Pluto’s heart-shaped plains have stripes. Those stripes appear to be dunes, where methane ice makes up the “sand.”
The New Horizons spacecraft snapped images of those plains when it flew by Pluto in July 2015. Those images reveal hundreds of linear ridges that appear to be a new type of dune, say Matt Telfer and his colleagues. Telfer is a planetary scientist at the University of Plymouth in England. His team describes those dunes in the June 1 Science.
The ridges run parallel to a mountain range known as Al-Idrisi Montes. It sits at the western edge of Sputnik Planitia. Those wide plains of nitrogen ice form part of Pluto’s famous heart-shaped region. Winds between about 1 and 10 meters per second (2 to 22 miles per hour) likely carry methane ice from those mountains and across the plains.
The scientists used a computer model to investigate how the methane ice moves. The model even took into account Pluto’s thin atmosphere, which weakens winds. That model now proposes that Pluto’s winds would be strong enough to keep sand-sized methane ice particles moving once they get started. But the winds are probably too weak to lift the grains off the ground in the first place.
The grains could, however, get a lift from little puffs of air coming from Sputnik Planitia’s nitrogen ice. As the sun heats that ice, it turns into a vapor. That process by which solids turn directly into vapor is called sublimation (Sub-lih-MAY-shun).
Gusts of nitrogen vapor could lift the methane ice particles skyward and into the wind, the team’s research suggests.
“That’s a novel, interesting idea,” says Alexander Hayes. He’s a planetary scientist at Cornell University in Ithaca, N.Y., who was not involved in the work. But he knows about it and wrote a commentary about it in the same issue of Science. Still he cautions, sublimation alone could explain some of the features, without any need for wind.
Dunes are found across the solar system, from Earth to Mars and Saturn’s moon Titan. Each of these worlds has the ingredients for dunes. Those ingredients are a big supply of loose, grainy material and an atmosphere or fluid to move those grains around.
“When you look at dunes across the solar system, something that always strikes me is that they form the same patterns,” Hayes says. This is true “regardless of the environment,” he notes. Finding dunes on Pluto suggests that such features may be ubiquitous (Yu-BIH-qwih-tus). That means they are found in a lot of places — perhaps all over. “If you have the material and a way to move it, you form dunes,” Hayes says. “That’s what this is telling us.”
atmosphere The envelope of gases surrounding Earth or another planet.
colleague Someone who works with another; a co-worker or team member.
commentary (in science) An opinion piece, often written to accompany — and add perspective to — a paper by others, which describes new research findings.
computer model A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
lift An upward force on an object. It may occur when an object (such as a balloon) is filled with a gas that weighs less than air; it can also result when a low-pressure area occurs above an object (such as an airplane wing).
Mars The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
methane A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.
model A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
moon The natural satellite of any planet.
nitrogen A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.
novel Something that is clever or unusual and new, as in never seen before.
parallel An adjective that describes two things that are side by side and have the same distance between their parts. In the word “all,” the final two letters are parallel lines. Or two things, events or processes that have much in common if compared side by side.
particle A minute amount of something.
Pluto A dwarf planet that is located in the Kuiper Belt, just beyond Neptune. Pluto is the tenth largest object orbiting the sun.
Saturn The sixth planet out from the sun in our solar system. One of the four gas giants, this planet takes 10.7 hours to rotate (completing a day) and 29 Earth years to complete one orbit of the sun. It has at least 53 known moons and 9 more candidates awaiting confirmation. But what most distinguishes this planet is the broad and flat plane of seven rings that orbit it.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
titan The term for any gigantic being. The term comes from Greek mythology. The six sons and six daughters of the Greek gods Uranus and Gaea were known as titans. Capitalized Titan is a moon of Saturn.
ubiquitous (n. ubiquity) A term for something that is omnipresent — found essentially everywhere.