How big was the piece of space junk that forced the crew of the International Space Station to <a href=“”https://www.reuters.com/article/latestCrisis/idUSN12379555">evacuate for a few minutes on Thursday?

The question is of slightly more than academic importance. Stratcom (US Strategic Command), which does collision avoidance analysis for the ISS and other high-value assets, publicly catalogues space objects larger than 10cm diameter (on the Space-Track system).

But it appears the debris-spotters, who warned Nasa of a potential collision, may have sharper eyes than one would suspect from their recordings. Reuters put the junk at 0.83 cm (1/3 inch) across (a Nasa spokeswoman confirms this with the Independent) – though AP reckons it was about the size of a grapefruit (5 inches).

The debris was a old motor component that had been orbiting Earth since 1993 – not connected to the collision of two satellites on 10 February.

Wired has more about how to track space junk online.

Image: Orbital Debris in low-Earth orbit/Nasa Orbital Debris Program Service