New Horizons data provide more surprises from distant ice planet
The green marker shows the location and extent of the newly discovered ice plain. It was informally called "Sputnik Plain" baptized – after the first artificial satellitne of the earth. © NASA/JHUAPL/ SwRI
Dwarf planet with giant atmosphere: New Horizons spacecraft has revealed more surprising details about Pluto. Thus, it has a wide, surprisingly young plain of frozen carbon monoxide, whose structure resembles dried mud. In addition, the dwarf planet has an amazingly large atmosphere: it reaches at least into 1.600 kilometers in altitude and is blown by the solar wind to about 100.000-kilometer tail extended.
Only recently New Horizons transmitted photographs of a very young ice mountain on the Pluto, now already the next surprising information comes. In the latest images and data, an extensive craterless plain can be seen to the north of this ice mountain range. Its surface consists at least in part of frozen carbon monoxide, whose thickness increases toward the center of the plane.
Strange floes and gullies
This ice plain can’t be more than about 100 million years old, according to researchers on the New Horizons mission. Its surface structure is striking: it consists of floes about 20 kilometers in size, bordered by shallow gullies. Some of these gullies contain darker material, while others are framed by hill ranges.
In some areas, the interior of the floes is also dotted with small holes, as they typically form during sublimation of ice to water vapor. "The discovery of such a vast, craterless, very young plain exceeds all expectations," says Jeff Moore, leader of the mission’s geology team. The probe’s images also showed dark streaks several kilometers long stretching in one direction across the floes. It may be material that has been blown away by the wind.
Formation of the floes puzzling
How this plain could have formed and what gave it its strange structure is still a mystery. "This terrain is not easy to explain," says Moore. But the researchers have two theories about this. The irregularly shaped fragments may have been formed by contraction of the surface, similar to a mud surface drying up.
Alternatively, convection currents in Pluto’s icy crust could have led to these cracks and floes. A heat source inside the dwarf planet would then have to be the engine driving these currents. According to current knowledge, the crust of Pluto consists of frozen carbon monoxide, methane ice and nitrogen ice. The ice mountain, on the other hand, appears to be made of a particularly hard water ice.
Quite a huge atmosphere
The probe’s measurements also show that Pluto has a fairly extensive atmosphere for its rather small size. The nitrogen-rich gas envelope extends into 1.600 kilometers altitude. The spectrograph aboard New Horizons was able to determine their extent by looking back after the flyby and analyzing Pluto’s gas envelope against the light of the Sun.
"This is just the beginning for atmospheric research on Pluto," points out Andrew Steffl of the Southwest Research Institute in Boulder. "But already, data show us that Pluto’s atmosphere reaches higher than Earth’s, relatively speaking." The spacecraft has yet to transmit only a small portion of its atmospheric data. Researchers expect to have the full set of backlight measurements next month.
Solar wind creates gas tail
But the dwarf planet’s atmosphere appears to be not only large, but also quite fragile. Because New Horizons data show that Pluto has a giant tail of ionized gas. It fills the dwarf planet’s "slipstream" on the side away from the sun, which is at least 109.reaches 000 kilometers far out into space.
The tail is most likely generated by the solar wind. Because even at this enormous distance from our central star, this stream of energetic particles and radiation still has an effect. At Pluto, the sun’s UV light probably ionizes the atmosphere’s nitrogen atoms, and the solar wind sweeps them away. Venus and Mars also have similar plasma tails.
How much of its gas envelope Pluto loses due to this effect could be revealed by further data from the probe. "In August, we’ll get more data from New Horizons, which we can then combine with what we have so far to determine the rate of loss," says Fran Bagenal of the University of Colorado at Boulder. "Knowing this, we can also better answer questions about the evolution of Pluto’s atmosphere."
"We’ve only scratched the surface of the data so far," says the mission’s science director, Alan Stern of the Southwest Research Institute. "But already it seems clear to me that in exploring the solar system we have saved the best for last."