The New Horizons spacecraft – now just hours from its encounter with Pluto after a 3-billion-mile, 9-year journey – captured this image of the dwarf planet early in the morning on July 11, 2015. The spacecraft was 2.5 million miles (4 million kilometers) from Pluto. When New Horizons comes closest to Pluto this Tuesday, a single hemisphere of this world – what scientists are calling the encounter hemisphere – will be facing the spacecraft. The image above is the last look New Horizons will get of the other hemisphere – what scientists are calling Pluto’s farside.
This “farside” from New Horizons’ perspective is actually the hemisphere of Pluto that faces its large moon Charon.
Alan Stern of the Southwest Research Institute in Boulder – who is also New Horizons principal investigator – said in a statement:
The [July 11] image is the last, best look that anyone will have of Pluto’s far side for decades to come.
In the image, you can see four mysterious dark spots on Pluto (bottom, toward the right) that have scientists deeply intrigued. The spots are connected to a dark belt that circles Pluto’s equatorial region. What continues to pique the interest of scientists is their similar size and even spacing. New Horizons program scientist Curt Niebur at NASA Headquarters in Washington said:
It’s weird that they’re spaced so regularly.
Jeff Moore of NASA’s Ames Research Center, Mountain View, California, said:
We can’t tell whether they’re plateaus or plains, or whether they’re brightness variations on a completely smooth surface.
The large dark areas are now estimated to be 300 miles (480 kilometers) across, an area roughly the size of the state of Missouri.
Bottom line: The last, best look that anyone will have of Pluto’s far side for decades to come reveals more detail about four mysterious dark spots on Pluto’s surface.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.