Posted on by Fraser Cain

Comets May Be the Source of Earth’s Water

The new comet is indicated by the blue arrow. Image credit: Gemini Observatory Click to enlarge
Astronomers have discovered three icy comets that may help explain how the Earth’s oceans formed. These new comets have asteroid-like orbits, and formed in the warm inner Solar System, not in the outer reaches like most comets. This lends evidence to the theory that the main asteroid belt isn’t bone dry, as previously believed, but is actually quite rich in ice – a major source of our planet’s water.

Three icy comets orbiting among the rocky asteroids in the main asteroid belt between Mars and Jupiter may hold clues to the origin of Earth’s oceans.

The newly discovered group of comets, dubbed “main-belt comets” by University of Hawaii graduate student Henry Hsieh and Professor David Jewitt, has asteroid-like orbits and, unlike other comets, appears to have formed in the warm inner solar system inside the orbit of Jupiter rather than in the cold outer solar system beyond Neptune.

The existence of these main-belt comets suggests that asteroids and comets are much more closely related than previously thought and supports the idea that icy objects from the main asteroid belt could be a major source of Earth’s present-day water. This work appears in the March 23 edition of Science Express (pdf) and will also appear in an April print edition of Science.

The crucial observations were made on November 26, 2005, using the 8-meter Gemini North Telescope on Mauna Kea. Hsieh and Jewitt found that an object designated as Asteroid 118401 was ejecting dust like a comet. Together with a mysterious comet (designated 133P/Elst-Pizarro) known for almost a decade but still poorly understood, and another comet (designated P/2005 U1) discovered by the Spacewatch project in Arizona just a month earlier, “Asteroid” 118401 forms an entirely new class of comets.

“The main-belt comets are unique in that they have flat, circular, asteroid-like orbits, and not the elongated, often tilted orbits characteristic of all other comets,” said Hsieh. “At the same time, their cometary appearance makes them unlike all other previously observed asteroids. They do not fit neatly in either category.”

In both 1996 and 2002, the “original” main-belt comet, 133P/Elst-Pizarro (named after its two discoverers), was seen to exhibit a long dust tail typical of icy comets, despite having the flat, circular orbit typical of presumably dry, rocky asteroids. As the only main-belt object ever observed to take on a cometary appearance, however, 133P/Elst-Pizarro’s true nature remained controversial. Until now.

“The discovery of the other main-belt comets shows that 133P/Elst-Pizarro is not alone in the asteroid belt,” Jewitt said. “Therefore, it is probably an ordinary (although icy) asteroid, and not a comet from the outer solar system that has somehow had its comet-like orbit transformed into an asteroid-like one. This means that other asteroids could have ice as well.”

The Earth is believed to have formed hot and dry, meaning that its current water content must have been delivered after the planet cooled. Possible candidates for supplying this water are colliding comets and asteroids. Because of their large ice content, comets were leading candidates for many years, but recent analysis of comet water has shown that comet water is significantly different from typical ocean water on Earth.

Asteroidal ice may give a better match to Earth’s water, but until now, any ice that the asteroids may have once contained was thought to either be long gone or so deeply buried inside large asteroids as to be inaccessible for further analysis. The discovery of main-belt comets means that this ice is not gone and is still accessible (right on the surfaces of at least some objects in the main belt, and at times, even venting into space). Spacecraft missions to the main-belt comets could provide new, more detailed information on their ice content and in turn give us new insight into the origin of the water, and ultimately life, on Earth.

As conventionally defined, comets and asteroids are very different. Both are objects a few to a few hundred miles across that orbit throughout our solar system. Comets, however, are thought to originate in the cold outer solar system and consequently contain much more ice than the asteroids, most of which are thought to have formed much closer to the Sun in the asteroid belt between Mars and Jupiter.

Comets also have large, elongated orbits and thus experience wide temperature variations. When a comet approaches the Sun, its ice heats up and sublimates (changes directly from ice to gas), venting gas and dust into space, giving rise to a tail and a distinctive fuzzy appearance. Far from the Sun, sublimation stops, and any remaining ice stays frozen until the comet’s next pass close to the Sun. In contrast, objects in the asteroid belt have essentially circular orbits and are expected to be mostly baked dry of ice by their confinement to the inner solar system. Essentially, they should be just rocks. With the discovery of the main-belt comets, we now know this is not the case, and that, in general, the conventional definitions of comets and asteroids are in need of refinement.

This work is supported by a grant from the NASA Planetary Astronomy Program of the Science Mission Directorate.

More information: http://www.ifa.hawaii.edu/~hsieh/mbcs.html

Original Source: University of Hawaii

Posted on by Fraser Cain

Dead Star Cores Surrounded in Superhot Gas

A hot gas cloud whirling around a miniature ‘cannibal’ star. Image credit: ESA Click to enlarge
ESA’s XMM-Newton space telescope has observed the tiny cores of dead stars wrapped up in a nice warm blanket of superheated gas. These “low-mass X-ray binary” are pulling a steady stream of material from a larger companion star, and then whipping it up into a disk. This observation answers the question of why these dead stars sometimes blink off in the X-ray spectrum. That’s the time when we’re seeing this disk edge-on, and it’s obscuring our view of the star.

