Posted on by Fraser Cain

Rings Pose New Mysteries

Just two days after the Cassini spacecraft entered Saturn orbit, preliminary science results are already beginning to show a complex and fascinating planetary system.

One early result intriguing scientists concerns Saturn?s Cassini Division, the large gap between the A and B rings. While Saturn?s rings are almost exclusively composed of water ice, new findings show the Cassini Division contains relatively more “dirt” than ice. Further, the particles between the rings seem remarkably similar to the dark material that scientists saw on Saturn?s moon, Phoebe. These dark particles refuel the theory that the rings might be the remnants of a moon. The F ring was also found to contain more dirt.

Another instrument on Cassini has detected large quantities of oxygen at the edge of the rings. Scientists are still trying to understand these results, but they think the oxygen may be left over from a collision that occurred as recently as January of this year.

“In just two days, our ideas about the rings have been expanded tremendously,” said Dr. Linda Spilker, of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., deputy project scientist for the Cassini-Huygens mission. “The Phoebe-like material is a big surprise. What puzzles us is that the A and B rings are so clean and the Cassini Division between them appears so dirty.”

The visual and infrared mapping spectrometer onboard Cassini revealed the dirt mixed with the ice in the Cassini Division and in other small gaps in the rings, as well as in the F ring.

“The surprising fingerprint in the data is that the dirt appears similar to what we saw at Phoebe. In the next several months we will be looking for the origin of this material,” said Dr. Roger Clark, of the U.S. Geological Survey, Denver, Colo., and a member of the Cassini science team.

Cassini’s ultraviolet imaging instrument detected the sudden and surprising increase in the amount of atomic oxygen at the edge of the rings. The finding leads scientists to hypothesize that something may have collided with the main rings, producing the excess oxygen.

Dr. Donald Shemansky of the University of Southern California, Los Angeles, co-investigator for Cassini’s ultraviolet imaging spectrograph instrument, said, “What is surprising is the evidence of a strong, sudden event during the observation period causing substantial variation in the oxygen distribution and abundance.” Although atomic oxygen has not been previously observed, its presence is not a surprise because hydroxyl was discovered earlier from Hubble Space Telescope observations, and these chemicals are both products of water chemistry.

Cassini’s examination of Saturn’s atmosphere began while the spacecraft was still approaching the planet. Winds on Saturn near the equator decrease dramatically with altitude above the cloud tops. The winds fall off by as much 140 meters per second (approximately 300 miles per hour) over an altitude range of 300 kilometers (approximately 200 miles) in the upper stratosphere. This is the first time winds have been measured at altitudes so high in Saturn’s atmosphere.

“We are finally defining the wind field in three dimensions, and it is very complex,” said Dr. Michael Flasar of NASA Goddard Space Flight Center, Greenbelt, Md., principal investigator for Cassini’s composite infrared spectrometer. “Temperature maps obtained now that Cassini is orbiting Saturn are expected to show more detail, helping us to unravel the riddles of Saturn’s winds above the cloud tops.”

Early Friday (Pacific Time), Cassini imaged Saturn?s largest moon Titan, one of the prime targets for the mission. Titan is thought to harbor simple organic compounds that may be important in understanding the chemical building blocks that led to life on Earth. Although too cold to support life now, Titan serves as a frozen vault to see what early Earth might have been like. Scientists will receive the new data and images from Titan later Friday.

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://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Cassini Makes Its First Titan Flyby

The Cassini spacecraft has revealed surface details of Saturn’s moon Titan and imaged a huge cloud of gas surrounding the planet-sized moon.

Cassini gathered data before and during a distant flyby of the orange moon yesterday. Titan’s dense atmosphere is opaque at most wavelengths, but the spacecraft captured some surface details, including a possible crater, through wavelengths in which the atmosphere is clear.

“Although the initial images appear bland and hard to interpret, we’re happy to report that, with a combination of instruments, we have indeed seen Titan’s surface with unprecedented clarity. We also look forward to future, much closer flybys and use of radar for much greater levels of surface detail,” said Dr. Dennis Matson of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., project scientist for the international Cassini-Huygens mission.

Cassini’s visible and infrared mapping spectrometer pierced the smog that enshrouds Titan. This instrument, capable of mapping mineral and chemical features of the moon, reveals an exotic surface bearing a variety of materials in the south and a circular feature that may be a crater in the north. Near-infrared colors, some three times redder than the human eye can see, reveal the surface with unusual clarity.

