Tag Archives: comets

Space rocks: the difference between asteroids, comets, and meteors

Some objects in our solar system don’t orbit the Sun as neatly as planets do. Instead, rocky objects of different sizes and shapes float around our solar system, and sometimes, get really close to Earth and even enter our atmosphere. We give these objects names like shooting stars, asteroids, or comets, but which is which?

Asteroids vs Comets

Image credits: Giulia Forsythe.

Asteroids are essentially rocks that orbit the Sun. Most are small, but some can be pretty big — like Vesta, which measures 525 kilometers across, or Ceres the largest asteroid in our solar system, with a whopping 946-kilometer diameter. Overall, though, asteroids are usually quite small, and their combined mass is approximately equal to (or perhaps even smaller than) that of the Earth’s moon.

Most asteroids can be found in or nearby the Main Asteroid Belt — an area between Mars and Jupiter whose gravitational field keeps the dangerous rocks trapped and keeps them from flying about in the solar system (thanks for that, by the way). There are over a million asteroids larger than 1 kilometer (0.6 miles) in diameter, and millions of smaller ones in the asteroid belt. However, it’s hard to study them because they are basically small rocks with nothing to light them up.

Comets, on the other hand, have ice in their interior, and when they get close enough to the Sun, some of that ice starts melting away. The melting helps form the comet’s tail, along with ionized particles from gas molecules that are excited by the solar radiation. The orbits of comets are abnormal, typically very elongated ellipses that make them come really close to the Sun and then go away for a long time. This is what happens to Halley which can be seen every 75 years from Earth. 

Image Credit & Copyright: Rolando Ligustri (CARA Project, CAST) and Lukas Demetz.

So the main difference between asteroids and comets is in their composition: asteroids are made of metals and rock, whereas comets also contain ice and dust. This can be traced back to where they formed (asteroids generally formed closer to the Sun, where it was impossible to keep their ice).


Trojans are a special group of asteroids that share a planet’s orbit. They are so-called co-orbital objects found near the Lagrange points (points of gravitational equilibrium) of planets or larger moons — the Lagrange points, L4 and L5, to be precise. These regions of equilibrium make it so that a collision with neighboring planets is nearly impossible.

Jupiter has two large groups of trojans, the Trojan Camp and the Greek Camp — yes, astronomers really like wordplay.  The system is in a constant astronomical dance: Jupiter’s gravity pulls the trojans towards it, the Sun (which is much larger but also much farther away) also pulls the trojans, and the result is the swarm rotating in the Lagrange point and never leaving the area.

The time-lapsed animation above shows the movements of the inner planets, Jupiter and both swarms of Trojans (green) during the time period of the Lucy mission. The L4 Trojans lead Jupiter in its orbit and the L5 Trojans follow. Credits: Astronomical Institute of CAS/Petr Scheirich

Believe it or not, Earth has its own trojans as well. One was studied by astronomers, although it doesn’t have a charming name. It’s called 2010 TK7 and it was detected by the Wide-field Infrared Survey Explorer (WISE). 2010 TK7 is thought to be 300 meters wide, but thankfully it is in a stable position not threatening us.

Edgeworth-Kuiper Belt and Oort Cloud

Now, let us focus on the comets’ “home”. Comets are found both in the Edgeworth-Kuiper Belt and the Oort cloud. Those are both very distant regions in the Solar System that are far enough from the Sun to allow solid ice to exist. 

Kuiper Belt and Oort Cloud. Credits: JPL/NASA.

The doughnut-shaped Edgeworth-Kuiper Belt is located beyond Neptune’s orbit. Scientists believe the region is what was left of material to make a planet, but Neptune was more efficient and got the larger stuff to form itself, so the smaller rocks remained there without being massive enough to coalesce.

Pluto and many comets can be found in the Edgeworth-Kuiper Belt. In fact, being beyond Neptune’s orbit and in resonance with it is one of the reasons why it Pluto has lost its classification of a planet. As a consolation prize, Pluto is the largest object in this region.

Meanwhile, the Oort Cloud is much bigger and even more distant. You can think of it as a sort of shell for the solar system, like how a traditional Chinese paper lantern surrounds a candle. The cloud is technically just a theory because astronomers can’t observe it directly yet, but there is a lot of indirect information that supports its existence. Based on this evidence, the Oort cloud appears to be populated mainly by comets, but there are some asteroids as well. Like the other rocky/icy objects regions, the Oort Cloud is thought to be a remnant of the early Solar System.

