Posted on by Fraser Cain

Seeing the Planks in Einstein’s Cross

Image credit: Hubble
Spiral galaxy PGC 69457 is located near the boundary of fall constellations Pegasus and Aquarius some 3 degrees south of third magnitude Theta Pegasi – but don’t dig out that 60mm refractor to look for it. The galaxy is actually some 400 million light years away and has an apparent brightness of magnitude 14.5. So next fall may be a good time to hook up with that “astro-nut” friend of yours who is always heading off into the sunset to get well away from city lights sporting a larger, much larger, amateur instrument…

But there are plenty of 14th magnitude galaxies in the sky – what makes PGC 69457 so special?

To begin with most galaxies don’t “block” the view of an even more distant quasar (QSO2237+0305). And should others exist, few have just the right distribution of high-density bodies needed to cause light to “bend” in a way that an otherwise invisible object is visible. With PGC 69457 you get not one – but four – separate 17th magnitude views of the same quasar for the trouble of setting up one 20 inch truss tube dobsonian. Is it worth it? (Can you say “quadruple your observing pleasure”?)

But the phenomenon behind such a view is even more interesting to professional astronomers. What can we learn from such a unique effect?

The theory is already well established – Albert Einstein predicted it in his “General Theory of Relativity” of 1915. Einstein’s core idea was that an observer undergoing acceleration and one stationary in a gravitational field could not tell the difference between the two on their “weight”. By exploring this idea to its fullest, it became clear that not only matter but light (despite being massless) undergoes the same sort of confusion. Because of this, light approaching a gravitational field at an angle is “accelerated toward” the source of the gravity – but because the velocity of light is constant such acceleration only effects light’s path and wavelength – not its actual speed.

Gravitational lensing itself was first detected during the total solar eclipse of 1919. This was seen as a slight shift in the positions of stars near the Sun’s corona as captured on photographic plates. Because of this observation, we now know that you don’t need a lens to bend light – or even water to refract the image of those Koi swimming in the pond. Light like matter takes the path of least resistance and that means following the gravitational curve of space as well as the optical curve of a lens. The light from QSO2237+0305 is only doing what comes naturally by surfing the contours of “space-time” arcing around dense stars lying along the line of sight from a distant source through a more neighboring galaxy. The really interesting thing about Einstein’s Cross comes down to what it tells us about all the masses involved – those in the galaxy that refracts the light, and the Big One in the heart of the quasar that sources it.

In their paper “Reconstruction of the microlensing light curves of the Einstein Cross” Korean astrophysicist Dong-Wook Lee (et al) of Sejong University in association with Belgian astrophysicist J. Surdez (et al) of the University of Liege, found evidence of an accretion disk surrounding the black hole in Quasar QSO2237+0305. How is such a thing possible at the distances involved?

Lenses in general “collect and focus light” and those “gravitational lenses” (Lee at al posit a minimum of five low-mass but highly condensed bodies) within PGC 69457, do the same. In this way, light from a quasar that would normally travel well away from our instruments “wraps around” the galaxy to come toward us. Because of this we “see” 100,000 times more detail than otherwise possible. But there is a catch: Despite getting 100,000 times more resolution, we still only see light, not detail. And because there are several masses refracting light in the galaxy, we see more than one view of the quasar.

To get useful information from the quasar, you have to collect light over long periods of time (months to years) and use special analytical algorithms to pull the resulting data together. The method used by Lee and associates is called LOHCAM (LOcal Hae CAustic Modeling). (HAE itself is an acronym for High Amplification Events). Using LOHCAM and data available from OGLE (Optical Gravitational Lensing Experiment) and GLIPT (Gravitational Lens International Time Project), the team determined not only that LOHCAM works as hoped but that QSO2237+0305 may include a detectable accretion disk (from which it draws matter to power its light engine). The team has also determined the approximate mass of the quasars black hole, the size of the ultraviolet region radiating from it, and estimated the transverse motion of the black hole as it moves relative to the spiral galaxy.

