Much of the speculation about ISON and its likely consequence has been sadly misinformed -- indeed, complacent. Let me reiterate some basic facts here.

Fact: ISON is *not* a comet.

The astronomers think that ISON might once have been a moon of Neptune or Uranus, or perhaps it was locked in a stable point in Neptune's orbit, and was then perturbed somehow. But perturbed it was, and now it is on a thirty-six-hundred-year collision course with Earth.

Fact: ISON's impact will *not* be comparable to the Chicxulub impact which caused the extinction of the dinosaurs.

That impact was sufficient to cause mass death, and to alter -- drastically, and for all time -- the course of evolution of life on Earth. But it was caused by an impactor some ten kilometers across. ISON is *forty* times as large, and its mass is therefore some *sixty thousand times* as great.

Fact: ISON will *not* simply cause a mass extinction event, like Chicxulub.

It will be much worse than that.

The heat pulse will sterilize the land to a depth of fifty meters. Life might survive, but only by being buried deep in caves. We know no way, even in principle, by which a human community could ride out the impact. When ISON arrives, everybody will die.

Fact: ISON *cannot* be deflected with current technology.

It is possible we could turn aside small bodies -- a few kilometers across, typical of the population of near-Earth asteroids -- with such means as emplaced nuclear charges or thermonuclear rockets. The challenge of deflecting ISON is many orders of magnitude greater. Thought experiments on moving such bodes have been proposed, for example, using a series of gravitational assists -- not available in this case -- or using advanced technology such as nanotech von Neumann machines to dismantle and disperse the body. But such technologies are far beyond our current capabilities.