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There is something odd about the near-Earth asteroid 3200 Phaethon: it lights up as it approaches the Sun, although it does not have any ice reserves that would normally cause this effect. when they evaporate and scatter sunlight.
It’s the ice-laden comets that get brighter when heated, not rocky asteroids, which is why Phaethon has long intrigued astronomers. Now, a new study suggests that one particular chemical element could be behind this bizarre behavior.
“Phaethon is a curious object that activates as it approaches the Sun,” says astronomer Joseph Masiero of the California Institute of Technology.
“We know it is an asteroid and the source of the Geminids [meteor shower]. But it contains little or no ice, so we were intrigued by the possibility that sodium, which is relatively abundant in asteroids, could be the driving force behind this activity. “
Phaethon takes 524 days to complete a full orbit, during which the Sun heats it up to a maximum of 1,050 Kelvin (777 degrees Celsius or 1,430 degrees Fahrenheit). Any ice on the asteroid would have burned a long time ago, but the researchers used computer models to show that sodium could still be present, evaporating below the surface.
This warming and fizzing could explain not only the lightening of the asteroid, as sodium escapes through cracks and fissures in the crust, but also the ejection of rocks that can be seen from Earth during of the Geminid meteor shower every December. Phaethon’s weak gravitational pull would make it even easier to drop the debris.
We know that Geminid meteors are relatively low in sodium due to the light they give off when they burn in Earth’s atmosphere, and again this can be explained by the modeling done by the research team.
Experiments were then carried out on fragments of the Allende meteorite, which landed in Mexico in 1969 and likely originated from an asteroid like Phaethon. When heated, the behavior of the fragments confirmed that sodium could indeed turn into vapor and be released from an asteroid, at the kind of temperatures Phaethon is likely to experience.
“This temperature is around the point where sodium escapes from its rocky components,” says planetologist Yang Liu of NASA’s Jet Propulsion Laboratory (JPL). “So we simulated this heating effect over the course of a ‘day’ on Phaethon – his three hour rotation period.”
“By comparing the minerals in the samples before and after our lab tests, sodium was lost, while other elements were left out. This suggests that the same may be happening on Phaethon and seems to be in line with the findings. results of our models. “
As well as offering fascinating information on what’s going on on Phaethon, research also suggests that the distinction between rocky asteroids and icy comets may not be as clear as previously thought.
The results of the modeling and experiments here may well provide astronomers with useful data that applies to other low perihelion asteroids – those that fly close to the Sun.
“Our latest finding is that if the conditions are right, sodium can explain the nature of some active asteroids, making the spectrum between asteroids and comets even more complex than we previously thought,” says Masiero.
The research was published in the Journal of Planetary Sciences.
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