The Solar System - 4 Billion Miles Out and 32 deg Above The Eliptic

The cameras of Voyager 1 on Feb. 14, 1990, pointed back toward the sun and took a series of pictures of the sun and the planets, making the first ever "portrait" of our solar system as seen from the outside. In the course of taking this mosaic consisting of a total of 60 frames, Voyager 1 made several images of the inner solar system from a distance of approximately 4 billion miles and about 32 degrees above the ecliptic plane. Thirty-nine wide angle frames link together six of the planets of our solar system in this mosaic. Outermost Neptune is 30 times further from the sun than Earth. Our sun is seen as the bright object in the center of the circle of frames. The wide-angle image of the sun was taken with the camera's darkest filter (a methane absorption band) and the shortest possible exposure (5 thousandths of a second) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large as seen from Voyager, only about one-fortieth of the diameter as seen from Earth, but is still almost 8 million times brighter than the brightest star in Earth's sky, Sirius. The result of this great brightness is an image with multiple reflections from the optics in the camera. Wide-angle images surrounding the sun also show many artifacts attributable to scattered light in the optics. These were taken through the clear filter with one second exposures. The insets show the planets magnified many times. Narrow-angle images of Earth, Venus, Jupiter, Saturn, Uranus and Neptune were acquired as the spacecraft built the wide-angle mosaic. Jupiter is larger than a narrow-angle pixel and is clearly resolved, as is Saturn with its rings. Uranus and Neptune appear larger than they really are because of image smear due to spacecraft motion during the long (15 second) exposures. From Voyager's great distance Earth and Venus are mere points of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun.

Layers in a Mars Crater Record a History of Changes

February 11, 2010

PASADENA, Calif. -- Near the center of a Martian crater about the size of Connecticut, hundreds of exposed rock layers form a mound as tall as the Rockies and reveal a record of major environmental changes on Mars billions of years ago.

The history told by this tall parfait of layers inside Gale Crater matches what has been proposed in recent years as the dominant planet-wide pattern for early Mars, according to a new report by geologists using instruments on NASA's Mars Reconnaissance Orbiter.

"Looking at the layers from the bottom to the top, from the oldest to the youngest, you see a sequence of changing rocks that resulted from changes in environmental conditions through time," said Ralph Milliken of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This thick sequence of rocks appears to be showing different steps in the drying-out of Mars."

Using geological layers to understand stages in the evolution of a planet's climate has a precedent on Earth. A change about 1.8 billion years ago in the types of rock layers formed on Earth became a key to understanding a dramatic change in Earth's ancient atmosphere.

Milliken and two co-authors report in Geophysical Research Letters that clay minerals, which form under very wet conditions, are concentrated in layers near the bottom of the Gale stack. Above that, sulfate minerals are intermixed with the clays. Sulfates form in wet conditions and can be deposited when the water in which they are dissolved evaporates. Higher still are sulfate-containing layers without detectable clays. And at the top is a thick formation of regularly spaced layers bearing no detectable water-related minerals.

Rock exposures with compositions like various layers of the Gale stack have been mapped elsewhere on Mars, and researchers, including Jean-Pierre Bibring of the University of Paris, have proposed a Martian planetary chronology of clay-producing conditions followed by sulfate-producing conditions followed by dry conditions. However, Gale is the first location where a single series of layers has been found to contain these clues in a clearly defined sequence from older rocks to younger rocks.

"If you could stand there, you would see this beautiful formation of Martian sediments laid down in the past, a stratigraphic section that's more than twice the height of the Grand Canyon, though not as steep," said Bradley Thomson of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. He and John Grotzinger of the California Institute of Technology in Pasadena are Milliken's co-authors.

NASA selected Gale Crater in 2008 as one of four finalist sites for the Mars Science Laboratory rover, Curiosity, which has a planned launch in 2011. The finalist sites all have exposures of water-related minerals, and each has attributes that distinguish it from the others. This new report is an example of how observations made for evaluating the landing-site candidates are providing valuable science results even before the rover mission launches.