“At some wavelengths, we see dark regions of relatively pure water ice and brighter regions with a much higher amount of non-ice materials, such as simple hydrocarbons. This is different from what we expected. It’s preliminary, but it may change the way we interpret light and dark areas on Titan,” said JPL’s Dr. Kevin Baines, Cassini science-team member. “A methane cloud is visible near the south pole. It’s made of unusually large particles compared to the typical haze particles surrounding the moon, suggesting a dynamically active atmosphere there.”

This is the first time scientists are able to map the mineralogy of Titan. Using hundreds of wavelengths, many of which have never been used in Titan imaging before, they are creating a global map showing distributions of hydrocarbon-rich regions and areas of icy material.

Cassini’s camera also sees through the haze in some wavelengths. “We’re seeing a totally alien surface,” said Dr. Elizabeth Turtle of the University of Arizona, Tucson. “There are linear features, circular features, curvilinear features. These suggest geologic activity on Titan, but we really don’t know how to interpret them yet. We’ve got some exciting work cut out for us.”

Since entering orbit, Cassini has also provided the first view of a vast swarm of hydrogen molecules surrounding Titan well beyond the top of Titan’s atmosphere. Cassini’s magnetospheric imaging instrument, first of its kind on any interplanetary mission, provided images of the huge cloud sweeping along with Titan in orbit around Saturn. The cloud is so big that Saturn and its rings would fit within it. “The top of Titan’s atmosphere is being bombarded by highly energetic particles in Saturn’s radiation belts, and that is knocking away this neutral gas,” said Dr. Stamatios Krimigis of Johns Hopkins Applied Physics Laboratory, Laurel, Md., principal investigator for the magnetospheric imager. “In effect, Titan is gradually losing material from the top of its atmosphere, and that material is being dragged around Saturn.”

The study of Titan, Saturn’s largest moon, is one of the major goals of the Cassini-Huygens mission. Titan may preserve in deep-freeze many chemical compounds that preceded life on Earth. Friday’s flyby at a closest distance of 339,000 kilometers (210,600 miles) provided Cassini’s best look at Titan so far, but over the next four years, the orbiter will execute 45 Titan flybys as close as approximately 950 kilometers (590 miles). This will permit high-resolution mapping of the moon’s surface with an imaging radar instrument, which can see through the opaque haze of Titan’s upper atmosphere. In January 2005, the Huygens probe that is now attached to Cassini will descend through Titan’s atmosphere to the surface.

During the ring plane crossing, the radio and plasma wave science instrument on Cassini measured little puffs of plasma produced by dust impacts. While crossing the plane of Saturn’s rings, the instrument detected up to 680 dust hits per second. “The particles are comparable in size to particles in cigarette smoke,” said Dr. Don Gurnett of the University of Iowa, Iowa City, principal investigator for the instrument. “When we crossed the ring plane, we had roughly 100,000 total dust hits to the spacecraft in less than five minutes. We converted these into audible sounds that resemble hail hitting a tin roof.”

The spacecraft reported no unusual activity due to the hits and performed flawlessly, successfully going into orbit around Saturn on June 30. The engine burn for entering orbit went so well that mission managers have decided to forgo an orbital-adjustment maneuver scheduled for today.

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://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Post your Astro Photos

I’ve added a new section to the forum called “Astrophotography”. Unlike all the other sections of the forum, this one allows you to upload files to the server so you can post your pictures and share them with other members. If you’ve taken some great pictures with your telescope and camera, please post them here. Please include any technical information as well about your equipment, exposure times, software, etc., so we can all learn and improve our space photos.

Click here to access the “Astrophotography” section of the forum. As always, if you have any problems accessing the forum, setting up an account, or posting your photographs, please drop me an email and I’d be happy to help you out. Thanks to seeker372011 for getting things rolling. 🙂

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

A Connection Between Dark Energy and Dark Matter?

In the last few decades, scientists have discovered that there is a lot more to the universe than meets the eye: The cosmos appears to be filled with not just one, but two invisible constituents-dark matter and dark energy-whose existence has been proposed based solely on their gravitational effects on ordinary matter and energy.

Now, theoretical physicist Robert J. Scherrer has come up with a model that could cut the mystery in half by explaining dark matter and dark energy as two aspects of a single unknown force. His model is described in a paper titled “Purely Kinetic k Essence as Unified Dark Matter” published online by Physical Review Letters on June 30 and available online at http://arxiv.org/abs/astro-ph/0402316.

“One way to think of this is that the universe is filled with an invisible fluid that exerts pressure on ordinary matter and changes the way that the universe expands,” says Scherrer, a professor of physics at Vanderbilt University.

