What is the Shape of the Helix Nebula?

Looks can be deceiving, especially when it comes to celestial objects like galaxies and nebulas. These objects are so far away that astronomers cannot see their three-dimensional structure. The Helix Nebula, for example, resembles a doughnut in colorful images. Earlier images of this complex object ? the gaseous envelope ejected by a dying, sun-like star ? did not allow astronomers to precisely interpret its structure. One possible interpretation was that the Helix’s form resembled a snake-like coil.

Now, a team of astronomers using observations from several observatories, including NASA’s Hubble Space Telescope, has established that the Helix’s structure is even more perplexing. Their evidence suggests that the Helix consists of two gaseous disks nearly perpendicular to each other.

A team of astronomers, led by C. Robert O’Dell of Vanderbilt University in Nashville, Tenn., made its finding using highly detailed images from the Hubble telescope’s Advanced Camera for Surveys, pictures from Cerro Tololo Inter-American Observatory in Chile, and measurements from ground-based optical and radio telescopes which show the speed and direction of the outflows of material from the dying star. The Helix, the closest planetary nebula to Earth, is a favorite target of professional and amateur astronomers. Astronomers hope this finding will provide insights on how expelled shells of gas from dying stars like our Sun form the complex shapes called planetary nebulas. The results are published in the November issue of the Astronomical Journal.

“Our new observations show that the previous model of the Helix was much too simple,” O’Dell said. “About a year ago, we believed the Helix was a bagel shape, filled in the middle. Now we see that this filled bagel is just the inside of the object. A much larger disk, resembling a wide, flat ring, surrounds the filled bagel. This disk is oriented almost perpendicular to the bagel. The larger disk is brighter on one side because it is slamming into interstellar material as the entire nebula moves through space, like a boat plowing through water. The encounter compresses gas, making that region glow brighter. But we still don’t understand how you get such a shape. If we could explain how this shape was created, then we could explain the late stages of the most common form of collapsing stars.”

“To visualize the Helix’s geometry,” added astronomer Peter McCullough of the Space Telescope Science Institute in Baltimore, Md., and a member of O’Dell’s team, “imagine a lens from a pair of glasses that was tipped at an angle to the frame’s rim. Well, in the case of the Helix, finding a disk inclined at an angle to a ring would be a surprise. But that is, in fact, what we found.”

Another surprise is that the dying star has expelled material into two surrounding disks rather than the one thought previously to be present. Each disk has a north-south pole, and material is being ejected along those axes. “We did not anticipate that the Helix has at least two axes of symmetry,” O’Dell said. “We thought it had only one. This two-axis model allows us to understand the complex appearance of the nebula.”

Using the Helix data, the astronomers created a three-dimensional model showing the two disks. These models are important to show the intricate structure within the nebula. The team also produced a composite image of the Helix that combines observations from Hubble’s Advanced Camera for Surveys and the 4-meter telescope’s mosaic camera at Cerro Tololo. The Helix is so large that the team needed both telescopes to capture a complete view. Hubble observed the Helix’s central region; the Cerro Tololo telescope, with its wider field of view, observed the outer region.

The team, however, is still not sure how the disks were created, and why they are almost perpendicular to each other. One possible scenario is that the dying star has a close companion star. Space-based X-ray observations provide evidence for the existence of a companion star. One disk may be perpendicular to the dying star’s spin axis, while the other may lie in the orbital plane of the two stars.

The astronomers also believe the disks formed during two separate epochs of mass loss by the dying star. The inner disk was formed about 6,600 years ago; the outer ring, about 12,000 years ago. The inner disk is expanding slightly faster than the outer disk. Why did the star expel matter at two different episodes, leaving a gap of 6,000 years? Right now, only the Helix Nebula knows the answer, the astronomers said.

The sun-like star that sculpted the Helix created a beautiful celestial object. Will the Sun weave such a grand structure when it dies 5 billion years from now? “As a single star, it will create a similar glowing cloud of expelled material, but I wouldn’t expect it to have such a complex structure as the Helix,” McCullough said.

To study the intricate details of these celestial wonders, astronomers must use a range of observatories, including visible-light and radio telescopes. Astronomers also need the sharp eyes of Hubble’s Advanced Camera for Surveys. “The Hubble’s crisp vision has revealed a whole new realm of planetary nebula structure, which has advanced the field and delighted our eyes,” said team member Margaret Meixner of the Space Telescope Science Institute.

Original Source: Hubble News Release

New Storms Seen on Titan

Using adaptive optics on the Gemini North and Keck 2 telescopes on Mauna Kea, Hawai’i, a U.S. team has discovered a new phenomenon in the atmosphere of Saturn?s largest moon Titan.

Unlike previous observations showing storms at the south pole, these new images reveal atmospheric disturbances at Titan?s temperate mid latitudes?about halfway between the equator and the poles. Explaining the unexpected activity has proven difficult, and the team speculates that the storms could be driven by anything from short-term surface events to shifts in global wind patterns.

