Sodium sparkles on the asteroid Phaeton

In 1983, NASA’s IRAS satellite (3200) spotted Phaeton, an asteroid orbiting Earth at eight times the distance between Earth and the Moon depending on its paths. It is he, too, and the dust he lost in space, which is the source of Gemini meteors. It happens every year in the middle of December. Phaeton has attracted the attention of astronomers for a long time, especially because its brightness increases near the Sun and then presents an aspect that makes it look like a comet.

Phaeton strange asteroid

It is its trajectory that brings it so close to our star that Phaeton is also named after him: he is the son of Helios, the Greek god personifying the Sun. (3200) Phaeton looks like a large cannonball with a diameter of 5.8 km. One of its poles is marked by a deep depression that extends to the equator. The star is mainly made of rock, not ice like comets, and is surrounded by a cloud of particulate dust. Upon reaching the Earth’s atmosphere, it is consumed and the falling stars of Gemini are formed. Researchers at the California Institute of Technology and NASA’s Jet Propulsion Laboratory wanted to understand why the asteroid takes this comet’s side near the sun. Without sublimation the ice should not begin to sparkle unless another element plays the role of this ice.

Trail appears thanks to the Geminids watch. Before disintegrating, pieces of asteroids heat the air around them, which then reaches temperatures of several thousand degrees. A phenomenon that generates light whose color represents the elements taken from the asteroid. Sodium, for example, creates an orange tint. But Geminides are known to be low in sodium. Until now, scientists have assumed that these small pieces of rock lose their sodium after leaving the asteroid. This new study, published in Planetary Science JournalHe points out that sodium may indeed play a major role in flushing them out.

These radar images of asteroid 3200 Phaethon were created by astronomers at Arecibo Observatory on December 17, 2017. Credit: Arecibo Observatory / NASA / NSF.

Sodium sparkles

The authors suggest that as (3,200) Phaeton approaches the Sun, the sodium heats up and sublimates. This process would have rinsed away any trace of sodium on the surface for a long time, but not that found in the star’s rocks. Near our star, once it turns into gas, it escapes through cracks in the outer crust in jets powerful enough to carry rocky debris with them. This phenomenon is not very violent: due to the reduced gravitational pull of the star, it is not necessary to provide much energy to tear small fragments. Furthermore, the researchers believe, it’s not the explosions that allow the sodium to escape, but rather a kind of constant sizzling. This sparkling sodium could explain not only the comet-like gain in brightness, but also how the meteorites that make up Geminids will be ejected from the asteroid and why they contain so little sodium.

To see if sodium actually turns into steam on Phaeton, experiments were conducted on samples of the Allende meteorite, which fell on Mexico in 1969, at the JPL laboratory. The meteorite could come from an asteroid similar to Phaeton and belong to a class of stars that formed during the early days of the solar system. The samples were heated to the highest temperature the asteroid would be exposed to as it approached the Sun for 3 hours, the period covering a day on Phaeton. RESULTS: The sodium disappeared from the samples after heating. Therefore, this study supports the theory of sodium as a driver of asteroid activation. According to the researchers, other asteroids can interact in the same way as the Sun approaches, even expelling other elements that sublimate at higher temperatures from their rocks.