Space is where our future is -- trips to the Moon, Mars and beyond. Most people would think that aside from comets  and stars, there is little else out there. But, since our space journey started we have left so much trash  there that scientists are now concerned that if we don't clean it up, we may all be in mortal  danger. The first piece of space junk was created in 1964, when the American satellite Vanguard I stopped operating and lost its connection with the ground center. However, since it kept orbiting around the Earth without any consequences, scientists became increasingly comfortable abandoning  things that no longer served any useful purpose in space. It is estimated  that there are now over 500,000 pieces of man-made trash orbiting the Earth at speeds of up to 17,500 miles per hour. The junk varies from tiny pieces of paint chipped off rockets to cameras, huge fuel tanks, and even odd items like the million-dollar tool kit that astronaut Heidemarie Stefanyshyn Piper lost during a spacewalk. The major problem with the space trash is that it may hit working satellites and damage traveling spacecraft . Moreover, pieces of junk may collide  with each other and break into pieces which fall back to the Earth. To avoid this, scientists have invented several ways for clearing the sky. Ground stations have been built to monitor larger pieces of space trash to prevent them from crashing into working satellites or space shuttles. Future plans include a cooperative effort among many nations to stop littering in space and to clean up the trash already there. Which of the following statements is true about space junk?
It is huge, heavy machines. It never changes position. It floats slowly around the Earth. It may cause problems for space shuttles.