A celestial body named Phaethon, designated 3200 in the asteroid registry of the International Astronomical Union, exhibits properties akin to a comet. It illuminates and generates a trail when it nears the Sun, a characteristic that has been under observation for an extensive duration. Furthermore, Phaethon is the source of the annual Geminids meteor shower, which is a rarity for an asteroid.
Ordinarily, solid asteroids do not manifest a trail as they approach the Sun. Contrarily, comets, which are a blend of ice and rock, typically develop tails when their ice sublimates due to the Sun’s radiation, thereby releasing material from their surface, leaving behind a trail in their orbit. When the Earth crosses paths with such debris, the cometary fragments burn up in the atmosphere, creating a swarm of shooting stars or a meteor shower.
Phaethon’s comet-like characteristics were previously assumed to be due to dust escaping from the asteroid as it was scathed by the Sun. However, recent research shows that Phaethon’s comet-like activity cannot be attributed to dust.
A group of researchers led by Qicheng Zhang from the California Institute of Technology (Caltech) discovered this in their study.
NASA’s Solar Terrestrial Relations Observatory (STEREO) mission detected a brief trail emanating from Phaethon in 2009, as the asteroid arrived at its closest point to the Sun (perihelion) in its 524-day orbit around the Sun. This tail had not been observed by conventional telescopes since it only forms when Phaethon is too close to the Sun to be viewed by them. Thus, it can only be observed by solar observatories. The STEREO mission’s observations also disclosed that Phaethon’s tail formed during subsequent encounters with the Sun in 2012 and 2016. The appearance of the tail supported the hypothesis that dust was escaping from the asteroid’s surface as it was heated by the Sun.
However, in 2018, another solar mission observed part of the debris trail of the Geminids and was in for a surprise. Observations from NASA’s Parker Solar Space Probe showed that the trail contained far more material than could be shed by Phaethon during its close approaches to the Sun.
After further analysis of the available data, Zhang and his colleagues have concluded that Phaethon’s tail is made mostly of sodium gas.
Artist’s impression of the asteroid Phaethon being heated by the Sun. The asteroid’s surface heats up so much that the sodium inside Phaethon’s rocks is likely to vaporize and be ejected into space, causing it to shine like a comet and also form a tail like a comet (Image: NASA JPL/Caltech/IPAC)
This brings several mysteries. For example: if Phaethon gives off so little dust, how does the asteroid provide the material for the Geminids seen each December?
Zhang’s team suspects that some catastrophe a few thousand years ago (perhaps a piece of the asteroid that broke apart under the pressure of Phaethon’s rotation) caused it to eject the billions of tons of material estimated to make up the Earth. debris trail from the Geminids. In any case, the nature of said catastrophe remains a mystery.
The study is titled “Sodium Brightening of (3200) Phaethon near Perihelion”. And it has been published in the academic journal The Planetary Science Journal. (Fountain: NCYT by Amazings)
