Posted on by Fraser Cain

Saturn Has Oxygen But No Life

Image credit: Hubble
Data from the Cassini-Huygens satellite showing oxygen ions in the atmosphere around Saturn’s rings suggests once again that molecular oxygen alone isn’t a reliable indicator of whether a planet can support life.

That and other data are outlined in two papers in the Feb. 25 issue of the journal Science co-authored by University of Michigan engineering professors Tamas Gombosi, J. Hunter Waite and Kenneth Hansen; and T.E. Cravens from the University of Kansas. The papers belong to a series of publications on data collected by Cassini as it passed through the rings of Saturn on July 1.

Molecular oxygen forms when two oxygen atoms bond together and is known in chemical shorthand as O2. On Earth, it is a continual byproduct of plant respiration, and animals need this oxygen for life. But in Saturn’s atmosphere, molecular oxygen was created without life present, through a chemical reaction with the sun’s radiation and icy particles that comprise Saturn’s rings.

“That means you don’t need biology to produce an O2 atmosphere,” Waite said. “If we want indicators to use in the search for life on other planets, we need to know what to look for. But oxygen alone isn’t it.”

Because Saturn’s rings are made of water ice, one would expect to find atoms derived from water, such as atomic oxygen (one atom) rather than O2, Waite said. However, the paper, called “Oxygen Ions Observed Near Saturn’s A Ring,” suggests the formation of molecular oxygen atmospheres happens more often in the outer solar system than expected. There is earlier evidence of molecular oxygen atmospheres elsewhere in the solar system?for instance above the icy Galilean moons of Jupiter?he said.

Four U-M College of Engineering faculty members are involved in the Cassini mission to explore Saturn’s rings and some of its moons. Waite leads the team operating the ion and neutral mass spectrometer, the instrument that detected and measured the molecular oxygen ions. Other team members are J.G. Luhmann of the University of California, Berkeley; R.V. Yelle, of the University of Arizona, Tuscon; W.T. Kasprzak, of the Goddard Space Flight Center; R.L. McNutt of Johns Hopkins University; and W.H. Ip, of the National Central University, Taiwan.

A second, viewpoint paper called, “Saturn’s Variable Magnetosphere,” by Hansen and Gombosi, who is chair of the College of Engineering’s department of Atmospheric, Oceanic and Space Sciences, reviews key findings from the other Cassini teams, including new information that contradicts data gathered 25 years ago, when the space craft Voyager passed by the planet.

Original Source: UMICH News Release

Posted on by Fraser Cain

Wallpaper: Panoramic View of Saturn

While cruising around Saturn in early October, Cassini captured a series of images that have been composed into the largest, most detailed, global natural color view of Saturn and its rings ever made.

This grand mosaic consists of 126 images acquired in a tile-like fashion, covering one end of Saturn’s rings to the other and the entire planet in between. The images were taken over the course of 2 hours on October 6, 2004, while Cassini was approximately 6.3 million kilometers (3.9 million miles) from Saturn. Since the view seen by Cassini during this time changed very little, no re-projection or alteration of any of the images was necessary.

Three images (red, green and blue) were taken at each of 42 locations, or ?footprints?, across the planet. The full color footprints were mosaicked together to produce a final product that is 8,888 pixels across and 4,544 pixels tall.

The smallest features seen here are 38 kilometers (24 miles) across. Many of Saturn’s splendid features noted previously in single frames taken by Cassini are visible in this one detailed, all-encompassing view: Subtle color variations across the rings, the thread-like F ring, ring shadows cast against the blue northern hemisphere, the planet?s shadow making its way across the rings to the left, blue-grey storms in Saturn’s southern hemisphere to the right and tiny Mimas and even smaller Janus (both faintly visible at lower left).

The Sun-Saturn-Cassini, or phase, angle at the time was 72 degrees; hence, the partial illumination of Saturn in this portrait. Later in the mission, when the spacecraft?s trajectory takes it far from Saturn and also into the direction of the Sun, Cassini will be able to look back and view Saturn and its rings in a more fully-illuminated geometry.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Saturn’s “Dragon Storm”

A large, bright and complex convective storm that appeared in Saturn’s southern hemisphere in mid-September 2004 was the key in solving a long-standing mystery about the ringed planet.

