Posted on by Fraser Cain

What are the Risks of Radiation for Humans in Space?

Image credit: NASA
NASA has a mystery to solve: Can people go to Mars, or not?

“It’s a question of radiation,” says Frank Cucinotta of NASA’s Space Radiation Health Project at the Johnson Space Center. “We know how much radiation is out there, waiting for us between Earth and Mars, but we’re not sure how the human body is going to react to it.”

NASA astronauts have been in space, off and on, for 45 years. Except for a few quick trips to the moon, though, they’ve never spent much time far from Earth. Deep space is filled with protons from solar flares, gamma rays from newborn black holes, and cosmic rays from exploding stars. A long voyage to Mars, with no big planet nearby to block or deflect that radiation, is going to be a new adventure.

NASA weighs radiation danger in units of cancer risk. A healthy 40-year-old non-smoking American male stands a (whopping) 20% chance of eventually dying from cancer. That’s if he stays on Earth. If he travels to Mars, the risk goes up.

The question is, how much?

“We’re not sure,” says Cucinotta. According to a 2001 study of people exposed to large doses of radiation–e.g., Hiroshima atomic bomb survivors and, ironically, cancer patients who have undergone radiation therapy–the added risk of a 1000-day Mars mission lies somewhere between 1% and 19%. “The most likely answer is 3.4%,” says Cucinotta, “but the error bars are wide.”

The odds are even worse for women, he adds. “Because of breasts and ovaries, the risk to female astronauts is nearly double the risk to males.”

Researchers who did the study assumed the Mars-ship would be built “mostly of aluminum, like an old Apollo command module,” says Cucinotta. The spaceship’s skin would absorb about half the radiation hitting it.

“If the extra risk is only a few percent? we’re OK. We could build a spaceship using aluminum and head for Mars.” (Aluminum is a favorite material for spaceship construction, because it’s lightweight, strong, and familiar to engineers from long decades of use in the aerospace industry.)

“But if it’s 19%? our 40something astronaut would face a 20% + 19% = 39% chance of developing life-ending cancer after he returns to Earth. That’s not acceptable.”

The error bars are large, says Cucinotta, for good reason. Space radiation is a unique mix of gamma-rays, high-energy protons and cosmic rays. Atomic bomb blasts and cancer treatments, the basis of many studies, are no substitute for the “real thing.”

The greatest threat to astronauts en route to Mars is galactic cosmic rays–or “GCRs” for short. These are particles accelerated to almost light speed by distant supernova explosions. The most dangerous GCRs are heavy ionized nuclei such as Fe+26. “They’re much more energetic (millions of MeV) than typical protons accelerated by solar flares (tens to hundreds of MeV),” notes Cucinotta. GCRs barrel through the skin of spaceships and people like tiny cannon balls, breaking the strands of DNA molecules, damaging genes and killing cells.

Astronauts have rarely experienced a full dose of these deep space GCRs. Consider the International Space Station (ISS): it orbits only 400 km above Earth’s surface. The body of our planet, looming large, intercepts about one-third of GCRs before they reach the ISS. Another third is deflected by Earth’s magnetic field. Space shuttle astronauts enjoy similar reductions.

Apollo astronauts traveling to the moon absorbed higher doses–about 3 times the ISS level–but only for a few days during the Earth-moon cruise. GCRs may have damaged their eyes, notes Cucinotta. On the way to the moon, Apollo crews reported seeing cosmic ray flashes in their retinas, and now, many years later, some of them have developed cataracts. Otherwise they don’t seem to have suffered much. “A few days ‘out there’ is probably safe,” concludes Cucinotta.

But astronauts traveling to Mars will be “out there” for a year or more. “We can’t yet estimate, reliably, what cosmic rays will do to us when we’re exposed for so long,” he says.

Finding out is the mission of NASA’s new Space Radiation Laboratory (NSRL), located at the US Department of Energy’s Brookhaven National Laboratory in New York. It opened in October 2003. “At the NSRL we have particle accelerators that can simulate cosmic rays,” explains Cucinotta. Researchers expose mammalian cells and tissues to the particle beams, and then scrutinize the damage. “The goal is to reduce the uncertainty in our risk estimates to only a few percent by the year 2015.”

Once the risks are known, NASA can decide what kind of spaceship to build. It’s possible that ordinary building materials like aluminum are good enough. If not, “we’ve already identified some alternatives,” he says.