According to Scherrer, his model is extremely simple and avoids the major problems that have characterized previous efforts to unify dark matter and dark energy.

In the 1970s, astrophysicists postulated the existence of invisible particles called dark matter in order to explain the motion of galaxies. Based on these observations, they estimate that there must be about 10 times as much dark matter in the universe as ordinary matter. One possible explanation for dark matter is that it is made up of a new type of particle (dubbed Weakly Interacting Massive Particles, or WIMPs) that don’t emit light and barely interact with ordinary matter. A number of experiments are searching for evidence of these particles.

As if that weren’t enough, in the 1990s along came dark energy, which produces a repulsive force that appears to be ripping the universe apart. Scientists invoked dark energy to explain the surprise discovery that the rate at which the universe is expanding is not slowing, as most cosmologists had thought, but is accelerating instead. According to the latest estimates, dark energy makes up 75 percent of the universe and dark matter accounts for another 23 percent, leaving ordinary matter and energy with a distinctly minority role of only 2 percent.

Scherrer’s unifying idea is an exotic form of energy with well-defined but complicated properties called a scalar field. In this context, a field is a physical quantity possessing energy and pressure that is spread throughout space. Cosmologists first invoked scalar fields to explain cosmic inflation, a period shortly after the Big Bang when the universe appears to have undergone an episode of hyper-expansion, inflating billions upon billions of times in less than a second.

Specifically, Scherrer uses a second-generation scalar field, known as a k-essence, in his model. K-essence fields have been advanced by Paul Steinhardt at Princeton University and others as an explanation for dark energy, but Scherrer is the first to point out that one simple type of k-essence field can also produce the effects attributed to dark matter.

Scientists differentiate between dark matter and dark energy because they seem to behave differently. Dark matter appears to have mass and to form giant clumps. In fact, cosmologists calculate that the gravitational attraction of these clumps played a key role in causing ordinary matter to form galaxies. Dark energy, by contrast, appears to be without mass and spreads uniformly throughout space where it acts as a kind of anti-gravity, a repulsive force that is pushing the universe apart.

K-essence fields can change their behavior over time. When investigating a very simple type of k-essence field-one in which potential energy is a constant-Scherrer discovered that as the field evolves, it passes through a phase where it can clump and mimic the effect of invisible particles followed by a phase when it spreads uniformly throughout space and takes on the characteristics of dark energy.

“The model naturally evolves into a state where it looks like dark matter for a while and then it looks like dark energy,” Scherrer says. “When I realized this, I thought, ‘This is compelling, let’s see what we can do with it.'”

When he examined the model in more detail, Scherrer found that it avoids many of the problems that have plagued previous theories that attempt to unify dark matter and dark energy.

The earliest model for dark energy was made by modifying the general theory of relativity to include a term called the cosmological constant. This was a term that Einstein originally included to balance the force of gravity in order to form a static universe. But he cheerfully dropped the constant when astronomical observations of the day found it was not needed. Recent models reintroducing the cosmological constant do a good job of reproducing the effects of dark energy but do not explain dark matter.

One attempt to unify dark matter and dark energy, called the Chaplygin gas model, is based on work by a Russian physicist in the 1930s. It produces an initial dark matter-like stage followed by a dark energy-like evolution, but it has trouble explaining the process of galaxy formation.

Scherrer’s formulation has some similarities to a unified theory proposed earlier this year by Nima Arkani-Hamed at Harvard University and his colleagues, who attempt to explain dark matter and dark energy as arising from the behavior of an invisible and omnipresent fluid that they call a “ghost condensate.”

Although Scherrer’s model has a number of positive features, it also has some drawbacks. For one thing, it requires some extreme “fine-tuning” to work. The physicist also cautions that more study will be required to determine if the model’s behavior is consistent with other observations. In addition, it cannot answer the coincidence problem: Why we live at the only time in the history of the universe when the densities calculated for dark matter and dark energy are comparable. Scientists are suspicious of this because it suggests that there is something special about the present era.

Original Source: Vanderbilt University News Release

Posted on by Fraser Cain

Asteroids Make Tau Ceti Lethal

Image credit: David A. Hardy
Astronomers studying the Tau Ceti system have discovered that it contains ten times as much material in the form of asteroids and comets as our own solar system.

Tau Ceti, only 12 light years away, is the nearest sun-like star and is easily visible without a telescope. It is the first star to be found to have a disk of dust and comets around it similar in size and shape to the disk of comets and asteroids that orbits the Sun.