Saturn’s atmosphere and its rings are shown here in a false color composite made from Cassini images taken in near infrared light through filters that sense different amounts of methane gas. Portions of the atmosphere with a large abundance of methane above the clouds are red, indicating clouds that are deep in the atmosphere. Grey indicates high clouds, and brown indicates clouds at intermediate altitudes. The rings are bright blue because there is no methane gas between the ring particles and the camera.

The complex feature with arms and secondary extensions just above and to the right of center is called the Dragon Storm. It lies in a region of the southern hemisphere referred to as “storm alley” by imaging scientists because of the high level of storm activity observed there by Cassini in the last year.

The Dragon Storm was a powerful source of radio emissions during July and September of 2004. The radio waves from the storm resemble the short bursts of static generated by lightning on Earth. Cassini detected the bursts only when the storm was rising over the horizon on the night side of the planet as seen from the spacecraft; the bursts stopped when the storm moved into sunlight. This on/off pattern repeated for many Saturn rotations over a period of several weeks, and it was the clock-like repeatability that indicated the storm and the radio bursts are related. Scientists have concluded that the Dragon Storm is a giant thunderstorm whose precipitation generates electricity as it does on Earth. The storm may be deriving its energy from Saturn’s deep atmosphere.

One mystery is why the radio bursts start while the Dragon Storm is below the horizon on the night side and end when the storm is on the day side, still in full view of the Cassini spacecraft. A possible explanation is that the lightning source lies to the east of the visible cloud, perhaps because it is deeper where the currents are eastward relative to those at cloud top levels. If this were the case, the lightning source would come up over the night side horizon and would sink down below the day side horizon before the visible cloud. This would explain the timing of the visible storm relative to the radio bursts.

The Dragon Storm is of great interest for another reason. In examining images taken of Saturn’s atmosphere over many months, imaging scientists found that the Dragon Storm arose in the same part of Saturn’s atmosphere that had earlier produced large bright convective storms. In other words, the Dragon Storm appears to be a long-lived storm deep in the atmosphere that periodically flares up to produce dramatic bright white plumes which subside over time. One earlier sighting, in July 2004, was also associated with strong radio bursts. And another, observed in March 2004 and captured in a movie created from images of the atmosphere (http://photojournal.jpl.nasa.gov/catalog/PIA06082 and http://photojournal.jpl.nasa.gov/catalog/PIA06083) spawned three little dark oval storms that broke off from the arms of the main storm. Two of these subsequently merged with each other; the current to the north carried the third one off to the west, and Cassini lost track of it. Small dark storms like these generally get stretched out until they merge with the opposing currents to the north and south.

These little storms are the food that sustains the larger atmospheric features, including the larger ovals and the eastward and westward currents. If the little storms come from the giant thunderstorms, then together they form a food chain that harvests the energy of the deep atmosphere and helps maintain the powerful currents.

Cassini has many more chances to observe future flare-ups of the Dragon Storm, and others like it over the course of the mission. It is likely that scientists will come to solve the mystery of the radio bursts and observe storm creation and merging in the next 2 or 3 years.

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

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

Original Source: NASA/JPL/SSI

Posted on by Fraser Cain

Dr. David J. Tholen Answers Your Asteroid Questions

1.) Which class of Earth-crossing asteroids do you find most interesting, Atens or Apollos? (Erimus)

Personally, I find the Atens more interesting, simply because their orbits keep them out of the opposition region for a larger fraction of the time than the Apollos, making them comparatively more difficult to find. Current population statistics are biased against Atens because of the emphasis on the opposition region by the surveys.

2.) Which particular NEO do you find most interesting? (Erimus)

Which day of the week is it? Let’s see, if it’s Friday, I’d take 2000 SG344. This object is interesting because of its low velocity relative to Earth, which argues against it having been perturbed out the main belt. We can pretty much rule out it being manmade, now that another better candidate for the Apollo 12 S-IVB has been found. So, I’m leaning toward it being a piece of lunar ejecta, which could well be unique among the known objects. Because of its relatively high impact probabilities, I’ve given the object higher priority for astrometric observation, getting it a year and a half ago when it was magnitude 26, probably the faintest NEO ever observed.

If it’s Saturday, I’d go with 2004 MN4. It’s hard to ignore an object that will pass less than 6 Earth radii from the Earth just about 24 years from now, becoming bright enough to be visible to the unaided eye.