The central black hole in Quasar QSO2237+0305 is thought to have a combined mass of 1.5 billion Suns – a value rivaling those of the largest central black holes ever discovered. Such a mass number represents 1 percent of the total number of stars in our own Milky Way galaxy. Meanwhile and by comparison, QSO2237+0305’s black hole is roughly 50 times more massive than that in the center of our own galaxy.

Based on “double-peaks” in luminosity from the quasar, Lee et al used LOHCAM to also determine the size of QSO2237+0305’s accretion disk, its orientation, and detected a central obscuration region around the black hole itself. The disk itself is roughly 1/3rd of a light year in diameter and is turned face on towards us.

Impressed? Well let’s also add that the team has determined the minimum number of microlenses and related masses found in the lensing galaxy. Depending on transverse velocity assumed (in LOHCAM modeling), the smallest range from that of a gas giant – such as the planet Jupiter – through that of our own Sun.

So how does this “hole” thing work?

The OGLE and GLIPT projects monitored changes in the intensity of visual light streaming to us from each of the four 17th magnitude views of the quasar. Since most quasars are unresolvable,due to their great distances in space, by telescope. Fluctuations in luminosity are seen only as a single point of data based on the brightness of the entire quasar. However, QSO2237+0305 presents four images of the quasar and each image highlights luminosity originating from a different perspective of the quasar. By telescopically monitoring all four images simultaneously, slight variations in image intensity can be detected and recorded in terms of magnitude, date, and time. Over several months to years, a considerable number of such “high amplification events” can occur. Patterns emerging out of their occurrence (from one 17th magnitude view to the next) can then be analyzed to show motion and intensity. Out of this a super high resolution view of normally unseen structure within the quasar is possible.

Could you and your friend with that 20 inch dob-newtonian do this?

Sure – but not without some very expensive equipment and a good handle on some complex mathematical imaging algorithms. A nice place to start however might simply be to ogle the galaxy and hang with the cross for awhile…

Written by Jeff Barbour

Posted on by Fraser Cain

Why Colonize the Moon First?

Artist's concept for a Lunar base. Credit: NASA

NASA has a new Vision for Space Exploration: in the decades ahead, humans will land on Mars and explore the red planet. Brief visits will lead to longer stays and, maybe one day, to colonies.

First, though, we’re returning to the Moon.

Why the Moon before Mars?

“The Moon is a natural first step,” explains Philip Metzger, a physicist at NASA Kennedy Space Center. “It’s nearby. We can practice living, working and doing science there before taking longer and riskier trips to Mars.”

The Moon and Mars have a lot in common. The Moon has only one-sixth Earth’s gravity; Mars has one-third. The Moon has no atmosphere; the Martian atmosphere is highly rarefied. The Moon can get very cold, as low as -240o C in shadows; Mars varies between -20o and -100o C.

Even more important, both planets are covered with silt-fine dust, called “regolith.” The Moon’s regolith was created by the ceaseless bombardment of micrometeorites, cosmic rays and particles of solar wind breaking down rocks for billions of years. Martian regolith resulted from the impacts of more massive meteorites and even asteroids, plus ages of daily erosion from water and wind. There are places on both worlds where the regolith is 10+ meters deep.

Operating mechanical equipment in the presence of so much dust is a formidable challenge. Just last month, Metzger co-chaired a meeting on the topic: “Granular Materials in Lunar and Martian Exploration,” held at the Kennedy Space Center. Participants grappled with issues ranging from basic transportation (“What kind of tires does a Mars buggy need?”) to mining (“How deep can you dig before the hole collapses?”) to dust storms–both natural and artificial (“How much dust will a landing rocket kick up?”).

Answering these questions on Earth isn’t easy. Moondust and Mars dust is so … alien.

Try this: Run your finger across the screen of your computer. You’ll get a little residue of dust clinging to your fingertip. It’s soft and fuzzy–that’s Earth dust.

Lunar dust is different: “It’s almost like fragments of glass or coral–odd shapes that are very sharp and interlocking,” says Metzger. (View an image of lunar dust.)

“Even after short moon walks, Apollo 17 astronauts found dust particles had jammed the shoulder joints of their spacesuits,” says Masami Nakagawa, associate professor in the mining engineering department of the Colorado School of Mines. “Moondust penetrated into seals, causing the spacesuits to leak some air pressure.”

