Cross posting from the Nuclear Energy thread (as these are better suited for here)
http://science.nasa.gov/science-news/science-at-nasa/2004/27sep_shieldsup/ Shields Up!
A breeze of interstellar helium atoms is blowing through the solar system.
NASA
September 27, 2004: If you've ever watched Star Trek, you know the importance of shields. When a star explodes or a Klingon death ray lances out of the darkness, the captain yells two words, "Shields up!", and all is well. Deflector shields: Don't leave home without one.
The solar system, believe it or not, has got one.
The solar system's deflector shield is a giant magnetic bubble called "the heliosphere." It's part of the sun's magnetic field. No one knows the precise dimensions of the heliosphere, but it's bigger than the orbit of Pluto. All nine planets are inside it.
The heliosphere is important to life on our planet. A few million years ago, for instance, a cluster of massive stars drifted through our part of the Milky Way and exploded, one after another, like popcorn. Cosmic rays from the blasts were mostly deflected by the heliosphere, sparing early humanoids a radiation bath.
But the bubble isn't perfect. The fact is, "it's leaky," says space scientist Eberhard Moebius of the University of New Hampshire. "Some things do get through." (This happens on Star Trek, too. If the ship's shields were impenetrable, there would never be any drama.)
Take cosmic rays for example. They are fragments of atoms shattered and accelerated to light speed by supernova blasts. The heliosphere deflects about 90% of them; the rest, the most powerful 10%, penetrate the inner solar system.
The bubble is even more vulnerable to particles with no electric charge. Magnetic fields can deflect charged particles like cosmic rays, but not neutral atoms and molecules or bits of dust and rock. The bubble is an open door to these.
To wit: a stream of neutral helium atoms--"an interstellar breeze," says Moebius--is flowing into the solar system right now. "It's coming from the direction of the constellation Ophiuchus. Because the atoms in the stream are uncharged, the magnetic bubble does nothing to stop them."
Studying this stream is important because it can teach us a great deal about the heliosphere--How big is it? How leaky is it? It can also teach us about the interstellar "stuff" lurking just outside, says Moebius.
see captionThe stream, discovered 30 years ago, is actively monitored by a flotilla of NASA and European Space Agency spacecraft: SOHO, EUVE, ACE and, especially, Ulysses. Each measures something different. EUVE, for instance, can sense ultraviolet sunlight scattered from the stream, while Ulysses samples the stream itself, snatching atoms directly from the flow.
For many years the physical characteristics of the stream were only vaguely known. "But the ability we have now to take a close-up look at the stream using these modern spacecraft has made a difference," says Moebius. He recently led a research team at the International Space Science Institute in Switzerland; using data from the spacecraft they were able to pinpoint the stream's temperature, density and velocity:
Its temperature, 6000 C, is about the same as the surface temperature of the sun. A spacecraft flying through the stream won't melt, though, or even notice the heat. The gas in the stream is too wispy-thin, explains Moebius. "There are only 0.015 helium atoms per cubic centimeter." Earth's atmosphere at sea level, for comparison, is a thousand billion billion (1021) times denser. And, finally, the velocity of the stream is 26 km/s or 58,000 mph.
These numbers confirm what astronomers have long suspected. The solar system is colliding with a vast interstellar cloud.
Most people think space is empty, but it's not. The "void" between the stars is crowded with clouds of gas. Clouds on Earth are miles wide. Clouds in space are light years across. They range in character from inky-black and cold to colorful and glowing-hot. Stars are born in clouds, and they hurl even more clouds into space when they die. Interstellar clouds are everywhere, so it's no surprise that the solar system is running into one.
The question is, what kind of cloud?
This cloud, like most things in the Universe, consists mainly of hydrogen. We know this because the hydrogen absorbs telltale colors from the light of nearby stars. Astronomers use this absorption effect to trace the cloud's general outline: it is several light years wide and ragged-edged.
The cloud's abundant hydrogen doesn't easily penetrate the heliosphere because hydrogen atoms in the cloud are ionized by interstellar ultraviolet radiation. Like cosmic rays the hydrogen atoms are charged and, thus, held at bay. Helium atoms, on the other hand, are mostly neutral, so they slip into the solar system.
Although helium is only a minor ingredient of the cloud, it tells the researchers what the whole is like. The cloud's temperature is 6000 C, the same as the helium stream. Its velocity, 26 km/s, is the same, too. If the cloud contains a standard cosmic mix of hydrogen and helium--a reasonable assumption--then its overall density must be 0.264 atoms per cubic centimeter.
Arcania? Not at all.
These numbers are important. They are vital to the size and "leakiness" of the heliosphere. The bubble is inflated from the inside by the solar wind and compressed on the outside by the cloud. It's a balancing act. If the pressure of the cloud (a function of temperature, density and velocity) is high, it defeats the solar wind and makes the bubble smaller, lowering our defenses against cosmic rays.
Thousands of years from now, some researchers believe, the solar system will pass completely through this cloud and emerge in a low-pressure cavity blown by those supernovas a few million years ago. The heliosphere will expand, providing improved protection against cosmic rays.
