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Prometheus' pull on particles in Saturn F-ring ROYAL ASTRONOMICAL SOCIETY NEWS RELEASE Posted: April 4, 2006 The rings around all the giant planets in our Solar System are thought to be stabilised by small "shepherd moons" that orbit in or near the rings and stabilize them by gravitational influences.
Images from Saturn's F ring region obtained by the Cassini Imaging Science Subsystem (ISS) cameras have revealed structure never seen before in a planetary ring. Periodic structures such as azimuthal gaps - "channels" of low optical depth - and "streamers" have been discovered. These features can be seen in Movie1. The origin of these features has been explored by a team at Queen Mary, University of London (QMUL) using numerical integrations. On Tuesday, Carlos Chavez of QMUL will be explaining to the RAS National Astronomy Meeting in Leicester the results of their computer models, which explain the close and complex relationship between Prometheus and the tangled F ring. "The models are in excellent agreement with structures observed in the Cassini images," said Chavez. "We have found that the gaps are not due to a lack of particles, but to a forced change in orbital elements by a close encounter with Prometheus," he explained. "The moon's gravity temporarily pulls some of the particles away from the main stream as it passes by." "It is like a crowd of people walking in a number of lines in the same direction down a street. Suddenly, someone else comes from the other side of the street and collides with a few of them. He then tells them to come with him, and walks away. Only people in the closest lines follow him, which produces gaps in the crowd. However, they return back to the main group shortly afterwards." The most dramatic case will happen in late 2009, when the F ring and Prometheus are anti-aligned. Once per orbit during this anti-alignment Prometheus will be at apoapsis (its furthest point from Saturn) and the nearby ring particles will be at periapsis (closest point to Saturn). At that time, Prometheus and the ring particles are at their closest to each other. The QMUL team explored how these events will affect collisions between the ring particles and Prometheus. They found a low number of collisions - only 0.6% of the particles collided per orbit. This was unexpected, since it was originally thought that Prometheus is a "thieving moon" stealing particles from the F ring. What actually happens is that the particles are only temporarily pulled away and then drift back into the ring. The ring-moon interactions are also likely to have an effect on the surface of Prometheus. Like our Moon and most other planetary satellites, Prometheus has a synchronous rotation, always showing the same face to Saturn. The team at QMUL investigated the location on Prometheus' surface where the particles would be expected to collide. They found that, in the synchronous co-rotating reference frame, the collisions surprisingly occurred on the trailing face of Prometheus, and preferably in the equatorial region. This scenario has important implications for the surface features of Prometheus, and the team expects to find differences in albedo (reflectivity) between the trailing and leading faces. "It would be like a man colliding with other people while facing continuously in a particular direction and hitting them with only one side of his body," said Chavez. Other members of the QMUL team examining the links between Prometheus and the F ring are: Prof. Carl D. Murray, Dr. Kevin Beurle, Dr. Nicholas J. Cooper, and Dr. Michael W. Evans. The 2006 RAS National Astronomy Meeting is hosted by the University of Leicester. It is sponsored by the Royal Astronomical Society, the UK Particle Physics and Astronomy Research Council (PPARC), the University of Leicester and the National Space Centre, Leicester. |
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A total solar eclipse occurred March 29. This video from Side, Turkey shows the period of totality when the moon slid between the Earth and Sun. The eclipse revealed the Sun's glowing outer halo of million-degree gas, called the solar corona.
In early March, NASA cancelled its Dawn mission built to orbit two of the solar system's largest asteroids using ion engine propulsion. Technical problems and cost overruns were blamed. But in this news conference from March 27, agency officials announce NASA's decision to reverse the cancellation and restart the mission.
Lockheed Martin holds this news conference in Houston on March 24 to announced that it is partnering with the State of Texas to locate the Crew Exploration Vehicle (CEV) program office in Houston, as well as systems engineering, software development and qualification testing, if the corporation wins the NASA contract to build the next generation spacecraft for NASA.
As the Expedition 12 mission aboard the International Space Station winds down, officials managing the flight from Mission Control in Houston hold this retrospective briefing to talk about the highs and lows, the science, the spacewalks and everything in between.
International Space Station officials preview the next Expedition mission to the orbiting outpost, which is scheduled for launch March 29. The preview was given during a briefing March 22 from Johnson Space Center.
One of the iconic moments of the early space shuttle program was astronaut Bruce McCandless floating above the brilliantly blue Earth completely disconnected from his spacecraft. He was testing the Manned Maneuvering Unit, a jet-powered backpack that would enable spacewalkers to travel away from the space shuttle to service satellites. In this post-flight presentation, the crew of Challenger's STS-41B mission of February 1984 narrate the film highlights from their mission that also included the first shuttle landing at Kennedy Space Center.