If it’s Monday, I’d go with 2004 XZ130. With a record small semimajor axis of 0.617 AU and a record small aphelion distance of 0.898 AU, it’s the kind of asteroid I’ve been interested in finding for a long time. Because it never gets into the opposition region, it would never be found by an opposition survey. Not much is known about this population of asteroid, because of the observational bias. We’re taking the first steps toward reducing that bias.

Oh, it’s Thursday. Let’s see, choices, choices…

3) What is the impact to the Earth, if an asteroid were to hit the Earth? Will it changes the weather or give any chemical or other effects? have we prepared for that? Should ordinary people know and be aware of it? (Fari)

It all depends on the size of the object that hits. If it’s small like a meteorite, it would have no significant effect. Something larger, like the one that produced Meteor Crater in Arizona, won’t change the weather, but significant local damage would occur. An object of the kind that is believed to have wiped out the dinosaurs would indeed have a major effect on the weather. So much dust would be ejected into the Earth’s stratosphere, that sunlight would be blocked, halting photosynthesis and disrupting the food chain all the way up to humans. Some of us have personally witnessed the length of time it can take for small amounts of dust to settle out of the stratosphere, given the El Chicon and Mt. Pinatubo volcanic eruptions of the 1980s and 1990s. Imagine how long it would take for a large amount of dust to settle out of the statosphere.

Currently, humans are not prepared to deal with a major asteroid impact.

Ordinary people who wish to be scientifically literate should be aware of the situation, but it’s not something over which to lose sleep.

4) What do you believe the chances are that the earth will be hit by an asteriod/comet that could cause world wide devastation within our lifetime? (Guest_SeanO)

Very small, less than one in ten thousand. That’s based on an assumed human life span of approximately 100 years (a little long, but we’re dealing with just an order of magnitude estimate here) and an average of one such impact every million years.

5) Do you have any speculations you could share with us about the exploitation of these objects, especially the sort of required technologies and favoured strategies required? (eburacum45)

It is true that some asteroids became hot enough for a long enough time to melt internally and differentiate, with the heavy metals sinking to their cores. Once catastrophically disrupted by a collision with another asteroid, the cores have been exposed, with some of the fragments falling to Earth, producing our nickel-iron meteorites. Some entrepreneurs are very interested in these cores because of the rare metals that could be extracted from them, such as gold, silver, and platinum.

Meanwhile, others are interested in exploiting the material necessary to sustain human existence in outer space. The one item that is most essential to human life is water. That’s one reason why there is so much interest in looking for water in the permanently shaded regions of the lunar poles. But some near-Earth asteroids may be rich in hydrated minerals, so it might be possible to extract water from these objects. Now, water sounds a lot more mundane than gold, silver, or platinum, but when you consider the alternative of hauling water up from the bottom of the deep gravity well that is Earth, you begin to realize that a source of water in outer space would be worth its weight in gold.

In both cases, a source of energy would be needed for the extraction process, but the Sun provides ample amounts of that. We just need to find an efficient way of harnessing that power. Some people want to change the orbit of an asteroid and park it around the Earth, sort of like a second moon, so that it is easier to get to on a routine basis. Needless to say, most of this work is very speculative in nature. Some scientists are probably actively thinking about ways to do the job, but I’m not aware of any major development of infrastructure at this time. One challenge is to work in the weak gravity field of an asteroid. Many terrestrial approaches simply won’t work very well on an asteroid because of the weak gravity.

6) Why is the asteroid belt so far away, in relation to the rocky planets? Why for instance do we not have an asteroid belt between Earth and Venus? (Guest)

The rocky planets range from 0.4 to 1.5 AU from the Sun, and the main asteroid belt extends from roughly 2.1 to 3.2 AU. Practically next door neighbors considering the scale of the Solar System, which extends to roughly 50 AU when you think of the trans-Neptunian objects, and even farther when you think of the Oort cloud comets, like 50,000 AU. So the asteroid belt doesn’t seem all that far away to me.

Asteroids between Venus and Earth do not have particularly stable orbits, at least compared to the 2 to 3 AU region of the Solar System. Nevertheless, some asteroids are believe to inhabit this region of space. Because they never reach the opposition region, they are harder to find. Looking in the part of the sky close to the Sun has been a research interest of mine for over a decade, and we’re just now finding the first inhabitants of this region. The numbers are too small at this time to be thinking in terms of a “belt”, but who knows what we’ll find after an extended investigation?

