Web edition: April 26, 2004
Print edition: May 1, 2004; Vol.165 #18 (p. 287)

Skins game

I know some people who carefully shield their bodies from the sun with sunscreen and clothing, and their skin is extremely pale. But if tanning acts as a protector ("Sunny Solution: Lotion speeds DNA repair, protects mice from skin cancer," SN: 3/6/04, p. 147: http://www.sciencenews.org/articles/20040306/fob2.asp), is it actually safer to maintain a "healthy" tan?

Chris Esse
Beverly Hills, Calif.

Scientists continue to debate this question vigorously. Some say any tanning indicates skin-cell damage, but others disagree.—J. Travis

Little splash?

I would guess that a rock measuring 1 kilometer across, landing near New Zealand 500 years ago, would have done much more than create a tsunami 300 to 500 feet high ("Killer Waves," SN: 3/6/04, p. 152: http://www.sciencenews.org/articles/20040306/bob8.asp). Was the object one km across before encountering Earth's atmosphere?

Don Arthur
North Coventry, Pa.

Yes. The object's estimated size is before it hit the atmosphere. The damage it inflicted is indicated by the large crater it left on the ocean floor.—S. Perkins

Why on Earth

I can think of a place other than the moon where NASA could develop a closed life-support system for staging rehearsals of manned Mars exploration ("A New Flight Plan: Back to the moon," SN: 3/13/04, p. 170: http://www.sciencenews.org/articles/20040313/bob9.asp). Why not Earth? Advantages would include a protective atmosphere, a day length closer to the Martian sol, bone-and-muscle-friendly gravity, and easy access to mechanical and medical resources. The cost would be much less than that of a moon base, and crew rotation would involve motor vehicles rather than launch vehicles. Why not keep the rehearsal safe and relatively cheap?

Jeffry D. Mueller
Eldersburg, Md.

What babies face

"Born to Heal: Screening embryos to treat siblings raises hopes, dilemmas," SN: 3/13/04, p. 168: http://www.sciencenews.org/articles/20040313/bob8.asp) quotes a pediatrician as saying, "we're moving to selection on the basis of a trait that is of no benefit to the child to be born." I disagree. The child to be born would have the benefit of a healthy older sibling. Even saving the parents from the trauma of a dying child is a benefit to the new child.

Jay M. Pasachoff
Williams College
Williamstown, Mass.