Tag: comets

NASA releases numerous images of interstellar Comet 3I/Atlas

9:50 am

Comet 3I/Atlas as seen by Mars Reconnaissance Orbiter

NASA yesterday released a slew of images of interstellar Comet 3I/Atlas, taken by numerous in-space probes at Mars and elsewhere.

The picture to the right, cropped to post here, is probably the one with the most detail, taken by Mars Reconnaissance Orbiter (MRO) from Mars orbit on October 2, 2025. In addition, images were captured by:

None of these pictures show the comet in any great detail. All however confirm once again that it is a comet, not an interstellar alien spacecraft as some idiots in academia have been proposing wildly. The Maven observations in ultra-violet wavelengths for example identified hydrogen and other isotopes coming off the comet as it is heated by the Sun. MRO’s image to the right once again showed the comet’s coma and tail.

Above all, these observations were great engineering experiments for all the science teams, demonstrating that they could point their instruments in an unplanned direction and capture a very faint object quite far away.

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Europe’s Trace Gas Orbiter circling Mars gets images of interstellar Comet 3I/Atlas

4:47 pm

Interstellar Comet 3I/Atlas
Click for movie.

Using Europe’s Trace Gas Orbiter (TGO) that is in orbit around Mars, engineers have obtained images of the interstellar Comet 3I/Atlas.

The image to the right is a screen capture of the last image in a movie they created from all the pictures. I have added the arrow to indicate the comet, which underlines the fact that these images really don’t tell us that much about the comet itself. It is hardly more than a few pixels across, with no real detail resolved. However, the data has still been found useful.

Until September, figuring out the location and trajectory of 3I/ATLAS relied on Earth-based telescopes. Then between 1 and 7 October, ESA’s ExoMars TGO turned its eyes towards the interstellar comet from its orbit around Mars. The comet passed relatively close to Mars, approaching to about 29 million km during its closest phase on 3 October.

The Mars probe got about ten times closer to 3I/ATLAS than telescopes on Earth and it observed the comet from a new viewing angle. The triangulation of its data with data from Earth helped to make the comet’s predicted path much more accurate.

While the scientists initially anticipated a modest improvement, the result was an impressive ten-fold leap in accuracy, reducing the uncertainty of the object’s location.

All the data continues to confirm that 3I/Atlas is nothing more than comet, though like all comets unique in its own way. This refined location data will also improve the on-going observations of Europe’s Jupiter probe Juice, presently on its way to Jupiter and in the best position to see 3I/Atlas.

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Comet C/2025 K1 — NOT interstellar 3I/Atlas — breaks up as it passes closest to the Sun

12:10 pm

The broken apart nucleus of Comet 3I/Atlas
Click for original image.

CORRECTION: I originally posted this story thinking the comet imaged was the interstellar Comet 3I/Atlas. It is not. It is a different one. I have changed to post below to correct my error.

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Sometime on November 11, 2025, the nucleus of interstellar C/2025 K1 broke into three pieces as it passed through its closest and hottest point to the Sun.

The image to the right, cropped and reduced to post here, comes from images of the break-up taken by the Virtual Telescope project, which gathers data from many small telescopes remotely.

From the first link, translated by Google from the Italian:

Its trajectory led it, in early October, to pass through a point of minimum distance from the Sun (perihelion) quite close to our star, about 0.33 astronomical units, just outside the orbit of Mercury. Because of this “short” distance from the Sun, it experienced high solar irradiation, which caused a significant increase in the temperature of the surface and internal layers of the nucleus.

These are precisely the conditions under which a “breakup” event is expected: depending on the internal properties of the nucleus—namely, its porosity, its state of cohesion, its composition, and the percentage of ice—it is possible that the increase in temperature could cause significant “outgassing,” a sudden and violent outflow of gaseous and dusty material, and the consequent fragmentation of the nucleus, sometimes into a few pieces of roughly similar size, sometimes into a cloud of fragments and debris that spread along the trajectory of the original comet.

…”From an initial quick analysis of the images, we can confirm that there are certainly two fairly similar pieces, whose brightness maxima are separated by approximately 2,000 km (distance projected on the star field); “Furthermore, we can intuit the presence of a third, smaller and fainter fragment to the left of the pair,” observes Mazzotta Epifani.

It will be interesting to see if the same thing happens to interstellar Comet 3I/Atlas as it makes its own pass close to the Sun.

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Update on the plans to observe interstellar Comet 3I/Atlas using interplanetary spacecraft

10:16 am

Link here. The key take-away is that nothing is being repurposed to attempt to fly to Comet 3I/Atlas. Instead, as expected the science teams for all the Mars orbiters will turn their instruments to the comet when it is at its closest point to Mars, about 19 million miles away.

Don’t expect any Earth-shattering revelations:

The cameras on these spacecraft were designed to photograph the surface of Mars from Mars orbit, and won’t be able to pick out much detail on such a relatively small comet 30 million km away. But the cameras may be able to capture images of its long tail and also gather data that scientists can use to find out more about what 3I/ATLAS is made of.

