Category: Moon

A single grain of moondust hangs suspended in Abba’s vacuum chamber. Image credit: NASA Click to enlarge
Each morning, Mian Abbas enters his laboratory and sits down to examine–a single mote of dust. Zen-like, he studies the same speck suspended inside a basketball-sized vacuum chamber for as long as 10 to 12 days.

The microscopic object of his rapt attention is not just any old dust particle. It’s moondust. One by one, Abbas is measuring properties of individual dust grains returned by Apollo 17 astronauts in 1972 and the Russian Luna-24 sample-return spacecraft that landed on the Moon in 1976.

“Experiments on single grains are helping us understand some of the strange and complex properties of moondust,” says Abbas. This knowledge is important. According to NASA’s Vision for Space Exploration, astronauts will be back on the moon by 2018–and they’ll have to deal with lots of moondust.

The dozen Apollo astronauts who walked on the moon between 1969 and 1972 were all surprised by how “sticky” moondust was. Dust got on everything, fouling tools and spacesuits. Equipment blackened by dust absorbed sunlight and tended to overheat. It was a real problem.

Many researchers believe that moondust has a severe case of static cling: it’s electrically charged. In the lunar daytime, intense ultraviolet (UV) light from the sun knocks electrons out of the powdery grit. Dust grains on the moon’s daylit surface thus become positively charged.

Eventually, the repulsive charges become so strong that grains are launched off the surface “like cannonballs,” says Abbas, arcing kilometers above the moon until gravity makes them fall back again to the ground. The moon may have a virtual atmosphere of this flying dust, sticking to astronauts from above and below.

Or so the theory goes.

But do grains of lunar dust truly become positively charged when illuminated by ultraviolet light? If so, which grains are most affected–big grains or little grains? And what does moondust do when it’s charged?

These are questions Abbas is investigating in his “Dusty Plasma Laboratory” at the National Space Science and Technology Center in Huntsville, Alabama. Along with colleagues Paul Craven and doctoral student Dragana Tankosic, Abbas injects a single grain of lunar dust into a chamber and “catches” it using electric force fields. (The injector gives the grain a slight charge, allowing it to be handled by electric fields.) With the grain held suspended literally in mid-air, they “pump the chamber down to 10-5 torr to simulate lunar vacuum.”

Next comes the mesmerizing part: Abbas shines a UV laser on the grain. As expected, the dust gets “charged up” and it starts to move. By adjusting the chamber’s electric fields with painstaking care, Abbas can keep the grain centered; he can measure its changing charge and explore its fascinating characteristics.

Like the Apollo astronauts, Abbas has already discovered some surprises–even though his experiment is not yet half done.

“We’ve found two things,” says Abbas. “First, ultraviolet light charges moondust 10 times more than theory predicts. Second, bigger grains (1 to 2 micrometers across) charge up more than smaller grains (0.5 micrometer), just the opposite of what theory predicts.”

Clearly, there’s much to learn. For instance, what happens at night, when the sun sets and the UV light goes away?

That’s the second half of Abbas’s experiment, which he hopes to run in early 2006. Instead of shining a UV laser onto an individual lunar particle, he plans to bombard dust with a beam of electrons from an electron gun. Why electrons? Theory predicts that lunar dust may acquire negative charge at night, because it is bombarded by free electrons in the solar wind–that is, particles streaming from the sun that curve around behind the moon and hit the night-dark soil.

When Apollo astronauts visited the Moon 30+ years ago, they landed in daylight and departed before sunset. They never stayed the night, so what happened to moondust after dark didn’t matter. This will change: The next generation of explorers will remain much longer than Apollo astronauts did, eventually setting up a permanant outpost. They’ll need to know, how does moondust behave around the clock?

Stay tuned for answers from the Dusty Plasma Lab.

Original Source: NASA News Release

Lunar surface from Apollo 17. Image credit: NASA. Click to enlarge.
“If you can’t lick ’em, join ’em,” goes a cliché that essentially means “figure out how to live with whatever you can’t get rid of.”

