Water's Early Journey in a Solar System

The building blocks of comets, and apparently Saturn's largest moon, Titan, formed under similar conditions in the disk of gas and dust that formed the sun.

NASA's Spitzer Space Telescope observed a fledgling solar system like the one depicted in this artist's concept, and discovered deep within it enough water vapor to fill the oceans on Earth five times. This water vapor starts out in the form of ice in a cloudy cocoon (not pictured) that surrounds the embryonic star, called NGC 1333-IRAS 4B (buried in center of image). Material from the cocoon, including ice, falls toward the center of the cloud. The ice then smacks down onto a dusty pre-planetary disk circling the stellar embryo (doughnut-shaped cloud) and vaporizes. Eventually, this water might make its way into developing planets.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see Titan's Building Blocks Might Pre-date Saturn.

Titan

Only a sharp and careful eye can make out the subtle variations in Titan's clouds when viewed in visible light. However, these subtle features sometimes become more readily apparent when imaged at other wavelengths of light. This infrared image clearly reveals a band around the Titan's north pole.

Cassini scientists are regularly monitoring Titan, hoping to understand more about Titan's dense atmosphere and clouds.

This view looks toward the leading side of Titan. North on Titan is up and rotated 31 degrees to the left. The image was taken with the Cassini spacecraft narrow-angle camera on January 26, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 889 nanometers.

The view was acquired at a distance of approximately 1.5 million miles (2.4 million kilometers) from Titan. Image scale is 9 miles (14 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Radio Occultation of Titan During Cassini Flyby

Cassini will attempt to bounce signals off of Saturn's moon Titan once more during a flyby on June 18, 2014, revealing important details about the moon's surface.

As NASA's Cassini spacecraft zooms toward Saturn's smoggy moon Titan for a targeted flyby on June 18, mission scientists are excitedly hoping to repeat a scientific tour de force that will provide valuable new insights into the nature of the moon's surface and atmosphere.

For Cassini's radio science team, the last flyby of Titan, on May 17, was one of the most scientifically valuable encounters of the spacecraft's current extended mission. The focus of that flyby, designated "T-101," was on using radio signals to explore the physical nature of Titan's vast northern seas and probe the high northern regions of its substantial atmosphere.

The Cassini team hopes to replicate the technical success of that flyby during the T-102 encounter, slated for June 18, during which the spacecraft will attempt similar measurements of Titan. During closest approach, the spacecraft will be just 2,274 miles (3,659 kilometers) above the surface of the moon while traveling at 13,000 miles per hour (5.6 kilometers per second).

During the upcoming flyby, if all goes well as before, Cassini's radio science subsystem will bounce signals off the surface of Titan, toward Earth, where they will be received by the ground stations of NASA's Deep Space Network. This sort of observation is known as a bistatic scattering experiment and its results can yield clues to help answer a variety of questions about large areas of Titan's surface: Are they solid, slushy or liquid? Are they reflective? What might they be made of?

During the May encounter, Cassini beamed radio signals over the two largest bodies of liquid on Titan, seas named Ligeia Mare and Kraken Mare. During that first attempt, scientists could not be certain the signals would successfully bounce off the lakes to be received on Earth. They were thrilled when ground stations received specular reflections -- essentially the glint -- of the radio frequencies as they ricocheted off Titan.

"We held our breath as Cassini turned to beam its radio signals at the lakes," said Essam Marouf, a member of the Cassini radio science team of San Jose State University in California. "We knew we were getting good quality data when we saw clear echoes from Titan's surface. It was thrilling."

A second technical accomplishment -- an experiment to send precision-tuned radio frequencies through Titan's atmosphere -- also makes the May and June flybys special. The experiment, known as a radio occultation, provides information about how temperatures vary by altitude in Titan's atmosphere. Preparing for these experiments tested just how thoroughly the Cassini team has come to understand the structure of Titan's atmosphere during nearly a decade of study by the mission.

During this type of radio occultation, a signal is beamed from Earth through the atmosphere of Titan toward the Cassini spacecraft, which responds back to Earth with an identical signal. Information about Titan is imprinted in the signal as it passes through the moon's atmosphere, encountering differences in temperature and density. The trick is that the transmitted signal must be varied during the experiment so that it remains nearly constant when received by the spacecraft.

In order to give the occultation experiments any chance of success, the team has to account for not only the relative motions of the spacecraft and the transmitting antennas on the rotating planet Earth, but also the ways the signal is bent by different layers in Titan's atmosphere.

While this procedure has been used successfully for several Saturn occultations in the past two years, it had not yet been tried at Titan. And since the Titan occultations last just a few minutes, the team was concerned about how quickly the frequency lockup between ground and spacecraft could be established, if at all. For comparison, NASA's Magellan mission tried the technique at Venus in the 1990s, without success.

As they waited for signs of confirmation during the May encounter, the team saw the signal lock occur in only a few seconds, indicating that their predictions were spot-on. Data on Titan's atmosphere flowed in, adding new information to the mission's campaign to monitor the changing of the seasons on this alien moon.