The only man-made objects to ever reach distances beyond Neptune are the Voyagers and Pioners spacecraft. Voyager 1 reached over 14,480,000,000 miles from Earth, over 155 times the distance between the Earth and the Sun (called an “astronomical unit”) — and yet this is not even close to the Oort cloud. The 44-year mission would still need to move another 1,845 astronomical units to get there, which will take nearly another 44 years based on its current speed.

New Horizons is the fifth spacecraft to traverse the Kuiper Belt, but the first to conduct a scientific study of this mysterious region beyond Neptune. Credit: NASA/JHUAPL/SwRI/Magda Saina

Shooting stars

So what about shooting stars? These are small bodies called meteors entering Earth’s atmosphere and heating up to the point they become bright. When some of their minerals survive entering the air, the meteorite is the piece of rock left that reaches the ground. 

“Shooting star” is a pretty vague term, and astronomers don’t really like to use it. Instead, they class these objects as either meteors or meteorites. Meteors are rocks that burn up completely before reaching the planet’s surface, whereas a meteorite reaches the surface intact (or at least some part of it does). Meteorites are also smaller than asteroids.

Whenever Earth moves closer to certain asteroids, or when a comet comes near us, the debris can form a meteor shower. When the asteroid or comet passes near us, the debris enters the atmosphere and burns. Most of the debris is as tiny as blueberries, in fact, Earth is bombarded by 5,200 metric tons of micrometeorites (smaller than 1 millimeter) a year, but because they are so small they aren’t a threat.

Since we are orbiting the Sun, we get close to the same location every year, so we have periodic meteor showers like Orionids, Geminids, and many others named after the constellation they will appear at. It is easier to see the showers under a dark sky, without city lights to interfere. Also, depending on whether the phenomenon will happen near the horizon or not, you may find trouble with buildings blocking your view.

Perseid meteor shower, Wednesday, Aug. 11, 2021, in Spruce Knob, West Virginia.

In the end, the differences between the rocks aren’t so difficult, right? The comet is icy different from the asteroids. Comets are periodic and can be seen every 80 years or so. Many asteroids are near Jupiter who keeps most of them there – phew. Meteors are small objects that enter the atmosphere and if some of them survive, the remains are meteorites.

Comets have a heavy metal atmosphere

Using data collected by the Very Large Telescope (VLT) a team of astronomers has discovered iron and nickel in the atmosphere of around 20 different solar system comets–including some located far away from the Sun.

These findings will come as a surprise to astronomers because even though such heavy metals have been known to exist in solid form within comet interiors before, the vapour of such elements has only previously been associated with cometary atmospheres in hot environments.

This is the first time such vapour has been seen in the cooler atmospheres of comets that exist far from a star and could indicate some previously unknown mechanism or material on the surface of comets.

“It was a big surprise to detect iron and nickel atoms in the atmosphere of all the comets we have observed in the last two decades, about 20 of them, and even in ones far from the Sun in the cold space environment,” says Jean Manfroid, of the University of Liège, Belgium.

ESO/L. Calçada, SPECULOOS Team/E. Jehin, Manfroid et al.

This wasn’t the only surprise the team found, however. The Belgian astronomers–who have been studying comets with the VLT for 20 years–observed nickel and iron in the atmosphere of the comet in equal amounts.

Generally, iron is about ten times more abundant in the solar system than nickel, and comets are believed to be material left over from the formation of planetary bodies within the solar system. That means it’s something of a mystery why the comets the team observed should have such a relatively large abundance of nickel.

“Comets formed around 4.6 billion years ago, in the very young Solar System, and haven’t changed since that time. In that sense, they’re like fossils for astronomers,” Emmanuel Jehin, also from the University of Liège. This discovery went under the radar for many years.”

Manfroid and Jehin are two of the authors of a paper published in the latest edition of the journal Nature documenting the team’s findings. And that isn’t the only research revealing metal in the atmosphere of such a body published in Nature this month.

The discovery is accompanied by the revelation that a separate team of researchers, this time located in Poland, has also found traces of nickel vapour in the atmosphere around the interstellar visitor 2l/Borisov.

This comet may sound familiar as it made headlines in 2019 when it became only the second object found within the solar system which originated from outside our planetary system.

A paper detailing this second finding is also published in this month’s Nature.

Heavy Metal Rocks

Astronomers have known for some time that a variety of metals exist within the icy and rocky interiors of comets. There have even been suggestions that spent comets could be mined for precious or useful metals like gold, silver, platinum and iron.