ESA’s XMM-Newton has seen vast clouds of superheated gas, whirling around miniature stars and escaping from being devoured by the stars’ enormous gravitational fields – giving a new insight into the eating habits of the galaxy’s ‘cannibal’ stars.

The clouds of gas range in size from a few hundred thousand kilometres to a few million kilometres, ten to one hundred times larger than the Earth. They are composed of iron vapour and other chemicals at temperatures of many millions of degrees.

“This gas is extremely hot, much hotter than the outer atmosphere of the Sun,” said Maria Diaz Trigo of ESA’s European Science and Technology Research Centre (ESTEC), who led the research.

ESA’s XMM-Newton x-ray observatory made the discovery when it observed six so-called ‘low-mass X-ray binary’ stars (LMXBs). The LMXBs are pairs of stars in which one is the tiny core of a dead star.

Measuring just 15?20 kilometres across and comparable in size to an asteroid, each dead star is a tightly packed mass of neutrons containing more than 1.4 times the mass of the Sun.

Its extreme density generates a powerful gravitational field that rips gas from its ‘living’ companion star. The gas spirals around the neutron star, forming a disc, before being sucked down and crushed onto its surface, a process known as ‘accretion’.

The newly discovered clouds sit where the river of matter from the companion star strikes the disc. The extreme temperatures have ripped almost all of the electrons from the iron atoms, leaving them carrying extreme electrical charges. This process is known as ‘ionisation’.

The discovery solves a puzzle that has dogged astronomers for several decades. Certain LMXBs appear to blink on and off at X-ray wavelengths. These are ‘edge-on’ systems, in which the orbit of each gaseous disc lines up with Earth.

In previous attempts to simulate the blinking, clouds of low-temperature gas were postulated to be orbiting the neutron star, periodically blocking the X-rays. However, these models never reproduced the observed behaviour well enough.

XMM-Newton solves this by revealing the ionised iron. “It means that these clouds are much hotter than we anticipated,” said Diaz. With high-temperature clouds, the computer models now simulate much better the dipping behaviour.

Some 100 known LMXBs populate our galaxy, the Milky Way. Each one is a stellar furnace, pumping X-rays into space. They represent a small-scale model of the accretion thought to be taking place in the very heart of some galaxies. One in every ten galaxies shows some kind of intense activity at its centre.

This activity is thought to be coming from a gigantic black hole, pulling stars to pieces and devouring their remains. Being much closer to Earth, the LMXBs are easier to study than the active galaxies.

“Accretion processes are still not well understood. The more we understand about the LMXBs, the more useful they will be as analogues to help us understand the active galactic nuclei,” says Diaz.

Original Source: ESA Portal

Posted on by Fraser Cain

Our Brown Dwarf Neighbour

An image of the cool brown dwarf orbiting a star near the Sun. Image credit: UA Steward Observatory. Click to enlarge
Astronomers have discovered a brown dwarf in our galactic neighbourhood, only 12.7 light years away – this makes it the second closest brown dwarf ever discovered. The failed star is circling another star that was only recently discovered in the southern constellation Pavo. The primary star is small, with only 1/10th the mass of our Sun, and the brown dwarf orbits at 4.5 times the distance of the Earth to the Sun.

Astronomers have discovered a unique “brown dwarf” right in our solar neighborhood.

If your city were the galaxy, it would be like finding someone you didn’t know about living upstairs in your house, one of the discoverers said.

The rare object is only 12.7 light years from Earth, circling a primary star that itself was discovered only recently in the southern hemisphere constellation Pavo (the Peacock).

Only one other brown dwarf system has been found closer to Earth, and it’s only marginally closer.

The primary star is only one-tenth the mass of our sun. This is the first time astronomers have found a cool brown dwarf companion to such a low-mass star. Until now, none has been found orbiting stars less than half the mass of our sun.

The brown dwarf is 4.5 AU from the star, or four and one-half times farther from its star than Earth is from our sun. Astronomers estimate that the brown dwarf is between nine and 65 times as massive as Jupiter.

Brown dwarfs are neither planets nor stars. They are dozens of times more massive than our solar system’s largest planet, Jupiter, but too small to be self-powered by hydrogen fusion like stars.

Only about 30 similarly cool brown dwarfs have been found anywhere in the sky, and only about 10 have been discovered orbiting stars.

“Besides being extremely close to Earth and in orbit around a very low-mass star, this object is a ‘T dwarf ‘ – a very cool brown dwarf with a temperature of about 750 degrees Celsius (1,382 degrees Fahrenheit),” said Beth Biller, a graduate student at The University of Arizona.

“It is also likely the brightest known object of its temperature because it is so close,” Biller said. “And it’s a rare example of a brown dwarf companion within 10 astronomical units of its primary star.”

Biller, along with Markus Kasper of the European Southern Observatory (ESO) and Laird Close of UA’s Steward Observatory, led the team who discovered the brown dwarf, designated SCR 1845-6357B.

“What’s really exciting about this is that we found the brown dwarf around one of the 25 stellar systems nearest to the sun,” Close said. “Most of these nearby stars have been known for decades, and only just recently a handful of new objects have been found in our local neighborhood.”

