科学家发现冥王星上有冰火山的新证据

Scientists from the American space agency NASA say they have found evidence of large ice volcanoes on the dwarf planet Pluto.

The finding is based on images and data collected by NASA's New Horizons spacecraft. Researchers report in a new study that they identified numerous round-shaped formations on Pluto's surface.

The formations suggest the presence of geological activity linked to ice volcanoes, also called cryovolcanoes. The scientists said it is the first time these kinds of structures have been observed in our solar system. Some measured at least seven kilometers tall and 100 kilometers wide.

"The particular structures we studied are unique to Pluto, at least so far," planetary scientist Kelsi Singer said in a statement. She is a member of the New Horizons team, based at the Southwest Research Institute in Boulder, Colorado. She was the lead writer of the study, which recently appeared in Nature Communications.

Singer said it is difficult to know exactly when the ice volcanoes formed. But the team believes the volcanoes could be as young as a few hundred million years, or even younger. "It is possible that these processes are going on even in the present day," Singer added.

Like Earth and our solar system's other planets, Pluto formed about 4.5 billion years ago. It is smaller than Earth's moon and orbits about 5.8 billion kilometers from the sun. That distance is about 40 times farther than Earth's orbit. Pluto's surface includes flat land, mountains, craters and valleys.

The researchers studied an area southwest of Sputnik Planitia, a large, heart-shaped area filled with nitrogen ice.

One of the tallest structures, called Wright Mons, may have formed when several volcanic formations came together, the team said. Wright Mons is similar in size to Hawaii's large Mauna Loa volcano, although it is shaped differently.

The researchers said Pluto is geologically active. There is evidence of flowing nitrogen ice glaciers. In addition, the dwarf planet has areas where nitrogen ice vaporizes during the day and turns back into ice at night.

Lynnae Quick is a planetary scientist who specializes in ice volcanoes at NASA's Goddard Space Flight Center in Maryland. She said the findings were "extremely significant."

Quick told the French Press Agency, AFP, that scientists believed Pluto should have lost much of its inside heat a long time ago. The new research, however, suggests it "was able to hold onto enough energy to facilitate widespread geological activity rather late in its history," she said.

Quick added that the findings may help scientists re-examine the possibility that similar volcanic activity might have happened on other small, icy worlds far away from the sun.

Singer described Pluto as a "geological wonderland," with many areas completely different from each other. "If you just had a few pieces of a puzzle of Pluto, you would have no idea what the other areas looked like," she added.

I'm Bryan Lynn.

Reuters, Agence France-Presse and NASA reported on this story. Bryan Lynn adapted the reports for VOA Learning English.

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dwarf – adj. used to describe something that is much smaller than the normal size

geology – n. the study of rocks and soil and the physical structure of the Earth

unique – adj. different from everyone and everything else

crater – n. a big hole in the ground created by the force of an object

glacier – n. a very large area of ice that moves slowly down a slope or valley or over a wide area of land

vaporize – v. to turn, or cause something to turn, from a solid or liquid state into gas

significant – adj. important or noticeable

facilitate – v. to make something possible or easier

puzzle – n. a game or toy in which you have to fit separate pieces together