Posted on by Fraser Cain

Catching Stars in the Act of Forming Planets

Image credit: Harvard CfA
How old is too old? Pro football players tend to peak in their late 20s, and few continue their careers beyond the age of 35. For young stars, the peak age for planet formation is around 1 to 3 million years. By 10 million years old, their resources are exhausted and they retire to a life on the stellar “main sequence.”

Using telescopes on the ground and in space, a team of astronomers led by Lee W. Hartmann and Aurora Sicilia-Aguilar (Harvard-Smithsonian Center for Astrophysics) is studying Sun-like stars in their waning formative years, within clusters older than previously explored. They seek to refine our understanding of planet formation by studying dusty protoplanetary disks around such stars. Their results, presented today at the 204th meeting of the American Astronomical Society in Denver, Colorado, better define the time span during which planets might form.

“While the planets that may be forming cannot be detected directly,” said Sicilia-Aguilar, “we can see changes in the circumstellar dusty accretion disks caused as the planets sweep up and accumulate mass.”

“The data also has shown dramatic differences between stars of 3 and 10 million years of age: the younger stars frequently have dusty disks capable of forming planets, while such disks are essentially absent in the older population,” she continued.

The team used data from the Smithsonian Institution’s Whipple Observatory telescopes, the WIYN telescope at Kitt Peak National Observatory, and from the Spitzer Space Telescope (the latter made available as part of the Guaranteed Time Program of Infrared Array Camera PI Giovanni Fazio), to make these findings.

“We are trying to understand the evolution of protoplanetary disks around stars not too different from the Sun,” said team leader Lee W. Hartmann. “Many stars about 1 million years old have disks, but by 10 million years, almost none have disks. We are trying to find stars at an in-between age and `catch them in the act’ of forming planets.”

Circumstellar dust disks enshroud young stars, and astronomers understand this to be a common feature of stellar evolution and of possible planetary system formation. The initial protoplanetary disks contain the gas and dust that provide the raw materials for the formation of later planetary systems.

“After stars form planets in their disks and clear out most of the material-either by accretion onto the star, accretion onto planets, or ejection-small amounts of dust can remain in so-called ‘debris disks.’ Most or all of this debris dust is thought to be continuously generated by the collision of small bodies, much like the zodiacal light in our solar system,” said Hartmann.

The team is presenting the first identification of low mass stars in the young clusters Trumpler 37 and NGC 7160. (These clusters are loose associations of stars that have formed together in the comparatively recent past.) “The cluster members confirm the age estimates of 1 to 5 million years for Tr37 and 10 million years for NGC 7160,” said Sicilia-Aguilar.

“We do find active accretion in some of the stars in Tr37. The average accretion rate is equivalent to swallowing up 10 Jupiter masses in a million years,” said Sicilia-Aguilar. “This is consistent with models of viscous disk evolution.”

“In comparison, we have detected no signs of active accretion so far in the older cluster NGC 7160, suggesting that disk accretion ends within 10 million years. This probably coincides with the major phase of giant planet formation.”

Trumpler 37 is of more immediate interest, said Hartmann, because we hope to find stars with Jupiter-size planets that are still accumulating material from the disks, so the disks are not completely cleared out yet. However, there may be a few objects in the 10 million-year-old cluster NGC 7160 that are also still forming their giant planets. Not all disks evolve at the same rate.

“Thus we expect eventually to find out more about the frequency of debris disks, and the rate at which the dust in such disks is removed, by studying the 10-million-year-old cluster NGC 7160 and comparing it to Trumpler 37,” said Hartmann.

In addition to Sicilia-Aguilar and Hartmann, team members include Cesar Briceno (Centro de Investigaciones de Astronomia), James Muzerolle (University of Arizona), and Nuria Calvet (Smithsonian Astrophysical Observatory). This work was supported by NASA grant NAG5-9670.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

New Black Holes Found in a Virtual Observatory

Image credit: ESA
A European team has used the Astrophysical Virtual Observatory (AVO) to find 30 supermassive black holes that had previously escaped detection behind masking dust clouds. The identification of this large population of long-sought ?hidden? black holes is the first scientific discovery to emerge from a Virtual Observatory. The result suggests that astronomers may have underestimated the number of powerful supermassive black holes by as much as a factor of five.