Three instruments on NASA's Mars Reconnaissance Orbiter have provided key data about the layered mound in Gale Crater. Images from the High Resolution Imaging Science Experiment camera reveal details used to map hundreds of layers. Using stereo pairs of the images, the U.S. Geological Survey has generated three-dimensional models used to discern elevation differences as small as a meter (about a yard). Observations by the Compact Reconnaissance Imaging Spectrometer for Mars yielded information about minerals on the surface. The Context Camera provided broader-scale images showing how the layers fit geologically into their surroundings.

Thomson said, "This work demonstrates the synergy of the instruments on the Mars Reconnaissance Orbiter. We wouldn't have as complete a picture if we were missing any of the components."

The mission has been studying Mars since 2006. It has returned more data from the planet than all other Mars missions combined. More information about this mission is at http://www.nasa.gov/mro.

Dwarf Galaxies Provide Clues to Early Star Formation in Universe

An astronomer at Lowell Observatory studies how stars form in tiny, "dwarf" galaxies, which may provide insight into the birth of the first starts after the Big Bang. Here, a color-enhanced optical image of the galaxy DDO 87 in the constellation Ursa Major that shows the stars. Credit: Lowell Observatory.

Full Story..........

When you picture a galaxy in your mind's eye, it's often a spiral with magnificent structure — long, swirling, milky-white arms of stars and gas.
Lowell Observatory astronomer Deidre Hunter has spent most the last 17 years methodically studying unfamiliar galaxies that you might not expect — small, diffuse galaxies: the dwarf irregulars — to learn all she can about star formation and what it can tell her and her colleagues about the birth of the first stars after the Big Bang.

In an NSF-funded project called LITTLE THINGS — for Local Irregulars That Trace Luminosity Extremes (LITTLE) and The HI Nearby Galaxy Survey (THINGS) — Hunter's team is mapping the gasses in these diffuse, enigmatic galaxies to discern the many processes of star formation.

The LITTLE THINGS team is closely studying 41 dwarf-irregular galaxies through the lens of numerous data sets. And the galaxies are small, relatively speaking. One, DDO 75, has 1/3500 the mass of the Milky Way. Another, Leo T, was recently discovered in the Local Group of galaxies, the closest neighbors to our own Milky Way.

"Leo T is comparable in brightness to a large star cluster that contains several million stars; in contrast, the Milky Way contains about 300 billion stars," Hunter said. Some of the galaxies in our sample area are not much brighter than a large star cluster."

The process of star formation is very inefficient. Some 50 to 90 percent of the gas present in star-forming molecular clouds, including the gas in the tiny irregular galaxies, remains after stars form.
"This produces the nebulae," Hunter said. "They are like signposts that say, 'massive stars are found here.' In a general sense it's like weather clouds on Earth. You need these molecular clouds that form out of the ubiquitous atomic hydrogen gas to precipitate stars."
Hunter added that there are probably multiple processes going on, which adds to the complexity and time-intensive nature of the LITTLE THINGS study. In the dwarf galaxies, there's star-induced star formation. There's also turbulence. "It's not just density, but also the motions of the gas," Hunter says.

The data sets Hunter and her colleagues are using include optical-wavelength data Hunter already collected and analyzed using research telescopes at Lowell’s Anderson Mesa facility near Flagstaff. But some of the new, key data is in radio wavelengths, and they come from NSF's Very Large Array (VLA) located west of Socorro, New Mexico.
In May of 2007, Hunter was invited to give a talk at the VLA. Afterwards, a scientist with the facility suggested she put in a large proposal, that is, a proposal for a large amount of VLA telescope time. She and her team had been unsuccessful in previous smaller requests for the needed hours, but this time, the team was rewarded: about 400 hours to study a subsample of dwarf galaxies that represent a range of characteristics.
One of Hunter's collaborators, Lowell predoctoral student Megan Jackson, is looking at the motions of the stars, their velocities, and their rotation. Fellow Lowell predoc Hongxin Zhang is looking closely at existing ultraviolet and optical data sets from the galaxies, helping define their star-formation histories.

