Category Archives: Cassini

Titan’s Haze

A newly released Cassini image looking through Titan’s atmosphere.

Original caption: In this view, individual layers of haze can be distinguished in the upper atmosphere of Titan, Saturn’s largest moon. Titan’s atmosphere features a rich and complex chemistry originating from methane and nitrogen and evolving into complex molecules, eventually forming the smog that surrounds the moon.

This natural color image was taken in visible light with the Cassini spacecraft wide-angle camera on March 31, 2005, at a distance of approximately 20,556 miles (33,083 kilometers) from Titan. The view looks toward the north polar region on the moon’s night side. Part of Titan’s sunlit crescent is visible at right.

Credit: NASA/JPL-Caltech/Space Science Institute

Cassini’s Veil of Ice

Almost like abstract art, at least to me. The little moon Pan stands out nicely in this image too.

Original caption: Saturn’s rings, made of countless icy particles, form a translucent veil in this view from NASA’s Cassini spacecraft.

Saturn’s tiny moon Pan, about 17 miles (28 kilometers) across, orbits within the Encke Gap in the A ring. Beyond, we can see the arc of Saturn itself, its cloud tops streaked with dark shadows cast by the rings.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 12, 2016, at a distance of approximately 746,000 miles (1.2 million kilometers) from Pan.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

The Cassini mission is a cooperative project of NASA, ESA (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. 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, Colorado.

Image: NASA/JPL-Caltech/Space Science Institute

A Distant Star

In a list of epic space missions to ever fly Cassini would be in good company near the top. In particular I like the star to the right of Enceladus. I am a little surprised to even see it. Generally exposure times would preclude any background stars at all, but the image was probably enhanced only enough to enhance the plumes of Enceladus the star was bright enough to show up. The question is what star was it? I like these types of mysteries, I may never solve it, however it won’t be for a lack of trying.

Original caption: Saturn’s moon Enceladus drifts before the rings, which glow brightly in the sunlight. Beneath its icy exterior shell, Enceladus hides a global ocean of liquid water. Just visible at the moon’s south pole (at bottom here) is the plume of water ice particles and other material that constantly spews from that ocean via fractures in the ice. The bright speck to the right of Enceladus is a distant star.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 6, 2011, at a distance of approximately 90,000 miles (145,000 kilometers) from Enceladus.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

Image: NASA/JPL-Caltech/Space Science Institute

Two Views of Saturn from Cassini

Two views of Cassini in what NASA titled “Alpha and Omega”.

NASA — These two images illustrate just how far Cassini traveled to get to Saturn. On the left is one of the earliest images Cassini took of the ringed planet, captured during the long voyage from the inner solar system. On the right is one of Cassini’s final images of Saturn, showing the site where the spacecraft would enter the atmosphere on the following day.

In the left image, taken in 2001, about six months after the spacecraft passed Jupiter for a gravity assist flyby, the best view of Saturn using the spacecraft’s high-resolution (narrow-angle) camera was on the order of what could be seen using the Earth-orbiting Hubble Space Telescope. At the end of the mission (at right), from close to Saturn, even the lower resolution (wide-angle) camera could capture just a tiny part of the planet.

The left image looks toward Saturn from 20 degrees below the ring plane and was taken on July 13, 2001 in wavelengths of infrared light centered at 727 nanometers using the Cassini spacecraft narrow-angle camera. The view at right is centered on a point 6 degrees north of the equator and was taken in visible light using the wide-angle camera on Sept. 14, 2017.

The view on the left was acquired at a distance of approximately 317 million miles (510 million kilometers) from Saturn. Image scale is about 1,900 miles (3,100 kilometers) per pixel. The view at right was acquired at a distance of approximately 360,000 miles (579,000 kilometers) from Saturn. Image scale is 22 miles (35 kilometers) per pixel.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. 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, Colorado.

For more information about the Cassini-Huygens mission visit https://saturn.jpl.nasa.gov and https://www.nasa.gov/cassini. The Cassini imaging team homepage is at https://ciclops.org.

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

A Farewell Mosaic to Saturn

Yes there really are six moons visible in this image — click the image to help spot them. If you still can’t spot them all (and I could not at first) you will find a link to an annotated version below NASA’s caption:

NASA — After more than 13 years at Saturn, and with its fate sealed, NASA’s Cassini spacecraft bid farewell to the Saturnian system by firing the shutters of its wide-angle camera and capturing this last, full mosaic of Saturn and its rings two days before the spacecraft’s dramatic plunge into the planet’s atmosphere.