Some spectroscopic data will be obtained, but it likely will not be much better than what Webb and other Earth-based telescopes have gotten already.

Similarly, the science team for Europe’s Juice mission, on its way to Jupiter, will take a look, but the distances and orbital positioning will likely limit what it can detect as well.

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Gemini South telescope captures Comet 3I/Atlas’s growing tail

1:43 pm

Comet 3I/Atlas
Click for original image.

Using the Gemini South telescope in Chile, astronomers have taken new images of interstellar Comet 3I/Atlas as it moves through the solar system, this time capturing the slow growth of its tail.

The picture to the right, cropped, reduced, and sharpened to post here, shows that tail trailing off to the left. The stars are streaks because it required four exposures in different wavelengths to produce the image. The comet was held steady while the stars shifted after each exposure.

In the images captured during the session, the comet displays a broad coma — a cloud of gas and dust that forms around the comet’s icy nucleus as it gets closer to the Sun — and a tail spanning about 1/120th of a degree in the sky (where one degree is about the width of a pinky finger on an outstretched arm) and pointing away from the Sun. These features are significantly more extended than they appeared in earlier images of the comet, showing that 3I/ATLAS has become more active as it travels through the inner Solar System.

So far, all the evidence continues to show that though 3I/Atlas has an interstellar origin, it is a relatively ordinary comet, simply unique in the manner all objects of a category are unique. As the scientists pour over the comet’s spectroscopy we might find its make-up is somewhat different than comets from our own solar system, but the data so far suggests that the differences are not likely to be that startling.

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First Hubble images of interstellar comet 3I/Atlas released

5:03 pm

Comet 3I/Atlas, taken by Hubble
Click for original.

An undergraduate student has just released the first pictures taken by the Hubble Space Telescope of the interstellar object 3I/Atlas, confirming that it is a comet as indicated by the earlier image taken by the Gemini North telescope.

One of those images, taken only hours ago, is the inset on the map showing the comet’s route through the solar system to the right. The streaks on the image are either stars or cosmic rays. Though this image is of significantly lower quality than the Gemini North picture, it once again shows both the comet’s nucleus and developing coma.

A preprint [pdf] of a new research paper based on data from both telescopes further confirms this conclusion:

[T]hese results suggest that 3I/ATLAS hosts a coma containing large water ice grains, and that its dust continuum is stable over at least week-long timescales. The spectral characteristics further distinguish 3I from known ultrared trans-Neptunian objects and align it more closely with active Jupiter-family comets.

The last conclusion is very significant. Though the path and speed of this interstellar object says it must come from beyond the solar system, its cometary make-up more resembles comets that reside in the inner solar system. These facts strongly imply that there is at least one other solar systems not very different from our own.

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Viewing Comet Tsuchinshan-ATLAS when it enters the evening sky

9:20 am

Link here. For those living in the northern hemisphere, Comet Tsuchinshan-ATLAS will be bright and visible to the naked eye just after sunset beginning tomorrow.

“As soon as October 11th, ambitious comet spotters may pick up the comet during twilight just above the western horizon,” says Sky & Telescope Contributing Editor Bob King. “Binoculars will help you see the comet throughout its appearance.”

About 40 minutes after sunset on Friday, find a spot with a good view down to the western horizon. The first thing that will catch your eye will be the bright planet Venus, the Evening Star — that’s your starting point. Hold your fist out at arm’s length; the comet is about 2½ fists to Venus’s right. The comet will still look tiny in Friday’s twilight — like a hazy star with a small tail — and will set while twilight is still in progress.

Comet Tsuchinshan-ATLAS (pronounced choo-cheen-SHAHN) will remain visible for the next ten days, with the best viewing likely from October 13th to October 16th.

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Viewing Comet Tsuchinshan-ATLAS

9:02 am

While the newly discovered Comet Tsuchinshan-ATLAS in the past week reached naked eye visibility in the dawn sky, in the next few weeks it will shift into the evening sky on October 11, 2024 while brightening to peak levels.

Although Comet Tsuchinshan-ATLAS will be visible in both hemispheres, the northern one is favored because the comet tracks north. Also, sunsets are getting earlier and twilights shorter, while the opposite is happening in southern latitudes.

Observers should be aware that the Moon will interfere for several nights, from about Oct. 15-20 (full Moon is on Oct. 17th), around the same time the comet climbs out of twilight.

As it begins to fade, the comet will be visible at an increasing height above the horizon each night through the end of October. At its brightest it is expected to be one of the brightest objects in the sky.

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Eruption on comet results in its tail splitting as it brightens by 100x

9:28 am

On July 20, 2023 the Comet 12P/Pons-Brooks suddenly erupted for the first time in almost seven decades, making it a hundred times brighter than normal while splitting its tail in two.

As of July 26, the comet’s coma had grown to around 143,000 miles (230,000 kilometers) across, or more than 7,000 times wider than its nucleus, which has an estimated diameter of around 18.6 miles (30 km), Richard Miles, an astronomer with the British Astronomical Association who studies cryovolcanic comets, told Live Science in an email.

