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People have been
hunting for sungrazing comets for hundreds of years, but as of
1979 we only knew of less than a dozen. Today,
we have seen about 2,500. Why did the number increase?
Understanding this starts with the Kreutz path. In the
late 1800s, Heinrich Kreutz observed that many recent comets
traveling near the sun appeared to follow the same orbit. On this Kreutz
path, as we've come to call it, it takes the comet about 800 years
to complete one loop around the sun. While there are other orbits of
sungrazers, Kreutz comets are the most common. All of the comets
in this orbit came from a single comet, observed thousands of years ago.
As the comet moved closer to the sun, the ice binding it
together evaporated, breaking it into smaller pieces that the sun's gravity
pulled apart. Every time the comet comes around the Kreutz path, this can
happened again, resulting in a new generation of comets. It might
sound like this would clutter the solar system full of comets, but that is not the case.
Some of the new comets are small enough that they become completely vaporized
as they approach the sun. There are more comets observed, not because
there are more in the solar system but because we have better ways to see them.
Spotting a sungrazer from the ground is difficult because of the blinding sunlight.
Now, spacecraft designed to observe the sun make the job a lot
easier. Since the joint ESA/NASA mission SOHO launched in 1995,
it has shown us thousands more comets than any tool before.
To date, it has found 2,387 comets.
With SOHO we can now see the smaller, fainter comets
close to the sun, just long enough to ad them to our list of sungrazers
before they vaporize. The spacecraft's data is available online,
so now, anyone can discover a comet. Roughly 75%
of these comets have been found by amateur astronomers.
Other solar observatories, such as NASA's SDO, weren't expected to provide
good comet observations, but they captured some beautiful images, creating
more possibilities for comet research using unexpected tools. Now
that we can observe comets better than ever - who knows? - maybe you
will spot the next sungrazer.
beeping