Posted on by Fraser Cain

Simulating Titan’s Atmosphere in the Lab

Image credit: ESA
It takes at least three elements to harbor life as we know it: water, energy and an atmosphere. Among Mars and the moons around both Jupiter and Saturn, there is evidence of one or two of these three elements, but less is known if a complete set is available. Only Saturn’s moon, Titan, has an atmosphere comparable to Earth’s in pressure, and is much thicker than the martian one (1% of Earth’s sea level pressure).

The most interesting point about simulations of Titan’s hydrocarbon haze is that this smoggy component contains molecules called tholins (from the Greek word, muddy) that can form the foundations of the building blocks of life. For example, amino acids, one of the building blocks of terrestrial life, form when these red-brown smog-like particles are placed in water. As Carl Sagan pointed out, Titan may be regarded as a broad parallel to the early terrestrial atmosphere with respect to its chemistry and in this way, it is certainly relevant to the origins of life.

This summer, NASA’s Cassini spacecraft, launched in 1997, is scheduled to go into orbit around Saturn and its moons for four years. In early 2005, the piggybacking Huygens probe is scheduled to plunge into the hazy Titan atmosphere and land on the moon’s surface. There are 12 instruments onboard the Cassini Spacecraft orbiter, and 6 instruments onboard the Huygens Probe. The Huygens probe is geared primarily towards sampling the atmosphere. The probe is equipped to take measurements and record images for up to a half an hour on the surface. But the probe has no legs, so when it sets down on Titan’s surface its orientation will be random. And its landing may not be by a site bearing organics. Images of where Cassini is in its current orbit are continuously updated and available for view as the mission progresses.

Astrobiology Magazine had an opportunity to talk with research scientist, Jean-Michel Bernard of the University of Paris, about how to simulate Titan’s complex chemistry in a terrestrial test tube. His simulations of Titan’s environment build on the classic prebiotic soup, first pioneered fifty years ago by University of Chicago researchers, Harold Urey and Stanley Miller.

Astrobiology Magazine (AM): What first stimulated your interest in the atmospheric chemistry of Titan?

Jean-Michel Bernard (JB): How do two simple molecules (nitrogen and methane) create a very complex chemistry? Does chemistry become biochemistry? The recent discoveries of life in extreme conditions on Earth (bacteria in the South Pole at -40?C and archaea at more than +110?C in the vicinity of hydrothermal sources) allow to suppose that life could be present on other worlds and other conditions.

Titan has astrobiological interest because it is the only satellite in the solar system with a dense atmosphere. Titan’s atmosphere is made of nitrogen and methane. The energetic particles coming from the Sun and Saturn’s environment allow complex chemistry, such as formation of hydrocarbons and nitriles. The particles also generate a permanent haze around the satellite, rains of methane, winds, seasons Recently, lakes of hydrocarbons seem to have been detected on Titan’s surface. I think that this discovery, if it is confirmed by the Cassini-Huygens mission, will be of great interest.

It would make Titan an analog to the Earth, since it would have an atmosphere (gas), lakes (liquid), haze and soil (solid), the three necessary environments for the appearance of life.

The composition of Titan’s haze is unknown. Only optical data are available and they are difficult to analyze due to the complexity of this carbonaceous material. Many experiments have been carried out in order to mimic the chemistry of Titan’s atmosphere, most notably the aerosols analogs named “tholins” by Carl Sagan’s group. It seems that tholins could be involved in the origin of life. Indeed, hydrolysis of these Titan aerosol analogs gives rise to the formation of amino acids, the precursors of life.

AM: Can you describe your experimental simulation for extending the Miller-Urey experiments in a way that is customized for Titan’s low temperatures and unique chemistry?

JB: Since the Miller-Urey experiments, many experimental simulations of supposed prebiotic system have been carried out. But after the retrieval of Voyager’s data, it appeared necessary to come back to this approach to simulate Titan’s atmosphere. Then several scientists carried out such simulation experiments by introducing a nitrogen-methane mixture in a system like Miller’s apparatus. But a problem became obvious due to the difference between the experimental conditions and Titan’s conditions. The pressure and temperature were not representative of Titan’s environment. Then we decided to carry out experiments which reproduce the pressure and the temperature of Titan’s stratosphere: a gas mixture of 2% of methane in nitrogen, a low pressure (about 1 mbar) and a cryogenic system in order to have a low temperature. Furthermore, our system is placed in a glove box containing pure nitrogen in order to avoid contamination by ambient air of the solid products.

AM: What do you consider the best energy source for triggering Titan’s synthetic chemistry: the magnetosphere of Saturnian particles, solar radiation, or something else?

JB: Scientists debate about what energy source would best simulate the energy sources in Titan’s atmosphere. Ultraviolet (UV) radiation? Cosmic rays? Electrons and other energetic particles coming from Saturn’s magnetosphere? All these sources are involved, but their occurence depends of the altitude: extreme ultraviolet radiation and electrons in the ionosphere, UV light in the stratosphere, while cosmic rays occur in the troposphere.

