Who can forget last October, when astronomers all over the world were astounded by the huge outburst of Comet Holmes? The eruption was the largest for more than a century. (Click on image to animate.) Fortunately for the world, a UK telescope was in the right place and the right time to capture the first images of this once-in-a-lifetime event.
The SuperWASP-North facility on the island of La Palma was built by UK scientists to discover planets around other stars. The 8 cameras that make up the system operate robotically, automatically scanning large areas of the sky each night. By coincidence, at 2339 GMT on the evening of 24 October 2007, it was pointing towards Comet 17P Holmes.
"By the time SuperWASP spotted the comet, it had already brightened by a factor of 1000" explains Dr. Henry Hsieh. "But this was still almost 3 hours before anyone else noticed it." (The lucky astronomer and the honor belongs to amateur astronomer Juan Antonio Henriquez Santana who saw the eruption from Tenerife. Score a point for those of us who scan the skies!). Over the next 2 hours the comet continued brightening, until SuperWASP could no longer accurately measure it - it was too bright for the cameras. for movie click here [link=http://www.universetoday.com/wp-content/uploads/2008/04/anim-holmes2.gif]Holmes discharge[/link]
Last October, astronomers all over the world were astounded when the normally very faint Comet Holmes erupted in the largest outburst for more than a century. Speaking at the RAS National Astronomy Meeting in Belfast on Wednesday 2 April, Queen's University Belfast astronomer Dr. Henry Hsieh will describe how a UK telescope was in the right place at the right time to capture the first images of this once-in-a-lifetime event.
The SuperWASP-North facility on the island of La Palma was built by UK scientists to discover planets around other stars. The 8 cameras that make up the system operate robotically, automatically scanning large areas of the sky each night. By coincidence, at 2339 GMT on the evening of 23 October 2007, it was pointing towards Comet 17P Holmes.
"By the time SuperWASP spotted the comet, it had already brightened by a factor of 1000," explains Dr. Hsieh. "But this was still almost 2 hours before anyone else noticed it." (That honour belongs to amateur astronomer Juan Antonio Henriquez Santana who saw the eruption from Tenerife).
Over the next 2 hours the comet continued brightening, until SuperWASP could no longer accurately measure it - it was too bright for the cameras!
Comets are bodies orbiting the Sun composed of frozen gases and microscopic solid particles in a small solid nucleus. When they come close to the Sun, they heat up and some of the icy material turns to gas, producing characteristic tails. But during this outburst, Comet Holmes released a large amount of its material all at once.
Two days after the eruption began, sunlight reflecting from the ejected material had made the comet one million times brighter than it was originally making it easily visible to observers across the northern hemisphere.
Dr. Hsieh comments "Over the next few weeks, SuperWASP continued to observe Comet Holmes as the cloud of dust and gas surrounding the 3-km diameter nucleus of the comet steadily expanded.� By 31st October, the cloud was already 900,000 km across or more than twice the distance from the Earth to the Moon."
"Using our SuperWASP observations, we measured the speed of expansion of the outer edge of this cloud to be over 1500 km per hour and by 17 November measured the size of the cloud to be more than 2 million km across - much larger than the Sun."
Two weeks after the outburst, SuperWASP captured an added bonus - the faint and delicate tail of the comet composed of the gas released from the nucleus. As astronomers watched over the next few weeks, this tail gradually faded and moved away from the comet.
Although many images were gathered by astronomers around the world, the precise cause of the outburst is still a mystery. All they know right now is that it happened once before - in 1892 - and may well happen again. http://star.pst.qub.ac.uk/~hhh/holmes/
StefanR
Re: Recovered: Holmes gets very bright
NASA's Spitzer Gets Sneak Peek Inside Comet Holmes He notes that the shell surrounding the comet also acts peculiarly. The shape of the shell did not change as expected from November 2007 to March 2008. Vaubaillon said this is because the dust grains seen in March 2008 are relatively large, approximately one millimeter in size, and thus harder to move.
"If the shell was comprised of smaller dust grains, it would have changed as the orientation of the sun changes with time," said Vaubaillon. "This Spitzer image is very unique. No other telescope has seen comet Holmes in this much detail, five months after the explosion."
