VOA慢速英语--科学家发现金星可能存在生命的迹象（在线收听）

Scientists Wonder About Possible Sign of Life on Venus

Space scientists have found what could be a possible sign of life in the atmosphere of Venus.

The finding comes from a study published Monday in Nature Astronomy.

The astronomers studied Venus with the James Clerk Maxwell Telescope in Hawaii. They confirmed their observations with the ALMA radio telescope in Chile.

The telescopes found evidence of the chemical phosphine in the thick clouds covering the planet. Phosphine is a poisonous gas. On Earth, it is only associated with life. However, the organizers of the study and other experts agree that the presence of phosphine is not proof of life on another planet.

David Clements helped to prepare a report on the study. He is with Imperial College London. Clements said of the evidence, "It's not a smoking gun." But he added that it may "be suggesting something."

As astronomers look for signs of life outside our solar system, one method is to look for chemicals that result only from biological processes. These processes are known as biosignatures.

After three astronomers met in a bar in Hawaii, they decided to look for biosignatures a little closer to Earth – the planet Venus. The three looked for phosphine, a molecule made up of three hydrogen atoms and a single phosphorous atom.

Phosphine can form only two ways on Earth. It can be created by an industrial process, or it can come from a biological process in animals and microbes that is not well understood. Some scientists consider it a waste product.

Clements said phosphine can be found in the bottom of ponds, the insides of animals like badgers and in the waste of penguins.

Sara Seager, also involved in the study, is a planetary scientist with the Massachusetts Institute of Technology. She said the astronomers carefully looked at all the possibilities for production of the phosphine: volcanoes, lightning strikes or meteorites falling into the atmosphere. "...Not a single process we looked at could produce phosphine in high enough quantities to explain our team's findings," she said.

Could life be responsible?

The astronomers debated how life could exist on a planet like Venus, where there is no water and the surface temperature is 425 degrees Celsius.

"Venus is hell. Venus is Earth's evil twin," said Clements.

But Seager noted that 50 kilometers above the planet's surface, in Venus' thick carbon dioxide clouds, it is about room temperature. The clouds are mostly made up of sulfuric acid. But they also contain droplets with very small amounts of water.

The scientists asked themselves if the phosphine could be coming from microbes living inside the sulfuric acid droplets. Seager and Clements suggested that, when the droplets fall to the ground, they might dry out but could collect in other droplets and reanimate.

While life is a possibility, several other scientists say more proof is needed.

Cornell University astronomer Lisa Kaltenegger said the idea of the gas possibly being a sign of a biological process is exciting. But she is not sure life is the only explanation.

Justin Filberto, with the Lunar and Planetary Institute in Houston, told The Associated Press that the levels of phosphine might be explained by volcanoes. He said recent studies that were not considered in the new research suggest that Venus may have far more active volcanoes than scientists had thought. But Clements said that explanation would make sense only if Venus were at least 200 times more active than Earth.

David Grinspoon is an astrobiologist with the Planetary Science Institute. He wrote a book suggesting that life could exist on Venus. Grinspoon was excited, but "cautious" about the new study's finding. It "almost seems too good to be true," he said.

Clements noted that his head tells him there is "probably a 10 percent chance that it's life." But he added, his heart "...wants it to be much bigger because it would be so exciting."

Words in This Story

associated – adj. connected or linked with something else

solar – adj. involving the Sun

bar – n. a place where alcoholic drinks are served

microbe – n. an extremely small living thing only observed through a microscope

pond – n. a small body of water

meteorite – n. a rock or larger object that reaches Earth without breaking up in the atmosphere

hell – n. a place of destruction

droplet –n. a very tiny amount of a liquid