?We were fortunate to catch these new mid-latitude clouds when they first appeared in early 2004,” said team leader Henry Roe (California Institute of Technology). “We are not yet certain how their formation is triggered. Continued observations over the next few years will show us whether these clouds are the result of a seasonal change in weather patterns or a surface-related phenomenon.”

The causes of these storms might include activities that disturb the atmosphere from the surface. It?s possible that geysers of methane ?slush? are brewing from below, or a warm spot on Titan?s surface is heating the atmosphere. Cryovolcanism?volcanic activity that spews an icy mix of chemicals?has also been suggested as one mechanism that would cause disturbances. It?s also possible that the storms are driven by seasonal shifts in the global winds that circulate in the upper atmosphere. Hints about what is happening on this frigid world could be obtained as the Huygens probe from the Cassini mission drops through Titan?s atmosphere in mid-January, 2005.

The Gemini-Keck II observations were the result of good timing and telescope availability. According to Gemini scientist Chad Trujillo, Titan?s weather patterns can be stable for many months, with only occasional bursts of unusual activity like these recently discovered atmospheric features. The chances of catching such occurrences depend largely on the availability of flexible scheduling like that used at Gemini. “This flexible scheduling is absolutely critical to Titan meteorology studies,? he said. ?Imagine how hard it would be to understand the Earth’s diverse meteorological phenomena if you only saw a weather report a few nights every year.”

Like Earth, Titan is surrounded by a thick atmosphere of mostly nitrogen. Conditions on Earth allow water to exist in liquid, solid, or vapor states, depending on localized temperatures and pressures. The phase changes of water between these states are an important factor in the formation of weather in our atmosphere. Titan’s atmosphere is so cold that any water is frozen solid, but conditions are such that methane can move between liquid, solid, and gaseous states. This leads to a methane meteorological cycle on Titan in analogy to the water-based weather cycle on Earth.

As it does on Earth, seasonal solar heating can drive atmospheric activity on Titan, and this could be the mechanism behind the previously observed south polar clouds. However, the new temperate-latitude cloud formations cannot be explained by the same solar heating process If a seasonal circulation shift is causing the newly discovered features, the team theorizes that they will drift northward over the next few years as Titan?s year progresses through the southern summer and into autumn. If it is being caused by geological changes, such as methane geysers or a geologic ?warm? spot on the surface, the feature should stay at the observed 40-degree latitude as the surface activity spurs changes in atmospheric convection and methane cloud formation. Continued storm formations will be easily distinguishable in future ground-based observations using Gemini, Keck and other adaptive-optics enabled telescopes.

?Using adaptive optics from the Earth allows us to see things that just a few years ago would have been invisible,? said Keck Scientist Antonin Bouchez. ?These observations show that ground-based telescopes are a perfect complement to space missions like Cassini.?

This research is scheduled for publication in the January 1, 2005 issue of the Astrophysical Journal.

Original Source: Gemini News Release

Cassini’s First Flyby of Dione

Dione is a small heavily cratered moon 560 km (350 miles) in diameter orbiting Saturn once every 2.73 days, which is actually the same period as its axial rotation. The moon lies at a distance of 377,400 kilometres (234,555 miles) from its parent planet. Dione is also known to share its orbit around Saturn with a small asteroid named Helene, that occupies a stable point ahead of it in orbit. The surface temperature of Dione is very similar to that of Titan at -186 degrees centigrade, and cryogenic activity is known to have helped shape the moon?s surface, although, unlike Titan, Dione has no known atmosphere.

The Cassini flyby this week has helped to confirm that some time in the moon?s past there were two episodes of cryo-volcanic flooding widely spaced in time that affected different regions. It is believed these episodes may be the result of tidal heating caused by the orbital interaction with another of Saturn?s moons named Enceladus.

As the Cassini Orbiter passed by Dione it took detailed images of an uncharted surface region of the area known as the ?Trailing Hemisphere,? centered on Latitude 0?, and Longitude 270? that is dominated by three craters, one large named Amata, with two smaller craters nearby named Catillus and Coras. Geologically speaking, this is the most interesting area of the moon for planetary astronomers, because this region of Dione is marked by two distinct white ray systems.

The largest, Palatine Linea, streaks down towards the moon?s south polar region that ends with a large unnamed crater. The new Cassini images show this area to be composed of long linear groves, and rills, with intermittent small craters at varying distances.

The second white linear feature, named Padua Linea, is about half the size Palatine Linea, and is also crossed with linear rills that stretch from Dione?s equator at Longitude 240 ? down to the southeast, ending at Latitude -20?. The largest crater dominating the area named Cassandra is shown prominently in the Cassini photographs.

Cassini also imaged the ?Leading Hemisphere? for the first time between Longitude 180 ? 145 degrees, at Latitude of around 40 degrees either side of the moon?s equator, and again it is shown to be covered in small impact craters.