That may be superb advice for living and working on the moon.

Scientists and engineers figuring out how to return astronauts to the moon, set up habitats, and mine lunar soil to produce anything from building materials to rocket fuels have been scratching their heads over what to do about moondust. It’s everywhere! The powdery grit gets into everything, jamming seals and abrading spacesuit fabric. It also readily picks up electrostatic charge, so it floats or levitates off the lunar surface and sticks to faceplates and camera lenses. It might even be toxic.

So what do you do with all this troublesome dust? Larry Taylor, Distinguished Professor of Planetary Sciences at the University of Tennessee has an idea:

Don’t try to get rid of it–melt it into something useful!

“I’m one of those weird people who like to stick things in ordinary kitchen microwave ovens to see what happens,” Taylor confessed to several hundred scientists at the Lunar Exploration Advisory Group (LEAG) conference at NASA’s Johnson Space Center last month.

At home in Tennessee, his most famous experiment involves a bar of Irish Spring soap, which quickly turns into “an abominable monster” when you hit the microwave’s Start button. But that’s not the one he told about at LEAG.

Apropos to the moon, he once put a small pile of lunar soil brought back by the Apollo astronauts into a microwave oven. And he found that it melted “lickety-split,” he said, within 30 seconds at only 250 watts.

The reason has to do with its composition. The lunar regolith, or soil, is produced when micrometeorites plow into lunar rocks and sand at tens of kilometers per second, melting it into glass. The glass contains nanometer-scale beads of pure iron – so called “nanophase” iron. It is those tiny iron beads that so efficiently concentrate microwave energy that they “sinter” or fuse the loose soils into large clumps.

This observation has inspired Taylor to imagine all kinds of machinery for sending to the moon that could fuse lunar dust into useful solids.

“Picture a buggy pulled behind a rover that is outfitted with a set of magnetrons,” that is, the same gizmo at the guts of a microwave oven. “With the right power and microwave frequency, an astronaut could drive along, sintering the soil as he goes, making continuous brick down half a meter deep–and then change the power settings to melt the top inch or two to make a glass road,” he suggested.

“Or say that you want a radio telescope,” he continued. “Find a round crater and run a little microwave ‘lawnmower’ up and down the crater’s sides to sinter a smooth surface. Hang an antenna from the middle–voila, instant Arecibo!” he exclaimed, referring to the giant 305-meter-diameter radio telescope in Puerto Rico formed out of a natural circular valley.

Technical challenges remain. Sintering moondust in a microwave oven on Earth isn’t the same as doing it on the airless moon. Researchers still need to work out details of a process to produce strong, uniformly sintered material in the harsh lunar environment.

But the idea has promise: Sintered rocket landing pads, roads, bricks for habitats, radiation shielding–useful products and dust abatement, all at once.

“The only limit,” says Taylor, “is imagination.”

Original Source: Science@NASA News Release

Artist illustration of SMART-1. Image credit: ESA. Click to enlarge.
ESA’s SMART-1 mission in orbit around the Moon has had its scientific lifetime extended by ingenious use of its solar-electric propulsion system (or ‘ion engine’).

In February this year, the SMART-1 mission was granted financial support to extend the mission by one year, starting at the end of July 2005. However, whether SMART-1 could actually survive that length of time all depended on the propulsion system, the ion engine, and the small amount of xenon fuel left on board.

Without using the remaining fuel and letting the orbit decay naturally, SMART-1 would have ended its mission sometime before May 2006. Engineers and flight controllers at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, were aware that the ion engine could not use all the fuel left on board. They had to keep two kilograms of fuel to maintain sufficient gaseous pressure inside the tank to be able to control the engine thrust.

However, ESA and industry worked together to find a way to stretch the technology of SMART-1’s engine to set a new record. New simulations and analysis allowed the SMART-1 flight control team to successfully operate the engine until the almost the last drop of fuel was consumed and an orbit with one-year lifetime was reached.

