NASA's Swift Monitors Departing Comet Garradd

Swift's UVOT acquired this image of Comet Garradd (C/2009 P1) on April 1, 2012, when the comet was 142 million miles away, or 636 times farther than the moon. 

Red shows sunlight reflected from the comet's dust; violet shows ultraviolet light produced by hydroxyl (OH), a fragment of water. NGC 2895 is a barred spiral galaxy located 400 million miles away in the constellation Ursa Major. 

The UVOT image (outlined) is placed within a wider visible image of the region from the Digital Sky Survey. 

Credit: NASA/Swift/D. Bodewits (UMD) and S. Immler (GSFC) and DSS/STScI/AURA.

An outbound comet that provided a nice show for skywatchers late last year is the target of an ongoing investigation by NASA's Swift satellite. Formally designated C/2009 P1 (Garradd), the unusually dust-rich comet provides a novel opportunity to characterize how cometary activity changes at ever greater distance from the sun.

A comet is a clump of frozen gases mixed with dust. These "dirty snowballs" cast off gas and dust whenever they venture near the sun. What powers this activity is frozen water transforming from solid ice to gas, a process called sublimation. Jets powered by ice sublimation release dust, which reflects sunlight and brightens the comet. Typically, a comet's water content remains frozen until it comes within about three times Earth's distance to the sun, or 3 astronomical units (AU), so astronomers regard this as the solar system's "snow line."

"Comet Garradd was producing lots of dust and gas well before it reached the snow line, which tells us that the activity was powered by something other than water ice," said Dennis Bodewits, an assistant research scientist at the University of Maryland, College Park, and the study's lead investigator. "We plan to use Swift's unique capabilities to monitor Garradd as it moves beyond the snow line, where few comets are studied."

Comets are known to contain other frozen gases, such as carbon monoxide and dioxide (CO and CO2), which sublimate at colder temperatures and much farther from the sun. These are two of the leading candidates for driving cometary activity beyond the snow line, but phase transitions between different forms of water ice also may come into play.

C/2009 P1 was discovered by Gordon J. Garradd at Siding Spring Observatory, Australia, in August 2009. Astronomers say that the comet is "dynamically new," meaning that this is likely its first trip through the inner solar system since it arrived in the Oort cloud, the cometary cold-storage zone located thousands of AU beyond the sun.

Comet Garradd was closest to the sun on Dec. 23, 2011, and passed within 118 million miles (1.27 AU) of Earth on March 5, 2012. The comet remains observable in small telescopes this month as it moves south though the constellations Ursa Major and Lynx.

Although Swift's prime task is to detect and rapidly locate gamma-ray bursts in the distant universe, novel targets of opportunity allow the mission to show off its versatility. One of Swift's instruments, the Ultraviolet/Optical Telescope (UVOT) is ideally suited for studying comets.

The instrument includes a prism-like device called a grism, which separates incoming light by its wavelength. While Swift's UVOT cannot detect water directly, the molecule quickly breaks up into hydrogen atoms and hydroxyl (OH) molecules when exposed to ultraviolet sunlight. The UVOT detects light emitted by hydroxyl and other important molecular fragments - such as cyanide (CN), carbon monosulfide (CS) and diatomic and triatomic carbon (C2 and C3, respectively) - as well as the sunlight reflected off of cometary dust.

"Tracking the comet's water and dust production and watching its chemistry change as it moves deeper into the solar system will help us better understand how comets work and where they formed," said Stefan Immler, a researcher and Swift team member at NASA's Goddard Space Flight Center in Greenbelt, Md.

SOHO Supersonic snowballs: Comets interacting with the Sun's atmosphere

This coronagraph image from the Solar and Heliospheric Observatory (SOHO) shows Comet Lovejoy receding from the sun after its close encounter.

The horizontal lines through the comet's nucleus are digital artifacts caused by saturation of the detector. Yes, Lovejoy is that bright! To view a movie of Comet Lovejoy's path please go here. 

