Cassini to Carry Out Enceladus Flyby

Since July 2004, the NASA Cassini spacecraft has been conducting remarkable scientific observations around the gas giant Saturn. In addition to looking at the planet and its intricate ring system, the probe has also carried out numerous flybys of its many moons, providing astronomers with a wealth of data about many of them, and their interactions with the ring system and Saturn's magnetosphere. An additional flyby from this series will take place today/tomorrow, as Cassini will swing by the peculiar moon Enceladus. According to mission managers, based at the NASA Jet Propulsion Laboratory, in Pasadena, California, the spacecraft will fly low above the surface of the moon, in order to conduct an intricate and sensitive gravity experiment. During the mission, planetary scientists hope to be able to extract a wealth of data as to the internal composition of Enceladus, which is undoubtedly one of the most interesting bodies in our solar system. The scheduled flight path will take the space probe about 100 kilometers (60 miles) above the surface, at the point of closest approach. This will take place on April 27 Pacific time and April 28 UTC. One of the things that makes Enceladus stand out from the crowd of Saturnine moons is the fact that astronomers believe it may house a liquid ocean. Naturally, liquid water cannot endure in the frigid temperatures of its surface, but the experts say that it may be buried several kilometers, under a thick ice crust. But the real interest is the south polar region, which featured cracks known as tiger stripes. Through these landscape features, Enceladus emits plumes of water and ice vapors, which apparently play an important role in fueling one of Saturn's rings with material. The new flyby will take Cassini straight through the plume emissions. During the flight, the instruments aboard the spacecraft will remain silent. In fact, the only thing experts need in order to conduct this experiment is a steady link between the probe and the NASA Deep Space Network on Earth. “Detecting any wiggle will help scientists understand what is under the famous "tiger stripe" fractures that spew water vapor and organic particles from the south polar region. Is it an ocean, a pond or a great salt lake? The experiment will also help scientists find out if the sub-surface south polar region resembles a lava lamp. Scientists have hypothesized that a bubble of warmer ice periodically moves up to the crust and repaves it, explaining the quirky heat behavior and intriguing surface features,” the JPL team says in a statement.

Asteroid To Fly by Within Moon's Orbit Thursday

A newly discovered asteroid, 2010 GA6, will safely fly by Earth this Thursday at 4:06 p.m. Pacific (23:06 U.T.C.). At time of closest approach 2010 GA6 will be about 359,000 kilometers (223,000 miles) away from Earth - about 9/10ths the distance from to the moon.

The asteroid, approximately 22 meters (71 feet) wide, was discovered by the Catalina Sky Survey, Tucson, Az.

"Fly bys of near-Earth objects within the moon's orbit occur every few weeks," said Don Yeomans of NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif.

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes.

The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet.

Cassini Doubleheader: Flying By Titan and Dione

(NASA) – In a special double flyby early next week, NASA’s Cassini spacecraft will visit Saturn’s moons Titan and Dione within a period of about a day and a half, with no maneuvers in between. A fortuitous cosmic alignment allows Cassini to attempt this doubleheader, and the interest in swinging by Dione influenced the design of its extended mission.

The Titan flyby, planned for Monday, April 5, will take Cassini to within about 7,500 kilometers (4,700 miles) of the moon’s surface. The distance is relatively long as far as encounters go, but it works to the advantage of Cassini’s imaging science subsystem. Cassini’s cameras will be able to stare at Titan’s haze-shrouded surface for a longer time and capture high-resolution pictures of the Belet and Senkyo areas, dark regions around the equator that ripple with sand dunes.

In the early morning of Wednesday, April 7 in UTC time zones, which is around 9 p.m. on Tuesday, April 6 in California, Cassini will make its closest approach to the medium-sized icy moon Dione. Cassini will plunge to within about 500 kilometers (300 miles) of Dione’s surface.

This is only Cassini’s second close encounter with Dione. The first flyby in October 2005, and findings from the Voyager spacecraft in the 1990s, hinted that the moon could be sending out a wisp of charged particles into the magnetic field around Saturn and potentially exhaling a diffuse plume that contributes material to one of the planet’s rings. Like Enceladus, Saturn’s more famous moon with a plume, Dione features bright, fresh fractures. But if there were a plume on Dione, it would certainly be subtler and produce less material.

Cassini plans to use its magnetometer and fields and particles instruments to see if it can find evidence of activity at Dione. Thermal mapping by the composite infrared spectrometer will also help in that search. In addition, the visual and infrared mapping spectrometer will examine dark material found on Dione. Scientists would like to understand the source of this dark material.

Cassini has made three previous double flybys and another two are planned in the years ahead. The mission is nearing the end of its first extension, known as the Equinox mission. It will begin its second mission extension, known as the Solstice Mission, in October 2010.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate in Washington. The Cassini orbiter was designed, developed and assembled at JPL.