I think the appropriate question should be: What is the experimental goal? If it is to understand the hydrogen cyanide (HCN) chemistry in Titan’s stratosphere, a simulation with UV radiation of HCN is appropriate. If the goal is to determine the effects of electric fields generated by galactic cosmic rays in the troposphere, a corona discharge of a simulated Titan-atmosphere is preferable.

In studying Titan’s stratospheric conditions, we chose to use an electric discharge in our simulation. This choice is contested by a minority of scientists because the main energy source in Titan’s stratosphere is UV radiation. But our results validated our experiment. We detected all the organic species observed on Titan. We predicted the presence of CH3CN (acetonitrile) before its observation. We detected for the first time dicyanoacetylene, C4N2, an unstable molecule at room temperature that has also been detected in Titan’s atmosphere. The middle infrared signature of the solid products created in our experiment was in line with Titan observations.

AM: How are your results part of the planned atmospheric testing for the Cassini-Huygens probe?

JB: After collaborating with a team from the Observatoire Astronomique de Bordeaux in France, we determined the dielectric constants of aerosol analogs. This will allow us to estimate how Titan’s atmosphere and surface properties could affect the performance of the Cassini-Huygens radar experiments. The altimeter onboard the Huygens probe could be affected by the aerosol properties, but complementary experiments must be carried out to confirm this result.

Two years ago, we introduced a gas mixture, N2/CH4/CO (98/1.99/0.01). The goal was to determine the impact of carbon monoxide, the most abundant oxygenated compound on Titan. Surprisingly, we detected oxirane in the gaseous phase as the major oxygenated product. This unstable molecule was discovered in the interstellar medium but theoretical models do not predict it for Titan’s chemistry. Yet maybe this molecule is present on Titan.

Currently, we are analyzing the first molecules, radicals, atoms and ions (or ‘species’) created inside our experimental reactor. We are using infrared spectrometry and UV-visible emission to study excited species like CN, CH, NH, C2, HCN, C2H2. Next, we will observe the correlation between the abundance of these species and the structures of the solid products. . Coupling these experimental results with a theoretical model developed in collaboration with the University of Porto in Portugal, we will have a better understanding about the chemistry occurring into the experimental reactor. This will allow us to analyze the Cassini-Huygens data and Titan’s haze formation.

Our team is involved at the mission science level as well, as one of the scientists of the mission is also in our group at the Laboratoire Inter-Universitaire des Syst?mes Atmosph?riques, LISA). Our laboratory tholins will be used as guides to calibrate several of the instruments on the Huygens probe and the Cassini orbiter.

There are 18 instruments on board the probe and orbiter. Calibration tests are needed for gas chromatography and mass spectroscopy [GC-MS]. The GC-MS will identify and measure chemicals in Titan’s atmosphere.

Calibration tests are also needed for the Aerosol Collector and Pyrolyser (ACP). This experiment will draw in aerosol particles from the atmosphere through filters, then heat the trapped samples in ovens to vaporize volatiles and decompose the complex organic materials.

The Composite Infrared Spectrometer (CIRS), a thermal measuring instrument on the orbiter, also needs to be calibrated. Compared to previous deep space missions, the spectrometer onboard Cassini-Huygens is a significant improvement, with a spectral resolution ten times higher than the Voyager spacecraft’s spectrometer.

AM: Do you have future plans for this research?

JB: Our next step is an experiment developed by Marie-Claire Gazeau, called “SETUP”. The experiment has two parts: a cold plasma in order to dissociate nitrogen, and a photochemical reactor in order to photodissociate methane. This will give us a better global simulation of Titan’s condition.

Original Source: NASA Astrobiology Magazine

Posted on by Fraser Cain

New Insights Into Martian Atmosphere

Image credit: Joint Astronomy Center
Astronomers have detected hydrogen peroxide (H2O2) in the atmosphere of Mars for the first time. This is the first time that a chemical catalyst of this sort has been found in a planetary atmosphere other than the Earth’s. Catalysts control the reactions of the most important chemical cycles in the Earth’s atmosphere. The result shows that scientists’ knowledge of the Earth’s atmosphere can be used to explain the chemistry of atmospheres on other planets, and vice versa. The work is announced in the March issue of the journal “Icarus”. The observations were made at the James Clerk Maxwell Telescope (JCMT), situated near the 14000-ft summit of Mauna Kea in Hawaii.

Dr Todd Clancy, at the Space Science Institute (SSI) in Boulder, Colorado, led the research team. He says “Mars is one of three observable terrestrial atmospheres. Unlike Venus, Mars is hospitable enough to be considered a possible human habitat in the future. And unlike the Earth, Mars is not extensively explored and so presents an opportunity to discover new and exciting phenomena.”

Dr Brad Sandor, also at SSI, explains “We took advantage of the excellent 2003 opposition of Mars, when the Earth and Mars passed close by each other in their orbits around the sun, to measure Martian atmospheric H2O2 for the first time.”

