Monday, June 18, 2007
Poor Pluto, Dwarfed Again
Pluto just can't catch a break.
It's official: Not only is Pluto now a "dwarf planet," the category to which it was relegated last year, but scientists have determined that it is not even the largest of that new class. Eris, an object in the solar system's Kuiper Belt, is larger.
The discovery of Eris in 2005 and early estimates that it was probably larger than Pluto helped set off the controversy that resulted in Pluto's demotion from planet status. In a paper published in last week's issue of Science, California Institute of Technology astronomer Michael Brown has used precise calculations to show that Eris is 1.27 times the size of Pluto.
If Eris is not a planet, the International Astronomical Union decided last year, Pluto cannot be either. The decision prompted one of the most spirited debates about astronomy in a long time -- countless schoolchildren protested Pluto's demotion to also-ran status.
Pluto and Eris, which was formerly known as Xena, are now considered dwarf planets -- celestial bodies that have enough mass for their gravity to form them into nearly spherical shape but are small enough to be ruled, in gravitational terms, by other planets.
Brown used data from the Hubble Space Telescope and the W.M. Keck Observatory in Hawaii to study the orbital movement of Eris's moon, Dysnomia, which allowed him to calculate Eris's mass. Scientists expect to find many other objects of similar size in coming years, which is why they decided it is impractical to call them all planets.
-- Shankar Vedantam
Winged Victory for Va. Scientist
A scientist at the Virginia Museum of Natural History has discovered a gliding reptile that lived 220 million years ago and probably spent much of its time in trees.
Two fossils show that Mecistotrachelos apeoros had a long neck and flaps of skin between its limbs and torso that probably allowed it to soar to neighboring trees, they report in the latest issue of the Journal of Vertebrate Paleontology. It most likely ate insects and is probably related to the protorosaurs, a group of extinct carnivorous reptiles marked by long necks, researchers said.
The fossils were excavated from the Solite Quarry along the Virginia-North Carolina border. The area was once the site of a lake, and many animal and plant fossils have been found in shale layers there. Because the fossils cannot be separated from the rock, researchers inspected them using CT scans, an X-ray technique normally used to create images of a patient's internal organs.
"One of the really neat things about the new glider is the feet," said geologist Nicholas Fraser, director of research and collections at the museum, who found the fossils. "They are preserved in a hooked posture, which is unusual and strongly suggests a grasping habit, further emphasizing a lifestyle in the trees."
-- Christopher Lee
Some Nerves Resistant to Cold
Extreme cold is extremely dangerous.
Cold's hazards begin at an organism's surface -- usually its skin -- which can freeze and cease to be pliable or watertight. Penetrating deeper, cold can alter the function of muscles and tendons, essential for locomotion. The body's core, where the most complicated physiology occurs, is also temperature-sensitive. Below a certain temperature, the brain, the heart and other vital organs begin to work erratically and eventually stop.
So how does the body perceive life-threatening cold in time?
The simple answer is that it senses extreme cold as pain that it will go to great lengths to alleviate by . . . getting out of the cold. But that is harder to achieve than one might think. Cold affects the chemical and electrical function of nerves, causing them to fire sluggishly, and eventually go silent. A message like "Danger! Danger! Extreme Cold!" would seem to be always on the verge of being blocked by the effects of cold itself.
Katharina Zimmerman, Andreas Leffler, Peter W. Reeh and their colleagues at Friedrich-Alexander University in Germany explain in the current issue of Nature how the message gets through.
All nerves cells have "voltage-gated channels" in their membranes that let sodium ions flow in and out quickly, a key event in nerve firing. Using rats and mice, the researchers showed that some pain-signaling nerves have a specific channel subtype called Nav1.8, which works even at very low temperatures. It makes the nerves almost completely cold-resistant.
That channel is used for other purposes by coldblooded animals. Warmblooded animals employ it for a more specific purpose -- "to detect and avoid tissue-damaging levels of cold," the authors write.
The new findings help explain why cold hands and feet can be extremely painful long after they have lost fine sensation or why they can even be felt at all.
-- David Brown