VOA慢速英语--NASA称本努小行星的新数据表明它仍可能对地球构成威胁

The U.S. space agency NASA says new data from observations of the asteroid¹ Bennu still suggests that the object could one day hit Earth.

But, the scientists studying the asteroid predict in a new study there is very little chance that Bennu will strike Earth in the coming centuries.

Bennu and other asteroids² are considered near-Earth objects (NEOs). Scientists identify such objects as those having the possibility of coming within 50 million kilometers of Earth's orbit.

Bennu was discovered in 1999. It is believed to have formed in the first 10 million years of our solar system's history – more than 4.5 billion years ago. It moves into near-Earth space because of gravitational interactions with other planets. It also takes in heat from the sun that provides added push. Bennu makes its closest pass to Earth every six years.

The latest data on Bennu was collected by NASA's Osiris-Rex spacecraft, which spent more than two years observing the asteroid. Last October, Osiris-Rex also successfully collected samples from Bennu. The spacecraft is now on a trip back to Earth, with NASA expecting its arrival in September 2023.

The main goal of the Osiris-Rex mission was to collect the samples. Scientists say they hope the material can help them better understand how planets formed and how life began on Earth.

But new data from Osiris-Rex also permitted scientists to get a better idea about Bennu's current and future movements, including the chances that it could strike Earth. The new details recently appeared in a study in the publication Icarus.

One of the study's findings is a prediction that Bennu will make a close pass to Earth in 2135. At that time, scientists say the asteroid will pass Earth within half the distance of Earth to the moon.

Before the Osiris-Rex mission, researchers put the chances of Bennu hitting Earth through the year 2200 at 1-in-2,700. With the new data, scientists believe the chances are 1-in-1,750, through the year 2300.

Even though the new prediction increases the chances of a hit by Bennu, NASA researchers who spoke³ to reporters about the finding said people should not be overly concerned.

"We shouldn't be worried about it too much," said Davide Farnocchia, the lead writer of the study. He is a scientist with NASA's Center for Near Earth Object Studies at the Jet Propulsion Laboratory (JPL) in California.

Farnocchia noted⁴ that the risk from Bennu "is smaller than from the undiscovered population of objects of similar size." He added that "overall, the situation has improved" because scientists now have a much better idea of Bennu's path.

Lindley Johnson is NASA's planetary defense⁵ officer. He was asked about the destruction that could result from a possible strike by Bennu. He said a hit would not destroy all life on Earth. But the event would create a crater⁶ about 10 to 20 times the size of the asteroid. Bennu is thought to be about 500 meters wide.

Johnson added that the total area of destruction from a hit would be much larger, covering an area up to 100 times the size of the crater. He noted that there could be other, yet undiscovered objects out there that could present more of a threat.

"We are still looking for what we don't know out there -- the objects that haven't been found yet," Johnson said. He noted that researchers were also studying ways to redirect the orbit of an asteroid should it ever become necessary to do so.

But Johnson added: "We really don't think we need to do anything about Bennu."

Words in This Story

asteroid – n. one of many large rocks that circle the sun

sample – n. a small amount of something that gives you information about the thing it was taken from

mission – n. a flight by an aircraft or spacecraft to perform a specific task

crater – n. a round hole made by an explosive force such as a bomb or an object falling from the sky

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 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。

3 spoke   

n.（车轮的）辐条；轮辐；破坏某人的计划；阻挠某人的行动 v.讲，谈（speak的过去式）；说；演说；从某种观点来说

参考例句：

• They sourced the spoke nuts from our company.他们的轮辐螺帽是从我们公司获得的。
• The spokes of a wheel are the bars that connect the outer ring to the centre.辐条是轮子上连接外圈与中心的条棒。

4 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

5 defense   

n.防御，保卫；[pl.]防务工事；辩护，答辩

参考例句：

• The accused has the right to defense.被告人有权获得辩护。
• The war has impacted the area with military and defense workers.战争使那个地区挤满了军队和防御工程人员。

6 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。