The Earth’s atmosphere has been studied much more than that of Mars. Scientists have had to rely on their terrestrial experience to guess how the Martian atmosphere reacts to solar radiation, and how its overall photochemical balance is controlled.

Models predicted that hydrogen peroxide was the key catalytic chemical that controls Mars atmospheric chemistry. Until now, scientists were unable to detect the predicted amount of H2O2, so some researchers argued that the models were wrong.

However, the new measurements of hydrogen peroxide made with the JCMT agree with the predictions of standard photochemistry. Dr Clancy continues “We have largely confirmed that the chemical balance of the Mars atmosphere is determined by the products of the photolysis of water vapor, without the need for special or unknown changes to current theory.”

Dr Gerald Moriarty-Schieven of the National Research Council of Canada worked on the project with Dr Clancy and Dr Sandor, and is based at the Joint Astronomy Centre in Hawaii, which operates the JCMT. He explains more about the JCMT observations: “The 2003 opposition was especially favorable since it occurred when Mars was closest to the sun in its orbit, and hence unusually close to us as we passed by. Mars was at its warmest, when the most H2O2 is available to observe, and the JCMT can make especially sensitive H2O2 measurements.”

What impact does this result have for the search for life on Mars? Dr Clancy says “Hydrogen peroxide is actually used as an antiseptic here on Earth, and so it would tend to retard any biological activity on the surface on Mars. For this reason, as well as the ultraviolet radiation and lack of water, bacteria-like organisms are not expected to be viable on the surface. Most arguments for finding life on Mars now center on subsurface regions.”

Original Source: JACH News Release

Posted on by Fraser Cain

Mars Express’ Image of Hecates Tholus

Image credit: ESA
The colour image (with north at the top) shows the summit caldera of Hecates Tholus, the northernmost volcano of the Elysium volcano group. The volcano reveals multiple caldera collapses. On the flanks of Hecates Tholus, several flow features related to water (lines radiating outwards) and pit chains related to lava can be observed. The volcano has an elevation of 5300 m, the caldera has a diameter of maximum 10 km and a depth of 600 m. The image centre is located at 150? East and 31.7? North.

Credits: ESA/DLR/FU Berlin (G. Neukum)

Original Source: ESA News Release

Posted on by Fraser Cain

Record for Furthest Galaxy is Broken Again

Image credit: ESO
Using the ISAAC near-infrared instrument on ESO’s Very Large Telescope, and the magnification effect of a gravitational lens, a team of French and Swiss astronomers [2] has found several faint galaxies believed to be the most remote known.

Further spectroscopic studies of one of these candidates has provided a strong case for what is now the new record holder – and by far – of the most distant galaxy known in the Universe.

Named Abell 1835 IR1916, the newly discovered galaxy has a redshift of 10 [3] and is located about 13,230 million light-years away. It is therefore seen at a time when the Universe was merely 470 million years young, that is, barely 3 percent of its current age.

This primeval galaxy appears to be ten thousand times less massive than our Galaxy, the Milky Way. It might well be among the first class of objects which put an end to the Dark Ages of the Universe.

This remarkable discovery illustrates the potential of large ground-based telescopes in the near-infrared domain for the exploration of the very early Universe.

Digging into the past
Like palaeontologists who dig deeper and deeper to find the oldest remains, astronomers try to look further and further to scrutinise the very young Universe. The ultimate quest? Finding the first stars and galaxies that formed just after the Big Bang.

More precisely, astronomers are trying to explore the last “unknown territories”, the boundary between the “Dark Ages” and the “Cosmic Renaissance”.

Rather shortly after the Big Bang, which is now believed to have taken place some 13,700 million years ago, the Universe plunged into darkness. The relic radiation from the primordial fireball had been stretched by the cosmic expansion towards longer wavelengths and neither stars nor quasars had yet been formed which could illuminate the vast space. The Universe was a cold and opaque place. This sombre era is therefore quite reasonably dubbed the “Dark Ages”.

A few hundred million years later, the first generation of stars and, later still, the first galaxies and quasars, produced intense ultraviolet radiation, gradually lifting the fog over the Universe.

This was the end of the Dark Ages and, with a term again taken over from human history, is sometimes referred to as the “Cosmic Renaissance”.

Astronomers are trying to pin down when – and how – exactly the Dark Ages finished. This requires looking for the remotest objects, a challenge that only the largest telescopes, combined with a very careful observing strategy, can take up.

Using a Gravitational Telescope
With the advent of 8-10 meter class telescopes spectacular progress has been achieved during the last decade. Indeed it has since become possible to observe with some detail several thousand galaxies and quasars out to distances of nearly 12 billion light-years (i.e. up to a redshift of 3 [3]). In other words astronomers are now able to study individual galaxies, their formation, evolution, and other properties over typically 85 % of the past history of the Universe.