Since the 1980s astronomers have seen thousands of comets falling towards the Sun, most of them too small to survive a close approach, let alone to re-emerge.

Until recently no such objects had been seen very close to the Sun as the glare of sunlight made them impossible to observe.

Now a team of scientists led by Professor Emeritus John Brown, Astronomer Royal for Scotland (Edinburgh's Royal Observatory) and former Regius Professor of Astronomy at Glasgow University, have worked out which comets make it through this fiery journey, which fizzle out high up and which explode just above the surface.

Prof. Brown presented this new work in a paper at the National Astronomy Meeting in Manchester on Friday 30 March.

Comets are giant dusty snowballs believed to date from the epoch of the formation of the Sun and planets, so carry important information about the early history and composition of the Solar system.

The comets we see spend most of their time very far from the Sun, orbiting in the so called Oort Cloud, before being disrupted into orbits that carry them towards our nearest star over tens of thousands of years.

When comets reach the inner Solar System, their dusty ices melt and vapourise to form huge tails blown back by the solar wind and by sunlight.

The largest, like the famous Comet Hale Bopp seen in the late 1990s, have nuclei tens of kilometres across and masses of 10 million million tonnes.

Objects this large only lose a tiny fraction of their material on each passage around the Sun, so are able to survive thousands of journeys through the Solar System.

In contrast, the smallest objects may only be 10 metres across with a mass of 1000 tonnes. If these small comets make a close approach to the Sun, they are vapourised by sunlight and by the friction of the atmospheric gas.

In the culmination of work carried out over the last few years, Professor Brown and his colleagues are now able to predict how comets lose their mass and are destroyed in the solar atmosphere, their behaviour depending on whether or not their orbital path reaches into the 'lower atmosphere' 7000 km (roughly 1% of the solar radius) from the top of the brightest visible solar layer, the photosphere.

Jupiter helps Halley's Comet give us more spectacular meteor displays

The dramatic appearance of Halley's comet in the night sky has been observed and recorded by astronomers since 240 BC.

Now a study shows that the orbital influences of Jupiter on the comet and the debris it leaves in its wake are responsible for periodic outbursts of activity in the Orionid meteor showers.

The results will be presented by Aswin Sekhar at the National Astronomy Meeting in Manchester on Tuesday 27th March.

Halley's comet orbits the Sun every 75-76 years on average. As its nucleus approaches the Sun, it heats up and releases gas and dust that form the spectacular tail. This outgassing leaves a trail of debris around the orbit.

When the Earth crosses Halley's path, twice per orbit, dust particles (meteoroids) burn up in the Earth’s atmosphere and we see meteor showers: the Orionids in October and the Eta Aquariids in May.

Previous research has suggested that Orionid meteoroids have at times fallen into 'resonances' with Jupiter's orbit – a numerical relationship that influences orbital behaviour.

Sekhar's new study suggests that Halley itself has been in resonances with Jupiter in the past, which in turn would increase the chances of populating resonant meteoroids in the stream.

The particles ejected during those times experience a tendency to clump together due to periodic effects from Jupiter.

Image of 2007 Orionids, showing Orion constellation in the backdrop. Credit: S. Quirk    

"This resonant behaviour of meteoroids means that Halley's debris is not uniformly distributed along its orbital path."

"When the Earth encounters one of these clumps, it experiences a much more spectacular meteor shower than usual," said Sekhar, of Armagh Observatory.

Sekhar has modelled Halley’s orbital evolution over more than 12 000 years into the past and 15 000 years into the future.

The model suggests that from 1404 BC to 690 BC, Halley was trapped in a 1:6 resonance with Jupiter (in which Halley completed one orbit for every six orbits of Jupiter around the Sun).

Later, from 240 BC to 1700 AD, the comet’s orbit had a 2:13 relationship with Jupiter’s orbit. Debris deposited during these two periods can be directly attributed to heightened activity in the Orionid meteor showers in some years.