How about a spaceship made of plastic?

“Plastics are rich in hydrogen–an element that does a good job absorbing cosmic rays,” explains Cucinotta. For instance, polyethylene, the same material garbage bags are made of, absorbs 20% more cosmic rays than aluminum. A form of reinforced polyethylene developed at the Marshall Space Flight Center is 10 times stronger than aluminum, and lighter, too. This could become a material of choice for spaceship building, if it can be made cheaply enough. “Even if we don’t build the whole spacecraft from plastic,” notes Cucinotta, “we could still use it to shield key areas like crew quarters.” Indeed, this is already done onboard the ISS.

If plastic isn’t good enough then pure hydrogen might be required. Pound for pound, liquid hydrogen blocks cosmic rays 2.5 times better than aluminum does. Some advanced spacecraft designs call for big tanks of liquid hydrogen fuel, so “we could protect the crew from radiation by wrapping the fuel tank around their living space,” speculates Cucinotta.

Can people go to Mars? Cucinotta believes so. But first, “we’ve got to figure out how much radiation our bodies can handle and what kind of spaceship we need to build.” In labs around the country, the work has already begun.

Original Source: NASA Science Story

Posted on by Fraser Cain

Interstellar Cloud of Gas is a Natural Lens

Image credit: Chandra
Imagine making a natural telescope more powerful than any other telescope currently operating. Then imagine using it to view closer to the edge of a black hole where its mouth is like a jet that forms super-hot charged particles and spits them millions of light-years into space. The task would seem to take one to the edge of no-return, a violent spot four billion light-years from Earth. That place is called a quasar named PKS 1257-326. Its faint twinkle in the sky is given the more catchy name of a ‘blazar’, meaning it is a quasar that varies dramatically in brightness, and may mask an even more mysterious, inner black hole of enormous gravitational power.

The length of a telescope needed to peer into the mouth of the blazar would have to be gigantic, about a million kilometers wide. But just such a natural lens has been found by a team of Australian and European astronomers; its lens is remarkably, a cloud of gas. The idea of a vast, natural telescope seems too elegant to avoid peering into.

The technique, dubbed ‘Earth-Orbit Synthesis’, was first outlined by Dr Jean-Pierre Macquart of the University of Groningen in The Netherlands and CSIRO’s Dr David Jauncey in a paper published in 2002. The new technique promises researchers the ability to resolve details about 10 microarcseconds across – equivalent to seeing a sugar cube on the Moon, from Earth.

“That’s a hundred times finer detail than we can see with any other current technique in astronomy,” says Dr. Hayley Bignall, who recently completed her PhD at the University of Adelaide and is now at JIVE, the Joint Institute for Very Long Baseline Interferometry in Europe. “It’s ten thousand times better than the Hubble Space Telescope can do. And it’s as powerful as any proposed future space-based optical and X-ray telescopes.”

Bignall made the observations with the CSIRO Australia Telescope Compact Array radio telescope in eastern Australia. When she refers to a microarcsecond, that is a measure of angular size, or how big an object looks. If for instance the sky were divided by degrees as a hemisphere, the unit is about a third of a billionth of one degree.

How does the largest telescope work? Using the clumpiness inside a cloud of gas is not entirely unfamiliar to night-watchers. Like atmospheric turbulence makes the stars twinkle, our own galaxy has a similar invisible atmosphere of charged particles that fill the voids between stars. Any clumping of this gas naturally can form a lens, just like the density change from air-to-glass bent and focused the light in what Galileo first saw when he pointed his first telescope towards the star. The effect is also called scintillation, and the cloud acts like a lens.

Seeing better than anyone else may be remarkable, but how to decide where to look first? The team is particularly interested using ‘Earth-Orbit Synthesis’ to peer close to black holes in quasars, which are the super-bright cores of distant galaxies. These quasars subtend such small angles on the sky as to be mere points of light or radio emission. At radio wavelengths, some quasars are small enough to twinkle in our Galaxy’s atmosphere of charged particles, called the ionized interstellar medium. Quasars twinkle or vary much more slowly than the twinkling one might associate with visible stars. So observers have to be patient to view them, even with the help of the most powerful telescopes. Any change in less than a day is considered to be fast. The fastest scintillators have signals that double or treble in strength in less than an hour. In fact the best observations made so far benefit from the annual motion of the Earth, since the yearly variation gives a complete picture, potentially allowing astronomers to see the violent changes in the mouth of a black-hole jet. That’s one of the team’s goals: “to see to within a third of a light-year of the base of one of these jets,” according to CSIRO’s Dr David Jauncey. “That’s the ‘business end’ where the jet is made.”

