Weighing factors in obesity In “Obesity research gets weightier” (SN: 12/29/12, p. 28) Nathan Seppa says that green space and a nearby grocery store reduce the incidence of obesity. I think I understand how the green space affects it (clean air, physical activity, et cetera), but I don’t understand how the grocery store does. Is there anything showing a connection? Ted Grinthal, Berkeley Heights, N.J. The connection lies in access to fresh fruits and vegetables, which fight obesity. The researchers counted grocery stores that sold fruits and veggies within a half mile of neighborh... (p. 31)

Early puberty’s cause Regarding “Early Arrival” (SN: 12/1/12, p. 26): In 1960 I left the Ohio Valley of grass- and corn-fed cows to teach in the Los Angeles area. When I arrived, I found that eighth- and ninth-grade girls looked physically like 25-year-old women in Ohio. I asked the other teachers what was going on. They all responded, “beef growth hormones.” If researchers would track earlier puberty in preteen girls alongside the use of growth hormones in cattle, they would most likely find matching graphs. Is this another horror of fast food such as hormone-laden hamburgers? ... (p. 31)

Trust no one “Trust affects kids’ patience” (SN: 11/17/12, p. 10) refers only to children. But based on my own experience, I’d expect it to apply to adults as well. If you tell me I can have $100 now or $200 in an hour, what I do will depend on whether or not I trust you to come through with the $200 in an hour. I’d expect this to apply to anyone who is old enough to have a concept of the future and has had experience with trustworthy and untrustworthy people. Ted Grinthal, Berkeley Heights, N.J. Updated writing tips Thanks for the reprint of the 1950 “Hints for writing ... (p. 4)

Curiosity cleanup In the article “Protecting the planet” (SN: 11/3/12, p. 32), the sidebar “Keeping Mars clean” gives the impression that Curiosity had not been contaminated, while the opposite is true. Apparently the sterilized craft was opened up and microbial contamination likely occurred. Curiosity’s drill bits may be contaminated with Earth microbes. So now NASA is in the catch-22 position that if they do find water they cannot use the drill. The entire gist of the article is to give an erroneous impression that Curiosity was clean, when in fact Catharine Conley has been quot... (p. 31)

To spot a planet “Planetary peekaboo” (SN: 9/22/12, p. 26) says that to hunt for faraway planets, the Kepler spacecraft “watches for blinks occurring when a planet dims a star’s light by passing in front of it.” For a star to dim when a planet moves in front of it requires us to be in the same plane as the orbits of the remote planets. Evidently it’s expected that this is commonly true. Why is that? Bryan Mumford, Santa Barbara, Calif. That’s correct: To see a planet passing between Earth and its star, the system and Earth need to be aligned just right. Astronomers don’t... (p. 31)

Quick facial thinking I have always found it remarkable that the average person can identify probably thousands of individuals by face “Face Smarts,” (SN: 10/6/12, p. 20) and perhaps hundreds by voice, as well as some just by their gait. Clearly such identification at a distance must have been a crucial survival advantage during our evolution; this unfortunately suggests to me that the larger threat to earlier humans was not lions or tigers and the like, but rather other members of our own species. Peter Benson, North Oaks, Minn. Timing human history “No home for Homo ... (p. 30)

Fractious debate Rachel Ehrenberg’s feature story on hydraulic fracturing “The Facts Behind the Frack,“ (SN: 9/8/12, p. 20) spurred a big response from readers. We received letters voicing strong opinions on both sides of the fracking debate. The article was intended as an overview of what science has to say about the risks of fracking and, due to space constraints, could not cover every aspect of the issue. Here is a selection of the letters we received. “The facts behind the frack” was right on the money — timely and well balanced. As a geophysicist, I’ve been asked by... (p. 30)

Consider numbers I have been a faithful subscriber to Science News for a long time, since I subscribed for my kids in the 1960s. I don’t have a degree but was a naval aviator for 32 years. I just cannot get used to converting kilometers per hour to miles per hour each time I encounter astronomical rates of speed in your articles. My flight career in the U.S. Navy began from helicopters, through patrol planes, then F-4B Phantom jets. Everything was in knots, nautical miles and Mach number. During combat tours in Vietnam we got used to kilometers, but miles and miles per hour never left us.... (p. 31)

Higgs love Tom Siegfried’s essay “Behind the Higgs” (SN: 7/28/12, p. 26) may be the best piece of science journalism I’ve seen. He explained enough about the Higgs boson’s importance in the scheme of things for me to read about different aspects of the work and see how they fit into the whole picture, but even more, to get how impressive the symmetry of the picture is (pun intended) and how validating of the scientific method itself the work has been. Ed Sylvester, Tempe, Ariz. I love aha moments, and though there has been tons of press on the Higgs boson, it wasn’t until I ... (p. 31)

Cartilage risk I enjoyed Nathan Seppa’s article “Cartilage creation,” (SN: 8/11/12, p. 22) about attempts to generate new cartilage from somatic stem cells. He writes that cartilage evolved “in ancestors who lived shorter lives, carried less body weight and roamed an unpaved world.” Implications: The risk of osteoarthritis increases with age, body weight and impact on concrete, such as a long-term runner might experience. Is there solid scientific experience for all three of these putative risk factors? William Check, San Francisco, Calif. Yes. First, osteoarthritis stemming... (p. 4)