Why don't we see space junk in the photos of the Earth | 2017-02-02 | daily-sun.com

Why don't we see space junk in the photos of the Earth

Sun Online Desk     2nd February, 2017 04:19:07 printer

Why don't we see space junk in the photos of the Earth

An assortment of satellites grace the sky in an illustration that is definitely not to scale.

The space above the planet is getting increasingly and worryingly crowded with satellites and space junk. There are about 4,256 human-made satellites orbiting the Earth, of which about 1,149 are still working.


Most of these are fairly small, ranging from tiny CubeSats that are only four inches on each side to communications satellites that can be over 100 feet long.


That’s still tiny when you consider that the Earth is 7,917.5 miles across. Even our space station is puny when compared to our planet. Measuring 357 feet end-to-end, the International Space Station (ISS) is by far the largest human-made object orbiting the Earth. Even that isn’t large enough to register on Earth-observing instruments such as the DSCOVR satellite's EPIC camera, which takes absolutely gorgeous pictures of the Earth from a million miles away.


Jay Herman, the lead scientist of EPIC, says that the smallest objects EPIC's camera can make out are about eight to 10 kilometers wide. At that range, the ISS wouldn’t even register as a blip in an image of the Earth.


Even satellites with closer vantage points and higher resolutions are out of luck. NASA's Terra and Aqua satellites carry the MODIS (or Moderate Resolution Imaging Spectroradiometer) instrument and operate only about 440 miles above the Earth’s surface.


“With the MODIS satellite, which has a resolution of one kilometer, you’d probably barely be able to make out something like the ISS," says Herman. "If it did pass through the field of view, you might see a bright spot, but you wouldn’t see many details, so it would be really hard to identify.” And that’s only if the ISS and Terra or Aqua happened to be in the same area.


That’s not to say that there are no orbiting observatories capable of taking images of other satellites or space junk. “Some of the commercial high-resolution satellites would be able to see the ISS and probably even smaller spacecraft,” Herman says.


But even then, it’s a matter of perspective and position. Satellites are designed to not crash into each other, which means that it’s very rare that their paths cross, and many of them operate at different altitudes. The ISS orbits at a height of around 250 miles, for example, while other satellites orbit closer to Earth or much further away. “The commercial satellites would be able to see the ISS, which is in a fairly low orbit,” Herman says. "But they wouldn’t be able to see MODIS, which is in a higher orbit than the commercial high-resolution satellites."