It is not possible to “see” into a black hole, because these collapsed stars are so dense, that their overpowering gravity doesn’t even allow light to escape. Only the behavior of matter outside a horizon some distance away from a black-hole can signal that they even exist. The largest telescope may help the astronomers understand the size of a jet at its base, the pattern of magnetic fields there, and how a jet evolves over time. “We can even look for changes as matter strays near the black hole and is spat out along the jets, ” says Dr Macquart.

Astrobiology Magazine had the opportunity to talk with Hayley Bignall about how to make a telescope from gas clouds, and why peering deeper than anyone before may offer insight into remarkable events near black holes. Astrobiology Magazine (AM): How did you first become interested in using gas clouds as part of a natural focus for resolving very distant objects?

Hayley Bignall (HB): The idea of using interstellar scintillation (ISS), a phenomenon due to radio wave scattering in turbulent, ionized Galactic gas “clouds”, to resolve very distant, compact objects, really represents the convergence of a couple of different lines of research, so I will outline a little of the historical background.

In the 1960s, radio astronomers used another kind of scintillation, interplanetary scintillation, due to scattering of radio waves in the solar wind, to measure sub-arcsecond (1 arcsecond = 1/3600 degrees of arc) angular sizes for radio sources. This was higher resolution than could be achieved by other means at the time. But these studies largely fell by the wayside with the advent of Very Long Baseline Interferometry (VLBI) in the late 1960s, which allowed direct imaging of radio sources with much higher angular resolution – today, VLBI achieves resolution better than a milliarcsecond.

I personally became interested in potential uses of interstellar scintillation through being involved in studies of radio source variability – in particular, variability of “blazars”. Blazar is a catchy name applied to some quasars and BL Lacertae objects – that is, Active Galactic Nuclei (AGN), probably containing supermassive black holes as their “central engines”, which have powerful jets of energetic, radiating particles pointed almost straight at us.

We then see effects of relativistic beaming in the radiation from the jet, including rapid variability in intensity across the whole electromagnetic spectrum, from radio to high-energy gamma rays. Most of the observed variability in these objects could be explained, but there was a problem: some sources showed very rapid, intra-day radio variability. If such short time-scale variability at such long (centimeter) wavelengths were intrinsic to the sources, they would be far too hot to stay around for years, as many were observed to do. Sources that hot should radiate all their energy away very quickly, as X-rays and gamma-rays. On the other hand, it was already known that interstellar scintillation affects radio waves; so the question of whether the very rapid radio variability was in fact ISS, or intrinsic to the sources, was an important one to resolve.

During my PhD research I found, by chance, rapid variability in the quasar (blazar) PKS 1257-326, which is one of the three most rapidly radio variable AGN ever observed. My colleagues and I were able to show conclusively that the rapid radio variability was due to ISS [scintillation]. The case for this particular source added to mounting evidence that intra-day radio variability in general is predominantly due to ISS.

Sources which show ISS must have very small, microarcsecond, angular sizes. Observations of ISS can in turn be used to “map” source structure with microarcsecond resolution. This is much higher resolution than even VLBI can achieve. The technique was outlined in a 2002 paper by two of my colleagues, Dr Jean-Pierre Macquart and Dr David Jauncey.

The quasar PKS 1257-326 proved to be a very nice “guinea pig” with which to demonstrate that the technique really works.

AM: The principles of scintillation are visible to anyone even without a telescope, correct–where a star twinkles because it covers a very small angle in the sky (being so far away), but a planet in our solar system doesn’t scintillate visibly? Is this a fair comparison of the principle for estimating distances visually with scintillation?

HB: The comparison with seeing stars twinkle as a result of atmospheric scintillation (due to turbulence and temperature fluctuations in the Earth’s atmosphere) is a fair one; the basic phenomenon is the same. We don’t see planets twinkle because they have much larger angular sizes – the scintillation gets “smeared out” over the planet’s diameter. In this case, of course, it is because the planets are so close to us that they subtend larger angles on the sky than stars.

