Tianwen-2 - Unravelling the secrets of asteroids

China is set to mount the latest mission to retrieve a sample of an asteroid and bring it home. Stuart Atkinson investigates

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Asteroids were once dismissed by astronomers as "the vermin of the skies", constantly getting in the way of more important observations. Not anymore. The former vermin have become one of the hottest areas of space research. Asteroids can reveal the history of our Solar System and offer a tantalising wealth of metals and minerals, not to mention their importance as a threat to our very existence on this planet. This month, China prepares to join in the quest to understand these space rocks with the launch of its most complex planetary mission to date, Tianwen-2. The spacecraft aims to visit not one but two asteroids, returning a fragment of one to Earth and cementing the nation's place as a major player in space exploration.

Cosmic time capsules

The mission is the latest step in a long journey of learning about these space rocks, which began with the discovery of the first asteroid, Ceres, by the astronomer Giuseppe Piazzi on 1 January 1801. Today, we know the positions and orbits of many thousands of asteroids with great accuracy and more are being found all the time. Around the world, survey telescopes are taking images of the sky, finding asteroids and tracking their orbits around the Sun, some of which pass perilously close to Earth.

Eyebrows were raised in genuine concern earlier this year when an asteroid was found that, at first glance, had a small chance of colliding with Earth in seven years.

Luckily for us, the Statue of Liberty-sized 2024 YR4 will miss us, so there was no need to start training Bruce Willis to fly a souped-up Space Shuttle with a nuke in its payload bays.

We won't always be so lucky, and YR4 served as a timely reminder that one day astronomers will find an asteroid on a direct collision course with our planet.