“Armageddon” or Not?

thomastech · #1 (**permalink**) 20-July-2003, 11:28 PM

Quote:

Imperial College of Science, Technology and Medicine

July 16, 2003

Fewer Earthbound asteroids will hit home

Scientists say pancake model of asteroid impact won't stick

Scientists report in Nature today that significantly fewer asteroids could
hit the Earth's surface than previously reckoned.

Researchers from Imperial College London and the Russian Academy of Sciences
have built a computer simulation that predicts whether asteroids with a
diameter up to one kilometre (km) will explode in the atmosphere or hit the
surface.

The results indicate that asteroids with a diameter greater than 200 metres
(the length of two football pitches) will hit the surface approximately once
every 160,000 years - way down on previous estimates of impacts every 2,500
years.

The findings also predict that many more asteroids blow up in the atmosphere
than previous estimates, which means the hazard posed by impact-generated
tidal waves or tsunamis is lower than previous predictions. The researchers
suggest that proposals to extend monitoring of Near Earth Objects (NEO) to
include much smaller objects should be reviewed.

Dr Phil Bland of Imperial's Department of Earth Science and Engineering and
a Royal Society University Research Fellow, said:

"There is overwhelming evidence that impacts from space have caused
catastrophes for life on Earth in the past, and will do so again.

"On the Moon it's easier to track the number, frequency and size of
collisions because there is no atmosphere, so everything hits the surface.
On Earth the atmosphere acts like a screen and geological activity erodes
many craters too.

"Massive impacts of the type thought to have wiped out the dinosaurs leave
an indelible print on the Earth but we have not been able to accurately
document the effect of smaller impacts. Now, we have a handle on the size of
'rock' we really need to worry about and how well the Earth's atmosphere
protects us."

When small asteroids hit the atmosphere the two forces collide like two
objects smashing together, which often breaks the asteroid into fragments.
Until now, scientists have relied on the 'pancake' model of asteroid impact
to calculate whether the asteroid will explode in the atmosphere. This
treats the cascade of fragments as a single continuous liquid that spreads
out over a larger area - to form a 'pancake'. But a new model known as the
'separate fragment' (SF) model, which was developed by co-author of the
study, Dr Natalya Artemieva of the Russian Academy of Science, has
challenged this approach.

"While the pancake model can accurately predict the height from the Earth's
surface at which the asteroid will break up, it doesn't give an accurate
picture of how the asteroid will impact," explains Dr Bland. "The SF model
tracks the individual forces acting on each fragment as it descends through
the atmosphere."

To create a more accurate model of how asteroids interact with the
atmosphere the researchers ran more than 1,000 simulations using both
models. Objects made of either iron or stone, known as 'impactors', were
used to reflect the composition of asteroids and experiments were run with
varying diameters up to 1 km.

The researchers found the number of impacts for iron impactors were
comparable using both models. For stone the pancake model significantly
overestimated the survivability rate across the range used.

The SF simulations also allowed the researchers to define the different
styles of fragmentation and impact rates for iron and stone, which
correspond closely with crater records and meteorite data.

"Our data show that over most of the size range we investigated stony
asteroids need to be 1,000 times bigger than the iron ones to make a similar
sized crater. Much larger objects are disrupted in the atmosphere than
previously thought.

"But we are not out of the woods yet," added Dr Bland "asteroids that
fragment in the atmosphere still pose a significant threat to human life."

Dr Phil Bland is a member of the Meteorite and Impact Group that includes
scientists from Imperial College London and the Natural History Museum.

Publication: Nature (17 July 2003)

Title: "Efficient disruption of small asteroids by Earth's atmosphere"

Authors: P.A Bland (1) and N.A Artemieva (2)

(1) Department of Earth Science and Engineering, Exhibition Road, Imperial
College London, SW7 2AZ, Uk
(2) Institute for Dynamics of Geospheres, Russian Academy of Sciences,
Leninsky Prospect 38/6 Moscow, 117939 Russia.

About Imperial College London

Consistently rated in the top three UK university institutions, Imperial
College London is a world leading science-based university whose reputation
for excellence in teaching and research attracts students (10,000) and staff
(5,000) of the highest international quality.

Innovative research at the College explores the interface between science,
medicine, engineering and management and delivers practical solutions, which
enhance the quality of life and the environment - underpinned by a dynamic
enterprise culture.

