NASA’s Cassini spacecraft is back in contact with Earth after its successful first-ever dive through the narrow gap between the planet Saturn and its rings on April 26, 2017. The spacecraft is in the process of beaming back science and engineering data collected during its passage, via NASA’s Deep Space Network Goldstone Complex in California’s Mojave Desert.
Before Cassini, we had only brief glimpses of the discoveries awaiting us at Saturn. Pioneer 11 and Voyagers 1 and 2 conducted flybys decades ago, taking pictures, measurements and observations as they zoomed past. These missions shed new light on Saturn’s complicated ring system, discovered new moons and made the first measurements of Saturn’s magnetosphere. But these quick encounters didn’t allow time for more extensive scientific research.
Cassini changed all that. It began the first in-depth, up-close study of Saturn and its system of rings and moons in 2004. It became the first spacecraft to orbit Saturn, beginning a mission that yielded troves of new insights over more than a decade. The Saturnian system proved to be rich ground for exploration and discoveries, and Cassini’s science findings changed the course of future planetary exploration.
♦ Cassini imaged lightning on Saturn’s night side and day side, both of which had never been done before.
♦ Saturn’s 30-year storm (or annual storm for Saturn), appeared 10 Earth years earlier than usual, allowing Cassini to study the phenomenon up close during its mission.
♦ Cassini imaged, first in the infrared and later in visible wavelengths of light, the hexagonal jet stream around Saturn’s north pole, and revealed its remarkable symmetry.
Scientists have never before studied the size, temperature, composition and distribution of Saturn’s rings from Saturn orbit. Cassini has captured extraordinary ring-moon interactions, observed the lowest ring-temperature ever recorded at Saturn, discovered that the moon Enceladus is the source for Saturn’s E ring, and viewed the rings at equinox when sunlight strikes the rings edge-on, revealing never-before-seen ring features and details.
♦ The particles that make up Saturn’s rings range in size from smaller than a grain of sand to as large as mountains.
♦ Cassini found that water jets from the moon Enceladus provide much of the material in Saturn’s E-ring, a diffuse ring outside of the bright, main rings.
♦ Cassini studied features in Saturn’s rings called “spokes,” which can be longer than the diameter of Earth. Scientists think they’re made of tiny icy particles that are lifted by an electrostatic charge and only last a few hours.
♦ During Saturn’s equinox, when the rings face the sun edge-on, Cassini watched ring particles produce elongated shadows that revealed unexpectedly immense ring chunks that measured miles (kilometers) in size.
The Voyager and Pioneer flybys of the 1970s and 1980s provided rough sketches of Saturn’s moons. But during its many years in Saturn orbit, Cassini discovered previously unknown moons, solved mysteries about known ones, studied their interactions with the rings and revealed how sharply different the moons are from one another.
♦ Saturn’s dozens of moons range in size from larger than planet Mercury down to about the size of a sports arena.
♦ Cassini found water continually spewing out of jets around the south polar region of Saturn’s moon Enceladus, and scientists concluded that its subsurface ocean has all the ingredients for life – liquid water, heat, and food (methane).
♦ Among Saturn’s natural satellites, Cassini found the only known world aside from Earth’s moon to have a statically charged surface (Hyperion).
♦ Saturn’s moons contribute material to Saturn’s rings and magnetosphere, but the moons also collect material from Saturn’s rings and magnetosphere.
Brief Top 10 Discoveries:
1. The Huygens probe makes first landing on a moon in the outer solar system (Titan)
This image was returned Jan. 14, 2005, by the European Space Agency’s Huygens probe after its successful descent to land on Titan. This colored view, following processing to add reflection spectra data, gives a better indication of the actual color of the surface.
Titan: Saturn’s Largest Moon
2. Discovery of active, icy plumes on the Saturnian moon Enceladus
The discovery of Enceladus’s massive plume was such a surprise that mission designers completely reshaped the mission to get a better look. The discovery became even more important when Cassini found evidence of water-based ice in the plume. Life as we know it relies on water, so the search for life suddenly extended to this small, bright moon. The recent discovery of signs of an subsurface ocean makes Enceladus one of the most exciting science destinations in our solar system.
3. Saturn’s rings revealed as active and dynamic — a laboratory for how planets form
The disturbance visible at the outer edge of Saturn’s A ring in this image from NASA’s Cassini spacecraft could be caused by an object replaying the birth process of icy moons.