All of the eight images returned by Cassini today show that much of Dione is heavily potholed with small craters with intermittent large impact craters at wide intervals, all of which are uncharted and unnamed. Therefore, Cassini has confirmed what planetary scientists had believed all along; that the resurfacing events on Dione must have taken place long before the resurfacing of Enceladus, because Dione?s least cratered areas have far more craters than those on Enceladus itself.

While the images of Dione returned today are the best ever close range images taken of this moon, the Cassini space craft is due to fly by Dione even closer next October, when it will pass just 500 Km (311 miles) above the moon?s surface.

The moon Dione has a visual magnitude of +10.4 so that it’s visible in medium sized telescopes, and amateur astronomers can view the moon over the next few months for themselves. Saturn is at opposition on 13 January, and lies in the zodiac constellation of Gemini (The Twins).

By Science Correspondent Richard Pearson

Radiation Concentrates During Solar Storms

The beauty of science is that nothing is for certain. There are times when scientists think they have something figured out and then nature throws them for a loop. Just such an event happened last fall when the Sun erupted in some massive, record-shattering explosions that hurled billion of tons of electrified gas toward Earth.

Scientists realize that space is dangerous for unprotected satellites and astronauts, but they thought that they had found a small safe zone around Earth’s radiation belt — a shelter from these dangerous solar storms. It turns out that when the solar storm is strong enough, even this safe zone can become a major hot zone for dangerous radiation.

“Space weather matters — we now know that no matter what orbit we choose, there is the possibility that a spacecraft could get blasted by a significant dose of radiation. We need to take this into account when designing spacecraft. We also need to the ability to continuously monitor space weather so satellite operators can take protective measures during solar storms,” said Dr. Daniel Baker, Director of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.

The region is more of a gap between the two Van Allen radiation belts that surround Earth. The two belts resemble one donut inside the other. The belts are comprised of high-speed electrically charged particles trapped in the Earth’s magnetic field. It can almost be thought of as a giant umbrella in space shielding Earth from these space events.

The safe zone is considered prime real estate for satellites in “middle Earth orbits” because they would be exposed to relatively small doses of radiation and cost less to build. While there are currently no satellites in that particular orbit, many are being seriously considered including some from the Air Force.

To call the Sun active in late October / early November is an understatement. Within a two-week period, the Sun released an unusually high number of coronal mass ejections (CMEs) into space, and experienced explosions many times more powerful than anything ever observed. For some perspective, flares are usually ranked by number and class. A large flare might be X-2, for example. The Nov. 4 flare was ranked X-28, although more precisely, “off the scale” because it was hard to get an exact measurement. To add to the drama, the Sun is headed into its period of minimum activity within its 11-year cycle, making the number and intensity of the fall flares unusually high. The maximum and most active period occurred around 2000-2001.

Fortunately the science community has a number of satellites to track solar comings and goings. The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) satellite flies through the Van Allen radiation belts, taking measurements of the particle types and their energy and abundance. It observed the formation of a new belt in the safe zone on Oct. 31, 2003. That new belt made the safe zone hazardous for more than five weeks until the radiation was able to drain away and be absorbed by our Earth’s atmosphere. Other satellites helped researchers track the solar storms as they generated auroras on Earth, and spread out to Mars, Jupiter, Saturn, and the very edges of the solar system.

“This was an extreme event, a natural experiment that will be used to better understand how radiation belts work,” summed up Dr. Baker. “We were fortunate to have a suite of spacecraft in place to observe this event. This is why it’s important to systematically and continuously observe space weather, because there is always the potential to be surprised by nature.”

Original Source: NASA News Release

Experiments Chosen for Mars Science Laboratory

NASA has selected eight proposals to provide instrumentation and associated science investigations for the mobile Mars Science Laboratory (MSL) rover, scheduled for launch in 2009. Proposals selected today were submitted to NASA in response to an Announcement of Opportunity (AO) released in April.

The MSL mission, part of NASA’s Mars Exploration Program, will deliver a mobile laboratory to the surface of Mars to explore a local region as a potential habitat for past or present life. MSL will operate under its own power. It is expected to remain active for one Mars year, equal to two Earth years, after landing.

In addition to the instrumentation selected, MSL will carry a pulsed neutron source and detector for measuring hydrogen (including water), provided by the Russian Federal Space Agency. The project also will include a meteorological package and an ultraviolet sensor provided by the Spanish Ministry of Education and Science.

“This mission represents a tremendous leap forward in the exploration of Mars,” said NASA’s Deputy Associate Administrator for the Science Mission Directorate, Dr. Ghassem Asrar. “MSL is the next logical step beyond the twin Spirit and Opportunity rovers. It will use a unique set of analytical tools to study the red planet for over a year and unveil the past and present conditions for habitability of Mars,” Asrar said.

“The Mars Science Laboratory is an extremely capable system, and the selected instruments will bring an analytical laboratory to the martian surface for the first time since the Viking Landers over 25 years ago,” said Douglas McCuistion, Mars Exploration Program director at NASA Headquarters.

