EcoAlert: NEO Shield –Early Warning of the Potential Threat to Earth from a Comet or Monster Asteroid


NEOShield is a new international project that will assess the threat posed by Near Earth Objects (NEO) and look at the best possible solutions for dealing with a big asteroid or comet on a collision path with our planet. On average, an object about the size of car will enter the Earth’s atmosphere once a year, producing a spectacular fireball in the sky. Data from Nasa's Wise telescope suggests there are likely to be about 19,500 NEOs in the 100-1,000m size range, and the vast majority of these have yet to be identified and tracked. 

About every 2,000 years, a comet or asteroid the size of a football field will impact the Earth, causing significant damage. And then, every few million years, a mega rock turns up that has a width measured in kilometres that has the potential to change the course of Earth's evolutionary history.

The effort is being led from the German space agency's (DLR) Institute of Planetary Research in Berlin, drawing on expertise from across Europe, Russia and the US. At the end of its three-and-a-half-year study period, propose to the politicians that they launch a mission to demonstrate the necessary technology.

"We're going to collate all the scientific information with a view to mitigation," explains project leader Prof Alan Harris at DLR. "What do you need to know about an asteroid in order to be able to change its course – to deflect it from a catastrophic course with the Earth?

Using updated information, NASA scientists have recently recalculated the path of the Apophis asteroid -approximately the size of two-and-a-half football fields. The refined path indicates a significantly reduced likelihood of a hazardous encounter with Earth in 2036.

"Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004," said near-Earth object scientist Steve Chesley at NASA's Jet Propulsion Laboratory. "Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million."

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, Schumacher-Levi, 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.

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 China, Indonesia, India, Japan, the United States, the Philippines, Italy, the United Kingdom, Brazil and Nigeria.

“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, 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 KT 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.

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

The latest estimates indicate that we've probably found a little over 90% of the true monsters out there and none look like they'll hit us. New telescopes technologies are coming that will significantly improve detection success. In the meantime, the prudent course would be to develop a strategy for the inevitable.

The strongest prevention candidates according to NEOShield experts in an interview with the BBC include:

Kinetic impactor: This mission might look like Nasa's Deep Impact mission of 2005, or the Don Quijote mission that Europe designed but never launched. It involves perhaps a shepherding spacecraft releasing an impactor to strike the big rock or comet. This gentle nudge, depending when and how it's done, could change the velocity of the rock ever so slightly to make it arrive "at the crossroads" sufficiently early or late to miss Earth.

Gravity tractor: This involves positioning a spacecraft close to a target object and using long-lived ion thrusters to maintain the separation between the two. Because of gravitational attraction between the spacecraft and the NEO, it is possible to pull the asteroid or comet off its trajectory.

"It's like using gravity as a tow-rope," says Prof Harris. "It's not straightforward of course. Can you be sure those thrusters will keep working for the time they're needed – a decade or more? Do you have confidence that the spacecraft can look after itself autonomously all that time? These are the sorts of technical problems we will look at."

In both scenarios, the effects are small, but if initiated years – even decades – in advance should prove effective enough.

One method often discussed but about which there is great uncertainty is "blast deflection" – the idea that you would detonate a nuclear device close to, or on the surface of (even buried under the surface), an incoming rock.

The Daily Galaxy via BBC News

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