Sekhar’s work suggests that the unusual Orionid outburst observed in 1993 was due to 2:13 resonant meteoroids ejected from Halley around 240 BC.

He predicts that the next similar display of meteors from this 2:13 resonance will be in 2070 AD.

"The real beauty of this area of science lies in the convergence of cometary physics and orbital dynamics."

"The close correlation between historical records from ancient civilisations and the predictions using modern science make it even more elegant," said Sekhar.

He added, "There are enough unsolved problems pertaining to Halley and its meteor streams to keep us occupied till the next apparition of the comet in 2061!"

Provided by Royal Astronomical Society

Spectacular Christmas Comet Amazes ESO Skywatchers

This photo comes from a time-lapse sequence taken by Gabriel Brammer from ESO just two days ago on 22 December 2011. 

Gabriel was finishing his night shift as support astronomer at the Paranal Observatory when the comet rose over the horizon just before dawn.

CREDIT: G. Brammer/ESO

A stunning comet that survived a recent brush with the sun is amazing astronomers again, this time in dazzling new photos captured just before sunrise over Chile.

The comet Lovejoy may not be the famed Star of Bethlehem, but it still provided a jaw-dropping sight for astronomer Gabriel Brammer, photographed the comet rising ahead of the sun on Dec. 22 at Paranal Observatory in Chile's high Atacama Desert.

Brammer is a support astronomer for the European Southern Observatory (ESO), which runs the Paranal facility. His time-lapse photos of comet Lovejoy show it rising ahead of the sun as the Paranal astronomers fire a laser beam, which serves as a guide star, into the sky. Our Milky Way galaxy and the moon are also visible in the images.

"On the last morning of my shift I tried to try catching it on camera before sunrise," Brammer said in a statement.

"The tail of the comet was easily visible with the naked eye, and the combination of the crescent moon, comet, Milky Way and the laser guide star was nearly as impressive to the naked eye as it appears in the long-exposure photos."

NASA SDO: Comet Lovejoy's Journey around the Sun - YouTube

Comet Lovejoy traveled behind the Sun and reemerged as seen by NASA's Solar Dynamics Observatory.

Credit: NASA SDO

ESA SOHO: The beginning of the end for comet Lovejoy

Comet Lovejoy seen by SOHO

The SOHO spaceborne solar observatory today captured comet Lovejoy in its field of view for the first time, indicating that the icy body is on its final destructive plunge towards the Sun.

Announced on 2 December, the newly discovered comet Lovejoy is on a near-collision course with the Sun and is expected to plunge to its fiery fate late on 15 December.

At its closest approach, it will pass just 140 000 km above the solar surface.

At that distance, the icy comet is not expected to survive the Sun’s fierce heat.

Indeed, comets are such tenuous collections of ice and rocks that it could disintegrate at any moment.

If the comet does stay the course, we will not see its demise because its closest approach will take place on the far side of the Sun.

The ESA–NASA SOHO spacecraft is an exceptional discoverer of comets, spotting 2110 since its launch in 1995.

However, comet C/2011 W3 was discovered from the ground by the Australian astronomer Terry Lovejoy, hence it is now carries his name.

Terry was an early pioneer of using SOHO data over the Internet to discover comets. He can now claim to be the first person to discover a Sun-grazer from both ground and space telescopes.

Comet Lovejoy is from the ‘Kreutz group’ – believed to be a fragment of a previous comet that broke up centuries ago.

Other fragments of that great comet have become some of the brightest in history: comet Ikeya–Seki became so bright in 1965 that it was visible even in the daytime sky.

Unfortunately, comet Lovejoy is not expected to become as bright as Ikeya–Seki.

“On average, new Kreutz-group comets are discovered every few days by SOHO, but from the ground they are much rarer to see or discover,” says Karl Battams, Naval Research Laboratory, who curates the Sun-grazing comets webpage.