Close said, “If you think of the galaxy as being the size of Tucson, it’s kind of like finding someone living in the upstairs of your house that you didn’t know about before.”

Close helped develop the special adaptive optics camera, the NACO Simultaneous Differential Imager(SDI), that the team used to image the brown dwarf. The camera is used on ESO’s Very Large Telescope (VLT) in Chile. Another SDI camera is used at the 6.5-meter MMT Observatory on Mount Hopkins, Ariz.

“This is also a valuable object to the scientific community because its distance is well known,” said ESO’s Markus Kasper. This will allow astronomers to measure the brown dwarf’s luminosity accurately and, eventually, to calculate its orbital motion, Kasper said. “These properties are vital for understanding the nature of brown dwarfs.”

The discovery of this brown dwarf suggests there may be more cool brown dwarfs in binary systems than single brown dwarfs floating free in the solar neighborhood, Close said. A “binary system” is where a brown dwarf revolves around a star or another brown dwarf.

Astronomers now have found five cool brown dwarfs in binary systems but only two single, isolated cool brown dwarfs within 20 light years of the sun, Close noted. They can expect to find more T dwarf companions in some newly found stellar systems within 33 light years of our solar system, he added.

Evidence that T dwarfs in binary systems outnumber single, isolated T dwarfs in the solar neighborhood has ramifications for theories that predict single brown dwarfs will form more often than binary ones, Close said.

The NACO Simultaneous Differential Imager(SDI) uses adaptive optics to remove the blurring effects of Earth’s atmosphere to produce extremely sharp images. The camera enhances the ability of the VLT to detect faint companions that would otherwise be lost in the glare of their primary stars.

Close and Rainer Lenzen of the Max Planck Institute for Astronomy in Heidelberg, Germany, developed the SDI camera to search for methane-rich extrasolar planets. The SDI camera splits light from a single object into four identical images, then passes the beams through three slightly different methane-sensitive filters. When the filtered light beams hit the detector array, astronomers subtract the images so the bright star disappears and its far dimmer, methane-rich companion pops into view.

The team will publish the discovery in the Astrophysical Journal Letters in the article, “Discovery of a Very Nearby Brown Dwarf to the Sun: A Methane Rich Brown Dwarf Companion to the Low Mass Star SCR 1845-6357.” In addition to Biller, Kasper and Close, team members include Wolfgang Brandner of the Max Planck Institute in Heidelberg, Germany, and Stephan Kellner of the W.M. Keck Observatory in Waimea, Hawaii.

Original Source: UA News Release

Posted on by Fraser Cain

Saturn’s Ring Spokes May Return

Spoke features in Saturn’s B-ring captured by Voyager 2 in August 1981. Image credit: NASA Click to enlarge
When Voyager first visited Saturn 26 years ago, it returned photographs of unusual spokelike structures in the rings. The Hubble Space Telescope confirmed the spokes in the 1990s, but then they faded out. It’s believed that the spokes are caused when electrically charged particles collect above the surface of the rings, scattering light from the Sun differently than the rings themselves. Scientists think they might be due to return around July this year, as they depend on the ring’s angle towards the Sun, which is now decreasing.

Unusual spokes that appear fleetingly on the rings of Saturn only to disappear for years at a time may become visible again by July, according to a new study spearheaded by the University of Colorado at Boulder.

The spokes, which are up to 6,000 miles long and 1,500 miles in width, were first spotted 26 years ago by the Voyager spacecraft, said CU-Boulder Professor Mihaly Horanyi of the Laboratory for Atmospheric and Space Physics. But when the Cassini spacecraft arrived at Saturn in July of 2004, the striking radial features that cut across Saturn’s ring plane were nowhere to be found — an event that disappointed and puzzled many scientists, he said.

The Hubble Space Telescope occasionally observed the ring spokes in the late 1990s, said Horanyi, a professor of physics at CU-Boulder. But the spokes gradually faded, a result of Saturn’s seasonal, orbital motion and its tilted axis of rotation that altered the light-scattering geometry.

“The spokes were switched off by the time Cassini arrived,” said Horanyi. “We think it is a seasonal phenomena related to the sun rising and setting over the ring plane that changes the physical environment there, making it either friendly or hostile to their formation.”

A paper on the subject appears in the March 17 issue of Science magazine. The paper was authored by doctoral student Colin Mitchell and Horanyi of CU-Boulder’s LASP, Ove Havnes of the University of Trosmo in Norway and Carolyn Porco of the Space Science Institute in Boulder.

The spokes are made up of tiny dust particles less than a micron in width — about 1/50th the width of a human hair — that collect electrostatic charges in the plasma environment of the rings and become subject to electrical and magnetic forces, said Horanyi. The right conditions cause them to gain an extra electron, allowing them to leap en masse from the surface of ring debris for brief periods, collectively forming the giant spokes that appear dark against the lit side of the rings and bright against the unlit side of the rings.

The researchers hypothesize that the conditions for the spokes to form are correlated to a decrease in the angle of the ring plane to the sun. “Because the rings are more open to the sun now than when Voyager flew by, the charging environment above the rings has prevented the formation of the spokes until very recently,” the researchers wrote in Science.

