What is a co-orbital asteroid?
Asteroids regularly stay in the vicinity of Earth. They then “corkscrew” around the planet without really going into a true orbit, rather like a buoy bobbing in the wake of a boat’s propeller.
They can remain in this unstable state for years or even centuries, until they dip close enough to Earth to gain the acceleration required to free themselves from its gravity.
A target for future exploration missions
If an asteroid was found to be on a collision course with Earth, knowing more about its texture and density would help us to devise a plan to counter the threat: a racket is fine for hitting a tennis ball, but a steel ball would punch right through it.
The idea is to launch a probe to intercept an asteroid, to land seismometers on its surface and then to fire an impactor into it and measure how it sustains the impact.
We will then know how much energy would be needed to deflect it from its course—one further illustration of the vital role of space missions in protecting our planet and populations.