7) Are two (or more) asteroids ever found in orbit around each other, or will objects that small inevitably drift apart? (gnosys)

There are approximately four dozen asteroids known to have satellites in orbit around them. In some cases, the primary is large and the secondary is small, as in the case of Dactyl orbiting Ida, as imaged by the Galileo spacecraft while en route to Jupiter. In other cases, the two components are more nearly equal in size, such as 90 Antiope. Satellites of asteroids have been found among the near-Earth population, the main belt between Mars and Jupiter, and among the trans-Neptunian objects.

As long as the satellite is in a bound orbit, a source of energy would be necessary to cause them to separate.

Posted on by Fraser Cain

Views of Titan From Earth

On January 14, 2005, the ESA Huygens probe arrived at Saturn’s largest satellite, Titan. After a faultless descent through the dense atmosphere, it touched down on the icy surface of this strange world from where it continued to transmit precious data back to the Earth.

Several of the world’s large ground-based telescopes were also active during this exciting event, observing Titan before and near the Huygens encounter, within the framework of a dedicated campaign coordinated by the members of the Huygens Project Scientist Team. Indeed, large astronomical telescopes with state-of-the art adaptive optics systems allow scientists to image Titan’s disc in quite some detail. Moreover, ground-based observations are not restricted to the limited period of the fly-by of Cassini and landing of Huygens. They hence complement ideally the data gathered by this NASA/ESA mission, further optimising the overall scientific return.

A group of astronomers [1] observed Titan with ESO’s Very Large Telescope (VLT) at the Paranal Observatory (Chile) during the nights from 14 to 16 January, by means of the adaptive optics NAOS/CONICA instrument mounted on the 8.2-m Yepun telescope [2]. The observations were carried out in several modes, resulting in a series of fine images and detailed spectra of this mysterious moon. They complement earlier VLT observations of Titan, cf. ESO Press Photos 08/04 and ESO Press Release 09/04.

The new images show Titan’s atmosphere and surface at various near-infrared spectral bands. The surface of Titan’s trailing side is visible in images taken through narrow-band filters at wavelengths 1.28, 1.6 and 2.0 microns. They correspond to the so-called “methane windows” which allow to peer all the way through the lower Titan atmosphere to the surface. On the other hand, Titan’s atmosphere is visible through filters centred in the wings of these methane bands, e.g. at 2.12 and 2.17 microns.

Eric Gendron of the Paris Observatory in France and leader of the team, is extremely pleased: “We believe that some of these images are the highest-contrast images of Titan ever taken with any ground-based or earth-orbiting telescope.”

The excellent images of Titan’s surface show the location of the Huygens landing site in much detail. In particular, those centred at wavelength 1.6 micron and obtained with the Simultaneous Differential Imager (SDI) on NACO [4] provide the highest contrast and best views. This is firstly because the filters match the 1.6 micron methane window most accurately. Secondly, it is possible to get an even clearer view of the surface by subtracting accurately the simultaneously recorded images of the atmospheric haze, taken at wavelength 1.625 micron.

The images show the great complexity of Titan’s trailing side, which was earlier thought to be very dark. However, it is now obvious that bright and dark regions cover the field of these images.

The best resolution achieved on the surface features is about 0.039 arcsec, corresponding to 200 km on Titan. ESO PR Photo 04c/04 illustrates the striking agreement between the NACO/SDI image taken with the VLT from the ground and the ISS/Cassini map.

The images of Titan’s atmosphere at 2.12 microns show a still-bright south pole with an additional atmospheric bright feature, which may be clouds or some other meteorological phenomena. The astronomers have followed it since 2002 with NACO and notice that it seems to be fading with time. At 2.17 microns, this feature is not visible and the north-south asymmetry – also known as “Titan’s smile” – is clearly in favour in the north. The two filters probe different altitude levels and the images thus provide information about the extent and evolution of the north-south asymmetry.

Because the astronomers have also obtained spectroscopic data at different wavelengths, they will be able to recover useful information on the surface composition.

The Cassini/VIMS instrument explores Titan’s surface in the infrared range and, being so close to this moon, it obtains spectra with a much better spatial resolution than what is possible with Earth-based telescopes. However, with NACO at the VLT, the astronomers have the advantage of observing Titan with considerably higher spectral resolution, and thus to gain more detailed spectral information about the composition, etc. The observations therefore complement each other.