But interestingly, an irregularity in the shape of the expanded coma makes the comet look as though it has sprouted horns. Other experts have also likened the deformed comet to the Millennium Falcon, one of the iconic spaceships from Star Wars, Spaceweather.com reported.

It is believed the tail’s shape is the result of the shape of the comet’s nucleus, which probably had a solid ridge acting as a barrier to material at that point.

The comet, which orbits the Sun every 71 years, will make its closest approach to Earth in the spring of 2024, when it will likely be visible to the naked eye.

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The inexplicable tail of the asteroid Phaethon is from sodium, not dust

9:39 am

For years astronomers have puzzled over the strange behavior of the asteroid Phaethon, which though rocky would still produce a tail like a comet whenever its orbit took it close to the Sun.

New research by astronomers using several space telescopes designed to study the Sun has determined that this tail is made of sodium, not dust as previously believed, which also suggests that many of the other “comets” these solar telescopes have detected close to the Sun might instead be asteroids like Phaeton.

Hoping to find out what the tail is really made of, Zhang looked for it again during Phaethon’s latest perihelion in 2022. He used the Solar and Heliospheric Observatory (SOHO) spacecraft — a joint mission between NASA and the European Space Agency (ESA) – which has color filters that can detect sodium and dust. Zhang’s team also searched archival images from STEREO and SOHO, finding the tail during 18 of Phaethon’s close solar approaches between 1997 and 2022.

In SOHO’s observations, the asteroid’s tail appeared bright in the filter that detects sodium, but it did not appear in the filter that detects dust. In addition, the shape of the tail and the way it brightened as Phaethon passed the Sun matched exactly what scientists would expect if it were made of sodium, but not if it were made of dust.

Knowing these new facts, it might make it possible to map the asteroids that orbit very close to the Sun but are hard to detect optically using standard telescopes because of the Sun’s brightness. Instead, astronomers might be able to map them using these solar telescopes.

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Newly discovered comet could be brightest object in sky in October ’24

9:02 am

Comet Tsuchinshan-ATLAS, discovered simultanuously by telescopes in China and South Africa, has the possibility of becoming brightest object in sky when it makes its closest approach to the Earth in October 2024.

As viewed from Earth, the comet may be as luminous as the brightest stars in the sky during its upcoming flyby, according to EarthSky. This is brighter than the green comet C/2022 E3 that just passed by Earth in January. That comet had a brightness of around magnitude +4.6, just visible to the naked eye. The new comet may have a brightness of magnitude 0.7, potentially peaking at magnitude -5, similar to Venus at its brightest.

The comet is presently between Jupiter and Saturn. Its 80,000 year long orbit will make its next close approach to the Sun on September 28, 2024.

Whether this will become a naked eye object of beauty of course remains totally uncertain. Its orbit, which appears stable but with rare swings past the Sun, suggests it will have lots of ice to sublimate into a bright tail. This also suggests the comet will survive this close approach without breaking up, since it has likely done this frequently in the past.

At the same time, the brightness of comets is unpredictable. We won’t really know how bright it will become until it is on it approach to the Sun, in the early fall of 2024.

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Viewing the Green Comet

9:12 am

Link here. Though there has been much hype about this comet, which has a 50,000 year orbit as well as an unusual color, it really doesn’t deserve that hype because it will barely become bright enough to be visible to the naked eye.

Nonetheless, in the northern hemisphere it will be in the sky all night during the month of February, so if you are in a good dark sky location, you should try to spot it. On February 1st it will be closest to Earth.

According to In-the-Sky, from New York City C/2022 E3 (ZTF) is circumpolar, meaning it is permanently above the horizon, and should therefore be visible for most of the night. It will be visible in the Camelopardalis constellation while at perigee, a large but faint area of sky devoid of bright stars and located close to the north celestial pole.

The comet will become visible at around 6:49 p.m. EST (2349 GMT) on Wednesday (Feb. 1) when it will be 49 degrees over the northern horizon. C/2022 E3 (ZTF) will climb to its highest point in the sky, 58 degrees over the northern horizon, at around 9:46 p.m. EST (0246 GMT). Following this it will disappear in the dawn light at around 5:57 a.m. EST (1057 GMT) on Feb. 2 while at around 30 degrees over the horizon to the north.

The link provides more information for finding it, which will likely be seen best with binoculars.

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Comet K2: big and doing unexpected things

9:19 am

Link here. The article provides a nice overview of the observations so far of this very distant but very large comet making its suspected first close approach to the Sun this week, though still beyond the orbit of Mars and barely visible to amateurs.

K2 was first sighted in May 2017 at a much farther distance from the Sun than most comet discoveries. It had developed a coma much earlier than expected, which scientists now think came from from carbon monoxide.

