Page 1053 | Astronomy Magazine

Chandrayaan-1 now in lunar transfer trajectory

Chandrayaan-1 lunar transfer orbit.

European Space Agency

November 5, 2008
After launch October 22, the spacecraft began an elliptical 7-hour orbit around Earth, between 158 and 14,205 miles (255 and 22,860 kilometers) above our planet. After five engine firings, Chandrayaan-1 spiraled outwards in increasingly elongated ellipses around Earth, until it reached its lunar transfer orbit November 3 at 6:26 p.m. EST.

In the fifth and last orbit-raising maneuver, the spacecraft’s 440 Newton liquid-fuel propelled engine fired for about 2.5 minutes. The lunar transfer orbit’s farthest point from Earth is about 236,121 miles (380,000 km).

The spacecraft Control Centre at the Indian Space Research Organization Telemetry Tracking and Command Network in Bangalore is monitoring the spacecraft. Chandrayaan-1’s Terrain Mapping camera (TMC) was successfully tested October 29 and provided its first images of Earth.

Chandrayaan-1 will approach the Moon November 8, 2008, when the spacecraft’s liquid-fuel propelled engine will be fired again. This maneuver, called lunar orbit insertion, will decelerate the spacecraft to allow the Moon’s gravity to capture it into an elliptical lunar orbit. A series of further maneuvers will then lower the altitude of Chandrayaan-1 around the Moon until it reaches its final 62-miles (100-km) circular orbit.

NASA’s Phoenix continues to weaken

This illustration shows NASA’s Phoenix Mars Lander on the Red Planet.

NASA/JPL-Caltech/University of Arizona

November 5, 2008
Information received during the weekend indicates NASA’s Phoenix Mars Lander is running out of power each afternoon or evening but reawakening after its solar arrays catch morning sunlight. Since October 30, Phoenix communicated with controllers daily through relays to Mars orbiters.

The fraction of Sun above the horizon is declining every day at the martian arctic landing site. Plus, dust raised by a storm last week continues to block some of the sunshine.

“This is exactly the scenario we expected for the mission’s final phase, though the dust storm brought it a couple weeks sooner than we had hoped,” said Phoenix Project Manager Barry Goldstein of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California. “We will be trying to gain some additional science during however many days we have left. Any day could be our last.”

Mission engineers at JPL and at Lockheed Martin Space Systems, Denver, are attempting this week to upload commands to be stored in the lander’s flash memory for science activities to be conducted when the lander wakes up each day.

“Weather observations are our top priority now,” said Phoenix Principal Investigator Peter Smith. “If there’s enough energy, we will try to get readings from the conductivity probe that has been inserted into the soil, and possibly some images to assess frost buildup.”

Phoenix landed on Mars May 25. It accomplished its main science goals during the 3 months originally planned as its prime mission, then continued operating, now in its sixth month.

‘Ghost of Mirach’ materializes in space telescope image

The “Ghost of Mirach” galaxy as seen in the ultraviolet.

NASA/JPL-Caltech

November 4, 2008
NASA’s Galaxy Evolution Explorer (GALEX) has lifted the veil off a ghost known to haunt the local universe, providing new insight into the formation and evolution of galaxies.

The eerie creature, called NGC 404, is a lenticular galaxy. These disk shaped galaxies have no spiral arms and host little ongoing star formation. NGC 404 is the nearest example of a lenticular galaxy, but it lies hidden in the glare from a red giant star called Mirach. For this reason, NGC 404 became known to astronomers as the “Ghost of Mirach.”

When GALEX spied the galaxy in ultraviolet light, a spooky ring materialized.

“We thought this celestial ghost was essentially dead, but we’ve been able to show that it has an extended ring of new stars. The galaxy has a hybrid character in which the well-known, very old stellar population tells only part of the story,” said David Thilker of Johns Hopkins University in Baltimore. “It’s like the living dead.”

Thilker and members of the GALEX team spotted the Ghost of Mirach in images taken during the space telescope’s all-sky survey. GALEX is a relatively low-cost NASA mission, launched in 2003, that surveys the visible sky in ultraviolet light, something never before accomplished. Because Earth’s atmosphere absorbs ultraviolet photons — a good thing for us living creatures who are susceptible to the damaging light — ultraviolet telescopes must operate from space.