Scintillation is not really useful for estimating distances to quasars, however: objects that are further away do not always have smaller angular sizes. For example, all pulsars (spinning neutron stars) in our own Galaxy scintillate because they have very tiny angular sizes, much smaller than any quasar, even though quasars are often billions of light-years away. In fact, scintillation has been used to estimate pulsar distances. But for quasars, there are many factors besides distance which affect their apparent angular size, and to complicate matters further, at cosmological distances, the angular size of an object no longer varies as the inverse of distance. Generally the best way of estimating the distance to a quasar is to measure the redshift of its optical spectrum. Then we can convert measured angular scales (e.g. from scintillation or VLBI observations) to linear scales at the redshift of the source

AM: The telescope as described offers a quasar example that is a radio source and observed to vary over an entire year. Are there any natural limits to the types of sources or the length of observation?

HB: There are angular size cut-offs, beyond which the scintillation gets “quenched”. One can picture the radio source brightness distribution as a bunch of independently scintillating “patches” of a given size, so that as the source gets larger, the number of such patches increases, and eventually the scintillation over all the patches averages out so that we cease to observe any variations at all. From previous observations we know that for extragalactic sources, the shape of the radio spectrum has a lot to do with how compact a source is – sources with “flat” or “inverted” radio spectra (i.e. flux density increasing towards shorter wavelengths) are generally the most compact. These also tend to be “blazar”-type sources.

As far as the length of observation goes, it is necessary to obtain many independent samples of the scintillation pattern. This is because scintillation is a stochastic process, and we need to know some statistics of the process in order to extract useful information. For fast scintillators like PKS 1257-326, we can get an adequate sample of the scintillation pattern from just one, typical 12-hour observing session. Slower scintillators need to be observed over several days to get the same information. However, there are some unknowns to solve for, such as the bulk velocity of the scattering “screen” in the Galactic interstellar medium (ISM). By observing at intervals spaced over a whole year, we can solve for this velocity – and importantly, we also get two-dimensional information on the scintillation pattern and hence the source structure. As the Earth goes around the Sun, we effectively cut through the scintillation pattern at different angles, as the relative Earth/ISM velocity varies over the course of the year. Our research group dubbed this technique “Earth Orbital Synthesis”, as it is analogous to “Earth rotation synthesis”, a standard technique in radio interferometry.

AM: A recent estimate for the number of stars in the sky estimated that there are ten times more stars in the known universe than grains of sand on Earth. Can you describe why jets and black holes are interesting as difficult-to-resolve objects, even using current and future space telescopes like Hubble and Chandra?

HB: The objects we are studying are some of the most energetic phenomena in the universe. AGN can be up to ~1013 (10 to the power of 13, or 10,000 trillion) times more luminous than the Sun. They are unique “laboratories” for high energy physics. Astrophysicists would like to fully understand the processes involved in forming these tremendously powerful jets close to the central supermassive black hole. Using scintillation to resolve the inner regions of radio jets, we are peering close to the “nozzle” where the jet forms – closer to the action than we can see with any other technique!

AM: In your research paper, you point out that how fast and how strongly the radio signals vary depends on the size and shape of the radio source, the size and structure of the gas clouds, the Earth’s speed and direction as it travels around the Sun, and the speed and direction in which the gas clouds are travelling. Are there built-in assumptions about either the shape of the gas cloud ‘lens’ or the shape of observed object that is accessible with the technique?

The Ring Nebula, although not useful imaging through, has the suggestive look of a far-away telescope lens. 2,000 light years distant in the direction of the constellation, Lyra, the ring is formed in the late stages of the inner star’s life, when it sheds a thick and expanding outer gas layer. Credit: NASA Hubble HST

HB: Rather than think of gas clouds, it is perhaps more accurate to picture a phase-changing “screen” of ionized gas, or plasma, which contains a large number of cells of turbulence. The main assumption which goes into the model is that the size scale of the turbulent fluctuations follows a power-law spectrum – this seems to be a reasonable assumption, from what we know about general properties of turbulence. The turbulence could be preferentially elongated in a particular direction, due to magnetic field structure in the plasma, and in principle we can get some information on this from the observed scintillation pattern. We also get some information from the scintillation pattern about the shape of the observed object, so there are no built-in assumptions about that, although at this stage we can only use quite simple models to describe the source structure.

AM: Are fast scintillators a good target for expanding the capabilities of the method?