The astronomers’ discovery, being published in Monthly Notices of the Royal Astronomical Society, suggests that even though Tau Ceti is the nearest Sun-like star, any planets that may orbit it would not support life as we know it due to the inevitable large number of devastating collisions. It also suggests that the tranquil space environment around the Earth may be more unusual than previously realized.

Though the star Tau Ceti is similar to the Sun, any planets it has are unlikely to be havens for life, say a team of UK astronomers. Using submillimeter images of the disk of material surrounding Tau Ceti, they found that it must contain more than ten times as many comets and asteroids than there are in the Solar System.

With so many more space rocks hurtling around the star, devastating collisions of the sort that could lead to the destruction of life would be much more likely in the Tau Ceti system than in our own planetary system.

Publication of the result in Monthly Notices of the Royal Astronomical Society coincides with an exhibit ‘Hunting for Planets in Stardust’ at the Royal Society Summer Exhibition by the same science team from the UK Astronomy Technology Centre in Edinburgh and the University of St. Andrews.

The similarity between Tau Ceti and our own sun ends with their comparable sizes and luminosities, explains Jane Greaves, Royal Astronomical Society Norman Lockyer Fellow and lead scientist: ‘Tau Ceti has more than ten times the number of comets and asteroids that there are in our Solar System. We don’t yet know whether there are any planets orbiting Tau Ceti, but if there are, it is likely that they will experience constant bombardment from asteroids of the kind that is believed to have wiped out the dinosaurs. It is likely that with so many large impacts life would not have the opportunity to evolve.’

The discovery means that scientists are going to have to rethink where they look for civilizations outside our Solar System.

Jane Greaves continues, ‘We will have to look for stars which are even more like the Sun, in other words, ones which have only a small number of comets and asteroids. It may be that hostile systems like Tau Ceti are just as common as suitable ones like the Sun.’

The reason for the larger number of comets is not fully understood explains Mark Wyatt, another member of the team: ‘It could be that the Sun passed relatively close to another star at some point in its history and that the close encounter stripped most of the comets and asteroids from around the Sun.’

The new results are based on observations taken with the world’s most sensitive submillimetre camera, SCUBA. The camera, built by the Royal Observatory, Edinburgh, is operated on the James Clerk Maxwell Telescope in Hawaii. The SCUBA image shows a disk of very cold dust (-210 degrees C) in orbit around the star. The dust is produced by collisions between larger comets and asteroids that break them down into smaller and smaller pieces.

Original Source: NASA Astrobiology Story

Posted on by Fraser Cain

Saturn’s Rings Up Close

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

Posted on by Fraser Cain

New Observations of Procyon Defy Expectations

MOST, Canada?s first space telescope, celebrates its first birthday today, but its latest surprising results could spoil the party for other astronomers whose earlier results are now being questioned.

The MOST team used their tiny but powerful satellite as a stellar stethoscope to take the pulse of one of the best-known stars in the Galaxy, called Procyon (PRO-see-yon), and were shocked to discover their cosmic patient is a ?flat liner?. The star shows none of the pulsations predicted by over 20 years of earlier theory and observations from Earth. The journal Nature will publish these unexpected findings on July 1.

?The lack of a pulse doesn’t mean the star Procyon is dead,? explained MOST Mission Scientist Dr. Jaymie Matthews of the University of British Columbia. ?But it does mean that some of our long-held theories about stars like this need to be put on the critical list. And that future space missions following in the path of MOST will have to revise their target lists and observing strategies in light of this null result.?

MOST, which stands for Microvariability and Oscillations of STars, is a Canadian Space Agency mission. UBC is the main contractor for the instrument and scientific operations of the MOST mission.

MOST is not much bigger than a suitcase but is able to measure the brightness variations of stars more precisely than any other instrument on Earth or in space. It was launched one year ago on June 30, aboard a modified Russian nuclear missile. To mark the occasion, MOST scientists celebrated with a birthday party complete with cake and dehydrated ?space? ice cream.

?MOST is only one year old, but it?s proving to be a very precocious child,? said Roger Colley, a senior official from the Canadian Space Agency. ?In its first six months of operation, MOST has already given us new perspectives on the stars we thought we knew best, the ones in our own Galactic backyard. In that way, it?s providing new insights into the Sun, the star we need to understand better to predict the future of our home planet.?

