer. Image credit: NASA / JHUAPL / SwRI
When will the photos get better? Unlike the other mission to a dwarf planet, Dawn (which is now approaching Ceres), New Horizons will not see its target look significantly larger for a long time. Dawn began its approach imaging of Ceres when it was already quite close to the asteroid, only 1.2 million kilometers away. New Horizons was 203 million kilometers away from Pluto when it took these optical navigation photos. Even traveling at more than 14 kilometers per second, it is going to take months for New Horizons to get close enough to Pluto to begin to see details on the surface. It will be May before New Horizons improves on the best work astronomers did with Hubble data. It will be late June or even July before New Horizons gets enough pixels across Pluto's disk to tell craters, ridges, and chasms from colorful patterns on the surface.
But there is something that Pluto has, which Ceres doesn't: a system full of moving moons. So even though New Horizons won't see details on Pluto's surface for months, we will be able to enjoy the rhythmic dance of the six known bodies in the Pluto system. The do-si-do of Pluto and Charon around their mutual center of gravity was visible even last summer, a year before the flyby.
The two images in this animation are the first two photos of New Horizons' scientific observations of Pluto. Image credit: NASA / JHUAPL / SwRI
The photos that New Horizons took on January 25 and 27 had exposures too short for the incredibly faint smaller moons to register on New Horizons' camera detector. It's taking other images with longer exposures that should, soon, reveal the second- and third-largest of Pluto's satellites, Nix and Hydra. Pluto's fourth- and fifth-largest moons, Styx and Kerberos, won't be visible until May. There could be other, as-yet-undiscovered moons, but since any such bodies would be fainter than Styx and Kerberos, New Horizons doesn't have a chance of discovering them until at least June.
To see moons in motion, it's not sufficient to take a single photo; New Horizons has to shoot many photos, separated in time by hours to days, to catch all the dynamics of the system. Lots of photos require lots of data volume. The spacecraft has 16 Gigabytes of onboard storage space, but can only relay that data to Earth at a rate of 125 kilobytes per second. So as the spacecraft shoots its photos, it's building up a sizeable data backlog. The only way for New Horizons' engineers to get the data to Earth faster is to set New Horizons spinning, allowing it to shut off its guidance system and use the spare power to run both of its radio transmitters simultaneously. The mission has planned two long spin periods, one after each of two planned course-trimming rocket firings, for March 10 to April 4 and May 15 to May 27. For those weeks, New Horizons won't be photographing Pluto and its moons, but it will be able to empty its memory banks to make room for more of the best images and movies anyone has ever taken of Pluto.
So as exciting as it is to see the first pictures of New Horizons' Pluto science mission, we still have to be patient through several more months of the long approach to get the pictures we really want. In the meantime, enjoy Ceres! Dawn took this photo of Ceres yesterday, from a distance 1400 times closer to Ceres than New Horizons presently is to Pluto.
This photo was captured on February 4, 2015, when Dawn was 145,000 kilometers from Ceres. It has been enlarged by a factor of 10 and sharpened to increase detail. Image credit: NASA / JPL / UCLA / MPS / DLR / IDA