“Carbon monoxide has been detected in other comets closer to the sun, although in much lower quantities than water. Carbon monoxide is very volatile and hard to freeze into a solid.” Jewitt and his colleagues theorized that as the comet slightly warmed while moving toward the planetary region of the solar system, the carbon monoxide ice near its surface turned into a gas that streamed into the vacuum of interplanetary space like constant wind. This wind stirred up dust particles from the comet’s surface, creating the round puffball-like coma.

But it took several failed attempts to measure the chemical composition of the comet to confirm the theory, Jewitt said. The team finally succeeded last year when the comet reached the orbit of Jupiter, and the scientists finally spotted carbon monoxide in the heart of the comet.

Comet K2 also did not develop a comet tail as expected. This appears to be because the particles in its coma are much larger than expected, something that at present is a complete puzzle.

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Citizens enlisted to find changes to Comet 67P/C-G during Rosetta mission

9:56 am

The European Space Agency (ESA) and Zooniverse have partnered to create a new citizen science project, allowing anyone to more easily review the archive of high resolution photos taken by Rosetta of Comet 67P/C-G and look for changes that occurred during the probe’s mission to the comet.

“The Rosetta archive, which is openly accessible to scientists and the public, contains a vast amount of data collected by this extraordinary mission that have only been partially explored,” says Bruno Merín, head of ESA’s ESAC Science Data Centre near Madrid, Spain. “In the past few years, astrophotographers and space enthusiasts have spontaneously identified changes and signs of activity in Rosetta’s images. Except for a few cases, though, it has not been possible to link any of these events to surface changes, mostly due to the lack of human eyes sifting through the whole dataset. We definitely need more eyes!”

This is why ESA partnered with the Zooniverse, the world’s largest and most popular platform for people-powered research. The new Rosetta Zoo project presents a particular set of data: pairs of images collected by Rosetta’s OSIRIS camera showing Comet 67P’s surface before and after perihelion.

Volunteers are invited to view images of roughly the same region side by side and identify a variety of changes, from large-scale dust transport to comet chunks that moved or even vanished. Sometimes this may require zooming in or out a few times, or rotating the images to spot changes on different scales, getting up close and personal with the iconic comet.

Using Rosetta Zoo will require no software, nor will anyone need to register to use it. You simply go to the website and begin comparing pairs of images, for as long as you wish, marking differences you spot of the same locations.

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Astronomers confirm comet with largest nucleus ever found

9:29 am

Using the Hubble Space Telescope astronomers determined that the nucleus of Comet Bernardinelli-Bernstein (C/2014 UN271) is about 80 miles wide, making it the largest comet on record.

The estimated diameter is approximately 80 miles across, making it larger than the state of Rhode Island. The nucleus is about 50 times larger than found at the heart of most known comets. Its mass is estimated to be a staggering 500 trillion tons, a hundred thousand times greater than the mass of a typical comet found much closer to the Sun.

The behemoth comet, C/2014 UN271 (Bernardinelli-Bernstein) is barreling this way at 22,000 miles per hour from the edge of the solar system. But not to worry. It will never get closer than 1 billion miles away from the Sun, which is slightly farther than the distance of the planet Saturn. And that won’t be until the year 2031.

The previous record holder is comet C/2002 VQ94, with a nucleus estimated to be 60 miles across. It was discovered in 2002 by the Lincoln Near-Earth Asteroid Research (LINEAR) project.

This measurement does have a great deal of uncertainty, as Hubble cannot yet resolve the nucleus, and thus its diameter was determined by computer models based on the size of the comet’s coma, or surrounding atmosphere.

The comet itself has an orbit 3 million years long, which means it has zipped into the inner solar system many many times. The reason its nucleus remains so large is because its orbit never gets that close to the Sun, so its material does not get burned off so much with each perihelion. That it exists suggests there could be many such large comets which never dip close to the Sun.

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Orbit of biggest comet ever detected refined

10:59 am

Astronomers have now been able to better refine the orbit and size of Comet Bernardinelli-Bernstein, comet with the largest nucleus ever detected.

A new analysis, led by Bernardinelli and Bernstein themselves, found that the comet nucleus is around 150 km wide, based on its brightness. If so, that makes it the largest comet ever discovered, by quite a margin. Most are only a few kilometers to several dozen kilometers wide, while some particularly big ones, like Hale-Bopp, may be up to 80 km (50 miles) wide. The previous record-holder, Sarabat’s Comet of 1729, has been estimated at about 100 km wide.

The team was also able to calculate the orbit of Comet BB in more detail. This object is on an incredibly long round trip into and out of the solar system – at its most distant point, some 1.5 million years ago, it was about 40,400 AU away. Last time it swung through our neighborhood was about 3.5 million years ago, when it came within 18 AU of the Sun.

But its current inward journey will be its closest so far. Astronomers have already calculated that in 2031, Comet BB will peak at 10.9 AU, almost reaching the orbit of Saturn.

It is presently unclear how bright the comet will be when it reachest its closest point. It will be much farther from the Sun than most bright comets, but its large size may change what is normally expected.

