An asteroid like a comet? Does the mysterious celestial body Phaeton shed sodium?

In addition to planets and satellites, there are countless small celestial bodies in the solar system. Typical examples are comets and asteroids, but the existence of ambiguous stars of which none can be said has been discovered one after another and has become the focus of interest in astronomical science and space science. Regarding one of these stars, the asteroid Phaeton, a research group in the United States has published research results that suggest that the substance that erupts like a comet is sodium. In Japan, preparations have officially begun to send a spacecraft to this star. It will be noticed if the actual situation becomes clear.

An “active asteroid” that actively releases matter

A comet with a beautiful tail in the night sky. The main component of your body is ice water, which is also made of gas, such as carbon dioxide and carbon monoxide, and dust, and is described as a “dirty snowball.” Many have elongated elliptical orbits, in contrast to the orbits of planets like Earth, which are close to circles. It gets hotter every time it gets close to the sun, and the ice evaporates, releasing gas and dust. It creeps in the opposite direction to the sun. On the other hand, asteroids are mainly rocky and do not emit anything noticeably when approaching the Sun.

Recently, however, the existence of a mysterious “active asteroid” that actively releases matter between stars classified as asteroids has been discovered one after another. One of the best-known stars, Phaeton, is 5.8 kilometers in diameter, has an elongated orbit of 1.4 years, and is closer to the Sun than Mercury, temporarily releasing matter. At the closest approach, Phaeton’s surface temperature reaches 750 degrees. It is the same carbonaceous star as “Ryugu” visited by the Japanese spacecraft “Hayabusa2”, and it contains almost no ice. It is considered one of the largest “potentially dangerous asteroids” that can get very close to Earth.

What the heck does this Phaeton emit when approaching the sun? A research group from the California Institute of Technology and NASA made a hypothesis and challenged the experiment. “We focus on sodium, which is relatively abundant in asteroids,” said Joseph Masiello of the same university in a NASA statement.

“The distinction between asteroids and comets is complicated”

The hypothesis is this. When Phaeton gets close to the Sun and heats up, the sodium vaporizes and is released into space. However, the only sodium that has already been depleted in this way is the surface. It still stays indoors, and it can still vaporize and explode whenever it gets close to the sun.

Then, in 1969, a chunk of carbonaceous “Allende meteorite” that fell into Mexico was brought to the laboratory and heated to a near maximum temperature as Phaeton approached the sun. Upon examination after the experiment, sodium was lost from the debris, but other elements remained. The research group said the results were consistent with the hypothesis and suggested that the same could happen in Phaeton.

The distinction between asteroids and comets seems to depend not only on the presence or absence of ice, but also on which element vaporizes at high temperatures. “Sodium can explain the nature of some active asteroids (besides Phaeton),” Masiello said. “The distinction between asteroids and comets is more complicated than we think.” The results were published in the American planetary science journal “Planetary Science Journal” on the 16th.

The phaeton scattered in elliptical orbits is also known to be the cause of the “Geminid meteor shower” that is observed on Earth every December. The dust is known to be low in sodium due to the color of the light it emits when it leaps into Earth’s atmosphere and turns into a meteor.

Japan challenges “one-shot game” sent by spaceship

Japan sends a spaceship to the mysterious Phaeton. Deep space exploration technology demonstrator “DESTINY +”. After leaving earth, collect and analyze the dust in outer space as you navigate. When approaching Phaeton, the surface is observed in detail with multiple cameras, and the trajectory and chemical composition of the emitted dust is analyzed. He does not land or return substances to earth like “Hayabusa” and “Hayabusa2”, but instead analyzes them on the spot.

We also take on ambitious challenges in navigation technology. Conventionally, the spacecraft has been launched into interplanetary space by rocket at the same time. On the other hand, DESTINY + once put into orbit around the earth with a rocket, it soars in altitude for one to two years with an energy-saving electric propulsion device “ion engine” and accelerated by using the gravitational pull of the moon. (swing-by). ), Heading for interplanetary space. We will continue to devise ways to reduce energy consumption, paving the way for the realization of low-cost spacecraft.

In 2011, researchers began studying it as a “DESTINY” demonstrator for engineering purposes, and then added the science purpose to “DESTINY +”. Some of the scientific instruments will be developed by Germany. The project team was officially launched on May 1 this year. According to the schedule of the government’s basic space plan, etc., the small rocket “Epsilon S” under development will be launched in 2024.

Small celestial bodies, like comets and asteroids, seem to go unnoticed compared to planets like water, gold, fire, and wood. However, it is said to be a time capsule that retains the initial state of the solar system relatively well without being absorbed by a large star and without deteriorating. The importance of solving the mystery of active asteroids like Phaeton is not limited to history for space fans, “reviewing the distinction between comets and asteroids.” Not only can the understanding of the history of the solar system be hidden, but also the clues to solve the mystery of the existence of life on earth.

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