The Phaethon asteroid (also known as the 3200 Phaethon) can reportedly vent sodium vapor when it orbits close enough to the sun, according to a study published in the Planetary Science Journal last month.
The asteroid could have activity similar to a comet while in orbit, according to the study.
The primary difference between asteroids and comets is that the latter contain lots of different ices, whereas asteroids are mainly made of rock.
The icy surfaces vaporize when a comet heats up while getting close to the sun. As for the Phaethon asteroid in particular, the article states that this is due to sodium being heated to such an extent as it passes Mercury in its orbit around the sun that may be fizzing from the asteroid into outer space.
It was previously thought that asteroids lost their sodium when meteoroids broke away from the asteroid as small pieces of debris. The researchers behind this study now believe that an asteroid's sodium can vaporize if close enough to the sun.