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Comet spewed out an unusual amount of alcohol during solar flyby

1:04 pm

A review of the data gathered when Comet 46P/Wirtanen made its close fly-by of the Sun in 2018 has found that the comet released an unusual amount of alcohol during that flyby.

The data also showed that the temperature of the comet’s coma did not cool as much as expected at larger distances from the comet.

“46P/Wirtanen has one of the highest alcohol-to-aldehyde ratios measured in any comet to date,” said Neil Dello Russo, a cometary scientist at Johns Hopkins University Applied Physics Laboratory and co-author of the study. “This tells us information about how carbon, oxygen, and hydrogen molecules were distributed in the early solar system where Wirtanen formed.”

Keck Observatory data also revealed a strange characteristic. Normally, as comets orbit closer to the Sun, the frozen particles in their nucleus heat up, then boil off, or sublimate, going directly from solid ice to gas, skipping the liquid phase. This process, called outgassing, is what produces the coma – a giant cloak of gas and dust glowing around the comet’s nucleus. As the comet gets even closer to the Sun, solar radiation pushes some of the coma away from the comet, creating the tails.

With comet 46P/Wirtanen however, the team made a strange discovery: Another process beyond solar radiation is mysteriously heating up the comet.

“Interestingly, we found that the temperature measured for water gas in the coma did not decrease significantly with distance from the nucleus, which implies a heating mechanism,” said co-author Erika Gibb, professor and chair of the Department of Physics and Astronomy at University of Missouri–St. Louis.

They have theories about why they got these results, such as a chemical reaction with sunlight or the presence of large ice chunks breaking off the comet that reflect light and increase the ambient temperature of the coma. Nothing is confirmed however.

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Astronomers discover “comet” bigger than the largest comets approaching inner solar system

9:25 am

Astronomers have discovered an object 80 to 100 miles in diameter, larger than the largest comets, approaching the inner solar system and coming from the theorized Oort Cloud of material thought to exist between a tenth and a third of a light year from the Sun.

The object is probably rich in ice like a comet and is currently around three billion kilometres from the Sun. It will reach its closest point, known as perihelion, in 2031. At that time, it will be positioned below the plane of the solar system, near the orbit of Saturn.

Part of the interest in C/2014 UN271 is that it may be something of a transition object. Astronomers believe that many of the long period comets, that occasionally appear with bright tails, actually come from the Oort Cloud. Stars wandering near the Sun can nudge these objects from their positions and over millennia they work their way inwards, with the gravity of the giant planets tweaking their paths on each visit until they reside where we see them today.

“The fact that [C/2014 UN271] has a perihelion so far away from the Sun might be telling us that it’s done this a couple of times but is still in that process of eventually becoming some of those long period comets we know and love,” explains Meg Schwamb a Kuiper Belt and Oort Cloud expert at Queen’s University Belfast.

Initially astronomers thought because of its size that it was not a comet, but new observations have detected the first signs of a coma, suggesting that it will provide us a very interesting and extended show when it reaches its closest point in 2031. Because that perihelion is around the orbit of Saturn, the object will not be traveling very fast, so its passage through the inner solar system will take several years. Its size also suggests it will have a lot of material that can sublimate off to produce a tail.

The object was discovered by two astronomers, Gary Bernstein and Pedro Bernardinelli. If it turns out to be a comet it will then be named Comet Bernardinelli-Bernstein, or Comet B-B for short.

UPDATE: It is official. The object is now officially a comet, and named Comet Bernardinelli-Bernstein.

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Orbit of pristine comet in outer solar system is shifting inward

10:43 am

The orbit of a pristine comet that until now has kept it in the outer solar system, where it never got warm enough shed any material, is now shifting inward to join what is dubbed the Jupiter-family of comets, whose orbits are generally within that of Jupiter.

Although it has likely lost some supervolatile ices such as carbon dioxide ice (also known as dry ice) in the outer solar system beyond Jupiter, it is unlikely to have ever been in the inner solar system (where Earth, the other rocky planets, and [Jupiter-family comets] orbit), which is warm enough for water ice to sublime (‘evaporate’ from solid to gas),” Steckloff said. “This means that [Comet 2019] LD2 is a pristine comet, and presents a unique opportunity to observe how pristine [Jupiter-family comets] behave as their water ice begins to sublime for the first time and drive comet activity. Moreover, this transition is likely to finish in only 40 years from now, which is a blink of an eye for astronomy. This means that people alive today will be able to follow this object all the way through its transition into the [Jupiter-family] population.”

In 2019, when 2019 L2 was first identified, it was thought to be an asteroid that had suddenly become active, like a comet. Astronomers soon realized this was a mistake, that it was a comet whose orbit was being changed by its interaction with Jupiter.

The new data refines this conclusion, and confirms that observations of 2019 L2 will provide a lot of information about the make-up of the early solar system. More important, the comet’s orbit will allow for many observations, over a long period of time, unlike most comets that zip around the Sun in a year or so and then are gone.