The first GALEX images of the Ghost of Mirach hinted at a surrounding ultraviolet-bright extended structure. Subsequent, longer exposure observations show a clumpy, never-before-seen ring of stars surrounds the lenticular galaxy.

What is this mysterious ultraviolet ring doing around an otherwise nondescript lenticular galaxy? As it turns out, previous imaging with the National Science Foundation’s Very Large Array radio telescope in New Mexico had discovered a gaseous ring of hydrogen that matches the ultraviolet ring GALEX observed. The authors of this Very Large Array study attributed the gas ring to a violent collision between NGC 404 and a small neighboring galaxy 900 million years ago.

The ultraviolet observations demonstrate that when the hydrogen from the collision settled into the plane of the lenticular galaxy, stars began to form in a ghostly ring. Young, relatively hot stars forming in stellar clusters sprinkled throughout NGC 404’s ring give off the ultraviolet light that GALEX was able to see.

“Before the Galaxy Evolution Explorer image, NGC 404 was thought to contain only very old and evolved red stars distributed in a smooth elliptical shape, suggesting a galaxy well into its old age and no longer evolving significantly,” said Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena, California. “Now we see it has come back to life, to grow once again.”

“The Ghost of Mirach has been lucky enough to get a new lease on life through the rejuvenating, chance merger with its dwarf companion,” added Thilker.

The findings indicate the evolution of lenticular galaxies might not yet be complete. They may, in fact, continue to form stars in a slow, piecemeal fashion as they suck the raw, gaseous material for stars from small, neighboring galaxies. It seems the Ghost of Mirach might act more like a vampire than a ghost.

First rocket parts of NASA’s new launch system arrive in Florida

Artist concept of Ares I-X rocket.

NASA/JPL-Caltech

November 4, 2008
The first major flight hardware of the Ares I-X rocket has arrived in Florida to begin preparation for the inaugural test flight of NASA’s next-generation launch system. The test flight is targeted for July 12, 2009.

The Ares I-X upper stage simulator traveled to Port Canaveral aboard the Delta Mariner, a ship that also transports the Delta IV rocket for United Launch Alliance. The journey began October 22 on the Ohio River as the barge traveled toward the Mississippi River for its voyage to Port Canaveral. By November 6, the flight hardware will move off the barge into high bay 4 of the Vehicle Assembly Building at NASA’s Kennedy Space Center in Merritt Island, Florida.

The upper stage simulator consists of 11 individual components that were designed and manufactured during a 2-year period at NASA’s Glenn Research Center in Cleveland. The components represent the size, outer shape, and weight of the second stage of the Ares I rocket, and will integrate together in the Vehicle Assembly Building. The upper stage simulator eventually will be stacked atop the solid rocket booster segments of the Ares I-X rocket.

The Ares I-X test flight will provide NASA an early opportunity to test and prove hardware, facilities, and ground operations associated with the Ares I crew launch vehicle. It also will allow NASA to gather critical data during ascent of the integrated Orion crew exploration vehicle and the Ares I rocket. The data will ensure the entire vehicle system is safe and fully operational before astronauts begin traveling to orbit.

NASA delays Hubble servicing mission

Hubble Space Telescope.

NASA

October 31, 2008
The decision to delay the servicing mission comes after engineers completed assessments of the work needed to get a second data handling unit for the telescope ready to fly. The unit will replace one that failed on Hubble in late September, causing the agency to postpone the servicing mission that had been targeted for October 14.

“We now have done enough analysis of all the things that need to happen with the flight spare unit to know that we cannot be ready for a February launch,” said NASA’s Astrophysics Division Director Jon Morse at NASA headquarters in Washington. “The February date was an initial estimate, assuming minimal hardware preparations and test durations that are no longer viewed as realistic. We’ve communicated our assessment to the Space Shuttle Program so it can adjust near-term plans. We will work closely with the Shuttle Program to develop details for a new launch opportunity.”

“Getting ourselves in a position to be ready to launch the Hubble mission will involve many steps, and a significant one took place earlier today,” said Hubble Program Manager Preston Burch at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We held a flight certification peer review meeting where every aspect for doing this effort — the inspections needed, all the tests to be conducted, the certification process, and the final flight preparations — was examined. The conclusion was that we have a very good plan in place.”