Further in the past, however, observations of galaxies and quasars become scarce. Currently, only a handful of very faint galaxies are seen approximately 1,200 to 750 million years after the Big Bang (redshift 5-7). Beyond that, the faintness of these sources and the fact their light is shifted from the optical to the near infrared has so far severely limited the studies.

An important breakthrough in this quest for the earliest formed galaxy has now been achieved by a team of French and Swiss astronomers [2] using ESO’s Very Large Telescope (VLT) equipped with the near-infrared sensitive instrument ISAAC. To accomplish this, they had to combine the light amplification effect of a cluster of galaxies – a Gravitational Telescope – with the light gathering power of the VLT and the excellent sky conditions prevailing at Paranal.

Searching for distant galaxies
The hunt for such faint, elusive objects demands a particular approach.

First of all, very deep images of a cluster of galaxies named Abell 1835 were taken using the ISAAC near-infrared instrument on the VLT. Such relatively nearby massive clusters are able to bend and amplify the light of background sources – a phenomenon called Gravitational Lensing and predicted by Einstein’s theory of General Relativity.

This natural amplification allows the astronomers to peer at galaxies which would otherwise be too faint to be seen. In the case of the newly discovered galaxy, the light is amplified approximately 25 to 100 times! Combined with the power of the VLT it has thereby been possible to image and even to take a spectrum of this galaxy. Indeed, the natural amplification effectively increases the aperture of the VLT from 8.2-m to 40-80 m.

The deep near-IR images taken at different wavelengths have allowed the astronomers to characterise the properties of a few thousand galaxies in the image and to select a handful of them as potentially very distant galaxies. Using previously obtained images taken at the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea and images from the Hubble Space Telescope, it has then been verified that these galaxies are indeed not seen in the optical. In this way, six candidate high redshift galaxies were recognised whose light may have been emitted when the Universe was less than 700 million years old.

To confirm and obtain a more precise determination of the distance of one of these galaxies, the astronomers obtained Director’s Discretionary Time to use again ISAAC on the VLT, but this time in its spectroscopic mode. After several months of careful analysis of the data, the astronomers are convinced to have detected a weak but clear spectral feature in the near-infrared domain. The astronomers have made a strong case that this feature is most certainly the Lyman-alpha emission line typical of these objects. This line, which occurs in the laboratory at a wavelength of 0.1216 ?m, that is, in the ultraviolet, has been stretched to the near infrared at 1.34 ?m, making Abell 1835 IR1916 the first galaxy known to have a redshift as large as 10.

The most distant galaxy known to date
This is the strongest case for a redshift in excess of the current spectroscopically confirmed record at z=6.6 and the first case of a double-digit redshift. Scaling the age of the Universe to a person’s lifetime (80 years, say), the previous confirmed record showed a four-year toddler. With the present observations, we have a picture of the child when he was two and a half years old.

From the images of this galaxy obtained in the various wavebands, the astronomers deduce that it is undergoing a period of intense star formation. But the amount of stars formed is estimated to be “only” 10 million times the mass of the sun, approximately ten thousand times smaller than the mass of our Galaxy, the Milky Way.

In other words, what the astronomers see is the first building block of the present-day large galaxies. This finding agrees well with our current understanding of the process of galaxy formation corresponding to a successive build-up of the large galaxies seen today through numerous mergers of “building blocks”, smaller and younger galaxies formed in the past.

It is these building blocks which may have provided the first light sources that lifted the fog over the Universe and put an end to the Dark Ages.

For Roser Pell?, from the Observatoire Midi-Pyr?n?es (France) and co-leader of the team, “these observations show that under excellent sky conditions like those at ESO’s Paranal Observatory, and using strong gravitational lensing, direct observations of distant galaxies close to the Dark Ages are feasible with the best ground-based telescopes.”

The other co-leader of the team, Daniel Schaerer from the Geneva Observatory and University (Switzerland), is excited: “This discovery opens the way to future explorations of the first stars and galaxies in the early Universe.”

More information
The information presented in this Press Release is based on a research article in the European research journal “Astronomy & Astrophysics” (A&A, volume 416, page L35; “ISAAC/VLT observations of a lensed galaxy at z=10.0” by Roser Pell?, Daniel Schaerer, Johan Richard, Jean-Fran?ois Le Borgne, and Jean-Paul Kneib). It is available on the web at the EDP web site.

Additional explanations and images are available on the authors’ web page, at http://obswww.unige.ch/sfr and http://webast.ast.obs-mip.fr/galaxies/

Original Source: ESO News Release

Posted on by Fraser Cain

Closest Youngest Star Found

Image credit: UC Berkeley
Astronomers at the University of California, Berkeley, have discovered the nearest and youngest star with a visible disk of dust that may be a nursery for planets.

The dim red dwarf star is a mere 33 light years away, close enough that the Hubble Space Telescope or ground-based telescopes with adaptive optics to sharpen the image should be able to see whether the dust disk contains clumps of matter that might turn into planets.