Black holes collect dust. They lurk at the centres of active galaxies in environments not unlike those found in violent tornadoes on Earth. Just as in a tornado, where debris is often found spinning about the vortex, so in a black hole, a dust torus surrounds its waist. In some cases astronomers can look along the axis of the dust torus from above or from below and have a clear view of the black hole. Technically these objects are then called ?type 1 sources?. ?Type 2 sources? lie with the dust torus edge-on as viewed from Earth so our view of the black hole is totally blocked by the dust over a range of wavelengths from the near-infrared to soft X-rays.

While many dust-obscured low-power black holes (called ?Seyfert 2s?) have been identified, until recently few of their high-power counterparts were known. The identification of a population of high-power obscured black holes and the active galaxies in which they live has been a key goal for astronomers and will lead to greater understanding and a refinement of the cosmological models describing our Universe.

The European AVO science team led by Paolo Padovani from Space Telescope-European Coordinating Facility and the European Southern Observatory in Munich, Germany, now announces the discovery of a whole population of the obscured, powerful supermassive black holes. Thirty of these objects were found in the so-called GOODS (Great Observatories Origins Deep Survey) fields. The GOODS survey consists of two areas that include some of the deepest observations from space- and ground-based telescopes, including the NASA/ESA Hubble Space Telescope, and have become the best studied patches in the sky.

Padovani and the team used an innovative technique. Using a Virtual Observatory (VO) they combined information from multiple wavelengths from Hubble, ESO?s Very Large Telescope and NASA’s Chandra. This unprecedented team effort by the largest telescopes in the world made this discovery possible. The majority of the sources are so faint that it is currently not possible to take spectra of them and the VO techniques made it possible for the researchers to work seamlessly with images and catalogues from many different sources.

According to Paolo Padovani: ?This discovery means that surveys of powerful supermassive black holes have so far underestimated their numbers by at least a factor of two, and possibly by up to a factor of five.?

The paper describing these results has just been accepted by the European journal Astro?nomy & Astrophysics and will be published in an upcoming issue. This is the first refereed scientific paper based on end-to-end use of Virtual Observatory tools. The results in the paper show that the VO has evolved beyond the demonstration level to become a real research tool.

The European Astrophysical Virtual Observatory (AVO), funded partly by the European Commission, is the specific VO used for this project. With this work AVO demonstrates cutting-edge science by giving astronomers easy access to manipulation of image and catalogue data on remote computer networks. Until now objects were normally identified by taking a spectrum with a telescope, but now science is moving into an era where objects are pinpointed efficiently by using easily accessible multiwavelength information.

“These discoveries highlight the kind of scientific impact that Virtual Observatory technologies and standards will have on astronomy world-wide”, said Peter Quinn (European Southern Observatory), director of the AVO. “The Astrophysical Virtual Observatory wants to continue to work with astronomers in Europe to enable more discoveries like this, using combined data from ground- and space-based observatories”.

The team already has plans to investigate the new population of dusty black holes by using even more telescopes: the European Southern Observatory?s Very Large Telescope (near-infrared), NASA?s Spitzer Space Telescope (far-infrared) using emerging new VO tools. This will give further insight into the nature of these sources.

Original Source: ESA News Release

Posted on by Fraser Cain

Detailed Image of Saturn’s Storms

Image credit: NASA/JPL/Space Science Institute
Several dark spots, or storms, are huddled in the mid-latitude region of Saturn’s southern hemisphere. The largest of these storms is about 3000 kilometers (1860 miles) across, or about as wide as Japan is long. Also visible are light-colored, lacy cloud patterns indicative of atmospheric turbulence. The image was taken with the narrow angle camera through a near-infrared filter on May 7, 2004 from a distance of 28.2 million kilometers (17.5 million miles) from Saturn. Image scale is 168 kilometers (104 miles) per pixel. The image has been contrast-enhanced to aid visibility.

