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Asteroids: the clear and present danger
EVERY now and then, we are presented with a warning of the possibility of a dangerous and deadly impact by an asteroid. These large and small rocky pieces that roam our solar system may or may not come soaring out of the skies to wreak havoc on our dear planet but scientists refuse to be sitting ducks in case, Heaven forbid, an asteroid does come too close for comfort. In order to even visualize a way in which a disaster like this can be averted, scientists are first conducting many studies of these space rocks.
Research has shown that families of asteroids, which have been cleaved out of the same large space rock, have different orbits and directions. It is important to understand how and why the behaviour varies in rocks from the same family even though they have been formed at the same time. Stephen Slivan, an MIT researcher, observed these oddly directed rocks and carried out a study with interesting results while examining the changes in ten rocks of the “Koronis” family.
Sibling rivalry
This particular family of asteroids is thought to have formed when two huge space rocks collided with each other approximately 2 billion yeas ago. Their sizes range from 20-40km across. Sullivan expected the rocky family to spin and point in some random direction as a result of their chaotic birth. To his surprise, six rocks were pointing in one direction while four of the ten he studied, seemed to be going their own way.
What could be the cause of this parting-of-the-ways? Why were the others going in a different direction? A group of scientists and researchers carried out a study of this strange behaviour of the rocks. They based their study on the fact that sunlight has an effect on the surface of the space rocks due to uneven heating. This is just like when the sunlight reaches one part of Earth where there is daylight while the other side is dark and cooler because it is night. The part, which is warmer facing sunlight “re-radiates” the solar energy that it has received, especially in the afternoons. This causes a recoil force. And because of this process, the orbit of an asteroid around the sun shifts slightly over time. The effect is called the “Yarkovsky Effect” after the Russian engineer discovered it in 1900. Today, scientists are of the view that the Yarkovsky effect could be used to change the course of an asteroid, which threatens to hit us.
The way they think this can be done is by painting the asteroid white in colour and letting sunlight do the rest. The fact remains that this method can only be accomplished if the warning comes very well in advance. How the rock will be painted is another story. It is also worthwhile to keep in mind that the Yarkovsky effect works best with small pieces of rock.
The YORP effect
After the Yarkosvsky effect, another similarly presumed effect called the “YORP effect”, which was named after Yarkovsky and his colleagues, also had been suggested by scientists. This too relied on the assumption that the spin rate and direction of an asteroid would be altered due to the effects of sunlight.
In the latest research, computer models of asteroids being affected by the light of the sun were simulated and it was observed that the “recoil effect” could only be accomplished over eons. In other words, it would take a very long time to change or even slightly alter the course of an asteroid’s rotation in order to change its path. William Bottke, study team member from the Southwest Research Institute, explains, “like the story about the tortoise and the hare, slow and steady sunlight wins the race over fast-acting, but less effective, jolt of collisions between asteroids”.
This effect would determine how long the length of the day would be on the asteroid by forcing it to a certain rotation rate and influencing and controlling the direction of the polar axis. Scientists call this, “spin-orbit resonance”. “These results give us a new way to look at asteroids. It is our hope that this work will stimulate observational studies into many different regions of the main asteroid belt. We have only scratched the surface of this interesting problem,” said David Vokrouhlicky of Charles University in Prague.
This study was published in the Sept 11 issue of the journal Nature. Richard Binzal, an MIT astronomer, also wrote his own analysis. He opines that the study carried out by Sullivan “almost defied belief” and that other asteroid families would have to be observed and studied to prove the computer model right. “A light touch might be the best way to influence asteroid spins,” he wrote.
Bold, new search system
Nasa has been urged by experts to increase resources for a better and bolder search for asteroids that might pose a threat for Earth. These include the large and deadly, doomsday scenario-types as well as the smaller sized space rocks. The estimates at present are $236 million at least. This would prove far more expensive than the asteroid detection program that already exists but support for a wider and better search is stronger than ever. Already, the space agency leads the hunt for the large NEO’s (Near Earth Objects) that threaten Earth and cause damage on a global scale. At present Nasa allots $3.5 million per year for the search. On the protest of many that Nasa should be putting in a greater effort to look for the relatively small, one kilometer, asteroids which have a greater chance of hitting the planet, Nasa has to take the demand more seriously. The trouble is, these small rocks are more expensive to look for.
At present, the date set for the search is 2008 and panelists feel, could be done with the present technology available. The search could yield 90 per cent cataloguing of potentially threatening smaller asteroids, which are as small as 140 metres by the year 2028. Published by the “Near Earth Object Science Definition Team”, the report was posted to a Nasa website.
Benny Peiser, researcher at Liverpool John Moores University has been an advocate for the hunt and has voiced his own government’s lack of interest for the detection of the smaller asteroids for sometime.
“The report’s recommendations are not only in line with what we have been arguing for some time-it surpasses our expectations by far,” he said. Though the report did not mean that Nasa wa actually bound in any way to do as it says but it has given a great degree of hope to the researchers.
“I’m hopeful the pressure will be brought to bear to initiate this next generation of search,” said Donald Yeomans, who is the vice-chair of the report. He also said the increased pressure would also have to be applied on a congressional level by astronomers as well as the general public. Yeomans presently heads Nasa’s Near Earth Object Program at the Jet Propulsion Laboratory. The panel, he says, should have greater acceptance as it includes members from public and private institutions including the US Air Force.
It has been estimated that an asteroid, twice the size of a football field, 140 metres or even bigger, could impact Earth every 15,000 to 20,000 years, according to Yeoman. The search for these asteroids which are capable of causing great regional damage could be Earth-based or space-based. If it were conducted from Earth, it would cost $236 million and take 20 years. The search from space, on the other hand, would cost $397 million but would do the job in just seven years. At present, all the asteroid search programmes are done from the ground. Which decision is preferred is still to be seen.
The report, however, could not have been better timed. It came right at the time of yet another asteroid scare generated by the media. Covering 90 per cent of all NEO’s would put Earthlings in a much better position to understand and deal with any possible threat, agree experts. Peiser was optimistic when he stated to Space.com that, “we have the technology now to essentially solve the asteroid impact hazard for good within the next one or two generations. And it’s not even as expensive as some sceptics have thought”.
He added, “accepting these recommendations would be Nasa’s perfect opportunity to get back on their feet and show the world that American space policy has neither lost its vision nor its no-nonsense approach that is tremendously popular both in the U.S. and around the world.”
His words do make sense. What remains to be seen is whether the United States will actually be able to keep its promise to save the world from any global catastrophe, now or in the future?
The writer
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