A lot of asteroids pass by Earth, but: its own moon.
The double asteroid reached its closest approach on May 25 and the European Southern Observatory managed to snag some snapshots.
ESO released an image of the asteroid on Monday alongside an artist's impression of what it might look like. The real image looks like a couple of fuzzy blobs, but it shows the distinctly double nature of the asteroid.
The exoplanet-spotting SPHERE instrument on the ESO'S Very Large Telescope in Chile is extremely sensitive. ESO says it's "one of the very few instruments in the world capable of obtaining images sharp enough to distinguish the two components of the asteroid." The larger body and the smaller one are separated by a mere 1.6 miles (2.6 kilometers). SPHERE stands for Spectro-Polarimetric High-contrast Exoplanet REsearch.
Asteroid 1994 KW4 is classified as "potentially hazardous," though it didn't pose a threat to Earth. It passed at a very safe distance away. ESO used the asteroid as a test of the International Asteroid Warning Network. Multiple organizations coordinated on an observation campaign.
Researchers aim to learn more about passing asteroids so us earthlings can better figure out how to deflect dangerous rocks or mitigate damage from impacts. Asteroid 1994 KW4 is particularly intriguing because it resembles another binary asteroid named Didymos that could threaten Earth in the distant future.
NASA is working on sending its where it will crash into the asteroid's moonlet in 2022 and try to knock it a little off course. It sounds like a sci-fi movie, but NASA hopes it will show that asteroids could potentially be nudged away from Earth.
Studying harmless 1994 KW4 is one more key step in preparing for battle with asteroids.