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

Progress 14P Docks With Station

Image credit: NASA
An unmanned Russian resupply ship smoothly linked up to the International Space Station this morning, delivering two and a half tons of food, water, fuel, spare parts and supplies to the two residents on board.

With Expedition 9 Commander Gennady Padalka and NASA Science Officer and Flight Engineer Mike Fincke looking on, the ISS Progress 14 docked to the aft port of the Zvezda Service Module at 8:55 a.m. CDT (1355 GMT) as the two craft flew 230 statute miles above Central Asia.

Padalka and Fincke were in Zvezda, prepared to take over manual control of the operation if it had been necessary, but the Progress craft automatically docked to the module through pre-programmed computer command with no problem.

The Progress was launched Tuesday from the Baikonur Cosmodrome in Kazakhstan and chased the Station for two days, using its engine to conduct rendezvous maneuvers in fine-tuning its course for today?s docking.

The Progress was the first ship to arrive at the ISS since Padalka and Fincke took over Station operations last month. The next Progress is scheduled to launch to the Station in late July.

After leak checks are completed to insure a tight seal between Progress and Zvezda, Padalka will open up the ship?s hatch later today so he and Fincke can begin unloading its cargo Friday.

Next week, Padalka and Fincke will turn their attention to preparations for a spacewalk no earlier than June 16, Moscow time, in Russian Orlan spacesuits out of the Pirs Docking Compartment to replace a power controller on the Station?s truss that failed April 21, resulting in the temporary loss of one of the four Control Moment Gyros (CMGs) that govern the orientation of the complex.

On Wednesday, Fincke and Padalka took turns maneuvering the Station?s Canadarm2 robotic arm to a position along the S0 Truss for camera views of the spacewalk worksite and downlink television of the spacewalk tasks as they are conducted during the planned 4-? hour excursion. The two crewmembers will begin checking out their Orlan spacesuits next Thursday and are expected to climb into the suits June 11 in a dress rehearsal of the suit up and a thorough checkout of the suit systems that will clear the way for the spacewalk.

The spacewalk will be under the control of both U.S. and Russian mission personnel. Russian flight controllers will be directing Padalka and Fincke as they exit the Pirs and climb onto the telescoping Russian Strela cargo crane to be transported some 50 feet to the intersection of the U.S. and Russian segments of the Station. Once they dismount from the Strela, Padalka and Fincke will be under the direction of U.S. flight controllers as they move to the S0 Truss via handrails and tethers to swap out the failed Remote Power Control Module (RPCM) that rendered CMG 2 inoperable.

After power is restored to the CMG, the spacewalkers will make their way back to the Strela crane and, under the direction of Russian flight controllers once again, will swing back to the Pirs to reenter the Russian airlock and end the spacewalk.

Padalka and Fincke also conducted biomedical experiments and routine housekeeping tasks this week as they set their sights on the start of spacewalk preparations.

Information on the crew’s activities aboard the Space Station, future launch dates, as well as Station sighting opportunities from anywhere on the Earth, is available on the Internet at:

http://spaceflight.nasa.gov/

Details on Station science operations can be found on an Internet site administered by the Payload Operations Center at NASA’s Marshall Space Flight Center in Huntsville, Ala., at:

http://scipoc.msfc.nasa.gov/

The next ISS status report will be issued on Friday, June 4, or earlier, if events warrant.

Original Source: NASA News Release

Posted on by Fraser Cain

Spitzer Finds Youngest Planet

Image credit: NASA/JPL
NASA has announced new findings from the Spitzer Space Telescope, including the discovery of significant amounts of icy organic materials sprinkled throughout several “planetary construction zones,” or dusty planet-forming discs, which circle infant stars.

These materials, icy dust particles coated with water, methanol and carbon dioxide, may help explain the origin of icy planetoids like comets. Scientists believe these comets may have endowed Earth with some of its water and many of its biogenic, life-enabling materials.

