New research shows that Phaethon’s comet-like activity cannot be explained by any kind of dust.
Also known as 1983 TB, Phaethon was discovered on October 11, 1983 by astronomers Simon Green and John Davies in data from NASA’s Infrared Astronomical Satellite (IRAS).
With a diameter of about 3.2 miles (5.1 km), this asteroid is the third largest near-Earth asteroid classified as ‘potentially hazardous’ after asteroids (53319) 1999 JM8 and 4183 Cuno.
Phaethon is the parent body of the Geminid meteor shower of mid-December.
It is categorized as a so-called Apollo asteroid, as its orbital semi-major axis is greater than that of the Earth’s at 118 million miles (190 million km, or 1.27 AU).
In 2009, NASA’s Solar Terrestrial Relations Observatory (STEREO) spotted a short tail extending from Phaethon as the asteroid reached its closest point to the Sun — or perihelion — along its 524-day orbit.
Regular telescopes hadn’t seen the tail before because it only forms when Phaethon is too close to the Sun to observe, except with solar observatories.
STEREO also saw Phaethon’s tail develop on later solar approaches in 2012 and 2016.
The tail’s appearance supported the idea that dust was escaping the asteroid’s surface when heated by the Sun.
However, in 2018, observations from NASA’s Parker Solar Probe showed that the trail contained far more material than Phaethon could possibly shed during its close approaches to the Sun.
California Institute of Technology Ph.D. student Qicheng Zhang and colleagues wondered whether something else, other than dust, was behind Phaethon’s comet-like behavior.
“Comets often glow brilliantly by sodium emission when very near the Sun, so we suspected sodium could likewise serve a key role in Phaethon’s brightening,” Zhang said.
An earlier study, based on models and lab tests, suggested that the Sun’s intense heat during Phaethon’s close solar approaches could indeed vaporize sodium within the asteroid and…
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