HB: Fast scintillators are good simply because they don’t require as much observing time as slower scintillators to get the same amount of information. The first three “intra-hour” scintillators have taught us a lot about the scintillation process and about how to do “Earth Orbit Synthesis”.

AM: Are there additional candidates planned for future observations?

HB: My colleagues and I have recently undertaken a large survey, using the Very Large Array in New Mexico, to look for new scintillating radio sources. The first results of this survey, led by Dr Jim Lovell of the CSIRO’s Australia Telescope National Facility (ATNF), were recently published in the Astronomical Journal (October 2003). Out of 700 flat spectrum radio sources observed, we found more than 100 sources which showed significant variability in intensity over a 3-day period. We are undertaking follow-up observations in order to learn more about source structure on ultra-compact, microarcsecond scales. We will compare these results with other source properties such as emission at other wavelengths (optical, X-ray, gamma-ray), and structure on larger spatial scales, such as that seen with VLBI. In this way we hope to learn more about these very compact, high brightness temperature sources, and also, in the process, learn more about properties of the interstellar medium of our own Galaxy.

It seems that the reason for very fast scintillation in some sources is that the plasma “scattering screen” causing the bulk of the scintillation is quite nearby, within 100 light-years of the solar system. These nearby “screens” are apparently quite rare. Our survey found very few fast scintillators, which was somewhat surprising as two of the three fastest known scintillators were discovered serendipitously. We thought that there might be many more such sources!

Original Source: Astrobiology Magazine

Posted on by Fraser Cain

Mars Express Image of Kasei Vallis

Image credit: ESA
This vertical view shows the mouth of Kasei Vallis, one of the largest outflow channels on Mars.

The image was taken by the High Resolution Stereo Camera (HRSC) onboard Mars Express in orbit 61 from an altitude of 272 km. The resolution is 12 m per pixel. The image centre is located at 29.8? north and 309? east, the image width is 130 km, North is up.

The part of the outflow channel seen in this image has most probably been carved by glaciers or gigantic water-related outflows from terrestrial subglacial lakes. The blackish-bluish colour is related to sediments. The bright streaks oriented NE-SW are related to wind forces.

This image has been selected for release because of the various details which give an insight into the erosional history of the outflow channel. The image also illustrates how difficult it is to achieve near-true colour in images of Mars when atmospheric dust and haze have a major disturbing influence on the scene.

Original Source: ESA News Release

Posted on by Fraser Cain

Largest Mirror in Space Under Development

Image credit: ESA
Unlike conventional reflecting telescopes, whose mirrors are made from special glass or sometimes metal, Herschel’s telescope mirrors are being made from a novel ceramic material.

The manufacture of the shaped blank that will be used to create the flight model primary mirror for Herschel’s telescope was completed late last year. The blank is 3.5 metres in diameter and was fabricated by brazing together twelve segments. The segments were formed by isostatic pressing and sintering of silicon carbide. The mirror blank is the biggest silicon carbide structure in the world and, when completed, the mirror will be the largest single-component telescope reflector ever made for use in space. Larger mirrors are planned for future missions but they will be composed of multiple, deployable sections.

The silicon carbide segment manufacture and blank fabrication was performed by Boostec (Tarbes, France). The prime contractor for the Herschel telescope is EADS Astrium SAS (Toulouse, France).

All the major telescope components – the primary and secondary mirrors and the hexapod that supports the secondary mirror – are made from silicon carbide, allowing the telescope mass to be reduced to 300 kg rather than the 1.5 tonnes that would have resulted from using conventional materials. In addition to substantial mass savings, silicon carbide also offers the excellent structural stability and thermal properties needed to maintain a mirror location accuracy of better than 10 ?m.

The mirror blank will now be machined by Boostec to remove the internal stiffeners, used to provide mechanical stability during manufacture, and reduce the shell thickness to 2.5 mm. After machining, the mirror will be polished by Opteon (Turku, Finland) to obtain a parabolic surface with a roughness of less than 30 nm. The mirror accuracy will be such that the completed telescope will have a total wavefront error of less than 6 ?m RMS.

The polished mirror will be coated by vacuum deposition at the Calar Alto Observatory (Almer?a, Spain), first with a 10 nm thick adhesive layer of nickel-chrome and then with a 300 nm reflective layer of aluminium.

Original Source: ESA News Release

What is the biggest telescope in the world?

