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  Earth's "New" Companion and a "New" Visitor From Space


    Tania ta Maria

It seems as if the Earth-Moon system does not travel alone after all. We
have a companion, one that we seem to have had for thousands of years,
but has only recently been discovered. No, it is not a satellite since
the object does /not/ revolve around Earth the way the Moon does. It
merely tags along.

Dubbed Asteroid 3753, also known as 1986 TO, this chunk, which shares
the same orbit with Earth, was discovered by Paul Wiegert and Kimmo
Innanen of Ontario's York University, Canada, and Seppo Mikkola of
Tuorla Observatory in Piikkiö, Finland.

The asteroid's own orbit, which interacts with both the Earth-Moon
system and the Sun, is a rather complex one. If one were to visualize
Earth's orbit as a triple lane, Earth would be moving at a constant
speed in the central one with the asteroid moving somewhat slower in the
outer one. Then, just as Earth is about to overtake its companion, the
asteroid switches to the inner lane and speeds up. But just before it
passes Earth, it switches back to the outer lane and slows down again.
And so it goes, a game of tag which neither Earth nor the asteroid ever
wins. In a three dimensional view, these maneuvers by the asteroid make
it spiral along its path.

This relationship will not last forever. In the course of a time-span
that will last "thousands of years," the asteroid's gravitational
interactions with Venus, Mars, and Jupiter will eventually eject it out
of the Earth-Moon system. As Wiegert succinctly phrased it: "Having
waltzed with Earth for thousands of years, [the asteroid] may go looking
for a new dance partner."

An immediate question that comes to mind is: How many other such and/or
similar companions could Earth have had in the past?

Meanwhile, another asteroid, 1997 XF11, which was discovered by Jim
Scotti of the University of Arizona, is even now on its way to a
rendezvous with Earth. Estimated to be about a mile in diameter, the
asteroid was originally expected to pass as close as 30,000 miles from
the centre of Earth. The date of its closest approach has been
calculated to be 30 years from now, at 1:30 p.m. Eastern Daylight Time,
on Thursday, October 26 in the year 2028. If it really comes that close,
said Dr. Brian Marsden of the International Astronomical Union (IAU), it
will be bright enough in the evening skies of Europe to be visible with
the unaided eye.

Can it hit us? At first the experts were not quite sure, and the IAU had
to admit that the computations were still rough. For that reason,
amateur astronomers were asked to look for the asteroid. "It should be
quite accessible for a while with large telescopes," Marsden said,
"which, in addition to helping establish whether a collision in 2028 is
possible, could usefully provide more definite information about the
object's size."

But then the asteroid was re-discovered on some films which had been
shot at the Palomar Observatory back in 1990 and new calculations,
covering an 8-year arc of the asteroid's trajectory, indicated that its
former predicted position had been in error. According to JPL
scientists, Donald Yeomans and Paul Chodas, it is now believed that our
coming visitor will be passing "at a rather comfortable distance of
about 600,000 miles," and that chances of an impact with Earth are very
close to nil.

While we can all sigh with relief, may we not, perhaps, consider this as
yet another warning?