Soon to be making its long-awaited flyby of dwarf planet Pluto, New Horizons has sent its last and best ever image of the world’s mysterious dark spots that have been puzzling astronomers ever since they were brought into focus earlier on in the mission’s journey.
The spots appear on the side of Pluto that faces its largest moon, Charon, meaning that the spacecraft will not see the features again since it will make its flyby of the dwarf planet’s opposite side. “[This is] the last, best look that anyone will have of Pluto’s far side for decades to come,” says the spacecraft’s Principal Investigator, Alan Stern of the Southwest Research Institute in Boulder, Colorado.
Joined up by a dark belt that circles Pluto’s equatorial region, the similarly sized dark spots are strangely and evenly spaced. “We can’t tell whether they’re plateaus or plains, or whether they’re brightness variations on a completely smooth surface,” says Jeff Moore, who is based at NASA’s Ames Research Center in California.
The New Horizons team have estimated that the dark regions are about 480 kilometres (300 miles) across, an area that’s about the size of the state of Missouri in Midwestern United States. As the spacecraft has edged closer to the dwarf planet, the spots have shown themselves to be much more complex than they initially appeared. The boundaries between the dark and bright terrain have also been brought into focus and boast irregularity.
The spots are not the only features that interest the spacecraft’s scientists. The New Horizons Geology, Geophysics and Imaging (GGI) team are also interested in seeking out other surface features such as impact craters, made when lumps of space rock struck Pluto. “When we combine images like this of the far side with composition and colour data the spacecraft has already acquired but not yet sent to Earth, we expect to be able to read the history of this face of Pluto,” says Moore.
On Tuesday at 7:49 AM EDT, New Horizons will zip past the dwarf planet Pluto at 49,600 kilometres per hour (30,800 miles per hour), passing within 12,500 kilometres (7,767 miles) of the dwarf planet’s surface and rapidly gathering data of the icy world.
Check out our sister magazine How It Works‘ video to find out more about the New Horizon mission.