Zhang has been limited with his current sets of infrared data, so he is embarking on an observing program using a special instrument called Mimir attached to the 1.8-meter Perkins Telescope at Anderson Mesa, also at Lowell. The Perkins is operated through a partnership with Boston University, and Mimir is a powerful, $2.5-millon infrared instrument built by a team led by Dan Clemens of Boston University.
As for the massive amount of VLA radio data, much has to be collected, sorted, and analyzed. Kim Herrmann, a Lowell Observatory postdoctoral fellow, is part of the LITTLE THINGS team and she is reducing the VLA data.
"When Kim came to Flagstaff, she had never dealt with radio interferometric data," Hunter said. "But she quickly came up to speed and has now become a local expert. She has calibrated more LITTLE THINGS data than any other person on the team, and she is exactly the kind of person we need on the team. Right now, we're in this grunge phase of the project; it is very tedious. If all goes well, and I'm not distracted by other tasks, it takes me one month per galaxy to reduce the VLA data."
The extensive data are poised to re-shape astronomers' understanding of star formation. "The crux of the problem is that the standard models for galaxies don't work for dwarfs. Dwarfs should not be forming stars at all."

But indeed they are. They are forming stars even at their outer edges. The little-understood portions of dwarf irregular galaxies are what intrigue Hunter most of all.
"It's the outer disks — because they are so extreme," she said. "These are such extreme environments that they are very stringent tests for star formation."

Small Ground-Based Telescope Detects Exo-Planet Atmosphere

February 03, 2010


NASA astronomers have successfully demonstrated that a David of a telescope can tackle Goliath-size questions in the quest to study Earth-like planets around other stars. Their work, reported today in the journal Nature, provides a new tool for ground-based observatories, promising to accelerate by years the search for prebiotic, or life-related, molecules on planets orbiting stars beyond our solar system.

The scientists reported on a new technique used with a relatively small Earth-based telescope to identify an organic molecule in the atmosphere of a Jupiter-size planet nearly 63 light-years away. The measurement revealed details of the exoplanet's atmospheric composition and conditions, an unprecedented achievement from an Earth-based observatory.

The surprising new finding comes from a venerable 30-year-old, 3-meter-diameter (10-foot) telescope that ranks 40th among ground-based telescopes - NASA's Infrared Telescope Facility atop Mauna Kea, Hawaii.

The new technique promises to further speed the work of studying planet atmospheres by enabling studies from the ground that were previously possible only through a few very high-performance space telescopes. "Given favorable observing conditions, this work suggests we may be able to detect organic molecules in the atmospheres of terrestrial planets with existing instruments," said lead author Mark Swain, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. This can allow fast and economical advances in focused studies of exoplanet atmospheres, accelerating our understanding of the growing stable of exoplanets.

"The fact that we have used a relatively small, ground-based telescope is exciting because it implies that the largest telescopes on the ground, using this technique, may be able to characterize terrestrial exoplanet targets," Swain said.

Currently, more than 400 exoplanets are known. Most are gaseous like Jupiter, but some "super-Earths" are thought to be large terrestrial, or rocky, worlds. A true Earth-like planet, with the same size as our planet and distance from its star, has yet to be discovered. NASA's Kepler mission is searching from space now, and is expected to find several of these earthly worlds by the end of its three-and-a-half-year prime mission.

On Aug. 11, 2007, Swain and his team turned the infrared telescope to the hot, Jupiter-size planet HD 189733b in the constellation Vulpecula. Every 2.2 days, the planet orbits a K-type main sequence star slightly cooler and smaller than our sun. HD189733b had already yielded breakthrough advances in exoplanet science, including detections of water vapor, methane and carbon dioxide, using space telescopes. Using the new technique, the astronomers successfully detected carbon dioxide and methane in the atmosphere of HD 189733b with a spectrograph, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Their key work was development of a novel calibration method to remove systematic observation errors caused by the variability of Earth's atmosphere and instability due to the movement of the telescope system as it tracks its target.

"As a consequence of this work, we now have the exciting prospect that other suitably equipped yet relatively small ground-based telescopes should be capable of characterizing exoplanets," said John Rayner, the NASA Infrared Telescope Facility support scientist who built the SpeX spectrograph used for these measurements. "On some days we can't even see the sun with the telescope, and the fact that on other days we can now obtain a spectrum of an exoplanet 63 light-years away is astonishing."

