There may be more of them out there than we know:

With about 1 percent of incoming comets ending up on relatively short-period Earth-crossing orbits, it is expected that several thousand dormant comets could be currently posing a potential threat to our planet.

Recent surveys of the Earth's immediate vicinity should have turned up some 400 such objects, whereas only a handful have so far been found.

The researchers dismiss the current belief that all the "missing" comets have disintegrated into meteor streams. If this had happened, they argue, then we should be seeing a far greater number of meteor showers and a much brighter zodiacal cloud than is observed.

They propose instead that the majority of these comets have become exceedingly black, with such low surface reflectivities that they could not be observed against the blackness of space by optical means.

This can also be put in that scary category of asteroids that we can't see coming at us from the Sunward side. We need an interferometric IR telescope on the sun facing side of the Moon to watch the Earth's backside for celestial interlopers.

Maybe this is where they're going?

Of course - people assume that the black comets are dangerous. I thought we lived in a progressive society.

Josh, which side would that be? The moon is tidally locked to the *Earth*

Josh, how's a comet approach so close to the exact direction of the Sun that, e.g. a simple coronagraph approach (using a small disk to block the Sun's light) wouldn't work? Are you talking about a comet that's actually in front of the Sun's disk? Coming at us straight out of the Sun? Seems a tad unlikely.

Oh no, there have been several instances ,here recently even, when an a surprise asteroid has popped up from the sunward side. There are large number of NEO's orbiting between us and the sun. These guys are often detected way to late. Even if we had the ability to deflect them we probably couldn't do it time cause we just can't see them until they have passed through our orbital plane. The problem in detecting these objects is much the same as detecting planets orbiting other stars. The Sun is so bright and the objects so dim that you can't just look directly at them because the sun washes out the imagery. Even a coronagraph wouldn't help because if anything that would intensify the glare from the Sun's corona. Through the use of a interferometic telescope we can polarize the solar light out of synch in such a manner as to greatly reduce the glare. Then, the dimmer objects within close proximity of the Sun would become more easily detected. This is a new technic that has only really just begun to be tested using existing interferometric telescopes like the Keck in Hawaii. In the future this technology is going to be incorporated into the next generation of alien planet hunting space telescope. However, I am assuming that this technology could be of great use to the asteroid and comet hunters.

I did mispeak about a telescope on the Sun facing side of the Moon though. I should have said Earth facing side. Now that I'm thinking more about that we could have 4 telescopes equatorially positioned at 90 degree longitudinal intervals that could pull continuous double duty of celestial and solar/NEO observations.

thanks, Josh

Of course - people assume that the black comets are dangerous. I thought we lived in a progressive society.

LOL

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