The Hubble flight spare, known as the Science Instrument Command and Data Handling system, has been at Goddard since it was originally delivered as a back-up system in 1991. The unit currently is undergoing testing and examination to identify and correct any problems. That work will continue until mid-December.

The unit will then undergo environmental assessments that include electro-magnetic interference checks, vibration tests, and extended time in a thermal vacuum chamber. Environmental testing is anticipated to run from mid-December to early March 2009. Final testing will be conducted on the unit, and delivery to NASA’s Kennedy Space Center in Florida is expected in early April.

“The equipment we are dealing with has a flight-proven design,” said Burch. “The original unit on Hubble ran for more than 18 years. We have a lot of spare parts if we encounter problems, and we have most of the same test equipment that was used with the original unit. We also have a lot of experience on our Hubble electrical replica, which uses the engineering model data handling unit.”

The vast majority of the flight hardware, tools and support equipment that will be used during the mission will be stored at Kennedy. Mission scientists will conduct a small amount of new work such as re- lubricating the latches on the Soft Capture Mechanism and testing the motors on the Flight Support System. The Wide Field Camera 3 will remain in its carrier. The Cosmic Origins Spectrograph is in a special double-layered purge system in its shipping container to help support its environmental needs. The new batteries to be installed during the mission are in cold storage at Goddard and will be returned to Kennedy in 2009.

In the meantime, science observations on Hubble that had been suspended continue to move toward standard operations. The current primary camera on the telescope, the Wide Field Planetary Camera 2, was brought back online. On Wednesday, calibration images with the Advanced Camera for Surveys’ Solar Blind Channel were completed. Regular science observations resumed Thursday, and the first science image from the camera was released.

NASA gives go-ahead to November 14 shuttle launch NASA managers completed a review October 30 of space shuttle Endeavour’s readiness for flight and selected the official launch date for the STS-126 mission. Commander Chris Ferguson and his six crewmates are scheduled to lift off to the International Space Station at 7:55 p.m. EST November 14.

Endeavour’s STS-126 flight will feature important repair work to the station and prepare it for housing six crew members during long-duration missions. The primary focus of the 15-day flight and its four planned spacewalks is to service the station’s two Solar Alpha Rotary Joints, that allow its solar arrays to track the sun. Endeavour will carry about 32,000 pounds (14,515 kilograms) to orbit, including supplies and equipment necessary to double the crew size from three to six members in spring 2009. The new station cargo includes additional sleeping quarters, a second toilet, and a resistance exercise device.

NASA’s Hubble Space Telescope is back in business

This Hubble image shows interacting galaxies Arp 147.

NASA/ESA/M. Livio (STScI)

October 31, 2008
Just a couple of days after the orbiting observatory was brought back online, Hubble aimed its prime working camera, the Wide Field Planetary Camera 2 (WFPC2), at a pair of gravitationally interacting galaxies called Arp 147.

The galaxy pair was photographed October 27-28, 2008. Arp 147 lies in the constellation Cetus, and it is more than 400 million light-years away Earth.

The image shows the camera functions as it did before going offline.

The two galaxies happen to be oriented so that they appear to mark the number 10. The left-most galaxy, or the “one” in the image, is relatively undisturbed apart from a smooth ring of starlight. It appears nearly on edge to our line of sight. The right-most galaxy, resembling a “zero,” exhibits a clumpy, blue ring of intense star formation.

The blue ring probably formed after the galaxy on the left passed through the galaxy on the right. Just as a pebble thrown into a pond creates an outwardly moving circular wave, a propagating density wave was generated at the point of impact and spread outward. As this density wave collided with material in the target galaxy that was moving inward due to the gravitational pull of the two galaxies, shocks and dense gas were produced, stimulating star formation.

The dusty reddish knot at the blue ring’s lower left probably marks the location of the original nucleus of the galaxy that was hit.

WFPC2 used three separate filters to capture the picture. The blue, visible-light, and infrared filters are represented by the colors blue, green, and red, respectively.

Astronomers continue the search for antimatter

This view of the Bullet Cluster, located about 3.8 billion light-years from Earth, combines an image from NASA’s Chandra X-ray Observatory with optical data from the Hubble Space Telescope and the Magellan telescope in Chile.