Drs. Dan Watson and William Forrest of the University of Rochester, N.Y, identified the ices. They surveyed five very young stars in the constellation Taurus, 420 light-years from Earth. Previous studies identified similar organic materials in space, but this is the first time they were seen unambiguously in the dust making up planet- forming discs.

In another finding, Spitzer surveyed a group of young stars and found intriguing evidence that one of them may have the youngest planet detected. The observatory found a clearing in the disc around the star CoKu Tau 4. This might indicate an orbiting planet swept away the disc material, like a vacuum leaving a cleared trail on a dirty carpet. The new findings reveal the structure of the gap more clearly than ever before. Because CoKu Tau 4 is about one million years old, the possible planet would be even younger. As a comparison, Earth is approximately 4.5-billion years old.

“These early results show Spitzer will dramatically expand our understanding of how stars and planets form, which ultimately helps us understand our origins,” said Dr. Michael Werner, Spitzer project scientist at NASA’s Jet Propulsion Laboratory , Pasadena, Calif., which manages the mission.

Spitzer also discovered two of the farthest and faintest planet- forming discs ever observed. These discs surround two of more than 300 newborn stars uncovered for the first time in a stunning new image of the dusty stellar nursery called RCW 49. It is approximately 13,700 light-years from Earth in the constellation Centaurus.

“Preliminary data suggest that all 300 or more stars harbor discs, but so far we’ve only looked closely at two. Both were found to have discs,” said Dr. Ed Churchwell of the University of Wisconsin, Madison, Wis., principal investigator of the RCW 49 research, with Dr. Barbara Whitney of Space Science Institute, Boulder, Colo.

Planet-forming, or “protoplanetary,” discs are a natural phase in a star’s life. A star is born inside a dense envelope of gas and dust. Within this envelope, and circling the star, is a flat, dusty disc, where planets are born.

“By seeing what’s behind the dust, Spitzer has shown us star and planet formation is a very active process in our galaxy,” Churchwell said.

Spitzer’s exquisitely sensitive infrared eyes can see planet-forming discs in great detail. “Previously, scientists could study only a small sample of discs, but Spitzer is already on its way toward analyzing thousands of discs,” Werner said.

Spitzer’s infrared spectrograph instrument, which breaks apart infrared light to see the signatures of various chemicals, was used to observe the organic ices and the clearing within CoKu Tau 4’s disc. Spitzer’s infrared array camera found the new stars in RCW 49. Papers on the research will appear in the September 1 issue of the journal Astrophysical Journal Supplements. For images and information about the research on the Internet, visit: http://www.spitzer.caltech.edu/ and http://photojournal.jpl.nasa.gov .

Original Source: NASA News Release

Posted on by Fraser Cain

Decreasing Earthshine Could Be Tied to Global Warming

Image credit: BBSO
Scientists who monitor Earth’s reflectance by measuring the moon’s “earthshine” have observed unexpectedly large climate fluctuations during the past two decades. By combining eight years of earthshine data with nearly twenty years of partially overlapping satellite cloud data, they have found a gradual decline in Earth’s reflectance that became sharper in the last part of the 1990s, perhaps associated with the accelerated global warming in recent years. Surprisingly, the declining reflectance reversed completely in the past three years. Such changes, which are not understood, seem to be a natural variability of Earth’s clouds.

The May 28, 2004, issue of the journal Science examines the phenomenon in an article, “Changes in Earth’s Reflectance Over the Past Two Decades,” written by Enric Palle, Philip R. Goode, Pilar Montaes Rodriguez, and Steven E. Koonin. Goode is distinguished professor of physics at the New Jersey Institute of Technology (NJIT), Palle and Monta=F1es Rodr=EDguez are postdoctoral associates at that institution, and Koonin is professor of theoretical physics at the California Institute of Technology. The observations were conducted at the Big Bear Solar Observatory (BBSO) in California, which NJIT has operated since 1997 with Goode as its director. The National Aeronautics Space Administration funded these observations.