The selected proposals will conduct preliminary design studies to focus on how the instruments can be accommodated on the mobile platform, completed and delivered consistent with the mission schedule. NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif., manages the MSL Project for the Science Mission Directorate.

Selected investigations and principal investigators:

— “Mars Science Laboratory Mast Camera,” Michael Malin, Malin Space Science Systems (MSSS), San Diego, Calif. Mast Camera will perform multi-spectral, stereo imaging at lengths ranging from kilometers to centimeters, and can acquire compressed high-definition video at 10 frames per second without the use of the rover computer.

— “ChemCam: Laser Induced Remote Sensing for Chemistry and Micro-Imaging,” Roger Wiens, Los Alamos National Laboratory, Los Alamos, N.M. ChemCam will ablate surface coatings from materials at standoff distances of up to 10 meters and measure elemental composition of underlying rocks and soils.

— “MAHLI: MArs HandLens Imager for the Mars Science Laboratory,” Kenneth Edgett, MSSS. MAHLI will image rocks, soil, frost and ice at resolutions 2.4 times better, and with a wider field of view, than the Microscopic Imager on the Mars Exploration Rovers.

— “The Alpha-Particle-X-ray-Spectrometer for Mars Science Laboratory (APXS),” Ralf Gellert, Max-Planck-Institute for Chemistry, Mainz, Germany. APXS will determine elemental abundance of rocks and soil. APXS will be provided by the Canadian Space Agency.

— “CheMin: An X-ray Diffraction/X-ray Fluorescence (XRD/XRF) instrument for definitive mineralogical analysis in the Analytical Laboratory of MSL,” David Blake, NASA’s Ames Research Center, Moffett Field, Calif. CheMin, will identify and quantify all minerals in complex natural samples such as basalts, evaporites and soils, one of the principle objectives of Mars Science Laboratory.

— “Radiation Assessment Detector (RAD),” Donald Hassler, Southwest Research Institute, Boulder, Colo. RAD will characterize the broad spectrum of radiation at the surface of Mars, an essential precursor to human exploration of the planet. RAD will be funded by the Exploration Systems Mission Directorate at NASA Headquarters.

— “Mars Descent Imager,” Michael Malin, MSSS. The Mars Descent Imager will produce high-resolution color-video imagery of the MSL descent and landing phase, providing geological context information, as well as allowing for precise landing-site determination.

— “Sample Analysis at Mars with an integrated suite consisting of a gas chromatograph mass spectrometer, and a tunable laser spectrometer (SAM),” Paul Mahaffy, NASA’s Goddard Space Flight Center, Greenbelt, Md. SAM will perform mineral and atmospheric analyses, detect a wide range of organic compounds and perform stable isotope analyses of organics and noble gases.

Original Source: NASA News Release

Deep Impact Prepared for Launch

Launch and flight teams are in final preparations for the planned Jan. 12, 2005, liftoff from Cape Canaveral Air Force Station, Fla., of NASA’s Deep Impact spacecraft. The mission is designed for a six-month, one-way, 431 million kilometer (268 million mile) voyage. Deep Impact will deploy a probe that essentially will be “run over” by the nucleus of comet Tempel 1 at approximately 37,000 kilometers per hour (23,000 miles per hour).

“From central Florida to the surface of a comet in six months is almost instant gratification from a deep space mission viewpoint,” said Rick Grammier, Deep Impact project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It is going to be an exciting mission, and we can all witness its culmination together as Deep Impact provides the planet with its first man-made celestial fireworks on our nation’s birthday, July 4th.”

The fireworks will be courtesy of a 1-by-1 meter (39-by-39 inches) copper-fortified probe. It is designed to obliterate itself as it excavates a crater possibly large enough to swallow the Roman Coliseum. Before, during and after the demise of this 372-kilogram (820-pound) impactor, a nearby spacecraft will be watching the 6-kilometer-wide (3.7-mile) comet nucleus, collecting pictures and data of the event.

“We will be capturing the whole thing on the most powerful camera to fly in deep space,” said University of Maryland astronomy professor Dr. Michael A’Hearn, Deep Impact’s principal investigator. “We know so little about the structure of cometary nuclei that we need exceptional equipment to ensure that we capture the event, whatever the details of the impact turn out to be.”

Imagery and other data from the Deep Impact cameras will be sent back to Earth through the antennas of the Deep Space Network. But they will not be the only eyes on the prize. NASA’s Chandra, Hubble and Spitzer space telescopes will be observing from near-Earth space. Hundreds of miles below, professional and amateur astronomers on Earth will also be able to observe the material flying from the comet’s newly formed crater.

Deep Impact will provide a glimpse beneath the surface of a comet, where material and debris from the solar system’s formation remain relatively unchanged. Mission scientists are confident the project will answer basic questions about the formation of the solar system, by offering a better look at the nature and composition of the celestial travelers we call comets.

