Comets


Meteor

Constant Comet Threat

Halley's Comet
© Lick ObservatoryHalley's Comet becomes visible to the unaided eye about every 76 years as it nears the sun.
It certainly captures the imagination: a star passing silently by our solar system knocks a deadly barrage of comets towards Earth. However, recent simulations by one group of researchers has shown that these star-induced comet showers may not be as dramatic as once thought.

The idea of nearby stars influencing comets goes back to 1950, when the astronomer Jan Hendrik Oort hypothesized an invisible repository of comets - the so-called Oort cloud - swarming around the solar system out to a distance of 100,000 AU (one AU is the distance between the sun and the Earth).

Oort assumed that stars passing through the cloud would cause a fresh batch of comets to fall in towards the sun, where they become visible to astronomers. Such a disturbance could have long term effects.

"The comets we see now could be from a stellar passage hundreds of millions of years ago," said Hans Rickman of the Uppsala Astronomical Observatory in Sweden.

However, Rickman and his colleagues have confirmed that star encounters alone cannot explain comet behavior. Using a computer model of the Oort cloud, they show that gravity effects from the galaxy are equally important. The results are reported in a recent article in the journal Celestial Mechanics and Dynamical Astronomy.

Comment: Have you read Cosmic Turkey Shoot?


Meteor

Odd Comet Possibly from Another Star System

The bizarre chemical make-up of a comet suggests the blob of ice is an interloper, possibly flung into our solar system from beyond, astronomers now say, adding that the wacky comet is forcing them to create a new category for such objects.

The comet, called Machholz 1, was discovered in 1986 by Donald Machholz of Loma Prieta, Calif. Since then, the icy denizen has made a few appearances, including one in 2007.
Comet Machholz 1
© SOHO/LASCO (ESA & NASA)This image taken by the ESA-NASA sunwatching spacecraft SOHO reveals Comet Machholz 1 close to the sun on Jan. 8, 2002. SOHO's coronograph hid the bright sun, the size of which is shown by the inner ring.

"A large fraction of comets in our own solar system have escaped into interstellar space, so we expect that many comets formed around other stars would also have escaped," said David Schleicher, a planetary astronomer at Lowell Observatory in Arizona. "Some of these will have crossed paths with the sun, and Machholz 1 could be an interstellar interloper."

Telescope

New telescope to search for comet-like objects

Honolulu - A University of Hawaii professor says the Big Island will be home to a new telescope.

Professor Robert Fox of the university's Hilo campus says the device can fit into a garage-size building and will search for comet-like objects beyond Neptune.

Fox says it will not be placed atop Mauna Kea, site of several telescopes. He says other Big Island sites are being considered.

Telescope

Big bang's afterglow may reveal birthplace of comets

A vast reservoir of comets that is too far away to see might be detectable in maps of radiation left over from the big bang, a new study suggests.

Comets that take longer than 200 years to orbit the Sun come from all directions in the sky. That has long led scientists to believe that they were nudged out of a diffuse halo of icy objects that surrounds the solar system - the Oort Cloud.
Image
© www.jonlomberg.comOort Cloud objects orbit the Sun in a spherical outer shell shown here, as well as in an inner cloud that might be more disc-like. If the inner cloud is squashed enough, it could be detected in radiation left over from the big bang.

The objects probably formed from the same disc of material that gave rise to the planets but were scattered outwards by Jupiter and Saturn a few hundred million years after their birth.

The Oort Cloud is too dim to be seen by telescopes, but astronomers believe it has two components. Based on observations of long-period comets, an outer portion seems to extend from 20,000 to 200,000 astronomical units from the Sun (where 1 AU is the Earth-Sun distance).

Info

Did lack of comet impacts help life evolve?

It seems we got off lightly in the cosmic lottery. Deadly comet impacts may be much rarer in our solar system than in others nearby.

We can't directly measure the rate of comet collisions in other solar systems but we can detect signs of the dust that such smashes kick up because the dust gets warmed by the star and so gives off infrared radiation. That radiation shows up as extra infrared in the spectrum of light coming from the star. Because such dust should dissipate quickly, it is thought to provide a good snapshot of the recent collision rate.

