Category Archives: Cassini

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).

The Last Signals from Cassini

The end of mission activities for Cassini will be here with live commentary from JPL at 11:00 UT/7:00 ET.

Expected LOS is 12:00 UTC / 08:00 EDT

About the image (NASA) – ASA’s Cassini spacecraft gazed toward the northern hemisphere of Saturn to spy subtle, multi-hued bands in the clouds there.

This view looks toward the terminator — the dividing line between night and day — at lower left. The sun shines at low angles along this boundary, in places highlighting vertical structure in the clouds. Some vertical relief is apparent in this view, with higher clouds casting shadows over those at lower altitude.

Images taken with the Cassini spacecraft narrow-angle camera using red, green and blue spectral filters were combined to create this natural-color view. The images were acquired on Aug. 31, 2017, at a distance of approximately 700,000 miles (1.1 million kilometers) from Saturn. Image scale is about 4 miles (6 kilometers) per pixel.

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

Apoapsis

On 12 September 2017 at 05:27 UT / 01:27 EDT the Cassini spacecraft reached apoapsis or the farthest point from Saturn it will reach. For Cassini apoapse was 1.3 million km / 800,000 miles.

Cassini is now headed right toward Saturn for the last time. The spacecraft will plunge into the Saturian atmosphere in just a few days, on 15 September 2017.

The signal from Cassini has to travel 83 minutes before reaching Earth. By the time we lose the signal from the spacecraft about 11:55 UT / 07:55 EDT on the 15th, the spacecraft will have already encountered Saturn. The time could change a little because of atmospheric drag during the final orbits.

If I calculated this correctly the “at Saturn” event time would be 10:32 UT / 06:32 EDT based on that original estimate.

Definition of Apoapsis vs. Apogee.

The image above of the moon Titan is one of the very last we will see from the mission and was taken on 10 September 2017.

Image: NASA/JPL-Caltech/Space Science Institute

Cassini’s Legacy

As the Cassini mission draws to a close, NASA shares thoughts about the mission and what the future might bring.  I for one am all in for the Ice Giants Mission idea, robotic missions have proven to be a good value.

The image shown here (credit: NASA/JPL-Caltech/Space Science Institute) was taken on 08 Sept 2017 and returned to Earth on 09 Sept 2017.

As the Cassini spacecraft nears the end of a long journey rich with scientific and technical accomplishments, it is already having a powerful influence on future exploration. In revealing that Saturn’s moon Enceladus has many of the ingredients needed for life, the mission has inspired a pivot to the exploration of “ocean worlds” that has been sweeping planetary science over the past decade.

“Cassini has transformed our thinking in so many ways, but especially with regard to surprising places in the solar system where life could potentially gain a foothold,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at Headquarters in Washington. “Congratulations to the entire Cassini team!”

Onward to Europa

Jupiter’s moon Europa has been a prime target for future exploration since NASA’s Galileo mission, in the late 1990s, found strong evidence for a salty global ocean of liquid water beneath its icy crust. But the more recent revelation that a much smaller moon like Enceladus could also have not only liquid water, but also chemical energy that could potentially power biology, was staggering.

Many lessons learned during Cassini’s mission are being applied to planning NASA’s Europa Clipper mission, planned for launch in the 2020s. Europa Clipper will fly by the icy ocean moon dozens of times to investigate its potential habitability, using an orbital tour design derived from the way Cassini has explored Saturn. The Europa Clipper mission will orbit the giant planet — Jupiter in this case — using gravitational assists from its large moons to maneuver the spacecraft into repeated close encounters with Europa. This is similar to the way Cassini’s tour designers used the gravity of Saturn’s moon Titan to continually shape their spacecraft’s course.

In addition, many engineers and scientists from Cassini are serving on Europa Clipper and helping to develop its science investigations. For example, several members of the Cassini Ion and Neutral Mass Spectrometer and Cosmic Dust Analyzer teams are developing extremely sensitive, next-generation versions of their instruments for flight on Europa Clipper. What Cassini has learned about flying through the plume of material spraying from Enceladus will help inform planning for Europa Clipper, should plume activity be confirmed on Europa.

Returning to Saturn

Cassini also performed 127 close flybys of Saturn’s haze-enshrouded moon Titan, showing it to be a remarkably complex factory for organic chemicals — a natural laboratory for prebiotic chemistry. The mission investigated the cycling of liquid methane between clouds in its skies and great seas on its surface. By pulling back the veil on Titan, Cassini has ushered in a new era of extraterrestrial oceanography ­– plumbing the depths of alien seas — and delivered a fascinating example of earthlike processes occurring with chemistry and at temperatures markedly different from our home planet.

In the decades following Cassini, scientists hope to return to the Saturn system to follow up on the mission’s many discoveries. Mission concepts under consideration include spacecraft to drift on the methane seas of Titan and fly through the Enceladus plume to collect and analyze samples for signs of biology.

