NASA’s New Horizons space probe will probably be skimming, mere thousands of kilometres, passed Pluto around about now. That means the photos it sends in the next few days will doubtless be far sharper than the above image of Pluto and Charon, taken from a distance of approximately twenty million kilometres.

While it’s been known for sometime Pluto is reddish-brown in colour, I didn’t realise it was referred to as the solar system’s “other red planet”, with Mars being, I guess, the red planet. While both have reddish hues, their colouring comes about in quite different ways:

What color is Pluto? The answer, revealed in the first maps made from New Horizons data, turns out to be shades of reddish brown. Although this is reminiscent of Mars, the cause is almost certainly very different. On Mars the coloring agent is iron oxide, commonly known as rust. On the dwarf planet Pluto, the reddish color is likely caused by hydrocarbon molecules that are formed when cosmic rays and solar ultraviolet light interact with methane in Pluto’s atmosphere and on its surface.

Also, isn’t referring to Pluto as “other red planet”, with the operative word being planet, likely to start all sorts of arguments?

Originally published Tuesday 14 July 2015.