The team has revived and modernized an old method of determining Earth’s reflectance, or albedo, by observing earthshine, sunlight reflected by the Earth that can be seen as a ghostly glow of the moon’s “dark side”-or the portion of the lunar disk not lit by the sun. As Koonin realized some 14 years ago, such observations can be a powerful tool for long-term climate monitoring. “The cloudier the Earth, the brighter the earthshine, and changing cloud cover is an important element of changing climate,” he said.

Precision earthshine observations to determine global reflectivity have been under way at BBSO since 1994, with regular observations commencing in late 1997.

“Using a phenomenon first explained by Leonardo DaVinci, we can precisely measure global climate change and find a surprising story of clouds. Our method has the advantage of being very precise because the bright lunar crescent serves as a standard against which to monitor earthshine, and light reflected by large portions of Earth can be observed simultaneously,” said Goode. “It is also inexpensive, requiring only a small telescope and a relatively simple electronic detector.”

By using a combination of earthshine observations and satellite data on cloud cover, the earthshine team has determined the following:

Earth’s average albedo is not constant from one year to the next; it also changes over decadal timescales. The computer models currently used to study the climate system do not show such large decadal-scale variability of the albedo.

The annual average albedo declined very gradually from 1985 to 1995, and then declined sharply in 1995 and 1996. These observed declines are broadly consistent with previously known satellite measures of cloud amount.

The low albedo during 1997-2001 increased solar heating of the globe at a rate more than twice that expected from a doubling of atmospheric carbon dioxide. This “dimming” of Earth, as it would be seen from space, is perhaps connected with the recent accelerated increase in mean global surface temperatures.

2001-2003 saw a reversal of the albedo to pre-1995 values; this “brightening” of the Earth is most likely attributable to the effect of increased cloud cover and thickness.

These large variations, which are comparable to those in the earth’s infrared (heat) radiation observed in the tropics by satellites, comprise a large influence on Earth’s radiation budget.

“Our results are only part of the story, since the Earth’s surface temperature is determined by a balance between sunlight that warms the planet and heat radiated back into space, which cools the planet,” said Palle. “This depends upon many factors in addition to albedo, such as the amount of greenhouse gases (water vapor, carbon dioxide, methane) present in the atmosphere. But these new data emphasize that clouds must be properly accounted for and illustrate that we still lack the detailed understanding of our climate system necessary to model future changes with confidence.”

Goode says the earthshine observations will continue for the next decade. “These will be important for monitoring ongoing changes in Earth’s climate system. It will also be essential to correlate our results with satellite data as they become available, particularly for the most recent years, to form a consistent description of the changing albedo. Earthshine observations through an 11-year solar cycle will also be important to assessing hypothesized influences of solar activity on climate.”

Monta=F1es Rodr=EDguez says that to carry out future observations, the team is working to establish a global network of observing stations. “These would allow continuous monitoring of the albedo during much of each lunar month and would also compensate for local weather conditions that sometimes prevent observations from a given site.”

BBSO observations are currently being supplemented with others from the Crimea in the Ukraine, and there will soon be observations from Yunnan in China, as well. A further improvement will be to fully automate the current manual observations. A prototype robotic telescope is being constructed and the team is seeking funds to construct, calibrate, and deploy a network of eight around the globe.

“Even as the scientific community acknowledges the likelihood of human impacts on climate, it must better document and understand climate changes,” said Koonin. “Our ongoing earthshine measurements will be an important part of that process.”

Original Source: Caltech News Release

Posted on by Fraser Cain

Star Production is Still High in our Galaxy

Image credit: Spitzer Space Telescope
Some of the first data from a new orbiting infrared telescope are revealing that the Milky Way – and by analogy galaxies in general – is making new stars at a much more prolific pace than astronomers imagined.

The findings from NASA’s Spitzer Space Telescope were announced today (May 27) at a NASA headquarters press briefing by Edward Churchwell, a University of Wisconsin-Madison astronomer and the leader of a team conducting the most detailed survey to date of our galaxy in infrared light.

