My first Magazine Sky & Telescope - 01.2019

FROM OUR READERS Martian Makeover? Has the face of Mars been changed forever? The planet’s huge dust storm recently, com- bined with terrible weather all summer here in the Florida panhandle, really messed up the opportunity to observe the best opposition in over a decade. But the few photos I’ve taken and most of the ones I’ve seen look nothing like the Mars I knew before the storm. Will the “dust settle,” so to speak, and will all be back to normal? Just curious. Bob Hess Panama City, Florida Sean Walker replies: The dust has pretty much settled out of the atmo- sphere. There is still some reduced contrast, but it’s nearly back to normal. However, there have been some small but noticeable changes in albedo markings, as shown in the ac- companying image. You’ll ﬁ nd more information about the dust storm on page 52. p This image of Mars was taken by Damian Peach in early September under near-perfect seeing conditions with the 1-meter Chilescope. 6 JA N UA RY 2 019 • SK Y & TELESCOPE Inside Enceladus Patience Rewarded The News Note entitled “Organics Inside Enceladus: Complex Enough for Life?” (S&T: Oct. 2018, p. 8) mentions a strain of bacteria that could live on methane under the ice of Enceladus. But perhaps there’s another way for life to exist there. Here on Earth, most life forms get their energy to live by combining the oxygen freely available in the atmo- sphere with sugars and fats stored in their bodies. But suppose life in the oceans of Enceladus does it backward? In principle, they could use hydrogen and methane dissolved in the water as fuel and store the oxygen in their bodies, in the form of unstable oxides such as hydrogen peroxide or ammo- nium nitrate. Some creatures on Earth store oxygen-releasing chemicals inside themselves; for example, the bombar- dier beetle uses hydrogen peroxide to create its noxious sprays. Hydrothermal vents in Earth’s oceans produce all kinds of reactive chemicals, including sulfuric acid. If the vents assumed to be on Enceladus release similar compounds, then those could provide energy to create the oxygen-storage compounds. Or perhaps life there uses the temperature differ- ence between the vents and the ambient water to provide energy. Future space probes should be designed to look for evidence of such “reverse” life forms. I had to chuckle at the letter about tele- scope delivery times (S&T: Aug. 2018, p. 7), because something similar hap- pened to me more than 40 years ago. My parents and I expected to receive an Edmund Scientiﬁ c 4.25-inch reﬂ ec- tor as a birthday present sometime in December 1973. But we failed to take the arrival of Comet Kohoutek into account. Edmund was inundated with orders from eager would-be astrono- mers, and we had to wait until February 1974 to get my new scope. It was frustrating — but worth it. After my dad helped me set it up, I trained it on Saturn and still remem- ber the thrill of seeing those beautiful rings. Even now, after all these years, I get some use out of my old standby. Conan McCann Fayetteville, Arkansas Name That Gadget “Backyard Spectroscopy with RSpec” by Rod Mollise (S&T: Sept. 2018, p. 68) includes a photograph of a laptop with a device attached to the USB port. What is this device? I’m just starting to get into RSpec with the Star Analyser 100. William Woods Weyers Cave, Virginia “ Rod Mollise replies: The device is the imaging camera I used to capture the spectra described in the Test Report. Speciﬁ cally, it’s a ZWO ASI120MC, an inexpensive color video-type camera that I ﬁ nd works very well with RSpec. Dean Christensen Fresno, California What’s Cooking? Would you elaborate on the statement in 75, 50 & 25 Years Ago (S&T: Sept. 2018, p. 7) that Edward Harrison’s model was “cooked-up”? If Harrison’s model passed all the major observa- tional tests, why was it cooked up? Could his universe’s 35 billion years old be more accurate than the current guesstimate of 13.8 billion? Curt McCann Corvallis, Oregon “ Monica Young replies: “Cooked-up” is pretty accurate because Harrison was explicitly trying to come up with an al- ternative to the Big Bang. So he cooked up his model to do just that, by choosing values for the Hubble constant and the density of the universe today, even though they didn’t match observations at the time. But 25 years later we have an incredible amount of data that wasn’t available then. Harrison had access to blobby COBE data on the cosmic microwave background, but WMAP, which provided a detailed view of the CMB, didn’t launch until 2001, and Planck, which provided even more exquisite detail, didn’t launch until 2009. The ﬂ uctua- tions measured in the temperatures of the CMB opened the era of precision cosmol- ogy and also pinned down the Hubble con-

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