The MOST Canadian space telescope was launched from northern Russia, in June 2003, aboard a former Soviet ICBM (Intercontinental Ballistic Missile) converted to peaceful use. Weighing only 54 kg, this suitcase-sized microsatellite is packed with a small telescope and electronic camera to study stellar variability.

Its first prime target was Procyon, the eighth brightest star in the night sky, similar to the Sun but more massive and further along in life. Astronomers had concluded that Procyon was the best candidate for the new technique of ?asteroseismology? ? using surface vibrations to probe the inside of a star, similar to how geophysicists use earthquake vibrations to probe the Earth’s core.

MOST monitored Procyon up to eight times per minute for 32 days, with lapses totalling only seven hours over that entire time. Accumulating about 250,000 individual measurements, MOST reached a level of light-measuring precision at least 10 times better than the best ever achieved before from Earth or space. The MOST team was surprised to find that Procyon was not vibrating, and soon showed that a more careful treatment of stellar models indicated that it should indeed be stable.

The lack of waves detected on the surface of Procyon has ironically generated waves in the worldwide community of stellar astronomers. These results contradict theories and observational evidence that had mounted over the last 20 years. Several planned international space missions have been designed based on the firm belief that stars like Procyon pulsate. The MOST findings mean target lists and observing strategies for these satellites may have to be seriously revamped.

Future targets for MOST include other stars representing the Sun at various stages in its life, and stars known to have giant planets. MOST is designed to be able to register the tiny changes in brightness that will occur as a planet orbits its parent star. The way in which the light changes will tell astronomers about the atmospheric composition of these mysterious worlds, and even if they have clouds.

?It?s like doing a weather report for a planet outside our Solar System,? says Dr. Jaymie Matthews, MOST Mission Scientist, of the University of British Columbia.

MOST (Microvariability & Oscillations of STars) is a Canadian Space Agency mission. UBC is the main contractor for the instrument and scientific operations of the MOST mission.

Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor.

MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

Other partners include the Harvard-Smithsonian Center for Astrophysics, Universit? de Montr?al, and St. Mary?s University in Halifax.

For more information on MOST, visit: www.astro.ubc.ca/MOST/

For more information on the Canadian Space Agency, visit: www.space.gc.ca/asc/eng/default.asp

Original Source: UBC News Release

Posted on by Fraser Cain

Wallpaper: Star Formation in Nearby Galaxy

NASA’s Hubble Space Telescope captures this iridescent tapestry of star birth in a neighboring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B, lies in the Large Magellanic Cloud (LMC), located only 160,000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. This new Hubble image zooms in on N11B, which is a small subsection within an area of star formation cataloged as N11. N11 is the second largest star-forming region in the LMC. Within the LMC, N11 is surpassed in size and activity only by the immense Tarantula nebula (also known as 30 Doradus.)

The image illustrates a perfect case of sequential star formation in a nearby galaxy where new star birth is being triggered by previous-generation massive stars. A collection of blue- and white-colored stars near the left of the image are among the most massive stars known anywhere in the universe. The region around the cluster of hot stars in the image is relatively clear of gas, because the stellar winds and radiation from the stars have pushed the gas away. When this gas collides with and compresses surrounding dense clouds, the clouds can collapse under their own gravity and start to form new stars. The cluster of new stars in N11B may have been formed this way, as it is located on the rim of the large, central interstellar bubble of the N11 complex. The stars in N11B are now beginning to clear away their natal cloud, and are carving new bubbles in turn. Yet another new generation of stars is now being born in N11B, inside the dark dust clouds in the center and right-hand side of the Hubble image. This chain of consecutive star birth episodes has been seen in more distant galaxies, but it is shown very clearly in this new Hubble image.

Farther to the right of the image, along the top edge, are several smaller dark clouds of interstellar dust with odd and intriguing shapes. They are seen silhouetted against the glowing interstellar gas. Several of these dark clouds are bright-rimmed because they are illuminated and are being evaporated by radiation from neighboring hot stars.

This image was taken with Hubble’s Wide Field Planetary Camera 2 using filters that isolate light emitted by hydrogen and oxygen gas. The science team, led by astronomers You-Hua Chu (University of Illinois) and Y?el Naz? (Universite de Li?ge, Belgium) are comparing these images of N11B, taken in 1999, with similar regions elsewhere in the LMC. This color composite image was co-produced and is being co-released by the Hubble Heritage Team (STScI) and the Hubble European Space Agency Information Center (HEIC).

Original Source: Hubble News Release

Posted on by Fraser Cain

Cassini Arrives at Saturn Safely

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

Posted on by Fraser Cain

Cassini Will Arrive Today

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