Comets Archives

May 6, 2008January 24, 2021 by Fraser Cain

Comet Strikes Increase as We Pass Through the Galactic Plane

There are just so many ways the Universe is out to get us. Astronomers have already considered the threat from our Sun’s orbit around the center of the Milky Way. When our Sun rises up out of flat plane of the Milky Way, it appears we might be less protected from intergalactic radiation and cosmic rays. Well, it looks like passing through the middle of the galactic plane might have its own share of risks: an increased number of comets might be hurled towards the Earth because of gravitational interaction with the densest parts of our galaxy.

Researchers at the Cardiff Centre of Astrobiology have built a computer model of the Solar System’s journey around the Milky Way. Instead of making a perfectly flat orbit around the galaxy’s centre, it actually bounces up and down. At times it can rise right up out of the galactic plane – getting 100 light years above – and then dip down below it. They calculated that we pass through the plane every 35 to 40 million years.

And this time period seems to match dangerous periods of impacts on Earth. According to the number and age of craters on Earth, we seem to suffer increased impacts every 36 million years. Uh oh, that’s a match.

In fact, one of these high points of comet activity would have been 65 million years – the same time that an asteroid strike wiped out the dinosaurs.

And here’s the bad news. According to their calculations, the Solar System will be passing through the galactic plane in the near future, and should see an increased risk of impact. Our risk of impact could increase 10-fold.

There might be a silver lining to the bounce, though. The impacts might have helped life spread across the galaxy.

While the “bounce” effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.

Centre director Professor Chandra Wickramasinghe said: “This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale.”

Here’s more info on the story from Bad Astronomy.

Original Source: Cardiff News Release

April 2, 2008December 24, 2015 by Tammy Plotner

Planet Finder Catches a Comet!

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.

Orbiting the Sun, comets are mainly composed of frozen gases and microscopic solid particles in a small solid nucleus. As they pass by our solar system’s nearest star, they heat up, releasing gas pockets and other frozen materials. Most of us understand outgassing and the properties of cometary 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 scored again – the faint and delicate tail of Comet Holmes 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. Keep watching!

January 25, 2008December 26, 2015 by Fraser Cain

Comet Dust is Very Similar to Asteroids

Just so it’s clear in your mind: comets are dirty snowballs, asteroids are rocks. Got the difference? Wait… not so fast. Scientists studying the cometary dust picked up by NASA’s Stardust spacecraft, and they’re finding it’s surprisingly asteroid like.

When Stardust flew past comet Wild 2 in 2006, scientists knew they would be scooping up materials created with the very formation of the solar system. But they didn’t think the dust from Wild 2 would resemble meteorites more than ancient, unaltered comet.

Comets are thought to contain large amounts of primitive material in the Solar System. Both the ancient ices that formed out of the stellar disk, but also the rain of interstellar material falling into the Solar System.

According to researchers at Lawrence Livermore National Laboratory, the particles that fell off Wild 2 formed very close to the Sun when it was young. They had been baked and blasted by the intense ultraviolet radiation of a newly forming star. Furthermore, they didn’t find the kind of primordial materials and ices that should have been present on an ancient comet like Wild 2.

“The material is a lot less primitive and more altered than materials we have gathered through high altitude capture in our own stratosphere from a variety of comets,” said LLNL’s Hope Ishii, lead author of the research that appears in the Jan. 25 edition of the journal, Science. “As a whole, the samples look more asteroidal than cometary.”

But Wild 2 is clearly a comet and not an asteroid. It’s got a tail; what could be more cometlike? It’s a reminder that there isn’t a clearly defined line between the two objects – there’s a continuum between them.

The researchers were expecting to see very specific minerals in the Stardust samples that should be coming from comets: glass with embedded metal and sulfides, and sliver-like whiskers of the crystallin silicate enstatite. They found only a single sample of enstatite in their samples and it was oriented the wrong way.

There were similar minerals found, but the researchers realized that they were being created when particles from the comet slammed into the Stardust collector. They were able to recreate this process in the lab.

For future studies, the researchers are hoping to get their hands on larger-grained materials, called micro-rocks. These would suffer less alteration from the impact with the Stardust collectors.

Original Source: LLNL News Release

December 14, 2007December 26, 2015 by Fraser Cain

Deep Impact Has a New Target

It seemed like such a shame. NASA built Deep Impact to see what happens when you smash a refrigerator-sized object into a comet. Mission accomplished, science gathered. But what about the flyby part of the spacecraft? It captured images of the collision with Comet Tempel 1, and then flew on without a target. Well, NASA announced this week that it has a new target: Comet Hartley 2.