Web Site:
:huh:

Fraser · #2 (**permalink**) 21-July-2003, 12:03 AM

It doesn't discount asteroids striking the Earth and causing massive damage. It's happened before and it'll happen again. Understanding the risks and potential damage is very important, because it helps determine our priorities for searching out potentially destructive rocks. Estimates for the number of large NEOs and their potential chance of striking the Earth has varied over the years.

It sounds like people had been overestimating the risks in the past.

So, less chance of people dying, that's a good thing.

thomastech · #3 (**permalink**) 21-July-2003, 01:31 AM

If one does come our way "NASA"...

I would be glad to offer my services...

All I want in return is to never have to pay taxes again!...

... Bruce Willis has already saved the planet 17 Times...

Give somebody else a chance!

DippyHippy · #4 (**permalink**) 24-July-2003, 12:43 AM

A couple of years back I wrote a freelance piece on NEO's for Astronomy magazine... it didn't get picked up because they felt it was "too enyclopedic" LOL (Hell, they asked me to only write 1500 words so a short piece will read like an encyclopedia entry)

Anyway, at the time, the number of people actively searching for NEO's worlwide was about the same as the number of people manning your average McDonalds "restuarant"

It's up to Fraser, but I can copy and paste the article I wrote if anyone's interested.

Dips

Fraser · #5 (**permalink**) 24-July-2003, 01:04 AM

Feel free to post your article. That's what this whole section is about.

Bjarne · #6 (**permalink**) 24-July-2003, 02:53 PM

I'd Love to read it as well!!

DippyHippy · #7 (**permalink**) 25-July-2003, 03:35 AM

Okay I'll add it when I get home *S* I didn't know if anyone wanted to read a long post and I didn't know if Fraser would object to a 1500 word post either LOL

Dips

Fraser · #8 (**permalink**) 25-July-2003, 05:22 AM

I don't mind if it's 1,500 words at all. I've put in an upper limit of post size, so I guess you run the risk of hitting that, but other than that... go crazy.

universe-R-us · #9 (**permalink**) 26-July-2003, 03:55 AM

Yes Dips, post your piece on NEO's. I take this subjest to heart, and would enjoy reading it.

DippyHippy · #10 (**permalink**) 26-July-2003, 07:13 AM

Sorry guys, I meant to post it yesterday when I got home from work but I forgot... :unsure: This was written two years ago and I haven't looked at it recently so be aware some of these facts and figures have since changed. However, it was accurate at the time because the guys listed at the end of the piece checked it for me (particularly Brian Marsden and William Bottke, who were great sources of information)

Anyway, here it is...

On October 28 1937, a small asteroid was discovered by the German astronomer Karl Reinmuth and named Hermes. Two days later it came within 750,000 km of the Earth, the closest known approach by an asteroid at that time. It was then lost and has not been seen since. Its fate remains unknown.

Twenty-eight years later the asteroid 1999 VP11 came within 400,000 km of the Earth – just a little further than our own Moon. Unlike Hermes, no one knew about this close encounter until 34 years later and yet both asteroids could have caused a global catastrophe. 1999 VP11 is now classed as Near Earth Object. (NEO).

NEO’s are asteroids that come within 45 million kilometers of the Earth’s orbit, three-tenths the distance from the Earth to the Sun. At the time of writing, there are 1,413 known NEO’s, 489 of which are wider than a kilometer.

310 of the known NEO’s are larger than 200 meters across and come within 7,500,000 km of the Earth. These are classed as Potentially Hazardous Asteroids (PHA) – 1999 VP11 is one such example.

Four and a half billion years ago, the unwanted building blocks of the solar system formed a belt of rocks between the orbits of Mars and Jupiter. Many of the smaller rocks coalesced to become single, larger rocks bound together only by the mutual attraction of gravity. In time, these vagabonds would be known as the “rubble pile” asteroids.

Such is the case with asteroid 1997 XB26, a kilometer wide rubble pile asteroid that exists only within the infinite space of this author’s mind. Although this asteroid is fictitious, the following scenario could happen.

For much of 1997 XB26’s life, it roamed the asteroid belt before falling under the influence of Jupiter for roughly a million years. With the asteroid orbiting the sun every four years and Jupiter taking 12, the pair fell into a resonance which caused them to be regularly aligned at the same place in their orbits. Despite at least a hundred million kilometres between them, Jupiter was able give the asteroid the boost it needed to leave its peers behind and join the inner solar system.

