Posted on by Fraser Cain

Building Life from Star-Stuff

Supernova Remnant N 63A. Image credit: Hubble Click to enlarge
Life on Earth was made possible by the death of stars. Atoms like carbon and oxygen were expelled in the last few dying gasps of stars after their final supplies of hydrogen fuel were used up.

How this star-stuff came together to form life is still a mystery, but scientists know that certain atomic combinations were necessary. Water – two hydrogen atoms linked to one oxygen atom -was vital to the development of life on Earth, and so NASA missions now search for water on other worlds in the hopes of finding life elsewhere. Organic molecules built mostly of carbon atoms are also thought to be important, since all life on Earth is carbon-based.

The most popular theories of the origin of life say the necessary chemistry occurred at hydrothermal vents on the ocean floor or in some sunlit shallow pool. However, discoveries in the past few years have shown that many of the basic materials for life form in the cold depths of space, where life as we know it is not possible.

After dying stars belch out carbon, some of the carbon atoms combine with hydrogen to form polycyclic aromatic hydrocarbons (PAHs). PAHs — a kind of carbon soot similar to the scorched portions of burnt toast — are the most abundant organic compounds in space, and a primary ingredient of carbonaceous chondrite meteorites. Although PAHs aren’t found in living cells, they can be converted into quinones, molecules that are involved in cellular energy processes. For instance, quinones play an essential role in photosynthesis, helping plants turn light into chemical energy.

The transformation of PAHs occurs in interstellar clouds of ice and dust. After floating through space, PAH soot eventually condenses into these “dense molecular clouds.” The material in these clouds blocks out some but not all of the harsh radiation of space. The radiation that does filter through modifies the PAHs and other material in the clouds.

Infrared and radio telescope observations of the clouds have detected the PAHs, as well as fatty acids, simple sugars, faint amounts of the amino acid glycine, and over 100 other molecules, including water, carbon monoxide, ammonia, formaldehyde, and hydrogen cyanide.

The clouds have never been sampled directly — they’re too far away — so to confirm what is occurring chemically in the clouds, a research team led by Max Bernstein and Scott Sandford at the Astrochemistry Laboratory at NASA’s Ames Research Center set up experiments to mimic the cloud conditions.

In one experiment, a PAH/water mixture is vapor-deposited onto salt and then bombarded with ultraviolet (UV) radiation. This allows the researchers to observe how the basic PAH skeleton turns into quinones. Irradiating a frozen mixture of water, ammonia, hydrogen cyanide, and methanol (a precursor chemical to formaldehyde) generates the amino acids glycine, alanine and serine — the three most abundant amino acids in living systems.

Scientists have created primitive organic cell-like structures, or vesicles.

Because UV is not the only type of radiation in space, the researchers also have used a Van de Graaff generator to bombard the PAHs with mega-electron volt (MeV) protons, which have similar energies to cosmic rays. The MeV results for the PAHs were similar although not identical to the UV bombardment. A MeV study for the amino acids has not yet been conducted.

These experiments suggest that UV and other forms of radiation provide the energy needed to break apart chemical bonds in the low temperatures and pressures of the dense clouds. Because the atoms are still locked in ice, the molecules don’t fly apart, but instead recombine into more complex structures.

In another experiment led by Jason Dworkin, a frozen mixture of water, methanol, ammonia and carbon monoxide was subjected to UV radiation. This combination yielded organic material that formed bubbles when immersed in water. These bubbles are reminiscent of cell membranes that enclose and concentrate the chemistry of life, separating it from the outside world.

The bubbles produced in this experiment were between 10 to 40 micrometers, or about the size of red blood cells. Remarkably, the bubbles fluoresced, or glowed, when exposed to UV light. Absorbing UV and converting it into visible light in this way could provide energy to a primitive cell. If such bubbles played a role in the origin of life, the fluorescence could have been a precursor to photosynthesis.

Fluorescence also could act as sunscreen, diffusing any damage that otherwise would be inflicted by UV radiation. Such a protective function would have been vital for life on the early Earth, since the ozone layer, which blocks out the sun’s most destructive UV rays, did not form until after photosynthetic life began to produce oxygen.

From space clouds to the seeds of life

Dense molecular clouds in space eventually gravitationally collapse to form new stars. Some of the leftover dust later clumps together to form asteroids and comets, and some of these asteroids clump together to form planetary cores. On our planet, life then arose from whatever basic materials were at hand.

