NASA’s Cassini mission, which launched in 1997 and has been studying Saturn and its many moons since 2004, was recently awarded the Trophy for Current Achievement by the Smithsonian National Air and Space Museum – the institution’s highest group honor, presented annually in recognition of outstanding achievements in aerospace science and technology.
“This joint mission has produced an unprecedented science return,” said William Knopf, Cassini program executive at NASA Headquarters in Washington. “Missions like Cassini pave the way for future robotic and human exploration throughout our solar system and beyond.”
Since its establishment in 1985, the award has been presented to seven NASA planetary mission teams – the Cassini mission team, the Voyager spacecraft team in 1989, the Mars Pathfinder team in 1998, the Chandra X-Ray Observatory team in 2000, the NEAR mission team in 2001, the Mars Exploration Rover team in 2006, and the Stardust Comet Sample Return Mission team in 2008. Astronauts and shuttle mission teams (STS-121 in 2007) have also been presented with the award in years past.
Managed by NASA’s Jet Propulsion Laboratory in California, the Cassini-Huygens mission is to study Saturn and its many moons in unprecedented detail. Cassini is the fourth spacecraft to visit Saturn and the first to enter into orbit around the gas giant. On Christmas day of 2004 the spacecraft released the Huygens probe to land on Saturn’s largest moon Titan – the first landing ever accomplished in the outer solar system and the most distant landing of any spacecraft to date. Huygens, supplied by the European Space Agency, descended into Titan’s atmosphere, deployed a parachute, and landed on what has been described by scientists as “Titanium mud” at the shoreline of a methane lake. During its 2.5 hour descent through Titan’s atmosphere, Huygens operated a fully instrumented robotic laboratory, sending back data and images for nearly 90 minutes after landing.
Titan has long intrigued scientists because it is the only moon in the solar system known to have a dense atmosphere, and the only other planetary body other than Earth known to have stable bodies of surface liquid – making it a possible host for microbial extraterrestrial life on the surface, in the atmosphere, or below the surface.
The Cassini mission has discovered four new moons and two new rings around Saturn, and has continued to observe seasonal changes in the planet’s atmosphere. Cassini’s mission has been extended twice since 2008, and will continue to observe changes in Saturn and its moons during the planet’s northern summer solstice through 2017. Eventually, a pass of Titan will change Cassini’s orbit in such a way that it will plunge into Saturn’s atmosphere.
The award presented to the Cassini mission team by the Smithsonian comes just weeks after the release of new movies from Cassini’s pass of Jupiter in 2000, which revealed invisible waves shaking up jet streams in the planet’s atmosphere – an interaction that takes place on Earth and influences our daily weather.
“This is the first time anyone has actually seen direct wave motion in one of Jupiter’s jet streams,” said Amy Simon-Miller, Associate Director for Strategic Science and the paper’s lead author. The movies are part of an in-depth study conducted by scientists and astronomers led by Simon-Miller at NASA’s Goddard Space Flight Center in Maryland. “By comparing this type of interaction in Earth’s atmosphere to what happens on a planet as radically different as Jupiter, we can learn a lot about both planets.”
“Cassini Spies Wave Rattling Jet Stream on Jupiter” - Video Credit: JPLnews
These movies confirm, for the first time, that Jupiter’s jet streams wander off course same as Earth’s. Earth’s jet streams move from west to east, but not in a straight line. Instead they travel north and south in their eastward trek, tracing out what’s called a Rossby wave. Researcher’s have long known of Rossby waves in the atmosphere of Jupiter’s northern hemisphere, but the phenomenon was never witnessed in the southern atmosphere until the release of these movies – which zoomed in on a single jet stream and captured a line of “chevrons” formed along the edge of the jet stream.
The chevrons, which are small, dark, and V-shaped, zip west to east with the wind, and eventually the line starts to ripple, with each chevron moving north and south in turn – proving that, like Earth, Jupiter’s jet streams wander off course.
“That’s the signature of the Rossby wave,” said David Choi, the postdoctoral fellow at NASA Goddard who strung together about a hundred Cassini still images to make each time-lapse movie. “The chevrons in the fast-moving jet stream interact with the slower-moving Rossby wave, and that’s when we see the chevrons oscillate.”
It has also been discovered that the chevrons blowing along Jupiter’s jet streams are influenced by gravity inertia waves, same as on Earth. Characterizing these waves may reveal important clues to the layering of Jupiter’s deep atmosphere, helping researchers to better understand what affects weather on Earth. Although Jupiter and Earth are very different planets (Jupiter has no land or seasons), they have very similar weather phenomena. “Being able to understand and study another planet can teach us a lot more about what’s common in an atmosphere on the Earth,” says Simon-Miller.
“We are just starting to investigate the long-term behavior of this alien atmosphere,” said co-author Gianluigi Adamoli, an amateur astronomer in Italy. “Understanding the emerging analogies between Earth and Jupiter, as well as the obviously profound differences, helps us learn fundamentally what an atmosphere is and how it can behave.”
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA), and the Italian Space Agency.
For more information about Cassini, visit www.nasa.gov/cassini and www.saturn.jpl.nasa.gov