“Circumstellar disks are signposts for planet formation, and this is the nearest and youngest star where we directly observe light reflected from the dust produced by extrasolar comets and asteroids – i.e., the objects that could possibly form planets by accretion,” said Paul Kalas, assistant research astronomer at UC Berkeley and lead author of a paper reporting the discovery.

“We’re waiting for the summer and fall observing season to go back to the telescopes and study the properties of the disk in greater detail. But we expect everyone else to do the same thing – there will be lots of follow-up.”

A paper announcing the discovery will be published online in Science Express this week, and will appear in the printed edition of the journal in March. Coauthors with Kalas are Brenda C. Matthews, a post-doctoral researcher with UC Berkeley’s Radio Astronomy Laboratory, and astronomer Michael C. Liu of the University of Hawaii. Kalas also is affiliated with the Center for Adaptive Optics at UC Santa Cruz.

The young M-type star, AU Microscopium (AU Mic), is about half the mass of the sun but only about 12 million years old, compared to the 4.6 billion year age of the sun. The team of astronomers found the star while searching for dust disks around stars emitting more than expected amounts of infrared radiation, indicative of a warm, glowing dust cloud.

The image of AU Mic, obtained last October with the University of Hawaii’s 2.2-meter telescope atop Mauna Kea, shows an edge-on disk of dust stretching about 210 astronomical units from the central star – about seven times farther from the star than Neptune is from the sun. One astronomical unit, or AU, is the average distance from the Earth to the sun, about 93 million miles.

“When we see scattered infrared light around a star, the inference is that this is caused by dust grains replenished by comets and asteroid collisions,” Kalas said. Because 85 percent of all stars are M-type red dwarfs, the star provides clues to how the majority of planetary systems form and evolve.

Other nearby stars, such as Gliese 876 at 16 light years and epsilon-Eridani at 10 light years, wobble, providing indirect evidence for planets. But images of debris disks around stars are rare. AU Mic is the closest dust disk directly imaged since the discovery 20 years ago of a dust disk around beta-Pictoris, a star about 2.5 times the mass of the sun and 65 light years away. Though the two stars are in opposite regions of the sky, they appear to have been formed at the same time and to be traveling together through the galaxy, Kalas said.

“These sister stars probably formed together in the same region of space in a moving group containing about 20 stars,” Kalas said. This represents an unprecedented opportunity to study stars formed under the same conditions, but of masses slightly larger and slightly smaller than the sun.

“Theorists are excited, too, at the opportunity to understand how planetary systems evolve differently around high-mass stars like beta-Pictoris and low-mass stars like AU Mic,” he said.

The pictures of AU Mic were obtained by blocking glare from the star with a coronagraph like that used to view the sun’s outer atmosphere, or corona. The eclipsing disk on the University of Hawaii’s 2.2-meter telescope blocked view of everything around the star out to about 50 AU. At this distance in our solar system, only the Kuiper Belt of asteroids and the more distant Oort cloud, the source of comets, would be visible.

Kalas said that sharper images from the ground or space should show structures as close as 5 AU, which means a Jupiter-like planet or lump in the dusty disk would be visible, if present.

“With the adaptive optics on the Lick 120-inch telescope or the Keck 10-meter telescopes, or with the Hubble Space Telescope, we can improve the sharpness by 10 to 100 times,” Kalas said.

In a companion paper accepted for publication in The Astrophysical Journal, the Berkeley-Hawaii team reports indirect evidence for a relatively dust-free hole within about 17 AU of the star. This would be slightly inside the orbit of Uranus in our own solar system.

“Potential evidence for the existence of planets comes from the infrared spectrum, where we notice an absence of warm dust grains,” he said. “That means that grains are depleted within about 17 AU radius from the star. One mechanism to clear out the dust disk within 17 AU radius is by planet-grain encounters, where the planet removes the grains from the system.”

“The dust missing from the inner regions of AU Mic is the telltale sign of an orbiting planet. The planet sweeps away any dust in the inner regions, keeping the dust in the outer region at bay,” said Liu.

Aside from further observations with the 2.2-meter telescope in Hawaii, Kalas and his colleagues plan to use the Spitzer Space Telescope, an infrared observatory launched last August by the National Aeronautics and Space Administration (NASA), to conduct a more sensitive search for gas.

The research was supported by the NASA Origins Program and the National Science Foundation’s Center for Adaptive Optics.

Original Source: UC Berkeley News Release

Posted on by Fraser Cain

Opportunity Watches a Sunset on Mars

Image credit: NASA/JPL
Dust gradually obscures the Sun during a blue-sky martian sunset seen in a sequence of newly processed frames from NASA’s Mars Exploration Rover Opportunity.

“It’s inspirational and beautiful, but there’s good science in there, too,” said Dr. Jim Bell of Cornell University, Ithaca, N.Y., lead scientist for the panoramic cameras on Opportunity and its twin, Spirit.

The amount of dust indicated by Opportunity’s observations of the Sun is about twice as much as NASA’s Mars Pathfinder lander saw in 1997 from another site on Mars.