During the observation, a total of 80 wide-angle images were acquired in just over two hours. This view is constructed from 42 of those wide-angle shots, taken using the red, green and blue spectral filters, combined and mosaicked together to create a natural-color view.

Six of Saturn’s moons — Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus — make a faint appearance in this image. (Numerous stars are also visible in the background.)

A second version of the mosaic is provided in which the planet and its rings have been brightened, with the fainter regions brightened by a greater amount. (The moons and stars have also been brightened by a factor of 15 in this version.)

The ice-covered moon Enceladus — home to a global subsurface ocean that erupts into space — can be seen at the 1 o’clock position. Directly below Enceladus, just outside the F ring (the thin, farthest ring from the planet seen in this image) lies the small moon Epimetheus. Following the F ring clock-wise from Epimetheus, the next moon seen is Janus. At about the 4:30 position and outward from the F ring is Mimas. Inward of Mimas and still at about the 4:30 position is the F-ring-disrupting moon, Pandora. Moving around to the 10 o’clock position, just inside of the F ring, is the moon Prometheus.

This view looks toward the sunlit side of the rings from about 15 degrees above the ring plane. Cassini was approximately 698,000 miles (1.1 million kilometers) from Saturn, on its final approach to the planet, when the images in this mosaic were taken. Image scale on Saturn is about 42 miles (67 kilometers) per pixel. The image scale on the moons varies from 37 to 50 miles (59 to 80 kilometers) pixel. The phase angle (the Sun-planet-spacecraft angle) is 138 degrees.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

Click here for the annotated version.  You might even need to see the original image, although it is a rather large file and the link is directly at the NASA site — click here.

Also, the NASA site was down for quite a long time yesterday, not sure why but if you click that image link and nothing happens it might be down again.

PLUS!!!  For everyone in the US, have a safe holiday tomorrow and drive carefully!

Credits: NASA/JPL-Caltech/Space Science Institute

 

Saturn’s C Ring

Cassini keeps on giving even after it became part of Saturn and the end of the epic mission.

Original caption from NASA:

Saturn’s C ring is home to a surprisingly rich array of structures and textures (see also PIA21618). Much of the structure seen in the outer portions of Saturn’s rings is the result of gravitational perturbations on ring particles by moons of Saturn.

Such interactions are called resonances. However, scientists are not clear as to the origin of the structures seen in this image which has captured an inner ring region sparsely populated with particles, making interactions between ring particles rare, and with few satellite resonances.

In this image, a bright and narrow ringlet located toward the outer edge of the C ring is flanked by two broader features called plateaus, each about 100 miles (160 kilometers) wide.

Plateaus are unique to the C ring. Cassini data indicates that the plateaus do not necessarily contain more ring material than the C ring at large, but the ring particles in the plateaus may be smaller, enhancing their brightness. This view looks toward the sunlit side of the rings from about 53 degrees above the ring plane. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Aug. 14, 2017.

The view was acquired at a distance of approximately 117,000 miles (189,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 74 degrees. Image scale is 3,000 feet (1 kilometer) per pixel.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. 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, Colorado.

Image: NASA/JPL-Caltech/Space Science Institute

Saturn Moon Dione

One of the last images of the Saturn moon Dione from the Cassini spacecraft shows nice detail on the moon surface. Scientists say that the subtle variations in brightness hint at differences in composition, as well as the size and shape of grains in Dione’s surface material, or regolith.

The view was obtained at a distance of approximately 224,000 miles (360,000 kilometers) from Dione which isn’t too much different than our Earth-moon distance. Image scale is 1.4 mile (2.2 kilometers) per pixel

The Cassini spacecraft entered the Saturn atmosphere right on schedule on 15 September 2017.

Image: NASA/JPL-Caltech/Space Science Institute

The Last Moments of Cassini

The Cassini team released a description of Cassini’s last moments. The spacecraft was a fighter to the very end especially when one considers that it was traveling around 4.5 times faster than the ISS is around Earth.

Here’s a excerpt from the NASA description:

Data show that as Cassini began its final approach, in the hour before atmospheric entry it was subtly rocking back and forth by fractions of a degree, gently pulsing its thrusters every few minutes to keep its antenna pointed at Earth. The only perturbing force at that time was a slight tug from Saturn’s gravity that tried to rotate the spacecraft.