Cassini first imaged a “puny version” of Saturn’s spoke rings from a distance of 98,000 miles in early September that were only about 2,200 miles in length and about 60 miles wide, said Horanyi. The team believes the spoke sighting may have been an “early bird” event.

As the ring plane angle decreases when Saturn is near its two seasonal equinoxes, the conditions appear to become more suitable for the formation of the eerie spokes, said Horanyi. Although Cassini currently is orbiting too close to the ring plane to make observations, the researchers expect the spoke activity to have returned by the time the spacecraft increases its inclination in July 2006.

Once the spokes are visible again, the research team believes there will be spoke activity for about eight years, based on the fact that it takes Saturn about 30 Earth-years to complete one orbit around the sun, said Horanyi. The eight-year period should be followed by about six-to-seven years of a spoke hiatus, he said.

The dust grains levitated by plasma during spoke-forming periods are probably hovering less than 50 miles above the rings themselves and they scatter light from the sun differently than do the rings themselves, he said.

But there are still many questions about the spokes, said Horanyi. “We don’t know if they form by rapidly expanding, or if they form all at once,” he said. During the Voyager mission, they were absent during one observation, but fully developed in a follow-up observation made just five minutes later, Horanyi said.

“This is a weird phenomena; we don’t have the full story on it yet,” he said.

Original Source: CU-Boulder News Release

Posted on by Fraser Cain

March 29 Total Eclipse

Partial solar eclipse across the United States on May 10, 1994. Image credit: Sky & Telescope Click to enlarge
Those lucky enough to live in parts of Africa, Turkey and Central Asia will experience a total eclipse of the Sun on Wednesday, March 29, 2006. Even larger areas of the Earth will get to see the Sun dim in a partial solar eclipse, from Brazil to China. If you’re lucky enough to be watching from the thin path of totality, the Sun will be completely obscured by the Moon, making the corona visible like a fiery ring.

On Wednesday, March 29, 2006, a total eclipse of the Sun will sweep across parts of West and North Africa, Turkey, and Central Asia. The eclipse will be partial across a much wider region, including most of Africa, all of Europe, and much of western and southern Asia.

The accompanying maps provided by Sky & Telescope magazine tell the story. They will help skywatchers in those regions of the world to plan their activities for the big day.

A solar eclipse happens when the Moon crosses the face of the Sun as seen from your viewpoint on Earth. The globe map shows the entire region of Earth that will be touched by any part of this eclipse, including the complete path of totality: where the Sun will become completely covered by the Moon. As the map shows, the total eclipse starts at sunrise at the tip of Brazil, crosses the Atlantic in the morning, the Sahara Desert at midday, Turkey in the afternoon, and ends at sunset in Central Asia. Red lines on the globe map indicate how much of the Sun’s diameter is covered at maximum partial eclipse. Purple lines tell when this happens, in Universal Time (UT; also called Greenwich Mean Time or GMT).

The close-up map of Europe and the Middle East gives more detail. Here, blue and red lines tell the start and end times of partial eclipse, respectively, again in UT/GMT. The partial eclipse for any site is at its maximum halfway between these times. The black lines on the map tell the percentage of the Sun’s diameter that will be covered at maximum eclipse.

Although a partial solar eclipse can’t hold a candle to a total one, it’s a memorable celestial event in its own right. Can you see a change in the illumination of the landscape around you? A partial eclipse has to be surprisingly deep to alter the light visibly, because our eyes are very good at adjusting to ambient light levels. But when this does happen, the world seems to take on an odd, silvery feel like no other. Look for crescent-shaped dapplings on the ground where sunlight shines through leaves. In a safely solar-filtered telescope (see below), look for mountain silhouettes on the Moon’s dark edge. Look too for a difference between the Moon’s complete darkness and the not-so-complete darkness of any sunspots that the edge of the Moon approaches.

Warning: Never look at the bright surface of the Sun without proper eye protection! Examples are special “eclipse glasses” properly designed for the purpose, a #14 rectangular arc-welder’s filter, or special astronomers’ solar filters (see our list of solar filter suppliers). Staring at the bright Sun can burn your retina, leaving a permanent blind spot in the center of your vision. The only reason a partial eclipse poses a special danger is because it can prompt people to look directly at the Sun, something they wouldn’t normally do. See our complete descriptions of the various ways to watch safely, including the “projection method” using a pinhole, binoculars, or a telescope.

Looking while the Sun is totally eclipsed, on the other hand, is safe. At that time, of course, none of the Sun’s bright surface is in view.

People who’ve never tried photographing a solar eclipse before can get fine results by following Sky & Telescope’s tips for photographers.

More on this particular eclipse appears in the January and March 2006 issues of Sky & Telescope, the Essential Magazine of Astronomy.

For detailed local predictions at any given location, please see NASA’s Web site for this eclipse.

Original Source: Sky and Telescope

Posted on by Fraser Cain

Giant Protoplanets Should Get Destroyed

Inward migration of a group of protoplanets, where they’re represented by white circles. Image credit: QMUL Click to enlarge
Astronomers think they’ve got a handle on many aspects of planetary formation. But two British researchers have discovered a problem with the formation of gas giant planets. Under their model, the cores of these massive planets should be drawn inward by their parent star in only 100,000 years – not nearly enough time to form into a stable orbit. It could be that the first generations of planets never get past the “clump” stage before they’re destroyed. It’s only the later generations that actually survive long enough to become planets.