Focusing the telescope on a compact cluster of stars at the heart of a distant nebula known as RCW49, Churchwell and his colleagues discovered more than 300 newly forming stars. Each of the stars, known to astronomers as protostars, has a swirling disk of circumstellar dust and creates ideal conditions for the formation of new solar systems.

“In this one small area, we have a stellar nursery like no one has ever seen before,” says Churchwell, an expert on star formation. “The sheer number of objects is astounding, and may force us to rewrite our ideas of star formation and how much of it is going on in the Milky Way.

“I am dead sure there are many regions like this throughout the galaxy. It is not unique.”

For years, astronomers have probed objects like the nebula RCW49, a thick, obscuring cocoon of dust and gas, with radio telescopes. Listening in, they have learned that these hidden pockets of space are the places where most of the new stars that populate a galaxy are born.

With the Spitzer Space Telescope, astronomers can now look deep inside these regions to directly observe star formation: “We can peel away the dust layers to see what is going on and we’re seeing things in incredible detail. This telescope is almost perfectly tuned to study star formation and it will provide us with a huge database of protostars. And this is what makes galaxies tick, these areas of massive star formation,” Churchwell says.

Indeed, his team has been able to catalog not only a large number of protostars from this one small region of space, but also the spectrum of newborn stars’ various stages of early development.

“We’re finding stars at different points in their evolutionary history,” Churchwell explains. “We hope to be able to fill out the entire early evolutionary sequence of a star’s development.”

Of special interest to astronomers is the potential for protostars to form planetary systems. The stars are formed from large disks of cool dust and gas, known as accretion disks. The nascent stars grow as material spirals inward from the disk to the star.

The same disks, astronomers think, provide the raw material for planets. “Protostars, we believe, develop planetary systems from these accretion disks,” Churchwell notes.

The Spitzer Space Telescope is the last of NASA’s Great Observatory Program. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the telescope project.

The Great Observatory program, which also includes the Hubble Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-ray Observatory, is designed to sample the cosmos across a wide portion of the electromagnetic spectrum.

The Spitzer Space Telescope was launched into an Earth-trailing heliocentric orbit in August of 2003.

Churchwell’s team, which uses the Infrared Array Camera, one of three scientific instruments aboard the telescope, is charged with creating an infrared mosaic of a swath of the inner Milky Way composed of 300,000 image frames of 1.2 second exposures each.

“We’re making a complete survey of the inner two-thirds of our galaxy,” Churchwell explains. “We can’t survey the very center of the galaxy because it is too bright and would swamp our detectors.”

When completed, the survey will provide a wealth of data from regions of space previously obscured by foreground clouds of dust and gas. There will be many more surprises, Churchwell says.

The data are being analyzed by a team of about 20 scientists in Madison and around the country who make up the GLIMPSE or Galactic Legacy Infrared Mid-Plain Survey Extraordinaire. The final data products will be archived and released to the astronomy community by the Spitzer Space Science Center in Pasadena, Calif.

Churchwell says the orbiting observatory is performing superbly. “From the perspective of the Infrared Array Camera, it’s almost picture perfect. The images are beautiful. It’s a real success story for NASA,” he says.

Original Source: UW-Madison News Release

Posted on by Fraser Cain

Saturn From Hubble and Cassini

Image credit: NASA
As Saturn grows closer through the eyes of the Cassini spacecraft, which is hurtling toward a rendezvous with the ringed world on June 30 (July 1, Universal Time), both Cassini and the Earth-orbiting Hubble Space Telescope snapped spectacular pictures of the planet and its magnificent rings.

Cassini is approaching Saturn at an oblique angle to the Sun and from below the ecliptic plane. Cassini has a very different view of Saturn than Hubble’s Earth-centered view. For the first time, astronomers can compare views of equal-sharpness of Saturn from two very different perspectives.