A series of re-boost manoeuvres, beginning in August 2005 has allowed the mission to be extended by one year, until July 2006. The engine was shutdown finally on 17 September after the last of these re-boost operations. SMART-1 is now coasting around the Moon ready to restart science observations on 1 October.

These re-boosts also brought the spacecraft into the optimal orbit to perform the more complex scientific observations to come in the extended phase. This orbit will have a perilune (lowest point of its orbit) closer to the equator than before, with very good solar illumination conditions over the whole year.

“This mission has given ESA a valuable experience about electric propulsion operations and navigation that can be exploited in future missions,” says Octavio Camino-Ramos, SMART-1 Spacecraft Operations Manager at ESOC.

From now on SMART-1 will be left in a natural orbit determined by lunar gravity, but also by perturbations by Earth and the Sun. Analyses show that SMART-1 will end its life naturally, through impact with the Moon surface, around mid August 2006.

Bernard Foing, ESA’s SMART-1 Project Scientist, said, “The first scientific phase of the mission, from March to July 2005, was essentially dedicated to simple observations of the Moon and the study of the behaviour of spacecraft and instruments in the difficult thermal conditions of the lunar environment. From early October, with the extended scientific phase, SMART-1 will perform more complex science operations.”

This autumn, science operations will include so-called ‘push broom’ observations, in which the spacecraft will be able to take colour images of the Moon surface by superimposing sequences of images of the same area taken with different colour filters.

“Multi-colour observations, surveys of the composition of the Moon, studies of polar regions illumination, the search for ice, support for future international lunar missions, and low-altitude observations until impact are our major objectives for this year,” added Bernard Foing.

Original Source: ESA News Release

Artist illustration of future astronauts on the Moon. Image credit: NASA. Click to enlarge.
NASA today announced the Regolith Excavation Challenge, a new Centennial Challenges prize competition that will award $250,000 to the winning team and has the potential to significantly contribute to the nation’s space exploration goals. The competition is in collaboration with the California Space Education and Workforce Institute (CSEWI).

The Regolith Excavation Challenge will award the prize money to the team that can design and build autonomously operating systems to excavate lunar regolith, or “moon dirt,” and deliver it to a collector.

The challenge will be conducted in a “head-to-head” competition format in late 2006 or early 2007 and will require teams to excavate and deliver as much regolith as possible in 30 minutes. A detailed set of rules for the competition will be finalized later this year.

“Excavation of lunar regolith is an important and necessary step toward using the resources on the moon to establish a successful base for life on its surface,” said NASA’s acting Associate Administrator for the Exploration Systems Mission Directorate, Douglas R. Cooke. “The unique physical properties of the lunar regolith make excavation a difficult technical challenge,” he added.

“This challenge continues NASA’s efforts to broaden interest in innovative concepts,” said Brant Sponberg, NASA’s Centennial Challenges program manager. “We hope to see teams from a broad spectrum of technical areas take part in this competition,” he noted.

“CSEWI is pleased to collaborate with NASA and to participate with the Centennial Challenges Regolith Excavation Prize Competition,” said CSEWI Director, the Honorable Andrea Seastrand. “This is a challenge that places all companies, institutions and individuals on a level playing field, thereby widening the doors of opportunity for technology innovators. While welcoming entities with existing NASA relationships, this challenge stimulates and reaches out to the nation’s untapped intellectual capital,” she added.

NASA’s Centennial Challenges program promotes technical innovation through a novel program of prize competitions. It is designed to tap the nation’s ingenuity to make revolutionary advances to support the Vision for Space Exploration and NASA goals. NASA’s Exploration Systems Mission Directorate manages the program.

CSEWI is a charitable, nonprofit corporation. It was formed to create understanding, enthusiasm and appreciation for space enterprise and space technology, and inspire parents, educators and students to engage in space-related education and enrichment activities. The Institute hopes to stimulate greater awareness and understanding of the space enterprise work force and research needs throughout academia, and attract, integrate and retain a robust space work force.

