Pluto ‘paints’ its largest moon Charon red

Posted: September 15, 2016 by oldbrew in atmosphere, solar system dynamics

Charon's 'red spot' [image credit:]

Charon’s ‘red spot’ [image credit:]

Scientists have discovered ‘atmospheric transfer’ taking place between Pluto and its binary partner Charon.

In June 2015, when the cameras on NASA’s approaching New Horizons spacecraft first spotted the large reddish polar region on Pluto’s largest moon, Charon, mission scientists knew two things: they’d never seen anything like it elsewhere in our solar system, and they couldn’t wait to get the story behind it, as reports.

Over the past year, after analyzing the images and other data that New Horizons has sent back from its historic July 2015 flight through the Pluto system, the scientists think they’ve solved the mystery.

As they detail this week in the international scientific journal Nature, Charon’s polar coloring comes from Pluto itself – as methane gas that escapes from Pluto’s atmosphere and becomes “trapped” by the moon’s gravity and freezes to the cold, icy surface at Charon’s pole. This is followed by chemical processing by ultraviolet light from the sun that transforms the methane into heavier hydrocarbons and eventually into reddish organic materials called tholins.

“Who would have thought that Pluto is a graffiti artist, spray-painting its companion with a reddish stain that covers an area the size of New Mexico?” asked Will Grundy, a New Horizons co-investigator from Lowell Observatory in Flagstaff, Arizona, and lead author of the paper. “Every time we explore, we find surprises. Nature is amazingly inventive in using the basic laws of physics and chemistry to create spectacular landscapes.”

The team combined analyses from detailed Charon images obtained by New Horizons with computer models of how ice evolves on Charon’s poles. Mission scientists had previously speculated that methane from Pluto’s atmosphere was trapped in Charon’s north pole and slowly converted into the reddish material, but had no models to support that theory.

“This study solves one of the greatest mysteries we found on Charon, Pluto’s giant moon,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, and a study co-author. “And it opens up the possibility that other small planets in the Kuiper Belt with moons may create similar, or even more extensive ‘atmospheric transfer’ features on their moons.”

Full report: Pluto ‘paints’ its largest moon Charon red |

  1. oldbrew says:

    Paper: The formation of Charon’s red poles from seasonally cold-trapped volatiles

    ‘The polar location on Charon implicates the temperature extremes that result from Charon’s high obliquity and long seasons in the production of this material.’

    Re. binary planets:
    ‘Currently, the most commonly proposed definition for a double-planet system is one in which the barycenter, around which both bodies orbit, lies outside both bodies. Under this definition, Pluto and Charon are double (dwarf) planets, since they orbit a point clearly outside of Pluto, as visible in animations created from images of the New Horizons space probe in June 2015.’

  2. oldbrew says:

    Wikipedia gives these stats for Charon:

    Semi-major axis
    17536±4 km to system barycenter, 19571±4 km to the center of Pluto

    The ratio of the numbers is 1: (√5)/2 (~99.65% true)

    Perigee:apogee ratio of Earth’s Moon is very similar:

    Perigee 362600 km
    (356400–370400 km)
    Apogee 405400 km
    (404000–406700 km)

    405400 / 362600 = 1.1180364
    (√5)/2 = 1.1180339

    1,2 and √5 are the dimensions of the Conway triangle

  3. oldbrew says:

    ‘New Horizons’ observations of Charon’s other pole, currently in winter darkness – and seen by New Horizons only by light reflecting from Pluto– confirmed that the same activity was occurring at both poles.’