THE more we learn about comets the more mysterious they become. When NASA’s Deep Impact spacecraft blasted into Tempel 1 it demonstrated that the comet is a fluffy ball of powder, nothard-packed ice (New Scientist, 10 September, p 32). Now the Spitzer Space Telescope’s infrared spectrometer has detected clay and carbonates in the mix streaming off the comet, materials that can only be formed by liquid water, not ice.
It seems unlikely that liquid water could exist on the surface of objects much further from the sun than Mars. Yet comets like Tempel 1 are thought to have formed…