Two British astronomers, Paul Cresswell and Richard Nelson present new numerical simulations in the framework of the challenging studies of planetary system formation. They find that, in the early stages of planetary formation, giant protoplanets migrate inward in lockstep into the central star. Their results will soon be published in Astronomy & Astrophysics.

In an article to be published in Astronomy & Astrophysics, two British astronomers present new numerical simulations of how planetary systems form. They find that, in the early stages of planetary formation, giant protoplanets migrate inward in lockstep into the central star.

The current picture of how planetary systems form is as follows: i) dust grains coagulate to form planetesimals of up to 1 km in diameter; ii) the runaway growth of planetesimals leads to the formation of ~100 ? 1000 km-sized planetary embryos; iii) these embryos grow in an “oligarchic” manner, where a few large bodies dominate the formation process, and accrete the surrounding and much smaller planetesimals. These “oligarchs” form terrestrial planets near the central star and planetary cores of ten terrestrial masses in the giant planet region beyond 3 astronomical units (AU).

However, these theories fail to describe the formation of gas giant planets in a satisfactory way. Gravitational interaction between the gaseous protoplanetary disc and the massive planetary cores causes them to move rapidly inward over about 100,000 years in what we call the “migration” of the planet in the disc. The prediction of this rapid inward migration of giant protoplanets is a major problem, since this timescale is much shorter than the time needed for gas to accrete onto the forming giant planet. Theories predict that the giant protoplanets will merge into the central star before planets have time to form. This makes it very difficult to understand how they can form at all.

For the first time, Paul Cresswell and Richard Nelson examined what happens to a cluster of forming planets embedded in a gaseous protoplanetary disc. Previous numerical models have included only one or two planets in a disc. But our own solar system, and over 10% of the known extrasolar planetary systems, are multiple-planet systems. The number of such systems is expected to increase as observational techniques of extrasolar systems improve. Cresswell and Nelson’s work is the first time numerical simulations have included such a large number of protoplanets, thus taking into account the gravitational interaction between the protoplanets and the disc, and among the protoplanets themselves.

The primary motivation for their work is to examine the orbits of protoplanets and whether some planets could survive in the disc for extended periods of time. Their simulations show that, in very few cases (about 2%), a lone protoplanet is ejected far from the central star, thus lengthening its lifetime. But in most cases (98%), many of the protoplanets are trapped into a series of orbital resonances and migrate inward in lockstep, sometimes even merging with the central star.

Cresswell and Nelson thus claim that gravitational interactions within a swarm of protoplanets embedded in a disc cannot stop the inward migration of the protoplanets. The “problem” of migration remains and requires more investigation, although the astronomers propose several possible solutions. One may be that several generations of planets form and that only the ones that form as the disc dissipates survive the formation process. This may make it harder to form gas giants, as the disc is depleted of the material from which gas giant planets form. (Gas giant formation may still be possible though, if enough gas lies outside the planets’ orbits, since new material may sweep inward to be accreted by the forming planet). Another solution might be related to the physical properties of the protoplanetary disc. In their simulations, the astronomers assumed that the protoplanetary disc is smooth and non-turbulent, but of course this might not be the case. Large parts of the disc could be more turbulent (as a consequence of instabilities caused by magnetic fields), which may prevent inward migration over long time periods.

This work joins other studies of planetary system formation that are currently being done by a European network of scientists. Our view of how planets form has drastically changed in the last few years as the number of newly discovered planetary systems has increased. Understanding the formation of giant planets is currently one of the major challenges for astronomers.

Original Source: Astronomy & Astrophysics

Posted on by Fraser Cain

Spitzer Sees Distant Galaxy Clusters

Spitzer spots galactic clusters bonding back when the universe was about 4.6 billion years old. Image credit: NASA Click to enlarge
NASA’s Spitzer Space Telescope recently turned up clusters of galaxies located 7-9 billion light years from Earth. These galaxies are located at the very limits of Spitzer’s observing ability with its 85-centimeter (33-inch) telescope. Galaxy clusters are some of the largest structures in the Universe, consisting of thousands of galaxies and trillions of stars. This discovery gives astronomers more evidence about what kinds of structures existed in the early Universe.

Astronomers using NASA’s Spitzer Space Telescope have conducted a cosmic safari to seek out a rare galactic species. Their specimens — clusters of galaxies in the very distant universe — are few and far between, and have hardly ever been detected beyond a distance of 7 billion light-years from Earth.

To find the clusters, the team carefully sifted through Spitzer infrared pictures and ground-based catalogues; estimated rough distances based on the cluster galaxies’ colors; and verified suspicions using a spectrograph instrument at the W.M. Keck Observatory in Hawaii.

Ultimately, the expedition resulted in quite a galactic catch — the most distant galaxy cluster ever seen, located 9 billion light-years away. This means the cluster lived in an era when the universe was a mere 4.5 billion years old. The universe is believed to be 13.7 billion years old.

