Asteroids that speed up unexpectedly may be ‘dark comets’ in disguise

Some small objects in space appear to fire jets of gas that can’t be seen with telescopes, suggesting they should be classed in a new category between asteroids and comets.

Comets periodically emit bursts of gas and dust as they approach the sun, which melts their icy surfaces. These events give off as much as 10 kilograms of dust per second, which reflects sunlight and makes the bursts visible, often contributing to a tail behind the comet. Asteroids, being rockier, don’t produce …