“Understanding conditions that lead to the formation of planets is a goal of NASA’s mission of exploration,” said Andy Dantzler, acting director of the Solar System division at NASA Headquarters, Washington, D.C. “Deep Impact is a bold, innovative and exciting mission which will attempt something never done before to try to uncover clues about our own origins.”

With a closing speed of about 37,000 kilometers per hour (23,000 miles per hour), what of the washing machine-sized impactor and its mountain-sized quarry?

“In the world of science, this is the astronomical equivalent of a 767 airliner running into a mosquito,” said Don Yeomans, a Deep Impact mission scientist at JPL. “It simply will not appreciably modify the comet’s orbital path. Comet Tempel 1 poses no threat to Earth now or in the foreseeable future.”

Ball Aerospace & Technologies in Boulder, Colo., built NASA’s Deep Impact spacecraft. It was shipped to Florida Oct. 17 to begin final preparations for launch.

Principal Investigator A’Hearn leads the mission from the University of Maryland, College Park. JPL manages the Deep Impact project for the Science Mission Directorate at NASA Headquarters. Deep Impact is a mission in NASA’s Discovery Program of moderately priced solar system exploration missions.

For more information about Deep Impact on the Internet, visit: http://www.nasa.gov/deepimpact.

For more information about NASA and agency programs on the Internet, visit: http://www.nasa.gov.

Original Source: NASA/JPL News Release

Rovers Find Another Indication of Martian Water

Scientists have identified a water-signature mineral called goethite in bedrock that the NASA’s Mars rover Spirit examined in the “Columbia Hills,” one of the mission’s surest indicators yet for a wet history on Spirit’s side of Mars.

“Goethite, like the jarosite that Opportunity found on the other side of Mars, is strong evidence for water activity,” said Dr. Goestar Klingelhoefer of the University of Mainz, Germany, lead scientist for the iron-mineral analyzer on each rover, the Moessbauer spectrometer. Goethite forms only in the presence of water, whether in liquid, ice or gaseous form. Hematite, a mineral that had previously been identified in Columbia Hills bedrock, usually, but not always, forms in the presence of water.

The rovers’ main purpose is to look for geological evidence of whether their landing regions were ever wet and possibly hospitable to life. The successful results so far — with extended missions still underway — advance a NASA goal of continuing Mars exploration by robots and, eventually, by humans, said Doug McCuistion, Mars Exploration Program Director at NASA Headquarters.

Klingelhoefer presented the new results from a rock in the “West Spur” of Mars’ “Husband Hill” at a meeting of the American Geophysical Union in San Francisco this week.

Spirit has now driven past the West Spur to ascend Husband Hill itself. One remaining question is whether water was only underground or ever pooled above the surface, as it did at Opportunity’s site. “As we climb Husband Hill and characterize the rock record, we’ll be looking for additional evidence that the materials were modified by ground water and searching for textural, mineralogical and chemical evidence that the rocks were formed in or modified by surface water,” said Dr. Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rover instruments.

The amount of worrisome friction in Spirit’s right front wheel has been decreasing. Meanwhile, rover wranglers at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., continue to minimize use of that wheel by often letting it drag while the other five wheels drive. “Babying that wheel seems to be helping,” said JPL’s Jim Erickson, rover project manager. Both rovers continue working in good health about eight months after their primary three-month missions. “Looks as though Spirit and Opportunity will still be with us when we celebrate the landing anniversaries in January,” Erickson said.

Opportunity has completed six months of inspecting the inside of “Endurance Crater” and is ready to resume exploration of the broad plains of the Meridiani region. It has recently seen frost and clouds marking the seasonal changes on Mars. At this week’s conference, rover science-team member Dr. Michael Wolff of the Brookfield, Wisconsin branch of the Boulder, Colorado-based Space Science Institute is reporting those and other atmospheric observations. “We’re seeing some spectacular clouds,” Wolff said. “They are a dramatic reminder that you have weather on Mars. Some days are cloudy. Some are clear.”

A portion of Mars’ water vapor is moving from the north pole toward the south pole during the current northern-summer and southern-winter period. The transient increase in atmospheric water at Meridiani, just south of the equator, plus low temperatures near the surface, contribute to appearance of the clouds and frost, Wolff said. Frost shows up some mornings on the rover itself. The possibility that it has a clumping effect on the accumulated dust on solar panels is under consideration as a factor in unexpected boosts of electric output from the panels.

As its last major endeavor inside Endurance Crater, Opportunity made a close inspection of rock layers exposed in a part of the crater wall called “Burns Cliff.” Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rover instruments, said, “In the lower portion of the cliff, the layers show very strong indications that they were last transported by wind, not by water like some layers higher up. The combination suggests that this was not a deep-water environment but more of a salt flat, alternately wet and dry.”

JPL has managed the Mars Exploration Rover project since it began in 2000. Images and additional information about the rovers and their discoveries are available on the Internet at http://www.nasa.gov/vision/universe/solarsystem/mer_main.html and at http://marsrovers.jpl.nasa.gov. Information about NASA and agency programs is available on the Web at http://www.nasa.gov.