Oh, and we don’t call it Deep Impact any more. That was so 2005. Now it’s called EPOXI. And if that sounds like an acronym, you’re right. Here’s the full designation: Extrasolar Planet Observation and Deep Impact Extended Investigation.

EPOXI was originally supposed to meet up with Comet Boethin, but NASA astronomers lost sight of the comet. They lost a comet? Actually, they think it might have broken up into smaller pieces, which are now too small for detection. Unfortunately, this loss pushed back its next cometary encounter by two years.

So the spacecraft is now heading for Comet Hartley 2. If all goes well, it’ll reach the object on October 11, 2010, passing within 1,000 km (620 miles) of the nucleus. As a target for scientific observation, Comet Hartley 2 will do the job nicely. Just like Boethin, it has a small, bright nucleus.

While it’s making this journey, the spacecraft will point the larger of its two telescopes at nearby extrasolar planetary systems, and help gather additional data. It’ll be looking to study the physical properties of giant planets, search for rings and moons and planets as small as three Earth masses.

One intriguing mission will have EPOXI observe the Earth as if it’s an extrasolar planet, to help refine the techniques and data necessary to characterize future terrestrial planet discoveries.

EPOXI made a three-minute rocket burn on November 1st, 2007, putting it on course to reach Hartley 2. Before this encounter, it’ll make three Earth flybys, gathering the additional velocity it needs to reach its meetup with Hartley 2 in 2010.

Original Source: NASA/JPL News Release

November 27, 2007December 26, 2015 by Fraser Cain

Comet Holmes is Fading Away

For a little while there, Comet 17P/Holmes was the largest object in the Solar System, flaring up by a factor of over a million. Its cloud of gas and dust expanded outward to cover a diameter of 1.4 million km (870,000 miles) – bigger than the Sun. Well, the party’s over. Comet Holmes is fading away again. But will it follow history and flare up again?

This image of Comet Holmes was captured by the MMT observatory on November 4th, 2007 using an instrument called “Megacam”. This is one of the largest CCD cameras on Earth, putting 36 9-megapixel CCD chips together to form a single array with 300 megapixels.

The camera captured images of the comet with three separate exposures in three colours to produce this full colour image.

If you want to see Holmes before it fades into obscurity again, you’re going to need binoculars. Although it’s still a 3rd magnitude object, and should be visible with the unaided eye, it’s so large in the sky that it’s actually quite faint now.

Astronomers are hoping that it’ll repeat history. During its last outburst back in 1892, the comet underwent a second bright flareup five months after the first one. So, if history is any judge, we might just see the comet brighten again, and we’ll all get another chance to see it before it’s gone for good.

Original Source: CfA News Release

November 15, 2007December 26, 2015 by Fraser Cain

Finally, Hubble’s View of Comet Holmes

All right, here’s the picture we’ve all been waiting for. Step aside ground-based observatories, papa Hubble’s here with images of Comet Holmes, which is now larger than the Sun. But don’t get fooled. That beautiful image on the left was taken by amateur astronomer Alan Dyer from Alberta, Canada. Hubble’s version on the right. It’s not as pretty, but it’s got inner bigness.

You already know the story. Comet Holmes was a boring comet out near the orbit of Jupiter when it flared up on October 23rd. The coma of gas and dust expanded away from the comet, and now it extends to a volume larger than the Sun.

Of course, astronomers scrambled to turn the mighty Hubble Space Telescope to join in on the sky show. The space observatory’s Wide Field Planetary Camera 2 monitored the object for several days, capturing images on October 29, 31 and November 4.

The Hubble image on the right reveals the comet’s nucleus down to a resolution as small as 54 km (33 miles) across. The image was processed to reveal differences in dust distribution near the nucleus.

Astronomers found that there’s twice as much dust along the east-west direction as the north-south direction. This gives the comet a bowtie appearance. Even 12 days after the outburst, when this picture was captured, the nucleus is still surrounded by bright dust.

This isn’t the first time that Hubble has viewed Comet Holmes. Luckily, it actually captured an image back in June 15, 1999. Back then, there was no dust around the object, and Hubble couldn’t reveal the nucleus. By measuring its brightness, astronomers estimated that Holmes is approximately 3.4 km (2.1 miles) across.

Once Holmes settles down again, astronomers will use Hubble to make another accurate measurement of its brightness. By calculating the difference, astronomers will be able to figure out how much mass it lost during this outburst.

Original Source: Hubble News Release

November 13, 2007December 26, 2015 by Fraser Cain

Comet Holmes is Bigger than the Sun

All right, that title is a little misleading. In fact, when I first read the original press release, my skepticism alarms went off. But it’s true, the amazing Comet Holmes now has a halo that’s larger than the Sun. Not bad for a comet that, until three weeks ago, was just a tiny dim dirty snowball orbiting near Jupiter.