X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

October 31, 2008
Scientists are on the hunt for evidence of antimatter left over from the very early universe. New results using data from NASA’s Chandra X-ray Observatory and Compton Gamma Ray Observatory suggest the search may have become even more difficult.

Elementary particles make up antimatter. Each has the same mass as its corresponding matter counterparts &#8212 protons, neutrons, and electrons &#8212 but the opposite charges and magnetic properties. When matter and antimatter particles collide, they annihilate each other and produce energy.

According to the Big Bang model, the universe was awash in particles of both matter and antimatter shortly after the Big Bang. Most of this material annihilated, but because there was slightly more matter than antimatter &#8212 less than one part per billion &#8212 only matter was left behind, at least in the local universe.

Black holes and pulsars power relativistic jets that scientists believe produce trace amounts of antimatter, but they’ve found no evidence for antimatter remaining from the infant universe.

How could any primordial antimatter have survived? Scientists believe there was an extraordinary period just after the Big Bang, called inflation, when the universe expanded exponentially in just a fraction of a second.

“If clumps of matter and antimatter existed next to each other before inflation, they may now be separated by more than the scale of the observable universe, so we would never see them meet,” said Gary Steigman of Ohio State University, who conducted the study. “But they might be separated on smaller scales, such as those of superclusters or clusters, which is a much more interesting possibility.”

This illustration shows the annihilation that occurs when antimatter and matter collide.

NASA/CXC/M. Weiss

In that case, collisions between two galaxy clusters, the largest gravitationally bound structures in the universe, might show evidence for antimatter. X-ray emission shows how much hot gas is involved in such a collision. If some of the gas from either cluster has antimatter particles, then there will be annihilation and gamma rays will accompany X rays.

Steigman used data obtained by Chandra and Compton to study the Bullet Cluster, an area where two large galaxy clusters crashed into one another at extremely high velocities. At a relatively close distance, and with a favorable side-on orientation as viewed from Earth, the Bullet Cluster provides an excellent test site to search for the signal for antimatter.

“This is the largest scale over which this test for antimatter has ever been done,” said Steigman, whose paper was published in the October 2 issue of The Journal of Cosmology and Astroparticle Physics. “I’m looking to see if there could be any clusters of galaxies which are made of large amounts of antimatter.”

The observed amount of X rays from Chandra and the non-detection of gamma rays from the Compton data show the antimatter fraction in the Bullet Cluster is less than three parts per million.

Moreover, simulations of the Bullet Cluster merger show these results rule out any significant amounts of antimatter over scales of about 65 million light-years, an estimate of the original separation of the two colliding clusters.

“The collision of matter and antimatter is the most efficient process for generating energy in the universe, but it just may not happen on very large scales,” said Steigman. “But, I’m not giving up yet as I’m planning to look at other colliding galaxy clusters that have recently been discovered.”

Finding antimatter in the universe could tell scientists about how long the period of inflation lasted.

“Success in this experiment, although a long shot, would teach us a lot about the earliest stages of the universe,” said Steigman.

Steigman placed tighter constraints on the presence of antimatter on smaller scales by looking at single galaxy clusters that do not involve such large, recent collisions.

Phoenix plays it “safe”

Phoenix spacecraft on Mars.

NASA/JPL-Caltech/University of Arizona

October 30, 2008
NASA’S Phoenix Mars Lander entered safe mode late Tuesday, October 28, in response to a low-power fault brought on by deteriorating weather conditions. While engineers anticipated that a fault could occur due to the diminishing power supply, the lander unexpectedly switched to the “B” side of its redundant electronics and shut down one of its two batteries.

During safe mode, the lander stops non-critical activities and awaits further instructions from the mission team. Within hours of receiving information of the safing event, mission engineers at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California, and at Lockheed Martin in Denver sent commands to restart battery charging. It is not likely that any energy was lost.

Weather conditions at the landing site in the north polar region of Mars have deteriorated in recent days, with overnight temperatures falling to -141°Farenheit (-96°Celsius), and daytime temperatures only as high as -50°F (-45°C), the lowest temperatures experienced so far in the mission. A mild dust storm blowing through the area, along with water-ice clouds, further complicated the situation by reducing the amount of sunlight reaching the lander’s solar arrays, thereby reducing the amount of power it could generate. Low temperatures caused the lander’s battery heaters to turn on October 28 for the first time, creating another drain on precious power supplies.