Original Source: NASA/JPL News Release

Cassini Flies Past Mysterious Titan Again

With a diameter of 5,150 kilometres, Titan is the largest of Saturn?s family of moons; it’s even bigger than the planets Mercury or Pluto. It has an atmosphere of orange-yellow smog composed mostly of nitrogen with an abundance of hydrocarbon organic compounds including methane; although, it seems to have very few clouds. On October 26, Cassini passed close to Titan revealing a first glimpse of the moon’s strange surface. It discovered a rugged yet level landscape with few craters, meaning that the planet must be geologically active. Mysterious oily flows of cryogenic ice ooze across the surface. Planetary scientists have been thrilled by the results so far.

Titan is cold. Its surface temperature is -180? C – way too cold for liquid water, yet it’s close to the triple point of methane, where this hydrocarbon gas can exist in all three physical states at its surface: solid ice, liquid or gaseous.

Cassini turned its Ultraviolet Imaging Spectrograph (UVIS) towards the star Spica (Alpha Virginis), then Lambda Scorpi, and for the next 8 hours observed the stars as they were obscured by Titan’s atmosphere. This sensitive instrument is different from other types of spectrometers because it can take both spectral and spatial readings. It’s particularly adept at determining the composition of gases. Spatial observations take a wide-by-narrow view, only one pixel tall and 60 pixels across. The spectral dimension is 1,024 pixels per spatial pixel. Additionally, it’s capable of taking so many images that it can create movies to show the ways in which this material is moved around by other forces. This provided a vertical profile of the main constituents of the atmospheric layers that have a similar temperature profile to the Earth.

Close approach occurred before Cassini passed up through Saturn’s ring plane, and returned some of the best close up images of the ring system to date. Then Cassini began using its radar to map part of Titan’s surface terrain at a small solar phase angle. The experiment was looking for signs of hot spots on the moon’s surface that would indicate the presence of active cryo-volcanoes, and even lighting in Titan’s atmosphere.

The 2.6-meter Huygens lander probe will separate from its mother ship on Christmas Eve, travelling towards Titan and entering the moon’s atmosphere on 14 January. Much of Huygens’s science will take place during its atmospheric decent, which will be relayed to Cassini, and then transmitted back to Earth’s waiting scientists and the media. If Huygens actually lands successfully on Titan, it’ll be a major bonus for the mission.

Huygens will be attempting to determine the origin of Titan’s molecular nitrogen atmosphere. Planetary scientists want to answer the question: “Is Titan’s atmosphere primordial (accumulated as Titan formed) or was it originally accreted as ammonia, which subsequently broke down to form nitrogen and hydrogen?”

If nitrogen from the solar nebula (out of which our Solar System formed) was the source of nitrogen on Titan, then the ratio of argon to nitrogen in the solar nebula should be preserved. Such a finding would mean that we have truly found a sample of the “original” planetary atmospheres of our Solar System

Huygens will also try to detect lightning on Titan. The extensive atmosphere of Titan may host Earth-like electrical storms and lightning. Although no evidence of lightning on Titan has been observed so far, the Cassini Huygens mission provides the opportunity to determine whether such lightning exists. In addition to the visual search for lightning, the study of plasma waves in the vicinity of Titan may offer another method. Lightning discharges a broad band of electromagnetic emission, part of which can propagate along magnetic field lines as whistler-mode emission.

By Science Correspondent Richard Pearson

What’s Up This Week – Dec 13 – Dec 19, 2004

Image credit: George Varros
Monday, December 13 – Tonight will be one of the most hauntingly beautiful and most mysterious displays of celestial fireworks all year – the Geminid meteor shower. First noted in 1862 by Robert P. Greg in England, and B. V. Marsh and Prof. Alex C. Twining of the United States in independent studies, the annual appearance Geminid stream was weak, producing no more than a few per hour, but it has grown in intensity during the last century and a half. By 1877 astronomers were realizing a new annual shower was occurring with an hourly rate of about 14. At the turn of the century it had increased to an average of over 20, and by the 1930s from 40 to 70 per hour. Only eight years ago observers recorded an outstanding 110 per hour during a moonless night… And now it is moonless again!

So why are the Geminids such a mystery? Most meteor showers are historic, documented and recorded for hundred of years, and we know them as being cometary debris. When astronomers first began looking for the Geminids parent comet, they found none. After decades of searching, it wasn’t until October 11,1983 that Simon Green and John K. Davies, using data from NASA’s Infrared Astronomical Satellite, detected an orbital object that was the next night confirmed by Charles Kowal that matched the Geminid meteoroid stream. But this was no comet, it was an asteroid. Originally designated as 1983 TB, but later renamed 3200 Phaethon, this apparently rocky solar system member has a highly elliptical orbit that places it within 0.15 AU of the Sun about every year and half. But asteroids can’t fragment like a comet – or can they? Original hypothesis were that since Phaethon’s orbit passes through the asteroid belt, that it may have collided with other asteroids causing rocky debris. This sounded good, but the more we studied the more we realized the meteoroid “path” occurred when Phaethon neared the Sun. So now our asteroid is behaving like a comet, yet it doesn’t develop a tail.