“Detecting a galaxy cluster 9 billion light-years away is very exciting,” said the study’s lead investigator, Dr. Peter Eisenhardt of NASA’s Jet Propulsion Laboratory. “It’s really amazing that Spitzer’s 85-centimeter telescope can see 9 billion years back in time.”

Using the same methods, the astronomers also found three other clusters living between 7 and 9 billion light-years away.

“Spitzer is an excellent instrument for detecting very distant galaxy clusters because they stand out so brightly in the infrared,” said co-investigator Dr. Mark Brodwin, also of JPL. “You can think of these distant galaxy cluster surveys as a game of ‘Where’s Waldo?’ With an optical telescope you can spot ‘Waldo,’ or the distant galaxy clusters, by carefully searching for them amongst a sea of faint galaxies.”

“But in the Spitzer data, it’s as though Waldo is wearing a bright neon hat and can be easily picked out of the crowd,” Brodwin added.

Galaxy clusters are the largest gravitationally bound structures in the universe. A typical cluster can contain thousands of galaxies and trillions of stars. Because of their huge size and mass, they are relatively rare. For example, if Earth were to represent the entire universe, then countries would be the equivalent of galaxies, and continents would be the galaxy clusters.

Galaxy clusters grow like snowballs, picking up new galaxies from gravitational interactions over billions of years. For this reason, team members say these behemoths should be even rarer in the very distant universe.

“The ultimate goal of this research is to find out when the galaxies in this and other distant clusters formed,” said co-investigator Dr. Adam Stanford, of the University of California at Davis. Stanford is the lead author of a paper on the most distant galaxy cluster’s discovery, which was published in the December 2005 issue of Astrophysical Journal Letters.

This is the second time Eisenhardt and Stanford have broken the record for capturing the most distant galaxy cluster. Both say they accidentally broke the record in 1997 when they detected a cluster located 8.7 billion light-years away. The discovery was made by a deep survey of a 0.03-degree patch of sky, or an area significantly smaller than a pea held out at arms length, for 30 nights at the Kitt Peak National Observatory in Arizona.

“We were lucky in 1997 because we weren’t looking for galaxy clusters and found the most distant one ever detected in a very small patch of sky,” said Stanford. “Because galaxy clusters are so massive and rare, you typically need to deeply survey a large area of sky to find them.”

“With Spitzer’s great infrared sensitivity we surveyed more deeply in 90 seconds than we could in hours of exposure in the 1997 observations, and we used this advantage to survey a region 300 times larger,” adds Eisenhardt.

The 9 billion-year-old cluster is just one of 25 the team captured on their Spitzer safari. They are currently preparing for more observations this spring at the W.M. Keck Observatory to confirm the distance of additional galaxy clusters from their sample. According to Eisenhardt, some of the clusters awaiting confirmation may be even more distant than the current record holder.

Original Source: Spitzer Space Telescope

Posted on by Fraser Cain

Defending Against Radiation

The sun is a major source of radiation for life on Earth. Image credit: NASA/ESA/SOHO. Click to enlarge
Space travel has its dangers. One of the biggest risks will come from the various types of radiation that flood space. Scientists are learning how life on Earth has evolved different kinds of tricks to resist radiation. Some animals and plants have evolved protective covering or pigmentation, but some forms of bacteria can actually repair damage to its DNA from radiation. Future space travelers might take advantage of these techniques to minimize the harm they get from long exposure.

In Star Wars and Star Trek movies, people travel between planets and galaxies with ease. But our future in space is far from assured. Issues of hyperdrive and wormholes aside, it doesn’t seem possible that the human body could withstand extended exposure to the harsh radiation of outer space.

Radiation comes from many sources. Light from the sun produces a range of wavelengths from long-wave infrared to short-wavelength ultraviolet (UV). Background radiation in space is composed of high-energy X-rays, gamma rays and cosmic rays, which all can play havoc with the cells in our bodies. Since such ionizing radiation easily penetrates spacecraft walls and spacesuits, astronauts today must limit their time in space. But being in outer space for even a short time greatly increases their odds of developing cancer, cataracts, and other radiation-related health problems.

To overcome this problem, we may find some useful tips in nature. Many organisms already have devised effective strategies to protect themselves from radiation.

Lynn Rothschild of the NASA Ames Research Center says that radiation has always been a danger for life on Earth, and so life had to find ways to cope with it. This was especially important during the Earth’s earliest years, when the ingredients for life were first coming together. Because our planet did not initially have much oxygen in the atmosphere, it also lacked an ozone (O3) layer to block out harmful radiation. This is one reason why many believe life originated underwater, since water can filter out the more damaging wavelengths of light.

Yet photosynthesis ? the transformation of sunlight into chemical energy ? developed relatively early in the history of life. Photosynthetic microbes like cyanobacteria were using sunlight to make food as early as 2.8 billion years ago (and possibly even earlier).

Early life therefore engaged in a delicate balancing act, learning how to use radiation for energy while protecting itself from the damage that radiation could cause. While sunlight is not as energetic as X-rays or gamma rays, the UV wavelengths are preferentially absorbed by DNA bases and by the aromatic amino acids of proteins. This absorption can damage cells and the delicate DNA strands that encode the instructions for life.

