Asteroids under the influence

On Saturday, 25 May, binary asteroid 1999 KW4 will make its closest approach to Earth. Attracted by our star’s gravitational pull, it will pass five million km above our heads – about 13 times further than the Moon – and dozens of telescopes around the globe will use this opportunity to collect as much information as they can about its size, shape and composition.

First discovered in 1999, this 1600-m diameter rock completes one full orbit of the Sun every 188 days (see the 1999 KW4 orbit visualisation, here). The goal of this collaborative observation campaign by the International Asteroid Warning Network is to understand what its possible to discover with relatively little notice, in case of the future close approach of a potentially threatening asteroid.

Near-Earth asteroid 1999 KW4 is a binary object, making this close encounter particularly interesting. Comprising one smaller body orbiting a larger asteroid roughly three times its diameter, this asteroid system a useful test case for the upcoming investigation into the Didymos pair of asteroids – target of the upcoming NASA-ESA asteroid deflection mission.

The asteroid itself is the faint blob at the centre of this animation, which has been made from two 90-second exposures taken on 9 May 2019 by the 0.6-metre telescope on the French island of Réunion in the Indian Ocean, all thanks to the newly established cooperation between ESA and the Observatoire des Makes.