Comet Holmes made its spectacular outburst on October 24, 2007. Formally dim enough to only be visible in the most powerful telescopes, it quickly brightened up to be seen with the unaided eye – even in light-polluted cities (like my very own Vancouver).

Astronomers from the University of Hawaii’s Institute for Astronomy recently measured the halo surrounding Comet Holmes to be 1.4 million kilometres (0.9 million miles). And as I mentioned in the opening paragraph, that makes it larger than the Sun. Of course, it’s just a thin halo of gas and dust particles, but still, that’s pretty impressive.

Just to get a sense of the change, Holmes has brightened by a factor of 500,000x. All this gas and dust is pouring out of a tiny nucleus only 3.6 km (2.2 miles) in diameter.

In the image captured by the Institute for Astronomy, you can make out the brighter nucleus, near the centre of the halo. And then there’s a hazy tail pointing towards the lower right of the image.

Over the next few months, astronomers predict the cometary halo will expand even larger; although, it will be fading away as the dust disperses over a larger volume.

Holmes performed a similar outburst back in 1892, and it brightened again just a couple of months later. Astronomers are hoping it’ll make another double outburst, just like it did before.

Original Source: IfA News Release

November 9, 2007December 26, 2015 by Fraser Cain

Rosetta Is Returning to Earth for Another Flyby

Mark your calendars for November 13th, 2007. That’s the day ESA’s Rosetta spacecraft will be making a close encounter with Earth on its way to Comet 67/P Churyumov-Gerasimenko. What’s going on? The comet’s out there guys, why is Rosetta back home? Well, it’s all about speed.

Launching spacecraft is an energy intensive business. You can only get a spacecraft going so fast when it launches directly from Earth. But using a technique called gravity assist, spacecraft can use the gravity of a planet – such as the Earth – to get a speed boost. Most of the robotic explorers do it.

In order for Rosetta to make its encounter with Comet 67/P Churyumov-Gerasimenko in 2014, it needs to be going much faster. It already got a gravity assist from Earth back in March 4, 2005, and another with Mars on February 25, 2007. Now its time for a third on November 13. We won’t be done with Rosetta yet, either. The spacecraft is due to make a 4th and final flyby on November 13, 2009.

Before it returns for the 4th flyby, Rosetta will swing out across the asteroid belt and observe asteroid Lutetia, testing out its scientific equipment.

Finally, in 2014, Rosetta will reach Comet 67/P Churyumov-Gerasimenko and begin some serious investigations; even landing a probe down on its surface.

Original Source: ESA News Release

October 31, 2007December 26, 2015 by Fraser Cain

Detailed Images of Comet Holmes

Late last week, the normally dim Comet 17P/Holmes suddenly blazed into view, increasing in brightness by a factor of a million. Before the eruption you needed a large telescope to see it, and now you can make it out with the unaided eye – even in the light-polluted city skies.

There are now many amateur and professional astronomers turning their gaze towards the newly brightened comet.

Eric Allen has been capturing images for several days, and stitched them together into an animation that shows the expanding coma. Even cooler, he compares it to Jupiter visually, so you can see just how big and bright it has gotten.

UK astronomers tuned in with the powerful Isaac Newton Telescope in La Palma, showing the fuzzy coma. They also tucked in an image of the Earth in the bottom corner, for scale.

Astronomers from the University of Montreal captured this image that seems to show that the comet has an actual tail.

Probably the best image I’ve seen was captured by Mario Motta from the Amateur Telescope Makers in Boston. His image shows what clearly looks like a jet, blasting off one side of the comet.

Still want more images? Space Weather has this enormous photo gallery of images of Comet 17P/Holmes.

Over the next few days/weeks, I’m sure some even bigger telescopes will be joining the fray, so stay tuned.

October 24, 2007January 24, 2021 by Fraser Cain

Comet 17P/Holmes Erupts in the Sky

Astronomers from Europe and Asia are reporting that the normally dim Comet 17P/Holmes has had an eruption. Instead of being 17th magnitude – only visible to powerful telescopes – it’s now 3rd magnitude. This makes it easy to spot with the unaided eye, even in cities with heavy light pollution.

To confirm this discovery, head outside after the skies are dark, and look to the Northeast. The comet is currently in the constellation Perseus, which is below the more familiar Cassiopeia. If you’re familiar with the constellations at all, you’ll now see a new, bright yellow star. A telescope reveals the fuzzy corona surrounding the comet.

One report from Japan says, “Perseus does not look ‘Perseus’ familiar to us due to the bright stellar object now.”

Spaceweather and Bad Astronomy have more details.

Thanks to BAUT member Keith G for the photograph. Here’s a link to the forum where people are discussing it.