Hot and cold on the topic

No mention was made in "In the Zone: Extrasolar planet with the potential for life" (SN: 4/28/07, p. 259) of the possibility that, being so close to its star and having a 13-day orbital period, the planet would keep the same surface to the star. Having one side baked by unrelenting sunlight and the other side frozen would leave only a narrow ring between eternal day and eternal night that might have what could be called average conditions suitable for liquid water. I would think that the probability for life to start and survive would be very unlikely.

Edmund Smith
Brogue, Pa.

In some models of planets, especially those with atmospheres, heat flows between the day and night sides, so the temperatures aren't so extreme.—R. Cowen

Kids' stuff

The lines on the cave ceilings remind me very much of what a large pot of finger paint looks like after children extract what they want to draw with ("Children of Prehistory: Stone Age kids left their marks on cave art and stone tools," SN: 4/28/07, p. 264). I could easily see my children (especially when younger) drawing on their own faces and bodies all kinds of designs using the colored clay.

Dan Woitulewicz
Detroit, Mich.

I appreciated conjectures by John Shea regarding manufacture of ancient stone tools by children rather than adults. As a modern-day flint knapper of 20 years, I have long suspected that many artifacts from ancient sites were made by beginners. Many of them look like the same junk I made my first 2 years of knapping.

Michael Williams
Columbia, Mo.

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