In the course of their observations, the team found unexpected bright infrared emission from methane that stands out on the day side of HD189733b, indicating some kind of activity in the planet's atmosphere. Swain said this puzzling feature could be related to the effect of ultraviolet radiation from the planet's parent star hitting the planet's upper atmosphere, but more detailed study is needed. "This feature indicates the surprises that await us as we study exoplanet atmospheres," he added.

"An immediate goal for using this technique is to more fully characterize the atmosphere of this and other exoplanets, including detection of organic and possibly prebiotic molecules" like those that preceded the evolution of life on Earth, said Swain. "We're ready to undertake that task." Some early targets will be the super-Earths. Used in synergy with observations from NASA's Hubble, Spitzer and the future James Webb Space Telescope, the new technique "will give us an absolutely brilliant way to characterize super-Earths," Swain said.

Cassini Captures Ghostly Dance Of Saturn's Northern Lights

Go to this page to see video Saturn "Northern Lights"

November 24, 2009


PASADENA, Calif. – In the first video showing the auroras above the northern latitudes of Saturn, Cassini has spotted the tallest known "northern lights" in the solar system, flickering in shape and brightness high above the ringed planet.

The new video reveals changes in Saturn's aurora every few minutes, in high resolution, with three dimensions. The images show a previously unseen vertical profile to the auroras, which ripple in the video like tall curtains. These curtains reach more than 1,200 kilometers (750 miles) above the edge of the planet's northern hemisphere.

The new video and still images are online at: http://www.nasa.gov/cassini , http://saturn.jpl.nasa.gov and http://ciclops.org .

Auroras occur on Earth, Jupiter, Saturn and a few other planets, and the new images will help scientists better understand how they are generated.

"The auroras have put on a dazzling show, shape-shifting rapidly and exposing curtains that we suspected were there, but hadn't seen on Saturn before," said Andrew Ingersoll of the California Institute of Technology in Pasadena, who is a member of the Cassini imaging team that processed the new video. "Seeing these things on another planet helps us understand them a little better when we see them on Earth."

Auroras appear mostly in the high latitudes near a planet's magnetic poles. When charged particles from the magnetosphere -- the magnetic bubble surrounding a planet -- plunge into the planet's upper atmosphere, they cause the atmosphere to glow. The curtain shapes show the paths that these charged particles take as they flow along the lines of the magnetic field between the magnetosphere and the uppermost part of the atmosphere.

The height of the curtains on Saturn exposes a key difference between Saturn's atmosphere and our own, Ingersoll said. While Earth's atmosphere has a lot of oxygen and nitrogen, Saturn's atmosphere is composed primarily of hydrogen. Because hydrogen is very light, the atmosphere and auroras reach far out from Saturn. Earth's auroras tend to flare only about 100 to 500 kilometers (60 to 300 miles) above the surface.

The speed of the auroral changes in the video is comparable to some of those on Earth, but scientists are still working to understand the processes that produce these rapid changes. The height will also help them learn how much energy is required to light up auroras.

"I was wowed when I saw these images and the curtain," said Tamas Gombosi of the University of Michigan in Ann Arbor, who chairs Cassini's magnetosphere and plasma science working group. "Put this together with the other data Cassini has collected on the auroras so far, and you really get a new science."

Ultraviolet and infrared instruments on Cassini have captured images of and data from Saturn's auroras before, but in these latest images, Cassini's narrow-angle camera was able to capture the northern lights in the visible part of the light spectrum, in higher resolution. The movie was assembled from nearly 500 still pictures spanning 81 hours between Oct. 5 and Oct. 8, 2009. Each picture had an exposure time of two or three minutes. The camera shot pictures from the night side of Saturn.

The images were originally obtained in black and white, and the imaging team highlighted the auroras in false-color orange. The oxygen and nitrogen in Earth's upper atmosphere contribute to the colorful flashes of green, red and even purple in our auroras. But scientists are still working to determine the true color of the auroras at Saturn, whose atmosphere lacks those chemicals.

Beautiful first set of pictures from WISE.

Click Here for full press release.

Methane Glows in Exo-planet's Atmosphere

(Note - Methane in the atmosphere is a good indicator of life)

The glow of methane has been detected in the atmosphere of Jupiter-sized alien planet orbiting close to its parent star.