The large molecules necessary to build living cells are:

* Proteins
* Carbohydrates (sugars)
* Lipids (fats)
* Nucleic acids

Meteorites have been found to contain amino acids (the building blocks of proteins), sugars, fatty acids (the building blocks of lipids), and nucleic acid bases. The Murchison meteorite, for instance, contains chains of fatty acids, various types of sugars, all five nucleic acid bases, and more than 70 different amino acids (life uses 20 amino acids, only six of which are in the Murchison meteorite).

Because such carbonaceous meteorites are generally uniform in composition, they are thought to be representative of the initial dust cloud from which the sun and solar system were born. So it seems that nearly everything needed for life was available at the beginning, and meteorites and comets then make fresh deliveries of these materials to the planets over time.

If this is true, and if molecular dust clouds are chemically similar throughout the galaxy, then the ingredients for life should be widespread.

The downside of the abiotic production of the ingredients for life is that none of them can be used as “biomarkers,” indicators that life exists in a particular environment.

Max Bernstein points to the Alan Hills meteorite 84001 as an example of biomarkers that didn’t provide proof of life. In 1996, Dave McKay of NASA’s Johnson Space Center and his colleagues announced there were four possible biomarkers within this martian meteorite. ALH84001 had carbon globules containing PAHs, a mineral distribution suggestive of biological chemistry, magnetite crystals resembling those produced by bacteria, and bacteria-like shapes. While each alone was not thought to be evidence for life, the four in conjunction seemed compelling.

After the McKay announcement, subsequent studies found that each of these so-called biomarkers also could be produced by non-living means. Most scientists therefore are now inclined to believe that the meteorite does not contain fossilized alien life.

“As soon as they had the result, people went gunning for them because that’s the way it works,” says Bernstein. “Our chances of not making an error when we come up with a biomarker on Mars or on Europa will be much better if we’ve already done the equivalent of what those guys did after McKay, et al., published their article.”

Bernstein says that by simulating conditions on other planets, scientists can figure out what should be happening there chemically and geologically. Then, when we visit a planet, we can see how closely reality matches the predictions. If there’s anything on the planet that we didn’t expect to find, that could be an indication that life processes have altered the picture.

“What you have on Mars or on Europa is material that’s been delivered,” says Bernstein. “Plus, you have whatever has formed subsequently from whatever conditions are present. So (to look for life), you need to look at the molecules that are there, and keep in mind the chemistry that may have happened over time.”

Bernstein thinks chirality, or a molecule’s “handedness,” could be a biomarker on other worlds. Biological molecules often come in two forms that, while chemically identical, have opposite shapes: a “left-handed” one, and its mirror image, a “right-handed” one. A molecule’s handedness is due to how the atoms bond. While handedness is evenly dispersed throughout nature, in most cases living systems on Earth have left-handed amino acids and right-handed sugars. If molecules on other planets show a different preference in handedness, says Bernstein, that could be an indication of alien life.

“If you went to Mars or Europa and you saw a bias the same as ours, with sugars or amino acids having our chirality, then people would simply suspect it was contamination,” says Bernstein. “But if you saw an amino acid with a bias towards the right, or if you saw a sugar that had a bias towards the left — in other words, not our form — that would be really compelling.”

However, Bernstein notes that the chiral forms found in meteorites reflect what is seen on Earth: meteorites contain left-handed amino acids and right-handed sugars. If meteorites represent the template for life on Earth, then life elsewhere in the solar system also may reflect that same bias in handedness. Thus, something more than chirality may be needed for proof of life. Bernstein says that finding chains of molecules, “such as a couple of amino acids linked together,” also could be evidence for life, “because in meteorites we tend to just see single molecules.”

Original Source: NASA Astrobiology

Posted on by Fraser Cain

The New Forum is Online

As I mentioned a few days ago, Phil Plait from Bad Astronomy and I have decided to merge our two forums into one super-space forum. The new forum is now live, and accessible from http://www.bautforum.com. This new forum has more than 10,000 members, and almost 550,000 posts.

Although the forum is functional and ready for conversations, we’ll still be tweaking it over the next few days, weeks, months. Let us know if you find any bugs. Please also let us know if you’re having any problems logging in with your username.

I look forward to seeing you there.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Researchers find clue to start of universe

Station with active crossed dipole. Image credit: Haystack Observatory Click to enlarge
If you want to hear a little bit of the Big Bang, you’re going to have to turn down your stereo.