“The problem is, if you’re going to access solar radiation for photosynthesis, you’ve got to take the good with the bad — you’re also exposing yourself to the ultraviolet radiation,” says Rothschild. “So there’s various tricks that we think early life used, as life does today.”

Besides hiding under liquid water, life makes use of other natural UV radiation barriers such as ice, sand, rocks, and salt. As organisms continued to evolve, some were able to develop their own protective barriers such as pigmentation or a tough outer shell.

Thanks to photosynthetic organisms filling the atmosphere with oxygen (and thereby generating an ozone layer), most organisms on Earth today don’t need to contend with high energy UV-C rays, X-rays or gamma rays from space. In fact, the only organisms known to survive space exposure ? at least in the short term – are bacteria and lichen. Bacteria need some shielding so they won’t get fried by the UV, but lichen have enough biomass to act as a protective spacesuit.

But even with a good barrier in place, sometimes radiation damage does occur. The lichen and bacteria hibernate while in space ? they do not grow, reproduce, or engage in any of their normal living functions. Upon return to Earth, they exit this dormant state and, if there was damage inflicted, proteins in the cell work to piece together DNA strands that were broken apart by radiation.

The same damage control occurs with organisms on Earth when they’re exposed to radioactive materials such as uranium and radium. The bacterium Deinococcus radiodurans is the reigning champion when it comes to this sort of radiation repair. (Complete repair is not always possible, however, which is why radiation exposure can lead to genetic mutations or death.)

“I live in eternal hope of unseating D. radiodurans,” says Rothchild. Her search for radiation-resistant microorganisms has brought her to Paralana hot spring in Australia. Uranium-rich granite rocks emit gamma rays while lethal radon gas bubbles up from the hot water. Life in the spring is therefore exposed to high levels of radiation ? both below, from the radioactive materials, and above, from the intense UV light of the Australian sun.

Rothschild learned about the hot spring from Roberto Anitori of Macquarie University’s Australian Centre for Astrobiology. Anitori has been sequencing the 16S ribosomal RNA genes and culturing the bacteria that live quite happily in the radioactive waters. Like other organisms on Earth, the Paralana cyanobacteria and other microbes may have devised barriers to shield themselves from the radiation.

“I have noticed a tough, almost silicone-like layer on some of the microbial mats there,” says Anitori. “And when I say “silicon-like,” I mean the sort you use on window pane edging.”

“Apart from possible shielding mechanisms, I suspect that the microbes at Paralana also have good DNA repair mechanisms,” adds Anitori. At the moment, he can only speculate about the methods used by the Paralana organisms to survive. However, he does plan to closely investigate their radiation resistance strategies later this year.

In addition to Paralana, Rothschild’s investigations have brought her to extremely arid regions in Mexico and the Bolivian Andes. As it turns out, many organisms that evolved to live in deserts are also quite good at surviving radiation exposure.

Prolonged water loss can cause DNA damage, but some organisms have evolved efficient repair systems to combat this damage. It’s possible that these same dehydration repair systems are used when the organism needs to repair radiation-inflicted damage.

But such organisms may be able to avoid damage altogether simply by being dried out. The lack of water in desiccated, dormant cells makes them much less susceptible to the effects of ionizing radiation, which can harm cells by producing free radicals of water (hydroxyl or OH radical). Because free radicals have unpaired electrons, they eagerly try to interact with DNA, proteins, lipids in cell membranes, and anything else they can find. The resulting wreckage can lead to organelle failure, block cell division, or cause cell death.

Eliminating the water in human cells is probably not a practical solution for us to minimize our radiation exposure in space. Science fiction has long toyed with the idea of putting people into suspended animation for long space journeys, but turning humans into shriveled, dried-out raisins and then rehydrating them back to life isn’t medically possible – or very appealing. Even if we could develop such a procedure, once the human raisinettes were rehydrated they would again be susceptible to radiation damage.

Perhaps someday we can genetically engineer humans to have the same super radiation-repair systems as microorganisms like D. radiodurans. But even if such tinkering with the human genome was possible, those hardy organisms aren’t 100 percent resistant to radiation damage, so health problems would persist.

So of the three known mechanisms that life has devised to combat radiation damage – barriers, repair, and desiccation – the most immediately practical solution for human spaceflight would be to devise better radiation barriers. Anitori thinks his studies of the Paralana Spring organisms could someday help us engineer such barriers.

“Perhaps we will be taught by nature, mimicking some of the shielding mechanisms used by microbes,” he states.

And Rothschild says radiation studies also could provide some important lessons as we look toward establishing communities on the moon, Mars, and other planets.

“When we start to build human colonies, we’re going to take organisms with us. You’re ultimately going to want to grow plants, and possibly make an atmosphere on Mars and on the moon. We may not want to spend the effort and the money to protect them completely from the UV and cosmic radiation.”

In addition, says Rothschild, “humans are just full of microbes, and we couldn’t survive without them. We don’t know what effect the radiation will have on that associated community, and that may be more of a problem than the direct effect of radiation on the humans.”

She believes her studies also will be useful in the search for life on other worlds. Assuming that other organisms in the universe also are based on carbon and water, we can postulate what sort of extreme conditions they could survive in.