In sunlit areas, adds Nakagawa, fine dust levitated above the Apollo astronauts’ knees and even above their heads, because individual particles were electrostatically charged by the Sun’s ultraviolet light. Such dust particles, when tracked into the astronauts’ habitat where they would become airborne, irritated their eyes and lungs. “It’s a potentially serious problem.”

Dust is also ubiquitous on Mars, although Mars dust is probably not as sharp as moondust. Weathering smooths the edges. Nevertheless, Martian duststorms whip these particles 50 m/s (100+ mph), scouring and wearing every exposed surface. As the rovers Spirit and Opportunity have revealed, Mars dust (like moondust) is probably electrically charged. It clings to solar panels, blocks sunlight and reduces the amount of power that can be generated for a surface mission.

For these reasons, NASA is funding Nakagawa’s Project Dust, a four-year study dedicated to finding ways of mitigating the effects of dust on robotic and human exploration, ranging from designs of air filters to thin-film coatings that repel dust from spacesuits and machinery.

The Moon is also a good testing ground for what mission planners call “in-situ resource utilization” (ISRU)–a.k.a. “living off the land.” Astronauts on Mars are going to want to mine certain raw materials locally: oxygen for breathing, water for drinking and rocket fuel (essentially hydrogen and oxygen) for the journey home. “We can try this on the Moon first,” says Metzger.

Both the Moon and Mars are thought to harbor water frozen in the ground. The evidence for this is indirect. NASA and ESA spacecraft have detected hydrogen–presumably the H in H2O–in Martian soil. Putative icy deposits range from the Martian poles almost to the equator. Lunar ice, on the other hand, is localized near the Moon’s north and south poles deep inside craters where the Sun never shines, according to similar data from Lunar Prospector and Clementine, two spacecraft that mapped the Moon in the mid-1990s.

If this ice could be excavated, thawed out and broken apart into hydrogen and oxygen … Voila! Instant supplies. NASA’s Lunar Reconnaissance Orbiter, due to launch in 2008, will use modern sensors to search for deposits and pinpoint possible mining sites.

“The lunar poles are a cold place, so we’ve been working with people who specialize in cold places to figure out how to land on the soils and dig into the permafrost to excavate water,” Metzger says. Prime among NASA’s partners are investigators from the Army Corps of Engineers’ Cold Regions Research and Engineering Laboratory (CRREL). Key challenges include ways of landing rockets or building habitats on ice-rich soils without having their heat melt the ground so it collapses under their weight.

Testing all this technology on the Moon, which is only 2 or 3 days away from Earth, is going to be much easier than testing it on Mars, six months away.

So … to Mars! But first, the Moon.

Original Source: Science@NASA Article

Posted on by Fraser Cain

India and Europe Agree on Lunar Mission

Image credit: ESA
On 17 March the ESA Council, at its meeting in Paris, unanimously approved a cooperation agreement between ESA and the Indian Space Research Organisation for India?s first moon mission ? Chandrayaan-1.

The Indian Space Research Organisation (ISRO), founded in 1969, launched its first satellite in 1975. Since then it has developed a number of launch vehicles as well as satellites for Earth observation, remote sensing, telecommunications and weather forecasting. India has its own launch site at Sriharikota but has also used Europe?s Spaceport in French Guiana to launch its satellites. Chandrayaan-1 marks its first venture into planetary space science.

Under the agreement Europe will coordinate and support the provision of three instruments: CIXS-2, the Chandrayaan-1 Imaging X-Ray Spectrometer; SARA, a Sub-keV Atom Relecting Analyzer; and SIR-2, a Near-Infrared Spectrometer. It will also support the hardware for the High-Energy X-ray Spectrometer (HEX). Direct ESA in-kind contributions are also foreseen under this historical agreement. In return, all data resulting from the instruments will be made immediately available to ESA Member States through ESA.

The instruments requested are identical to those on ESA?s SMART-1. Launched in 2003, SMART-1, having demonstrated a new solar electric propulsion motor and tested other technologies on its way to the moon, has just started its science phase. It will make the first comprehensive inventory of key chemical elements in the lunar surface.

