Pluto May Have Started Out Very Hot

Pluto¹ is a cold little world far from us in the outer reaches of our solar system. But researchers believe Pluto may have been born as a much warmer place. They say it may even have sheltered a subsurface or underground ocean – one that still exists today.

A report on Pluto appeared earlier this month in the scientific journal Nature Geosciences. The lead author was Carver Bierson, a planetary scientist at the University of California Santa Cruz.

In the report, researchers pointed² to evidence for a "hot start" situation at Pluto's beginning, some 4.5 billion years ago. Their study was based on images of the dwarf³ planet's surface as well as computer models of the subsurface.

"When Pluto was forming, new material would have been coming in and impacting its surface," Bierson said. "Each impact is like an explosion that would warm the nearby area."

Bierson explained that if Pluto had formed slowly, the surface would have cooled between each impact and generally stayed very cold. But if Pluto had formed quickly, the surface may not have had time to cool down.

"If Pluto formed in less than 30,000 years," he said, "the heat from these impacts could have been sufficient to lead to an early ocean."

Pluto may have an icy outer shell hundreds of kilometers thick atop an ocean of water, possibly mixed with salts and ammonia. A solid rocky core could lie below, Bierson said.

The researchers believe that parts of the ocean would gradually freeze over time. Water expands as it freezes, and cracks on Pluto's surface may be evidence of this. At present, Pluto's surface temperature is about minus 230 degrees Celsius⁴.

A subsurface ocean could make Pluto a possible, although unlikely, candidate for having living organisms.

Bierson said it was possible that contact between water and the rocky core could have created certain chemical ingredients.

"Are those the right ingredients for life?" Bierson asked. "We don't know. We need to learn more about how life forms, or how life could form, to find these answers."

I'm John Russell.

Words in This Story

solar – adj. related to the sun

journal – n. a magazine that reports on things of special interest to a group of people

author – n. writer

dwarf – adj. related to or involving something that is much smaller than the usual size

impact – v. formal to hit (something) with great force

sufficient – adj. somewhat formal having or providing as much as is needed

core – n. the central or most important part of something

ingredient – n. a part or piece of something

1 Pluto   

n.冥王星

参考例句：

• Pluto is the furthest planet from the sun.冥王星是离太阳最远的行星。
• Pluto has an elliptic orbit.冥王星的轨道是椭圆形的。

2 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

3 dwarf   

n.矮子，侏儒，矮小的动植物；vt.使…矮小

参考例句：

• The dwarf's long arms were not proportional to his height.那侏儒的长臂与他的身高不成比例。
• The dwarf shrugged his shoulders and shook his head. 矮子耸耸肩膀，摇摇头。

4 Celsius   

adj.摄氏温度计的，摄氏的

参考例句：

• The temperature tonight will fall to seven degrees Celsius.今晚气温将下降到七摄氏度。
• The maximum temperature in July may be 36 degrees Celsius.七月份最高温度可能达到36摄氏度。