Planet Killers : Earth Has No Defense Against Asteroids

Writer Tad Friend spoke about near-earth asteroids and efforts to shield Earth from their
impacts. In the last 15 years, there’s been real progress in detecting such asteroids, yet
we still don’t have a plan in place about what to do if a collision is likely, he reported.
He outlined three different options:

Gravity Tracker– a small rocket that would hover near an asteroid and tweak its orbit, gradually over time.
Kinetic Impactor– running a heavy object into the asteroid to knock it off course.
Nuclear Weapons– for an asteroid that is much larger/closer to us.

Biography:

Tad Friend is a staff writer at The New Yorker since 1998 and writes the magazine’s “Letter from California.” Mr. Friend’s recent pieces have included articles about the electric-car and rocket-ship entrepreneur Elon Musk, and the man in charge of executions at San Quentin.

Wikipedia
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones. These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet and was not observed to have the characteristics of an active comet, but as small objects in the outer Solar System were discovered, their volatile-based surfaces were found to more closely resemble comets, and so were often distinguished from traditional asteroids. Thus the term asteroid has come increasingly to refer specifically to the small bodies of the inner Solar System out to the orbit of Jupiter, which are usually rocky or metallic. They are grouped with the outer bodies—centaurs, Neptune trojans, and trans-Neptunian objects—as minor planets, which is the term preferred in astronomical circles. This article will restrict the use of the term ‘asteroid’ to the minor planets of the inner Solar System.

There are millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun’s solar nebula that never grew large enough to become planets. A large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter or co-orbital with Jupiter (the Jupiter Trojans). However, other orbital families exist with significant populations, including the near-Earth asteroids. Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, S-type, and M-type. These were named after and are generally identified with carbon-rich, stony, and metallic compositions, respectively.