Pluto's Battle Scars A Wild West at Solar System's Far Reaches

Pluto may have been downgraded to a dwarf planet, but its mysteries still loom large. When NASA's New Horizons reconnaissance probe flew past Pluto and its moon Charon in 2015, the resulting footage reveals a novel world of icy peaks, freezing planes and frozen volcanoes not seen anywhere else in the solar system.

Now, researchers are looking for more footage of one of the solar system's most enigmatic regions: the vast ring of icy debris known as the Kuiper Belt.

In a new study published today (Feb. 28) in the journal Science, a team of planetary scientists led by researchers at the Southwest Research Institute in Boulder, Colorado, portrayed in New Horizons maps of Pluto and Charron to the scars left by trillions Kuiper Belt objects (KBOs). These systems orbit the Kuiper Belt at the edge of the solar system (and Pluto itself is the largest of them). [When Space Attacks: The 6 Craziest Meteor Impacts]

By studying impact craters, the researchers discovered that Pluto and Charon had been more than 4 billion years old. This suggests that the Kuiper Belt is primarily populated by large, ancient objects that are close to the formation of the solar system.

Kelsi Singer, senior research scientist at the Southwest Research Institute and member of the New Horizons team, told Live Science. "We can use the number of craters to say how old is a surface, which helps us learn more about the Kuiper Belt as a whole."

Scars of Pluto

Generally, parts of a planet are considered to be relatively new, Singer said. The Pluto, for example, is a bright sheet of the name of the heart, named for its shape. Because there is no impact on this area, it is believed to be relatively young compared to the rest of Pluto's surface.

In contrast, past evidence suggests that some crater-rich regions are about 4 billion years old, Singer said. By closely studying the sizes of the craters in those regions, the researchers can get a snapshot of the types of objects moving through the Kuiper Belt billions of years ago, not long after the solar system.

In the new study, the team examined nearly 3,000 impact craters from New Horizons' 2015 observations. Something stood out: While the craters came in a wide range of sizes, they were two kilometers apart (0.6 and 1.2 miles) in diameter.

"This is surprising to us, because we are based on the Kuiper Belt on what we knew about the asteroid belt [between Mars and Jupiter], "Singer said." It turns out to be smaller in the Kuiper Belt than we thought. That tells us something about the area's collisional history. "

How? Well, small celestial objects are created by collisions between larger objects, Singer said. A small number of small objects in the Kuiper Belt are more likely to be "primordial" relics of the early solar system, Singer said .

These findings were made with recent observations of the KBO called Ultima Thule, a 21-mile-long (34 km), snowman-shaped object orbiting about 1 trillion miles (1.6 billion km) beyond Pluto's orbit.

"When New Horizons got to Ultima Thule in January, it looked like a pretty primordial body," Singer said. "There's a big impact on it, and it does not look like it's ever broken apart and reformed."

If the Kuiper Belt is indeed full of ancient objects like these, studying the region's mysteries, Singer said. For its part, New Horizons will continue on the frontier of this debris at the edge of our solar system. What the probe will find next is anyone's guess.

Originally published on Live Science.