NASA investigates the comet-like activity of asteroid Phaethon

NASA scientists have been studying an interesting asteroid called Phaethon that is exhibiting comet-like activity. Recent laboratory models and tests have suggested that the asteroid could be venting sodium vapor as it orbits near the sun. That bidding could explain the increase in brightness observed by scientists.

Comets are heated by the sun when they fly to the inner solar system causing the ice under their surface to vaporize into space, creating the iconic comet tail when the vaporizing ice throws dust and rock into space. The icy composition of the comet is well known, and it's well-known that asteroids are mostly rock. However, because of their mostly rocky construction, asteroids don't typically exhibit comet-like activity.

A new study has determined that asteroid Phaethon may be exhibiting comet-like activity despite its lack of significant quantities of ice. Phaethon, which is the source of the annual Geminid meteor shower, is about 3.6-miles wide. It routinely brightens as it nears the sun leading NASA scientists to wonder what causes that brightening.

The new study has found that the reason for the increase in brightness is likely sodium. Phaethon has an elongated 524-day orbit, taking it within the orbit of Mercury. During its pass close to the sun, the asteroid's surface is heated to around 1390 degrees Fahrenheit. At that temperature, any water, carbon dioxide, or monoxide ice near the surface would have disappeared long ago.

However, because of the high temperatures, sodium could be "fizzing" out of the asteroid's rocky surface into space. Scientists note that sodium is abundant in asteroids, and they believe that is driving the curious behavior of Phaethon. The study's findings suggest that sodium might play a key role in ejecting Geminid meteoroids from the surface of Phaethon.