(ORDO NEWS) — Using ground and space observations, the team of researchers carefully tracked the hard-to-reach comet. It’s called Comet 323P/SOHO and it was discovered over 20 years ago in 1999. But it is difficult to observe because of its proximity to the sun.
They found that the Sun was slowly tearing the comet apart.
Comets with the designation SOHO were discovered using the SOHO spacecraft. The Solar and Heliospheric Observatory (SOHO) is a joint ESA-NASA mission launched in 1995. Its mission is to study the Sun, and although the mission was scheduled for two years, it has been running for over 26 years.
As a by-product of its solar observations, the spacecraft detected 4,000 comets. Most of these comets are a class of comets very close to the Sun.
Astronomers believe that most solar comets are pieces of a much larger comet that has broken apart. 323P is a solar comet. Small comets can completely evaporate on one close approach to the Sun, while larger ones can survive this. For most of them, their small perihelion spells their final doom.
The perihelion of comet 323P/SOHO is only 0.04 astronomical units. Its orbital period is just over four years. In 2020, observations with the Subaru Telescope showed that the comet had no cometary features as it approached perihelion. But everything has changed.
“However, in our observations after perihelion, it developed a long, narrow tail that mimics a decaying cloud of cometary debris,” the authors write in their paper.
The article is titled “Protracted Death of the Periodic Solar Comet 323P/SOHO”. The first author is Man-To Hui from the State Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology. The rest are from institutions in the US, Germany, Canada and Taiwan.
A comet has less perihelion than Mercury. Astronomers think they are main belt asteroids or short period comets that were pulled closer to the sun by the gravitational influence of giant planets or by ancient impacts.
According to astronomers, their lifetime rarely exceeds 10 million years due to their orbit in the inner solar system. Not only do they have to contend with the gravitational force of the sun, they often cross the paths of the terrestrial planets.
The comet’s nucleus has a diameter of only about 172 meters. It rotates rapidly, at a speed of 0.522 hours, the fastest rotation of any known comet in the solar system. According to the authors of this article, this means that the core has a high cohesive strength. This strength may help it survive more gravitational collisions with the sun.
This study is one of the first cases of observation of such comets using ground-based observatories.
The team concluded that the comet may have been a regular Jupiter-family comet as recently as 1,000 years ago. But the Jupiter-family comets themselves originated as Kuiper Belt objects and contain a lot of frozen volatiles. They should form a conspicuous tail when heated by the sun.
323P can continue to survive close passes with the sun, due in part to its high cohesive strength. But that won’t last, partly because of its rotational instability and partly because of its strong orbital resonance with Saturn. This resonance will decrease its perihelion and increase its orbital eccentricity. For these reasons, comet 323P/SOHO is doomed.
According to the article, “…323P has a 99.7% chance of colliding with the Sun in the next two millennia.”
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