The sunset clip uses several of the more than 11,000 raw images that have been received so far from the 18 cameras on the two Mars Exploration Rovers and publicly posted at http://marsrovers.jpl.nasa.gov. During a briefing today at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., Bell showed some pictures that combine information from multiple raw frames.

A patch of ground about half the area of a coffee table, imaged with the range of filters available on Opportunity’s panoramic camera, has soil particles with a wide assortment of hues — “more spectral color diversity than we’ve seen in almost any other data set on Mars,” Bell said.

Opportunity is partway through several days of detailed observations and composition measurements at a portion of the rock outcrop in the crater where it landed last month. It used its rock abrasion tool this week for the first time, exposing a fresh rock surface for examination. That surface will be studied with its alpha particle X-ray spectrometer for identifying chemical elements and with its Moessbauer spectrometer for identifying iron-bearing minerals. With that rock-grinding session, all the tools have now been used on both rovers.

Dr. Ray Arvidson of Washington University, St. Louis, deputy principal investigator for the rovers’ science work, predicted that in two weeks or so, Opportunity will finish observations in its landing-site crater and be ready to move out to the surrounding flatland. At about that same time, Spirit may reach the rim of a larger crater nicknamed “Bonneville” and send back pictures of what’s inside. “We’ll both be at the rims of craters,” he said of the two rovers’ science teams, “one thinking about going in and the other thinking about going out onto the plain.”

Not counting occasional backup moves, Spirit has driven 171 meters (561 feet) from its lander. It has about half that distance still to go before reaching the crater rim. The terrain ahead looks different than what’s behind, however. “It’s rockier, but we’re after rocks,” Arvidson said.

Spirit can traverse the rockier type of ground in front of it, said Spirit Mission Manager Jennifer Harris of JPL. As it approached the edge of a small depression in the ground earlier this week, the rover identified the slope as a potential hazard, and “did the right thing” by stopping and seeking an alternate route, she said.

However, engineers are also planning to transmit new software to both rovers in a few weeks to improve onboard navigation capabilities. “We want to be more robust for the terrain we’re seeing,” Trosper said. The software revisions will also allow engineers to turn off a heater in Opportunity’s arm, which has been wasting some power by going on during cold hours even when not needed.

As it heads toward “Bonneville” to look for older rocks from beneath the region’s current surface layer, Spirit is stopping frequently to examine soil and rocks along the way. Observations with its microscope at one wavy patch of windblown soil allowed scientists to study how martian winds affect the landscape. Coarser grains are concentrated on the crests, with finer grains more dominant in the troughs, a characteristic of “ripples” rather than of dunes, which are shaped by stronger winds. “This gives us a better understanding of the current erosion process due to winds on Mars,” said Shane Thompson, a science team collaborator from Arizona State University, Tempe.

The rovers’ main task is to explore their landing sites for evidence in the rocks and soil about whether the sites’ past environments were ever watery and possibly suitable for sustaining life.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Wallpaper: Cassini’s Latest View of Saturn

Image credit: NASA/JPL
Four months before its scheduled arrival at Saturn, the Cassini- Huygens spacecraft sent its best color postcard back to Earth of the ringed world. The spacecraft is expected to send weekly postcards, as it gets closer to the ringed giant.

The view from Cassini shows Saturn growing larger and more defined as the spacecraft nears a July 1, 2004, arrival date. On February 9, Cassini’s narrow angle camera, one of two cameras onboard the spacecraft, took a series of exposures through different filters, which were combined to form the color image released today.

“We very much want everyone to enjoy Cassini’s tour of this magnificent planetary system,” said Dr. Carolyn Porco, leader of the Cassini imaging science team at the Space Science Institute in Boulder, Colo. “And I can say right now the views out the window will be stunning.”

Cassini was 69.4 million kilometers (43.2 million miles) from Saturn when the images were taken. The smallest features visible in the image are approximately 540 kilometers (336 miles) across. Finer details in the rings and atmosphere than previously seen are beginning to emerge and will grow in sharpness and clarity over the coming months. The thickness of the middle B ring of Saturn, and the comparative translucence of the outer A ring, when seen against the planet, as well as subtle color differences in the finely-banded Saturn atmosphere, are more apparent.

“I feel like a kid on a road trip at the beginning of our tour,” said Dr. Dennis Matson, project scientist for the Cassini-Huygens mission to Saturn and its largest moon Titan. “We’ve been driving this car for nearly 3.5 billion kilometers (2.2 billion miles) and it’s time to get off and explore this ringed world and its many moons. I can hardly wait, but in the meantime, these weekly color images offer a glimpse of our final destination.”

In the coming months, imaging highlights will include near daily, multi-wavelength imaging of Saturn and its rings; imaging of Titan beginning in April; Titan movie sequences starting in late May, when the resolution exceeds that obtainable from Earth; and a flyby of Saturn’s distant moon, Phoebe, in June, at a spacecraft altitude of 2,000 kilometers (1,243 miles).