"This was like trying to hit a hole-in-one in golf, except that the hole is close to a billion miles away, and moving," said Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory in Pasadena, California. "This was our first attempt to precisely predict and compensate for the effect of Titan's atmosphere on the uplinked radio signal from Earth, and it worked to perfection."

Illustration credit: NASA/JPL-Caltech

Atlas Emerging From Shadow

The Cassini spacecraft captures a glimpse of the moon Atlas shortly after emerging from Saturn's shadow. Although the sunlight at Saturn's distance is feeble compared to that at the Earth, objects cut off from the Sun within Saturn's shadow cool off considerably.

Scientists study how the moons around Saturn cool and warm as they enter and leave Saturn's shadow to better understand the physical properties of Saturn's moons.

This view looks toward the sunlit side of the rings from about 44 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on January 23, 2014.

The view was acquired at a distance of approximately 1.6 million miles (2.6 million kilometers) from Atlas and at a Sun-Atlas-spacecraft, or phase, angle of 93 degrees. Image scale is 10 miles (16 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Phoebe, Approaching and Departing

As it entered the Saturn system, NASA's Cassini spacecraft performed its first targeted flyby of one of the planet's moons. On June 11, 2004, Cassini passed Phoebe, the largest of Saturn's outer or "irregular" moons, at an altitude of just 1,285 miles (2,068 kilometers). This was the sole close flyby of one of the outer moons of Saturn in the entire Cassini mission.

This montage of two views is published by the Cassini team to mark the 10th anniversary of the Phoebe flyby.

The image on the left side shows Cassini's view on approach to Phoebe, while the right side shows the spacecraft's departing perspective. Most of the left-side view was previously released as PIA06073; an area on its upper right side is newly filled in here. Most of the view on the right side has not previously been released, although the crater at upper left is seen in PIA06074.

Phoebe's shape is approximately spherical (see PIA06070 and PIA15507 for more details), with a diameter of 136 miles (219 kilometers) on its longest axis and 127 miles (204 kilometers) on its shortest axis, which is also the rotation axis. This is approximately 16 times smaller than Earth's moon.

For several reasons, Phoebe is thought to be a captured object that does not share a joint origin with Saturn and the inner, "regular" satellites. It orbits in a retrograde direction, opposite to the direction of Saturn's other major moons. Its overall density was determined by Cassini scientists to be quite large for a moon of Saturn. The prevailing view is that Phoebe might have formed in the Kuiper Belt, far beyond the orbit of Saturn. It might thus be a small cousin of the largest Kuiper Belt object, Pluto.

The image mosaic on the left, recorded about 45 minutes before closest approach to Phoebe, is composed of six frames from Cassini's Narrow-Angle Camera (NAC), plus one Wide-Angle Camera (WAC) image to fill the gap on the upper-right limb. The image has a spatial resolution of 260 feet (80 meters) per pixel. The sun-Phoebe-spacecraft, or phase, angle is 80 degrees.

The image at right, taken about half an hour after closest approach, is composed of eight NAC frames. The spatial resolution is 210 feet (65 meters) per pixel, and the phase angle is 83 degrees.

The images have been slightly rescaled from their original formats and sharpened. Because Phoebe is a very dark object, contrast enhancement was also necessary. At such high phase angles, the brightest parts of the surface, except where bright ice is exposed, reflect only about four percent of the incoming sunlight. The mosaics are composed of monochromatic, or single-color, images. Since Phoebe is a very dark object with no obvious coloration, a natural color view would probably look somewhat similar.

Image credit: NASA/JPL-Caltech/Space Science Institute

F-Ring Streamer-Channels

Prometheus is caught in the act of creating gores and streamers in the F ring. Scientists believe that Prometheus and its partner-moon Pandora are responsible for much of the structure in the F ring.

The orbit of Prometheus (53 miles, or 86 kilometers across) regularly brings it into the F ring. When this happens, it creates gores, or channels, in the ring where it entered. Prometheus then draws ring material with it as it exits the ring, leaving streamers in its wake. This process creates the pattern of structures seen in this image. This process is described in detail, along with a movie of Prometheus creating one of the streamer/channel features, in PIA08397.

This view looks toward the sunlit side of the rings from about 8.6 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on February 11, 2014.

The view was acquired at a distance of approximately 1.3 million miles (2.1 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 147 degrees. Image scale is 8 miles (13 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Crescent Titan and Its South Polar Vortex

Titan's polar vortex stands illuminated where all else is in shadow. Scientists deduce that the vortex must extend higher into Titan's atmosphere than the surrounding clouds because it is still lit in images like this. Although the south polar region is now in winter, the Sun can still reach high features like the vortex.

Titan (3,200 miles, or 5,150 kilometers across) is Saturn's largest moon. For a color image of the south polar vortex on Titan, see PIA14919. For a movie of the vortex, see PIA14920.

This view looks toward the Saturn-facing hemisphere of Titan. North on Titan is up and rotated 32 degrees to the right. The image was taken with the Cassini spacecraft wide-angle camera on February 3, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 742 nanometers.

The view was obtained at a distance of approximately 134,000 miles (215,000 kilometers) from Titan. Image scale is 8 miles (13 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute