This AW&ST editorial makes too much sense so it may not happen. But it should.

NASA is staring at a great deal that it shouldn't refuse. Deep Impact was spectacularly successful last week in hitting and observing the comet Tempel 1, and mission leader Mike A'Hearn is proposing that the surviving flyby spacecraft, by all accounts in excellent health with undamaged instruments, be sent to chase another comet (see p. 28).

Humanity's up-close knowledge of comets is weak at best. Given their origins in the outer nether regions of the solar system, they offer a good look at leftover primordial matter that has been cooked by the Sun much less than anything else mankind can reach. A number of scientists think they were a significant source of the Earth's water and maybe even simple and complex organic chemicals that are the basis of life. Their structure is not understood, and the photos of Tempel 1 show further diversity of features that have piqued scientists' interest. It has several remarkably smooth patches that present a real puzzle, and the first clear evidence of impact craters on a comet. And at some point, we might discover a comet headed for Earth. The more we know about what they're made of and how they're held together, the better we'll be able to do something about it.

Only five comets have been approached by spacecraft, and only three of those have yielded clear pictures of their nuclei. As of now, only the European Space Agency's Rosetta probe is set to make a comet visit, in 2014. Adding a fresh Deep Impact mission would expand our knowledge on comets by 20% and more, given the quality of data produced by its modern instruments.

Deep Impact is equipped with a uniquely strong set of telescopes, able to resolve to the meter level at safe flyby distances. It also has a powerful imaging infrared spectrometer with very sharp spectral and spatial acuity, and a fast shutter speed to boot. That can reveal what a comet is made of, in photographic detail.

A'Hearn's proposal is a three-year mission extension to encounter the comet Boethin in December 2008. The trajectory includes an Earth flyby in January 2008 to gain the extra energy to meet the comet. He estimates the cost would be $30 million. The Deep Impact primary mission cost $333 million with the launcher. Getting what is a new mission on a proven spacecraft, without the risk of launch, at a 90% discount, sounds like a good deal.

Deep Impact needs a trajectory change soon if it is to have enough propellant for a new mission. That change remained forbidden by NASA Headquarters as the spacecraft team celebrated their hard-won success on July 4, a sign of money troubles and uncertainty about directions at the agency. Clear heads prevailed on July 5 and the course change was approved--but not the extended mission. We urge NASA to go all the way and support this very cost-effective proposal that should make fresh discoveries and substantially grow our knowledge of these interesting bodies, with a proven high-quality performer.