Auroras on Saturn

Astronomers using the NASA/ESA Hubble Space Telescope have captured new images of the dancing auroral lights at Saturn’s north pole. Taken in April and May 2013 from Hubble’s perspective in orbit around Earth, these observations provide a detailed look at previously unseen dynamics in the choreography of the auroral glow.

The ultraviolet images, taken by Hubble’s super-sensitive Advanced Camera for Surveys, capture moments when Saturn’s magnetic field is affected by bursts of particles streaming from the Sun.

Saturn’s magnetosphere – the vast magnetic ‘bubble’ that surrounds the planet – is compressed on the Sunward side of the planet, and streams out into a long ‘magnetotail’ on the nightside.

It appears that when particles from the Sun hit Saturn, the magnetotail collapses and later reconfigures itself, an event that is reflected in the dynamics of its auroras.

Saturn was caught during a very dynamic light show – some of the bursts of light seen shooting around Saturn’s polar regions traveled more than three times faster than the speed of the gas giant’s roughly 10-hour rotation period!

The new observations were taken as part of a three-year Hubble observing campaign, and are presented in a paper published in the journal Geophysical Research Letters. The images complement those taken by the international Cassini spacecraft orbiting Saturn.

Image credit: NASA/ESA, Acknowledgement: J. Nichols (University of Leicester)

The Formation of Aerosols in Titan's Haze

This illustration shows the various steps that lead to the formation of the aerosols that make up the haze on Titan, Saturn's largest moon.

When sunlight or highly energetic particles from Saturn's magnetosphere hit the layers of Titan's atmosphere above 1000 km, the nitrogen and methane molecules there are broken up. This results in the formation of massive positive ions and electrons, which trigger a chain of chemical reactions that produce a variety of hydrocarbons. Many of these hydrocarbons have been detected in Titan's atmosphere, including Polycyclic Aromatic Hydrocarbons (PAHs), which are large carbon-based molecules that form from the aggregation of smaller hydrocarbons. Some of the PAHs detected in the atmosphere of Titan also contain nitrogen atoms.

PAHs are the first step in a sequence of increasingly larger compounds. Models show how PAHs can coagulate and form large aggregates, which tend to sink, due to their greater weight, into the lower atmospheric layers. The higher densities in Titan's lower atmosphere favor the further growth of these large conglomerates of atoms and molecules. These reactions eventually lead to the production of carbon-based aerosols, large aggregates of atoms and molecules that are found in the lower layers of the haze that enshrouds Titan, well below 500 km.

The formation scenario of aerosols in Titan's atmosphere depicted in this illustration is based on the simulations described by Lavvas et al., 2011 (The Astrophysical Journal, 728, 80); doi:10.1088/0004-637X/728/2/80.

Illustration credit: ESA/ATG medialab

Note: For more information, see Cassini Sees Precursors to Aerosol "Snow" on Titan.

Particle Population in Saturn's Magnetosphere

This is an artist's concept of the Saturnian plasma sheet based on data from Cassini magnetospheric imaging instrument. It shows Saturn's embedded "ring current," an invisible ring of energetic ions trapped in the planet's magnetic field.

Saturn is at the center, with the red "donut" representing the distribution of dense neutral gas outside Saturn's icy rings. Beyond this region, energetic ions populate the plasma sheet to the dayside magnetopause filling the faintly sketched magnetic flux tubes to higher latitudes and contributing to the ring current. The plasma sheet thins gradually toward the nightside. The view is from above Saturn's equatorial plane, which is represented by grid lines. The moon Titan's location is shown for scale. The location of the bow shock is marked, as is the flow of the deflected solar wind in the magnetosheath.

Illustration credit: NASA/JPL/JHUAPL

Note: For more information, see 'Tis the Season -- for Plasma Changes at Saturn.

Saturn's Bow Shock

The international Cassini spacecraft exploring the magnetic environment of Saturn. The image is not to scale. Saturn’s magnetosphere is depicted in grey, while the complex bow shock region – the shock wave in the solar wind that surrounds the magnetosphere – is shown in blue. While crossing the bow shock on 3 February 2007, Cassini recorded a particularly strong shock (an Alfvén Mach number of approximately 100) under a 'quasi-parallel' magnetic field configuration, during which significant particle acceleration was detected for the first time. The findings provide insight into particle acceleration at the shocks surrounding the remnants of supernova explosions.

