A Chinese spacecraft has been only the fourth to fly past an asteroid and capture close-up images. Here are a series of images of the 4 km long asteroid Toutatis which is considered a NEA (Near Earth Asteroid) though it won’t make another pass near the earth for another 50 years. This is a much smaller asteroid than has been imaged so closely before. It is really amazing that a spacecraft millions of miles from Earth can be directed to fly within just 3.2 km of this object flying through space.
I have referenced this same asteroid in a past post. That post was about the rotation of asteroids and what they tell us about the age of the solar system (As the Asteroid Tumbles: Asteroid and the Age of the Solar System). I noted there that most large asteroids rotate regularly around their principle axis. But there are some asteroids that are small or rotate very slowly (as Toutatis does) then they are predicted to be chaotic tumblers through space. All tumbling objects should work their way toward a regular axis of rotation and their size and speed determines how long it will take for that to happen. In the case of Toutatis the predicted time to regular rotation is around 60 billion years. Given the solar system is predicted to be less than 5 billion years old it is not surprising that this asteroid is still tumbling through space. Other larger asteroids with predicted times of achieving regular rotation under 4 billion years do rotate regularly unless they have had an interaction with another asteroid or planet that has thrown them back into a chaotic tumble.
You can read how the predicted and observed rotations of asteroids can be used as an independent prediction of the age of the solar system in my prior post (As the Asteroid Tumbles) and find the data behind that post in the article linked below.
References: For details on the rotational periods of asteroids the technical details can be found in the paper below:
Pravec, P. Harris, AW and Warner BD. 2007. NEA (Near Earth Asteroids) rotations and binaries. In: Near Earth Objects, our Celestial Neighbors: Opportunity and Risk, Proceedings if IAU Symposium 236. Edited by G.B. Valsecchi and D. Vokrouhlický, and A. Milani. Cambridge: Cambridge University Press, 2007., pp.167-176.