Universe Today

This is a narrow-angle camera image of Saturn’s rings taken after the successful completion of the orbit insertion burn when the spacecraft had crossed the ring plane and was looking upwards at the lit face of the rings. The image shows details in the Encke gap (325 kilometers, 202 miles wide) in Saturn’s A ring. The center of the gap lies at a distance of 133,600 kilometers (83,000 miles) from Saturn. The image shows a ring in the center of the gap. The wavy inner edge of the gap and the wake-like structures emanating from its inner edge are caused by the tiny moon Pan that orbits in the middle of the gap. Two fainter ring features are also visible in the gap region.

Cassini was approximately 195,000 kilometers (121,000 miles) above the ringplane when the image was obtained. Image scale is approximately 1 kilometer per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, 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 Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

After a seven-year cruise through the Solar System, the joint NASA/ESA/ASI Cassini-Huygens spacecraft last night successfully entered orbit around Saturn.

The Cassini orbiter is now ready to begin its four-year survey of the planet and its moons, while the Huygens probe will be prepared for the next major mission milestone: its release toward the largest moon, Titan, in December.

?This shows international space co-operation at its best,? said ESA?s Director of Science, Prof. David Southwood, after confirmation of the orbit insertion. ?Few deep space planetary missions have carried the hopes of such a large community of scientists and space enthusiasts around the world. Congratulations to the teams in the US and Europe who made this possible and to all participants in the programme, who have a lot to do over the years ahead.?

The Saturn Orbit Insertion was the last and most critical manoeuvre performed by the spacecraft to achieve its operational orbit. If it had failed, the spacecraft would have just flown past Saturn and got lost in the outer Solar System.

Cassini-Huygens was launched from Cape Canaveral, Florida, on 15 October 1997, atop a Titan 4B/Centaur, the most powerful expendable launch vehicle in the US fleet at the time. To reach Saturn it had to perform a series of gravity assist manoeuvres around Venus (April 1998 and June 1999), Earth (August 1999) and Jupiter (December 2000).

Last night, Cassini-Huygens approached Saturn from below the plane of its rings. Using its high-gain antenna dish as a shield to protect its fragile body from dust impacts, it first crossed the ring plane at 02:03 UT, some 158 500 kilometres from the centre of Saturn, in the gap that separates the F ring from the G ring. About 25 minutes later, at 02:36 UT, the probe fired one of its twin main engines for a 96-minute burn to enter orbit. The signal confirming this ignition took 84 minutes to reach Earth, some 1500 million kilometres from Saturn.

The burn went smoothly and reduced Cassini-Huygens?s relative velocity to Saturn while the probe passed only 19 000 kilometres from the planet?s upper clouds. After completion of the burn, the probe was tilted first toward Earth to confirm insertion and then toward Saturn?s rings in order to take close-up pictures as it flew only a few thousand kilometres above them. This was a unique opportunity to attempt to discriminate individual components within the rings, as Cassini is not planned to come this close to them again. The orbiter?s instruments also took advantage of its proximity to the planet to make an in-depth study of its atmosphere and environment.

A second crossing of the ring plane took place at 05:50 UT.

The spacecraft is in perfect shape to begin its tour of the Saturnian system with at least 76 orbits around the ringed planet and 52 close encounters with seven of its 31 known moons. This tour actually began before insertion with a close fly-by of an eighth moon, Phoebe, on 11 June. The primary target for Cassini-Huygens will be the largest of these moons, Titan, with a first fly-by at an altitude of 1200 kilometres on 26 October.

During the coming months, ESA?s scientists will prepare for the release of their main contribution to the mission, the Huygens probe, which will be released on 25 December to enter the atmosphere of Titan on 14 January 2005. Built for ESA by an industrial team led by Alcatel Space, this 320 kilogram probe carries six science instruments to analyse and characterise the atmosphere and its dynamics during its descent. If the probe survives the impact on reaching the surface, it will also analyse the physical properties of its environment after landing.

Actually bigger than Mercury, Titan features a hazy nitrogen-rich atmosphere containing carbon-based compounds. The chemical environment on Titan is thought to be similar to that of Earth before life, although colder (-180?C) and lacking liquid water. The in situ results from Huygens, combined with global observations from repeated fly-bys of Titan by the Cassini orbiter, are expected to help us understand the evolution of the early Earth’s atmosphere and provide clues about the mechanisms that led to the dawn of life on our planet.

The Cassini orbiter, the largest and most complex deep-space vehicle ever launched, carries 12 science instruments developed by US and international teams to conduct in-depth studies of Saturn, Titan, the icy moons, the ring system and the magnetospheric environment. Two of the orbiter?s instruments were provided by Europe.