Because the signature of glowing methane, which might be triggered in a similar way to Earth's auroras, is so strong, it could help scientists better understand the atmospheres of exoplanets, if it turns out to be a common feature among them.

The detection was also made from a ground-based telescope and not space-based one, suggesting that many more detailed measurements of exoplanet atmospheres will be made in the coming years, possibly even the signatures of biological activity, researchers said.

Methane is belched out by certain kinds of microbes on Earth (as well as by big animals, such as cows), and scientists think this is one form that potential alien life could take. (Methane is also created through geophysical and chemical processes on Earth that have nothing to do with life.)

"That's not where we are today, but that's where we're going," said Mark Swain of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who led the team that made the methane discovery.

Glowing methane

Scientists detected this particular signature of methane in the atmosphere of an extrasolar planet dubbed HD 189733b, which was one of the first exoplanets to have its atmosphere "sniffed" my spectrometers, which measure the range of light given off by a particular object and show the light signatures that are peculiar to different elements and molecules.

Water vapor, carbon dioxide, and methane have already been detected in HD 189733b's atmosphere, though that first methane detection had a different signature than the new one.

The new detection seems to be from the fluorescence of methane in the atmosphere of the planet. (An Earth analogue to this phenomenon would be something like the aurora borealis, Swain said.)

The finding, detailed in the Feb. 4 issue of the journal Nature, was unexpected if not a total surprise, as similar signatures have been seen in the atmospheres of bodies in our own solar system.

"It's not particularly surprising since we have seen fluorescent methane in Jupiter, Saturn and even Titan," said Seth Redfield of Wesleyan University in Middletown, Conn., who was not involved with the finding, but has previously made detections of sodium in the same exoplanet's atmosphere. Redfield wrote an opinion article about the new discovery in the same issue of Nature.

Understanding atmospheres

For the atmospheric signatures collected for exoplanets so far, astronomers have assumed that heat is what is causing the emission of various atmospheric constituents, as most are so-called hot Jupiters, which orbit very close to their stars and are bathed in large amounts of stellar radiation.

But heat can't explain the fluorescence of methane. "The light is being generated by something other than heat," Swain told SPACE.com.

But the energy source driving the emission is still a mystery.

"We don't know the answer for that today," Swain said, but he added that two possible sources where collisions with photons or charged particles from the stellar wind. The solar wind from our sun is not known to cause methane fluorescence in any planets in our solar system.

But the fluorescence does tell astronomers something about the atmosphere of the planet: that the part where the fluorescence is happening is likely "very tenuous layers in the atmosphere of the planet," Swain said.

This is because fluorescence is what in physics is called a non-locally thermodynamic equilibrium process.

So in an atmosphere that is in locally thermodynamic equilibrium, energy moves between particles primarily through collisions – this can happen because the atmosphere is thick and the molecules are relatively close together. This is the case in the lower portions of Earth's atmosphere.

But when the atmosphere thins out, its molecules can become far enough apart that the time between collisions is long enough that energy can get to molecules through other means. A similar process occurs in the upper portions of Earth's atmosphere, where things like the solar wind can collide with particles — this is what creates the auroras that flash over Earth's poles.

So it's possible that the signature of methane fluorescence from HD 189733b is coming from a different part of the atmosphere than the previous methane signature, though Swain cautions that it will take more observations and new atmospheric models to really characterize the exoplanet's atmosphere.

Future detections

Swain and his team are already at work looking for this fluorescent signature in other exoplanets. If it turns out to be a common feature, "it could change how detectable these exoplanets are," because the signature is strong and unique, Swain said.

Redfield said the finding is exciting because it adds to the list of known exoplanet atmospheric components, which are building up at a time when "we're just getting use to finding exoplanets." In a decade, exoplanet atmosphere detections will likely be as routine as exoplanet detections now are, he said.

Making more detections of methane in particular could be helpful because it can be a by-product of biological processes. Building a better understanding of what kinds of methane are out there and where in exoplanet atmospheres the gas occurs could help scientists determine which signatures are most likely to be related to alien biology.

"This is one step on a much longer journey," Redfield said.

The finding is also exciting, both Swain and Redfield said, because it was made with a relatively modest-sized ground-based telescope, NASA's Infrared Telescope Facility (IRTF) in Hawaii, whereas most other atmospheric detections were made with space-based telescopes, such as Hubble and the Spitzer Space Telescope.

