Every day, observers at the Japan Spaceguard Association stare steadfastly at the skies 36,000 km above the equator. And they are deadly serious about their job — to guard Japanese satellites from colliding with space junk and debris.

"Due to gravity, the sky above the Indian Ocean is the 'grave' where satellites that have completed their missions gather," explained Noritsugu Takahashi, board chairman of the nonprofit organization. "In the case of an approaching old satellite possibly headed for collision with a Japanese satellite along the path, we will reposition the Japanese satellite."

But Takahashi's group was founded in 1996 on a different premise — surveilling the skies to discover threats to Earth, such as an asteroid or comet.