Phobos Flyby Images: Proposed Landing Sites for the Forthcoming Phobos-Grunt Mission

The High Resolution Stereo Camera (HRSC) onboard the ESA spacecraft Mars Express took this image of the Phobos Grunt landing area using the HRSC nadir channel on 7 March 2010, HRSC Orbit 7915. The image resolution is 4.4m per pixel and the insert marks the proposed landing region and sites for Phobos-Grunt. (Credit: ESA/DLR/FU Berlin (G. Neukum))

Images from the recent flyby of Phobos, on 7 March 2010, have been released. The images show Mars' rocky moon in exquisite detail, with a resolution of just 4.4 metres per pixel. They show the proposed landing sites for the forthcoming Phobos-Grunt mission.

ESA's Mars Express spacecraft orbits the Red Planet in a highly elliptical, polar orbit that brings it close to Phobos every five months. It is the only spacecraft currently in orbit around Mars whose orbit reaches far enough from the planet to provide a close-up view of Phobos.

Like our Moon, Phobos always shows the same side to the planet, so it is only by flying outside the orbit that it becomes possible to observe the far side. Mars Express did just this on 7, 10 and 13 March 2010. Mars Express also collected data with other instruments.

Phobos is an irregular body measuring some 27 × 22 × 19 km. Its origin is debated. It appears to share many surface characteristics with the class of 'carbonaceous C-type' asteroids, which suggests it might have been captured from this population. However, it is difficult to explain either the capture mechanism or the subsequent evolution of the orbit into the equatorial plane of Mars. An alternative hypothesis is that it formed around Mars, and is therefore a remnant from the planetary formation period.

In 2011 Russia will send a mission called Phobos-Grunt (meaning Phobos Soil) to land on the martian moon, collect a soil sample and return it to Earth for analysis.

For operational and landing safety reasons, the proposed landing sites were selected on the far side of Phobos within the area 5°S-5°N, 230-235°E. This region was imaged by the HRSC high-resolution camera of Mars Express during the July-August 2008 flybys of Phobos. But new HRSC images showing the vicinity of the landing area under different conditions, such as better illumination from the Sun, remain highly valuable for mission planners.

It is expected that Earth-based ESA stations will take part in controlling Phobos-Grunt, receiving telemetry and making trajectory measurements, including implementation of very long-baseline interferometry (VLBI). This cooperation is realized on the basis of the agreement on collaboration of the Russian Federal Space Agency and ESA in the framework of the 'Phobos-Grunt' and 'ExoMars' projects.

Mars Express will continue to encounter Phobos until the end of March, when the moon will pass out of range. During the remaining flybys, HRSC and other instruments will continue to collect data.

Adapted from materials provided by European Space Agency

Phobos flyby season starts again

Mars Express has begun a series of flybys of Phobos, the largest moon of Mars. The campaign will reach its crescendo on 3 March, when the spacecraft will set a new record for the closest pass to Phobos, skimming the surface at just 50 km. The data collected could help untangle the origin of this mysterious moon.

The latest Phobos flyby campaign began 16 February at 05:52 UTC, when Mars Express drew to within 991 km of Phobos' airless surface. The flybys will continue at varying altitudes until 26 March when Phobos moves out of range. They offer prime chances for doing additional science with Mars Express, a spacecraft that was designed to study the red planet below rather than the grey moon alongside.

"Because Mars Express is in an elliptical and polar orbit with a maximum distance from Mars of about 10 000 km, we regularly pass Phobos. This represents an excellent opportunity to perform extra science," says Olivier Witasse, Mars Express Project Scientist.

Back in 2009, the mission team decided that the orbit of Mars Express needed to be adjusted to prevent the closest approach of the spacecraft drifting onto the planet's nightside. The flight control team at the European Space Operations Centre in Darmstadt, Germany, presented a number of possible scenarios, including one that would take the spacecraft to just 50 km above Phobos. "That was the closest they would let us fly to Phobos," says Witasse.

Precise gravity measurements

Heavy emphasis is being placed upon the closest flyby because it is an unprecedented opportunity to map Phobos' gravity field. At that range, Mars Express should feel differences in the pull from Phobos depending which part of the moon is closest at the time. This will allow scientists to infer the moon's internal structure.

Previous Mars Express flybys have already provided the most accurate mass yet for Phobos, and the High Resolution Stereo Camera (HRSC) has provided the volume. When calculating the density, this gives a surprising figure because it seems that parts of Phobos may be hollow. The science team aim to verify this preliminary conclusion.

In particular, the MARSIS radar will operate in a special sequence to try to see inside the moon, looking for structures or some clue to the internal composition. "If we know more about how Phobos is built, we might know more about how it formed," says Witasse.

The origin of Phobos is a mystery. Three scenarios are possible. The first is that the moon is a captured asteroid. The second is that it formed in situ as Mars formed below it. The third is that Phobos formed later than Mars, out of debris flung into Martian orbit when a large meteorite struck the red planet.

All the instruments will be used during the campaign, including HRSC. Although no imaging will be possible during the first five flybys, including the closest one, because Mars Express approaches from the nightside, high-resolution pictures will be possible from 7 March onwards. One task for HRSC is to image the proposed landing sites for the Russian mission Phobos-Grunt.

"It is always busy," says Witasse about running the science mission. "The Phobos flybys make it even more exciting."