After that who knows? Another cloud might come along compress the bubble again. The ISSI team's research, eventually, could tell us how the heliosphere will react.
Shields up? Shields down? It's not science fiction any more.
http://science.nasa.gov/science-news/science-at-nasa/2005/10aug_crackling/ Crackling Planets
Astronauts on the Moon and Mars are going to have to cope with an uncommon amount of static electricity.
August 10, 2005: Have you ever walked across a wool carpet in leather-soled shoes on a dry winter day, and then reached out toward a doorknob? ZAP! A stinging spark leaps between your fingers and the metal knob.
That's static discharge--lightning writ small.
Static discharge is merely annoying to anyone on Earth living where winters have exceptionally low humidity. But to astronauts on the Moon or on Mars, static discharge could be real trouble.
"On Mars, we think the soil is so dry and insulating that if an astronaut were out walking, once he or she returned to the habitat and reached out to open the airlock, a little lightning bolt might zap critical electronics," explains Geoffrey A. Landis, a physicist with the Photovoltaics and Space Environmental Effects Branch at NASA Glenn Research Center in Cleveland, Ohio.
This phenomenon is called triboelectric charging.
The prefix "tribo" (pronounced TRY-bo) means "rubbing." When certain pairs of unlike materials, such as wool and hard shoe-sole leather, rub together, one material gives up some of its electrons to the other material. The separation of charge can create a strong electric field.
Here on Earth, the air around us and the clothes we wear usually have enough humidity to be decent electrical conductors, so any charges separated by walking or rubbing have a ready path to ground. Electrons bleed off into the ground instead of accumulating on your body.
But when air and materials are extraordinarily dry, such as on a dry winter's day, they are excellent insulators, so there is no ready pathway to ground. Your body can accumulate negative charges, possibly up to an amazing 20 thousand volts. If you touch a conductor, such as a metal doorknob, then--ZAP!--all the accumulated electrons discharge at once.
On the Moon and on Mars, conditions are ideal for triboelectric charging. The soil is drier than desert sand on Earth. That makes it an excellent electrical insulator. Moreover, the soil and most materials used in spacesuits and spacecraft (e.g., aluminized mylar, neoprene-coated nylon, Dacron, urethane-coated nylon, tricot, and stainless steel) are completely unlike each other. When astronauts walk or rovers roll across the ground, their boots or wheels gather electrons as they rub through the gravel and dust. Because the soil is insulating, providing no path to ground, a space suit or rover can build up tremendous triboelectric charge, whose magnitude is yet unknown. And when the astronaut or vehicle gets back to base and touches metal--ZAP! The lights in the base may go out, or worse.
Physicist Joseph Kolecki and colleagues at NASA Glenn first noticed this problem in the late 1990s before Mars Pathfinder was launched. "When we ran a prototype wheel of the Sojourner rover over simulated Martian dust in a simulated Martian atmosphere, we found it charged up to hundreds of volts," he recalls.
That discovery so concerned the scientists that they modified Pathfinder's rover design, adding needles half an inch long, made of ultrathin (0.0001-inch diameter) tungsten wire sharpened to a point, at the base of antennas. The needles would allow any electric charge that built up on the rover to bleed off into the thin Martian atmosphere, "like a miniature lightning rod operating in reverse," explains Carlos Calle, lead scientist at NASA's Electrostatics and Surface Physics Laboratory at Kennedy Space Center, Florida. Similar protective needles were also installed on the Spirit and Opportunity rovers.
On the Moon, "Apollo astronauts never reported being zapped by electrostatic discharges," notes Calle. "However, future lunar missions using large excavation equipment to move lots of dry dirt and dust could produce electrostatic fields. Because there's no atmosphere on the Moon, the fields could grow quite strong. Eventually, discharges could occur in vacuum."
"On Mars," he continues, "discharges can happen at no more than a few hundred volts. It's likely that these will take the form of coronal glows rather than lightning bolts. As such, they may not be life threatening for the astronauts, but they could be harmful to electronic equipment."
So what's the solution to this problem?
Here on Earth, it's simple: we minimize static discharge by grounding electrical systems. Grounding them means literally connecting them to Earth--pounding copper rods deep into the ground. Ground rods work well in most places on Earth because several feet deep the soil is damp, and is thus a good conductor. The Earth itself provides a "sea of electrons," which neutralizes everything connected to it, explains Calle.
There's no moisture, though, in the soil of the Moon or Mars. Even the ice believed to permeate Martian soil wouldn't help, as "frozen water is not a terribly good conductor," says Landis. So ground rods would be ineffective in establishing a neutral "common ground" for a lunar or Martian colony.
On Mars, the best ground might be, ironically, the air. A tiny radioactive source "such as that used in smoke detectors," could be attached to each spacesuit and to the habitat, suggests Landis. Low-energy alpha particles would fly off into the rarefied atmosphere, hitting molecules and ionizing them (removing electrons). Thus, the atmosphere right around the habitat or astronaut would become conductive, neutralizing any excess charge.
