Jupiter - Our Cosmic Protector?
by Dennis Overbye
July 25, 2009

from TheNewYorkTimes Website
 

Jupiter Takes One for the Team
 

An object, probably a comet that nobody saw coming, plowed into the giant planet’s colorful cloud tops sometime Sunday, splashing up debris and leaving a black eye the size of the Pacific Ocean.

This was the second time in 15 years that this had happened. The whole world was watching when Comet Shoemaker-Levy 9 fell apart and its pieces crashed into Jupiter in 1994, leaving Earth-size marks that persisted up to a year.

That’s Jupiter doing its cosmic job, astronomers like to say. Better it than us.

Part of what makes the Earth such a nice place to live, the story goes, is that Jupiter’s overbearing gravity acts as a gravitational shield deflecting incoming space junk, mainly comets, away from the inner solar system where it could do for us what an asteroid apparently did for the dinosaurs 65 million years ago. Indeed, astronomers look for similar configurations — a giant outer planet with room for smaller planets in closer to the home stars — in other planetary systems as an indication of their hospitableness to life.

Anthony Wesley, the Australian amateur astronomer who first noticed the mark on Jupiter and sounded the alarm on Sunday, paid homage to that notion when he told The Sydney Morning Herald,

“If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hovering up all these large pieces before they come for us.”

But is this warm and fuzzy image of the King of Planets as father-protector really true?

“I really question this idea,” said Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics, referring to Jupiter as our guardian planet.

As the former director of the International Astronomical Union’s Central Bureau for Astronomical Telegrams, he has spent his career keeping track of wayward objects, particularly comets, in the solar system.

Jupiter is just as much a menace as a savior, he said. The big planet throws a lot of comets out of the solar system, but it also throws them in.

Take, for example, Comet Lexell, named after the Swedish astronomer Anders Lexell. In 1770 it whizzed only a million miles from the Earth, missing us by a cosmic whisker, Dr. Marsden said. That comet had come streaking in from the outer solar system three years earlier and passed close to Jupiter, which diverted it into a new orbit and straight toward Earth.

The comet made two passes around the Sun and in 1779 again passed very close to Jupiter, which then threw it back out of the solar system.

“It was as if Jupiter aimed at us and missed,” said Dr. Marsden, who complained that the comet would never have come anywhere near the Earth if Jupiter hadn’t thrown it at us in the first place.

Hal Levison, an astronomer at the Southwest Research Institute, in Boulder, Colo., who studies the evolution of the solar system, said that whether Jupiter was menace or protector depended on where the comets came from.

Lexell, like Shoemaker Levy 9 and probably the truck that just hit Jupiter, most likely came from an icy zone of debris known as the Kuiper Belt, which lies just outside the orbit of Neptune, he explained. Jupiter probably does increase our exposure to those comets, he said.

But Jupiter helps protect us, he said, from an even more dangerous band of comets coming from the so-called Oort Cloud, a vast spherical deep-freeze surrounding the solar system as far as a light-year from the Sun. Every once in a while, in response to gravitational nudges from a passing star or gas cloud, a comet is unleashed from storage and comes crashing inward.

Jupiter’s benign influence here comes in two forms. The cloud was initially populated in the early days of the solar system by the gravity of Uranus and Neptune sweeping up debris and flinging it outward, but Jupiter and Saturn are so strong, Dr. Levison said, that, first of all, they threw a lot of the junk out of the solar system altogether, lessening the size of this cosmic arsenal.

Second, Jupiter deflects some of the comets that get dislodged and fall back in, Dr. Levison said.

“It’s a double anti-whammy,” he said.

Asteroids pose the greatest danger of all to Earth, however, astronomers say, and here Jupiter’s influence is hardly assuring. Mostly asteroids live peacefully in the asteroid belt between Mars and Jupiter, whose gravity, so the standard story goes, keeps them too stirred to coalesce into a planet but can cause them to collide and rebound in the direction of Earth.

That’s what happened, Greg Laughlin of the University of California at Santa Cruz, said, to a chunk of iron and nickel about 50 yards across roughly 10 million to 100 million years ago.

The result is a hole in the desert almost a mile wide and 500 feet deep in northern Arizona, called Barringer Crater.

A gift, perhaps, from our friend and lord, Jupiter.
 