Science activities will remain on hold for the next several days to allow the spacecraft to recharge and conserve power. Attempts to resume normal operations will not take place before the weekend.

“This is a precarious time for Phoenix,” said Phoenix Project Manager Barry Goldstein of JPL. “We’re in the bonus round of the extended mission, and we’re aware that the end could come at any time. The engineering team is doing all it can to keep the spacecraft alive and collecting science, but at this point survivability depends on some factors out of our control, such as the weather and temperatures on Mars.”

MESSENGER reveals more of Mercury’s hidden territory

This image of Mercury captured was by MESSENGER on the probe’s second approach.

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

October 29, 2008
A NASA spacecraft gliding over Mercury’s battered surface for the second time this year revealed more previously unseen real estate on the innermost planet.

The probe also produced several science firsts and is returning hundreds of new photos and measurements of the planet’s surface, atmosphere, and magnetic field.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft flew by Mercury shortly after 4:40 A.M. EDT, October 6. It completed a critical gravity assist to keep it on course to orbit Mercury in 2011 and unveiled 30 percent of Mercury’s surface never seen by a spacecraft.

“The region of Mercury’s surface that we viewed at close range for the first time this month is bigger than the land area of South America,” said Sean Solomon, principal investigator and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. “When combined with data from our first flyby and from Mariner 10, our latest coverage means that we have now seen about 95 percent of the planet.”

The spacecraft’s science instruments operated throughout the flyby. Cameras snapped more than 1,200 pictures of the surface, while the laser altimeter profiled the area’s topography. The comparison of magnetosphere observations from the spacecraft’s first flyby in January with data from the probe’s second pass provids key new insight into Mercury’s internal magnetic field and reveals new features of its magnetosphere. The magnetosphere is the volume surrounding Mercury that is controlled by the planet’s magnetic field.

“The previous flybys by MESSENGER and Mariner 10 provided data only about Mercury’s eastern hemisphere,” said Brian Anderson of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. “The most recent flyby gave us our first measurements on Mercury’s western hemisphere, and with them, we discovered that the planet’s magnetic field is highly symmetric.”

The probe’s Mercury Laser Altimeter (MLA), allowed scientists, for the first time, to correlate high-resolution topography measurements with high-resolution images.

“The MLA collected altimetry in regions where images from MESSENGER and Mariner 10 data are available, and new images were obtained of the region sampled by the altimeter in January,” said Maria Zuber, co-investigator and head of the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. “These topographic measurements now improve considerably the ability to interpret surface geology.”

The Mercury Atmospheric and Surface Composition Spectrometer observed Mercury’s thin atmosphere, known as an exosphere. The instrument searched for emissions from sodium, calcium, magnesium, and hydrogen atoms. Observations of magnesium are the first detection of this chemical in Mercury’s exosphere. Preliminary analysis suggests the spatial distributions of sodium, calcium, and magnesium are different. Simultaneous observations of these spatial distributions, also a first for the spacecraft, have opened a window into the interaction of Mercury’s surface and exosphere.

Spacecraft images reveal for the first time vast geologic differences on the surface.

“Now that MESSENGER’s cameras have imaged more than 80 percent of Mercury, it is clear that, unlike the moon and Mars, Mercury’s surface is more homogeneously ancient and heavily cratered, with large extents of younger volcanic plains lying within and between giant impact basins,” said co-investigator Mark Robinson of Arizona State University in Tempe.

See Astronomy.com’s comprehensive coverage of MESSENGER’s second flyby of Mercury.

NASA’s Phoenix mission faces survival challenges

Phoenix spacecraft on Mars.

NASA/JPL-Caltech/University of Arizona

October 29, 2008
Originally scheduled to last 90 days, Phoenix has completed a fifth month of exploration in the martian arctic. As expected, with the martian northern hemisphere shifting from summer to fall, the lander is generating less power due to shorter days and fewer hours of sunlight reaching its solar panels. At the same time, the spacecraft requires more power to run several survival heaters that allow it to operate even as temperatures decline.