The detections of atmospheres from the Earth's surface can only be made in particular wavelengths of light that aren't absorbed or scattered by the Earth's atmosphere, but ground-based detections are an important complement to space-based ones because ground-based telescopes are much bigger — while Hubble is 2.4-m telescope, the Keck telescopes (also in Hawaii) are 10 meters in diameter. This means that atmospheres could be observed with more detail or at fainter objects.

This capability "is going to prove really, really critical to understanding these exoplanet atmospheres," Redfield said.

Swain already has plans to use some bigger Earth-based telescopes in the future.

Solar Eclipse Seen From Space

http://www.space.com/common/media/video/player.php?videoRef=SP_100129_solar-eclipse-from-space

Slam! Two Asteroids Suspected in Space Collision

A mysterious trail of debris spotted in space suggests two asteroids recently slammed into each other.

Though such space rock collisions are thought to be common, direct evidence of the cosmic smashups has never been seen before. New images from NASA's Hubble Space Telescope, however, have caught the suspected collision on camera.

An X-shaped debris pattern was observed by Hubble on Jan. 25 and 29. The pictures, released today, show a comet-like object, dubbed P/2010 A2, with the X-pattern of filamentary structures near the nucleus.

"This is quite different from the smooth dust envelopes of normal comets," said study leader David Jewitt of the University of California at Los Angeles. "The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies."

The two asteroids likely smashed into each other with an average impact speed of more than 11,000 miles per hour, or five times faster than a rifle bullet.

The Hubble photos show that the main nucleus of P/2010 A2 lies outside its own halo of dust. This pattern has never been seen before in a comet-like object. The nucleus is estimated to be about 460 feet (140 meters) in diameter.

Scientists think this nucleus is the surviving remnant of the collision, and the tail is the rubble left over from the crash.

"If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight," Jewitt said.

P/2010 A2 orbits in the warm, inner regions of the asteroid belt between Mars and Jupiter. When the object was observed, it was approximately 180 million miles (290 million km) from the sun and 90 million miles (145 million km) from Earth.

The Hubble images were captured by its new Wide Field Camera 3, which was installed during the May 2009 space shuttle servicing trip. The camera can spot house-sized fragments at the distance of the asteroid belt

A Star is Born in Nearby Cosmic Nursery

A new panorama of a cosmic nebula offers an up-close glimpse of baby stars being born.

The nebula, dubbed NGC 3603, is called a starburst region because stars are coming into being in feverish bursts of activity. It lies about 22,000 light-years away from the sun, making it the closest region of the kind known in our galaxy. This near view offers astronomers a relatively local test bed for studying intense star formation processes that are usually hard to observe in detail because of their great distance from us.

The new view was captured by the European Southern Observatory's Very Large Telescope in the Atacama desert of Chile. The cosmic panorama displays the rich texture of the surrounding clouds of gas and dust in the area, with many of the hot newborn stars dotting the scene with blue light.

This nebula is also home to the most massive star ever to be "weighed" so far. This behemoth, part of a binary system called A1, is estimated to be roughly 116 times the mass of the sun.

NGC 3603 owes its shape to the intense light and winds coming from the young, massive stars that push out against the curtains of gas and clouds. The central cluster of stars inside the nebula harbors thousands of stars of all sorts: the majority have masses similar to or less than that of our sun, but most spectacular are several of the very massive stars that are close to the end of their lives.

Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars — extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae

This image shows the galaxy density in the COSMOS field surveyed by the Hubble Space Telescope, with colors representing the distance of the galaxies. The X-ray contours (in pink) show the extended X-ray emission as observed by the XMM-Newton spacecraft. Credit: ESA


To weigh the universe, scientists use two kinds of cosmic scales: one to measure all the regular matter out there, and another to deduce how much invisible dark matter remains hidden underneath.

These calculations have been taken further than ever before by a new study that tallied both types of mass in smaller and more distant groups of galaxies than any previous projects. The project found that these faraway galactic clusters have roughly the same proportion of dark matter to regular matter as the closer galaxy groups do.

