Is 2005 QN173 An Asteroid Or A Comet? All You Should Know About This Rare Object Of Space

It is believed that the rare object is tumbling through the main asteroid belt and could both be an asteroid or a comet. There are less than half a million main-belt asteroids that have been verified to have been active on multiple occasions. There are just eight objects around this size that consistently show activity.

The asteroids, that is the 2005QN 173, are in the main belt between Mars and Jupiter do not change their structure, but the 2005 QN173 just keeps shedding dust despite travelling 7,20,000 kilometres, suggesting that it could be covered in icy material that is vaporizing when it becomes active.

As part of the Asteroid Terrestrial Impact Last Alert System (ATLAS) survey, it was determined that the unique object could be active in July 2021 and Henry Hsieh, the lead author of the paper presented at the 53rd annual meeting of the American Astronomical Society’s Division for Planetary Sciences, has explained that the object can be categorized as both an asteroid and a comet.

2005 QN173: WHAT IS IT?

2005 QN 173

The 2005 QN173 asteroid was first spotted in 2005, and it possesses similar characteristics to any other asteroid. It has a dust cloud 3.2 kilometres wide that surrounds it. According to estimates, the tail of the comet in July 2021 spanned over 7,20,000 kilometres, a little less than twice the distance between the Earth and the Moon.

Researchers point out that the trail is narrow, barely 1,400 kilometres across, which poses a different challenge, saying “this extremely narrow tail indicates that dust is barely floating off the nucleus at extremely low speeds and that gas escaping from the comet is extremely weak.”


This object has a unique composition because it runs contrary to the conditions in the main asteroid belt between Mars and Jupiter. Most comets that are seen in the night sky, accompanied by a tail of vapourising ice and water, are from the more remote regions of the outer solar system, beyond the orbit of Neptune. They heat up as they approach the Sun and release gas and dust due to ice sublimation. As they move around the Sun, their tails become brighter and brighter.

In the meantime, the asteroids and comets in the main belt between Mars and Jupiter have all already lost their ice formation since they are closer to the Sun than they were nearly 4.6 billion years ago.

According to researchers, 2005 QN173, which was discovered in the asteroid belt between Mars and Jupiter, has been releasing ice and dust as it moves, leaving behind ice and dust residues that contradict its existence in the main belt of asteroids. There have been similar objects spotted since 2006 that have captured scientists’ attention since an important part of Earth’s water is thought to have been transported by asteroids from the main asteroid belt through impacts when Earth was formed.

Scientists at the Planetary Science Institute, who are leading researchers in the study of these objects, agreed that the blending of what were formerly thought to be completely separate objects, asteroids and comets, with each other, is what makes them so interesting.

Astronomers contend that studying these active objects provides valuable insights into the origin of life on Earth.

2005 QN173

2005 QN173, which is also known as Asteroid 248370, is just the eighth main-belt asteroid that has been active twice in its history of more than half a million known asteroids.

Hsieh, the lead author that led a paper detailing the discovery, and his colleagues measured that the asteroid had a solid nucleus at its head that measured more than two miles in diameter. Their measurements showed that the tail was over 450 thousand miles long. Taking planet Earth versus the moon into account, this is two times the distance between them.

Even though 2005 QN173 is enormously long, its tail is so thin that, if the whole asteroid was reduced to the length of a football field, its tail would be just 7 inches wide, and its core would be only a millimetre in diameter.

Due to a shorter sun-comet experience, comets develop icy tails, which are derived from the cold outer solar system around Neptune, while asteroids originate from the hot solar system around Jupiter. Comets have elongated orbits and rarely come close to the sun due to their extreme distance from the sun.

Asteroids, by contrast, spend a great deal of time in the sterile inner solar system near Jupiter, where they can still be found today, having spent around 4.6 billion years there.

This implies that since these objects are relatively close to the sun, any ice in them has likely been dispersed by now. Yet, an increasing number of asteroid families continues to defy this notion.