“If we did nothing, it wouldn’t be long before the power needed to operate the spacecraft would exceed the amount of power it generates on a daily basis,” said Phoenix Project Manager Barry Goldstein of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California. “By turning off some heaters and instruments, we can extend the life of the lander by several weeks and still conduct some science.”

Over the next several weeks, four survival heaters will be shut down, one at a time, in an effort to conserve power. The heaters keep the electronics within tested survivable limits. As each heater is disabled, some of the instruments are expected to cease operations as well. The energy saved will power the lander’s main camera and meteorological instruments until the end of the mission.

On October 28, engineers sent commands to disable the first heater. That heater warms Phoenix’s robotic arm, robotic-arm camera, and thermal and evolved-gas analyzer (TEGA), an instrument that bakes and sniffs martian soil to assess volatile ingredients. Shutting down this heater is expected to save 250 watt-hours of power per martian day.

The Phoenix team has parked the robotic arm on a representative patch of martian soil. No additional soil samples will be gathered. The thermal and electrical-conductivity probe (TECP), located on the arm’s wrist, has been inserted into the soil, and it will continue to measure soil temperature and conductivity, along with atmospheric humidity near the surface. The probe does not need a heater to operate and should continue to send back data for weeks.

Throughout the mission, the lander’s robotic arm dug and scraped martian soil and delivered it to the onboard laboratories. “We turn off this workhorse with the knowledge that it has far exceeded expectations and conducted every operation asked of it,” said Ray Arvidson, the robotic arm’s co-investigator and professor at Washington University, St. Louis.

When power levels necessitate further action, Phoenix engineers will disable a second heater that serves the lander’s pyrotechnic initiation unit. The unit hasn’t been used since landing, and disabling its heater is expected to add 4 to 5 days to the mission’s lifetime. Following that step, engineers would disable a third heater that warms Phoenix’s main camera — the Surface Stereo Imager — and the meteorological suite of instruments. Electronics that operate the meteorological instruments should generate enough heat to keep most of those instruments and the camera functioning.

In the final step, Phoenix engineers may turn off a fourth heater — one of two survival heaters that warm the spacecraft and its batteries. This would leave one remaining survival heater to run on its own.

“At that point, Phoenix will be at the mercy of Mars,” said Chris Lewicki, lead mission manger.

Engineers are also preparing for solar conjunction, when the Sun is directly between Earth and Mars. Between November 28 and December 13, Mars and the Sun will be within 2° of each other as seen from Earth. This positioning will block radio transmission between the spacecraft and Earth. During that time, no commands will be sent to Phoenix, but daily downlinks from Phoenix will continue through NASA’s Odyssey and Mars Reconnaissance orbiters. Controllers can’t predict whether the fourth heater would be disabled before or after conjunction.

NASA orbiter reveals details of a wetter Mars

NASA’s Mars Reconnaissance Orbiter has revealed Martian rocks containing a hydrated mineral similar to opal.

NASA/JPL-Caltech/University of Arizona

October 28, 2008
NASA’s Mars Reconnaissance Orbiter observed a new category of minerals spread across large regions of Mars. This discovery suggests liquid water remained on the planet’s surface a billion years later than scientists believed. This liquid water may have played an important role in shaping the planet’s surface and possibly hosting life.

Researchers examining data from the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars have found evidence of hydrated silica, commonly known as opal. The hydrated, or water-containing, mineral deposits are telltale signs of where and when water was present on ancient Mars.

“This is an exciting discovery because it extends the time range for liquid water on Mars and the places where it might have supported life,” Scott Murchie said, the spectrometer’s principal investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “The identification of opaline silica tells us that water may have existed as recently as 2 billion years ago.”

Until now, spacecraft orbiting Mars had observed only two major groups of hydrated minerals, phyllosilicates and hydrated sulfates. Clay-like phyllosilicates formed more than 3.5 billion years ago where igneous rock came into long-term contact with water. During the next several hundred million years, until approximately 3 billion years ago, hydrated sulfates formed from the evaporation of salty and sometimes acidic water.

The newly discovered opaline silicates are the youngest of the three types of hydrated minerals. They formed where liquid water altered materials created by volcanic activity or meteorite impact on the martian surface. One such location is the large martian canyon system Valles Marineris.

