VOA慢速英语--火星上发现的古代河流的新证据

Scientists say they have found the most detailed¹ evidence yet of long-flowing, ancient rivers on Mars.

The discovery supports existing evidence that Mars – which today is dry and cold – was once a water-rich planet. The researchers say their findings suggest rivers may have flowed on the surface of Mars for hundreds of thousands of years.

The evidence came from new satellite pictures of the Martian surface. These images were captured by a camera on NASA's Mars Reconnaissance Orbiter. The camera is able to take detailed pictures of the surface while orbiting the planet from about 400 kilometers away.

A team of scientists studied the images, which showed a rocky area within the planet's Hellas Impact Crater². An impact crater is formed when a space object crashes into a planet or moon. The Hellas Impact Crater, in the southern Martian hemisphere, is one of the largest formations of its kind in the solar system.

The team was led by Francesco Salese, a geologist³ at Utrecht University in the Netherlands. The research results were recently published in a study in Nature Communications.

Salese said the scientists studied sedimentary rocks from a 200 meter high rocky cliff. Sedimentary rocks form when sediment⁴, transported by water or wind, settles and forms solid rock.

"These are sedimentary rocks, 3.7 billion years old, and were formed by rivers that were likely active for over 100,000 years of Martian history," Salese said in a statement.

"OK, it is not like reading a newspaper, but the extremely high resolution imagery allowed us to ‘read' the rocks as if you are standing⁵ very close to the cliff," he added.

Salese said even without the ability to examine the cliff area up-close on Mars, the pictures show strong similarities to sedimentary rocks found on Earth.

The researchers created three-dimensional, or 3D, images of the area to get a more detailed understanding of it. The pictures suggested that some ancient Martian rivers were several meters deep.

William McMahon is another geologist who was part of the investigation⁶ team. He said sedimentary rocks have long been studied on Earth to learn what conditions were like on our planet millions, or even billions of years ago.

"Now we have the technology to extend this methodology to another terrestrial planet, Mars, which hosts an ancient sedimentary rock record which extends even further back in time than our own," McMahon said in a statement.

Another leader of the team was Joel Davis, a researcher with Britain's Natural History Museum. He said scientists had never before been able to examine such a rock formation with such great detail.

Davis said the discovery is "one more piece of the puzzle in the search for ancient life on Mars." He added that it also provides new evidence of how much water existed on Mars in ancient times.

"The rivers that formed these rocks weren't just a one-off event - they were probably active for tens to hundreds of thousands of years," Davis said.

Salese added that the findings show Mars had an environment able to support large, flowing rivers for extended periods of time.

"This kind of evidence, of a long-lived watery⁷ landscape, is crucial in our search for ancient life on the planet," Salese said.

I'm Bryan Lynn.

Words in This Story

crater – n. a large hole in the ground

geologist – n. a scientist who has studied rocks and soil in order to learn about the history of planets

cliff – n. an area of high, steep rocks

sediment – n. a solid substance that forms a layer at the bottom of a liquid

resolution – n. a measure of sharpness for an image

three-dimensional – adj. appearing to have length, depth and width

terrestrial – adj. relating to the Earth, not space

host – v. to serve as a host for something

puzzle – n. a game or activity in which you have to put pieces together or answer questions using skill

crucial – n. extremely important or necessary

1 detailed   

adj.详细的，详尽的，极注意细节的，完全的

参考例句：

• He had made a detailed study of the terrain.他对地形作了缜密的研究。
• A detailed list of our publications is available on request.我们的出版物有一份详细的目录备索。

2 crater   

n.火山口，弹坑

参考例句：

• With a telescope you can see the huge crater of Ve-suvius.用望远镜你能看到巨大的维苏威火山口。
• They came to the lip of a dead crater.他们来到了一个死火山口。

3 geologist   

n.地质学家

参考例句：

• The geologist found many uncovered fossils in the valley.在那山谷里，地质学家发现了许多裸露的化石。
• He was a geologist,rated by his cronies as the best in the business.他是一位地质学家，被他的老朋友们看做是这门行当中最好的一位。

4 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

5 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

6 investigation   

n.调查，调查研究

参考例句：

• In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
• He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。

7 watery   

adj.有水的，水汪汪的；湿的，湿润的

参考例句：

• In his watery eyes there is an expression of distrust.他那含泪的眼睛流露出惊惶失措的神情。
• Her eyes became watery because of the smoke.因为烟熏，她的双眼变得泪汪汪的。