Through Cassini, about 260 scientists from 17 countries hope to gain a better understanding of Saturn, its famous rings, its magnetosphere, Titan, and its other icy moons. “Cassini is probably the most ambitious exploration mission ever launched and is the fruit of an active international collaboration,” said Dr. Andre Brahic, imaging team member and professor at Universit? Paris 7-Denis Diderot, France. “It should be the prelude of our future, the exploration of our surroundings by humanity.”

Cassini will begin a four-year prime mission in orbit around Saturn when it arrives July 1. It will release its piggybacked Huygens probe about six months later for descent through Titan’s thick atmosphere. The probe could impact in what may be a liquid methane ocean.

JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Office of Space Science, Washington. The Space Science Institute is a non-profit organization of scientists and educators engaged in research in astrophysics, planetary science, Earth sciences, and in integrating research with education and public outreach. Cassini- Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency.

For the first image and other weekly images on the Internet each Friday, visit:

http://www.nasa.gov/

http://saturn.jpl.nasa.gov

http://ciclops.org/

For information about Cassini-Huygens on the Internet, visit:

http://saturn.jpl.nasa.gov/

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Rovers Losing Power as Mars Heads Towards Winter

Image credit: NASA/JPL
On sol 32, which ended at 4:15 a.m. Thursday, February 26, Opportunity awoke to “Let It Be” by the Beatles. Opportunity’s day was focused on getting a second Moessbauer instrument measurement of the hole created by the rock abrasion tool at the “McKittrick” rock site. The Moessbauer can detect spectral signatures of different iron-bearing minerals.

The data from the first Moessbauer spectrum of “McKittrick” was received on Earth Wednesday afternoon. The alpha proton X-ray spectrometer data from yestersol at this target was retransmitted to Earth again Wednesday to get missing packets of data that were not received during the first data communications relay. Opportunity also snapped pictures of the rock areas named “Maya” and “Jericho” with the panoramic camera and took miniature thermal emission spectrometer measurements of the sky and “El Capitan” throughout the sol.

The amount of power Opportunity is able to generate continues to dwindle due to the decreasing amount of sunlight (energy) reaching the solar panels during the martian seasonal transition to winter. Because of this, the engineers are adjusting the rover?s daily communications activities. To minimize power use for communications sessions, engineers began a new “receive only” morning direct-from-earth communication relay. This lower-power communication mode was successful. Opportunity will continue with this approach to maximize the available power for driving and science activities as Mars moves farther away from Earth and the Sun in its elliptical orbit.

In conjunction with the morning communications session change, engineers added a second afternoon Mars Odyssey orbiter relay pass, which uses less power in transmitting data volume than direct-to-Earth communication. This additional Odyssey pass more than compensated for the elimination of the morning direct-to-Earth downlink. Engineers also continue to effectively use rover “naps” throughout the day to maximize energy savings.

The plan for sol 33, which ends at 4:55 a.m. Friday, February 27, is to take a very short trip (10 to 20 centimeters or 4 to 8 inches) towards the next rock abrasion tool target site, “Guadalupe.”

Original Source: NASA/JPL Status Report

Posted on by Fraser Cain

Winking Star Turns Out to Be a Binary System

Image credit: CfA
Since its discovery in 1998, the “winking star” called KH 15D has baffled astronomers seeking to explain its long-lasting (24-day) eclipses. Many hypothesized that the eclipses were caused by intervening blobs of material within a protoplanetary disk surrounding a single, young Sun-like star.

By examining the past history of these eclipses and how they are changing with time, astronomer Joshua Winn (Harvard-Smithsonian Center for Astrophysics) and colleagues have overturned this hypothesis and devised a new theory that explains nearly everything about the system.

They found that the “winking star” is actually a double star system. Something in the foreground, possibly a dusty disk of material surrounding the binary, intermittently blocks the light from one or both stars, as the stars orbit each other. Eventually, both stars will be completely covered by the dust curtain, and the “winking star” system will disappear from view.

“These two stars have been playing hide and seek with us. The second star used to peek out briefly, but now is completely obscured. Soon, it will be joined by the first star and both will remain hidden for decades,” says Winn.

Archives Reveal The Truth
The vital clues to understanding the “winking star” were found in archival sky photographs from Harvard College Observatory, in Massachusetts, and Asiago Observatory, in Italy. Examination of the Harvard photographs showed that during the first half of the 20th century, there were none of the total eclipses that are observed today. Asiago photographs taken between 1967 and 1982 held evidence of eclipses, but with a key difference: the system was brighter than it is today, both during eclipses and outside of eclipses. This extra light must have come from a second star that was visible in the 1970s, but is completely hidden today.

This insight was the key to unlocking the mystery of KH 15D. Before 1960, neither star was being eclipsed. Then, a curtain of dust drifted into the foreground as seen from the Earth, blocking part of the orbit of one of the stars. Throughout the 1970s, that star underwent eclipses as its orbital motion carried it behind the curtain. By 1998, the curtain had advanced enough to completely hide one of the stars-and the other star periodically drops out of sight as its orbit takes it behind the curtain. By about 2012, both stars will be completely hidden from view.

