2021-10-22

Strange solar system objects: like asteroids and comets

By yqqlm yqqlm

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888c 1528d90c98863c387c4eee371c950180 - Strange solar system objects: like asteroids and comets

this composite image shows the trajectory of 2005 qn173. This is a rare active object with the characteristics of both asteroids and comets. Its comet nucleus is located in the upper left corner of the image, and its tail runs through the diagonal of the image

scientists first discovered this strange object in 2005. It looks like a comet. It scatters dust and drags a long and thin tail, indicating that it is covered with a layer of material composed of water ice and evaporates into space. On the other hand, 2005 qn173 is different from comets, because the latter usually has an elliptical orbit and is regularly close to and away from the sun. This duality, as well as the fuzzy boundary between asteroids and comets, which were previously considered to be two completely different types of objects, are the key to how interesting these objects look

although it has comet like characteristics, the orbit of 2005 qn173 is definitely the orbit of an asteroid: it quietly orbits the sun in the outer layer of the asteroid belt between Mars and Jupiter, about once every five years. This summer, astronomers looked at the data collected by the asteroid ground impact continuous warning system (Atlas) survey in Hawaii on July 7 and noticed that the object had a “tail”. Astronomers also found this feature in additional observations made by telescopes at the Lowell Observatory in Arizona. Later, the researchers examined the previous observations of other institutions and found that the tail appeared again in the images collected by the Zwicky transient device in California on June 11

among these observations, 2005 qn173 is closest to the sun on May 14, that is, it is at the perihelion. Comets are more striking than typical main belt asteroids when they approach the sun at close range. The orbit of all stars around the sun is roughly an ellipse, so sometimes they will be closer to the sun and sometimes farther. The position closest to the sun is called the perihelion, and the earth’s perihelion falls in early January

at the same time, other scientists analyzed the observation results of 2005 qn173 collected by the dark energy camera in July 2016, which was the last time that the object was near the perihelion. They also found the tail of the object in these results

the activity near perihelion is consistent with the characteristics of comets: the increasing solar radiation turns frozen materials into gas, a process called sublimation. Typical comets spend most of their time far enough from the sun that their sublimation activities are “frozen”

most comets are found to come from the cold outer solar system. Outside Neptune’s orbit, they are there most of the time. The highly elongated orbit allows them to approach the sun and the earth only in a very short time. When they are close enough to the sun, their temperature will rise and release gas and dust due to the sublimation of ice, Resulting in a blurred appearance and characteristic spectacular comet tail

among the 500000 asteroid belt objects that scientists have inspected, this is the eighth object that has been active for many times, and it is one of the only 20 suspected “main belt comets”. The new study also includes the original observations excavated from the archives of various instruments, which observed the comet when it was not active from 2004 to 2020. The purpose of collecting these results is to better understand the celestial body itself. According to the statement issued by the researchers, these observations show that the comet’s nucleus is about 3.2 kilometers wide

then, the scientists synthesized the latest observations of the object by a series of instruments in July and August this year to better understand the activity of this strange main belt comet. In particular, the researchers measured that the tail of the object extended 720000 kilometers in July, slightly less than twice the distance between the earth and the moon

although the tail length of the object is amazing, it is not as wide as researchers think, which brings a new problem. This extremely narrow comet tail tells us that the speed of dust particles floating out of the comet nucleus is extremely slow, and the gas flow escaping from the comet is also extremely weak. This gas flow usually scatters dust from the comet into space. Such a slow speed usually makes it difficult for dust to escape the gravity of the comet nucleus itself. Therefore, This suggests that something else may be helping the dust escape. One possible explanation is that the comet nucleus rotates too fast and releases additional dust into space, but there is not enough observational evidence

researchers say that by February 2026, the object will be visible from the southern hemisphere, and its distance from the sun may make it active again

at present, this research has been accepted by the Astrophysical Journal Letters. Readers can also read the preprint of the paper on arxiv.org