3 June 2005
By Rusty Rockets
It looks like avian flu may finally be dislodged from its stranglehold on the number one position of the Apocalypse Top 40. Astute science observers will be aware that coming up fast is perennial favorite, the asteroid threat. But this threat isn't coming from a newly discovered asteroid. Rather, it's coming from already known asteroids and the lack of consensus from astronomers regarding the true threat they pose to the Earth.
Calculations on the extent of destruction from a near earth object (NEO) smacking into the Earth at Mach 300 no doubt played on many scientists' minds back around Christmas time. While the rest of the world watched the grim news from the Asian tsunami disaster, scientists were busy crunching the numbers on the orbit of an asteroid with the sexy moniker of 2004 MN4. We were eventually informed that the Earth would be spared - the asteroid would miss - albeit by a slim margin. Now I don't want to be alarmist, and by all means keep adding to your pension fund, but just remember that space has a lot of quirks, or is that quarks, that scientists still can't fathom.
We begin our journey into the vagaries of space by looking at developments surrounding the Pioneer 10 mission. Just to refresh your memory, during the 1970s NASA's exploratory spacecraft Pioneer 10 and Pioneer 11, who share identical design characteristics, were blasted off toward Jupiter and Saturn respectively. When their missions ended both spacecraft continued to head out beyond the solar system at 8 miles/second. Needless to say, both Pioneer 10 and Pioneer 11 have been constantly monitored by ground stations such as the Jet Propulsion Laboratory. But there's a mystery surrounding Pioneer 10. For some reason, it's decelerating and deviating from its hitherto predictable trajectory by approximately 250,000 miles, and nobody knows why. This inexplicable slow down is known as the 'Pioneer anomaly' in astronomical circles. Some seem sure that there is a very mundane explanation for the anomaly, such as systematic failure or drag caused by accumulated dust particles picked up by the craft on its long journey, but nobody is certain. And anyway, none of these explanations are very convincing when you consider that Pioneer 11, traveling in the opposite direction, is also experiencing the same anomalous behavior.
Some observers speculate that perhaps it's something to do with what is referred to as 'dark' matter. The only problem is that they cannot observe dark matter or predict how much of an effect it has on an object in space. So at the end of the day, we're still in the dark whether it's dark matter that's the culprit. (groan, ed.)
But given the unpredictable environmental factors and physical vagaries of deep space, how much faith should we place in the predicted trajectories of NEOs like 2004 MN4? Recently, scientists have suggested observing asteroids in the outer solar system to see if they are subject to the same anomalies as Pioneer 10. Researchers, Gary Page, David Dixon and John F. Wallin claim that "If a method of measuring the Pioneer Effect was available it might serve, once and for all, to either support or refute its existence as a real phenomenon".
Let's entertain the idea for a moment that asteroids are affected in the same way as Pioneer 10, that asteroids are subject to the gravity produced by dark matter that scientists are yet to see, let alone comprehend. What would the implications be for substantial asteroids like 2004 MN4 that orbit so close to Earth?
Originally, asteroid 2004 MN4, approximately 1000+ feet in diameter, was predicted to slam into the Earth on Friday the 13 April 2029. Mussolini would have been proud of that kind of scheduling. Anyway, after a revised estimate it was decided that the asteroid would not hit the Earth after all. This is quite common, as the more astronomers track an asteroid the better they can plot an accurate orbit. After taking these revisions into account, it is claimed that 2004 MN4 will miss the Earth by approximately 15,000 to 25,000 miles. Very close by cosmic standards, but a miss is still a miss. But hang on, isn't Pioneer 10 approximately 250,000 miles off-course at present? And nobody knows why. If asteroids can display anomalous behavior by margins similar to that of the Pioneer spacecraft, then astronomers telling us that a large asteroid will miss the Earth by a whisker suddenly don't sound so assuring. These sorts of conditional statements tend to be a bit loaded, but in this case they are well worth considering given what's at stake.
There seems to be no real plan of action should an asteroid come our way in any case. For starters there is a time factor involved. How long would it take to shift an asteroid out of its Earth destined trajectory? Apollo astronaut Rusty Schweickart has thought about this question and has decided that the time for action is now, starting by putting a transponder on some of the most Earth threatening asteroids in order to track their orbits. While Schweickart believes an impact is unlikely, he understands that planning to 'push' an asteroid out of the Earth's path could take over a decade. This could spell disaster if unforeseen anomalous behavior suddenly turns a miss into a bullseye. A transponder planted on the most worrisome of asteroids would be a good idea, because it would at least factor in the anomalous behavior to any calculations on asteroid orbits. While the Pioneer spacecraft are off-course, they can at least be tracked; they know where they're going, just not how or why. Of course the trouble with these kinds of missions is that they are expensive, and although Schweickart believes that the expected cost of $300 million is chicken feed as far as space missions go, he may have a hard time convincing the accountants at NASA that this is a good investment.