The findings could help astronomers understand more about dark matter, as well as its even stranger sibling – dark energy.

Invisible universe

Dark matter is a form of stuff that does not interact with light, so cannot be seen, but makes its presence felt by exerting a gravitational pull on normal matter.

Astronomers measure how much dark matter lies in galaxies by a fluke of physics called gravitational lensing. This phenomenon, predicted by Einstein's theory of general relativity, causes light to curve as it flies through space-time that has been dented by the gravity of large bodies of mass.

For example, groups of massive galaxies will gravitationally warp the space-time around them, forcing light to bend as it passes through, and causing them to look distorted when their light reaches our telescopes. Scientists can tell how much total mass there is by how much of this distortion occurs.

Next, researchers calculate how much normal matter is in a cluster of galaxies by looking at its X-ray light, since the light must be coming from only the regular stars and gas that make up the cluster.

Comparing these two calculations — the total matter to just the regular matter — gives a ratio astronomers call the mass-luminosity relation. So far, the mass-luminosity relation has been measured well for nearby, large galaxy clusters, but there has not been good enough X-ray data to probe farther or smaller, dimmer clusters of galaxies.

"We can map out the big cities, but no one's been able to map out the villages yet," said Alexie Leauthaud of the Lawrence Berkeley National Laboratory in Berkeley, Calif., leader of the new study.

New ranges

Astronomers used observations from the European Space Agency's XMM-Newton satellite and from NASA's Chandra satellite, as well as data from the Hubble Space Telescope's Cosmic Evolution Survey (COSMOS). These ultra-high resolution photos allowed the scientists to extend the mass-luminosity relation further than ever before.

With such dim objects, the gravitational lensing wasn't immediately apparent. So researchers used a statistical analysis to measure the orientation and shape of the galaxies to find small distortions due to so-called weak lensing.

They found that the same general ratio of dark matter to normal matter prevailed in these distant, small clusters as for nearby, larger clusters.

"We didn't know what to expect going down to lower masses or [farther distances], and we find this nice simple relationship," Leauthaud told SPACE.com. "Now the aim is to find out why we find this nice, simple relationship."

Dark energy enigma

The finding may help shed light on an even more bizarre aspect of the universe — dark energy. Dark energy is the name given to whatever mysterious force is causing the universe to accelerate as it expands.

"We want to try to understand the properties of dark energy," Leauthaud said. "One way to measure properties of dark energy is to measure the number of structures that have formed for a given amount of dark matter."

Dark energy basically works against gravity in a tug-of-war. While gravity constantly pulls mass inward, encouraging things to clump together and condense into smaller space, dark energy does the opposite. This force somehow pulls everything apart, causing everything in the universe to move away from everything else at ever-increasing speeds.

When mass clumps together enough to form galaxies, it means that gravity has won on those scales, helping things to stick together despite the pull of dark energy. So the more astronomers can measure when and how structures formed in the universe, the better they can understand just how far dark energy's pull reaches

Weird Rock Offers Glimpse Deep Inside Mars

NASA's Opportunity rover has discovered a peculiar rock on Mars that scientists think originated deep within the red planet.

The stone could reveal new secrets about the makeup of Mars' interior.

Dubbed "Marquette Island," the rock is a dark boulder not much bigger than a basketball that sits on a rippled Martian plain.

"Marquette Island is different in composition and character from any known rock on Mars or meteorite from Mars," said Opportunity principal investigator Steve Squyres of Cornell University in Ithaca, N.Y. "It is one of the coolest things Opportunity has found in a very long time."

Opportunity and its twin rover, Spirit, landed on Mars in 2004, and have drastically outlived their original 90-day mission plan. While Spirit is currently stuck in a sand trap with two broken wheels, Opportunity is still roving free.

In all of its 11 miles worth of traveling, Opportunity has found only one other rock of comparable size to Marquette Island and scientists think it was ejected from a distant crater. Called "Bounce Rock," that stone closely matched the composition of a meteorite that landed on Earth, but was thought to have originated on Mars.

The coarse-grained texture and basalt composition of Marquette Island indicates that it cooled slowly from molten rock, allowing crystals time to grow. That means that it likely originated deep in the crust, not at the surface where it would cool quicker and have finer-grained texture, scientists say.