This image features a comet located in the outer reaches of the Solar System: comet C/2016 R2 (PANSTARRS). (ESO/SPECULOOS Team/E. Jehin)

These solid metals within comets were not expected to be found as gases in the body’s atmosphere, though, unless that body is passing within close vicinity to a star.

It is the heat from these close brushes with stars like the Sun that causes solid metals within comets to ‘sublimate’–the process by which solid material changes directly into a gaseous state.

That means that distant comets in the cold environment of space away from the heat of the Sun shouldn’t have heavy metal atmospheres.

Yet, despite this, researchers have now found nickel and iron vapour in the atmospheres of comets up to 480 million kilometres from the Sun. A distance that is three astronomical units, or three times the distance between the Sun and the Earth.

In order to make this discovery, the team employed the technique of spectroscopy which reveals the signatures of specific chemical elements and the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on the VLT to assess the chemical composition of comets’ atmospheres.

The spectral lines of nickel and iron found by the team in comets’ atmospheres were extremely faint, which leads them to believe that the reason such elements have been missed in past is due to their tiny abundance. The team says that for every 100kg of water in the atmosphere of the comets they studied there is just one gram of iron and nickel respectively.

The Belgian astronomers believe that the equal amounts of iron and nickel together with the sublimation at low temperatures means there is something undiscovered at the surface of the comets they studied.

An artist’s impression of the completed ELT, which could play an important role in the investigation of cometary atmospheres. (ESO)

“Usually there is 10 times more iron than nickel, and in those comet atmospheres we found about the same quantity for both elements,” explains Damien Hutsemékers, also a member of the Belgian team from the University of Liège.”We came to the conclusion they might come from a special kind of material on the surface of the comet nucleus, sublimating at a rather low temperature and releasing iron and nickel in about the same proportions.”

The team intends to attempt to use new telescope technology such as the Mid-infrared ELT Imager and Spectrograph (METIS) on ESO’s upcoming Extremely Large Telescope (ELT)–currently under construction in the Atacama Desert region of Northern Chile– to discover what this material is.

The findings of this team are accompanied by the revelation that nickel vapour has also been discovered in the atmosphere of 2I/Borisov.

2I/Borisov: The Interstellar Intruder that keeps giving

The discovery that metal is also present in the atmosphere of the interstellar visitor 2I/Borisov was made by a team of astronomers in Poland. The team also used the VLT to catch a glimpse of the interstellar comet as it passed through the solar system.

The data collected with the VLT’s X-Shooter spectrograph revaled nickel vapour in the cold envlope surround 2I/Borisov.

ESO/L. Calçada/O. Hainaut, P. Guzik and M. Drahus

The discovery marks another surprise for astronomers, as again it details the discovery of sublimated heavy metals in a cold atmosphere.

“At first we had a hard time believing that atomic nickel could really be present in 2I/Borisov that far from the Sun,” says Piotr Guzik, the Jagiellonian University, Poland, a co-author on this second study. “It took numerous tests and checks before we could finally convince ourselves.”

This latter study shows that nickel was not uniquely present during the formation of our solar system, but as it can be seen in a comet from another planetary grouping, it may well be common in many such conglomerations.

 “All of a sudden we understood that gaseous nickel is present in cometary atmospheres in other corners of the Galaxy, Michał Drahus, also from the Jagiellonian University and another of the paper’s co-authors, says.

In unison, both these studies indicate that the comets of this solar system and the interstellar visitor 2I/Borisov share many similarities. Dahus adds: “Now imagine that our Solar System’s comets have their true analogues in other planetary systems — how cool is that?”

Jehin, meanwhile, believes these studies could inspire future research into cometary bodies and their atmospheres, and a re-examination of data already collected.

“Now people will search for those lines in their archival data from other telescopes,” the University of Liège researcher concludes. “We think this will also trigger new work on the subject.”

Comet NEOWISE Comes into Focus for a Close-up

Time is running out to catch a glimpse of the comet NEOWISE. The comet — the brightest object to grace the skies over the Northern Hemisphere in 25 years — will soon disappear from view. At least as far as the naked eye is concerned. Fortunately, the Hubble Space Telescope is on hand to capture stunning images of the comet — discovered on March 27th by NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope during its mission to search for near-Earth objects. 