Giant Planet Atmospheres

Atmospheric probes to all four of the outer planets have long been a priority for the science community, and the most recent Planetary Science Decadal Surveycontinues to support interest in sending such a mission to Saturn. By directly sampling Saturn’s upper atmosphere during its last orbits and final plunge, Cassini is laying the groundwork for an eventual Saturn atmosphere probe.

Farther out in the solar system, scientists have long had their eyes set on exploring Uranus and Neptune. So far, each of these worlds has been visited by only one brief spacecraft flyby (Voyager 2, in 1986 and 1989, respectively). Collectively, Uranus and Neptune are referred to as “ice giant” planets, because they contain large amounts of materials (like water, ammonia and methane) that form ices in the cold depths of the outer solar system. This makes them fundamentally different from the gas giant planets, Jupiter and Saturn, which are almost all hydrogen and helium, and the inner, rocky planets like Earth or Mars. It’s not clear exactly how and where the ice giants formed, why their magnetic fields are strangely oriented, and what drives geologic activity on some of their moons. These mysteries make them scientifically important, and this importance is enhanced by the discovery that many planets around other stars appear to be similar to our own ice giants.

A variety of potential mission concepts are discussed in a recently completed study, delivered to NASA in preparation for the next Decadal Survey — including orbiters, flybys and probes that would dive into Uranus’ atmosphere to study its composition. Future missions to the ice giants might explore those worlds using an approach similar to Cassini’s mission.

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

Saturn’s S-Rings

NASA – These are the highest-resolution color images of any part of Saturn’s rings, to date, showing a portion of the inner-central part of the planet’s B Ring. The view is a mosaic of two images that show a region that lies between 61,300 and 65,600 miles (98,600 and 105,500 kilometers) from Saturn’s center.

This image is a natural color composite, created using images taken with red, green and blue spectral filters. The pale tan color is generally not perceptible with the naked eye in telescope views, especially given that Saturn has a similar hue.

The material responsible for bestowing this color on the rings — which are mostly water ice and would otherwise appear white — is a matter of intense debate among ring scientists that will hopefully be settled by new in-situ observations before the end of Cassini’s mission.

The different ringlets seen here are part of what is called the “irregular structure” of the B ring. Cassini radio occultations of the rings have shown that these features have extremely sharp boundaries on even smaller scales (radially, or along the direction outward from Saturn) than the camera can resolve here. Closer to Saturn, the irregular structures become fuzzier and more rounded, less opaque, and their color contrast diminishes.

The narrow ringlets in the middle of this scene are each about 25 miles (40 kilometers) wide, and the broader bands at right are about 200 to 300 miles (300 to 500 kilometers) across. It remains unclear exactly what causes the variable brightness of these ringlets and bands — the basic brightness of the ring particles themselves, shadowing on their surfaces, their absolute abundance, and how densely the particles are packed, may all play a role.

Image: NASA/JPL-Caltech/Space Science Institute

Saturn’s North

The beautiful image of the north polar region of Saturn shown here was taken on 26 April 2017, the same day as the spacecraft’s Grand Finale started.  In just over two weeks Cassini will deorbit into the atmosphere of Saturn.

Image: NASA/JPL-Caltech/Space Science Institute

NASA – Although the pole is still bathed in sunlight at present, northern summer solstice on Saturn occurred on May 24, 2017, bringing the maximum solar illumination to the north polar region. Now the Sun begins its slow descent in the northern sky, which eventually will plunge the north pole into Earth-years of darkness. Cassini’s long mission at Saturn enabled the spacecraft to see the Sun rise over the north, revealing that region in great detail for the first time.

This view looks toward the sunlit side of the rings from about 44 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 166,000 miles (267,000 kilometers) from Saturn. Image scale is about 10 miles (16 kilometers) per pixel.

Voyager 2 Sees Neptune

On Aug. 25, 1989, NASA’s Voyager 2 made its historic flyby of Neptune and that planet’s largest moon Triton. The Cassini mission is publishing this image to celebrate the anniversary of that event.

I remember this well, I was downloading the images on Slow Scan Television (SSTV) along with many-many other ham radio operators. Good times!

This is cropped and magnified version of the original provided in monochrome with Triton visible as a point of light above and to the left of Neptune.

NASA – In imaging Neptune, Cassini’s solar system family portrait-taking is complete. The mission’s planetary photojournal includes all of the major planets except Mercury, which is too close to the Sun to be imaged, as well as dwarf planet Pluto.

This view was acquired by the Cassini narrow-angle camera on Aug. 10, 2017, at a distance of approximately 2.72 billion miles (4.38 billion kilometers) from Neptune. Red, blue and green filter images were combined to create the natural color image.

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