- News Home
17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
- About Us
Neptune's Hasty Moon
13 August 1998 6:00 pm
Ever since Newton, astronomers have been calculating the orbits of planets and moons and getting them exactly right. But Galatea, a small satellite of Neptune, is ahead of schedule, observers reported this week in a circular of the International Astronomical Union--and no one knows why. To explain this puzzling haste, astronomers are blaming everything from the gravitational tug of Neptune's mysterious Adams ring to the pull of other moons to an error in the original orbital calculations.
A team led by Claude Roddier of the Institute for Astronomy of the University of Hawaii, Manoa, learned that the 160-kilometer moon was straying from its orbital timetable on 6 July, when they tracked it down with the 3.6-meter Canada-France-Hawaii Telescope on Mauna Kea. The observations--the first in the 9 years since Galatea was discovered by the Voyager 2 spacecraft--showed that Galatea was 5 +/-1 degrees ahead of its predicted position, or 8.6 minutes ahead of schedule. The difference, they said, is "possibly due to [Galatea's] interaction with Neptune's Adams ring."
The Adams ring, lying a mere 1000 kilometers outside Galatea's orbit, has a strange, arclike appearance, indicating that its dust particles are spread unevenly around its full circumference. Galatea's gravity is presumably sweeping the particles into clumps. But for the ring to pull back strongly enough to affect the satellite's orbit, says Carolyn Porco of the Lunar and Planetary Laboratory of the University of Arizona, it "would have to have substantial mass." She speculates "that there are bigger bodies [hidden in the ring], which are the source of the dust that we actually see."
Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, isn't so sure that there's a deviation to explain. For Galatea's orbit to accumulate five degrees of drift in 9 years, its period would have to differ from its predicted value by a mere 0.07 seconds. "My own inclination is that the prediction is off simply because the observations used for it were only [a few images] from Voyager," he says. Even if it isn't, Marsden thinks that subtle perturbations from other moons, or from the oblate shape of Neptune itself, could have skewed Galatea's orbit.