Many people know that rubbish is a big problem on planet Earth.What many people don't know is that junk has become a problem in outer space too.These are garbage that comes from rockets，dead satellites and other fragments created when these one collided with another.
   According to BBC News，there are more than 22，000 pieces of space junk floating around the Earth.And these are"just the things that we can see from the surface of the Earth by telescopes.There are also millions of smaller pieces of junk that we can't see.
   Objects，like bits of old space rockets or satellites，move around the planet at very high speeds，so fast that even a very small piece can break important satellites or become dangerous to astronauts.If the tiniest piece of junk crashed into a spaceship it could damage the vehicle.
   To make things worse，when two objects in space crash，they break into many smaller pieces.
   For example，when a U.S.satellite hit an old Russian rocket in 2009，it broke into more than 2，000 pieces，increasing the amount of space junk.
   To reduce additional space junk，countries have agreed that all new space tools can only stay in space for 25 years at most.Each tool must be built to fall safely into the earth's atmosphere （大气）after that time.In the upper parts of the atmosphere it will burn up.
   Many scientists are also suggesting different ways to clean up space junk.In England scientists are testing a metal net that can be fired into space junk.The net catches the junk and then pulls it into the earth's atmosphere to burn up.The Germans are building robots that can collect pieces of space junk and bring them back to Earth to be safely destroyed.
   "The problem is becoming more challenging because we're sending more objects into space to help people use their mobile phones and computers，" says Marco Castronuovo，an Italian space researcher.
   "The time to act is now.The longer we leave the problem，the bigger it will become，" he says.

根据上面的短文内容填空。
（1）Rubbish is a big problem

not only

not only

on planet Earth but also in

outer space

outer space

.
（2）BBC News reports that over 22，000 pieces of space junk

floating

floating

around the Earth.
And they are just the ones that can

be seen

be seen

from the surface of the Earth by telescopes.
（3）The fast moving objects in the space are very dangerous.To make things worse，when two objects in space crash.jye.ai break into many smaller pieces.In 2009，a U.S，satellite hit

an old Russian rocket

an old Russian rocket

then it broke into

2，000 pieces

2，000 pieces

of space junk.
（4）To reduce additional space junk，countries have agreed that all new space tools can only stay in space for

25 years

25 years

They must be built to

fall safely

fall safely

into the earth's atmosphere after that time.
（5）Many scientists also suggest that space junk can be cleaned up in

different ways

different ways

.We know that scientists in

Western Europe

Western Europe

are acting to help clean up space junk now according to the article.