New infrared images reveal Pluto’s water ice, blue atmosphere
Infrared images taken by New Horizons‘ Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument released this week show plentiful water ice on Pluto’s surface as well as new details of its otherworldly, layered blue atmosphere.
An image of the night side of Pluto’s largest moon, Charon, taken three days after closest approach last summer, was also published.
A photo titled “Water Ice Concentration” – featuring two adjacent LEISA scans of Pluto taken on July 14 at 15 minutes apart from a distance of 67,000 miles (108,000 km) – highlights the surface regions that spectral scans confirm have high contents of water ice.
The images show water ice is more abundant on Pluto’s surface than previously thought, with two notable exceptions – the left side of Pluto’s “heart”, known as Sputnik Planum, and a region at the north of the encounter side known as Lowell Regio.
New Horizons has shown water ice to be the bedrock or crust upon which other, more volatile ices, form, settle, and move over time.
At Sputnik Planum and Lowell Regio, the bedrock water ice is covered by other ices including methane, carbon monoxide, and nitrogen ice.
The familiar map of Pluto on the left side of the photo is one of the first ones taken by LEISA using only a pure water ice template spectrum.
Because the spectral signature of water ice is easily hidden by methane ice, the first map depicts only those regions with high contents of water ice and low levels of methane ice.
To obtain a more accurate map, LEISA used a more sensitive method that shows the influence of all Pluto’s surface ices, resulting in the image on the right.
Mission scientists then combined both images to create what is known as a “combined multispectral data cube” of the entire encounter hemisphere in false color. Such photos are three-dimensional and comprised of images taken at every wavelength to which LEISA is sensitive.
LEISA’s image of Pluto’s atmosphere is the first glimpse of that atmosphere in infrared wavelengths. It was taken on July 14, from a distance of 112,000 miles (180,000 km). North is near the 10 o’clock position.
Sunlight coming from above and behind the planet scatters the atmospheric hazes, producing what appears to be a thin blue ring around Pluto.
The hazes are thought to be a photochemical smog composed of hydrocarbons including acetylene and ethylene, produced by the interaction of sunlight with methane and other surface molecules.
While the hydrocarbons are tiny, about a fraction of a micrometer, they scatter incoming sunlight, creating the eerie blue haze.
By combining these infrared images with photos taken in visible wavelengths, mission scientists are gaining insight into the particles’ size distribution.
White-colored sections of the atmosphere are produced by sunlight bouncing off surface regions that are especially smooth or reflective.
Most prominent of these is a large area on the west of a dark region informally known as Cthulhu Regio.
The lower sections of the haze are not visible in this image but will be in other LEISA photos still on the spacecraft.
This first LEISA photo covers the instrument’s full spectral range, 1.25 to 2.5 microns. The shortest wavelengths of that range were captured in the blue channel, the middle in the green channel, and the longest in the red channel.
The black and white photo of Charon’s night side shows a thin crescent lit by the Sun at the bottom left, with the south pole of the 750-mile (1,214-km) diameter moon near the top.
Night fell at the south pole in 1989 and will last until 2107, resulting in the region’s temperature being close to absolute zero.
In addition to its aesthetic beauty, this photo, which was created from 16 one-second exposures taken by the Long Range Reconnaissance Imager (LORRI) instrument on July 17 from a distance of 1.9 million miles (3.1 million km), presents a rare perspective that can be captured only from Pluto’s far side.
Mission scientists are using this image and other, similar ones, to map features on Charon that could not be observed during the flyby.
They can do this because Charon’s landscapes are somewhat visible due to “Plutoshine” – light reflected off Pluto the same way that “Earthshine” often lights up the new Moon.
On January 29, the New Horizons mission announced its welcome of new project manager Helene Winters, who will replace retiring 12-year manager Glen Fountain.
Winters, who recently served as project manager for the MESSENGER mission to Mercury, is a program manager at JHUAPL, which designed, built, and operates New Horizons.
“Over the past 15 years, New Horizons has had two of the finest project managers in the space business, the late Tom Coughlin, who helped conceive the mission, and the legendary Glen Fountain, who built New Horizons and flew us to Pluto,” Principal Investigator Alan Stern stated. “Helene Winters, from a new generation and with incredible experience behind her, is going to set new milestones flying the spacecraft farther, hopefully to the first ever flyby of a Kuiper Belt object and onward toward the edge of our planetary system!”
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.