A closer look at the 'dark' side of Pluto

An annotated image of Pluto with a reference globe showing Pluto’s orientation in the image.

NASA’s New Horizons spacecraft has taken its best image of four dark spots on Pluto that have been puzzling scientists. The spots appear on the "dark" side of Pluto – the one that always faces its largest moon, Charon, the one that cannot be seen from Earth and that will be invisible to the spacecraft when it makes its close flyby tomorrow morning.

New Horizons' principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, describes this image as “the last, best look that anyone will have of Pluto’s far side for decades to come”.

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. “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.”

The large dark areas are now estimated to be 480 kilometres across and more complex than they initially appeared.

In addition to solving the mystery of the spots, the New Horizons Geology, Geophysics and Imaging team is interested in identifying other surface features such as impact craters, formed when smaller objects struck the dwarf planet.

“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,” Moore says.

When New Horizons makes its closest approach to Pluto, it will focus on the opposing or “encounter hemisphere” of the dwarf planet.

New Horizons will pass about 12,500 kilometres from the dwarf planet.

Previous Cosmos news coverage of the New Horizons mission and related material here or read more about this historic mission in our Cosmos coverage here.

  1. http://blog.cosmosmagazine.com/search?q=pluto
  2. https://cosmosmagazine.com/pluto
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