That’s what neighbors of MIT’s Haystack Observatory found out. They were asked to make a little accommodation for science, and now the results are in: Scientists at Haystack have made the first radio detection of deuterium, an atom that is key to understanding the beginning of the universe. The findings are being reported in an article in the Sept. 1 issue of Astrophysical Journal Letters.

The team of scientists and engineers, led by Alan E.E. Rogers, made the detection using a radio telescope array designed and built at the MIT research facility in Westford, Mass. Rogers is currently a senior research scientist and associate director of the Haystack Observatory.

After gathering data for almost one year, a solid detection was obtained on May 30.

The detection of deuterium is of interest because the amount of deuterium can be related to the amount of dark matter in the universe, but accurate measurements have been elusive. Because of the way deuterium was created in the Big Bang, an accurate measurement of deuterium would allow scientists to set constraints on models of the Big Bang.

Also, an accurate measurement of deuterium would be an indicator of the density of cosmic baryons, and that density of baryons would indicate whether ordinary matter is dark and found in regions such as black holes, gas clouds or brown dwarfs, or is luminous and can be found in stars. This information helps scientists who are trying to understand the very beginning of our universe.

Until now the deuterium atom has been extremely difficult to detect with instruments on Earth. Emission from the deuterium atom is weak since it is not very abundant in space-there is approximately one deuterium atom for every 100,000 hydrogen atoms, thus the distribution of the deuterium atom is diffuse. Also, at optical wavelengths the hydrogen line is very close to the deuterium line, which makes it subject to confusion with hydrogen; but at radio wavelengths, deuterium is well separated from hydrogen and measurements can provide more consistent results.

In addition, our modern lifestyle, filled with gadgets that use radio waves, presented quite a challenge to the team trying to detect the weak deuterium radio signal. Radio frequency interference bombarded the site from cell phones, power lines, pagers, fluorescent lights, TV, and in one case from a telephone equipment cabinet where the doors had been left off. To locate the interference, a circle of yagi antennas was used to indicate the direction of spurious signals, and a systematic search for the RFI sources began.

At times, Rogers asked for help from Haystack’s neighbors, and in several instances replaced a certain brand of answering machine that was sending out a radio signal with one that did not interfere with the experiment. The interference caused by one person’s stereo system was solved by having a part on the sound card replaced by the factory.

The other members of the team working with Rogers are Kevin Dudevoir, Joe Carter, Brian Fanous and Eric Kratzenberg (all of Haystack Observatory) and Tom Bania of Boston University.

The Deuterium Array at Haystack is a soccer-field size installation conceived and built at the Haystack facility with support from the National Science Foundation, MIT and TruePosition Inc.

Original Source: MIT News Release

Posted on by Fraser Cain

Hubble’s Neptune Movies

Blue-green Neptune and its satellites. Image credit: NASA/ESA Click to enlarge
New NASA Hubble Space Telescope images of the distant planet Neptune show a dynamic atmosphere and capture the fleeting orbits of its satellites. The images have been assembled into a time-lapse movie revealing the orbital motion of the satellites.

Images were taken in 14 different colored filters probing various altitudes in Neptune’s deep atmosphere so that scientists can study the haze and clouds in detail.

These are several snapshots from the Neptune movie.

The natural-color view of Neptune (to left), common to naked eye telescopic views by amateur astronomers, reveals a cyan colored planet. Methane gas in Neptune’s atmosphere absorbs most of the red sunlight hitting the planet, making it look blue-green. The image was created by combining images in red, green, and blue light.

Neptune’s subtle features are more visible in the enhanced-color view (top right). Images taken in special methane filters show details not visible to the human eye (bottom right). The features seen in this enhanced image must be above most of the sunlight-absorbing methane to be detectable through these special filters.

The planet is so dark at the methane wavelengths that long exposures can be taken, revealing some of Neptune’s smaller moons. Clockwise from the top (in composite image at left), these moons are Proteus (the brightest), Larissa, Despina, and Galatea. Neptune had 13 moons at last count.

Neptune is the most distant giant planet in our Solar System, orbiting the Sun every 165 years. It is so large tht nearly 60 Earths could fit inside it. A day on Neptune is between 14 hours and 19 hours. The inner two thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is a mixture of heated gases comprised of hydrogen, helium, water and methane.