?More than twenty years have passed since Pioneer 11 and the Voyagers gave us a first glimpse of Saturn, as they crossed this complex system in only a few days,? explained Prof. Southwood, who is also principal investigator for Cassini?s magnetometer. ?Now, with Cassini, we are here to stay, watch and investigate. And with Huygens we will go even deeper and further, not only plunging into an extraterrestrial atmosphere but also an atmosphere like the early Earth?s. This means we are travelling billions of years back into our own past to investigate one of the Universe?s best kept secrets: where we came from.?

The Cassini-Huygens mission is a co-operation between NASA, ESA, the European Space Agency and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA?s Office of Space Science, Washington.

Original Source: ESA News Release

Saturn is now a day away for the Cassini spacecraft, a seasoned traveler that began its journey nearly seven years ago.

On June 30 at 7:36 p.m. Pacific Time (10:36 p.m. EDT), Cassini will begin executing a series of commands to enter orbit around the ringed planet. The spacecraft will fire its main engine for a crucial 96 minutes to slow down and be captured in orbit about Saturn.

Besides launch, orbit insertion is the next most critical part of the mission. “Everything has to go just right. The burn must occur for all 96 minutes, the turns must occur at the right time, the computers must keep the sequence going even in the event something unexpected should happen,” said Robert T. Mitchell, program manager for the Cassini-Huygens mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The spacecraft has been programmed to continue even in the event of an emergency. With a one-way light time of 1 hour and 24 minutes, we had to teach the spacecraft to take care of itself. We don’t want Cassini to call home if a problem arises, we want it to keep going. That is precisely what we’ve told the spacecraft: Don’t stop, keep going until you’ve put in all 96 minutes of burn,” he said.

During the orbit insertion, Cassini will fly closer to Saturn than at any other time during the spacecraft’s planned four-year tour of Saturn. This provides an unprecedented opportunity to study the planet and rings at close range. It will pass approximately 20,000 kilometers (12,427 miles) above Saturn’s cloud tops, closer than any other spacecraft in history. It will also be flying about 10 times closer to the rings than at any other point in the mission

Cassini carries 12 instruments that will study the planet, rings and moons in extensive detail. Riding aboard Cassini is a second spacecraft, the Huygens probe, built by the European Space Agency. It carries half a dozen instruments that will study Titan, Saturn’s largest moon, a prime target for both Cassini and the Huygens probe. Titan is the only moon in the solar system to have a dense atmosphere and resembles the early Earth in deep freeze.

“In a sense, Cassini and the Huygens probe are like time machines that will take us back to examine a world we’ve never seen before, a world that may resemble what our own world was like 4.5 billion years ago,” said Dr. Jean-Pierre Lebreton of the European Space Agency, who is mission manager and project scientist for the Huygens probe.

Eighty-five minutes before the engine burn, Cassini will rotate to point its main antenna dish forward. The Italian-built antenna, 4 meters (13 feet) in diameter, will offer shielding against dust particles the spacecraft may hit as it crosses a gap in the rings. The spacecraft will continue transmitting a monotone “carrier” signal with a secondary antenna for tracking from Earth. Cassini will pass twice through a known gap between the F and G rings, first while ascending shortly before the burn, then while descending shortly after the burn.

The engine burn will slow the spacecraft by 626 meters per second (1,400 miles per hour). Five science instruments will be on during the burn, and others will be used shortly after the engine cuts off. The magnetometer will measure the strength and direction of the magnetic field to understand the physics of Saturn’s magnetic dynamics. Lightning may also be detected. Another instrument will provide a record of the dust hits as the spacecraft flies through the ring plane. These observations may tell scientists the size of these tiny particles and the thickness of that ring region. The remote sensing instruments will assess the rings’ composition, temperature, and structure. Then the spacecraft will be oriented for the outbound ring plane crossing. After crossing the ring plane in the descending mode, Cassini will look back at the sunlit face of the rings to take more data before turning to Earth to transmit its data.

“Should something happen during the burn, the science sequence will stop,” said Dr. Dennis Matson, project scientist for the Cassini-Huygens mission at JPL. “We are prepared to live with this outcome. Getting into orbit is the priority. Getting the science is extra credit.”

The Cassini-Huygens mission is a cooperative project of NASA, 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 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 more information about the Cassini-Huygens mission, visit http://www.nasa.gov/cassini.

Original Source: NASA/JPL News Release

Despite the views of Titan?s surface that Cassini is able to provide, the moon remains inscrutable to the human eye. In true color images that are taken in the visible wavelengths, Titan?s photochemical smog, rich in organic material, gives the moon a smooth featureless orange glow.

