The near-Earth asteroid 3200 Phaethon is unusual in that it glows brightly as it approaches the Sun. However, there are no ice reserves to cause this phenomenon.
It's ice-laden comets, not rocky asteroids that make brighter when heated. This is why Phaethon is still a puzzle to astronomers. A new study has suggested that this strange behavior may be due to a particular chemical element.
Joseph Masiero, an astronomer at the California Institute of Technology, says that Phaethon is "a curious object that becomes active as it approaches Sun."
It is an asteroid, and it is the source of the Geminids (meteor shower). It is a small asteroid with little or no ice. We were therefore intrigued by the possibility of sodium, which is a relatively abundant element in asteroids, being the driving force behind this activity.
Phaethon takes 524 day to complete a full orbit. During this time, the Sun heats it to a maximum temperature of 1,050 Kelvin (777° Celsius or 1,430° Fahrenheit). The asteroid's ice would have been gone long ago. However, computer models were used by researchers to prove that there could be sodium still present beneath the surface.
The heating and fizzing may explain the brightening and escape of sodium through cracks in the crust. It also explains the meteor shower of Geminids rocks visible from Earth every December. The weak gravitational pull of Phaethon would make it easier to get debris off the surface.
The light that Geminid meteors emit as they burn up in Earth’s atmosphere makes them relatively low in sodium. This can be explained again by modeling by the research team.
The fragments of the Allende meteorite landed in Mexico in 1969. They were likely to have come from an asteroid such as Phaethon. The fragments' behavior when heated up confirmed that sodium can indeed become vapor and be released by an asteroid at the temperatures Phaethon is most likely to experience.
Yang Liu (planetary scientist at NASA's Jet Propulsion Laboratory, JPL) says that this temperature is around the temperature where sodium escapes from its rock components. "So, we simulated this heating effect over the course a day on Phaethon's three-hour rotation period."
"On comparing the minerals of the samples before and after our laboratory tests, we found that the sodium was lost while the other elements were retained." This suggests that Phaethon may be experiencing the same thing and is consistent with our models' results."
The research offers fascinating insight into Phaethon's activities, but it also suggests that there may not be as clear a distinction between rocky asteroids vs icy comets as previously thought.
Astronomers could benefit from the results of this modeling and experimentation by obtaining useful data for other low-perihelion asteroids that are close to the Sun.
Masiero says, "Our latest discovery is that sodium, if the conditions are right," may explain the nature some active asteroids. This will make the spectrum between comets and asteroids even more complicated."
The Planetary Science Journal published the research.