For more information about Centennial Challenges on the Internet, visit:
http://centennialchallenges.nasa.gov

For information about the California Space Education and Workforce Institute on the Internet, visit:
http://www.californiaspaceauthority.org/html/level-one/institute.html

Original Source: NASA News Release

The surface of the Moon is exposed to space radiation. Image credit: NASA Click to enlarge
On the Moon, many of the things that can kill you are invisible: breathtaking vacuum, extreme temperatures and space radiation top the list.

Vacuum and temperature NASA can handle; spacesuits and habitats provide plenty of air and insulation. Radiation, though, is trickier.

The surface of the Moon is baldly exposed to cosmic rays and solar flares, and some of that radiation is very hard to stop with shielding. Furthermore, when cosmic rays hit the ground, they produce a dangerous spray of secondary particles right at your feet. All this radiation penetrating human flesh can damage DNA, boosting the risk of cancer and other maladies.

According to the Vision for Space Exploration, NASA plans to send astronauts back to the Moon by 2020 and, eventually, to set up an outpost. For people to live and work on the Moon safely, the radiation problem must be solved.

“We really need to know more about the radiation environment on the Moon, especially if people will be staying there for more than just a few days,” says Harlan Spence, a professor of astronomy at Boston University.

To carefully measure and map the Moon’s radiation environment, NASA is developing a robotic probe to orbit the Moon beginning in 2008. Called the Lunar Reconnaissance Orbiter (LRO), this scout will pave the way for future human missions not only by measuring space radiation, but also by hunting for frozen water and mapping the Moon’s surface in unprecedented detail. LRO is a key part of NASA’s Robotic Lunar Exploration Program, managed by the Goddard Space Flight Center.

One of the instruments onboard LRO is the Cosmic Ray Telescope for the Effects of Radiation (CRaTER).

“Not only will we measure the radiation, we will use plastics that mimic human tissue to look at how these highly energetic particles penetrate and interact with the human body,” says Spence, who is the Principal Investigator for CRaTER.

By placing the radiation detectors in CRaTER behind various thicknesses of a special plastic that has similar density and composition to human tissue, Spence and his colleagues will provide much-needed data: Except for quick trips to the Moon during the Apollo program, most human spaceflight has occurred near Earth where our planet’s magnetic field provides a natural shield. In low-Earth orbit, the most dangerous forms of space radiation are relatively rare. That’s good for astronauts, but it leaves researchers with many unanswered questions about what radiation does to human tissue. CRaTER will help fill in the gaps.

Out in deep space, radiation comes from all directions. On the Moon, you might expect the ground, at least, to provide some relief, with the solid body of the Moon blocking radiation from below. Not so.

When galactic cosmic rays collide with particles in the lunar surface, they trigger little nuclear reactions that release yet more radiation in the form of neutrons. The lunar surface itself is radioactive!

So which is worse for astronauts: cosmic rays from above or neutrons from below? Igor Mitrofanov, a scientist at the Institute for Space Research and the Russian Federal Space Agency, Moscow, offers a grim answer: “Both are worse.”

Mitrofanov is Principle Investigator for the other radiation-sensing instrument on LRO, the Lunar Exploration Neutron Detector (LEND), which is partially funded by the Russian Federal Space Agency. By using an isotope of helium that’s missing one neutron, LEND will be able to detect neutron radiation emanating from the lunar surface and measure how energetic those neutrons are.

The first global mapping of neutron radiation from the Moon was performed by NASA’s Lunar Prospector probe in 1998-99. LEND will improve on the Lunar Prospector data by profiling the energies of these neutrons, showing what fraction are of high energy (i.e., the most damaging to people) and what fraction are of lower energies.

With such knowledge in hand, scientists can begin designing spacesuits, lunar habitats, Moon vehicles, and other equipment for NASA’s return to the Moon knowing exactly how much radiation shielding this equipment must have to keep humans safe.

