This collage of images from NASA's Cassini spacecraft shows Saturn's northern hemisphere and rings as viewed with four different spectral filters. Each filter is sensitive to different wavelengths of light and reveals clouds and hazes at different altitudes.
Clockwise from top left, the filters used are sensitive to violet (420 nanometers), red (648 nanometers), near-infrared (728 nanometers) and infrared (939 nanometers) light.
The image was taken with the Cassini spacecraft wide-angle camera on Dec. 2, 2016, at a distance of about 400,000 miles (640,000 kilometers) from Saturn. Image scale is 95 miles (153 kilometers) per pixel.
The images have been enlarged by a factor of two. The original versions of these images, as sent by the spacecraft, have a size of 256 pixels by 256 pixels. Cassini's images are sometimes planned to be compressed to smaller sizes due to data storage limitations on the spacecraft, or to allow a larger number of images to be taken than would otherwise be possible.
These images were obtained about two days before its first close pass by the outer edges of Saturn's main rings during its penultimate mission phase.
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.
NASA's Cassini spacecraft has sent to Earth its first views of Saturn’s atmosphere since beginning the latest phase of its mission. The new images show scenes from high above Saturn's northern hemisphere, including the planet's intriguing hexagon-shaped jet stream.
Cassini began its new mission phase, called its Ring-Grazing Orbits, on Nov. 30. Each of these weeklong orbits -- 20 in all -- carries the spacecraft high above Saturn's northern hemisphere before sending it skimming past the outer edges of the planet's main rings.
Cassini’s imaging cameras acquired these latest views on Dec. 2 and 3, about two days before the first ring-grazing approach to the planet. Future passes will include images from near closest approach, including some of the closest-ever views of the outer rings and small moons that orbit there.
"This is it, the beginning of the end of our historic exploration of Saturn. Let these images -- and those to come -- remind you that we’ve lived a bold and daring adventure around the solar system’s most magnificent planet," said Carolyn Porco, Cassini imaging team lead at Space Science Institute, Boulder, Colorado.
The next pass by the rings' outer edges is planned for Dec. 11. The ring-grazing orbits will continue until April 22, when the last close flyby of Saturn's moon Titan will once again reshape Cassini's flight path. With that encounter, Cassini will begin its Grand Finale, leaping over the rings and making the first of 22 plunges through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its innermost ring on April 26.
On Sept. 15, the mission's planned conclusion will be a final dive into Saturn's atmosphere. During its plunge, Cassini will transmit data about the atmosphere's composition until its signal is lost.
Launched in 1997, Cassini has been touring the Saturn system since arriving in 2004 for an up-close study of the planet, its rings and moons. Cassini has made numerous dramatic discoveries, including a global ocean with indications of hydrothermal activity within the moon Enceladus, and liquid methane seas on another moon, Titan.
Cassini, a NASA spacecraft orbiting Saturn, has been redirected, and experts at the University of Iowa are part of that discovery.
UI scientists helped to build part of Cassini. Their main focus was on the Radio and Plasma Wave System instrument of the spacecraft. The instrument measures radio and plasma waves as well as understands the processes in Saturn’s moons and atmosphere.
In April 2017, the spacecraft will move even closer to Saturn by moving through gaps between the rings of Saturn, said George Hospodarsky, a UI physics/astronomy associate research scientist and the lead operational planner on the project.
The rings are “pieces of comets, asteroids, or shattered moons that broke up before they reached the planet,” according to the NASA website.
On Sept. 15, 2017, Cassini will then enter Saturn’s atmosphere and act somewhat like a meteor burning up as part of the planetary-protection requirement by NASA. The protection is the practice of protecting Solar System bodies — planets, moons, comets, and asteroids — from contamination by Earth life and protecting Earth from possible life forms that may be returned from other Solar System bodies, according to NASA.
“We’re especially excited for April 26, 2017, when Cassini will thread the needle just above Saturn’s atmosphere and just below Saturn’s giant ring system for the very first time,” stated Bill Kurth, a UI physics/astronomy research scientist and the principal investigator of the project.
Kurth said Cassini executed a close flyby Saturn’s moon, Titan, which then switched its course. The spacecraft was brought into a ring grazing orbit just outside the F-ring of Saturn.
Scientists have detected hundreds of dust particles per second, along with the electromagnetic waves in space and planetary radio emissions. They also are looking for the interactions between the rings and Saturn.
Kurth said one of Saturn’s moons, Iapetus, could have water on it. If the Cassini were to crash into the moon, he said, it could dissipate some water particles or contaminate the habitat there, essentially ruining any future discoveries. NASA’s protection requirement was created to protect possible habitable planets, so no particles from a spacecraft could interfere with them.
Hospodarsky said the Cassini will take systematic measurements as well as pictures of storms and the atmosphere of Saturn.
“Basically, the project is in the process of getting ready for the end of the mission or what is known as the ‘grand finale,’ ” he said.
Linda Spilker, the Cassini Project scientist at the Jet Propulsion Lab in Pasadena, California, said the Radio and Plasma Wave System instrument will be key to understanding the particles in the gaps of Saturn’s rings. When Cassini flies through the F-ring in April, she said, it will use a dish to shield itself from the particles, and its antennas will help measure the particle hits.
In addition to collecting measurements, the instrument also helps NASA understand the magnetosphere of Saturn. The magnetosphere is caused through Saturn’s magnetic field, which is the second largest in the solar system.
“The scientists at the University of Iowa have helped us to better understand the complexity of Saturn’s magnetic bubble,” Spilker said.
The Cassini project began in July 2004 and will end after 17 years orbiting Saturn.
Quelle: The Daily Iowan