On April 29 and 30, 2005, Hubble images were taken every 4-5 hours, spaced at about a quarter of Neptune’s rotational period. These where combined to create a time-lapse movie of the dynamic planet.

Original Source: Hubble News Release

Posted on by Fraser Cain

Giant South African Telescope Online

NGC 6744 taken by SALT. Image credit: SALT Click to enlarge
Five years after breaking ground on a South African mountaintop near the edge of the Kalahari desert, astronomers today (Sept. 1, 2005) released the first images captured by the Southern African Large Telescope (SALT), now the equal of the world’s largest optical telescope and a prized window to the night skies of the southern hemisphere.

With a 10- by 11-meter hexagonal segmented mirror and state-of-the-art scientific instrumentation, the new telescope was constructed by an international consortium of universities and government agencies. Partners include the National Research Foundation of South Africa, UW-Madison’s College of Letters and Science, Poland’s Nicolas Copernicus Astronomical Centre and Rutgers University, among others.

The new $18 million observatory will provide unprecedented access to the astronomically rich skies of the southern hemisphere. Objects such as the Large and Small Magellanic Clouds, the galaxies nearest to our own Milky Way, will come into sharp view through the concerted focus of the 91 hexagonal mirror segments that comprise the SALT Telescope’s primary mirror array.

“We’re now players in the world of large telescopes,” says Eric Wilcots, a UW-Madison professor of astronomy. “We’re in an age in which answering the big, fundamental questions requires access to large telescopes in good, dark skies. SALT is just such a telescope.”

Access to the southern sky, says Wilcots, promises a bounty of observing: “The southern Milky Way is more spectacular and provides a richer treasure trove of objects than the northern Milky Way.”

Moreover, studies of thousands of individual stars in the Magellanic Clouds are planned to trace the history of those nearby galaxies. The results of those studies, Wilcots explains, can be extrapolated to galaxies in general, providing a more refined life history of objects like our own Milky Way.

Other southern sky objects of interest, according to Kenneth Nordsieck, a UW-Madison astronomer now in South Africa to help with the SALT Telescope’s commissioning, include Eta Carina, a nearby massive star that has been racked by a series of enigmatic and spectacular explosions over the past century; Omega Centauri, a globular cluster of stars in the Milky Way that some astronomers believe may be the fossil remains of another galaxy consumed long ago by the Milky Way; and Centaurus A, a nearby galaxy that recently experienced an explosion at its core.

A critical advantage for the SALT Telescope, according to astronomers, is its location in one of the darkest regions of the world. With no nearby cities or towns, the observatory will be little affected by the light pollution that seriously hampers many observatories in the Northern Hemisphere.

Together with Rutgers University, another member of the SALT consortium, Wisconsin astronomers and engineers have constructed and are now integrating into the observatory the primary scientific instrument for the telescope, a device known as the Prime Focus Imaging Spectrograph. When in place six stories above the primary mirror array, the $5 million device will give the SALT Telescope specialized capabilities to capture and analyze starlight in unprecedented ways.

Spectrometers are designed to parse light into its constituent wavelengths. The spectra they obtain are revealing, providing astronomers with far more information than simple images. They can help show the chemical makeup of objects, depict motion, and some wavelengths of light enable astronomers to see through the obscuring clouds of dust and gas that permeate space.

One specialized capability of the Prime Focus Imaging Spectrograph, according to Nordsieck, is the ability to make observations in the near ultraviolet, the same kind of light that causes sunburn. “This is one of the few big instruments that will be good in the ultraviolet,” says Nordsieck.

The images released today through the South African Astronomical Observatory, the SALT Observatory’s parent organization, were taken with a digital camera known as SALTICAM. They include stunning pictures of the Lagoon Nebula, a luminous stellar nursery; the globular star cluster 47 Tucanae; and NGC6744, a barred spiral galaxy that astronomers consider almost a twin of our own Milky Way.

“The declaration of first light signifies that SALT has arrived on the astronomical scene,” according to a statement issues by the South African Astronomical Observatory. Although a months-long period of commissioning and shakedown remains, “SALT is now in a very real sense an operational telescope.”

A critical upcoming milestone will be the integration of the Wisconsin-built Prime Focus Imaging Spectrograph, envisioned as the workhorse instrument for the SALT Telescope. Capable of capturing high-resolution pictures, movies and the telltale spectra of objects such as stars, galaxies and comets, the device will be perched high above the light gathering primary mirror array at the heart of the new telescope.