Once the composition of the surface at the location of the Huygens landing is known from the detailed analysis of the in-situ measurements, it should become possible to learn the nature of the surface features elsewhere on Titan by combining the Huygens results with more extended cartography from Cassini as well as from VLT observations to come.

Original Source: ESO News Release

Posted on by Fraser Cain

Gamma Rays Come from the Earth Too

A great mystery was set in motion a few years ago when a spacecraft designed to measure gamma-ray bursts — the most powerful explosions in the Universe — found that Earth was actually emitting some flashes of its own.

Named Terrestrial gamma-ray flashes (TGFs), these very short blasts of gamma rays lasting about one millisecond, are emitted into space from Earth’s upper atmosphere. Scientists believe electrons traveling at nearly the speed of light scatter off of atoms and decelerate in the upper atmosphere, emitting the TGFs.

The Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory discovered TGFs in 1994, but was limited in its ability to count them or measure peak energies. New observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite raise the maximum recorded energy of TGFs by a factor of ten and indicate that the Earth gives off about 50 TGFs every day, and possibly more.

“The energies we see are as high as those of gamma rays emitted from black holes and neutron stars,” said David Smith, an assistant professor of physics at UC Santa Cruz and author of a scientific paper on this topic.

The exact mechanism that accelerates the electron beams to produce TGFs is still uncertain, he said, but it probably involves the build-up of electric charge at the tops of thunderclouds due to lightning discharges. This results in a powerful electric field between the cloudtops and the ionosphere, the outer layer of Earth’s atmosphere.

TGFs have been associated with lightning strikes and may be related to red sprites and blue jets, side effects of thunderstorms that occur in the upper atmosphere and are typically only visible with high-altitude aircraft and satellites. The exact relationship between all these events is still unclear, though.

RHESSI was launched in 2002 to study X-rays and gamma-rays from solar flares, but its detectors pick up gamma rays from a variety of sources. While scientists estimate a global average rate of about 50 TGFs a day, the rate could be up to 100 times higher if, as some models indicate, TGFs are emitted as narrowly focused beams that would only be detected when the satellite is directly in their path.

Original Source: NASA News Release

Posted on by Fraser Cain

Matter Nears Light Speed Entering a Black Hole

The whole sky is filled with a diffuse, high energy glow: the cosmic X-ray background. In the last years the astronomers could show, that this radiation can almost completely be associated with individual objects. Similarly, Galileo Galilei in the beginning of the 17th century resolved the light of the Milky Way into individual stars. The X-ray background originates in hundreds of millions of supermassive Black Holes, which feed from matter in the centres of distant galaxy systems. Because the Black Holes are accreting mass, we observe them in the X-ray background during their growth phase. In today’s Universe, massive Black Holes are found in the centres of practically all nearby galaxies.

When matter rushes down the abyss of a Black Hole, it speeds around the cosmic maelstrom almost with the velocity of light and is heated up so strongly, that it emits its “last cry of help” in the form of high energy radiation, before it vanishes forever. Therefore the putatively invisible Black Holes are among the most luminous objects in the universe, if they are fed well in the centres of so called active galaxies. The chemical cal elements in the matter emit X-rays of a characteristic wavelength and can therefore be identified through their spectral fingerprint. Atoms of the element iron are a particularly useful diagnostic tool, because this metal is most abundant in the cosmos and radiates most intensely at high temperatures.

In a way similar to the radar traps, with which the police identifies speeding cars, the relativistic speeds of iron atoms circling the Black Hole can be measured through a shift in wavelength of their light. Through a combination of the effects predicted by Einstein’s special and general theory of relativity, however, a characteristically broadened, asymmetric line profile, i.e. a smeared fingerprint is expected in the X-ray light of Black Holes. Special relativity postulates that moving clocks run slow, and general relativity predicts that clocks run slow in the vicinity of large masses. Both effects lead to a shift of the light emitted by iron atoms into the longer wavelength part of the electromagnetic spectrum. However, if we observe the matter circling in the so called “accretion disk” (Fig. 1) from the side, the light from atoms racing towards us appears shifted to shorter wavelengths and much brighter than that moving away from us. These effects of Relativity are stronger, the closer the matter reaches to the black hole. Because of the curved spacetime they are strongest in fast rotating Black Holes. In the past years, measurements of relativistic iron lines have been possible in a few nearby galaxies – for the first time in 1995 with the Japanese ASCA satellite.