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Scientists finally map Philae’s full route to its final landing site on Comet 67/C-G

12:53 pm

Philae's journey across Comet 67/C-G
Click for full resolution image.

Using archival data from Rosetta, scientists have finally been able to map out the full route and all impact points made by the lander Philae on its journey to land on the Comet 67P/C-G in November 2014.

All that was known previously was the location of the first contact, that there had been another impact following the rebound, and the location of the final landing site where Philae came to rest after two hours and where it was found towards the end of the Rosetta mission in 2016 . “Now we finally know the exact place where Philae touched down on the comet for the second time. This will allow us to fully reconstruct the lander’s trajectory and derive important scientific results from the telemetry data as well as measurements from some of the instruments operating during the landing process,” explains Jean-Baptiste Vincent from the DLR Institute of Planetary Research, who was involved in the research published today.

…Analysis of the data revealed that Philae had spent almost two full minutes – not unusual in this very low gravity environment – at the second surface contact point, making at least four different surface contacts as the lander ‘ploughed’ through the rugged landscape. A particularly remarkable imprint, which became visible in the images, was made when the top of Philae sank 25 centimetres into the ice at the side of an open crevice, leaving visible traces of the sample drill and the lander’s top. The peaks in the magnetic field data resulting from the boom movement show that Philae took three seconds to make this particular ‘dent’.

This new data about this particular impact has helped the scientists determine a great deal about the comet’s make-up and density, finding that it is extremely fluffy.

The parameters of surface contact showed that this ancient, 4.5-billion-year-old mixture of ice and dust is extraordinarily soft – it is fluffier than the froth on a cappuccino, the foam in a bathtub or the whitecaps of waves meeting the coast.

They also found that the interior has many voids comprising 75% of the interior, with the “boulders” between having the density of Styrofoam.

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A UV aurora found on Comet 67P/C-G

9:06 am

Using data from Europe’s now completed Rosetta mission to Comet 67P/C-G, scientists have detected evidence that the comet’s interaction with the Sun’s solar wind creates an aurora above the comet in ultra-violet wavelengths.

The data indicate 67P/C-G’s emissions are actually auroral in nature. Electrons streaming out in the solar wind – the stream of charged particles flowing out from the Sun – interact with the gas in the comet’s coma, breaking apart water and other molecules. The resulting atoms give off a distinctive far-ultraviolet light. Invisible to the naked eye, far-ultraviolet has the shortest wavelengths of radiation in the ultraviolet spectrum.

Labeling this phenomenon as an aurora is a bit of hype, as nothing is visible. However, the discovery does tell scientists how this comet’s coma, produced when the comet heats up in its approach to the Sun, interacts with the solar wind, and this in turn can teach them more about that wind, as well as other comets.

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Hubble photographs Comet NEOWISE

12:38 pm

Comet NEOWISE, photographed by the Hubble Space Telescope
Click for full image.

Using the Hubble Space Telescope, astronomers have obtained close-up images of Comet NEOWISE after it had survived its closest approach to the Sun. The photo to the right, cropped and reduced to post here, is one of Hubble’s two images.

Comets often break apart due to thermal and gravitational stresses at such close encounters, but Hubble’s view suggests that NEOWISE’s solid nucleus stayed intact. This heart of the comet is too small to be seen directly by Hubble. The ball of ice may be no more than 4.8 kilometres across. But the Hubble image does captures a portion of the vast cloud of gas and dust enveloping the nucleus, which measures about 18 000 kilometres across in this image.

Hubble’s observation also resolves a pair of jets from the nucleus shooting out in opposite directions. They emerge from the comet’s core as cones of dust and gas, and then are curved into broader fan-like structures by the rotation of the nucleus. Jets are the result of ice sublimating beneath the surface with the resulting dust/gas being squeezed out at high velocity.

Below the fold is a six-second movie made of Hubble’s two images, showing how the jets changed over a three hour time period on August 8th.
» Read more

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Comet Neowise: NOW is the time to go see it

8:59 am

Comet Neowise is now visible each evening just after sunset. This article shows a bunch of images produced by people worldwide.

The comet will not be back for thousands of years, so this will be your only chance to see it. And usually good evening-view comets occur only once every few decades, usually not more than once or thrice every century. If you want to see a comet in all its glory, Comet Neowise is giving you a chance, and now is the time to look.

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It appears we will have a comet show in July!

8:55 am

After two other comets this spring suggested they might become bright naked eye objects and then fizzled, it now appears that Comet NEOWISE will deliver, having survived its closest approach to the Sun to now brighten towards first magnitude.

For the northern hemisphere, this is what to expect if you wish to see it:

In the morning sky, the first views of NEOWISE could come as early as July 5 or 6 in the morning sky, very low above the northeast horizon. By around July 11, the comet will reach an altitude of nearly 10 degrees — for comparison, 10 degrees is roughly equal to the width of your fist held at arm’s length. Then over the next 10 days it will gradually slide back down toward the north-northeast horizon, eventually disappearing from dawn visibility.

