Saturn Welcomes NASA’s Cassini Spacecraft As Exploration Begins
Although the Cassini spacecraft is scheduled to officially arrive at the
planet Saturn on June 30, scientists studying the planet’s magnetosphere
received an official welcome on June 27 when a burst of plasma wave noise
indicated that Cassini had crossed the planet’s bow shock — the region
where charged particles flowing outward from the sun collide with Saturn’s
magnetic field or magnetosphere.
University of Iowa Space Physicist Don Gurnett, head of the team that is
analyzing radio and plasma wave emissions, says, “This is exciting. After
nearly seven years, we finally got there! This marks the beginning of the
scientific investigation for the people who will study the planet’s
magnetosphere.”
Bill Kurth, Cassini team member and UI senior research scientist, compared
the bow shock to a sonic boom.
“The bow shock is similar to a jet aircraft sonic boom that forms across the
front of the plane. The charged particles flowing from the sun, called the
solar wind, pass Saturn and the other planets at a speed of about one
million miles an hour. We can compare the position of the bow shock with the
pressure of the solar wind to learn something about the size of Saturn’s
magnetosphere and how much its size is controlled by the solar wind,” he
says.
The June 27 Cassini bow shock crossing occurred at a distance of 49.2 Saturn
radii (2.97 million kilometers or 1.84 million miles) from Saturn and stands
in contrast to first encounters by previous spacecraft, all of which took
place much closer to the planet. The Pioneer spacecraft first crossed
Saturn’s bow shock at 23.7 Saturn radii, while Voyager 1 and Voyager 2
recorded crossings at 26.2 and 31.9 Saturn radii, respectively. Gurnett says
the difference between Cassini and the other spacecraft is probably due to
different flight trajectories.
“Cassini has encountered the bow shock quite a bit further out because the
spacecraft is coming in from the side of the planet. So our approach angle
is different from those of the other craft, primarily because Cassini is
going to be placed into orbit about Saturn, while the other spacecraft made
fly-bys,” he says.
The radio sounds of Saturn and other sounds of space can be heard by
visiting Gurnett’s Web site at:
http://www-pw.physics.uiowa.edu/space-audio
Cassini, carrying 12 scientific instruments, is on its way to the June 30,
2004 planetary rendezvous, when it will become the first spacecraft to orbit
Saturn and begin a four-year study of the planet, its rings and its 31 known
moons. The spacecraft is part of the Cassini-Huygens Mission that includes
the Huygens probe, a six-instrument European Space Agency probe, scheduled
to land on Titan, Saturn’s largest moon, in January 2005.
The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. JPL, a division of the California
Institute of Technology, Pasadena, Calif. manages the Cassini-Huygens
mission for NASA’s Office of Space Science, Washington, D.C. JPL designed,
developed and assembled the Cassini orbiter. For the latest images and
information about the Cassini-Huygens mission, visit:
http://www.nasa.gov/cassini
STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite
301, Iowa City, Iowa 52242-2500.
RESEARCH CONTACT: Don Gurnett, 818-393-0345 (JPL Office);
319-400-3156 (cell phone); Donald-gurnett@uiowa.edu.
MEDIA CONTACT: Gary Galluzzo, Writer, 319-384-0009
gary-galluzzo@uiowa.edu