Hubble Captures a stunning close-up Comet NEOWISE (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI))
Hubble Captures a stunning close-up Comet NEOWISE (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI))

The image taken by Hubble on 8th August — which represents the closest ever taken of the comet since it first lit up the sky — shows NEOWISE as it sweeps past the Sun. This is the first time that astronomers have managed to capture such a bright object as it passes our star.

Hubble snapped the object as it rapidly makes its way out of the solar system, with it not scheduled to return for 6,800 years. The comet caused a stir amongst amateur star watchers and the general public as it was visible with the naked eye under the right conditions.

“Nothing captures the imagination better than actually seeing its tails stretching into the sky in person,” Qicheng Zhang,  a graduate student studying planetary science at Caltech, Pasadena, CA, who has been heavily involved in the study of NEOWISE. “The comet last came around about 4,500 years ago. This was around when the Egyptian pyramids were being built.”

“My research area covers comets and their evolution under solar heating,” Zhang explains to ZME Science. “I also like to keep track of potentially bright comets to actually see in the sky, which included this particular comet.”

Colour image of the comet taken by Hubble on 8 August 2020 within the frame of a ground-based image of the comet that was taken from the Northern Hemisphere on 18 July 2020. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and Z. Levay)
Colour image of the comet taken by Hubble on 8 August 2020 within the frame of a ground-based image of the comet that was taken from the Northern Hemisphere on 18 July 2020. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and Z. Levay)

The image shows NEOWISE’s halo of glowing gas and dust illuminated by light from the Sun surrounding the icy nucleus of the comet, too small at little more than 4.8km across to be fully resolved by the telescope. In contrast, the dust halo that surrounds the comet’s heart is too large to be fully resolved by the space telescope, with its diameter measuring an estimated 18,000 km.

Zhang points out that as NEOWISE moves past the Sun, there is a chance we could still glimpse its icy core: “As the comet recedes from the Sun, the dust with clear and reveal the solid nucleus currently buried within, providing an opportunity to directly observe the source of all the activity that made the comet impressive last month.”

Let’s Stick Together: Why NEOWISE Survived and ATLAS Didn’t

Previous attempts to capture other bright comets as they pass the Sun have failed because these objects have disintegrated as they passed too close to the star. This break-up is driven by both the incredible heat of the Sun causing the icy heart of the comets to fragment, and the powerful gravitational influence of our star further pulling the comets apart. 

The most striking example of this came shortly after the discovery of NEOWISE, with the observation of the fragmentation of the comet ATLAS in April this year. The collapse of this comet — believed at the time to offer our best look at such an icy body — in 30 separate pieces was also caught by Hubble. 

ATLAS feels the heat. The comet, discovered in December 2019 breaks up under the intense heat and gravitational influence of the Sun ( NASA/ ESA/ STScI/ D. Jewitt (UCLA))
ATLAS feels the heat. The comet, discovered in December 2019 breaks up under the intense heat and gravitational influence of the Sun ( NASA/ ESA/ STScI/ D. Jewitt (UCLA))

Unlike comet ATLAS, itself only discovered in December 2019, comet NEOWISE somehow survived its close passage to the Sun–with its solid, icy nucleus able to withstand the blistering heat of the star– enabling Hubble to capture the comet in an intact state.

As the latest image of NEOWISE shows, however, it is not going to escape its encounter with the Sun completely unscathed. Jets can clearly be seen blasting out in opposite directions from the poles of the comet’s icy nucleus. These jets represent material being sublimated–turning straight from a solid to a gas skipping a liquid stage–beneath the surface of the comet. This ultimately results in cones of gas and dust erupting from the comet, broadening out as the move away from the main body, forming an almost fan-like shape.

This animation composed of three Hubble images of NEOWISE shows clearly jets of sublimated material erupting from the comet forming fan-like shapes. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and M. Kornmesser))

Far from being just a stunning image of a comet as it passes through the inner solar system, the Hubble images stand to teach astronomers much about NEOWISE and about comets in general.

“It’s a fairly large comet that approached closer to the Sun than the vast majority of comets of its size do,” Zhangs says. “These factors contributed to its high brightness and also made it a good candidate to see how solar heating alters comets, as the effects are theoretically amplified by its close approach to the Sun.

“That information is useful for interpreting observed characteristics of other comets that don’t approach as close to the Sun, and thus where the changes are more gradual and might not be directly observable.”

In particular, the colour of the comet’s dust halo, and the way it changes as NEOWISE moves away from the Sun, gives researchers a hint as to the effect of heat on such materials. This could, in-turn, help better determine the properties of the dust and gas that form what is known as the ‘coma’ around a comet.