For countless years it circled its parent star once every 671 days. Despite missing Mercury by four hours in February 1974, it remained unnoticed until one cold winter night, twenty-three years later. The date was December 5 1997 and amateur astronomer Tomi Andrews had spent the night photographing faint galaxies in Leo. At 5:30 a.m. she packed away her equipment and retreated to the warm comfort of her bed.

The resulting images showed a streak by her target galaxy, NGC 3611. Given the streak’s magnitude and with no faint halo surrounding it, Tomi surmised that this was no comet but rather an asteroid instead. The exposure time for the image had been 45 minutes. With the asteroid moving nearly three arc minutes across the sky during that time, she knew her rock was close.

An online search for a predicted asteroid close approach proved fruitless so she sent an e-mail to the Minor Planet Center to verify the discovery.

After comparing the data against all known asteroids, the Minor Planet Center in turn analysed the observations from Project LINEAR (Lincoln Near Earth Asteroid Research), the team responsible for 75% of all potential NEO observations. With a match found, the estimated orbital elements of the asteroid could be calculated. 1997 XB26 was now 90 million kilometers away and had passed into the constellation of Virgo. In the four days since its discovery it had moved 10 million kilometers closer to the Earth.

With the resulting ephemerides being published online, astronomers worldwide began searching for the wayward asteroid. However, despite their efforts, time was running out and by the end of the month, the asteroid had passed through Libra and into Scorpius, moving too close to the Sun for further observation.

For the Minor Planet Center, 1997 XB26 was cause for concern. At its closest approach, on Christmas Eve 1997, the asteroid had come within 68 million kilometers of the Earth and calculations hinted at a much closer encounter in 2001. Nearly two years would pass before the asteroid would be found again, appearing as a faint, 19th magnitude star moving slowly through Cancer.

Further observations refined the asteroid’s orbit and a team of experts convened to verify the computations. Within 72 hours, a meeting of the United Nations was arranged through the Office of Outer Space Affairs in Vienna. It was confirmed. - on October 31 2001 at 15:31 UT, asteroid 1997 XB26 would hit the Pacific Ocean at 20 km per second. Hawaiian observers would have a ringside seat to the last show on Earth. As they watched the rock rise at 5:00 a.m. local time, it would pass by a close conjunction of Mercury and Venus before falling below the horizon less than 30 minutes later. In that time, it would brighten from a 4th magnitude star to magnitude –0.6, a rival to Mercury in the sky.

From that point on, there would be nothing to do but wait. Just a few minutes later, the asteroid would hit the ocean, releasing half a million megatons of energy and causing hundred-meter tsunamis to hit the coastlines of every nation bordering the Pacific. Millions would die by water alone with many more being killed by the tons of burning rock raining down from the skies above. The shockwave of the impact would cause earthquakes around the world and volcanoes to erupt, throwing more dust into the air and darkening the skies for years to come.

The press called it Asteroid Andrews and like its discoverer, 1997 XB26 became a celebrity.

But the Earth is not without hope. Although years are needed to plan a mission, it would still be possible to deflect the asteroid with a nuclear detonation. A change in velocity of only a few meters per second is all that’s needed. However, with a rubble pile asteroid such as our theoretical example, care must be taken not to destroy it completely and therefore create a multitude of targets to contend with. The Earth’s atmosphere can only deal with rocks smaller than 50 meters.

Fortunately, LINEAR is not the only project searching for NEO’s. In 1998, NASA was assigned the task of finding 90% of the asteroids larger than a kilometer by 2008. Other organizations include NEAT (Near Earth Asteroid Tracking), Spacewatch, Spaceguard and LONEOS (Lowell Observatory Near Earth Object Search). In the past 20 years, these programs have increased the number of known NEO’s tenfold. There are also many amateur astronomers around the world actively observing potential NEO’s on behalf of the Minor Planet Center.

Out of the world’s estimated $20 trillion annual gross product, only $1.5 million is spent annually searching for NEO’s. The next time an asteroid shows up on a deep sky photo, it’s worth remembering that if every reader of Astronomy was to contribute $5, our global insurance policy could be renewed for another year.

The author would like to thank the following for their help in writing this article: William Bottke, Andrea Carusi, Jenifer B. Evans, Brian Marsden and Robert McMillan.

thomastech · #11 (**permalink**) 26-July-2003, 09:26 AM

"Good Job" Dips!