A far-better viewing perspective will become available in the evening sky starting around July 12, when it will appear low in the northwest sky. In the evenings to follow, the comet will rapidly climb higher in the sky.

On July 22, NEOWISE will make its closest approach to the Earth, a distance of 64 million miles (103 million km). By July 25, the comet will appear 30 degrees (“three fists”) up from the west-northwest horizon as darkness falls. And on July 30-31st, the comet will be passing just to the north of the fine star cluster of Coma Berenices or Berenice’s Hair.

Will this comet brighten more to become comparable to glorious Comet Hale-Bopp in 1997? Keep your fingers crossed.

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That Jupiter Trojan comet-like asteroid was neither an asteroid nor a Trojan

9:14 am

Astronomers have now found that the asteroid that had suddenly become active, like a comet, and they had thought was part of the asteroids in Jupiter orbit called Trojans, was neither an asteroid nor a Trojan.

Instead, it is an actual comet captured in a strange unstable orbit around Jupiter.

[W]hen amateur astronomer Sam Deen used software on the Jet Propulsion Laboratory’s solar-system dynamics website to calculate the object’s orbit, he found P/2019 LD2 recently had a close encounter with Jupiter that left its orbit unstable. The model showed that the comet had likely been a Centaur, part of a family of outer solar system asteroids, with an orbit reaching out to Saturn. Then, on February 17, 2017, it passed about 14 million kilometers from Jupiter, an encounter that sent the comet on a wild ride and inserted it into an odd Jupiter-like orbit.

Yet although the swing past Jupiter put P/2019 LD2 into a Jupiter-like orbit, it didn’t move it near to one of the two Lagrange points where the combination of gravitational forces from Jupiter and the Sun hold Trojan asteroids. Instead of being 60° — one-sixth of the giant planet’s orbit — from Jupiter, P/2019 LD2 is only 21° ahead of Jupiter.

The orbit is unstable. It will bring the comet to within 3 million miles of Jupiter in 2063, but beyond that predictions are impossible. The exact closeness of that approach cannot be predicted with much precision, partly because of the chaotic nature of the orbit, and partly because of the random orbital changes that can occur because the comet is venting.

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A Jupiter Trojan asteroid spouts a tail

9:54 am

The ATLAS telescope has discovered the first Jupiter Trojan asteroid to spout a tail like a comet.

Early in June 2019, ATLAS reported what seemed to be a faint asteroid near the orbit of Jupiter. The Minor Planet Center designated the new discovery as 2019 LD2. Inspection of ATLAS images taken on June 10 by collaborators Alan Fitzsimmons and David Young at Queen’s University Belfast revealed its probable cometary nature. Follow-up observations by the University of Hawaiʻi’s J.D. Armstrong and his student Sidney Moss on June 11 and 13 using the Las Cumbres Observatory (LCO) global telescope network confirmed the cometary nature of this body.

Later, in July 2019, new ATLAS images caught 2019 LD2 again – now truly looking like a comet, with a faint tail made of dust or gas. The asteroid passed behind the Sun and was not observable from the Earth in late 2019 and early 2020, but upon its reappearance in the night sky in April of 2020, routine ATLAS observations confirmed that it still looks like a comet. These observations showed that 2019 LD2 has probably been continuously active for almost a year.

While ATLAS has discovered more than 40 comets, what makes this object extraordinary is its orbit. The early indication that it was an asteroid near Jupiter’s orbit have now been confirmed through precise measurements from many different observatories. In fact, 2019 LD2 is a special kind of asteroid called a Jupiter Trojan – and no object of this type has ever before been seen to spew out dust and gas like a comet.

There are a number of mysteries here. First, why should it have suddenly become active, since its orbit is relatively circular (similar to Jupiter’s)? Second, it had been assumed that the Jupiter Trojans had been in their orbits for a long time and had long ago vented any ice on their surfaces. This discovery proves that assumption false. It suggests that either this asteroid is a comet that was recently captured, or that things can happen on these asteroids to bring some buried volatiles up to the surface, where they can then vent.

Above all, this asteroid shows that it is dangerous to assume all Jupiter Trojan asteroids are the same. I guarantee when we finally get a close look at a bunch, when the Lucy mission arrives beginning in 2027, the variety will be quite spectacular.

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Hubble photographs break-up of Comet ATLAS

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The break-up of Comet ATLAS
For the full images go to April 20 and April 23.

Cool image time! Scientists using the Hubble Space Telescope have captured the break-up of Comet ATLAS over a period of several days. The two images to the right, cropped and annotated to post here, were taken on April 20th and April 23rd respectively.

Hubble identified about 30 fragments on April 20, and 25 pieces on April 23. They are all enveloped in a sunlight-swept tail of cometary dust. “Their appearance changes substantially between the two days, so much so that it’s quite difficult to connect the dots,” said David Jewitt, professor of planetary science and astronomy at UCLA, Los Angeles, California, leader of one of two teams who photographed the doomed comet with Hubble. “I don’t know whether this is because the individual pieces are flashing on and off as they reflect sunlight, acting like twinkling lights on a Christmas tree, or because different fragments appear on different days.”