Installation is expected in mid-September. “It is progressing in fits and starts, about the way one would expect with something of this complexity,” says Nordsieck. “In the meantime, the telescope team has worked out a lot of kinks so there should be a relatively smooth commissioning.”

The development of the SALT Observatory, says Wilcots, is “a beacon for Southern African science. It is meant to inspire a new generation of African scientists, which will be the lasting value of SALT to Southern Africa.”

For UW-Madison, the telescope project represents a bridge from Madison to South Africa. “Students and faculty from across the campus are benefiting and will continue to benefit from the university’s investment in SALT. We now have a student exchange program with the University of Cape Town and we will be initiating an exchange with the University of the Western Cape in November,” says Wilcots.

He emphasizes that the South Africans are making a statement with their investment in the giant telescope. “It is meant to showcase the capability of Southern African scientists and engineers – and it has done that,” Wilcots says. “Keep in mind that there are only a handful, perhaps as few as three, black South Africans with Ph.Ds in astronomy. While we have problems with an underrepresented minority in science, South Africa has an under-represented majority.”

Original Source: UW-Madison News Release

Posted on by Fraser Cain

Rings from the Unlit Side

Saturn’s rings from their unlit side. Image credit: NASA/JPL/SSI Click to enlarge
This magnificent view looks down upon, and partially through, Saturn’s rings from their unlit side.
The densest part of the rings occults the bright globe of Saturn. Scientists can use observations like this to determine precisely the concentration of ring particles.

When the bright source is the signals coming from the spacecraft, the technique is called a ‘radio occultation.’ In a radio occultation measurement, a signal is beamed toward Earth from Cassini’s 4-meter-wide (13-foot) high-gain antenna. Researchers on Earth receive the signal as the spacecraft passes behind the rings. The reduction in Cassini’s radio signal tells researchers how densely packed the ring particles are. Scientists can also learn about the size distributions of the particles from occultations.

As an added (but tiny) bonus, Saturn’s moon Atlas (32 kilometers, or 20 miles across) is visible as a dark speck against the planet, just outside the A ring.

The image was taken in visible red light with the Cassini spacecraft wide-angle camera on Aug. 2, 2005, at a distance of approximately 617,000 kilometers (383,000 miles) from Saturn. The image scale is 37 kilometers (23 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

Spirit’s Mountaintop View

Mini-panorama taken by Spirit. Image credit: NASA/JPL Click to enlarge
Working atop a range of Martian hills, NASA’s Spirit rover is rewarding researchers with tempting scenes filled with evidence of past planet environments.

“When the images came down and we could see horizon all the way around, that was every bit as exhilarating as getting to the top of any mountain I’ve climbed on Earth,” said Chris Leger, a rover planner at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

The summit sits 82 meters (269 feet) above the edge of the surrounding plains. It is 106 meters (348 feet) higher than the site where Spirit landed nearly 20 months ago. Spirit and twin rover, Opportunity, successfully completed their three-month prime missions in April 2004. They have inspected dozens of rocks and soil targets since then, continuing their pursuit of geological evidence about formerly wet conditions on Mars.

“Spirit has climbed to the hilltop and looked over the other side, but NASA did not do this just to say we can do it. The Mars rovers are addressing fundamental questions about Martian history and planetary environments,” said NASA’s Mars Exploration Program Director Doug McCuistion.

The crest of “Husband Hill” offers Spirit’s views of possible routes into a basin to the south with apparently layered outcrops. Shortly after Spirit landed, it observed a cluster of seven hills about 3 kilometers (2 miles) east of its landing site. NASA proposed naming the range “Columbia Hills” in tribute to the last crew of Space Shuttle Columbia. The tallest of the hills commemorates Rick Husband, Columbia’s commander.

Volcanic rocks covering the plain Spirit crossed on its way to the hills bore evidence of only slight alteration by water. When Spirit reached the base of the hills five months after landing, it immediately began finding rocks with wetter histories.

“This climb was motivated by science,” said Steve Squyres of Cornell University, Ithaca, N.Y. Squyres is principal investigator for the rovers’ science instruments. “Every time Spirit has gained altitude, we’ve found different rock types. Also, we’re doing what any field geologist would do in an area like this: climbing to a good vantage point for plotting a route.”