“Each time we find an organism on Earth that can live further and further into an environmental extreme, we’ve increased the size of that envelope of what we know life can survive within,” says Rothschild. “So if we go to a place on Mars that has a certain radiation flux, desiccation, and temperature, we can say, ‘There are organisms on Earth that can live under those conditions. There’s nothing that precludes life from living there.’ Now, whether life is there or not is another matter, but at least we can say this is the minimum envelope for life.”

For instance, Rothschild thinks life could be possible in the salt crusts on Mars, which are similar to salt crusts on Earth where organisms find shelter from solar UV. She also looks at life living under ice and snow on Earth, and wonders if organisms could live a comparatively radiation-protected existence under the ice of Jupiter’s moon Europa.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Hazy Layers on Titan

Titan’s multiple hazy layers. Image credit: NASA/JPL/SSI Click to enlarge
This is a composite photograph consisting of 24 photos taken by Cassini of Saturn’s moon Titan. Up at the top of Titan it’s possible to see several layers of clouds in the atmosphere. The top layer is at an altitude of 500 km (300 miles) and probably consists of water ice. Why the atmosphere is separate like this is still a mystery, but scientists think it might have something to do with waves in the atmosphere.

This composite of 24 images from the Cassini spacecraft shows multiple layers in Titan’s stratospheric haze. The most prominent layer is located about 500 kilometers (300 miles) above the surface and is seen at all latitudes, encircling the moon. The material in this layer is probably a condensed substance, possibly water ice.

Several other layers are most apparent in the north polar hood (at top), but this view also shows some at other latitudes. The mechanisms that produce these layers are not understood, but waves in the atmosphere are thought to play a significant role.

The images in this composite were taken over a period of 23 minutes. The images were processed to enhance fine detail and then were combined to create this view. North on Titan (5,150 kilometers, or 3,200 miles across) is up.

The images were taken in visible light with the narrow-angle camera on Jan. 27, 2006 at a distance of approximately 2.3 million kilometers (1.4 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 155 degrees. Image scale is 13 kilometers (8 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 operations center is based at the Space Science Institute in Boulder, Colo.

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

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Is Dark Matter Made up of Sterile Neutrinos?

The Guitar nebula. Image credit: Palomar Observatory. Click to enlarge
Since it makes up a large part of the Universe, you’d think we’d know what dark matter is by now. Sorry, it’s still a mystery, but new theories are coming out all the time. An international team of researchers are now theorizing that dark matter could be a class of particles known as “sterile neutrinos”. These particles, formed right at the Big Bang, could account for the Universe’s missing mass, and would have the handy side effect of speeding up the early formation of stars.

Dark matter may have played a major role in creating stars at the very beginnings of the universe. If that is the case, however, the dark matter must consist of particles called “sterile neutrinos”. Peter Biermann of the Max Planck Institute for Radio Astronomy in Bonn, and Alexander Kusenko, of the University of California, Los Angeles, have shown that when sterile neutrinos decay, it speeds up the creation of molecular hydrogen. This process could have helped light up the first stars only some 20 to 100 million years after the big bang. This first generation of stars then ionised the gas surrounding them, some 150 to 400 million years after the big bang. All of this provides a simple explanation to some rather puzzling observations concerning dark matter, neutron stars, and antimatter.

Scientists discovered that neutrinos have mass through neutrino oscillation experiments. This led to the postulation that “sterile” neutrinos exist – also known as right-handed neutrinos. They do not participate in weak interactions directly, but do interact through their mixing with ordinary neutrinos. The total number of sterile neutrinos in the universe is unclear. If a sterile neutrino only has a mass of a few kiloelectronvolts (1 keV is a millionth of the mass of a hydrogen atom), that would explain the huge, missing mass in the universe, sometimes called “dark matter”. Astrophysical observations support the view that dark matter is likely to consist of these sterile neutrinos.

Biermann and Kusenko’s theory sheds light on a number of still unexplained astronomical puzzles. First of all, during the big bang, the mass of neutrinos created in the Big Bang would equal what is needed to account for dark matter. Second, these particles could be the solution to the long-standing problem of why pulsars move so fast.

Pulsars are neutron stars rotating at a very high velocity. They are created in supernova explosions and normally are ejected in one direction. The explosion gives them a “push”, like a rocket engine. Pulsars can have velocities of hundreds of kilometres per second – or sometimes even thousands. The origin of these velocities remains unknown, but the emission of sterile neutrinos would explain the pulsar kicks.

The Guitar Nebula contains a very fast pulsar. If dark matter is made of particles which reionized the universe – as Biermann and Kusenko suggest – the pulsar’s motion could have created this cosmic guitar.

Third, sterile neutrinos can help explain the absence of antimatter in the universe. In the early universe, sterile neutrinos could have “stolen” what is called the “lepton number” from plasma. At a later time, the lack of lepton number was converted to a non-zero baryon number. The resulting asymmetry between baryons (like protons) and antibaryons (like antiprotons) could be the reason why the universe has no antimatter.

“The formation of central galactic black holes, as well as structure on subgalactic scales, favours sterile neutrinos to account for dark matter. The consensus of several indirect pieces of evidence leads one to believe that the long sought-after dark-matter particle may, indeed, be a sterile neutrino”, says Peter Biermann

Original Source: Max Planck Society