NASA's Swift looks to comets for a cool view NASA's Swift Gamma-ray Explorer satellite rocketed into space in 2004 on a mission to study some of the highest-energy events in the universe. The spacecraft has detected more than 380 gamma-ray bursts, fleeting flares that likely signal the birth of a black hole in the distant universe. In that time, Swift also has observed 80 exploding stars and studied six comets. Comets? ... Comets are "dirty snowballs" made of frozen gases mixed with dust. X-rays come from superhot plasmas. What do cold comets have in common with exploding stars or the birth of black holes?
"It was a big surprise in 1996 when the NASA-European ROSAT mission showed that comet Hyakutake was emitting X-rays," says Dennis Bodewits, a NASA Postdoctural Fellow at the Goddard Space Flight Center in Greenbelt, Md. "After that discovery, astronomers searched through ROSAT archives. It turns out that most comets emit X-rays when they come within about three times Earth's distance from the sun." When Comet 17P/Holmes underwent a surprising outburst in October 2007, Bodewits tasked both Swift and NASA's Chandra X-ray Observatory to observe it. "The comet was too bright to observe with the UVOT. We were afraid we'd damage the instrument," Bodewits says. "Despite this, we're still not sure whether we detected Holmes with the XRT or Chandra."
At the time of the outburst, Holmes was about 19 degrees above the ecliptic, the plane in which the planets orbit the sun. At that elevation, the comet was probably experiencing a cooler, steadier flow from the solar wind. "The source of this cooler flow wasn't hot enough to produce the ions Holmes needed to make X-rays," Bodewits notes.
Four years ago today, Swift captured its first x-rays. The radiation came from Cygnus X-1, one of sky's strongest sources at these energies. The system, located within our galaxy, contains a hot, blue-giant star orbited by a black hole.
"Swift has operated two years longer than we had hoped," says Neil Gehrels, the mission's lead scientist at NASA's Goddard Space Flight Center. "And while gamma-ray bursts and stellar explosions are the satellite's bread and butter, it's clear that Swift has a lot to contribute to other areas of astronomy."
The comets, of which there could be thousands, are not currently monitored by observatories and space agencies.
Most comets and asteroids are monitored in case they start to travel towards earth.
But Bill Napier, from Cardiff University, said that many could be going by unnoticed.
"There is a case to be made that dark, dormant comets are a significant but largely unseen hazard," he said
Scientists estimate that there should be around 3,000 comets in the solar system, but only 25 have so far been identified.
"Dark" comets happen when the water on their surface has evaporated, causing them to reflect less light.
Astronomers have previously spotted comets heading towards earth just days before they passed.
In 1983 a comet called IRAS-Araki-Alcock passed at a distance of just 5 million kilometres, the closest of any comet for 200 years, but it was noticed just a fortnight beforehand.
Tests on another comet, called Comet Borrelly, in 2001 revealed it to have large dark patches across much of its surface.
Steve Larson of the University of Arizona's Catalina Sky Survey in Tucson, which monitors comets, said the idea of an unknown number of "dark" comets circling earth had "merit".
But Clark Chapman from the Southwest Research Institute in Boulder, Colorado, said that such comets "would absorb sunlight very well" and so could be detected by the heat they emit, reports New Scientist magazine.
Any explanations for their observations??
NO SNICKERING!!
Grey Cloud
Re: Dark comets 'could pose deadly threat to earth!!!
Hi Tzunamii, A bit of a non-story really, especially as it is in the Daily Telgraph. Napier of Clube and Napier is a catastrophist. They have a theory involving the Taurid meteors and comet Enke I think it is. They have written a couple of books. The rest of them just appear to be rent-a-quote scientists.
Just more doom and gloom reporting - worried people make better consumers.
Kwicky
Re: Dark comets 'could pose deadly threat to earth!!!
What does one call a comet nucleus with no water or volatiles? A giant hunk of rock? As-ter-oid? Wha-aa?
Kwicky
longcircuit
"Dark comets"âThreat or menace?