NASA News Release

Hadley Rille on the Moon. Image credit: ESA/Space-X. Click to enlarge
This image, taken by the Advanced Moon Micro-Imager Experiment (AMIE) on board ESA?s SMART-1 spacecraft, shows the Hadley Rille on the south-east edge of Mare Imbrium on the Moon.

AMIE obtained this image from an altitude of about 2000 kilometres. It covers an area of about 100 kilometres and shows the region around Hadley Rille centred at approximately 25? North and 3? East.
The sinuous rille follows a course generally to the north-east toward the peak of Mount Hadley, after which it is named (bright feature, top right). To the east of this rille, south-west of Mount Hadley, is Mount Hadley Delta, one of the largest Appenine mountains.

The Appenine mountains mark the edge of the impact basin holding Mare Imbrium, rising between 1800 and 4500 metres above the mare. They are the bright bumps in the lower half of the image.

The valley between these two peaks is fairly well known because NASA astronauts David R. Scott and James B. Irwin landed there during the Apollo 15 mission in 1971. The landing site is near the upper right part of the rille (26.1? North and 3.9? East) on a dark mare plain called Palus Putredinis (Marsh of Decay).

The rille begins at the curved gash on the left side of this image, and is seen clearest in the rectangular, mare-floored valley in the centre of the image. It is over 120 kilometres long, and up to 1500 metres across and over 300 metres deep in places.

The rille formed nearly 3300 million years ago. In contrast, lava channels on Hawaii are usually under 10 kilometres long and are only 50-100 metres wide. The Hadley C crater next to the rille is about 5 kilometres in diameter.

Sinuous rilles are probably the most recognisable of small volcanic features on the Moon. Many partially resemble river valleys on Earth. However, the lunar rilles usually flow away from small pit structures.

The rilles mark lava channels or collapsed lava tubes that formed during mare volcanism. Indeed, the lunar samples indicate that the Moon has always been dry, thus confirming the volcanic origin of the rilles.

Still, in some cases, the lunar flows may have melted their way down into older rocks, much like rivers cut into their flood plains on Earth. Similar lava channels and tubes are found in Hawaii, but these are all much, much smaller than those found on the Moon, indication that the very low lunar gravity has a strong influence on morphological processes.

Original Source: ESA Portal

Apollo 17 rover on the Moon. Image credit: NASA. Click to enlarge.
Inside the lunar lander Challenger, a radio loudspeaker crackled.

Houston: “We’ve got you on television now. We have a good picture.”

Gene Cernan, Apollo 17 commander: “Glad to see old Rover’s still working.”

“Rover,” the moon buggy, sat outside with no one in the driver’s seat, its side-mounted TV camera fixed on Challenger. Back in Houston and around the world, millions watched. The date was Dec. 19, 1972, and history was about to be made.

Suddenly, soundlessly, Challenger split in two (movie). The base of the ship, the part with the landing pads, stayed put. The top, the lunar module with Cernan and Jack Schmitt inside, blasted off in a spray of gold foil. It rose, turned, and headed off to rendezvous with the orbiter America, the craft that would take them home again.

Those were the last men on the Moon. After they were gone, the camera panned back and forth. There was no one there, nothing, only the rover, the lander and some equipment scattered around the dusty floor of the Taurus-Littrow valley. Eventually, Rover’s battery died and the TV transmissions stopped.

That was our last good look at an Apollo landing site.

Many people find this surprising, even disconcerting. Conspiracy theorists have long insisted that NASA never went to the Moon. It was all a hoax, they say, a way to win the Space Race by trickery. The fact that Apollo landing sites have not been photographed in detail since the early 1970s encourages their claims.

And why haven’t we photographed them? There are six landing sites scattered across the Moon. They always face Earth, always in plain view. Surely the Hubble Space Telescope could photograph the rovers and other things astronauts left behind. Right?

Wrong. Not even Hubble can do it. The Moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide. The biggest piece of left-behind Apollo equipment is only 9 meters across and thus smaller than a single pixel in a Hubble image.