"It is from deep in the crust and someplace far away on Mars, though exactly how deep and how far we can't yet estimate," Squyres said.

In contrast, most Martian basalt rocks that Spirit and Opportunity have encountered have different textures and composition.

At first, scientists thought Marquette Island could be a meteorite, but it appears to have a much lower nickel content than other meteorites Opportunity has found. And Marquette Island's interior contains more magnesium than typical Martian basalt rocks.

"It's like having a fragment from another landing site," said Ralf Gellert of the University of Guelph, in Ontario, Canada. Gellert is lead scientist for the alpha particle X-ray spectrometer on Opportunity's robotic arm. "With analysis at an early stage, we're still working on some riddles about this rock."

The rover team used Opportunity's rock abrasion tool to grind away some of Marquette Island's weathered surface and expose the interior.

This was the 38th rock target Opportunity has ground into, and one of the hardest. The tool was designed to grind into only one Martian rock, and this rock may not be its last.

"We took a conservative approach on our target depth for this grind to ensure we will have enough of the bit left to grind the next hard rock that Opportunity comes across," said Joanna Cohen of Honeybee Robotics Spacecraft Mechanisms Corp., in New York, which built and operates the tool.

While Marquette Island is intriguing, Opportunity couldn't stop too long to investigate — it left the site Jan. 12. The rover is mid-way on a journey toward a much larger crater, Endeavour, that scientists think will offer a host of scientific prospects.

"We're on the road again," said Mike Seibert, a rover mission manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The year ahead will include lots more driving, if all goes well. We'll keep pushing for Endeavour crater but watch for interesting targets along the way where we can stop and smell the roses."

Ganymede & Calisto - Surface Differences Explanation

Each of Jupiter's more than 60 moons has its own unique character, but scientists have often wondered at the striking differences between the surfaces and interiors of two of the gas giant's largest moons, Ganymede and Callisto.

A new study, detailed in the Jan. 24 issue of the journal Nature Geoscience, might have found an explanation for the disparate features of these Galilean moons: Ganymede was pummeled by more and faster comets impacts than its sister moon billions of years ago.

While Ganymede and Callisto are similar in size and both made up of a mixture of ice and rock, data from both the Galileo and Voyager missions show that they sport different looks, both on the inside and outside.

But just why the two moons looked so different is a problem that planetary scientists have been grappling with for 30 years. The solution to the problem could shed light on how our solar system, and planets in general, evolved.

"Similar to Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists," said Amy Barr of the Southwest Research Institute Planetary Science Directorate.

Ganymede has a surface that shows evidence of resurfacing by tectonic processes — the same forces that continually reshape the surface of the Earth. The moon also has a large rock/metal core, showing that its constituent materials separated out over time, with the heavier stuff settling to the interior of the planet (just as the iron present in Earth settled to the core, while the lighter rocky materials floated to the surface).

The surface of Callisto, on the other hand, shows no signs of resurfacing, and the separation of rock and ice within it seems to be incomplete.

Barr and her colleague Robin Canup created a model that looked at the possible role of comet impacts in the evolution of these two moons. The model simulated the impacts and rocky core formation and found that Ganymede and Callisto's evolutionary paths diverged around 3.8 billion years ago, during a period in the solar system's life called the Late Heavy Bombardment. (The pockmarked surface of Earth's moon shows that this period was dominated by large impacts).

In the model, Jupiter's strong gravity focuses comets that swing into the neighborhood into the paths of Ganymede and Callisto.

When a comet impacted either moon, the mixed ice and rock that made up the surface would have created a pool of liquid water, allowing rock in the melt pool to sink to the moon's center.

Because Ganymede is closer to Jupiter, it was hit by twice the number of impactors as Callisto was. The proximity to Jupiter also meant that the comets colliding with Ganymede were going faster than those that hit Callisto.

The model shows that if the impacts to Ganymede released enough energy, the process of rock sinking and core formation could have become self-sustaining.

"Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed. All of Ganymede's rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream," Barr said. "Callisto received fewer impacts at lower velocities and avoided complete melting."

These model findings help link the evolution of Jupiter's moons to the overall evolution of the solar system and the history of bombardment of Earth's own moon