行星地球面对面 危险近在咫尺？

A mountain-sized asteroid which crosses paths with the Earth every three years has been discovered by a Russian scientist.

近日，一名俄罗斯科学家发现了一颗山峰大小的小行星每三年都会经过地球的运行轨道。

Vladimir Lipunov, a professor at Moscow State University, said the space rock, named '2017 UR116', poses no immediate threat.

莫斯科国立大学（Moscow State University）教授弗拉基米尔（Vladimir Lipunov）表示，这颗名为“2017 UR116”的太空岩石目前对地球并未造成直接威胁。

But he warned that it could hit the Earth with an explosion 1,000 times greater than the surprise 2013 impact of a bus-sized meteor inRussia. That object entered Earth’s atmosphere over the city ofChelyabinsk, resulting in a series of ferocious blasts that blew out windows and damaged buildings for miles around.

但是，如果这颗小行星撞击地球，其产生的爆炸强度将会是2013年袭击俄罗斯的那颗公交车般大小的流星的1000倍。那颗流星穿越地球大气层，在车里雅宾斯克（Chelyabinsk）上空爆炸，火花四溅，击破了窗户，损坏了方圆数英里内的建筑。

Prof Lipunov said it is difficult to calculate the orbit of big rocks like '2017 UR116' because their trajectories are constantly being changed by the gravitational pull of other planets

弗拉基米尔教授表示，像“2017 UR116”这类大型的石块常常会受到其他行星万有引力的影响，不停地改变其运行轨迹。因此，很难计算出它们的运行轨道。

And he warns that its existence proves how little scientists know about other asteroids which could cause harm to the planet.

他还表示，这颗小行星的存在同时也说明，科学家对其他能对地球造成危害的行星所知甚少。

"We need to permanently track this asteroid, because even a small mistake in calculations could have serious consequences," he said.

他表示，有必要对这颗小行星的运行轨迹进行长期的观察，因为计算中的一个细微的错误都可能带来严重后果。

Of 100,000 near-Earth objects which can cross our planet's orbit and are large enough to be dangerous, only about 11,000 have so far been tracked and cataloged.

目前，有十万颗大型近地星体可以穿过地球的运行轨道并可能造成一定程度破坏。其中，能追踪并计算出轨迹的大约只有1万1千颗。

However NASA warned that '2017 UR116' did not pass close enough to the Earth to be considered a threat.

然而，美国国家航空航天局（NASA）表示，“2017 UR116”经过地球的运行轨道后，与地球的距离不算太近，因此不会构成威胁。

"While this approximately 400-meter-sized asteroid has a three-year orbital period around the sun and returns to the Earth's neighborhood periodically, it does not represent a threat because its orbital path does not pass sufficiently close to the Earth's orbit," NASA's Near Earth Object Program Office said in a statement.

美国国家航空航天局“近地星体”项目处（Near Earth Object Program Office）发表声明称，这颗直径约400米的小行星围绕太阳运转的轨道周期为3年，之后又会定期绕回地球附近。尽管它的运行轨道穿过了地球的运行轨道，但距离不近，因此不会构成威胁。

NASA said that computer models showed that the asteroid would be an impact threat for at least 150 years.

美国国家航空航天局表示，据计算机模型显示，这颗小行星至少需要150年的时间才能带来具有冲击性的威胁。

Systems are already in place to track large asteroids, but recent research suggests that rocks as small as 164 feet across would still be big enough to cause devastating results on Earth.

追踪大型小行星的系统已经启用。但近期研究认为，就算164英尺（约49.99米）大小的石块也足以给地球造成毁灭性的伤害。