Better pictures are coming. In 2008 NASA’s Lunar Reconnaissance Orbiter will carry a powerful modern camera into low orbit over the Moon’s surface. Its primary mission is not to photograph old Apollo landing sites, but it will photograph them, many times, providing the first recognizable images of Apollo relics since 1972.

The spacecraft’s high-resolution camera, called “LROC,” short for Lunar Reconnaissance Orbiter Camera, has a resolution of about half a meter. That means that a half-meter square on the Moon’s surface would fill a single pixel in its digital images.

Apollo moon buggies are about 2 meters wide and 3 meters long. So in the LROC images, those abandoned vehicles will fill about 4 by 6 pixels.

What does a half-meter resolution picture look like? This image of an airport on Earth has the same resolution as an LROC image. Moon buggy-sized objects (automobiles and luggage carts) are clear:

“I would say the rovers will look angular and distinct,” says Mark Robinson, research associate professor at Northwestern University in Evanston, Illinois, and Principal Investigator for LROC. “We might see some shading differences on top from seats, depending on the sun angle. Even the rovers’ tracks might be detectable in some instances.”

Even more recognizable will be the discarded lander platforms. Their main bodies are 4 meters on a side, and so will fill an 8 by 8 pixel square in the LROC images. The four legs jutting out from the platforms’ four corners span a diameter of 9 meters. So, from landing pad to landing pad, the landers will occupy about 18 pixels in LROC images, more than enough to trace their distinctive shapes.

Shadows help, too. Long black shadows cast across gray lunar terrain will reveal the shape of what cast them: the rovers and landers. “During the course of its year-long mission, LROC will image each landing site several times with the sunlight at different angles each time,” says Robinson. Comparing the different shadows produced would allow for a more accurate analysis of the shape of the objects.

Enough nostalgia. LROC’s main mission is about the future. According to NASA’s Vision for Space Exploration, astronauts are returning to the Moon no later than 2020. Lunar Reconnaissance Orbiter is a scout. It will sample the Moon’s radiation environment, search for patches of frozen water, make laser maps of lunar terrain and, using LROC, photograph the Moon’s entire surface. By the time astronauts return, they’ll know the best places to land and much of what awaits them.

Two high-priority targets for LROC are the Moon’s poles.

“We’re particularly interested in the poles as a potential location for a moon base,” Robinson explains. “There are some cratered regions near the poles that are in shadow year-round. These places might be cold enough to harbor permanent deposits of water ice. And nearby are high regions that are sunlit all year. With constant sunlight for warmth and solar power, and a potential source of water nearby, these high regions would make an ideal location for a base.” Data from LROC will help pinpoint the best ridge or plateau for setting up a lunar home.

Once a moonbase is established, what’s the danger of it being hit by a big meteorite? LROC will help answer that question.

“We can compare LROC images of the Apollo landing sites with Apollo-era photos,” says Robinson. The presence or absence of fresh craters will tell researchers something about the frequency of meteor strikes.

LROC will also be hunting for ancient hardened lava tubes. These are cave-like places, hinted at in some Apollo images, where astronauts could take shelter in case of an unexpected solar storm. A global map of these natural storm shelters will help astronauts plan their explorations.

No one knows what else LROC might find. The Moon has never been surveyed in such detail before. Surely new things await; old abandoned spaceships are just the beginning.

Original Source: NASA News Release

SMART-1’s detection of calcium, iron and other elements on the Moon. Image credit: ESA. Click to enlarge.
Thanks to measurements by the D-CIXS X-ray spectrometer, ESA?s SMART-1 spacecraft has made the first ever unambiguous remote-sensing detection of calcium on the Moon.

SMART-1 is currently performing the verification and calibration of its instruments, while it runs along its science orbit, reaching 450 kilometres from the Moon at its closest distance. During this calibration phase, which precedes the actual science observations phase, the SMART-1 scientists are getting acquainted with the delicate operations and the performance of their instruments in the warm environment of the lunar orbit.

