Letters from the June 11, 2005, issue of Science News

Dim prospects

To a layman like me, it seems almost impossible that light reflected from a body that lies “much farther from the star than Pluto does from the sun” could be seen from Earth at a distance of 450 light years, when Pluto, only 6 light hours away, reflects so little light to Earth (“Stellar Question: Extrasolar planet or failed star?” SN: 4/9/05, p. 228).

Peter Jeming
Seattle, Wash.

The researchers imaged a star with a companion farther away than Pluto’s distance from Sol. The question was whether this is a planet or a brown dwarf star. That we can see an image at all seems to preclude it from being a planet. It must be producing its own light somehow.

Matthew C. Cook
San Francisco, Calif.

Whether planet or brown dwarf, the body is emitting light. Very young planets generate their own infrared light by gravitational contraction of the material that coalesced to make them. Telescopes are now sensitive enough to detect and resolve infrared-bright planets that lie relatively far from their parent stars.—R. Cowen

Why autism?

In “Blood hints at autism’s source” (SN: 4/16/05, p. 254), researcher S. Jill James implicates low glutathione and heavy metal exposure in autism. This may be the case, but glutathione has a number of important functions that have nothing to do with heavy metal binding. As an antioxidant, glutathione reduces toxic free radicals. Glutathione is also a key factor in the maintenance of cellular redox poise. It goes without saying that it is also possible that low glutathione is correlated with, but not causative of, autism.

Todd P. Silverstein
Willamette University
Salem, Ore.

I would venture that at least part of the explanation for the rise in autism’s incidence is related to its recent recognition. When I was a kid, there was no such thing as autism. You can’t diagnose something you don’t recognize.

Andrew Nelson
Santa Barbara, Calif.

Studies published in the past 2 years have investigated the extent to which autism’s increasing incidence traces to changes in diagnosis. At least a few of these studies have found that incidence has increased even after accounting for better diagnosis.—J. Raloff