Mystery Cruise Control
The velocities of Pioneer 10 and 11, now speeding out of the solar system, are mysteriously changing, as if an extra force from the sun were tugging at them. Explanations have ranged from gas leaks and observational error to modified theories of gravity [see “A Force to Reckon With”; SciAm, October 2005].
Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues, who helped to uncover the Pioneer anomaly, have found similar unexpected changes with four spacecraft that have flown by Earth—namely, Galileo, the Near-Earth Asteroid Rendezvous (NEAR) mission, Cassini and Rosetta. They sped up or slowed down by amounts up to one part per million as they passed the planet.
The exception was MESSENGER, which approached Earth at a latitude of roughly 31 degrees north and left Earth at a latitude of about 32 degrees south—relatively equal distances from the equator. In comparison, the anomalous flybys were lopsided in how the craft approached and left Earth. For example, the NEAR mission came in at a latitude of roughly 20 degrees south and receded at about 72 degrees south (and then seemed to fly some 13 millimeters per second faster than expected). The greater the asymmetry, the greater the effect on velocity.
Although variations in Earth’s magnetic or gravitational fields might seem to explain the anomalies, satellites that orbit Earth seem unperturbed, Anderson says. Also, although gas in space can slow craft, it would not explain why some probes apparently sped up. He notes that one feature seemingly links the flyby and Pioneer anomalies: all the craft are on hyperbolic trajectories—orbits where they are not bound to their central bodies (the sun for the Pioneer craft, Earth for the others). “Maybe there’s something with hyperbolic trajectories we haven’t taken into account yet,” Anderson conjectures. —Charles Q. Choi
Fiber-Optic Black Holes
To study black holes, physicists have looked for laboratory analogues [see “An Echo of Black Holes”; SciAm, December 2005]. Fiber optics may make that possible. The key to making artificial event horizons is to force a fluidlike medium to slosh faster than waves can ripple through it. Researchers sent a red pulse through an optical fiber, which altered the fiber’s refractive index, and then beamed in longer-wavelength light crafted to chase down the pulse. The infrared beam blue-shifted, indicating that its wave fronts had piled up behind the pulse. Technically, blue-shifting is a feature of the event horizon of a white hole—an inside-out black hole. Still, the leading edge of the pulse would mimic the horizon of a black hole, writes the team in the March 7 Science.
Hair Today, Hair Tomorrow
Hair grows, falls out and may take time to come back—too long for many older adults [see “Hair: Why It Grows, Why It Stops;” SciAm, June 2001]. Elaine Fuchs of the Rockefeller University and her colleagues have shown that blocking a protein called NFATc1 results in shorter rest phases for the stem cells in the hair follicles. The hair in Fuchs’s study grew normally, suggesting that the resting phase, long thought to be a way to protect against mutation or the loss of the cells, is not as necessary as once thought. The work, in the January 25 Cell, helps to explain stem cell activity and could lead to new treatments that are able to reverse thinning hair.
Aquaculturists have tried—and failed—to get captive bluefin tuna to breed, as a means to save these overeaten animals [see “The Bluefin in Peril”; SciAm, March 2008]. After a three-year effort, Australian company Clean Seas Tuna Limited reported in March that it induced captive southern bluefin tuna to spawn. Bluefin larvae grow one millimeter a day, so years will pass before any young fish reach marketable size; hence, farmed tuna may not arrive in time to save some bluefin populations.