Read all about it here. How warm does space have to be for an 'active' comet's reflective water ice" to "evaporate away, leaving behind an organic crust that only reflects a small fraction of light?" As Anna Russell used to say when talking about the operas of Wagner: "I'm not making this up, you know!"
Well, shoot. I didn't really want to start a new topic, and looked through what I thought were relevant threads, but I obviously missed those two. It just goes to show one has to get up pretty early to beat others to a topic. Moderator/admin: feel free to move my original post to the other threads.
longcircuit
Lloyd
Re: Dark comets 'could pose deadly threat to earth!!!
* I came across this in an art book yesterday and figured it needs to be here on the forum somewhere. It's got comets, little girls who are half-serpent-comets, dormant trees of life on the stairway to heaven and possible world mountains. * It's called "The Truth about Comets and Little Girls", by Dorothea Tanning.
longcircuit
And now, the hidden asteroid menace
Read all about it here. What's next—"dark asteroids"?
longcircuit
mharratsc
Re: Dark comets 'could pose deadly threat to earth!!!
... so Grey Cloud said:
Just more doom and gloom reporting - worried people make better consumers.
... and Longcircuit posted a link from which I pulled these quotes:
But the most exciting and potentially worrying possibility is that there exists a previously unseen population of near Earth asteroids that orbit the Sun at approximately the same distance as the Earth
and:
And let's not waste too much time about it. By some reckonings, asteroid impacts represent the greatest threat to humankind that we are able to calculate.
Et tu, Technology Review??
Mike H.
electrodogg1
Mini Holmes - Comet explosion
From space.com
Comet Outburst Spawns Mini-Comets
space.com – Tue Sep 15, 9:01 pm ET
A comet recently spewed out a cluster of mini comets in a huge outburst that was the largest ever witnessed by astronomers.
A team of researchers began observing the comet 17P/Holmes in October 2007, after it was reported that the object, about 2.2 miles wide (3.6 km wide), had brightened by a million times in less than a day.
UCLA researcher Rachel Stevenson and colleagues noted multiple fragments flying rapidly away from the comet's nucleus. They continued observing for several weeks after the outburst using the Canada-France-Hawaii Telescope in Hawaii and watched as the dust cloud ejected by the comet grew to be larger than the sun.
The astronomers examined a sequence of images taken over nine nights using a digital filter that enhances small features. They found numerous tiny objects that moved away from the nucleus at speeds of up to 280 mph (125 meters per second). These objects were too bright to simply be bare rocks, but instead were more like mini comets, creating their own dust clouds as ice on their surfaces sublimated directly to vapor.
"Initially we thought this comet was unique simply because of the scale of the outburst," Stevenson said. "But we soon realized that the aftermath of the outburst showed unusual features, such as these fast-moving fragments, that have not been detected around other comets."
Although the outburst was impressive in the telescope images, it wasn't visible to the naked eye.
Scientists aren't sure of the exact cause of the outburst. Possibly, pressure inside the comet built up as it moved closer to the sun, until eventually part of the surface broke away, releasing a huge cloud of dust and gas, as well as larger fragments.
Even after ejecting mini comets, the solid nucleus of comet Holmes survived and continued on its orbit, seemingly unperturbed.
Holmes takes about 6 years to circle the sun, and travels between the inner edge of the asteroid belt to beyond Jupiter. The comet is now moving away from the sun but will return to its closest approach in 2014, when astronomers will examine it for signs of further outbursts.
Stevenson will present the findings at the European Planetary Science Congress in Potsdam, Germany on Wednesday.
So does this mean from an EU perspective that the current density on comet Holmes became too great and it split into many mini Holmes?
mharratsc
Re: Mini Holmes - Comet explosion
From what I've learned so far, I would say that the comet came under extreme electrical stress, and blew off some matter so as to provide more surface area than it currently had, thereby reducing the electrical stress (per square meter) that it was under.
This would be much akin to Wal Thornhill's theory on planetary formation via electrical stress from stellar bodies and gas giants, and lunar body formation from rocky planets.
How's that?
They did say that this event occurred shortly after Holmes had brightened by a factor of a million, and each of the 'mini-comets' showed a high level of electrical stress as well (they were incandescent like the parent comet).