Although it is still preparing for full lunar operations, D-CIXS has started already sending back high-quality data. D-CIXS is designed to measure the global composition of the Moon by observing how it glows in X-rays when the Sun shines on it. In fact, different chemical elements provide their ‘fingerprinting’, each glowing in a unique way.

On 15 January 2005, between 07:00 and about 09:00 Central European Time, a solar flare occurred, blasting a quantity of radiation that flooded the Solar System and the Moon. “The Sun was kind to us”, said Prof Manuel Grande of the Rutherford Appleton Laboratory, leader of the D-CIXS instrument team. “It set off a large X-ray flare just as we took our first look downwards at the lunar surface”.

The lunar surface reacts to the incoming solar radiation by glowing in different X-ray wavelengths. This enabled D-CIXS, , to distinguish the presence of chemical elements – including calcium, aluminium, silicon and iron – in Mare Crisium, the area of the lunar surface being observed at that moment. “It is the first time ever that calcium has been unambiguously detected on the Moon by remote-sensing instrumentation”, added Prof. Grande. Calcium is an important rock-forming element on the Moon.

“Even before our scientists have finished setting up the instruments, SMART-1 is already producing brand new lunar science”, said Bernard Foing, SMART-1 Project Scientist. “When we get D-CIXS and the other instruments fully tuned, with scientific data rolling in routinely, we should have a truly ground-breaking mission”.

Original Source: ESA News Release

The Moon and its dark spots. Image credit: NASA. Click to enlarge.
People of every culture have been fascinated by the dark “spots” on the Moon, which seem to compose the figure of a rabbit, frogs or the face of a clown. With the Apollo missions, scientists found that these features are actually huge impact basins that were flooded with now-solidified lava. One surprise was that these basins formed relatively late in the history of the early solar system – approximately 700 million years after the formation of the Earth and Moon. Many scientists now believe that these lunar impact basins bear witness to a huge spike in the bombardment rate of the planets – called the late heavy bombardment (LHB). The cause of such an intense bombardment, however, is considered by many to be one of the best-preserved mysteries of solar system history.

In a series of three papers published in this week’s issue of the journal Nature, an international team of planetary scientists, Rodney Gomes (National Observatory of Brazil), Harold Levison (Southwest Research Institute, United States), Alessandro Morbidelli (Observatoire de la C?te d’Azur, France) and Kleomenis Tsiganis (OCA and University of Thessaloniki, Greece) – brought together by a visitor program hosted at the Observatoire de la C?te d’Azur in Nice – proposed a model that not only naturally solves the mystery of the origin of the LHB, but also explains many of the observed characteristics of the outer planetary system.

This new model envisions that the four giant planets, Jupiter, Saturn, Uranus and Neptune, formed in a very compact orbital configuration, which was surrounded by a disk of small objects made of ice and rock (known as “planetesimals”). Numerical simulations by the Nice team shows that some of these planetesimals slowly leaked out of the disk due to the gravitational effects of the planets. The planets scattered these smaller objects throughout the solar system, sometimes outward and sometimes inward.

“As Isaac Newton taught us, for every action there is an equal and opposite reaction,” says Tsiganis. “If a planet throws a planetesimal out of the solar system, the planet moves toward the Sun, just a tiny bit, in compensation. If, on the other hand, the planet scatters the planetesimal inward, the planet jumps slightly farther from the Sun.”

Numerical simulations show that, on average, Jupiter moved inward while the other giant planets moved outward.

Initially, this was a very slow process, taking millions of years for the planets to move a small amount. Then, according to this new model, after 700 million years, the situation suddenly changed. At that time, Saturn migrated through the point where its orbital period was exactly twice that of Jupiter’s. This special orbital configuration caused Jupiter’s and Saturn’s orbits to suddenly become more elliptical.

“This caused the orbits of Uranus and Neptune to go nuts,” says Gomes. “Their orbits became very eccentric and they started to gravitationally scatter off each other – and Saturn too.”

