The closer New Horizons gets to Pluto, the more puzzling the dwarf planet becomes.
The latest image released by NASA highlights four mysterious dark spots lined up along Pluto’s equator. Each of the spots is about 300 miles across, and they are evenly spaced along a dark belt that rings the planet’s surface.
When New Horizons spied the spots a few weeks ago, mission scientists were left scratching their heads.
"It's a real puzzle -- we don't know what the spots are,” Alan Stern, the mission’s principal investigator, said at the time.
They still don’t.