Radial velocity measurements currently being made by John Johnson (UC Berkeley), a co-author of this study, will be able to test whether the visible star is moving back and forth, tugged by the gravity of a stellar-mass companion.

“The Asiago plates give very convincing evidence, but the radial velocity measurements will be the clincher,” says Johnson.

The New Picture of KH 15D
Assembling the observations of KH 15D like pieces of a jigsaw puzzle reveals two stars no older than 10 million years. (Our Sun, by contrast, is 5 billion years old.) They revolve around each other every 48 days in highly elliptical orbits, which explains the 48-day eclipse period. Their average distance apart is approximately 0.25 astronomical units (23 million miles), or two-thirds the distance from Mercury to the Sun. Yet their eccentric orbits take them as close to each other as only 0.07 AU (6.5 million miles).

“As binaries go, their orbit is not unusual” says co-author Krzysztof Stanek (CfA).

Winn agrees, adding, “The weird thing about this system is that there’s something blocking the light from these stars-something opaque, with a sharp edge.” The identity of this curtain is unknown, but it may be the edge of a disk of dust that surrounds both of the stars.

“Dust disks have been seen around other binary star systems,” says Matthew Holman (CfA), a co-author of the study. “We imagine that the disk in this system is inclined, relative to the plane of the orbit of the two stars. That would cause the disk to wobble, the way a Frisbee sometimes wobbles in the air after a bad throw.”

According to Holman’s calculations, the dust may exist in a ring located 2.6 AU (240 million miles) from the stars. The material in the ring itself makes one complete orbit about every 4 years, but the wobbling (or “precession”) of the ring has a much longer period of about 1000 years. A similar theory has been proposed independently by Eugene Chiang and Ruth Murray-Clay of UC Berkeley.

“Starting around 1960, the edge of this precessing disk happened to start blocking our view of the stars,” says Holman. “After another decade, the disk will precess a little further and completely block our view.” Some time after that, depending on how thick the ring is, the process will reverse itself as the stars are gradually uncovered, and the eclipses will stop.

Many questions about KH 15D still remain. For example, what is the nature of the disk? Why is it inclined to the orbital plane of the binaries? Why does it have such a sharp edge? The winking stars of KH 15D are likely to confound astronomers with these and other riddles for years to come.

This research will be published in the March 1, 2004 issue of The Astrophysical Journal Letters. The authors of the study are Joshua Winn (CfA), Matthew Holman (CfA), John Johnson (UC Berkeley), Krzysztof Stanek (CfA), and Peter Garnavich (University of Notre Dame).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics 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: CfA News Release

Posted on by Fraser Cain

Opportunity Grinds Away

Image credit: NASA/JPL
On sol 31, which ended at 3:36 a.m. Wednesday, February 25, Opportunity awoke to “Rock Around the Clock” by Bill Haley and his Comets. At 1:00 a.m. Local Solar Time, Opportunity sent data to Earth via the Mars Global Surveyor orbiter and then sent another whopping 145.6 megabits of data at 3:30 a.m. Local Solar Time via the Mars Odyssey orbiter.

During the morning hours, Opportunity collected data with the alpha particle X-ray spectrometer for five hours and took measurements with its miniature thermal emission spectrometer from inside its newly formed hole that was created on sol 30 by the rock abrasion tool. Later, Opportunity retracted and closed the door of the alpha particle X-ray spectrometer and swapped the Moessbauer spectrometer into the hole made by the abrasion tool for a leisurely 24-hour observation.

Opportunity also updated its “attitude knowledge,” which fine-tunes the rover’s information about its exact location and position on Mars. Updating the attitude knowledge allows the rover to more accurately point the high gain antenna toward Earth, which increases the communications capabilities. The attitude adjustment also enables scientists and engineers to point instruments onboard Opportunity more precisely at targets of interest, such as particular rocks and patches of soil. To adjust the attitude knowledge, engineers have the rover turn the panoramic camera to the Sun and watch the Sun travel across the sky for 15 minutes. The rover is then smart enough to take the Sun movement data collected from the panoramic camera to calculate its own location in the universe?..on Mars. The rover gathers attitude knowledge errors over time as it drives and uses the robotic arm extensively, but it only needs an attitude adjustment about once a week or after driving long distances.

Around 12:15 pm Local Solar Time, Opportunity went to sleep to recharge its batteries from its strenuous rock abrasion tool activities on sol 30, but reawakened briefly at 4 p.m. Local Solar Time and again in the evening to send data to Earth via additional overflights by the Mars Global Surveyor and Odyssey orbiters.

The plan for sol 32, which ends at 4:15 a.m. Thursday, February 26, is to take another unique set of Moessbauer measurements to look at the rover-created hole in a different spectrum. The goal is to then crawl slightly forward on sol 33 to position Opportunity to use the rock abrasion tool on the upper target of the El Capitan/McKittrick area.

Original Source: NASA/JPL News Release