Achieving a common ground on the Moon would be trickier, where there's not even a rarefied atmosphere to help bleed off the charge. Instead, a common ground might be provided by burying a huge sheet of foil or mesh of fine wires, possibly made of aluminum (which is highly conductive and could be extracted from lunar soil), underneath the entire work area. Then all the habitat's walls and apparatus would be electrically connected to the aluminum.
Research is still preliminary. So ideas differ amongst the physicists who are seeking, well, some common ground.
http://science.nasa.gov/science-news/science-at-nasa/2005/22apr_dontinhale/ Don't Breathe the Moondust
When humans return to the Moon and travel to Mars, they'll have to be careful of what they inhale.
NASA
April 22, 2005: This is a true story.
In 1972, Apollo astronaut Harrison Schmitt sniffed the air in his Lunar Module, the Challenger. "[It] smells like gunpowder in here," he said. His commander Gene Cernan agreed. "Oh, it does, doesn't it?"
The two astronauts had just returned from a long moonwalk around the Taurus-Littrow valley, near the Sea of Serenity. Dusty footprints marked their entry into the spaceship. That dust became airborne--and smelly.
Later, Schmitt felt congested and complained of "lunar dust hay fever." His symptoms went away the next day; no harm done. He soon returned to Earth and the anecdote faded into history.
But Russell Kerschmann never forgot. He's a pathologist at the NASA Ames Research Center studying the effects of mineral dust on human health. NASA is now planning to send people back to the Moon and on to Mars. Both are dusty worlds, extremely dusty. Inhaling that dust, says Kerschmann, could be bad for astronauts.
"The real problem is the lungs," he explains. "In some ways, lunar dust resembles the silica dust on Earth that causes silicosis, a serious disease." Silicosis, which used to be called "stone-grinder's disease," first came to widespread public attention during the Great Depression when hundreds of miners drilling the Hawk's Nest Tunnel through Gauley Mountain in West Virginia died within half a decade of breathing fine quartz dust kicked into the air by dry drilling--even though they had been exposed for only a few months. "It was one of the biggest occupational-health disasters in U.S. history," Kerschmann says.
This won't necessarily happen to astronauts, he assures, but it's a problem we need to be aware of--and to guard against.
Quartz, the main cause of silicosis, is not chemically poisonous: "You could eat it and not get sick," he continues. "But when quartz is freshly ground into dust particles smaller than 10 microns (for comparison, a human hair is 50+ microns wide) and breathed into the lungs, they can embed themselves deeply into the tiny alveolar sacs and ducts where oxygen and carbon dioxide gases are exchanged." There, the lungs cannot clear out the dust by mucous or coughing. Moreover, the immune system's white blood cells commit suicide when they try to engulf the sharp-edged particles to carry them away in the bloodstream. In the acute form of silicosis, the lungs can fill with proteins from the blood, "and it's as if the victim slowly suffocates" from a pneumonia-like condition.
Lunar dust, being a compound of silicon as is quartz, is (to our current knowledge) also not poisonous. But like the quartz dust in the Hawk's Nest Tunnel, it is extremely fine and abrasive, almost like powdered glass. Astronauts on several Apollo missions found that it clung to everything and was almost impossible to remove; once tracked inside the Lunar Module, some of it easily became airborne, irritating lungs and eyes.
Martian dust could be even worse. It's not only a mechanical irritant but also perhaps a chemical poison. Mars is red because its surface is largely composed of iron oxide (rust) and oxides of other minerals. Some scientists suspect that the dusty soil on Mars may be such a strong oxidizer that it burns any organic compound such as plastics, rubber or human skin as viciously as undiluted lye or laundry bleach.
"If you get Martian soil on your skin, it will leave burn marks," believes University of Colorado engineering professor Stein Sture, who studies granular materials like Moon- and Mars-dirt for NASA. Because no soil samples have ever been returned from Mars, "we don't know for sure how strong it is, but it could be pretty vicious."
Moreover, according to data from the Pathfinder mission, Martian dust may also contain trace amounts of toxic metals, including arsenic and hexavalent chromium--a carcinogenic toxic waste featured in the docudrama movie Erin Brockovich (Universal Studios, 2000). That was a surprising finding of a 2002 National Research Council report called Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface.
The dust challenge would be especially acute during windstorms that occasionally envelop Mars from poles to equator. Dust whips through the air, scouring every exposed surface and sifting into every crevice. There's no place to hide.
To find ways of mitigating these hazards, NASA is soon to begin funding Project Dust, a four-year study headed by Masami Nakagawa, associate professor in the mining engineering department of the Colorado School of Mines. Project Dust will study such technologies as thin-film coatings that repel dust from tools and other surfaces, and electrostatic techniques for shaking or otherwise removing dust from spacesuits.
These technologies, so crucial on the Moon and Mars, might help on Earth, too, by protecting people from sharp-edged or toxic dust on our own planet. Examples include alkaline dust blown from dry lakes in North American deserts, wood dust from sawmills and logging operations, and, of course, abrasive quartz dust in mines.
The road to the stars is surprisingly dusty. But, says Kerschmann, "I strongly believe it's a problem that can be controlled."