Jane Greaves of the University of St Andrews, UK, analysed observations by the Spitzer Space Telescope and found that the vast majority of sun-like stars near us have more dust than our solar system does and therefore have had more collisions in their vicinity. Our solar system may be one of the few that have been safe for life. Greaves presented her results at the Cosmic Cataclysms and Life symposium in Frascati, Italy, this month.
comet being torn to shreds around a dead star
© C GSF/Caltech/JPL/NASAThis artist's concept illustrates a comet being torn to shreds around a dead star, or white dwarf, called G29-38.

Comment: While comet impacts may be "much rarer" in our solar system than others, it certainly does not mean they do not strike ours. For a more enlightening and detailed study, read Forget about Global Warming, We are One Step From Extinction!


Telescope

Early warning of dangerous asteroids and comets

Pan-STARRS 1 prototype
© MIT Lincoln LaboratoryPan-STARRS 1 prototype, part of the Panoramic Survey Telescope and Rapid Response System, Haleakala mountain, Maui
Detectors developed at Lincoln Laboratory deployed in powerful telescope

Silicon chips developed at MIT Lincoln Laboratory are at the heart of a new survey telescope that will soon provide a more than fivefold improvement in scientists' ability to detect asteroids and comets that could someday pose a threat to the planet.

The prototype telescope installed on Haleakala mountain, Maui, will begin operation this December. It will feature the world's largest and most advanced digital camera, using the Lincoln Laboratory silicon chips. This telescope is the first of four that will be housed together in one dome. The system, called Pan-STARRS (for Panoramic Survey Telescope and Rapid Response System), is being developed at the University of Hawaii's Institute for Astronomy.

Telescope

Comet Particles Provide Glimpse Of Solar System's Birth Spasms

Scientists are tracking the violent convulsions in the giant cloud of gas and dust that gave birth to the solar system 4.5 billion years ago via a few tiny particles from comet Wild 2.

These convulsions flung primordial material billions of miles from the hot, inner regions of the gas cloud that later collapsed to form the sun, out into the cold, nether regions of the solar system, where they became incorporated into an icy comet.
Inti particle
© University of ChicagoA transmission electron microscope image (magnified 5,000 times) of a slice of the Inti particle, which NASA’s Stardust spacecraft collected in 2004 and returned to Earth two years later. Preparation of the sample caused some breakage. Scale bar is one micron, or one millionth of a meter.

"If you take a gas of solar composition and let it cool down, the very first minerals to solidify are calcium and aluminum-rich," said Steven Simon, Senior Research Associate in Geophysical Sciences at the University of Chicago. And comet Wild 2 does contain these and other minerals formed at high temperatures. "That's an indication of transport from the inner solar system to the outer solar system, where comets are thought to have formed," he said.

Telescope

NASA's Spitzer tries to unravel mysterious comet explosion

Washington: NASA's Spitzer Space Telescope has deeply observed comet Holmes to find out why it suddenly exploded in 2007.

Observations taken of the comet by Spitzer deepen the mystery, showing oddly behaving streamers in the shell of dust surrounding the nucleus of the comet.
The data also offer a rare look at the material liberated from within comet Holmes' nucleus, and confirm previous findings from NASA''s Stardust and Deep Impact missions.

"The data we got from Spitzer do not look like anything we typically see when looking at comets," said Bill Reach of NASA''s Spitzer Science Center at the California Institute of Technology, Pasadena, California.

"The comet Holmes explosion gave us a rare glimpse at the inside of a comet nucleus," he added.

Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident.

Meteor

Italian astronomer finds new comet

ROME -- An Italian astronomer said he has discovered a new comet --the fifth one he has found in less than a year.

Andrea Boattini, who is currently working at Mount Lemmon Infrared Observatory in Arizona, said he spotted the comet while scanning near-Earth objects, the Italian news service ANSA reported Wednesday.

The comet, technically named P/2008 T1, will also be known as Boattini T1. The astronomer said it was easy to spot because of its unusual blaze and fan-like tail.

Meteor

New comet discovered where comets aren't usually found

Calgary - Astronomer Rob Cardinal didn't expect the time he spent installing new software at the University of Calgary's Baker-Nunn telescope earlier this month to change his life.

But days later, his computer was telling him there had been some unusual movement through the telescope - motion that Mr. Cardinal hadn't detected while gazing through it.

But after some sleepless nights peering through cloud cover and finally spying what he'd missed, Mr. Cardinal is now the confirmed finder of C2008 T2, a never-before-identified comet travelling through the solar system.

Or, as it will also be known, Comet Cardinal.