The Nice team argues that this evolution of Uranus’ and Neptune’s orbits caused the LHB on the Moon. Their computer simulations show that these planets very quickly penetrated the planetesimal disk, scattering objects throughout the planetary system. Many of these objects entered the inner solar system where they peppered the Earth and Moon with impacts. In addition, the whole process destabilized the orbits of asteroids, which then would have also contributed to the LHB. Finally, the gravitational effects of the planetesimal disk caused Uranus and Neptune to evolve onto their current orbits.

“It’s very convincing,” says Levison. “We have made several dozen simulations of this process, and statistically the planets ended up on orbits very similar to the ones that we see, with the correct separations, eccentricities and inclinations. So, in addition to the LHB, we can also explain the orbits of the giant planets. No other model has ever accomplished either thing before.”

However, there was one more hurdle to overcome. The solar system currently contains a population of asteroids that follow essentially the same orbit as Jupiter, but lead or trail that planet by an angular distance of roughly 60 degrees. Computer simulations show that these bodies, known as the “Trojan asteroids,” would have been lost as the giant planets’ orbits changed.

“We sat around for months worrying about this problem, which seemed to invalidate our model,” says Morbidelli, “until we realized that if a bird can escape from an open cage, another one can come and nest in it.”

The Nice team found that some of the very objects that were driving the planetary evolution, and which caused the LHB, would also have been captured into Trojan asteroid orbits. In the simulations, the trapped Trojans turned out to reproduce the orbital distribution of the observed Trojans, which was unexplained up to now. The total predicted mass of the trapped objects was also consistent with the observed population.

Taken in total, the Nice team’s new model naturally explains the orbits of the giant planets, the Trojan asteroids and the LHB to unprecedented accuracy. “Our model explains so many things that we believe it must be basically correct,” says Mordibelli. “The structure of the outer solar system shows that the planets probably went through a shake up well after the planet formation process ended.”

Original Source: SWRI News Release

Astronauts in a lunar base will need a lot of air. Image credit: NASA. Click to enlarge.
NASA, in collaboration with the Florida Space Research Institute (FSRI), today announced a new Centennial Challenges prize competition.

The MoonROx (Moon Regolith Oxygen) challenge will award $250,000 to the first team that can extract breathable oxygen from simulated lunar soil before the prize expires on June 1, 2008.

For the MoonROx challenge, teams must develop hardware within mass and power limits that can extract at least five kilograms of breathable oxygen from simulated lunar soil during an eight-hour period. The soil simulant, called JSC-1, is derived from volcanic ash. The oxygen production goals represent technologies that are beyond existing state-of-the-art.

NASA’s Centennial Challenges promotes technical innovation through a novel program of prize competitions. It is designed to tap the nation’s ingenuity to make revolutionary advances to support the Vision for Space Exploration and NASA goals.

“The use of resources on other worlds is a key element of the Vision for Space Exploration,” said NASA’s Associate Administrator for the Exploration Systems Mission Directorate, Craig Steidle. “This challenge will reach out to inventors who can help us achieve the Vision sooner,” he added.

“This is our third prize competition, and the Centennial Challenges program is getting more and more exciting with each new announcement. The innovations from this competition will help support long-duration, human and robotic exploration of the moon and other worlds,” said Brant Sponberg, NASA’s Centennial Challenges program manager.

“Oxygen extraction technologies will be critical for both robotic and human missions to the moon,” said FSRI Executive Director Sam Durrance. “Like other space-focused prize competitions, the MoonROx challenge will encourage a broad community of innovators to develop technologies that expand our capabilities,” he added.

The Centennial Challenges program is managed by NASA’s Exploration Systems Mission Directorate. FSRI is a state-wide center for space research. It was established by Florida’s governor and legislature in 1999.

For more information about Centennial Challenges on the Internet, visit: http://centennialchallenges.nasa.gov

For more information about NASA and agency programs on the Internet, visit: http://www.nasa.gov/home/index.html

For information about the Florida Space Research Institute on the Internet, visit: http://www.fsri.org

Original Source: NASA News Release