So what exactly is this “thing”? Well, we do know that 3200 Phaethon orbits like a comet, yet has the spectral signature of an asteroid. By studying photographs of the meteor showers, scientists have determined that the meteors are more dense than cometary material and not as dense as asteroid fragments. This leads us to believe that Phaethon is probably an extinct comet that has gathered a thick layer of interplanetary dust during its travels, yet retains the ice-like nucleus. Until we are able to take physical samples of this “mystery”, we may never fully understand what Phaethon is, but we can fully appreciate the annual display it produces!

Thanks to the wide path of the stream, folks the world over get an opportunity to enjoy the show. The traditional peak time is tonight as soon as the constellation of Gemini appears around mid-evening and lasts through tomorrow morning. The radiant for the shower is right around bright star Castor, but meteors can originate from many points in the sky. From around 2:00 a.m. until dawn (when our local sky window is aimed directly into the stream) it is possible that we can see (animated clip by George Varros.) about one “shooting star” every 30 seconds. The most successful of observing nights are ones where you are comfortable, so be sure to use a reclining chair or pad the ground while looking up. Please get away from light sources when possible – it will triple the amount of meteors you see, dress warmly, take along refreshments and just enjoy the incredible and mysterious Geminids!

Tuesday, December 14 – So if you thought last night was great, then don’t plan on getting extra sleep tonight as we wait out the two-day old Moon to set and Orion to rise. Tonight we’re going to locate and explore Don Macholz tenth comet discovery – C/2004 Q2! This is definitely a “not to be missed” treat. Even the most modest of binoculars will reveal this spectacular comet. Located tonight on the Eridanus border you can easily locate Q2 by identifying the constellation of Lepus below Orion and simply sweeping the skies a short distance to the west. You cannot miss Macholz. It’s that bright and that easy!

Holding a rough magnitude of 5, Comet Macholz is visible to the naked eye at a dark site, but is sufficiently bright enough to be caught with small binoculars under less than perfect conditions. What can you expect to see? The coma (at the time of my observances prior to this article) is wonderfully huge and about the size of that great globular cluster, M13, yet it is definitely brighter! Veteran comet observers will appreciate its concentrated nucleus, extensive coma and twin dust and ion tails. For the novice, Macholz will indeed appear like a large, unresolvable globular cluster with a bright core, but look up, up and away at the stretch of tail. It’s the finest (in my humble opinion) since Ikeya/Zhang! If the constellation of Lepus is too low for your location, don’t worry. The wonderful Macholz will continue in the days ahead to climb northward until it reaches Taurus by month’s end. This one is awesome!

Wednesday, December 15, 2004 – For early evening viewers, tonight’s Moon will give a great opportunity to visit telescopically with some smaller features located within the fully disclosed Mare Crisium area. Near the terminator, look for two bright mountainous areas on the central western border of Crisium known as Olivium and Lavinium Promentoriums. Voyaging from this point toward the east across Crisium’s smooth floor, we will see the small punctuations of Craters Picard to the south and Pierce to the north. See how many nights you are still able to make out these features!

Thursday, December 16 – Tonight the Moon is once again our prominent sky feature, so why not venture there and visit one of the oldest features left on our visible lunar side? Start by identifying two prominent craters in the southeast quadrant – Metius and Fabricus. While viewing the area around these craters, note that Frabricus’ walls actually intrude upon Metius pointing to its younger age of formation. Around Fabricus, but not including Metius is the boundary of a mountain walled plain that extends into the terminator. High power and stable conditions will reveal many breaks in its hexagonal walls and its floor will be marred by many smaller craters and fissures. This is crater Jannsen, and in all probability is one of the oldest craters left on the Moon. Look for three prominent interior craters as well as an ancient rimae that will be at the shadow’s edge. It may not seem exciting, but remember crater Jannsen could be as much as five billion years old!

Friday, December 17 – As we continue our lunar exploration tonight, look for the “three ring circus” of easily identified craters Theophilus, Cyrillus and Catherina. It is here that you will find a very unique highlight – a very conspicuous lunar feature that was never officially named! Cutting its way across Mare Nectaris from Theophilus to shallow crater Beaumont in the south will appear a long, thin, bright line. What you are looking at is an example of lunar dorsum – nothing more than a wrinkle or low ridge. Chances are probably good that this ridge is just a “wave” in the lava flow that congealed when Mare Nectaris was formed and it is quite striking tonight because of the lighting angle. Has it been named? Yes. It is unofficially known as the “Dorsae Beaumont”, but whatever it may be called, it is surely a distinct feature that I think you’ll enjoy!