Comment

from Sott Website

 

Regarding the claim that Jupiter "protects us from an even more dangerous band of comets coming from the so-called Oort Cloud", let's see what Clube and Napier, British astronomers and writers of The Cosmic Serpent, have to say:

The giant comets normally reside far beyond the planets, in a spherical cloud surrounding the Sun, called the Oort cloud. There is also evidence for a flattened disk of comets closer to the inner solar system, called the Edgeworth/Kuiper belt. What prompts members of either of these comet repositories to enter the realm of the planets? Clube and Napier suggest a galactic influence.

 

The solar system periodically passes through the plane of the galaxy as the Sun (and the solar system with it) orbits the galactic center. Each passage may dislodge giant comets and divert them closer to the Sun. The outer planets, particularly Jupiter, may then perturb some of these giant comets into orbits which enter the inner solar system.

 

These comets, stressed both by gravity and by heat from the sun, may fragment into a cloud of smaller objects with dynamically similar orbits.

Chiron offers a good example of a giant comet as called for by Clube and Napier's giant comet hypothesis. Chiron is somewhere between 148 and 208 kilometers in diameter. Currently Chiron's unstable "parking orbit" lies mostly between Saturn and Uranus. Chiron may end up injected into the inner solar system within a hundred thousand years, or ejected from the solar system on a similar time scale. It is also possible that Chiron has already visited the inner solar system.

The Taurid complex and the Kreutz sungrazer group are two families of objects which most likely represent the fragmented remains of two giant comets in the current era. SOHO has recently discovered many new members of the Kreutz group which were previously unknown.

The Kreutz progenitor was injected into a retrograde orbit and attained the sungrazing state at a high inclination to the ecliptic. Hence the debris of its "children" does not pose a threat to the Earth. The Taurid progenitor on the other hand ended up in a short-period low-inclination prograde orbit.

 

This is why the Earth can encounter its debris with potentially calamitous results.

What would happen should the Earth pass through the orbit of a disintegrating giant comet just before or after the comet passes that same point? Since larger fragments tend to cluster close to the nucleus of the comet, chances would increase that the Earth would be bombarded by these larger fragments.

 

The severity of this comet fragment shower would far exceed any ordinary meteor shower. Not only would "shooting stars" and bright fireballs caused by small debris appear, but so too would large airbursts and possibly ground impacts.

 

These would result in significant destruction should they occur over an inhabited area. If a large enough fragment struck in the ocean - say, 200 meters or so in diameter - it would raise tsunamis even at a great distance that would sweep away coastal habitations.

Duncan Steel, a colleague of Clube and Napier, refers to this process as coherent catastrophism.

 

Widespread destruction derives from the coherent arrival of many impactors within a few days, as opposed to the sporadic arrival of objects spread randomly in space. The shower repeats for a period of years until the cometary orbit precesses so that the Earth no longer encounters the dense part of the debris field.

 

(Of course, sporadic debris unrelated to the disintegrating comet may impact at any time as well.)

New Image of Jupiter Impact in Infrared
by Nancy Atkinson

July 23, 2009

from UniverseToday Website

This mid-infrared composite image was obtained with the Gemini North telescope on Mauna Kea, Hawai'i,

on 22 July at ~13:30 UT with the MICHELLE mid-infrared spectrograph/imager.

The impact site is the bright yellow spot at the center bottom of Jupiter's disk.

After getting whacked unexpectedly by a small comet or asteroid, Jupiter is sporting a "bruise," which has been big news this week. In visible wavelengths, the impact site appears as a black spot.

But in a new image taken in near infrared by the Gemini North telescope on Mauna Kea, Hawai'i, the spot shows up in spectacular glowing yellow.

"We utilized the powerful mid-infrared capabilities of the Gemini telescope to record the impact's effect on Jupiter's upper atmosphere," said Imke de Pater from the University of California, Berkeley.

 

"At these wavelengths we receive thermal radiation (heat) from the planet's upper atmosphere. The impact site is clearly much warmer than its surroundings, as shown by our image taken at an infrared wavelength of 18 microns."

As Universe Today reported earlier, this new spot on Jupiter was first seen by Australian amateur astronomer Anthony Wesley on July 19th.

This set off a flurry of activity as the large ground based observatories have imaged Jupiter in attempt to learn more about the impact and the object that struck Jupiter. Astronomers now say the object was likely a small comet or asteroid, just a few hundreds of meters in diameter. Such small bodies are nearly impossible to detect near or beyond Jupiter unless they reveal cometary activity, or, as in this case, make their presence known by impacting a giant planet.