The Cassini orbiter carries specially-designed spectral filters that can pierce Titan?s veil. Its piggybacked Huygens probe will descend through the atmosphere in early 2005, giving an up-close-and-personal look at this mysterious orange moon.

Images taken with the narrow angle camera using red, green and blue spectral filters were combined to create this color view. The images were obtained at a Sun-Titan-spacecraft, or phase, angle of 67 degrees and from a distance of approximately 13.1 million kilometers (8.2 million miles) on June 10, 2004. Image scale is approximately 79 kilometers (49 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, 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 Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

On approach to Saturn, data obtained by the Cassini spacecraft are already posing a puzzling question: How long is the day on Saturn?

Cassini took readings of the day-length indicator regarded as most reliable, the rhythm of natural radio signals from the planet. The results give 10 hours, 45 minutes, 45 seconds (plus or minus 36 seconds) as the length of time it takes Saturn to complete each rotation. Here’s the puzzle: That is about 6 minutes, or one percent, longer than the radio rotational period measured by the Voyager 1 and Voyager 2 spacecraft, which flew by Saturn in 1980 and 1981.

Cassini scientists are not questioning Voyager’s careful measurements. And they definitely do not think the whole planet of Saturn is actually rotating that much slower than it did two decades ago. Instead, they are looking for an explanation based on some variability in how the rotation deep inside Saturn drives the radio pulse.

The radio sounds of Saturn’s rotation, which are also the first sounds from Saturn studied by Cassini, are like a heartbeat and can be heard by visiting http://www.jpl.nasa.gov/videos/cassini/0604/ and http://www-pw.physics.uiowa.edu/space-audio

“The rotational modulation of radio emissions from distant astronomical objects has long been used to provide very accurate measurements of their rotation period,” said Dr. Don Gurnett, principal investigator for the Cassini Radio and Plasma Wave Science instrument, University of Iowa, Iowa City. “The technique is particularly useful for the giant gas planets, such as Jupiter and Saturn, which have no surfaces and are covered by clouds that make direct visual measurements impossible.”

The first hint of something strange about that type of measurement at Saturn was in 1997, when a researcher from Observatoire de Paris reported that Saturn’s radio rotation period differed substantially from Voyager.

Dr. Michael D. Desch, Cassini Radio Plasma Wave Science team member, and scientist at NASA?s Goddard Space Flight Center in Greenbelt, Md., has analyzed Saturn radio data collected by Cassini from April 29, 2003, to June 10, 2004. “We all agree that the radio rotation period of Saturn is longer today than it was in during the Voyager flyby in 1980,” he said.

Gurnett said, “Although Saturn’s radio rotation period has clearly shifted substantially since the Voyager measurements, I don?t think any of us could conceive of any process that would cause the rotation of the entire planet to actually slow down. So it appears that there is some kind of slippage between the deep interior of the planet and the magnetic field, which controls the charged particles responsible for the radio emission.” He suggests the solution may be tied to the fact that Saturn’s rotational axis is nearly identical to its magnetic axis. Jupiter, with a more substantial difference between its magnetic axis and its rotational axis, shows no comparable irregularities in its radio rotation period.

“This finding is very significant. It demonstrates that the idea of a rigidly rotating magnetic field is wrong,” said Dr. Alex Dessler, a senior research scientist at the University of Arizona, Tucson. In that way, the magnetic fields of gas giant planets may resemble that of the Sun. The Sun?s magnetic field does not rotate uniformly. Instead, its rotation period varies with latitude. “Saturn’s magnetic field has more in common with the Sun than the Earth. The measurement can be interpreted as showing that the part of Saturn?s magnetic field that controls the radio emissions has moved to a higher latitude during the last two decades,” said Dressler.

“I think we will be able to unravel the puzzle, but it’s going to take some time,” said Gurnett. ?With Cassini in orbit around Saturn for four years or more, we will be in an excellent position to monitor long-term variations in the radio period, as well as investigate the rotational period using other techniques.”

Cassini, carrying 12 scientific instruments, is just two days from its planetary rendezvous with Saturn. On June 30 it will become the first spacecraft to orbit Saturn, when it begins a four-year study of the planet, its rings and its 31 known moons. The spacecraft recently flew past Saturn?s cratered moon Phoebe, where it captured spectacular images as well as data on its mass and composition.

The Cassini-Huygens mission is a cooperative project of NASA, 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 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 more information about the Cassini-Huygens mission, visit http://www.nasa.gov/cassini .

Original Source: NASA/JPL News Release