Now the researchers around G?nther Hasinger of the Max-Planck-Institute for extraterrestrial Physics, jointly with the group of Xavier Barcons at the Spanish Instituto de F?sica de Cantabria in Santander and Andy Fabian at the Institute of Astronomy in Cambridge, UK have uncovered the relativistically smeared fingerprint of iron atoms in the average X-ray light of about 100 distant Black Holes of the X-ray background (Fig. 2). The astrophysicists utilized the X-ray observatory XMM-Newton of the European Space Agency ESA. They pointed the instrument to a field in the Big Dipper constellation for more than 500 hours and discovered several hundred weak X-ray sources.

Because of the expansion of the Universe the galaxies move away from us with a speed increasing with their distance and thus their spectral lines all appear at different wavelength; the astronomers had first to correct the X-ray light of all objects into the rest frame of the Milky Way. The necessary distance measurements for more than 100 objects were obtained with the American Keck-Telescope. After having co-added the light from all objects, the researchers were very surprised about the unexpectedly large signal and the characteristically broadened shape of the iron line.

From the strength of the signal they deduced the fraction of iron atoms in the accreted matter. Surprisingly, the chemical abundance of iron in the “nutrition” of these relatively young Black Holes is about three times higher than in our Solar system, which had been created significantly later. The centres of galaxies in the early Universe therefore must have had a particularly efficient method to produce iron, possibly because violent star forming activity “breeds” the chemical elements rather quickly in active galaxies. The width of the line indicated that the iron atoms must radiate rather close to the black hole, consistent with rapidly spinning Black Holes. This conclusion is also found indirectly by other groups, who compared the energy in the X-ray background with the total mass of “dormant” Black Holes in nearby galaxies.

Original Source: Max Planck Society News Release

Want to update your computer desktop background? Here are some black background pictures.

Posted on by Fraser Cain

First Dark Matter Galaxy Discovered

A British-led team of astronomers have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter – the first ever detected. A dark galaxy is an area in the universe containing a large amount of mass that rotates like a galaxy, but contains no stars. Without any stars to give light, it could only be found using radio telescopes. It was first seen with the University of Manchester’s Lovell Telescope in Cheshire, and the sighting was confirmed with the Arecibo telescope in Puerto Rico. The unknown material that is thought to hold these galaxies together is known as ‘dark matter’, but scientists still know very little about what that is.

Dr. Jon Davies, one of the team of astronomers from Cardiff University, says; “The Universe has all sorts of secrets still to reveal to us, but this shows that we are beginning to understand how to look at it in the right way. It’s a really exciting discovery!”

When astronomers observe the visible Universe it is like looking out at the darkest night from a well-lit room. It is easy to see the street lights, car headlights and other well-lit rooms, but not the trees, the hedges and the mountains because they don’t emit any light. We live on a planet close to a star, so as astronomers our observing ‘room’ is always well-lit. This can make it difficult to find the dark, hidden objects.

The international team from the UK, France, Italy and Australia has been searching for dark galaxies using not visible light, but radio waves. They have been studying the distribution of hydrogen atoms throughout the Universe. Hydrogen gas emits radiation that can be detected at radio wavelengths. In the Virgo cluster of galaxies, about 50 million light years away, they found a mass of hydrogen atoms a hundred million times the mass of the Sun.

Dr Robert Minchin from Cardiff University is one of the UK astronomers who discovered the mysterious galaxy, named VIRGOHI21. He explains, “From the speed it is spinning, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone. If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope.”

Similar objects that have previously been discovered have since turned out to contain stars when studied with high-powered optical telescopes. Others have been found to be the remnants of two galaxies colliding. However, when the scientists studied the area in question using the Isaac Newton Telescope in La Palma, they found no visible trace of any stars, and no nearby galaxies that would suggest a collision. The astronomers first took observations of the dark object back in 2000 and it has taken almost five years to rule out all the other possible explanations. VIRGOHI21 appears to be the first dark galaxy ever detected.

Professor Andrew Lyne, Director of the Jodrell Bank Observatory, said that “he was very pleased that the efforts by engineers at the Observatory and Cardiff University in building the Multi-Beam receiver system used for these observations had proved so fruitful.” He praised those involved in the very complex data reduction required to analyse the data and said that “this exciting discovery shows that radio telescopes still have a very major role in helping to understand the Universe in which we live.”

