Have you ever wondered what happens to all of the old objects launched into space, such as rockets and satellites? It's called space junk, and much of it is still out there now. One large piece of space junk, disused rocket, hit the dark side of the moon on March 4. The rocket's origin is not clear, but scientists know that it was massive— (weigh) about 3 tons.
What is(significance) about this space junk crash is that it draws attention to some of the potential (danger) of space junk. First, the accumulation of space junk in Earth's orbit means that satellites and the International Space Station （ISS） are at risk． In 2016，tiny space debris（残骸），measured smaller than a millimeter, caused a tiny chip in the ISS'window. Imagine the damage that a (large) piece of debris could cause. The European Space Agency website states that objects "up to 1 cm in size could (able) an instrument or a critical flight system on a satellite" while objects over 10 cm "could shatter a satellite or spacecraft into pieces". In addition to potential damagespacecraft and satellites, space junk also poses a threat to the Earth(it). Crashes can send debris into the atmosphere where it can remain for many decades. Some powerful collisions can even send large debris hurtling（猛冲） toward Earth's surface where it can affect the local environment. Leftover rocket debris can contain toxic materials that(be) harmful to plants and animal life. Some people in Siberia have even reported serious health problems after rocket debris landed in their regions in 2012, a local doctor told the BBC.