Posted on by Fraser Cain

Glitch Delays X-43 Test

Image credit: NASA
The flight of NASA’s X-43A has been postponed, due to an incident with the rudder actuator on the booster. On Feb 11, during setup at Orbital Sciences Corporation for testing of the rudder and its actuator, an anomaly caused the actuator to go hard over and hit its mechanical stop, exceeding the torque to which the units were qualified.

Although the actuator may still function normally, it will have to be replaced. A joint government/contractor incident investigation is under way to determine the cause and corrective actions.

Before this incident, the program was considering a delay of the flight to late March to retune the booster autopilot, to optimize its performance based on the latest test data. With the requirement for a replacement actuator, the two activities will now be done in parallel. Planning is now focused on a late-March to early-April flight.

The X-43A is a high-risk, high-payoff flight research program. Designed to fly at seven and 10 times the speed of sound, and use scramjet engines instead of traditional rocket power, the small, 12-foot-long X-43A could represent a major leap forward toward the goal of providing faster, more reliable and less expensive access to space.

The stack, consisting of the X-43A and its modified Pegasus booster, will be air-launched by NASA’s B-52 carrier aircraft at 40,000 feet altitude. The booster will accelerate the experimental vehicle to Mach 7 at approximately 95,000 feet altitude. At booster burnout, the X-43 will separate and fly under its own power on a preprogrammed path. The flight will take place over a restricted Navy Pacific Ocean test range off the coast of Southern California.

Original Source: NASA News Release

Posted on by Fraser Cain

Venus Blazes Beside the Moon

Image credit: Sky and Telescope
Treat yourself to an eye-catching celestial treat on Monday evening, February 23, 2004. At dusk, just look to the west. There you’ll find Venus, the magnificently brilliant “Evening Star,” blazing to the right of the crescent Moon. Provided it’s clear, you can’t miss this celestial splendor. Venus will outshine every star in the sky and may even appear about as bright as the 3?-day-old Moon itself.

The Moon will have only about 15 percent of its disk illuminated by the Sun. But look closer and you will likely make out the rest of the lunar disk glowing faintly ? you may even see the Man in the Moon. This effect is known as earthshine. What you are seeing is reflected sunlight from Earth shining onto the Moon’s night landscape, providing a dull illumination.

Venus is so brilliant for two reasons: it’s closer to the Sun than Earth so it gets lit more brightly, and its white clouds reflect sunlight very well. Although the Moon and Venus look close together, they’re actually at very different distances. On the night of the 23rd, the Moon is 244,000 miles (392,000 kilometers) from Earth, but Venus is 370 times farther: 90 million miles (145 million km) away. Venus is sometimes called our sister planet because it is similar in size to Earth.

For members of the broadcast media, the timing of this celestial pairing will make for a perfect opportunity to take your cameras outside for a live shot during the evening news. Be sure to take advantage.

Original Source: Sky and Telescope News Release

Posted on by Fraser Cain

Opportunity Digs Out a Trench

Image credit: NASA/JPL
If you’re a geologist, you always keep a shovel handy. One of the best ways to understand the geologic history of an area is to dig down and examine the layers of material. NASA’s rovers couldn’t bring a shovel to Mars, but they still have a way to get a look down under the surface – they can dig a trench with their wheels.

Engineers perfected a technique here on Earth where the twin Mars Exploration Rovers lock up five of their six wheels and turn the sixth to excavate a trench down into the Martian soil. Depending on the kind of dirt, this “shovel” can get down more than 10 cm, and reveal the deeper layers.

And today, NASA’s Opportunity rover did just that.

The rover used its right front wheel to dig a trench into the soil at an area called Hematite ridge. After the rover completed the operation, engineers were able to confirm that it had scooped out dirt approximately 8 to 10 cm deep and 20 cm wide. The rover’s hazard cameras confirmed that the subsurface soil is much brighter than the dark-red topsoil.

The area was selected because it’s rich in hematite; a mineral on Earth which usually forms in the presence of liquid water (although, it can be created through volcanic processes as well).

With the deeper soil on the surface, the rover can now use its suite of scientific instruments to measure the soil, to help scientists get a better idea of what could have deposited the hematite.

Once Opportunity completes its analysis of the trenched soil, it will make its way to a site called El Capitan, which is part of a rock outcrop on the side of the crater that the rover landed inside.