Professor Mike Disney, a member of the team said: “As Sherlock Holmes famously said, ‘When you have eliminated the impossible, whatever is left – however improbable – must be the truth'”

Astronomers have been measuring the way in which stars and galaxies move for many years. These measurements indicate that there must be far more matter in the Universe than can be accounted for by the visible light we see. This ‘dark matter’ still holds many mysteries for astronomers – is it well mixed up amongst the stars, or is it separate from the stars? Another puzzle is that the current ideas about how galaxies form predict that there should be many more galaxies in the Universe than are visible to us. So, these two ideas – dark matter and the lack of galaxies – have led some astronomers to predict that there must be unseen ‘dark’ galaxies hidden in the Universe.

Finding a dark matter galaxy is an important breakthrough because, according to cosmological models, dark matter is five times more abundant than the ordinary (baryonic) matter that makes up everything we can see and touch.

The presence of dark matter in the Universe can be inferred by looking at the rotation of galaxies and measuring how fast their visible components are moving. The amount of matter in a galaxy dictates the gravitational force needed to hold it together. Astronomers have seen galaxies where the material is moving so fast that they should fly apart – as they don’t, there must be a stronger gravitational force acting than can be accounted for using visible matter. This has led astronomers to believe that there is more matter unseen – the mass of this ‘dark matter’ can be calculated from the gravitational force that must be acting to hold the galaxy together.

Dark galaxies are thought to form when the density of matter in a galaxy is too low to create the conditions for star formation. The observations of VIRGOHI21 may have other explanations, but they are consistent with the hydrogen being in a flat disc of rotating material – which is what is seen in ordinary spiral galaxies.

The Cardiff-led team hope to continue their unique observations to probe the hidden extent of the Universe that we live in.

Original Source: Jodrell Bank News Release

Posted on by Fraser Cain

Astrophoto: Jupiter by Paul F. Campbell

Amateur photographer Paul F. Campbell took this picture of Jupiter from just outside his home in Washington, PA. Paul used a Meade ETX autostar in polar mode only, which has been supercharged by Dr. Clay Sherrod. The camera that I use is a Sac 7 CCD run by Astrovideo. The photo started out as a 1 minute video, with frames taken at 1/50 second. Paul then processed the video in registax 3 and then cleaned up the final photo in Adobe Photoshop. If you’re an amateur astrophotographer, visit the Universe Today forum and post your pictures, we might feature it in the newsletter.

Posted on by Fraser Cain

Frozen Sea of Water Discovered on Mars

The discovery of a frozen sea close to the equator of Mars has brought the possibility of life on Mars one step closer. Open University scientist Dr John Murray is among the scientists who made the discovery from the High Resolution Stereo Camera images on board the Mars Express probe – the first European mission to another planet.

Dr Murray, of the Department of Earth Sciences, said: ?The fact that there have been warm and wet places beneath the surface of Mars since before life began on Earth, and that some are probably still there, means that there is a possibility that primitive micro-organisms survive on Mars today. This mission has changed many of my long-held opinions about Mars ? we now have to go there and check it out?.

The water that formed the sea appears to have originated beneath the surface of Mars, and to have erupted from a series of fractures known as the Cerberus Fossae, from where it flowed down in a catastrophic flood, and collected in a vast area 800 x 900 km about 5 million years ago. It initially averaged 45 metres deep, making it about the same size and depth as the North Sea. It was the pack-ice which formed on the surface of the sea that drew the attention of Mars Express scientists.

The young age of this feature has caused excitement among scientists. Although formed at the time when early hominids on Earth were evolving from apes, this is very young in geological terms, and suggests that vast flooding events, which are known to have occurred from beneath Mars? surface throughout its geological history, are still continuing to happen. The presence of liquid water for thousands of millions of years, even beneath the surface, is a possible habitat in which primitive life may have developed, and might still be surviving now. Clearly this must now be considered as a prime site for future missions looking for life.

The discovery was made by Dr Murray, Jan-Peter Muller (University College London), Gerhard Neukum (Free University, Berlin & Principal Investigator) and a team of international scientists working on the pictures sent back from Mars, and is to appear in the scientific journal Nature.

Mars Express, Europe?s first ever space mission to another planet, entered the orbit of Mars successfully on Christmas Day 2003, and since January 2004 the high resolution stereo camera on board has been taking a massive number of stereo images of the surface from altitudes as low as 270 km, showing details down to 10 metres.

Original Source: Open University News Release (Word Document)