“We see numerous outcrops of opal-like minerals, commonly in thin layers extending for very long distances around the rim of Valles Marineris and sometimes within the canyon system itself,” said Ralph Milliken of NASA’s Jet Propulsion Laboratory in Pasadena, California.

Milliken is lead author of an article that describes the identification of opaline silica. The article appears in the November 2008 issue of Geology. The study reveals that the minerals, which NASA’s Mars rover Spirit recently found in Gusev Crater, are widespread and occur in relatively young terrains.

In some locations, the orbiter’s spectrometer observed opaline silica with iron sulfate minerals, either in or around dry river channels. This pressure indicates the acidic water remained on the martian surface for an extended period of time. Milliken and his colleagues believe that low-temperature acidic water was involved in forming the opal in these areas. In areas where there is no evidence that the water was acidic, deposits may have formed under a wide range of conditions.

“What’s important is that the longer liquid water existed on Mars, the longer the window during which Mars may have supported life,” Milliken said. “The opaline silica deposits would be good places to explore to assess the potential for habitability on Mars, especially in these younger terrains.”

The spectrometer collects 544 colors, or wavelengths, of reflected sunlight to detect minerals on the surface of Mars. Its highest resolution is about 20 times sharper than any previous look at the planet in near-infrared wavelengths.

December 2008: New research on an old asteroid

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Astronomy‘s mission:
Astronomy promotes the science and hobby of astronomy through high-quality publications that engage, inform, entertain, and inspire. WAUKESHA, Wis. — Sudbury Basin, in what is today Sudbury, Ontario, was created 1.8 billion years ago when a giant meteorite struck Earth. What does this event tell us about early Earth? Did the impact cause ecological disruption and mass extinction?

In “Scientists unearth ancient impact’s secrets,” author Mark Jirsa, a geologist with the Minnesota Geological Survey in St. Paul, examines these questions and looks at the new research on Sudbury Basin.

“The Sudbury impact was such a massively energetic event,” writes Jirsa, “one cannot help but wonder about its global ramifications. … Who knows what more these rocks have to teach us?”

Read all about the Sudbury impact and more in the December 2008 issue of Astronomy magazine, on newsstands October 28.

Astronomy‘s December issue also includes a 16-page pullout guide to 2009 sky events. “Astronomy‘s Sky Guide 2009,” by Martin Ratcliffe and Richard Talcott highlights the most observable sky events in each month for 2009. Sky highlights for next year include:

Saturn hides its rings — The giant planet’s famous features turn edge-on to earthbound observers.
Total Solar Eclipse — The longest total eclipse of the Sun in nearly 2 decades occurs July 22 when it blazes a path over India and China.
Leonid meteor shower — In a year expected to have great meteor showers, the Leonids might be the best.

“How life could thrive on hostile worlds”
There are extreme organisms living on Earth that can survive in environments with high pressure, low temperatures, minimal water, and high acidity. These “extremophiles” show us just how weird life on other planets could be. “How life could thrive on hostile worlds,” by Chris Impey, discusses what these organisms are telling us about the potential for life on other planets. Impey is a University Distinguished Professor at the University of Arizona’s Steward Observatory.

“Astroimaging over ancient Greece”
Anthony Ayiomamitis, a Mediterranean astrophotographer, captures celestial portraits with ancient ruins. In “Astroimaging over ancient Greece,” Ayiomamitis describes how he images the sky and includes a gallery of his spectacular images.

December night-sky events visible without optical aid

December 1 — The Moon joins Venus and Jupiter in the night sky.
December 22 — The Ursid meteor shower peaks.
December 29 — Mercury joins Venus in a planetary conjunction.

Also in the December 2008 Astronomy

“How the Sun will die” — When Sun-like stars exhaust their fuel, they cast off shells of gas, creating colorful fireworks.
“Meade’s LX90-ACF eliminates coma” — High portability, easy setup, and high-quality optics make this scope a winner.
“The Sky this month” — Exclusive pullout star charts will guide you through December’s night sky.
The December issue of Astronomy also includes Astro news, Bob Berman’s Strange universe, Glenn Chaple’s Observing basics, Phil Harrington’s Binocular universe, Stephen James O’Meara’s Secret sky, New products, and Reader gallery.