Researchers are viewing possible routes south to apparently layered ledges and to a feature dubbed “home plate,” which might be a plateau of older rock or a filled-in crater.

The landing site and the Columbia Hills are within Gusev Crater, a bowl about 150 kilometers (95 miles) in diameter. The crater was selected as the landing site for the Spirit rover because the shape of the terrain suggests the crater once held a lake. Volcanic deposits appear to have covered any sign of ancient lakebed geology out on the plain, but scientists say the hills expose older layers that have been lifted and tipped by a meteorite impact or other event.

“We’re finding abundant evidence for alteration of rocks in a water environment,” said Ray Arvidson of Washington University, St. Louis, Mo. Arvidson is deputy principal investigator for the rovers’ science instruments. “What we want to do is figure out which layers were on top of which other layers. To do that it has been helpful to keep climbing for good views of how the layers are tilted to varying degrees. Understanding the sequence of layers is equivalent to having a deep drill core from drilling beneath the plains.”

Both Spirit and Opportunity have been extremely successful. Their solar panels are generating plenty of energy thanks to repeated dust-cleaning events. Spirit has driven 4,827 meters (3.00 miles), and Opportunity 5,737 meters (3.56 miles).

JPL manages the Mars Exploration Rover project for NASA’s Science Mission Directorate. For images and information about the rovers and their discoveries on the Web, visit: http://www.nasa.gov/vision/universe/solarsystem/mer_main.html or http://marsrovers.jpl.nasa.gov.

Original Source: NASA News Release

Posted on by Fraser Cain

Probing the Formation of Galaxy Clusters

XMM-Newton image of galaxy cluster. Image credit: ESA Click to enlarge
ESA?s X-ray observatory, XMM-Newton, has for the first time allowed scientists to study in detail the formation history of galaxy clusters, not only with single arbitrarily selected objects, but with a complete representative sample of clusters.

Knowing how these massive objects formed is a key to understanding the past and future of the Universe.
Scientists currently base their well-founded picture of cosmic evolution on a model of structure formation where small structures form first and these then make up larger astronomical objects.

Galaxy clusters are the largest and most recently formed objects in the known Universe, and they have many properties that make them great astrophysical ?laboratories?. For example, they are important witnesses of the structure formation process and important ?probes? to test cosmological models.

To successfully test such cosmological models, we must have a good observational understanding of the dynamical structure of the individual galaxy clusters from representative cluster samples.

For example, we need to know how many clusters are well evolved. We also need to know which clusters have experienced a recent substantial gravitational accretion of mass, and which clusters are in a stage of collision and merging. In addition, a precise cluster mass measurement, performed with the same XMM-Newton data, is also a necessary prerequisite for quantitative cosmological studies.

The most easily visible part of galaxy clusters, i.e. the stars in all the galaxies, make up only a small fraction of the total of what makes up the cluster. Most of the observable matter of the cluster is composed of a hot gas (10-100 million degrees) trapped by the gravitational potential force of the cluster. This gas is completely invisible to human eyes, but because of its temperature, it is visible by its X-ray emission.

This is where XMM-Newton comes in. With its unprecedented photon-collecting power and capability of spatially resolved spectroscopy, XMM-Newton has enabled scientists to perform these studies so effectively that not only single objects, but also whole representative samples can be studied routinely.

XMM-Newton produces a combination of X-ray images (in different X-ray energy bands, which can be thought of as different X-ray ?colours?), and makes spectroscopic measurements of different regions in the cluster.

While the image brightness gives information on the gas density in the cluster, the colours and spectra provide an indication of the cluster?s internal gas temperature. From the temperature and density distribution, the physically very important parameters of pressure and ?entropy? can be also derived. Entropy is a measure of the heating and cooling history of a physical system.

The accompanying three images illustrate the use of entropy distribution in the ?X-ray luminous? gas as a way of identifying various physical processes. Entropy has the unique property of decreasing with radiative cooling, increasing due to heating processes, but staying constant with compression or expansion under energy conservation.

The latter ensures that a ?fossil record? of any heating or cooling is kept even if the gas subsequently changes its pressure adiabatically (under energy conservation).

These examples are drawn from the REFLEX-DXL sample, a statistically complete sample of some of the most X-ray luminous clusters found in the ROSAT All-Sky Survey. ROSAT was an X-ray observatory developed in the 1990s in co-operation between Germany, USA and UK.