“We took images to show the colour and polarization of the dust released by the comet, to get a sense of what it looks like before it’s broken down by sunlight,” says Zhang. “That analysis is ongoing–and will take a while to do properly–but as the published images show, we’ve caught at least a couple of jets carrying dust out from the rotating nucleus.”

The information contained in the Hubble data will become clearer as researchers delve deeper into it. But, the investigation of NEOWISE’s cometary counterparts will benefit from future telescope technological breakthroughs. This will include spotting comets much more quickly and thus, further out from the Sun.

“When this comet was discovered by the NEOWISE mission, it was only 3 months from its close approach to the Sun and had already begun ramping up activity,” Zhang says. “More sensitive surveys, like the upcoming Legacy Survey of Space and Time (LSST) at the Rubin Observatory, will allow us to find such comets much earlier before they become active, enabling us to track them throughout their apparition from beginning to end.

“This will facilitate a more precise comparison of what changes the comets undergo during their solar encounter.”

The next step in Zhang’s research, however, will be comparing the qualities of comet NEOWISE to other such objects, particularly a recent interstellar visitor to our solar system: “This is one of three comets I have observed or have planned to observe in this manner, the others being the interstellar comet 2I/Borisov and the distant solar system comet C/2017 K2 (PANSTARRS),” the researcher concludes. “My team of collaborators and I will be evaluating all three comets to see how their differences in present location and formation/dynamical history translate into differences in physical properties.”

Ancient carvings show comet struck Earth, triggering mini Ice Age

Scientists have translated famous carvings found in Turkey, and they now believe it is indicative of a comet which struck Earth around 10,950 BCE — the same time a small ice age kicked off on Earth, changing the planet forever.

The carvings depict a dramatic event which shaped mankind and Earth for over a thousand years. Image credits: Alistair Coombs.

Some 10,950 years ago, the Younger Dryas period started to kick in. It was a huge disturbance to what was a generally warming Earth, sending the planet into an unexpected, thousand-year-long mini Ice Age. It was then that mankind started taking the first solid steps towards a true civilization, potentially as a result of this change in climate. This cold period has been studied to great extent, but we don’t really know what caused it. A comet impact is one of the leading hypotheses, but no evidence of a comet was ever found — until now.

Although it isn’t physical evidence, it’s still pretty intriguing. Researchers analyzed glyphs from a pillar known as the Vulture Stone, which suggest that a bunch of comet fragments hit the Earth some 13,000 years ago, which fits the timeline perfectly. A telling image is that of a decapitated man, which symbolizes great tragedy and loss of life.

“I think this research, along with the recent finding of a widespread platinum anomaly across the North American continent virtually seal the case in favour of [a Younger Dryas comet impact],” lead researcher Martin Sweatman of Edinburgh University told Sarah Knapton from The Telegraph“Our work serves to reinforce that physical evidence. What is happening here is the process of paradigm change.”

The pillar was located in Gobekli Tepe in southern Turkey, one of the most exciting archaeological sites in human history and the earliest temple we’ve ever found, established over 11,000 years ago (potentially much more), 6,000 years before Stonehenge. Although the details of the structure’s function remain a mystery, there is growing evidence indicating that the site served as an observatory — aside from a site of worship.

“It appears Gobekli Tepe was, among other things, an observatory for monitoring the night sky,” Sweatman told the Press Association. “One of its pillars seems to have served as a memorial to this devastating event – probably the worst day in history since the end of the Ice Age.”

Computer algorithms showed that the animal carvings fit with the shape of astronomical constellations. Image credits: Martin Sweatman and Stellarium.

The Vulture Stone had been found decades go, but the inscriptions on it still puzzled scientists. Now, the Edinburgh team believes they’ve found the key: the symbols are actually constellations, which helped researchers put a date on the symbols as well. They used computer models to match the carvings of animals to patterns fo stars, confirming firstly that the shapes fit the astronomical situation of the time, and secondly, that the 10,950 BCE date fits the theory. The date also matches cores from Greenland, which pinpoint the Younger Dryas period as beginning around 10,890 BCE. A few decades is a more than acceptable error rate when working at this scale.