ISRO plans to send a 1050 kg (523 kg initial orbit mass and 440 kg dry mass) remote sensing satellite to help unravel mysteries about the origin and evolution of the solar system in general and the Moon in particular. The satellite, which is expected to have an operational life of two years, will be launched by India?s Polar Satellite Launch Vehicle in 2007/2008.

ESA will give ISRO the benefit of its experience with SMART-1 and will further assist in operations facilitation as well as providing the science instruments.

ESA’s SMART-1 put Europe in the lead in the new race back to the Moon. As well as India and Japan, China and the USA also intend to launch lunar missions in the coming years. The cooperation with India will keep European scientists in the forefront.

The ESA Director of Science, David Southwood, said: “One should also see the cooperation in a wider context. Space science is a natural area for space agencies to learn to work together in technical matters. Such cooperation remains a strategic element in the Director General’s wider agenda for the Agency.”

Original Source: ESA News Release

Posted on by Fraser Cain

Cassini Sees Mimas Eclipse Janus

Saturn’s icy, impact-riddled moon Mimas slips briefly in front of Saturn’s moon Janus in this movie from Cassini. Mimas is 397 kilometers (247 miles) across, while Janus is 181 kilometers (113 miles) across.

The movie was created from 37 original images taken over the course of 20 minutes as the spacecraft’s narrow-angle camera remained pointed toward Janus. Although Mimas moves a greater distance across the field of view, Janus also moved perceptibly during this time. The images were aligned to keep Janus close to the center of the scene. Additional frames were inserted between the 37 Cassini images in order to smooth the appearance of Mimas’ movement — a scheme called interpolation. Close-up images from the few minutes surrounding the occultation are arranged into a strip along the bottom of the movie.

The terrain on Mimas seen here is about 80 degrees west of the terrain seen in a previously released movie (see Mimas on the Move), which showed the little moon appearing to cross Saturn’s ring plane from Cassini’s vantage point. In that previous movie, the rim of the large impact crater Herschel (130 kilometers, or 80 miles wide) was visible as a flattening of the moon’s eastern limb. In the new movie, Herschel is almost at dead center.

Contrast on Janus was mildly enhanced to aid the visibility of its surface. The right side of Mimas appears bright because the moon was partly overexposed in this image sequence.

The images for this movie were taken in visible light on March 5, 2005, when Cassini was approximately 1.8 million kilometers (1.1 million miles) from Mimas and 1.9 million kilometers (1.2 million miles) from Janus. The image scale is approximately 11 kilometers (7 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For additional images visit the Cassini imaging team homepage http://ciclops.org .

Original Source: NASA/JPL/SSI

Posted on by Fraser Cain

Ripples in Spacetime Could Explain Dark Energy

Why is the universe expanding at an accelerating rate, spreading its contents over ever greater dimensions of space? An original solution to this puzzle, certainly the most fascinating question in modern cosmology, was put forward by four theoretical physicists, Edward W. Kolb of the U.S. Department of Energy’s Fermi National Accelerator Laboratory, Chicago (USA): Sabino Matarrese of the University of Padova; Alessio Notari from the University of Montreal (Canada); and Antonio Riotto of INFN (Istituto Nazionale di Fisica Nucleare) of Padova (Italy). Their study was submitted yesterday to the journal Physical Review Letters.

Over the last hundred years, the expansion of the universe has been a subject of passionate discussion, engaging the most brilliant minds of the century. Like his contemporaries, Albert Einstein initially thought that the universe was static: that it neither expanded nor shrank. When his own Theory of General Relativity clearly showed that the universe should expand or contract, Einstein chose to introduce a new ingredient into his theory. His “cosmological constant” represented a mass density of empty space that drove the universe to expand at an ever-increasing rate.

When in 1929 Edwin Hubble proved that the universe is in fact expanding, Einstein repudiated his cosmological constant, calling it “the greatest blunder of my life.” Then, almost a century later, physicists resurrected the cosmological constant in a variant called dark energy. In 1998, observations of very distant supernovae demonstrated that the universe is expanding at an accelerating rate. This accelerating expansion seemed to be explicable only by the presence of a new component of the universe, a “dark energy,” representing some 70 percent of the total mass of the universe. Of the rest, about 25 percent appears to be in the form of another mysterious component, dark matter; while only about 5 percent comprises ordinary matter, those quarks, protons, neutrons and electrons that we and the galaxies are made of.

