Three days before New Horizons’ closest pass by Pluto and we already have the first final image of the mission: this is the last “best” view we will have of Pluto’s Charon-facing side, as the spacecraft will be acquiring its most detailed images of the planet’s opposite side on July 14.
Pluto and its largest moon Charon are locked together gravitationally, a scenario called tidal locking. The face of one is always aimed at the same face of the other, and they orbit around a point in space (the barycenter) that is located between the two (but closer to Pluto.) Thus the image above shows the side of Pluto that Charon always “sees.”*
This image, obtained by the LORRI camera on July 11, also shows some of Pluto’s already-intriguing geology – including the fascinating 300-mile-wide dark spots near the equator that were noticed several days prior. Now they can be discerned to have irregular borders and smaller dark spots alongside them.
“It’s weird that they’re spaced so regularly,” says New Horizons program scientist Curt Niebur at NASA Headquarters in Washington. Jeff Moore of NASA’s Ames Research Center, Mountain View, California, is equally intrigued. “We can’t tell whether they’re plateaus or plains, or whether they’re brightness variations on a completely smooth surface.”
On the morning of Tuesday, July 14, at 7:49 AM EDT, New Horizons will pass about 7,800 miles (12,500 kilometers) from the surface of Pluto. Its Ralph camera will acquire highly detailed images at resolutions down to 820 feet (250 meters) per pixel. The first data will arrive on Earth about four and a half hours after the event – even traveling at the speed of light, that’s how long it takes for a signal to get here from Pluto!
Source: New Horizons mission site
*The view is from a higher perspective than Charon gets, of course, since New Horizons is approaching the Pluto system from a polar angle.