Illustration credit: ESA

Note: For more information, see Cassini Sheds Light on Cosmic Particle Accelerators (ESA) and Cassini Sheds Light on Cosmic Particle Accelerators (JPL). Also, PIA16825: Magnetic Fields and Bow Shocks (Illustration) and PIA16739: Cassini at Saturn's Bow Shock (Artist Concept).

Saturn's Hot Plasma Explosions

This animation based on data obtained by NASA's Cassini spacecraft shows how the "explosions" of hot plasma on the night side (orange and white) periodically inflate Saturn's magnetic field (white lines). Cassini scientists have been able to compute the "pressure" that the hot plasma exerts on the surrounding magnetic field by using remote images of the previously invisible hot plasma taken by the ion and neutral camera, part of the magnetospheric imaging instrument on board Cassini.

These enormous clouds of hot plasma recur in the part of the magnetosphere known as the magnetotail roughly every 10 to 11 hours. They rotate around Saturn at a distance of about eight to 15 times the radius of Saturn. Scientists have finally been able to demonstrate that the pressure contained in these clouds is sufficient to inflate the magnetic field in a manner that is consistent with the periodic magnetic field signals that have puzzled them for so long. As the high- and low-pressure systems of atmospheric weather on Earth produce winds, pressures in space produce huge electrical currents, which in turn distort the magnetic field.

The animation is based on data that were collected from December 17 to 18, 2004.

Video credit: NASA/JPL/JHUAPL/University of Iowa

Note: For more information, see Hot Plasma Explosions Inflate Saturn's Magnetic Field.

Tinted Rhea

These three views of Saturn's moon Rhea were made from data obtained by NASA's Cassini spacecraft, enhanced to show colorful splotches and bands on the icy moon's surface. Scientists believe the reddish and bluish tints came from bombardments large and small.

Icy material sprayed by the moon Enceladus hits Rhea head-on in its orbit around Saturn and leaves a coral-colored tint. Darker, rust-colored reddish hues paint the trailing hemisphere, or the side that faces backward in the moon's orbit around Saturn. The reddish hues are thought to be caused by tiny particle strikes from circulating plasma, a gas-like state of matter so hot that atoms split into an ion and an electron, in Saturn's magnetic environment. Tiny, iron-rich "nanoparticles" may also be involved, based on earlier analyses by the Cassini visual and infrared mapping spectrometer team.

Rhea sports a chain of bluish splotches along the equator that appear where fresh, bluish ice has been exposed on older crater rims. Cassini imaging scientists recently reported that they did not see evidence in Cassini images of a ring around Rhea. However, scientists analyzing these enhanced-color views suggest the bluish material could have been exposed by the crash of orbiting material -- perhaps a ring -- to the surface of Rhea in the not too distant past.

These images were made by processing raw images obtained by Cassini's imaging cameras in November 2005. Scientists analyzed frames shot through visible-light, ultraviolet and infrared filters. The processing enhanced our views of these moons beyond what could be seen by the human eye.

The image on the left shows a composite image made from data in the infrared, green and ultraviolet filters. The middle view shows an image made from data analyzing the ratio of infrared to green wavelengths, indicating the relative redness of the features. The brighter the feature is in this middle view, the redder it is. The image on the right shows data analyzing the ratio of infrared to ultraviolet wavelengths. The darker the feature is, the bluer the tint

In each of these images, the trailing hemisphere is on the left side and leading hemisphere is on the right side. They are centered near 145 degrees west longitude, about 35 degrees east of the boundary between the leading and trailing hemispheres. The bright crater Inktomi can be seen near the center of the images on the left and right, but was more difficult to see in the middle image because of there is less contrast in the infrared/ultraviolet ratio.

Photo credit: NASA/JPL/SSI/LPI

Note: For a brief technical discussion about how Rhea got its tints, see PIA13425: Moons Under Bombardment.