New Horizons is now just 11 days from its historic flyby exploration of the Pluto system, some three billion miles away at the entrance to the realm of our Solar System’s still unexplored Kuiper Belt, and this morning (July 3) the mission team successfully uploaded the command load flight plan to the piano-sized spacecraft for its close flyby 7,800 miles above Pluto on July 14. At the same time, the images just keep getting better, now in true color (what your naked eye would see) and showing features as small as 100 miles across, revealing a reddish-brown world reminiscent of Mars as the spacecraft clears 720,000 miles every day on its journey to close out humanity’s initial reconnaissance of the major bodies in our Solar System.
“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,” said New Horizons principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colo. “This will make it possible to build sophisticated computer models to understand how Pluto has evolved to its current appearance.”
While Pluto’s color is no surprise, the processes to cause such coloration are surely different than on Mars, which orbits 2.5 billion miles closer to the Sun. Scientists are already thinking the color of Pluto might be due to hydrocarbon molecules that are formed when cosmic rays and solar ultraviolet light interact with methane in Pluto’s atmosphere and on its surface—as opposed to Mars, where the red color of its surface dust is caused as a result of iron rusting, since the surface dust is iron-oxide rich. The red comes about for the same reason leaving iron in the rain here on Earth does.
According to NASA: “Experts have long thought that reddish substances are generated as a particular color of ultraviolet light from the sun, called Lyman-alpha, strikes molecules of the gas methane (CH4) in Pluto’s atmosphere, powering chemical reactions that create complex compounds called tholins. The tholins drop to the ground to form a reddish ‘gunk’. Recent measurements with New Horizons’ Alice instrument reveal that a diffuse Lyman-alpha glow falling on Pluto 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 New Horizons co-investigator Michael Summers, George Mason University, Fairfax, Va.
Saturn’s moon Titan and Neptune’s moon Triton both have tholins, and laboratory experiments to simulate their atmospheres have also produced the compound.
Another mystery baffling the science team is the observations of four intriguing large dark spots along Pluto’s equator, which seem to be roughly the same size and evenly spaced. Each dark spot is estimated to be approximately 300 miles across (about the size of the state of Missouri), and they also appear to be generally evenly spaced along the equator, which may provide clues about how and why they formed as New Horizons gets closer and produces higher-resolution observations.
“Even at this resolution, Pluto looks like no other world in our solar system,” said mission scientist Marc Buie of the Southwest Research Institute, Boulder. “We’re already seeing a remarkable amount of detail, and the complexity continues to increase as the images get better.”
Observations are also starting to show other surface details as well, with significant albedo variations visible on both Pluto and its largest moon, Charon. Charon interestingly also has a dark spot, at one of its poles, which has scientists excited because poles on the terrestrial planets of our Solar System are not black, they’re white. New Horizons’ flyby will, hopefully, answer why and shed light as to why Charon is a grey color instead of being reddish-brown like Pluto. For all anyone knows these details might be the norm among the tiny worlds of the Kuiper Belt, as opposed to the Pluto system being the oddball astronomers have always previously believed.
VIDEO: New Horizons’ scientists combined the latest black-and-white map of Pluto’s surface features (left) with a map of the planet’s colors (right) to produce a detailed color portrait of the planet’s northern hemisphere (center). Credits: NASA/JHUAPL/SWRI
“It’s a bit unusual to see so much surface detail at this distance,” said New Horizons co-investigator William McKinnon of the Geology and Geophysics Investigation Team, Washington University in Saint Louis. “What’s especially noteworthy is the level of detail in both bodies. It’s certainly whetting our appetite for what’s to come.”
On July 14, when the spacecraft makes its closest approach, the images captured will have a resolution as sharp as a quarter-mile (400 meters) per pixel. To put it in perspective, that’s sharp enough to make out clear well-defined details of New York’s iconic Central Park if New Horizons was flying by Earth at the same distance (8,000 miles).
In order for the flyby to be a success, New Horizons must hit a target just 60 miles by 90 miles wide—at 30,000 mph—in order for the planned observations to hit their targets at the right place and at the right time, like a hole-in-one from 3 billion miles away.
During the flyby New Horizons will be 100 percent focused on science, rather than communicating with Earth. The first up-close images of this world at the frontier of exploration are expected to arrive sometime on July 15.
The book on Pluto is being written right now, and so much data will be collected that it will take 16 months for all of it to be sent back to Earth after the history making encounter billions of miles from home.
T-11 days and counting …
BOOKMARK our “Mission Tracker” for regular updates and LIVE COVERAGE of New Horizons’ approach and flyby of the Pluto system.
Missions » New Horizons »