In infrared, the impact site shows up in remarkable detail.

"The structure of the impact site is eerily reminiscent of the larger Shoemaker-Levy 9 sites 15 years ago," remarked Heidi Hammel (Space Science Institute), who was part of the team that supported the effort at Gemini.

In 1994, Hammel led the Hubble Space Telescope team that imaged Jupiter when it was pummeled by a shattered comet.

"The morphology is suggestive of an arc-like structure in the feature's debris field," Hammel noted.

The Gemini images were obtained with the MICHELLE spectrograph/imager, yielding a series of images at 7 different mid-infrared wavelengths.

Two of the images (8.7 and 9.7 microns) were combined into a color composite image by Travis Rector at the University of Alaska, Anchorage to create the final false-color image. By using the full set of Gemini images taken over a range of wavelengths from 8 to 18 microns, the team will be able to disentangle the effects of temperature, ammonia abundance, and upper atmospheric aerosol content.

Comparing these Gemini observations with past and future images will permit the team to study the evolution of features as Jupiter's strong winds disperse them.

"The Gemini support staff made a heroic effort to get these data," said de Pater. "We were on the telescope observing within 24 hours of contacting the observatory." Because of the transient nature of this event, the telescope was scheduled as a "Target of Opportunity" and required staff to react quickly to the request."

Backyard astronomer spots big bang on Jupiter

by Asher Moses
July 21, 2009

from SMH Website

An amateur Australian astronomer has set the space-watching world on fire after discovering that a rare comet or asteroid had crashed into Jupiter, leaving an impact the size of Earth.

Anthony Wesley, 44, a computer programmer from Murrumbateman, a village north of Canberra, made the discovery about 1am yesterday using his backyard 14.5-inch reflecting telescope.

The impact would have occurred no more than two days earlier and will only be visible for another few days. Within hours, his images had spread across the internet on science websites. NASA's Jet Propulsion Laboratory confirmed the discovery at 9pm yesterday using its large infrared telescope at the summit of Mauna Kea in Hawaii.

The only other time astronomers have discovered evidence of a space object having hit Jupiter was when the Shoemaker-Levy 9 comet collided with the giant planet in July, 1994. That event was also the first direct observation of two objects colliding in space.

Glenn Orton, the NASA scientist who confirmed Wesley's discovery, said:

"We are extremely lucky to be seeing Jupiter at exactly the right time, the right hour, the right side of Jupiter to witness the event. We couldn't have planned it better."

Orton said he was not yet sure whether the object that hit Jupiter was a comet, asteroid or some other piece of space junk.

But the impact mark is about the size of the Earth.

"It's been a whirlwind of a day and this, on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries, is amazing," he said.

To most people the image is unremarkable and appears as little more than a scar on Jupiter's vast gas surface.

Leigh Fletcher, an astronomer who worked with Orton on confirming the discovery last night, said:

"These are the most exciting observations I've seen in my five years of observing the outer planets."

Wesley said in a phone interview that documenting these sorts of impacts was the only way to get new data on how the solar system formed and what planets such as Jupiter are made of, as the impact throws up debris that would otherwise be invisible when looking through a telescope from Earth.

The collision also allows astronomers to examine Jupiter's role in cleaning up space debris in the solar system.

"If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hovering up all these large pieces before they come for us," he said.

"An impact event like this, even just knowing how often they happen, gives you some idea of how much debris is left over from the solar system when it formed and how quickly Jupiter is vacuuming up the remains of the bits and pieces floating around in the solar system."

Mike Salway, who runs the Australian amateur astronomy community website iceinspace.com.au, said astronomers around the world were raving about the discovery.

"Amateur astronomers are all over it at the moment - they all had their telescopes out last night looking for it," he said.

Wesley, who has been keen on astronomy since he was a child, said telescopes and other astronomy equipment were so inexpensive now that the hobby had become a viable pastime for just about anybody. His own equipment cost about $10,000.

In many cases, particularly with planets such as Jupiter, professional space watchers were turning to amateurs to provide them with new discoveries.

"A lot of the professional astronomers have access to large scopes but those scopes are in demand for all sorts of other jobs and you just can't afford to tie up a large telescope worth millions of dollars looking at Jupiter every night," Wesley said.

"These large telescopes only get built because of the interests of the consortium parties, and those interests need to be attended to, so it's really left to amateurs who've got no fixed agenda to image whatever they find interesting."

