太空岩石仍是科学家未解之谜

（单词翻译）

Space Rock Still a Mystery to Scientists

Oumuamua is the first interstellar object scientists have found passing through our solar system. Interstellar means it came from another star system like our own.

In November 2017, Oumuamua was seen moving between the Sun and the planet Mercury. One year later, there remains¹ a lot of mystery surrounding the space rock. Scientists are still excited about its discovery. But there is disagreement about what it is and how it got here.

A new research paper from Harvard University proposes that Oumuamua may have been sent by an alien life form. The paper has not yet been published.

But based on what many scientists are saying, and what astronomers² know about space rocks, Oumuamua seems to be acting³ like other space rocks.

Here is what scientists do know about Oumuamua: It moved very quickly – at a speed of about 136,000 kilometers an hour.

Michele Bannister is an astrophysicist at Queen's University Belfast in Northern Ireland. She told VOA that scientists only had about three weeks to look at Oumuamua before it moved out of sight.

It is reddish in color and about 400 meters long. In addition, it is 10 times longer than it is wide. Compared to other space objects, 400 meters is very small. So, finding Oumuamua was a major success for astronomers.

Thomas Zurbuchen is an official with NASA, America’s National Aeronautics⁴ and Space Administration. He said that for many years NASA has believed interstellar objects were ‘out there.' "And now―for the first time―we have direct evidence they exist,” he said.

As it moves through space, Oumuamua has been changing speed and direction by itself. Michelle Bannister calls this behavior "non-gravitational acceleration⁵."

Yet there is nothing unusual about such behavior. Bannister says the rock is probably filled with the things that comets and asteroids⁷ usually have a lot of, such as the gas carbon monoxide and the highly poisonous chemical cyanide.

When objects like these get close to the sun, they release gases at high speeds in a process called “sublimation.” This may be what caused Oumuamua to look like it was moving under its own power.

We'll never really know

But that explanation did not stop Harvard scientists Shmuel Bialy and Abraham Loeb from offering a few other possible explanations for the space rock.

By their mathematical estimate, the rock is less than one millimeter thin and very wide. One of their explanations suggests Oumuamua is sort of like a sail on a sailboat. They believe it may use energy from the sun to push itself through space.

The Harvard scientists proposed this because other studies suggest Oumuamua is not a comet or releasing any gas. And Bialy and Loeb have done the math to provide evidence.

The other possibility they suggest is that Oumuamua is a probe sent to our solar system by an alien society.

They have done the math to show how Oumuamua's path might make sense if it were aimed toward Earth.

It is important to note that the Harvard paper has yet to be reviewed by other scientists of similar expertise⁸.

Oumuamua is too small even for our best telescopes to examine. So researchers now have all the information they will ever have.

But there are likely a lot more Oumuamuas out there. Bannister says, “The galaxy⁹ is filled with flying rocks.” She says a countless¹⁰ number of rocks of different sizes are probably moving through the galaxy. And if we are lucky, she says, we should be able to see about one a year.

So, the Earth is getting visitors from other stars. But they are probably just rocks passing through the neighborhood.

I’m Alice Bryant.

Words in This Story

alien – adj. from somewhere other than the planet Earth

comet – n. an object in outer space that develops a long, bright tail when it passes near the sun

asteroid⁶ – n. any one of thousands of small planets that circle around the sun

millimeter – n. a length equal to 1/1000 meter

probe – n. a device that is used to obtain information from outer space

galaxy – n. any one of the very large groups of stars that make up the universe