“The hypothesis of dark energy is extremely fascinating,” explains Padova’s Antonio Riotto, “but on the other hand it represents a serious problem. No theoretical model, not even the most modern, such as supersymmetry or string theory, is able to explain the presence of this mysterious dark energy in the amount that our observations require. If dark energy were the size that theories predict, the universe would have expanded with such a fantastic velocity that it would have prevented the existence of everything we know in our cosmos.”

The requisite amount of dark energy is so difficult to reconcile with the known laws of nature that physicists have proposed all manner of exotic explanations, including new forces, new dimensions of spacetime, and new ultralight elementary particles. However, the new report proposes no new ingredient for the universe, only a realization that the present acceleration of the universe is a consequence of the standard cosmological model for the early universe: inflation.

“Our solution to the paradox posed by the accelerating universe,” Riotto says, “relies on the so-called inflationary theory, born in 1981. According to this theory, within a tiny fraction of a second after the Big Bang, the universe experienced an incredibly rapid expansion. This explains why our universe seems to be very homogeneous. Recently, the Boomerang and WMAP experiments, which measured the small fluctuations in the background radiation originating with the Big Bang, confirmed inflationary theory.

It is widely believed that during the inflationary expansion early in the history of the universe, very tiny ripples in spacetime were generated, as predicted by Einstein’s theory of General Relativity. These ripples were stretched by the expansion of the universe and extend today far beyond our cosmic horizon, that is over a region much bigger than the observable universe, a distance of about 15 billion light years. In their current paper, the authors propose that it is the evolution of these cosmic ripples that increases the observed expansion of the universe and accounts for its acceleration.

“We realized that you simply need to add this new key ingredient, the ripples of spacetime generated during the epoch of inflation, to Einstein’s General Relativity to explain why the universe is accelerating today,” Riotto says. “It seems that the solution to the puzzle of acceleration involves the universe beyond our cosmic horizon. No mysterious dark energy is required.”

Fermilab’s Kolb called the authors’ proposal the most conservative explanation for the accelerating universe. “It requires only a proper accounting of the physical effects of the ripples beyond our cosmic horizon,” he said.

Data from upcoming experiments will allow cosmologists to test the proposal. “Whether Einstein was right when he first introduced the cosmological constant, or whether he was right when he later refuted the idea will soon be tested by a new round of precision cosmological observations,” Kolb said. “New data will soon allow us to distinguish between our explanation for the accelerated expansion of the universe and the dark energy solution.”

INFN (Istituto Nazionale di Fisica Nucleare), Italy’s national nuclear physics institute, supports, coordinates and carries out scientific research in subnuclear, nuclear and astroparticle physics and is involved in developing relevant technologies.

Fermilab, in Batavia, Illinois, USA, is operated by Universities Research Association, Inc. for the Department of Energy’s Office of Science, which funds advanced research in particle physics and cosmology.

Original Source: Istituto Nazionale di Fisica Nucleare

Posted on by Fraser Cain

Many Faces of Hyperion

As it loops around Saturn, Cassini periodically gets a good view of Saturn’s moon Hyperion. Hyperion chaotically tumbles around in its orbit and is perhaps the largest irregularly-shaped moon in the solar system. New details about this oddball worldlet will certainly come to light in September, 2005, when Cassini is slated to approach Hyperion at a distance of 990 kilometers (615 miles). Hyperion is 266 kilometers (165 miles) across.

The images were taken in visible light with the Cassini spacecraft narrow-angle camera in October 2004 and February 2005, at distances ranging from 1.3 to 1.6 million kilometers (808,000 to 994,000 million miles) from Hyperion and at Sun-Hyperion-spacecraft, or phase, angles ranging from 42 to 66 degrees. Resolution in the original images was 8 to 10 kilometers (5 to 6 miles) per pixel. The images have been contrast-enhanced and magnified by a factor of two to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For additional images visit the Cassini imaging team homepage http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Mars is Still Geologically Active

Shifting glaciers and exploding volcanoes aren?t confined to Mars? distant past, according two new reports in the journal Nature.