A new bright spot on Venus
by Dr. Emily Baldwin
ASTRONOMY NOW
July 21, 2009

from AstronomyNow Website

An intense bright spot has appeared in the clouds of Venus. Could it be associated with volcanic activity on the surface?

The Solar System is breaking out in spots. First Jupiter took a smack from a passing asteroid or comet, manifesting as a dark scar in the Jovian atmosphere, and now Venus is sporting a brilliant white spot in its southern polar region.

In an alert to fellow amateur astronomers, Venus observer Frank Melillo reports on his images captured on 19 July:

"I have seen bright spots before but this one is an exceptional bright and quite intense area."

Venus' bright spot as captured by Frank Melillo from New York.

Image courtesy Frank Melillo.
 

He suggests that it could be explained as an atmospheric effect, but could it be a sign of volcanic activity at the planet's surface? Venus is covered in a thick cloak of clouds which prevents any visible observation of the surface.

Instead, radar is used to map the surface, but volcanic activity has never been observed directly.

"A volcanic eruption would be nice, but let's wait and find out!" says Venus specialist Dr Sanjay Limaye of the University of Wisconsin. "An eruption would have to be quite energetic to get a cloud this high."

Furthermore, at a latitude of 50 degrees south, the spot lies outside the region of known volcanoes on Venus.

Melillo comments that the spot will not be seen again as intense as it is now, thanks to the rapid rotation of the planet's atmosphere. "I hope that someone will image Venus on Thursday when this part of the atmosphere is facing us again," he says.

Further observations will help shed light on the genesis of the bright spot and how it evolves as the atmosphere churns over.






Jupiter collision a warning call to Earth

by Peter N. Spotts

Staff writer of The Christian Science Monitor

July 21, 2009

from ChristianScienceMonitor Website

The list of cosmic objects that could hit Earth is growing.

Scientists study satellite 'tractors' and nuclear weapons as ways to divert asteroids headed our way.

This detail image shows a large impact

shown on the bottom left on Jupiter's south polar region captured on July 20,

by NASA's Infrared Telescope Facility in Mauna Kea, Hawaii.
Infrared Telescope Facility/Handout/JPL/NASA/Reuters

When an object smacked into Jupiter over the weekend, giving astronomers their best cosmic-collision show since the comet Shoemaker-Levy 9 in 1994, the giant gas ball of a planet took the poke like the Pillsbury Dough Boy.

For all its scientific interest, however, the collision also serves as a stark reminder that the solar system remains a shooting gallery – with Earth, as well as Jupiter, on the wrong side of the firing line.

The object's signature on Jupiter's cloud tops initially was discovered by Australian amateur astronomer Anthony Wesley as he gathered digital images of the giant planet through his 14.5-inch telescope.

After alerting other astronomers to what appeared to be a "scar" in the cloud tops similar to those generated by the pieces of Shoemaker-Levy 9, NASA scientists trained a 3-meter (9.8-foot) infrared telescope on the planet and got a good look at the scar.

"It could be the impact of a comet," according to Glenn Orton, a scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in a statement yesterday. "But we don't know for sure yet."

When it comes to objects Earthlings should keep an eye on, the catalog scientists have amassed is swelling.

Since 1995, astronomers associated with 10 search projects have discovered more than 6,200 near-Earth asteroids of all sizes, according to data from JPL. Some 784 are at least a kilometer (0.62 miles) across or larger. Just over 1,000 of the total have been deemed "potentially hazardous" – those that pass Earth at a distance of less than 4.7 million miles.

And while the biggest ones have the potential to inflict the most damage, scientists are gaining a new appreciation of the punch even small ones can deliver.

Two and a half years ago, scientists at Sandia National Laboratories in Albuquerque, N.M., conducted advanced supercomputer simulations of the June 1908 event over Siberia that flattened and scorched trees over a region 30 miles across.

Estimates put the explosive clout of the air burst from either a meteor or comet fragment at between 10 and 20 megatons.

• The good news: Calculations on Sandia's supercomputer, in 3-D, push that explosive yield down to between three and five megatons.

• The bad news: The calculations also indicated that the asteroid or comet fragment was much smaller than previously estimated.

There are more small asteroids hurtling around us than large ones. Sometimes they can seem to come out of nowhere.