But it gets even more interesting. Computer models indicated that the comet would have been visible in the night sky for thousands of years. According to the models, the comet entered the solar system more than 20,000 years ago and was likely visible for most of this time. Brighter and brighter, generation after generation until it finally struck our planet. Considering the obvious symbolism humans attributed to it and the massive impact the comet had on the planet, it’s easy to understand why the event was given such a great importance and was immortalized on the Vulture Stone. For thousands of years, the Gobekli Tepe priests guarded the stone and probably told the story of the bright rock in the sky that came crashing down on Earth.

“If you consider that, according to astronomers, this giant comet probably arrived in the inner solar system some 20 to 30 thousand years ago, and it would have been a very visible and dominant feature of the night sky, it is hard to see how ancient people could have ignored this given the likely consequences.”

This isn’t the first time archaeology has given indications on such ancient events. Many paleolithic cave paintings and artifacts give indications on catastrophic, or otherwise significant astronomic events. It’s not exactly the most reliable evidence in the world, but when you can correlate computer models of comets with carvings from 13 millennia ago — that’s got to feel good.

The research has been published in Mediterranean Archaeology and Archaeometry.

Remembering Edmond Halley!


November 8 – it is the birthday of the famous English astronomer, geophysicist, mathematician, meteorologist, and physicist who is best known for computing the orbit of the eponymous Halley’s Comet.

What is Halley’s Comet?

Halley’s Comet or Comet Halley officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years.

Halley is the only known short-period comet that is clearly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime


One rather pretentious question that comes up when talking about comets is how on earth did it start orbiting around the sun in the first place and how long has it been orbiting?

Where do comets come from?

Comets come from two major areas of our solar system: the Kuiper Belt and the Oort  Cloud. Each of these regions contains billions of comets, but they’re so spaced apart that they get no closer to each other than Earth does to the sun.


How long has it been orbiting?

It is thought that Halley has been in its current orbit for around 60,000 to 200,000 years. However, it is very difficult to calculate any comet’s previous orbit with accuracy due to the fact that the orbit is always altered once it passes close to the Sun.


When will we see it again?

The last known sighting of the comet was in 1986 and the earliest it will come close enough to see is 2061!


The Halley’s Lunar and Martian Crater.

Among other things named honoring Halley is the Halley’s crater on the moon and on Mars.


Halley’s crater. ( Upper left )


PC: NASA, opencourse, hitrecord, ESA

Comet 67P/Churyumov-Gerasimenko. Credit: AFP/ESA/Rosetta/MPS

Comets stink: space probe finds odor of urine, rotten eggs and alcohol

Ever wondered how a comet smells? Well even if you could, you might wish you hadn’t: rotten eggs, horse pee, alcohol and bitter almonds are just a couple of the fragrances you could sniff.

A smelly comet

Comet 67P/Churyumov-Gerasimenko. Credit: AFP/ESA/Rosetta/MPS

Comet 67P/Churyumov-Gerasimenko. Credit: AFP/ESA/Rosetta/MPS

These volatile compounds were detected by  a mass spectrometer aboard the Rosetta probe which is currently studying the Comet 67P/Churyumov-Gerasimenko. The mass spectrometer analyzed the chemical signature of  gas given off by the “coma,” the comet’s head, and found numerous unexpected compounds. The Rosina team believed only the most volatile molecules — carbon dioxide and carbon monoxide — would be released as the comet’s icy surface started slowly to warm, but they were in for a surprise.

“The perfume of 67P/C-G is quite strong, with the odour of rotten eggs (hydrogen sulphide), horse stable (ammonia) and the pungent, suffocating odour of formaldehyde,” said Kathrin Altwegg, Rosina’s chief scientist.

“This is mixed with the faint, bitter, almond-like aroma of hydrogen cyanide.

“Add some whiff of alcohol (methanol) to this mixutre, paired with the vinegar-like aroma of sulphur dioxide and a hint of the sweet aromatic scent of carbon disulphide, and you arrive at the ‘perfume’ of our comet.”

Project leader Kathrin Altwegg of the University of Bern said the aroma will get stronger as 67P gets closer to the sun, causing it to release more gas and form the coma characteristic of comets. On August 13 next year, the comet and Rosetta will be 185 million kilometres from the Sun, their closest approach to our star.

Comets from another solar system

Image: Telegraph

In other comet-related news, astronomers have identified over 500 exocomets – comets swarming through solar systems other than our own. The discovery was made after more than  1,000 separate observations were programmed between the years of 2003 and 2011 through the HARPS instrument, which is a part of the ESO 3.6-meter telescope at the La Silla Observatory in Chile.

Flavein Kiefer, research team leader, says “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”