Planetary researchers involved in NASA’s New Horizons mission combined the latest black and white map of Pluto’s surface features with a map of the dwarf planet’s colors to produce a detailed color portrait of the dwarf planet’s northern hemisphere. According to the scientists, the reddish color of Pluto is likely caused by hydrocarbon molecules that are formed when cosmic rays and solar UV light interact with methane in the dwarf planet’s atmosphere and on its surface.
New Horizons mission’s first map of the dwarf planet Pluto is in approximate true color. Left: map of the planet’s northern hemisphere composed using black-and-white images from the LORRI instrument. Right: map of Pluto’s colors created using data from the Ralph instrument. Center: combined map, produced by merging the LORRI and Ralph data. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“Pluto’s reddish color has been known for decades, but New Horizons is now allowing us to correlate the color of different places on the surface with their geology and soon, with their compositions. This will make it possible to build sophisticated computer models to understand how Pluto has evolved to its current appearance,” said Dr Alan Stern of the Southwest Research Institute, who is the principal investigator for New Horizons.
Planetary scientists have long thought that reddish substances are generated as a particular color of UV light from the Sun, called Lyman-alpha, strikes methane molecules in Pluto’s atmosphere, triggering chemical reactions that create tholins. The tholins drop to the ground to form a reddish ‘gunk.’
Recent data from the New Horizons spacecraft reveal that a diffuse Lyman-alpha glow falling on the dwarf planet from all directions in interplanetary space is strong enough to produce almost as much tholin as the direct rays of the Sun.
“This means Pluto’s reddening process occurs even on the night side where there’s no sunlight, and in the depths of winter when the Sun remains below the horizon for decades at a time,” said Dr Michael Summers of George Mason University, a scientists for the New Horizons mission.
“Now the unique colors and characteristics of its varied terrains are coming into view,” said Dr Simon Porter, a member of the New Horizons team.
“Pluto’s largest dark spot is clearly more red than the majority of the surface, while the brightest area appears closer to neutral gray,” added Dr Alex Parker, a member of the New Horizons Composition team.
New Horizons remains on track for its July 14 flyby of the Pluto system. The spacecraft is almost 3 billion miles away, where radio signals, even traveling at light speed, need 4.5 hours to reach home. Two-way communication between the spacecraft and its operators requires a 9-hour round trip.