Last October, astronomers detected an asteroid an estimated two to five meters across. Some 21 hours later, it entered the atmosphere over northern Sudan sprinkling the Nubian desert with meteorites. The object's blast was estimated at roughly 1,000 tons of TNT.

For asteroid specialists, this was a live-fire test of protocols they'd developed to alert astronomers to monitor the object to refine orbital and impact-location estimates – and to alert national authorities that a direct hit was on the way.

The incident "underscored the successful evolution of the Near-Earth Object Program's discovery and orbit-prediction process," wrote JPL scientists Steve Chesley, Paul Chodas, and Don Yeomans in a post-event report on the incident.

The goal, of course, is to spot these objects and produce highly refined orbit estimates in time to take defensive action, if necessary.

And what might that action look like?

In a lengthy analysis of options that earned him a newly-minted PhD in aeronautical engineering from the University of Glasgow, Joan Pau Sanchez Cuartielles sorts through several approaches ranging from detonating a small nuclear bomb near an asteroid to using a modest-sized satellite as a kind of tractor that tugs the asteroid into a less dangerous orbit, connected to the asteroid by their mutual gravity.

The stand-off nuclear option (with an explosive yield tailored to the mass and density of the asteroid) turned out to be the most effective, although politically troublesome.

The gravity tug could be effective with long lead times, or if the goal is to nudge an asteroid just enough to ensure it avoids a gravitational sweet spot, or keyhole, that would put it on a collision course with Earth decades into the future.


 

Jupiter sports new 'bruise' from impact
by Lisa Grossman
21 July 2009

from NewScientist Website

Something has smashed into Jupiter, leaving behind a black spot in the planet's atmosphere, scientists confirmed on Monday.

This is only the second time such an impact has been observed.

The first was almost exactly 15 years ago, when more than 20 fragments of comet Shoemaker-Levy 9 collided with the gas giant.

"This has all the hallmarks of an impact event, very similar to Shoemaker-Levy 9," said Leigh Fletcher, an astronomer at NASA's Jet Propulsion Lab in Pasadena, California.

 

"We're all extremely excited."

The impact was discovered by amateur astronomer Anthony Wesley in Murrumbateman, Australia at about 1330 GMT on Sunday.

Wesley noticed a black spot in Jupiter's south polar region (see above image) – but he very nearly stopped observing before he saw it.

"By 1am I was ready to quit... then changed my mind and decided to carry on for another half hour or so," he wrote in his observation report.

Initially he suspected he was seeing one of Jupiter's moons or a moon's shadow on the planet, but the location, size and speed of the spot ruled out that possibility.

'Stroke of luck'
After checking images taken two nights earlier and not seeing the spot, he realized he had found something new and began emailing others. Among the people he contacted were Fletcher and Glenn Orton, also at JPL.

They had serendipitously scheduled observing time on NASA's InfraRed Telescope Facility in Hawaii for that night.

"It was a fantastic stroke of luck," Orton told New Scientist.

Their team began observations at about 1000 GMT on 20 July, and after six hours of observing confirmed that the spot was an impact and not a weather event.

"It's completely unlike any of the weather phenomena that we observe on Jupiter," Orton says.

Splash
The first clue was a near-infrared image of the upper atmosphere above the impact site.

An impact would make a splash like a stone thrown into a pool, scattering material in the atmosphere upwards. This material would then reflect sunlight, appearing as a bright spot at near-infrared wavelengths.

And that's exactly what the team saw.

"Our first image showed a really bright object right where that black scar was, and immediately we knew this was an impact," Orton says. "There's no natural phenomenon that creates a black spot and bright particles like that."

Supporting evidence came from measurements of Jupiter's temperature. Thermal images also showed a bright spot where the impact took place, meaning the impact warmed up the lower atmosphere in that area.

The researchers have also found hints of higher-than-normal amounts of ammonia in the upper atmosphere. Extra ammonia had been churned up by the previous Shoemaker-Levy comet impact.

Exotic chemistry
The Shoemaker-Levy impact also introduced some exotic chemistry into Jupiter's atmosphere. The energy from the collision fused some of the original atmospheric components into new molecules, such as hydrogen cyanide.

Scientists hope this new impact has done the same thing, since that would allow them to follow the new materials and learn how the atmosphere moves with time.

So what was the impactor?

"Not a clue," Orton says.

He speculates that it could have been a block of ice from somewhere in Jupiter's neighborhood, or a wandering comet that was too faint for astronomers to detect before the impact.