The view from Hubble, taken on March 22, 2004, is so sharp that many individual Saturnian ringlets can be seen. When Cassini returned its picture of Saturn on May 16, it was so close to the planet that the Imaging Science Subsystem narrow-angle camera could not fit the whole planet in its field-of-view. Cassini is still about 12.4 million miles (about 20 million kilometers) away and only 36 days from reaching Saturn.

Hubble’s exquisite optics, coupled with the high resolution of its Advanced Camera for Surveys, allow it to take pictures of Saturn which are nearly as sharp as Cassini’s, even though Hubble is nearly a billion miles farther from Saturn than Cassini. Cassini will ultimately far exceed the resolution of Hubble during its close encounter with Saturn. Cassini’s sharpness began to surpass Hubble’s when it came to within 14 million miles (23 million kilometers) of Saturn earlier this month.

Camera exposures in four filters (blue, blue-green, green, and red) were combined to form the Hubble image, to render colors similar to what the eye would see through a telescope focused on Saturn. The subtle pastel colors of ammonia-methane clouds trace a variety of atmospheric dynamics. Saturn displays its familiar banded structure, and haze and clouds of various altitudes. Like Jupiter, all bands are parallel to Saturn’s equator. Even the magnificent rings, at nearly their maximum tilt toward Earth, show subtle hues, which indicate the trace chemical differences in their icy composition.

Cassini has two cameras, a wide angle and narrow angle. This narrow angle image was made using a combination of three filters (red, green, blue) and was taken at a range of 15.1 million miles (24.3 million kilometers). The view is from 13 degrees below the equator. Enceladus, one of Saturn’s 31 known moons, appears near the south pole at the bottom of the image.

The differences between the Hubble and Cassini images are mainly due to the different sets of filters used.

Over two decades have passed since a spacecraft last visited Saturn ? NASA’s Voyager-2 flew by Saturn in August 1981. Since 1990, Hubble has produced high-resolution Saturn images, tracking storms and auroral activity while providing crisp views of the rings over time and from various angles.

Cassini will begin a four-year mission in orbit around Saturn when it arrives on June 30, 2004 PDT (July 1, 2004 UTC). Six months later it will release its piggybacked Huygens probe for descent through Titan’s thick atmosphere.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Cassini-Huygens mission is a cooperative mission 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 mission for NASA’s Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

Original Source: Hubble News Release

Posted on by Fraser Cain

Rings and Moons

Image credit: NASA/JPL/Space Science Institute
The multitude of grooves for which Saturn’s rings are famed, clumps in the F ring, and several Saturnian moons are visible in this image. Moons visible in the image are: Mimas (398 kilometers, 247 miles across) above the rings at left; Epimetheus (116 kilometers, 72 miles across) just above the A ring ansa; Enceladus (499 kilometers, 310 miles across) near upper right. The image was taken with the narrow angle camera on May 10, 2004 at a distance of 27.1million kilometers (16.8 million miles) from Saturn. Image scale is 162 kilometers (101 miles) per pixel. Contrast in the image was enhanced to aid visibility.

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.

Posted on by Fraser Cain

Wallpaper: Comet NEAT

Image credit: NOAO/AURA/NSF
This image of Comet C/2001 Q4 (NEAT) was taken at the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, AZ, on May 7, 2004.

The image was taken with the Mosaic I camera, which has a one-square degree field of view, or about five times the size of the Moon. Even with this large field, only the comet?s coma and the inner portion of its tail are visible. This color image was assembled by combining images taken through blue, green and red filters.

A small star cluster (C0736-105, or Melotte 72) is visible in the lower right of the image, between the head of the comet and the bright red star in the lower-right corner.

Comet C/2001 Q4 (NEAT) was discovered on August 24, 2001, by the Near Earth Asteroid Tracking (NEAT) system operated by NASA?s Jet Propulsion Laboratory, Pasadena, CA.

The comet will remain visible for several weeks with binoculars and small telescopes just after sunset, high in the western sky.

Image Credit: T. Rector (University of Alaska Anchorage), Z. Levay and L.Frattare (Space Telescope Science Institute) and WIYN/NOAO/AURA/NSF

Original Source: NOAO News Release