“This is the first ground-based discovery of a Kreutz-group comet in 40 years, so we really can't be sure just how bright it will get. “However, I do think that it will be the brightest Kreutz-group comet SOHO has ever seen.”

Comet Lovejoy’s spectacular progress can be monitored via the web at SOHO’s LASCO instrument page.


Further information

NASA SOHO: Newfound Comet to Dive Through Sun

The Solar and Heliospheric Observatory captured this shot of a huge coronal mass ejection on Oct. 1, 2011, shortly after a comet dove into the sun (inset, right).

CREDIT: SOHO/NASA/ESA

A newly discovered comet is racing toward a mid-December rendezvous with the sun — a rendezvous that it will likely not survive.

The comet is categorized by astronomers as a "sungrazer" and it is destined to do just that; literally graze the surface of the sun (called the photosphere) and pass through the sun's intensely hot corona, where temperatures have been measured at upwards of 3.6-million degrees Fahrenheit (2-million degrees Celsius).

While the comet will not collide with the sun, most astronomers say the odds are rather long that it will remain intact after its closest pass by the sun. The most exciting aspect of the event is that the comet's expected destruction should be visible on your computer monitor.

And there is a very slight chance that, should the comet somehow manage to survive, it might briefly become visible in broad daylight.

Discovery
The comet was discovered by Australian amateur astronomer Terry Lovejoy Nov. 27 using a C8 Schmidt-Cassegrain telescope, working with a QHY9 CCD camera.

At first, Lovejoy believed that the rapidly moving fuzzy image he saw was nothing more than a camera reflection. But two nights later, despite clouds and haze, he managed to find the fuzzy object again and take several new images.

Lovejoy then put out a call to some trusted observers to confirm his observations. He received that confirmation Dec. 1 from Mount John Observatory, based in the Mackenzie Basin on the South Island of New Zealand. By then, 31 separate observations of the comet had been collected to determine an orbit, and the first announcement of Lovejoy's discovery was made this past Friday (Dec. 2) by the Minor Planet Center of the International Astronomical Union.

Its official title is C/2011 W3 (Lovejoy). It is Terry Lovejoy's third comet discovery.

NASA: Comet Elenin Gone and Should Be Forgotten

Comet Elenin is no more. Latest indications are this relatively small comet has broken into even smaller, even less significant, chunks of dust and ice.

This trail of piffling particles will remain on the same path as the original comet, completing its unexceptional swing through the inner solar system this fall.

"Elenin did as new comets passing close by the sun do about two percent of the time: It broke apart," said Don Yeomans of NASA's Near-Earth Object Program Office in Pasadena, Calif.

"Elenin's remnants will also act as other broken-up comets act. They will trail along in a debris cloud that will follow a well-understood path out of the inner solar system.

After that, we won't see the scraps of comet Elenin around these parts for almost 12 millennia."

Twelve millennia may be a long time to Earthlings, but for those frozen inhabitants of the outer solar system who make this commute, a dozen millennia give or take is a walk in the celestial park.

Comet Elenin came as close as 45 million miles (72 million kilometers) to the sun, but it arrived from the outer solar system's Oort Cloud, which is so far away its outer edge is about a third of the way to the nearest star other than our sun.

For those broken up over the breakup of what was formerly about 1.2 miles (two kilometers) of uninspiring dust and ice, remember what Yeomans said about comets coming close to the sun - they fall apart about two percent of the time.

"Comets are made up of ice, rock, dust and organic compounds and can be several miles in diameter, but they are fragile and loosely held together like dust balls," said Yeomans.

"So it doesn't take much to get a comet to disintegrate, and with comets, once they break up, there is no hope of reconciliation."

Comet Elenin first came to light last December, when sunlight reflecting off the small comet was detected by Russian astronomer Leonid Elenin of Lyubertsy, Russia.