Glaciers moved from the poles to the tropics 350,000 to 4 million years ago, depositing massive amounts of ice at the base of mountains and volcanoes in the eastern Hellas region near the planet?s equator, based on a report by a team of scientists analyzing images from the Mars Express mission. Scientists also studied images of glacial remnants on the western side of Olympus Mons, the largest of the volcano calderas in the solar system. They found additional evidence of recent ice formation and movement on these tropical mountain glaciers, similar to ones on Mount Kilimanjaro in Africa.

In a second report, the international team reveals previously unknown traces of a major eruption of Hecates Tholus less than 350,000 million years ago. In a depression on the volcano, researchers found glacial deposits estimated to be 5 to 24 million years old.

James Head, professor of geological sciences at Brown University and an author on the Nature papers, said the glacial data suggests recent climate change in Mars? 4.6-billion-year history. The team also concludes that Mars is in an ?interglacial? period. As the planet tilts closer to the sun, ice deposited in lower latitudes will vaporize, changing the face of the Red Planet yet again.

Discovery of the explosive eruption of Hecates Tholus provides more evidence of recent Mars rumblings. In December, members of the same research team revealed that calderas on five major Mars volcanoes were repeatedly active as little as 2 million years ago. The volcanoes, scientists speculated, may even be active today.

?Mars is very dynamic,? said Head, lead author of one of the Nature reports. ?We see that the climate change and geological forces that drive evolution on Earth are happening there.?

Head is part of a 33-institution team analyzing images from Mars Express, launched in June 2003 by the European Space Agency. The High Resolution Stereo Camera, or HRSC, on board the orbiter is producing 3-D images of the planet?s surface.

These sharp, panoramic, full-color pictures provided fodder for a third Nature report. In it, the team offers evidence of a frozen body of water, about the size and depth of the North Sea, in southern Elysium.

A plethora of ice and active volcanoes could provide the water and heat needed to sustain basic life forms on Mars. Fresh data from Mars Express ? and the announcement that live bacteria were found in a 30,000-year-old chunk of Alaskan ice ? is fueling discussion about the possibility of past, even present, life on Mars. In a poll taken at a European Space Agency conference last month, 75 percent of scientists believe bacteria once existed on Mars and 25 percent believe it might still survive there.

Head recently traveled to Antarctica to study glaciers, including bacteria that can withstand the continent?s dry, cold conditions. The average temperature on Mars is estimated to be 67 degrees below freezing. Similar temperatures are clocked in Antarctica?s frigid interior.

?We?re now seeing geological characteristics on Mars that could be related to life,? Head said. ?But we?re a long way from knowing that life does indeed exist. The glacial deposits we studied would be accessible for sampling in future space missions. If we had ice to study, we would know a lot more about climate change on Mars and whether life is a possibility there.?

The European Space Agency, the German Aerospace Center and the Freie Universitaet in Berlin built and flew the HRSC and processed data from the camera. The National Aeronautics and Space Administration (NASA) supported Head?s work.

Original Source: Brown University

Posted on by Fraser Cain

Problem with Opportunity’s Mineral Finding Tool

Image credit: NASA/JPL
NASA has suspended use of one of the mineral-identifying tools on the Opportunity Mars rover while experts troubleshoot a problem with getting data from the instrument, the robot’s miniature thermal emission spectrometer.

“As always, our first priority is to protect the instrument, so we have turned it off while we plan diagnostic tests,” said Jim Erickson of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., project manager for the Mars Exploration Rover Project. “Opportunity’s other instruments are healthy and providing excellent science, and Spirit’s entire instrument suite is working well and being kept busy by the science team.”

Both Opportunity and Spirit, its twin, have been examining Mars since January 2004, more than four times as long as their successful three-month primary missions. While researchers work to diagnose the spectrometer-data problem and seek the best way to mend it or work around it, Opportunity is continuing its journey and observing a crater called “Vostok.” On the other side of the planet, meanwhile, martian winds have revealed themselves as dust devils in new images from Spirit and caused mixed effects on the rover itself, depositing dust on a camera and removing dust from solar panels.