[Another phrase from the "Movie"]

Quote:

"Its a Big A__ Sky"

The more people "Looking"... The Better! :unsure:

Bjarne · #12 (**permalink**) 30-July-2003, 05:21 PM

:blink: WOW!!! Great job Dips!

That was a great article. Is there any further developments to this project that you are aware of?? As I read the post I noted that you had the thing impact in the Pacific. THAT'S bad enough :unsure: , but did you do some research on the possibility of a land strike?! I spent some time looking but was unable to find anything on this.

Anybody else have thoughts or comments on this??

DippyHippy · #13 (**permalink**) 01-August-2003, 02:19 AM

Hi guys

Thanks for the comments. I did do some research into both land and sea strikes and came up with quite a bit of info but since it was such a short piece I didn't have room to go into detail. At the end of the day, we all know it would be very bad for mankind either way so I saw it as a secondary issue and concentrated instead on the facts and figures that readers might not know. I was especially indebted to Brian Marsden at the Minor Planet Center and William Bottke, both of whom I spoke to on the phone. It was something of an honour to speak to Brian because he's often on those asteroid documentaries that get made every so often.

I haven't looked into the subject matter since then although it does still interest me. Incidentally, it was slated for the October 2001 issue which was why I chose that date for the asteroid strike. I used Starry Night Pro 3 to create a fake asteroid and simulated it's path to see where it went. Truthfully, since it came under the gravitational influence of Jupiter, the Sun and Mercury at some time or other, it probably wouldn't have hit the Earth at all since I was unable to simulate the changes in the orbit. So for the purposes of the article, those bodies had no gravitational influence at all LOL

I named the discoverer after my "big sis" Tomi Andrews in Wisconsin. She got a kick out of discovering the asteroid that would bring Armageddon to Earth LOL

Dips

John Dedes · #14 (**permalink**) 09-August-2003, 03:03 PM

Humanity has already survived several impacts from smaller hits worldwide in the last few million years of mankinds existance, the last one being in a russian forest in the early 1900's. Today however and the greater population of the globe, any hit of any size would be catastrophic with an enormous loss of human life. The only sensible thing to do is have stellar rockets in orbit then use them to "push" away NEO after docking on to them. The evidence on this planet is clear on every continent ......and thats without the benefit of having visual impact evidence from the sea bed...but it would suggest from current evidence that we receive a "reasonable" hit every couple of hundred years.

Fraser · #15 (**permalink**) 09-August-2003, 03:22 PM

Welcome to the Universe Today forums John.

I heard a great solution on Quirks and Quarks the other day which involved a giant airbag on a spacecraft which could then repeatedly bump against a rotating asteroid to nudge it into a different trajectory.

Asteroids are a huge threat to life, and the first step is definitely to seek out all the largish Earth crossing objects. I wonder if we'll ever be able to find the 100 metre objects, though. And, we're still victims to comets which can come from nowhere at high velocities.

Tinaa · #16 (**permalink**) 21-August-2003, 03:45 AM

I remember reading something about a disturbance in the Oort Cloud when the solar system goes thru it's galactic orbit. Somehow we oscillate like a merry-go round. This is supposed to "knock " stuff in the Oort cloud around and maybe send it in towards Earth. I believe the article said that every 65,000 years or so the galactic tides are strong enough to send bigger and more comets into the inner solar system. It was suggested that this is why Earth has suffered several global extinctions. I thought this was pretty interesting.

I know there is a mission to go check out Pluto and the Kuiper Belt. I wonder if either of the Voyager crafts will be close to the Oort Cloud any time soon. I know they are headed out into space. Will the crafts be able to send back any info about the Oort Cloud? Is there really an Oort Cloud? How far out is it? Is it farther out than the heliopause? There is a lot of speculation. Could the Hubble or any of the new arrays maybe "see" something like the Oort Cloud?

DippyHippy · #17 (**permalink**) 25-August-2003, 04:13 AM

The Oort cloud stretches out to about halfway between the Sun and the Alpha Centauri system - ie, about 2 light years. I'm not sure how far away the nearest Oort cloud objects are though.

Dips

WendellG · #18 (**permalink**) 26-August-2003, 10:33 PM

Great article Dips! Being an amiture at all of this, I have a question. What is an Oort cloud?

Wendell

WendellG · #19 (**permalink**) 26-August-2003, 10:39 PM

Never mind, I just typed Oort Cloud into the computer and looked it up myself.

Wendell