"We don't know if the impact was produced by a comet or an asteroid," agrees Franck Marchis, an astronomer at the University of California, Berkeley, and the SETI Institute, who was part of a team that observed the spot on Sunday with the Keck Observatory in Hawaii.

If the object was large enough to be visible before impact, current surveys of asteroids may not have been looking in the right direction to find it, he says, adding that future surveys will spot more of the solar system's uncatalogued objects.

Asteroid or comet
Spectra collected by various observatories may help identify what the impactor was, since a large amount of water at the impact location would hint at a comet as the source.

"We will also compare the observations with those collected during [Shoemaker-Levy 9] 15 years ago," since that was a known comet, Marchis says.

Without having seen it, scientists can't tell how large the object was.

"But the impact scar we're seeing is about the same size as one of Jupiter's big storms, Oval BA, Fletcher told New Scientist. "That, I believe, is about the size of the Earth."

Marchis says Jupiter may be protecting Earth from getting hit by such objects.

"The solar system would have been a very dangerous place if we did not have Jupiter," he told New Scientist.

 

"We should thank our Giant Planet for suffering for us. Its strong gravitational field is acting like a shield protecting us from comets coming from the outer part of the solar system."

Stephen Hawking - "Asteroid Impacts Biggest Threat to Intelligent Life in the Galaxy"

by Casey Kazan with Rebecca Sato

June 26, 2009
from DailyGalaxy Website

Asteroids, Stephen Hawking believes, that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets.

We have observed, Hawking points out in Life in the Universe, the collision of a comet, Shoemaker-Levy 9, with Jupiter (below), which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere which had lifetimes on the order of weeks.

It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out.

Through Earth's history such collisions occur, on the average every one million year. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years.

Other planets in the galaxy, Hawking believes, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.

“The threat of the Earth being hit by an asteroid is increasingly being accepted as the single greatest natural disaster hazard faced by humanity,” according to Nick Bailey of the University of Southampton's School of Engineering Sciences team, who has developed a threat identifying program. [Image right - Comet Shoemaker-Levy 9 collision with Jupiter]

The team used raw data from multiple impact simulations to rank each country based on the number of times and how severely they would be affected by each impact.

The software, called NEOimpactor (from NASA's "NEO" or Near Earth Object program), has been specifically developed for measuring the impact of 'small' asteroids under one kilometer in diameter.

Early results indicate that in terms of population lost, China, Indonesia, India, Japan and the United States face the greatest overall threat; while the United States, China, Sweden, Canada and Japan face the most severe economic effects due to the infrastructure destroyed.

The top ten countries most at risk are:

1. Brazil

2. China

3. Indonesia

4. India

5. Italy

6. Japan

7. Nigeria

8. Philippines

9. United Kingdom

10. United States

“The consequences for human populations and infrastructure as a result of an impact are enormous,” says Bailey.

 

“Nearly one hundred years ago a remote region near the Tunguska River witnessed the largest asteroid impact event in living memory when a relatively small object (approximately 50 meters in diameter) exploded in mid-air.

 

While it only flattened unpopulated forest, had it exploded over London it could have devastated everything within the M25. Our results highlight those countries that face the greatest risk from this most global of natural hazards and thus indicate which nations need to be involved in mitigating the threat.”

What would happen to the human species and life on Earth in general if an asteroid the size of the one that created the famous K/T Event of 65 million years ago at the end of the Mesozoic Era that resulted in the extinction of the dinosaurs impacted our planet.

As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).

How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurrence.

The first this to understand about the K/T event is that is was absolutely enormous: an asteroid (or comet) six to 10 miles in diameter streaked through the Earth's atmosphere at 25,000 miles an hour and struck the Yucatan region of Mexico with the force of 100 megatons - the equivalent of one Hiroshima bomb for every person alive on Earth today. Not a pretty scenario!

Recent calculations show that our planet would go into another "Snowball Earth" event like the one that occurred 600 million years ago, when it is believed the oceans froze over (although some scientists dispute this hypothesis -see link below).

While microbial bacteria might readily survive such calamitous impacts, our new understanding from the record of the Earth's mass extinctions clearly shows that plants and animals are very susceptible to extinction in the wake of an impact.

Impact rates depend on how many comets and asteroids exist in a particular planetary system. In general there is one major impact every million years -a mere blink of the eye in geological time.