NASA Spitzer: Comets Raining Down on Neighbouring Solar System

This artist's conception illustrates a storm of comets around a star near our own, called Eta Corvi.

Evidence for this barrage comes from NASA's Spitzer Space Telescope, whose infrared detectors picked up indications that one or more comets was recently torn to shreds after colliding with a rocky body.

In this artist's conception, one such giant comet is shown smashing into a rocky planet, flinging ice- and carbon-rich dust into space, while also smashing water and organics into the surface of the planet.

A glowing red flash captures the moment of impact on the planet. Yellow-white Eta Corvi is shown to the left, with still more comets streaming toward it.

Spitzer detected spectral signatures of water ice, organics and rock around Eta Corvi, key ingredients of comets. This is the first time that evidence for such a comet storm has been seen around another star.

Eta Corvi is just about the right age, about one billion years old, to be experiencing a bombardment of comets akin to what occurred in our own solar system at 600 to 800 millions years of age, termed the Late Heavy Bombardment.

Scientists say the Late Heavy Bombardment was triggered in our solar system by the migration of our outer planets, which jostled icy comets about, sending some of them flying inward.

The incoming comets scarred our moon and pummeled our inner planets. They may have even brought materials to Earth that helped kick start life.

Image credit: NASA/JPL-Caltech

Comet Elenin: Debris of 'Doomsday' comet to Flyby Earth

Amateur astronomer Michael Mattiazzo of Castlemaine, Australia caught these two images of comet Elenin on Aug. 19 (left) and Sept. 6, 2011.

The images show a rapid dimming in the comet, possibly hinting at its disintegration.

CREDIT: Michael Mattiazzo

The moment long feared by conspiracy theorists is nearly upon us: The "doomsday comet" Elenin will make its closest approach to Earth Sunday (Oct. 16). Or what's left of it will, anyway.

Russian amateur astronomer Leonid Elenin had the good fortune to discover a comet on Dec. 10, 2010, and it's turned out to be quite a skywatching curiosity.

Initially, comet Elenin received quite a bit of attention from astronomers because its orbit would take it quite close to Earth, within 22 million miles (35 million kilometers), on Oct. 16, 2011. It looked like it was going to put on a good show.

Even as recently as Aug. 19, the comet was brighter than predicted, as observed and photographed by amateur astronomers in Australia, notably Michael Mattiazzo.

Comet Elenin started breaking up in August after being blasted by a huge solar storm, and a close pass by the sun on Sept. 10 apparently finished it off, astronomers say.

So what will cruise within 22 million miles (35.4 million kilometers) of our planet Sunday is likely to be a stream of debris rather than a completely intact comet.

The debris of Comet Elenin won't return to Earth for 12,000 years, astronomers say.

ESA Herschel Image: Comet Hartley 2

Early last November, small but active Comet Hartley 2 (103/P Hartley) became the fifth comet imaged close-up by a spacecraft from planet Earth.

Still cruising through the solar system with a 6 year orbital period, Hartley 2 is is making astronomical headlines again, though.

New Herschel Space Observatory measurements indicate that the water found in this comet's thin atmosphere or coma has the same ratio of the hydrogen isotope deuterium (in heavy water) as the oceans of our fair planet.

Hartley 2 originated in the distant Kuiper Belt, a region beyond the orbit of Neptune that is a reservoir of icy cometary bodies and dwarf planets.

Since the ratio of deuterium is related to the solar system environment where the comet formed, the Herschel results indicate that Kuiper Belt comets could have contributed substantial amounts of water to Earth's oceans.

Comet Hartley 2 appears in this starry skyscape from last November sporting a tantalizing greenish coma appropriately sailing through the nautical constellation Puppis. Below the comet are open star clusters M47 (right) and M46 (left).