The images provide views of the entropy distribution coded in colour where the values increase from blue, green, yellow to red and white.

Original Source: ESA Portal

Posted on by Fraser Cain

The Lure of Europa

Europa. Image credit: NASA Click to enlarge
The discovery that Jupiter’s moon Europa most likely has a cold, salty ocean beneath its frozen icy crust has put Europa on the short list of objects in our solar system that astrobiologists would like to study further. At the Earth System Processes II conference in Calgary, Canada, Ron Greeley, planetary geologist and professor of geology at Arizona State University in Phoenix, Arizona, gave a talk summing up what is known about Jupiter and its moons, and what remains to be discovered.

There have been six spacecraft that have explored the Jupiter system. The first two were Pioneer spacecraft in the 1970s that flew by the Jupiter system and made some brief observations. Those were followed by the Voyager I and II spacecraft, which gave us our first detailed views of the Galilean satellites. But most of the information we have has come from the Galileo mission. More recently, there was a flyby of the Cassini spacecraft, that went by Jupiter and made observations on its way to Saturn, where it is currently in operation. But nearly everything we know about the geology of the Jupiter system, and in particular the Galilean satellites (Io, Europa, Ganymede and Callisto), came from the Galileo mission. Galileo gave us an incredible wealth of information that we’re still in the process of analyzing today.

There are four Galilean satellites. Io, the innermost, is volcanically the most active object in the solar system. It derives its internal energy from tidal stressing in the interior, as it is being pushed-pulled between Europa and Jupiter. The explosive volcanism we see there is very impressive. There are plumes that are ejected some 200 kilometers (124 miles) above the surface. We also see effusive volcanism in the form of lava flows erupting onto the surface. These are very high-temperature, very fluid flows. On Io we see these flows extending for hundreds of kilometers across the surface.

All of the Galilean satellites are in elliptical orbits, which means that sometimes they’re closer to Jupiter, other times they’re farther away, and they’re being pushed-pulled by their neighbors. That generates internal friction to sufficient levels, in the case of Io, to melt the interior and “drive” the volcanoes. The same processes are taking place on Europa. And there is a possibility of silicate volcanism taking place beneath the icy crust on Europa.

Ganymede is the largest satellite in the solar system. It has an outer icy shell. We think that it has a sub-ice ocean of liquid water over a silicate core and perhaps a small internal metallic core. Ganymede has been subjected to geologic processes since its formation. It has a complex history, dominated by tectonic processes. We see a combination of very old features and very young features. We can see complex facture patterns on its surface that crosscut older fracture patterns. The surface is fractured into blocks that have been shifted about on the overriding, apparently liquid, interior. We also see the impact history dating from the period of early bombardment. Unscrambling the tectonic history of Ganymede is a work in process.

Callisto is the outermost of the Galilean satellites. It, too, has been subjected to impact bombardment, reflecting the early accretion history of the solar system in general, and the Jupiter system in particular. The surface is dominated by craters of all sizes. But we were surprised by the apparent lack of very tiny impact craters. We see very tiny impact craters on its neighbor, Ganymede; we don’t see them on Callisto. There is some process, we think, that is erasing the small craters – but only in selected areas on the moon. This is a mystery that has not been resolved: What is the process that is removing the tiny craters in some areas, or alternatively, might they not have formed there for some reason to begin with? Again, this is a topic of ongoing research.

What I want to talk about primarily, though, is Europa. Europa is about the size of Earth’s moon. It is primarily a silicate object, but it has an outer shell of H2O, the surface of which is frozen. The total volume of water that covers its silicate interior exceeds all of the water on Earth. The surface of that water is frozen. The question is: What’s beneath that frozen shell? Is there solid ice all the way to the bottom, or is there a liquid ocean? We think there is liquid water beneath the icy crust, but we don’t really know that for sure. Our ideas are based on models, and like all models, they are subject to further study.

The reason we think that there is a liquid ocean on Europa is from the behavior of the induced magnetic field around Europa that was measured by the magnetometer on Galileo. Jupiter has an enormous magnetic field. It, in turn, induces a magnetic field, not only on Europa, but also on Ganymede and Callisto. The way that induced magnetic field behaves is consistent with the presence of a subsurface salty liquid ocean, not just on Europa, but also on Ganymede and Callisto.