Known as 2005 QN173, the asteroid orbits the sun just like any other asteroid, but most of these rocks do not undergo great changes as they circle around. Research suggests that’s not the case for 2005 QN173, first spotted in 2005 (hence the name), according to new research. This object resembles a comet, shedding dust as it moves and bearing a long, thin tail, pointing to ice particles vaporizing quickly into space – even though comets typically follow elliptical paths that periodically approach and retreat from the sun.

As an asteroid with a cometlike orbit, it may be ice-capped and emit dust into space, which would be the characteristics of a comet, according to lead author Henry Hsieh, a planetary scientist at the Planetary Science Institute and there is an intriguing duality and blurring of boundaries between two previously thought of as two completely separate types of objects – asteroids and comets – which contributes to their fascination. 

2005 QN 173

While the object possesses comet-like characteristics, its orbit is that of an asteroid: It loops around the sun once every five years between Mars and Jupiter in the outer portion of the asteroid belt.

An astronomer looking through data gathered by the Asteroid Terrestrial Impact Last Alert System (ATLAS) survey in Hawaii on July 7 noticed that the object appeared to have a tail. Additional observations were made at Lowell Observatory in Arizona by a telescope that discovered the feature. Following the latest observations made by Zwicky, scientists decided to check previous observations made by other facilities. These images, gathered by the Zwicky Transient Facility in California, revealed another tail on June 11.

On May 14, the object had made its closest approach to the sun, a process known as perihelion, or perihelion being the closest point to the sun. (When a close approach of a comet towards the sun is much more dramatic  and exaggerating than that of an asteroid in the main belt, every object orbiting the sun moves closer and farther away from it over time. For instance, Earth’s perihelion falls early in the month of  January.)

In the meantime, other scientists examined observations of 2005 QN173 made by the Dark Energy Camera in July 2016, the last time the object was near perihelion, and lo and behold, they also detected a tail and really theses space stuffs are actually very interesting.

Around perihelion, frozen ice becomes gas as its temperature rises, mimicking a comet’s profile: the sun’s increasing heat turns ice into gas. The typical comet spends it’s most of its time on its way to the sun, not close enough to the sun to perform its activities.

Researchers have found that most comets come from the outer solar system, beyond Neptune’s orbit, and spend most of their lives there, with their highly elongated orbits only bringing them close to Earth for short periods, Hsieh said. During those periods when comets lie close enough to the sun, the ice below heats up and sublimates, releasing gas and dust, giving them the fuzzy appearance, and sometimes stunning tails, that comets have. 

It’s one of only 20 “main-belt comets” suspected out of half a million objects among the asteroid belt and  of the half-million objects in the belt examined until now, and eight of these have been confirmed to be active multiple times by scientists.

2005 QN 173

New research includes old measurements retrieved from the archives of various instruments collected between 2004 and 2020 at times when the comet wasn’t active, with the intention of better understanding the comet itself. As stated in the statement, these observations suggest the comet’s head is approximately 2 miles (3 km) in diameter.

In addition, the scientists analyzed fresh observations made this July and August by a variety of instruments to better understand the activity of the strange main-belt comet. The researchers were able to measure the tail of the body, which measured approximately 450,000 miles (720,000 kilometres) in length. The distance between the Earth and the Moon is about half that distance.

Although the tail is massive in length, it is not all that wide, which proves to be yet another puzzle for scientists.

According to Hsieh,  he believes that because  of the extremely narrow tail, the dust particles are barely floating off the comet’s nucleus at extremely slow speeds. Also, the gas escape from the comet is extremely weak, indicating that very little dust is being released to space by the comet.

Hsieh said that because of the slow speed, dust should normally have a hard time escaping from the nucleus itself due to its gravity, so something else might assist with the dust escape. Scientists might be able to explain this with the nucleus spinning so fast that it shoots extra dust into space, but they haven’t obtained enough observations to be sure.

As a result, scientists are marking their calendars for February 2026, when it will be visible from the Southern Hemisphere and will reach the appropriate distance from the sun, at which the object will likely become active again.

Detailed findings of the research are described in a paper accepted to The Astrophysical Journal Letters and freely available as a preprint on; the work will be presented at the American Astronomical Society’s Division for Planetary Sciences conference being conducted virtually this week.

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