On March 3 and 4, Opportunity transmitted data sets for 17 successful readings by its miniature thermal emission spectrometer but also reported that eight other attempted readings yielded incomplete data sets. This spectrometer, from high on the rover’s mast, observes rocks and other targets from afar. It measures the infrared radiation they emit in 167 different wavelengths, providing information about the targets’ composition. Two other types of spectrometers, mounted on the rover’s robotic arm, provide additional information about composition when the rover is close enough to touch the target.

Researchers are considering several possible root causes for the spectrometer-data problem. One possibility is malfunctioning of an optical switch that tells a mirror in the instrument when to begin moving. Another is that the mirror is not properly moving at a constant velocity. “If it is the optical switch, we could use a redundant one built into the instrument,” said Dr. Phil Christensen of Arizona State University, Tempe, lead scientist for the miniature thermal emission spectrometers on both rovers. He added that, if the root cause cannot be remedied, scientists could still get useful data from the instrument in its currently impaired condition.

Even a total loss of the miniature thermal emission spectrometer would not end the rover’s usefulness. In fact, NASA took a calculated risk by disabling this instrument on Opportunity 10 months ago, though the current problem appears unrelated to potential damage anticipated then. At that time, rover operators began using a “deep sleep” technique to conserve energy on Opportunity during reduced-sunshine months of Mars’ winter. Turning off power to overnight heaters let the instrument get cold enough to possibly damage its beam-splitter. However, the spectrometer kept working through the coldest months. Christensen said, “What we’re seeing now does not appear to be any problem with the beam-splitter.”

The rover team is not restricting use of Spirit’s miniature thermal emission spectrometer while troubleshooting the problem on Opportunity.

Spirit’s work capabilities grew with a sudden jump in output from solar panels on March 9, which caused the daily power supply to double. In a possibly related development three days earlier, some dust appeared to have blown onto lenses of Spirit’s front hazard-avoidance camera, enough for slight mottling in images from both the left and right eyes of the stereo camera, but not enough to affect the usefulness of the camera. Mottling in left-eye images cleared markedly the same day the power increased. Team members speculated that Spirit’s power boost, like similar ones on Opportunity in October, resulted from wind removing some accumulated dust from solar panels. Spirit captured pictures of dust-lofting whirlwinds on March 10, adding evidence for windy local conditions. Images the next day showed solar panels cleaned of most of their dust buildup.

Opportunity’s rear hazard-avoidance camera picked up some dust contamination three months ago. The dust on it has not affected operations and has neither decreased nor increased perceptibly since first noticed. No dust has contaminated lenses of the navigation cameras or panoramic cameras on either rover. From all cameras combined, the rovers have returned more than 72,000 images. Images and other geological data from Spirit and Opportunity are successfully providing unprecedented evidence about wet environmental conditions in Mars’ past.

JPL, a division of the California Institute of Technology in Pasadena, has managed NASA’s 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 http://marsrovers.jpl.nasa.gov.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Dark Energy in our Galactic Neighbourhood

Astrophysicists in recent years have found evidence for a force they call dark energy in observations from the farthest reaches of the universe, billions of light years away.

Now an international team of researchers has used data from powerful computer models, supported by observations from the Hubble Space Telescope, to find evidence of dark energy right in our own cosmic neighborhood.

The data paint a picture of the universe as a virtual sea of dark energy, with billions of galaxies as islands emerging from the sea, said Fabio Governato, a University of Washington research associate professor of astronomy and a researcher with Italy’s National Institute for Astrophysics.

In 1929 astronomer Edwin Hubble demonstrated that galaxies are moving away from each other, which supported the theory that the universe has been expanding since the big bang. In 1999 cosmologists reported evidence that an unusual force, called dark energy, was actually causing the expansion of the universe to accelerate.

However, the expansion is slower than it would be otherwise because of the tug of gravity among galaxies. As the battle between the attraction of gravity and the repellent force of dark energy plays out, cosmologists are left to ponder whether the expansion will continue forever or if the universe will collapse in a “big crunch.”