Saturday, December 18 – There’s still plenty of Moon to explore tonight, so why don’t we try locating an area where many lunar exploration missions made their mark? Binoculars will easily reveal the fully disclosed areas of Mare Serenitatis and Mare Tranquillitatis, and it is where these two vast lava plains converge that we will set our sites. Telescopically you will see a bright “peninsula” westward of where the two conjoin that extends toward the east, just off that look for bright and small crater Pliny. It is near this rather inconspicuous feature that the remains Ranger 6 lay forever preserved when it crashed on February 2, 1964. Unfortunately, technical errors occured and it was never able to transmit lunar pictures. Not so Ranger 8! On a very successful mission to the same relative area, this time we received 7137 “postcards from the Moon” in the last 23 minutes before hard landing. On the “softer side”, Surveyor 5 also touched down near this area safely after two days of malfunctions on September 10, 1967. Incredibly enough, the tiny Surveyor 5 endured temperatures of up to 283 degrees F, but was able to spectrographically analyze the area’s soil… And by the way, it also managed to televise an incredible 18,006 frames of “home movies” from its distant lunar locale.

Sunday, December 19 – Tonight’s outstanding lunar feature is easily seen in binoculars and a treasure-trove of detail to the telescope. Located roughly one-third the way from south to north limb, Crater Albategnius will stand out in bold relief near the terminator. A fine challenge for binoculars will be to see if you can make out its bright central peak from its darker lava covered floor. Telescopically, Albategnius is a real treat! Also an ancient formation, look for the large number of younger craters in its ruined walls. The largest of these is Crater Klein, but there are myriad others. A nice test of your optics and abilities to discern small features is to look for three shallow depressions east of the central peak. Good luck!

Until next week? Remember that many deep sky objects are still visible despite the Moon, so keep looking up and enjoying the wonders of our own Universe! Wishing you clear, dark skies and light speed… ~Tammy Plotner

Work Begins on Magellan Giant Telescope

The Carnegie Observatories of the Carnegie Institution, and the University of Arizona, Steward Observatory Mirror Lab, have signed an agreement to produce the first mirror for the Giant Magellan Telescope (GMT)?the first telescope of the next-generation of extremely large ground-based telescopes ( ELT) to begin mirror production. The telescope primary mirror will have a diameter of 83 feet (25.4 meters) with more than 4.5 times the collecting area of any current optical telescope.

?This agreement is historic for the future of astronomy,? stated Dr. Richard Meserve, president of the Carnegie Institution. ?It is the first of many milestones that we and our partners look forward to?both in constructing an enormous ground-based telescope and in the scientific discoveries that will result. Everyone in the eight-member GMT consortium is extremely excited by this step,? he added. The consortium includes the Carnegie Observatories, Harvard University, Smithsonian Astrophysical Observatory, University of Arizona, University of Michigan, Massachusetts Institute of Technology, University of Texas at Austin, and Texas A&M University.

The GMT is slated for completion in 2016 at a site in Northern Chile. Viewing conditions in Chile, such as at Carnegie’s Las Campanas Observatory, are some of the best in the world. The GMT will have ten times the resolution of the Hubble Space Telescope. With its powerful resolution and enormous collecting area, the GMT will be able to probe the secrets of planets that have formed around other stars in the Milky Way, peer back in time toward the Big Bang with unprecedented clarity, delve into the nature of dark matter and dark energy, and explore the formation of black holes?the most important questions in astronomy today.

?The Giant Magellan Telescope will allow an unprecedented view of extrasolar planets as well as a window out to the largest scales and back to the earliest moments of the universe. We plan to complete the GMT so that it will work in tandem with the future generation of planned ground- and space-based telescopes,? stated Dr. Wendy Freedman, director of the Carnegie Observatories. ?The real distinction of the GMT, however, is that it is building on a heritage of successful technology developed for the twin 6.5-meter Magellan telescopes at Las Campanas. Their performance has far exceeded our expectations. The Magellan telescopes have proven to be the best natural imaging telescopes on the ground, due in large part to the genius of its Project Scientist, Carnegie Observatories? Stephen Shectman, and Roger Angel and his team at the Steward Mirror Lab,? she continued.

The mirrors for the GMT will be made using the existing infrastructure at Steward that made the 6.5-meter Magellan mirrors and the 8.4-meter Large Binocular Telescope mirrors on Mt. Graham. The new telescope will be composed of seven, 8.4-meter primary mirrors, arranged in a floral pattern. One spare off-axis mirror will also be made. Seven of the eight mirrors will be off-axis and require new techniques in casting and polishing. The first off-axis mirror will be cast this coming summer (2005) to address the new challenges. ?The upcoming decade promises to be a very exciting one for astronomy. The National Academy of Sciences Astronomy and Astrophysics Survey Committee Report (2001) ranked the science for extremely large telescopes as the highest priority for ground-based optical astronomy,? said Jeremy Mould, Director of the National Optical Astronomy Observatory. Site testing at the Las Campanas Observatory is also underway along with many other aspects of the project. Detailed information about the design of the GMT and the science that it will perform is located at http://www.gmto.org/.

Original Source: Carnegie News Release