VOA慢速英语--科学家发现太阳系中最古老的天体

 ‘Alien Asteroid¹’ Could Be Oldest Object in Our Solar System

Astronomers³ have been closely watching an object that travels in an orbit around our sun.

Astronomers say this object -- an asteroid -- circles the sun in the same orbital path as the planet Jupiter, but moves in the opposite direction.

They say the asteroid came from somewhere else in the universe. And now some experts believe it could be be the oldest object in our solar system.

In late May, researchers reported on a close examination of the asteroid and its orbit. They said that evidence suggests the asteroid formed elsewhere and was captured by gravitational forces when our solar system was formed.

Their report was published in the Monthly Notices of the Royal Astronomical⁴ Society: Letters.

The researchers believe the sun, planets and other objects in our solar system formed from a swirling⁵ cloud of gas and dust. They say this took place about 4.5 billion years ago.

Fathi Namouni is an astronomer² with the Observatoire de la C?te d’Azur in France. He was the lead writer of the report on the asteroid.

Namouni told the Reuters news service that the asteroid is “a strong candidate for the oldest object in the solar system.”

The asteroid has a long, somewhat complex name. It is called (514107) 2015 BZ509, or “BZ” for short. It is nearly 3 kilometers wide. Scientists say they are unsure about the materials it is made of.

BZ travels in the opposite direction of all the planets and nearly everything else in our solar system. This kind of movement is called a retrograde orbit.

"How the asteroid came to move in this way, while sharing Jupiter's orbit, has until now been a mystery," Namouni explained. "If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids⁶."

BZ is not the first object that scientists recognize as having travelled from a different star system into our own. The first-known alien traveler was a large object called ‘Oumuamua.’ Researchers observed it passing through our solar system last year.

But Namouni said BZ and Oumuamua are very different. Oumuamua simply passed through our solar system, while BZ has been orbiting the sun for a long time.

Scientists have observed BZ with ground-based telescopes in the American states of Hawaii and Arizona. They said BZ apparently⁷ left its home star system when the star system interacted with other systems in a tight fitting star cluster.

“The solar system formed in a star cluster where each star has its own planets and asteroids. The close proximity⁸ of the star systems, assisted by their gravitational interactions, helped remove and capture asteroids,” Namouni said.

Helena Morais helped with the new research.

Morais is an astronomer at the Universidade Estadual Paulista in Brazil. She said the movement of BZ is similar to that of the planet Jupiter.

“They complete an orbit around the sun in the same amount of time while moving in opposite directions,” she said.

BZ may be important in discussions about the development of life on Earth.

“This discovery tells us that the solar system is likely to be home to more extra-solar asteroids and comets captured early in its history. Some of these objects may have collided with the Earth in the past possibly carrying water, biomolecules or even organic material,” Morais added.

The researchers said a number of other solar system objects with retrograde orbits are being investigated as possible “alien asteroids.”

I’m Pete Musto.

Words in This Story

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

solar system – n. a star other than our sun and the planets that move around it

swirl(ing) – v. to move in circles or to cause something to move in circles

alien – adj. from somewhere other than the planet Earth

interact(ed) – v. to come together and have an effect on each other

fit(ting) – v. to be the right size and shape for someone or something

cluster – n. a group of things or people that are close together

proximity – n. the state of being near

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

collide(d) – v. to hit something or each other with strong force

1 asteroid   

n.小行星；海盘车(动物)

参考例句：

• Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
• It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。

2 astronomer   

n.天文学家

参考例句：

• A new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
• He is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。

3 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

4 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

5 swirling   

v.旋转，打旋( swirl的现在分词 )

参考例句：

• Snowflakes were swirling in the air. 天空飘洒着雪花。 来自《现代汉英综合大词典》
• She smiled, swirling the wine in her glass. 她微笑着，旋动着杯子里的葡萄酒。 来自辞典例句

6 asteroids   

n.小行星( asteroid的名词复数 )；海盘车，海星

参考例句：

• Asteroids,also known as "minor planets",are numerous in the outer space. 小行星，亦称为“小型行星”，在外太空中不计其数。
• Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。

7 apparently   

adv.显然地；表面上，似乎

参考例句：

• An apparently blind alley leads suddenly into an open space.山穷水尽，豁然开朗。
• He was apparently much surprised at the news.他对那个消息显然感到十分惊异。

8 proximity   

n.接近，邻近

参考例句：

• Marriages in proximity of blood are forbidden by the law.法律规定禁止近亲结婚。
• Their house is in close proximity to ours.他们的房子很接近我们的。