NASA Cassini caught in Hyperion's particle beam inside Saturn's Magnetosphere

This stunning false-colour view of Saturn's moon Hyperion reveals crisp details across the strange, tumbling moon's surface. 

Differences in colour could represent differences in the composition of surface materials. 

The view was obtained during Cassini's close flyby on Sept. 26, 2005. 

Hyperion has a notably reddish tint when viewed in natural colour. 

The red color was toned down in this false-colour view, and the other hues were enhanced, in order to make more subtle colour variations across Hyperion's surface more apparent. 

Credit: NASA /JPL /Space Science Institute

Static electricity is known to play an important role on Earth's airless, dusty moon, but evidence of static charge building up on other objects in the solar system has been elusive until now.

A new analysis of data from NASA's Cassini mission has revealed that, during a 2005 flyby of Saturn's moon Hyperion, the spacecraft was briefly bathed in a beam of electrons coming from the moon's electrostatically charged surface.

The finding represents the first confirmed detection of a charged surface on an object other than our moon, although it is predicted to occur on many different bodies, including asteroids and comets.

The new analysis was led by Tom Nordheim, a doctoral candidate at Mullard Space Science Laboratory (MSSL), University College London, and was published recently in the journal Geophysical Research Letters.

Hyperion is porous and icy, with a bizarre, sponge-like appearance. Its surface is continuously bombarded by ultraviolet light from the sun and exposed to a rain of charged particles, electrons and ions, within the invisible bubble generated by Saturn's magnetic field, called the magnetosphere.

The researchers think Hyperion's exposure to this hostile space environment is the source of the particle beam that struck Cassini.

Measurements made by several of Cassini's instruments during a close encounter with Hyperion on September 26, 2005, indicate that something unexpected took place in the charged particle environment around the spacecraft.

Among those instruments, the Cassini Plasma Spectrometer (CAPS) detected that the spacecraft was magnetically connected to the surface of Hyperion for a brief period, allowing electrons to escape from the moon toward the robotic probe.

Most people are familiar with the electrostatic charge buildup that occurs when a balloon is rubbed against hair or a sweater.

Objects in space can also become electrostatically charged by exposure to solar ultraviolet light and incoming charged particles.

The Cassini data show that a similar process can take place on Hyperion.

The finding is surprising, as the small but odd-looking moon was thought to be a simple inert object, which would not undergo any strong interactions with the Saturnian magnetosphere.

Nevertheless, the team's analysis indicates that Cassini remotely detected a strongly negative voltage on Hyperion.

"It was rather like Cassini receiving a 200-volt electric shock from Hyperion, even though they were over 2,000 kilometers [1,200 miles] apart at the time," said Nordheim.

Scientists had previously suggested that surface features observed on the asteroid Eros and several of Saturn's moons are due to the motion of charged dust across their surfaces.

On small objects with low gravity, dust grains might even be able to overcome the force of gravity and escape into space.

Although mission controllers have detected no signs that the Hyperion electron beam caused damage to Cassini, strong electric charging effects could prove to be a hazard to future robotic and human explorers at planetary objects without atmospheres, including Earth's moon, where they could create the potential for powerful electrostatic discharges.

"Our observations show that this is also an important effect at outer planet moons and that we need to take this into account when studying how these moons interact with their environment," said Geraint Jones of MSSL, a member of the Cassini CAPS team who helped supervise the study.

Cassini's CAPS instrument was powered off in 2012, when the instrument began to draw excess current.

The team is based at Southwest Research Institute, San Antonio. Part of the CAPS instrument that made the detection discussed in this research, the CAPS electron spectrometer, was built by MSSL.

Nordheim and colleagues also utilized data from three other Cassini instruments in their analysis: the Radio and Plasma Wave Science instrument (RPWS), the Magnetospheric Imaging Instrument and the Magnetometer (MIMI).

Cassini spacecraft image: Saturn's moons Tethys, Hyperion and Prometheus

The Cassini spacecraft captures a rare family photo of three of Saturn's moons that couldn't be more different from each other!

As the largest of the three, Tethys (image center) is round and has a variety of terrains across its surface.

Meanwhile, Hyperion (to the upper-left of Tethys) is the "wild one" with a chaotic spin and Prometheus (lower-left) is a tiny moon that busies itself sculpting the F ring.

To learn more about the surface of Tethys (660 miles, or 1,062 kilometers across), see PIA17164.

More on the chaotic spin of Hyperion (168 miles, or 270 kilometers across) can be found at PIA07683, and discover more about the role of Prometheus (53 miles, or 86 kilometers across) in shaping the F ring in PIA12786.

This view looks toward the sunlit side of the rings from about 1 degree above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 14, 2014.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 22 degrees.

Image scale is 7 miles (11 kilometers) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

Cassini Solstice Mission: Hyperion Images

This image of Hyperion was taken by Cassini on August 25, 2011 and received on Earth August 26, 2011. 

The camera was pointing toward HYPERION at approximately 57,974 kilometers away, and the image was taken using the P120 and GRN filters. 

This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2012.

For more information on raw images check out our frequently asked questions section.

Image Credit: NASA/JPL/Space Science Institute 

NASA's Cassini spacecraft captured new views of Saturn's oddly shaped moon Hyperion during its encounter with this cratered body on Thursday, Aug. 25.

Raw images were acquired as the spacecraft flew past the moon at a distance of about 15,500 miles (25,000 kilometers), making this the second closest encounter.

Hyperion is a small moon - just 168 miles (270 kilometers) across. It has an irregular shape and surface appearance, and it rotates chaotically as it tumbles along in orbit.

This odd rotation prevented scientists from predicting exactly what terrain the spacecraft's cameras would image during this flyby.

However, this flyby's closeness has likely allowed Cassini's cameras to map new territory. At the very least, it will help scientists improve color measurements of the moon.

It will also help them determine how the moon's brightness changes as lighting and viewing conditions change, which can provide insight into the texture of the surface.

The colour measurements provide additional information about different materials on the moon's deeply pitted surface.

Cassini Set to Do Retinal Scan of Saturnian Eyeball Mimas

NASA's Cassini spacecraft made its closest examination yet of Mimas, an eyeball-shaped moon of Saturn that has also been likened to the Death Star of "Star Wars."

The spacecraft returned the highest-resolution images yet of this battered satellite.

Mimas bears the mark of a violent, giant impact from the past - the 140-kilometer-wide (88-mile-wide) Herschel Crater - and scientists hope the encounter will help them explain why the moon was not blown to smithereens when the impact happened. They will also be trying to count smaller dings inside the basin of Herschel Crater so they can better estimate its age.

In addition, Cassini's composite infrared spectrometer was used to determine the thermal signature of the moon, and other instruments made measurements to learn more about the surface composition.

The Mimas flyby involved a significant amount of skill because the spacecraft passed through a dusty region to get there. Mission managers have planned for the Cassini spacecraft to lead with its high-gain antenna to provide a barrier of protection.

At closest approach, the spacecraft came within 9,500 kilometers (5,900 miles) of the moon. Cassini began taking images and measurements shortly after closest approach.

Mimas is an inner moon of Saturn that averages 396 kilometers (246 miles) in diameter. The diameter of Herschel Crater is about one-third that of the entire moon. The walls of the crater are about 5 kilometers (3 miles) high, and parts of the floor are approximately 10 kilometers (6 miles) deep.