Posted on by Fraser Cain

Titan Could Help the Study of Oceanography

Image credit: Mark Robertson-Tessi
After a 7-year interplanetary voyage, NASA?s Cassini spacecraft will reach Saturn this July and begin what promises to be one of the most exciting missions in planetary exploration history.

After years of work, scientists have just completed plans for Cassini?s observations of Saturn?s largest moon, Titan.

“Of course, no battle plan survives contact with the enemy,” said Ralph Lorenz, an assistant research scientist at the University of Arizona?s Lunar and Planetary Laboratory in Tucson.

The spacecraft will deploy the European Space Agency?s Huygens probe to Titan for a January 2005 landing. Nearly half the size of Earth, frigid Titan is the only moon in the solar system with a thick atmosphere. Smog has prevented scientists from getting more than a tantalizing hint of what may be on the moon?s amazing surface.

“Titan is a completely new world to us, and what we learn early on will likely make us want to adjust our plans. But we have 44 flybys of Titan in only four years, so we have to have a basic plan to work to.”

Scientists have long thought that, given the abundant methane in Titan’s atmosphere, there might be liquid hydrocarbons on Titan. Infrared maps taken by the Hubble Space Telescope and ground-based telescopes show bright and dark regions on Titan’s surface. The maps indicate the dark regions are literally pitch-black, suggesting liquid ethane and methane.

Last year, data from the Arecibo telescope showed there are many regions on Titan that are both fairly radar-dark and very smooth. One explanation is that these areas are seas of methane and ethane. These two compounds, present in natural gas on Earth, are liquid at Titan’s frigid surface temperature, 94 degrees Kelvin (minus 179 degrees Celsius).

Titan will be an outstanding laboratory for oceanography and meteorology, Lorenz predicts.

“Many important oceanographical processes, like the transport of heat from low to high latitudes by ocean currents, or the generation of waves by wind, are known only empirically on Earth,” Lorenz said. “If you want to know how big waves get for a given windspeed, you just go out and measure both of them, get a lot of datapoints, and fit a line through them.

“But that’s not the same as understanding the underlying physics and being able to predict how things will be different if circumstances change. By giving us a whole new set of parameters, Titan will really open our understanding of how oceans and climates work.”

Cassini/Huygens will answer many questions, among them:

Are the winds strong enough to whip up waves that will cut cliffs in the lakesides? Will they form steep beaches, or will the strong tides caused by Saturn’s gravity be a bigger effect, forming wide, shallow tidal flats?

How deep are Titan’s seas? This question bears on the history of Titan’s atmosphere, which is the only other significant nitrogen atmosphere in the solar system, apart from the one you’re breathing now.

And do the oceans have the same composition everywhere? Just as there are salty seas and freshwater lakes on Earth, some seas on Titan may be more ethane-rich than others.

Lorenz began working on the Huygens project as an engineer for the European Space Agency in 1990, then earned his doctorate from the University of Kent at Canterbury, England, while building one of the probe’s experiments. He joined the University of Arizona in 1994 where he started work on Cassini’s Radar investigation. He is a co-author of the book, “Lifting Titan’s Veil” published in 2002 by Cambridge University Press.

Original Source: UA News Release

Posted on by Fraser Cain

Why is Mars So Dry?

Image credit: NASA/JPL
The MER rovers Spirit and Opportunity, now traveling on the surface of Mars, are exploring a geography drier than the driest desert on Earth. Despite the polar ice caps and suspected pockets of liquid water beneath the martian surface, the amount of water on Mars is but a teaspoon compared to the vast watery reserves of Earth. Why is Mars so dry?

The inner planets of our solar system – Mars, Earth, Venus and Mercury – formed by the accumulation of small rocks and dust that swirled around the sun in its earliest years. If the Earth and Mars are made of the same stardust, they should have been born with about the same ratio of water.

Many scientists think Mars once was very watery, but lost its oceans due to the low mass of the planet. This, combined with a thin atmosphere, allowed most of the water on Mars to evaporate out into space.

But according to a study by Jonathan Lunine of the Lunar and Planetary Laboratory at the University of Arizona, the Red Planet was dry from the very beginning.

