The Long Approach

The mission at Pluto is divided into several phases. In each phase, New Horizons will focus on the kind of science appropriate to its range from Pluto. New Horizons is traveling so fast that the actual close-approach part of the encounter happens in an incredibly short period; nearly all of the most important goals for the mission are met in the time from 2.5 hours before to 1 hour after closest approach. One exception to this is global image covering: Pluto takes about a week (6.4 days) to rotate, so the best global maps will be composed of images gathered beginning a couple of days before closest approach. The science observations for the encounter have been planned with both prime and backup observations and with redundancy among instruments to make sure the mission's goals are met if one observation or even one instrument fails. The observations focus primarily on Pluto, Charon, and Nix: rather than scatter observations across both Nix and Hydra, they chose to characterize Nix well and Hydra less well. The other two moons, Styx and Kerberos, are even smaller than Nix and Hydra (hence, more difficult to observe) and were discovered quite late in the mission planning process; they'll be imaged in group shots, optical navigation imagery and satellite system movies, but don't have science observations devoted to them specifically.

Approach Phase 1 : 180 to 100 days before closest approach (Jan 6-Apr 4; range to Pluto is 226-121 million km). SWAP and PEPSSI will measure plasma. LORRI will monitor motions of Pluto, Charon, and the smaller moons. Pluto is barely resolved.

: 180 to 100 days before closest approach (Jan 6-Apr 4; range to Pluto is 226-121 million km). SWAP and PEPSSI will measure plasma. LORRI will monitor motions of Pluto, Charon, and the smaller moons. Pluto is barely resolved. Approach Phase 2 : 100 to 21 days before closest approach (Apr 4-Jun 23; range to Pluto is 121-26 million km). Add in color observations, and search for satellites and rings. The start of this phase is chosen to roughly coincide with the time when LORRI has better resolution than Hubble, but Pluto will still be only a few pixels across.

: 100 to 21 days before closest approach (Apr 4-Jun 23; range to Pluto is 121-26 million km). Add in color observations, and search for satellites and rings. The start of this phase is chosen to roughly coincide with the time when LORRI has better resolution than Hubble, but Pluto will still be only a few pixels across. Approach Phase 3 : 21 to 1 days before closest approach (Jun 23-Jul 13; range to Pluto is 26-1.2 million km). Includes best, second-best, and third-best rotation coverage before closest approach, yielding the best global maps of Pluto and Charon. PEPSSI and SWAP may detect pickup ions and bow shock. LEISA and Alice can begin looking for variability in IR and UV. Search for clouds or hazes, tracking winds.

: 21 to 1 days before closest approach (Jun 23-Jul 13; range to Pluto is 26-1.2 million km). Includes best, second-best, and third-best rotation coverage before closest approach, yielding the best global maps of Pluto and Charon. PEPSSI and SWAP may detect pickup ions and bow shock. LEISA and Alice can begin looking for variability in IR and UV. Search for clouds or hazes, tracking winds. Near Encounter Phase : -1 to +1 days (Jul 13-15, within 1.2 million km) -- sequenced in 2008 and 2009. Most of the highest-priority observations.

: -1 to +1 days (Jul 13-15, within 1.2 million km) -- sequenced in 2008 and 2009. Most of the highest-priority observations. Departure Phase 1 : 1 to 21 days after closest approach (Jul 15-Aug 4; range to Pluto is 1.2 to 24 million km). Remote sensing of Pluto and Charon is performed for only 1 rotation. SWAP and PEPSSI study magnetotail, pickup ions. REX studies nightside temperatures. Nix and Hydra high-phase observations. Search for rings.

: 1 to 21 days after closest approach (Jul 15-Aug 4; range to Pluto is 1.2 to 24 million km). Remote sensing of Pluto and Charon is performed for only 1 rotation. SWAP and PEPSSI study magnetotail, pickup ions. REX studies nightside temperatures. Nix and Hydra high-phase observations. Search for rings. Departure Phase 2 : 21 to 100 days after closest approach (Aug 5-Oct 22; range to Pluto is 24 to 119 million km).

: 21 to 100 days after closest approach (Aug 5-Oct 22; range to Pluto is 24 to 119 million km). Departure Phase 3: 100 to 180 days after (Oct 22-Jan 1, 2016; range to Pluto is 119 to 203 million km). No remote sensing observations planned.

Optical Navigation imaging

Beginning in January, New Horizons will use its sharpest LORRI camera to take images of Pluto, Charon, Nix, and Hydra for optical navigation purposes. Navigators will use the photos to refine the precision of their predictions of where each body will be, when. Of course, the images will also be useful for science. Geologists will study them and compare them to Hubble observations to look for further surface changes on Pluto, and astrophysicists will use the navigational information to determine the masses of Pluto and Charon more precisely. Late in the approach, as Pluto looms larger, the New Horizons team has done its best to command images at smooth intervals for the future creation of a movie of New Horizons' approach.

While it's very exciting that New Horizons will begin imaging the Pluto system in January, it's important to keep your anticipation aligned with the reality of the photos. LORRI is a very high-resolution camera, but Pluto is not very big (it's smaller than any of Jupiter's Galilean moons) and will be, for the most part, far away from New Horizons. Small and far away means few pixels and not a lot of surface detail, even as late as June of next year. In the composite below, I looked at actual LORRI images of Jupiter's moons, taken during the flyby in 2007, and figured out when, in New Horizons' approach to Pluto, LORRI's imaging of Pluto should have comparable resolution. It's not a perfect comparison, for a couple of reasons. We know already that Pluto has a more contrasty surface than Io or Ganymede. Also, by June, every single image New Horizons takes of Pluto will be the best image ever taken of Pluto, so it's going to be thrilling no matter what. But there won't really be enough pixels for us to begin to say anything particularly insightful about what is happening on Pluto's surface until the beginning of July.