“To keep the antenna pointed at Earth, we used what’s called ‘bang-bang control,'” said Julie Webster, Cassini’s spacecraft operations chief at NASA’s Jet Propulsion Laboratory, Pasadena, California. “We give the spacecraft a narrow range over which it can rotate, and when it bangs up against that limit in one direction, it fires a thruster to tip back the other way.” (This range was indeed small: just two milliradians, which equals 0.1 degree. The reconstructed data show Cassini was subtly correcting its orientation in this way until about three minutes before loss of signal.)

At this point, about 1,200 miles (1,900 kilometers) above the cloud tops, the spacecraft began to encounter Saturn’s atmosphere. Cassini approached Saturn with its 36-foot-long (11-meter) magnetometer boom pointing out from the spacecraft’s side. The tenuous gas began to push against the boom like a lever, forcing it to rotate slightly toward the aft (or backward) direction. In response, the thrusters fired corrective gas jets to stop the boom from rotating any farther. Over the next couple of minutes, as engineers had predicted, the thrusters began firing longer, more frequent pulses. The battle with Saturn had begun.

With its thrusters firing almost continuously, the spacecraft held its own for 91 seconds against Saturn’s atmosphere — the thrusters reaching 100 percent of their capacity during the last 20 seconds or so before the signal was lost. The final eight seconds of data show that Cassini started to slowly tip over backward. As this happened, the antenna’s narrowly focused radio signal began to point away from Earth, and 83 minutes later (the travel time for a signal from Saturn), Cassini’s voice disappeared from monitors in JPL mission control. First, the actual telemetry data disappeared, leaving only a radio carrier signal. Then, 24 seconds after the loss of telemetry, silence.

These data explain why those watching the signal — appearing as a tall green spike on a squiggly plot of Cassini’s radio frequency — in mission control and live on NASA TV — saw what appeared to be a short reprieve, almost as though the spacecraft was making a brief comeback. The spike of the signal first began to diminish over a few seconds, but then rose briefly again before disappearing with finality.

Credit: NASA/JPL-Caltech

Crescent of Enceladus

Cassini may be gone, but the legacy lives on.

NASA – The brightly lit limb of a crescent Enceladus looks ethereal against the blackness of space. The rest of the moon, lit by light reflected from Saturn, presents a ghostly appearance.

Enceladus (313 miles or 504 kilometers across) is back-lit in this image, as is apparent by the thin crescent. However, the Sun-Enceladus-spacecraft (or phase) angle, at 141 degrees, is too low to make the moon’s famous plumes easily visible.

This view looks toward the Saturn-facing hemisphere of Enceladus. North on Enceladus is up. The above image is a composite of images taken with the Cassini spacecraft narrow-angle camera on March 29, 2017 using filters that allow infrared, green, and ultraviolet light. The image filter centered on 930 nm (IR) was is red in this image, the image filter centered on the green is green, and the image filter centered on 338 nm (UV) is blue.

The view was obtained at a distance of approximately 110,000 miles (180,000 kilometers) from Enceladus. Image scale is 0.6 miles (1 kilometer) per pixel.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

Credit: NASA/JPL-Caltech/Space Science Institute

Last Light for Cassini

NASA —  This monochrome view is the last image taken by the imaging cameras on NASA’s Cassini spacecraft. It looks toward the planet’s night side, lit by reflected light from the rings, and shows the location at which the spacecraft would enter the planet’s atmosphere hours later.

A natural color view, created using images taken with red, green and blue spectral filters, is also provided (Figure 1). The imaging cameras obtained this view at approximately the same time that Cassini’s visual and infrared mapping spectrometer made its own observations of the impact area in the thermal infrared.

This location — the site of Cassini’s atmospheric entry — was at this time on the night side of the planet, but would rotate into daylight by the time Cassini made its final dive into Saturn’s upper atmosphere, ending its remarkable 13-year exploration of Saturn.

The view was acquired on Sept. 14, 2017 at 19:59 UTC (spacecraft event time). The view was taken in visible light using the Cassini spacecraft wide-angle camera at a distance of 394,000 miles (634,000 kilometers) from Saturn. Image scale is about 11 miles (17 kilometers).