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

Astronomers say they have found a class of objects that blurs the line between asteroids and comets, appearing to fire jets of gas that can’t be seen with telescopes.

Comets are known to periodically emit bursts of gas and dust as the sun 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 such bursts. …