Science  27 Apr 2012:
Vol. 336, Issue 6080, pp. 397

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  1. Heat Held Back the Pioneers


    The world is once again safe from exotic “new” physics, at least any provoked by the Pioneer 10 and Pioneer 11 spacecraft. Something mysterious—perhaps a variation in Newton's laws—had been slightly slowing the spacecraft as they headed out of the solar system (Science, 2 September 2011, p. 1208). Blasted away from Earth in the early 1970s at more than 51,000 kilometers per hour, both spacecraft had been slowing by 1 kilometer per hour per decade.

    But that miniscule deceleration bothered many spacecraft navigators, so astrophysicist Slava Turyshev of NASA's Jet Propulsion Laboratory in Pasadena, California, and colleagues calculated in unprecedented detail the net effect of the subtle forces acting on the spacecraft. In a paper to be published in Physical Review Letters, the group reports that more of the heat from a Pioneer's radioisotope thermoelectric generator and from the onboard instrumentation it powered radiated in the forward direction than radiated back toward the sun. The skewed heat radiation—in effect an infinitesimal rocket—was just strong enough to apply the observed tiny braking.

  2. Human Ancestors Out-Hunted Large Carnivores

    When human ancestors began hunting for meat on the plains of Africa 2.5 million years ago, they apparently took more than their fair share of flesh. Within a million years, most large carnivores in the region—from saber-toothed cats to bear-sized otters—had gone extinct, according to a study presented last week at a workshop on climate change and human evolution at Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York.

    Homo erectus appeared in the fossil record 1.9 million years ago, and has been blamed for the extinction of many African mammals. To investigate when the decline began and which carnivores went extinct, vertebrate paleontologist Lars Werdelin of the Swedish Museum of Natural History in Stockholm studied the anatomy of fossils (including jaws, teeth, and snouts) of 78 species of carnivores to reconstruct their dietary breadth and analyze which types of carnivores disappeared.

    Cool cats.

    The skull and jaw of two different species of extinct saber-toothed cats, which lived during the heyday of carnivores 3 million to 3.5 million years ago in the Turkana Basin of Kenya.


    Many species of large carnivores had already gone extinct by the time H. erectus appeared, Werdelin found. And, he discovered, it was omnivores such as civet cats that suffered most from human scavenging by 1.5 million years ago. Only a few hyper-carnivores that ate only meat, such as lions and leopards, survived.