New Study Unveils the Composition of Asteroid Phaethon

Researchers from the University of Helsinki have solved the mystery of asteroid Phaethon's tail and meteor shower by studying its composition and temperature.

Temperatures estimated at one diurnal thermal skin depth beneath the subsurface and surface of Phaethon during perihelion passage. Note that Phaethon’s rotation every ~3.6 h causes temperature variation at each latitude, which are colored according to the legend. The lower temperature range at which gas species are produced via thermal decomposition are indicated as horizontal lines. Credit: Nature Astronomy (2023). DOI: 10.1038/s41550-023-02091-w

The researchers found that Phaethon is composed of at least olivine, carbonates, iron sulfides, and oxide minerals. When Phaethon passes close to the sun, its surface temperature rises to about 800°C. At this temperature, the carbonates produce carbon dioxide, the phyllosilicates release water vapor, and the sulfides release sulfur gas. The gas that is released from the asteroid's surface can cause the rock to break down, releasing dust and gravel. The pressure produced by carbon dioxide and water vapor is high enough to lift small dust particles from the surface of the asteroid.

"Sodium emission can explain the weak tail we observe near the sun, and thermal decomposition can explain how dust and gravel are released from Phaethon," says the study's lead author, postdoctoral researcher Eric MacLennan from the University of Helsinki.

"It was great to see how each one of the discovered minerals seemed to fall into place and also explain the behavior of the asteroid," says associate professor Mikael Granvik from the University of Helsinki.

The study was published in the journal Nature Astronomy.

Journal Information: Eric MacLennan et al, Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon, Nature Astronomy (2023). DOI: 10.1038/s41550-023-02091-w