4. Titan revealed as Earth-like world with rain, rivers, lakes and seas
Titan is the only place in the solar system other than Earth that we know has stable liquid on its surface, though its lakes are made of liquid ethane and methane rather than liquid water.
5. Studies of the great northern storm of 2010-2011
These red, orange and green clouds (false color) in Saturn’s northern hemisphere indicate the tail end of a massive storm that started in December 2010. Even after visible signs of the storm started to fade, infrared measurements continued to reveal powerful effects at work in Saturn’s stratosphere.
6. Radio-wave patterns shown not to be tied to Saturn’s interior rotation as previously thought
This spectrogram and video show a changing pattern of radio waves from Saturn known as Saturn Kilometric Radiation, as detected by NASA’s Cassini spacecraft. Recent data from the radio and plasma wave instrument show that the variation in radio waves controlled by the planet’s rotation is different in the northern and southern hemispheres.
7. Vertical structures in the rings imaged for the first time
Once about every 15 years, the Sun shines on the edge of the ring plane and northern and southern sides of the rings receive little sunlight. Cassini measured the thick, long shadows from this rare event to determine the heights of structures within the rings.
8. Study of prebiotic chemistry on Titan
Titan’s atmosphere is a zoo teaming with a variety of molecules — the most chemically complex in the solar system. Beginning with sunlight and methane, ever more complex molecules form until they become large enough to form the smog that covers the giant moon. Nearer the surface, methane, ethane, and other organics condense and fall to the surface where likely other prebiotic chemistry can take place.
9. Mystery of the dual bright-dark surface of the moon Iapetus solved
Dark material splatters the walls and floors of craters in the surreal, frozen wastelands of Iapetus. This image shows terrain in the transition region between the moon’s dark leading hemisphere and its bright trailing hemisphere. The view was acquired during Cassini’s only close flyby of the two-toned Saturn moon.
10. First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn’s poles
Saturn’s polar regions have surprised scientists with a the presence of a long-lived hexagonal-shaped jet stream in the north and two hurricane-like storms at both poles. The driving forces of each remain a mystery. In the remaining three years of Cassini’s mission, scientists hope to learn more of their properties and conditions surrounding their existence.
Dimensions: 22 feet (6.7 meters) high; 13.1 feet (4 meters) wide
Weight: 12,593 pounds (5,712 kg) with fuel, Huygens probe, adapter, etc; 4,685 pounds (2,125 kg) unfueled orbiter alone
Orbiter science instruments: composite infrared spectrometer, imaging system, ultraviolet imaging spectrograph, visual and infrared mapping spectrometer, imaging radar, radio science, plasma spectrometer, cosmic dust analyzer, ion and neutral mass spectrometer, magnetometer, magnetospheric imaging instrument, radio and plasma wave science
Power: 885 watts (633 watts at end of mission) from radioisotope thermoelectric generators
Dimensions: 8.9 feet (2.7 meters) in diameter
Weight: 705 pounds (320 kg)
Probe science instruments: aerosol collector pyrolyser, descent imager and spectral radiometer, Doppler wind experiment, gas chromatograph and mass spectrometer, atmospheric structure instrument, surface science package
Huygens Probe Titan Release: Dec. 24, 2004
Huygens Probe Titan Descent: Jan. 14, 2005
Huygens’ Entry Speed into Titan’s Atmosphere: about 12,400 mph (20,000 kph)
Launch vehicle: Titan IVB/ Centaur
Weight: 2.2 million pounds (1 million kg)
Launch: Oct. 15, 1997, from Cape Canaveral Air Force Station, Fla.
Earth-Saturn distance at arrival: 934 million miles (1.5 billion km) (10 times Earth to Sun distance)
Distance traveled to reach Saturn: 2.2 billion miles (3.5 billion km)
Saturn’s average distance from Earth: 890 million miles (1.43 billion km)
One-way Speed-of-Light Time from Saturn to Earth at Cassini Arrival: 84 minutes
One-way Speed-of-Light Time from Saturn to Earth During Orbital Tour: 67 to 85 minutes
Venus Fybys: April 26, 1998 at 176 miles (234 km); June 24, 1999 at 370 miles (600 km)
Earth Flyby: Aug. 18, 1999 at 727 miles (1,171 km)
Jupiter flyby: Dec. 30, 2000 at 6 million miles (10 million km) (closest approach 5:12 a.m. EST)
Saturn Arrival Date: July 1, 2004, UTC (June 30, 2004 PDT)
Primary Mission: 4 years
Two Extended Missions: Equinox (2008-2010) and Solstice (2010-2017)