There is a Hypothesis floating around that this asteroid my be affected more by the earth magnetic field than previously thought possible. This comes after a surprise event that occurred with the passing of the Holmes comet. It reacted strangely and it's dust cloud became the largest object in the solar system for a while. Scientists are thinking if this asteroid is charged negatively and passes through earth's positive magnetic field it might change it's orbit drastically. It's a hypothesis yet to proven this might prove it.
5g0, a comet is very different from an asteroid. A comet is loosely packed to call it basically a dusty snowball is not far from the truth. It outgasses due to solar heating and the solar wind and photon pressure blows the ejecta into the classic tail shape. I could see where maybe a strong field might induce a change in the rate at which the comet is ejecting debris causing a flare up. Maybe the effect caused a release in pent up pressure inside the cometary body. But that is not the same as being magnetically pushed off course.
Asteroids generally don't form comas. They are much denser and more solid than comets. Lets do a quick back of the envelope calc here. Assuming that the asteroid is a carbonaceous chondrite (and not the denser iron/nickel type which would be much more massive) it would have a density similar to that of a lump of rock like coal, (1500 Kg per cubic meter) and assuming the minimum size (150 meters) and a spherical shape (I doubt it these guys are always irregular!) we would get a mass of about 2650718801 Kgs. Or, in other words 2.65 million metric tons. I have never heard of a magnetic field in the solar system strong enough to push an object that massive off course in such a short time (it is what, 6 days to perigee now?).
Scientists are thinking if this asteroid is charged negatively and passes through earth's positive magnetic field it might change it's orbit drastically.
Don't all magnets have two poles, a negative and a positive?
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