That there are fewer pieces in the later image could also be because the smaller fragments had crumbled even more during the three days between photos, and thus were simply too small to see any longer.

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More data from interstellar Comet 2I/Borisov as it zipped past Sun in December

10:00 am

Astronomers studying interstellar Comet 2I/Borisov as it zipped past Sun in December have found that while in many ways it resembled solar system comets, the differences were revealing.

During its trip through the solar system, the comet lost nearly 61 million gallons (230 million liters) of water — enough to fill over 92 Olympic-size swimming pools. As it moved away from the Sun, Borisov’s water loss dropped off — and did so more rapidly than any previously observed comet. Xing said this could have been caused by a variety of factors, including surface erosion, rotational change and even fragmentation. In fact, data from Hubble and other observatories show that chunks of the comet broke off in late March.

…Swift’s water production measurements also helped the team calculate that Borisov’s minimum size is just under half a mile (0.74 kilometer) across. The team estimates at least 55% of Borisov’s surface — an area roughly equivalent to half of Central Park — was actively shedding material when it was closest to the Sun. That’s at least 10 times the active area on most observed solar system comets. Borisov also differs from solar system comets in other aspects. For example, astronomers working with Hubble and the Atacama Large Millimeter/submillimeter Array, a radio telescope in Chile, discovered Borisov produced the highest levels of carbon monoxide ever seen from a comet at that distance from the Sun.

Because more of the comet’s entire surface had water ice than seen in solar system comets, it suggests that the comet has never been close to another star before. That the water release dropped off precipitously however also suggests that that surface layer of ice was not very deep.

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Interstellar Comet 2I/Borisov has an excess of carbon monoxide

8:48 am

Astronomers using two difference space telescopes have found that Comet 2I/Borisov, the first known interstellar comet, has an abundance of carbon monoxide when compared to solar system comets.

The team used Hubble’s unique ultraviolet sensitivity to spectroscopically detect carbon monoxide gas escaping from comet Borisov’s solid comet nucleus. Hubble’s Cosmic Origins Spectrograph observed the comet on four separate occasions, from Dec. 11, 2019 to Jan. 13, 2020, which allowed the researchers to see the object’s chemical composition change quickly, as different ice mixtures, including carbon monoxide, oxygen, and water, sublimated under the warmth of the Sun.

The Hubble astronomers were surprised to find that the interstellar comet’s coma, the gas cloud surrounding the nucleus, contains a high amount of carbon monoxide gas, at least 50% more abundant than water vapor. This amount is more than three times higher than the previously measured quantity for any comet entering the inner solar system. The water measurement was made by NASA’s Neil Gehrels-Swift satellite, whose observations were conducted in tandem with the Hubble study.

Carbon monoxide ice is very volatile. It doesn’t take much sunlight to heat the ice and convert it to gas that escapes from a comet’s nucleus. For carbon monoxide, this activity occurs very far from the Sun, about 11 billion miles away, more than twice the distance of Pluto at its farthest point from the Sun. In contrast, water remains in its icy form until about 200 million miles from the Sun, the approximate distance of the inner edge of the asteroid belt.

However, for comet Borisov, the Hubble measurements suggest that some carbon monoxide ice was locked inside the comet’s nucleus, revealed only when the Sun’s heat stripped away layers of water ice. “The amount of carbon monoxide did not drop as expected as the comet receded from the Sun. This means that we are seeing the primitive layers of the comet, which really reflect what this object is made of,” Bodewits explained. “Because of the abundance of carbon monoxide ice that survived so close to the Sun, we think that comet Borisov comes from a much colder place and from a very different debris disk around a star than our own.”

With solar system comets, the ratios between water and carbon monoxide are the reverse, with much more water detected. They theorize, based on these results, that the comet might have come from a cool red dwarf star, but with the available data that is nothing more than a guess at this point.

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Confirmed: Comet ATLAS has broken apart

8:47 am

Astronomers have now confirmed the fact that Comet ATLAS has broken into several pieces, and will not put on a spectacular sky show this coming May.

Just a month ago, it looked like the icy wanderer, officially known as C/2019 Y4 Atlas, might put on a dazzling sky show around the time of its closest approach to the sun, or perihelion, which occurs on May 31.

But relatively lackluster behavior soon dimmed such hopes. And optimism surrounding the comet is now pretty much extinguished, for it’s no longer in one piece. Comet Atlas “has shattered both its and our hearts,” astrophysicist Gianluca Masi, the founder and director of the Virtual Telescope Project in Italy, said in an emailed statement on Sunday (April 12). “Its nucleus disintegrated, and last night I could see three, possibly four main fragments.”

A nice picture of the break-up can be seen here.

We are due for another great comet, like Comet Hale-Bopp in the late 1990s. Unfortunately, Comet ATLAS won’t be that comet.

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