CAPE CANAVERAL, Florida — The latest images sent back from NASA’s New Horizons spacecraft as it nears Pluto suggest that the dwarf planet may have a polar ice cap.
The images show that one of Pluto’s poles appears to be brighter than the rest of its surface. Scientists say that this brightening in Pluto’s polar region might be caused by a cap of highly reflective snow on the surface, which is likely to be frozen molecular nitrogen ice.
Pluto, the largest known body in the Kuiper Belt, has a nitrogen atmosphere, complex seasons, distinct surface markings, an ice-rock interior that may harbor an ocean, and at least five moons. Among these moons, the largest – Charon – may itself sport an atmosphere or an interior ocean, and possibly even evidence of recent surface activity. This animation shows a series of New Horizons images of Pluto and Charon taken at 13 different times spanning 6.5 Earth days from April 12 to April 18, 2015. During that time, the NASA spacecraft’s distance from Pluto decreased from about 69 million miles to 64 million miles. A 3x-magnified view of Pluto is displayed in the inset to the lower right, highlighting the changing brightness across the disk of Pluto as it rotates.
Also captured in the images is Pluto’s largest moon, Charon, rotating in its 6.4-day long orbit. The exposure times used to create this image set – a tenth of a second – were too short for the camera to detect Pluto’s four much smaller and fainter moons.
Since it was discovered in 1930, Pluto has remained an enigma. It orbits our sun more than 3 billion miles (about 5 billion kilometers) from Earth, and researchers have struggled to discern any details about its surface. These latest New Horizons images allow NASA scientists to detect clear differences in brightness across Pluto’s surface as it rotates.
Launched in January 2006 from Cape Canaveral, Florida, New Horizons is less than three months away from its closest fly-by of Pluto and its five moons on July 14, 2015. In early April, the probe sent back to Earth its first color image of Pluto and Charon.
“As we approach the Pluto system we are starting to see intriguing features such as a bright region near Pluto’s visible pole, starting the great scientific adventure to understand this enigmatic celestial object,” says John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “As we get closer, the excitement is building in our quest to unravel the mysteries of Pluto using data from New Horizons.” When the New Horizons mission was developed in 2001, it was a mission to just Pluto and Charon, before the four smaller moons were discovered by the Hubble Space Telescope (Nix and Hydra in 2005, Kerberos in 2011, and Styx in 2012).
The spacecraft’s suite of seven science instruments – which includes cameras, spectrometers, and plasma and dust detectors – will map the geology of Pluto and Charon and map their surface compositions and temperatures; examine Pluto’s atmosphere, and search for an atmosphere around Charon; study Pluto’s smaller satellites; and look for rings and additional satellites around Pluto.
But the spacecraft’s work doesn’t end with the July flyby. Because it only gets one shot at its target, New Horizons is designed to gather as much data as it can, as quickly as it can, taking about 100 times as much data on close approach as it can send home before flying away. And although the spacecraft will send select, high-priority datasets home in the days just before and after close approach, the mission will continue returning the data stored in onboard memory for a full 16 months.
Images Credits: NASA/JHU-APL/SwRI
