2023-04-26 12:15:41
The asteroid Phaethon (Phaethon in English), which has the number 3200 in the asteroid catalog of the International Astronomical Union, behaves as if it were a comet. It lights up and forms a tail when it is close to the Sun. This behavior has been observed for a long time. In addition, Phaethon is the source of the Geminids, an annual shower of shooting stars, despite the fact that the sources of shooting star showers are usually comets.
Mostly rocky asteroids do not typically form tails as they approach the Sun. Comets, however, are a mixture of ice and rock, and typically form tails when the Sun vaporizes their ice, ejecting material from their surfaces and leaving a trail along their orbits. When Earth passes through such a debris trail, those cometary fragments burn up in our atmosphere and produce a swarm of shooting stars, or a meteor shower.
Phaethon’s comet-like behavior was thought to be due to dust escaping from the asteroid as it was scorched by the Sun. However, a new study reveals that Phaethon’s comet-like activity cannot be explained by no dust.
The study is the work of Qicheng Zhang’s team, from the California Institute of Technology (Caltech) in the United States.
In 2009, NASA’s Solar Terrestrial Relations Observatory (STEREO) space mission captured a short tail extending from Phaethon as the asteroid reached its closest point to the Sun (perihelion) in its 524-day orbit around the Sun. Normal telescopes had not seen the tail before because it only forms when Phaethon is too close to the Sun to be observed by them. In such circumstances, it can only be seen by solar observatories. Observations from the STEREO mission also revealed Phaethon’s tail forming on subsequent approaches to the Sun, in 2012 and 2016. The tail’s appearance supported the idea 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 de Amazings)
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