Right now, NASA is tracking 127 asteroids that have a very small chance of striking the planet. That number is about to get a lot higher. Stronger telescopes, and a new mandate from Congress, will allow scientists to detect thousands of smaller asteroids more likely to hit Earth. And scientists are plotting ways to stop them, from "gravity tractors" to solar ray guns. "There is no question that these will hit the Earth," says Russell Schweickart, a former Apollo astronaut who is involved in a group studying asteroids. "The question is how often we will have to do something about it." In fact, Schweickart thinks world leaders might have to do something about it very soon, within the next 15 years.

Cometary evidence of a massive body in the outer Oort cloud

Approximately 25% of the 82 new class I Oort cloud comets have an anomalous distribution of orbital elements that can best be understood if there exists a bound perturber in the outer Oort cloud. Statistically significant correlated anomalies include aphelia directions, energies, perihelion distances and signatures of the angular momentum change due to the Galaxy. The perturber, acting in concert with the galactic tide, causes these comets to enter the loss cylinder - an interval of Oort cloud comet perihelion distances in the planetary region which is emptied by interactions with Saturn and Jupiter. More concisely, the impulse serves to smear the loss cylinder boundary inward along the track of the perturber. Thus it is easier for the galactic tide to make these comets observable. A smaller number of comets are directly injected by the impulsive mechanism. We estimate that the perturber-comet interactions take place at a mean istance of  25000 AU. The putative brown dwarf would have a mass of 3 +/- 2M Jupiter and an orbit whose normal direction is within 5 degrees of the galactic midplane. This object would not have been detected in the IRAS database, but will be detectable in the next generation of planet/brown dwarf searches, including SIRTF. It is also possible that its radio emissions would make it distinguishable in sensitive radio telescopes such as the VLA.