In 1997, Governato designed a computer model to simulate evolution of the universe from the big bang until the present. His research group found the model could not duplicate the smooth expansion that had been observed among galaxies around the Milky Way, the galaxy in which Earth resides. In fact, the model produced deviations from a purely radial expansion that were three to seven times higher than astronomers had actually observed, Governato said.

“The observed motion was small, and we could not duplicate it without the presence of dark energy,” he said. “When we added the dark energy, we got a perfect match.”

Governato is one of three authors of a paper describing the work, scheduled for publication in the Monthly Notices of the Royal Astronomical Society, an astronomy journal in the United Kingdom. Co-authors are Andrea Maccio of the University of Zurich in Switzerland and Cathy Horellou of Chalmers University of Technology in Sweden. The work was supported by grants from the National Science Foundation and Vetenskapsr?det, the Swedish Research Council.

The authors, part of an international research collaboration called the N-Body Shop that originated at the UW, ran simulations of universe expansion on powerful supercomputers in Italy and Alaska. Their findings provide supporting evidence for a sea of dark energy surrounding galaxies.

“We studied the properties of galaxies close to the Milky Way instead of looking billions of light years away,” Governato said. “It’s like traveling from Seattle to Portland, Ore., rather than from Seattle to New York, to measure the Earth’s curvature.”

Original Source: University of Washington News Release

Posted on by Fraser Cain

Enceladus has an Atmosphere

Image credit: NASA/JPL/SSI
The Cassini spacecraft’s two close flybys of Saturn’s icy moon Enceladus have revealed that the moon has a significant atmosphere. Scientists, using Cassini’s magnetometer instrument for their studies, say the source may be volcanism, geysers, or gases escaping from the surface or the interior.

When Cassini had its first encounter with Enceladus on Feb. 17 at an altitude of 1,167 kilometers (725 miles), the magnetometer instrument saw a striking signature in the magnetic field. On March 9, Cassini approached to within 500 kilometers (310 miles) of Enceladus’ surface and obtained additional evidence.

The observations showed a bending of the magnetic field, with the magnetospheric plasma being slowed and deflected by the moon. In addition, magnetic field oscillations were observed. These are caused when electrically charged (or ionized) molecules interact with the magnetic field by spiraling around the field line. This interaction creates characteristic oscillations in the magnetic field at frequencies that can be used to identify the molecule. The observations from the Enceladus flybys are believed to be due to ionized water vapor.

“These new results from Cassini may be the first evidence of gases originating either from the surface or possibly from the interior of Enceladus,” said Dr. Michele Dougherty, principal investigator for the Cassini magnetometer and professor at Imperial College in London. In 1981, NASA’s Voyager spacecraft flew by Enceladus at a distance of 90,000 kilometers (56,000 miles) without detecting an atmosphere. It’s possible detection was beyond Voyager’s capabilities, or something may have changed since that flyby.

This is the first time since Cassini arrived in orbit around Saturn last summer that an atmosphere has been detected around a moon of Saturn, other than its largest moon, Titan. Enceladus is a relatively small moon. The amount of gravity it exerts is not enough to hold an atmosphere very long. Therefore, at Enceladus, a strong continuous source is required to maintain the atmosphere.

The need for such a strong source leads scientists to consider eruptions, such as volcanoes and geysers. If such eruptions are present, Enceladus would join two other such active moons, Io at Jupiter and Triton at Neptune. “Enceladus could be Saturn’s more benign counterpart to Jupiter’s dramatic Io,” said Dr. Fritz Neubauer, co-investigator for the Cassini magnetometer, and a professor at the University of Cologne in Germany.

Since the Voyager flyby, scientists have suspected that this moon is geologically active and is the source of Saturn’s icy E ring. Enceladus is the most reflective object in the solar system, reflecting about 90 percent of the sunlight that hits it. If Enceladus does have ice volcanoes, the high reflectivity of the moon’s surface might result from continuous deposition of icy particles originating from the volcanoes.

Enceladus’ diameter is about 500 kilometers (310 miles), which would fit in the state of Arizona. Yet despite its small size, Enceladus exhibits one of the most interesting surfaces of all the icy satellites.

For images and information on the Cassini mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.

Original Source: NASA/JPL News Release