Lunine, writing in the journal Icarus in 2003 with colleagues John Chambers, Alessandro Morbidelli, and Laurie Leshin, says that Mars was originally a planetary embryo. In essence, a planetary embryo is a very large asteroid that can be as massive as Mercury or Mars. This pre-Mars embryo existed in the asteroid belt, which at the time was more widely dispersed in the solar system, spread out between 0.5 to 4 AU from the sun. Today the main asteroid belt is roughly at 2 to 4 AU, located between Mars (1.5 AU) and Jupiter (5.2 AU).

Lunine says that Mars grew to its present size from accumulations of smaller asteroids and comets. He says that the more massive Earth, in comparison, mostly formed from large planetary embryos colliding into each other.

“By chance Mars was not struck by giant asteroids while Earth was – the lucky versus unlucky pedestrian,” says Lunine. “But Mars was struck by much smaller bodies because these are so numerous.”

The Earth currently orbits the sun at 1 AU. Lunine says that planetary embryos in this orbit would not have had much water. Early in the sun’s evolution, during planetary formation, the dusty disk that surrounded the young star was very hot. Water-bearing compounds would not have been able to form in this disk at 1 AU.

Since Mars is further away from the sun than Earth, and closer to the cooler, “moist” regions of the asteroid belt, it would seem logical that Mars would have been born with more water. Yet Lunine says that Mars probably acquired only 6 to 27 percent of an Earth’s ocean (1 Earth ocean =1.5 ?1021 kg).

That’s because some of the planetary embryos that eventually constituted the Earth were saturated with water. While 90 percent of the embryos that formed the Earth were from the 1 AU region, and therefore dry, 10 percent were from 2.5 AU and beyond. Embryos coming from this distance would’ve had large supplies of water. Smaller asteroids coming from this distance would’ve contributed to the Earth’s water supply as well. At most, Lunine says that only 15 percent of Earth’s water came from comets.

Mars, meanwhile, had the bad luck to be born as a single dry rock. Mars eventually received some water late in the formation game, after its core had already formed and it had nearly reached its present mass. According to Lunine’s scenario, Jupiter also gained its present day mass around this time. Jupiter’s gravity then either sucked in nearby asteroids or caused them to scatter outwards. The proto-Mars somehow escaped being shifted by Jupiter’s gravity, but was bombarded by the outward-bound asteroids.

“The impacts of small asteroids and comets constituted a “late veneer” which added water to Mars, in contrast to the picture for Earth where water was added through collisions with Mercury-sized embryos throughout a growth period of some tens of millions of years,” the scientists write.

Although Mars doesn’t form in their computer model, the scientists think that may reflect the chaotic nature of planetary formation, where the directions of planetary embryos and asteroids are unpredictable and many outcomes are possible.

“There is a fair amount of randomness involved in building the terrestrial planets, so ending up with a Mars that did not happen to accrete many water-rich planetesimals is a possible occurrence,” says Alan Boss of the Carnegie Institution of Washington. “This may well help explain the paucity of water on modern-day Mars.”

Such differences in planetary formation also could occur among the inner planets of other solar systems. So far, astronomers know of 104 stars that have planets orbiting them. All of the extrasolar planets found so far are gas giants, but it seems likely that terrestrial planets like Mars and the Earth also could orbit distant stars, even though we do not yet have the technology to detect them.

If some inner terrestrial planets are formed by collisions of several planetary embryos, while others are embryos that only gather up moist comets and asteroids, then planets around these other stars could have very different amounts of water. Lunine suggests that the timing and formation of the gas giant planets in each solar system will play an important role in this process, just as Jupiter has influenced the character of our own solar system.

Lunine currently has a paper in Icarus, with Tom Quinn and Sean Raymond of the University of Washington, on the possible variation in water abundance for terrestrial planets around other stars. In addition, he is carefully watching the data collected by the MER rovers Spirit and Opportunity, as well as the satellites currently orbiting Mars.

“Odyssey, MER, and Mars Express will determine how much water exists at present, hopefully, and provide better constraints on past water abundance,” says Lunine. “I am particularly interested in the MARSIS radar results, and those of its successor – SHARAD.”

MARSIS is a radar device on the Mars Express satellite that can look through the top five kilometers of martian crust to search for layers of water and ice. The Italian space agency is planning to fly a shallow subsurface radar, called SHARAD, on NASA’s Mars Reconnaissance Orbiter to see if water ice is present at depths greater than one meter. While MARSIS has a higher penetration capability, it has much lower resolution than SHARAD will have.

Original Source: Astrobiology Magazine