We do know that the surface is water ice. We know that there are non-ice components present, which includes various salts. And we know that the surface has been geologically processed: it has been fractured, healed, broken up repeatedly. We also see relatively few impact craters on the surface. That indicates that the surface is geologically young. Europa could even be geologically active today. Images of one region, in particular, show a surface that has been severely broken up. The icy plates have been broken apart and shifted into new positions. Material has oozed between the cracks, then apparently frozen, and we think that this could be one of the places where there was upwelling material, perhaps driven by the tidal heating I talked about earlier.

We tend to forget the scale of things in the planetary sciences. But these icy blocks are huge. When we think about future exploration, we would like to get down on the surface and make certain key measurements. So we have to think about spacecraft systems that could land in this kind of terrain. Because it is these places that might have material derived from below the ice, they are the highest priority for exploration. And yet, as is often the case in planetary exploration, the most interesting places are the most difficult to get to.

So what would we like to know? First and most fundamental is the “ocean notion.” Does liquid water exist or not? Is the ice shell thick or thin? If there is an ocean there, how thick is that icy crust? This is very important to know when we think about exploring a possible liquid ocean on Europa: If we want to get into the ocean, how deep must we go through the ice? What is the age of the surface? We say “young,” but that’s only a relative term. Is it thousands, hundreds of thousands, millions, or even billions of years old? The models allow for quite a spread in ages, based on the impact crater frequency. What are the environments there today that are favorable for astrobiology? And what were the environments in the past? Were they the same, or have they changed through time? The answers to these questions require new data.

Another thing that drives our interest in exploring the Galilean satellites is trying to understand their geological histories. To some extent, the diversity that we see, from Io to Europa to Ganymede and Callisto, can be linked to the amount of tidal energy that’s driving the system. Maximum tidal energy drives the volcanism that is so dominant on Io. At the other extreme, very little tidal energy on Callisto results in the preservation of the impact-cratering record. Europa and Ganymede are in between these two extreme cases.

The total surface area of the three icy moons of Jupiter (Europa, Ganymede and Callisto) is greater than the surface area of Mars, and, in fact, is about equivalent to the entire land surface of Earth. So when we discuss the exploration of the icy Galilean satellites, there is a lot of terrain to cover.

As for future exploration, let me share a little history. Three years ago, NASA established the Prometheus project. The Prometheus project involves the development of nuclear power and nuclear propulsion, something that had not been considered seriously for quite some time. The first mission to be flown in the Prometheus project was the Jupiter Icy Moons Orbiter, or JIMO. The goal was to explore the three icy moons within the context of the Jupiter system. It was a very ambitious project. Well, earlier this year JIMO was cancelled. But it looks as though this coming year there will be approval for a geophysical orbiter for Europa. The initial steps for getting that spacecraft underway are being considered now. Europa is a very high priority for exploration, and in recognition of that priority, this mission is likely to happen.

Why are we so interested in Europa? When we talk about astrobiology, we consider the three ingredients for life: water, the right chemistry, and energy. Their presence doesn’t mean that the magic spark of life ever happened, but those are the things that we think are required for life. And so, as I outlined, all three of Jupiter’s icy moons are potential targets. But Europa is the highest priority, because it seems to have the maximum internal energy.

So, of course, first we would like to know: Is there an ocean, yes or no?

Then, what’s the three-dimensional configuration of the icy crust? We know that organisms can live in fractures and cracks in Arctic ice. Such cracks are likely to be present on Europa, too, and could be niches that are of high interest for astrobiology.

Then we want to map the organic and inorganic surface compositions. We see in the data that exist today that the surface is heterogeneous. It’s not just pure ice on the surface. There are some areas that seem to be richer in non-ice components than other places. We want to map that material.

We also want to map interesting surface features and identify the places that are most important for future exploration, including landers.

Then we want to understand Europa in the context of the Jupiter environment. For example, how does the radiation environment imposed by Jupiter affect surface chemistry on Europa?

Ultimately, we want to get down on the surface, because there are a number of things that we can do only from the surface. We have a great wealth of data from the Galileo mission, and hope to have even more from the potential Europa mission, but it’s remote-sensing data. Next, we want to get a lander onto the surface that could make some critical ground-truth measurements, to place the remote-sensing data into context. And so within the scientific community, we feel that the next mission to Europa and the Jupiter system ought to have a landed package of some kind. But whether this will actually happen or not, stay tuned!

Original Source: NASA Astrobiology