It also depends on how often those objects are perturbed from safe orbits that parallel the Earth's orbit to new, Earth-crossing orbits that might, sooner or later, result in a catastrophic K/T or Permian-type mass extinction.

The asteroid that hit Vredefort located in the Free State Province of South Africa is one of the largest to ever impact Earth, estimated at over 10 km (6 miles) wide, although it is believed by many that the original size of the impact structure could have been 250 km in diameter, or possibly larger (though the Wilkes Land crater in Antarctica, if confirmed to have been the result of an impact event, is even larger at 500 kilometers across).

The town of Vredefort is situated in the crater (image above).

Dating back 2,023 million years, it is the oldest astrobleme found on earth so far, with a radius of 190km, it is also the most deeply eroded. Vredefort Dome Vredefort bears witness to the world’s greatest known single energy release event, which caused devastating global change, including, according to many scientists, major evolutionary changes.

What has kept the Earth "safe" at least the past 65 million years, other than blind luck is the massive gravitational field of Jupiter, our cosmic guardian, with its stable circular orbit far from the sun, which assures a low number of impacts resulting in mass extinctions by sweeping up and scatters away most of the dangerous Earth-orbit-crossing comets and asteroids

Jupiter increases risk of comet strike on Earth
by David Shiga
24 August 2007

from NewScientist Website

Contrary to prevailing wisdom, Jupiter does not protect Earth from comet strikes. In fact, Earth would suffer fewer impacts without the influence of Jupiter's gravity, a new study says.

It could have implications for determining which solar systems are most hospitable to life.

Earth experienced an especially heavy bombardment

of asteroids and comets early in the solar system's history

(Illustration: Julian Baum)

A 1994 study showed that replacing Jupiter with a much smaller planet like Uranus or Neptune would lead to 1000 times as many long-period comets hitting Earth. This led to speculation that complex life would have a hard time developing in solar systems without a Jupiter-like planet because of more intense bombardment by comets.

But a new study by Jonathan Horner and Barrie Jones of Open University in Milton Keynes, UK, shows that if there were no planet at all in Jupiter's orbit, Earth would actually be safer from impacts.

The contradictory results arise because Jupiter affects comets in two different, competing ways.

Its gravity helps pull comets into the inner solar system, where they have a chance of hitting Earth, but can also clear away Earth-threatening comets by ejecting them from the solar system altogether, via a gravitational slingshot effect.
 

Tripled impacts
According to the new study, the worst scenario for Earth is when Jupiter is replaced by a planet with about the mass of Saturn.

"[Such a planet] is fairly capable of putting things into an Earth-crossing orbit, but still has some difficulty ejecting them, so they will stay on an Earth-crossing orbit for a much longer time," Horner told New Scientist.

The projected result was more than three times as many impacts as in the real solar system.

So both the new study and the one from 1994 suggest that a smaller planet in Jupiter's orbit would leave Earth worse off, although they disagree about how much worse.

That may be because they differ on the source of the comets they examine. Horner looked at objects coming from the Kuiper belt, a region just beyond Neptune's orbit where many dormant comets reside. The previous study, meanwhile, looked at the Oort cloud, a vast collection of dormant comets extending hundreds of times further from the Sun.

Ultimately, knowing what kinds of solar systems are safest from bombardment could help in the search for alien life.

But, despite the latest work, it is still unclear where we should be looking.
 

Asteroid threat
Alessandro Morbidelli of Nice Observatory in France, who studies solar system dynamics, says neither Horner's analysis nor the earlier study included the most important source of impacts - the asteroid belt. About 95% of the impacts on Earth are due to asteroids, he says.

He suspects that a smaller planet in place of Jupiter may lead to fewer asteroid impacts.

"Given that near-Earth asteroids dominate the impact rate, decreasing asteroid impacts might cause a decrease in the overall bombardment rate of the Earth," he told New Scientist.

Horner and Jones plan to extend their study to include asteroids, but Morbidelli says there are even more factors to examine.

"You can imagine solar systems where a much more massive and broader asteroid belt is preserved - it would be difficult to live in that solar system," he says.

 

"You can imagine giant planets migrating and destroying an asteroid belt. There are so many factors it is difficult to handle them all."

The results were presented Friday at the European Planetary Science Congress 2007 in Potsdam, Germany.

Video

Something Wicked this way comes
by thesignsteam
October 30, 2007

from YouTube Website

A short film about the Oort Cloud which surrounds our solar system and the growing evidence that we belong to a binary star system.