There’s a snowman in space | Science News for Students

There’s a snowman in space

The distant object, called Ultima Thule, is probably a conglomeration of rocky debris
Jan 29, 2019 — 6:45 am EST
an image of Ultima Thule, a space rock shaped like a snowman

This New Horizons spacecraft took this image at a distance of about 28,000 kilometers (17,400 miles). It shows the space rock’s unique shape.


On the far outskirts of the solar system lies a zone of very-distant objects revolving around our sun. It’s the Kuiper (KY-per) Belt. And this past New Year’s Day, a NASA spacecraft got a good snapshot of a snowman-shaped object there.

Nicknamed Ultima Thule, it’s known as a contact binary — or “two separate objects that are now joined together,” explained Alan Stern. And, he concluded, “It’s a snowman, if it’s anything at all.” (Twitter was quick to supply another analogy: the rolling BB-8 droid from Star Wars.)

Stern is a planetary scientist at the Southwest Research Institute in Boulder, Colo. He spoke January 2 in a news conference. It was held in Laurel, Md., at the Johns Hopkins University Applied Physics Laboratory. He described images that had just come back from the New Horizons spacecraft. It’s the same craft that snapped stunning close-ups of Pluto three years ago.

Ultima Thule’s snowman-like shape was a prized finding for planetary scientists. It supports the idea that planet-like bodies can grow from a slow clumping of small rocks. Ultima Thule seems to have done this. The space rock’s official name is 2014 MU69. Scientists actually think it may be one of the oldest and least-altered objects in the solar system. So, knowing how it formed might reveal how some planets formed.

a map of the Kuiper Belt showing the locations of images from New Horizons has
The hazy ring is an artist’s view of the Kuiper Belt. The rocks that populate it revolve about the sun. They are known as KBOs, short for Kuiper Belt objects. The New Horizons spacecraft, which launched in 2006, has been bringing photos of the solar system’s outer reaches, including Pluto in 2015.
NASA; adapted by L. Steenblik Hwang

“Think of New Horizons as a time machine,” says Jeff Moore. He is a planetary scientist at NASA’s Ames Research Center in Moffett Field, Calif. This spacecraft “has brought us back to the very beginning of solar system history — to a place where we can observe the most primordial building blocks of the planets.” Moore leads the New Horizons’ geology team. “It’s gratifying to see these perfectly formed contact binaries in their native habitat,” he says. “Our ideas of how these things form seem to be somewhat [supported] by these observations.”

Making sense of the photos

The pictures show the space rock from a distance of about 28,000 kilometers (17,400 miles). They reveal that MU69 is about 31 kilometers (19 miles) long. It has two round lobes, one about three times the size of the other. The spheres are connected by a narrow “neck.” That neck appears brighter than much of the rest of the rock.

The bright neck could be explained by small grains of surface material rolling downhill to settle there. Small grains tend to reflect more light than do large ones, explains Cathy Olkin. She is New Horizons deputy project scientist. She, too, works at the Southwest Research Institute. Even the brightest areas reflect only about one-eighth of the sunlight that hits them. The darkest reflect just 6 percent. (That’s about the same brightness as potting soil.)

Measurements also show that MU69 rotates once every 15 hours, give or take an hour. That’s a Goldilocks rotation speed, Olkin said. If it spun too fast, the odd-shaped rock would break apart. Fifteen hours is just right, she said.

The scientists also think each lobe’s round shape results from small rocks having glommed together to form bigger ones, Moore said. The collisions between the rocks likely happened very slowly. This would have let the rocks stick together rather than smashing into bits. The final collision was between the two spheres, which the team dubbed “Ultima” (the bigger one) and “Thule” (the smaller one).

That collision probably took place at no more than a few kilometers (miles) per hour. That’s “the speed at which you might park your car in a parking space,” Moore said. “If you had a collision with another car at those speeds, you may not even bother to fill out the insurance forms.”

New Horizons shows MU69’s color as reddish. The science team thinks the rusty hue comes from radiation that altered exotic ice. That ice would be some frozen material such as methane or nitrogen, not water. The scientists don’t, however, yet know what that ice is made from.

New Horizons is still sending data back to Earth. And, it will continue transmitting details of the flyby for the next 20 months. The data should soon reveal details of the space rock’s surface.

a composite of three different images of Ultima Thule
Three images of the space rock. Methane or nitrogen ice may give the this Kuiper Belt object its reddish color.

Power Words

(more about Power Words)

binary     Something having two integral parts.

droid     A fictional robot with artificial intelligence. The term was coined for use in the Star Wars universe, and is short for android.

exotic     An adjective to describe something that is highly unusual, strange or foreign (such as exotic plants).

geology     The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. Planetary geology is the science of studying the same things about other planets.

habitat     The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

hue     A color or shade of some color.

Kuiper Belt     An area of the solar system beyond the orbit of Neptune. It is a vast area containing leftovers from the formation of the solar system that continue to orbit the sun. Many objects in the Kuiper belt are made of ice, rock, frozen methane and ammonia. The best known of the larger Kuiper Belt objects is the dwarf planet Pluto. The belt extends out from the sun at a distance of 30 to 55 astronomical units. (An astronomical unit is equal to Earth’s from the sun.)

lobe     A rounded and somewhat flat projection. Many leaves, for instance, have lobed edges.

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.

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began.

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.

physics     The scientific study of the nature and properties of matter and energy.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, the object must be big enough to have pulled neighboring objects into the planet itself or to have slung them around the planet and off into outer space.

Pluto     A dwarf planet that is located in the Kuiper Belt, just beyond Neptune. Pluto is the tenth largest object orbiting the sun.

primordial     An adjective that refers to something that goes back to the beginning of time or to the earliest existence of something.

radiation     (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

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.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

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.

Twitter     An online social network that allows users to post messages containing no more than 280 characters (until November 2017, the limit had been just 140 characters).


Press Conference:​​ New Horizons news conference, January 2, 2019.