Draconid Meteor Outburst - Comet Giacobini-Zinner

On October 8th Earth is going to plow through a stream of dust from Comet 21P/Giacobini-Zinner, and the result could be an outburst of Draconid meteors. "We're predicting as many as 750 meteors per hour," says Bill Cooke of NASA's Meteoroid Environment Office.

"The timing of the shower favors observers in the Middle East, north Africa and parts of Europe."

Every 6.6 years Comet Giacobini-Zinner swings through the inner solar system. With each visit, it lays down a narrow filament of dust, over time forming a network of filaments that Earth encounters every year in early October.

"Most years, we pass through gaps between filaments, maybe just grazing one or two as we go by," says Cooke. "Occasionally, though, we hit one nearly head on--and the fireworks begin."

2011 could be such a year. Forecasters at NASA and elsewhere agree that Earth is heading for three or more filaments on October 8th. Multiple encounters should produce a series of variable outbursts beginning around 1600 Universal Time (noon EDT) with the strongest activity between 1900 and 2100 UT (3:00 pm - 5:00 pm EDT).

Forecasters aren't sure how strong the display will be, mainly because the comet had a close encounter with Jupiter in the late 1880s. At that time, the giant planet's gravitational pull altered the comet's orbit and introduced some uncertainty into the location of filaments it has shed since then.

Competing models place the filaments in slightly different spots; as a result, estimated meteor rates range from dozens to hundreds per hour.

Comet Giacobini-Zinner, a fairly frequent visitor to the inner solar system, was captured by the Kitt Peak 0.9-meter telescope on Halloween Night 1998 (UT November 1st, from 02:07 to 03:40).

North is up with east to the left. Since the comet was moving across the sky fairly quickly, and since colour images are made by combining successive exposures through three different filters, a conventional combination would have either a streaked comet or a set of colored dots for each star.

To avoid this, the complete sequence of images, lasting over ninety minutes, was specially processed. All frames for one color were combined with filtering that removed the moving comet: this stars-only image was subtracted from each comet frame, and the comet frames were registered and summed with further filtering to remove any residuals.

The two images, with stars only and with comet only, were then added together to produce a single-color image in which neither the comet nor the stars was trailed. These three frames were then united in the final color picture, shown here.

Credit: N.A.Sharp/NOAO/AURA/NSF

Double Comet Feature: Elenin & Garradd Now Showing in Night Sky

Skywatchers often ask "When's the next comet?" In fact, if you’re prepared to do a bit of searching, there are always several comets visible in the night sky, including two right now.

Some comets are like old friends, they keep coming back at regular intervals to visit.

These are called periodic comets; Comet Halley was the first such comet to be identified, by Edmond Halley back in 1705.

It returns to the inner solar system every 75 to 76 years; its last appearance was in 1986 and its next will be in 2061. At present Halley is out just beyond Neptune;s orbit.

Comet Watchers get ready for C/2009 R1

The C/2009 R1 comet is nearing the Earth and will be visible in the Northern hemisphere with a naked eye in mid-June, NASA said on its website. The comet, discovered in 2009 by well-known British-Australian astronomer and "comet-catcher" Robert H. McNaught, is already visible through powerful binoculars in the morning sky.

NASA said the comet will reach its closest proximity to the Earth by June 15 and could shine just above the horizon in the Perseus constellation. It could be brighter than Venus and visible during the day.

The comet's green plasma head, or coma, is larger than the planet Jupiter, while the long willowy ion tail stretches more than a million kilometers through space.

Russian astronomer Leonid Yelenin from the Keldysh Institute of Applied Mechanics said on Tuesday the comet would be clearly visible in Russia.

"It will be visible in the morning and will present a good object for observation, although its beautiful tail is unlikely to be discernable," Yelenin said.

He said the brightness of the comet could vary as it nears the Sun and could either fade quickly or suddenly increase its magnitude.

"Different models estimate its brightness at magnitude three or even one," he said.

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere.

The brighter the object appears, the lower the value of its magnitude. Very bright objects have negative magnitudes.