Monday, March 15, 2010
Flowing lava can carve or build paths very much like the riverbeds and canyons etched by water, and this probably explains at least one of the meandering channels on the surface of Mars. These results were presented on March 4, 2010 at the 41st Lunar and Planetary Science Conference by Jacob Bleacher at NASA’s Goddard Space Flight Center, Greenbelt, Md. Whether channels on Mars were formed by water or by lava has been debated for years, and the outcome is thought to influence the likelihood of finding life there.
"To understand if life, as we know it, ever existed on Mars, we need to understand where water is or was," says Bleacher. Geologists think that the water currently on the surface of Mars is either held in the soil or takes the form of ice at the planet's north and south poles. But some researchers contend that water flowed or pooled on the surface sometime in the past; water in this form is thought to increase the chance of some form of past or present life.
One of the lines of support for the idea that water once flowed on Mars comes from images that reveal details resembling the erosion of soil by water: terracing of channel walls, formation of small islands in a channel, hanging channels that dead-end and braided channels that branch off and then reconnect to the main branch. "These are thought to be clear evidence of fluvial [water-based] erosion on Mars," Bleacher says.
Lava is generally not thought to be able to create such finely crafted features. Instead, "the common image is of the big, open channels in Hawaii," he explains.
Bleacher and his colleagues carried out a careful study of a single channel on the southwest flank of Mars' Ascraeus Mons volcano, one of the three clustered volcanoes collectively called the Tharsis Montes. To piece together images covering more than 270 kilometers (~168 miles) of this channel, the team relied on high-resolution pictures from three cameras—the Thermal Emission Imaging System (THEMIS), the Context Imager (CTX) and the High/Super Resolution Stereo Color (HRSC) imager—as well as earlier data from the Mars Orbiter Laser Altimeter (MOLA). These data gave a much more detailed view of the surface than previously available.
Because the fluid that formed this and other Ascraeus Mons channels is long-gone, its identity has been hard to deduce, but the visual clues at the source of the channel seem to point to water. These clues include small islands, secondary channels that branch off and rejoin the main one and eroded bars on the insides of the curves of the channels.
But at the channel's other end, an area not clearly seen before, Bleacher and colleagues found a ridge that appears to have lava flows coming out of it. In some areas, "the channel is actually roofed over, as if it were a lava tube, and lined up along this, we see several rootless vents," or openings where lava is forced out of the tube and creates small structures, he explains. These types of features don't form in water-carved channels, he notes. Bleacher argues that having one end of the channel formed by water and the other end by lava is an "exotic" combination. More likely, he thinks, the entire channel was formed by lava.
To find out what kinds of features lava can produce, Bleacher, along with W. Brent Garry and Jim Zimbelman at the Smithsonian Institution in Washington, examined the 51-kilometer (~32 mile) lava flow from the 1859 eruption of Mauna Loa on the Big Island of Hawaii. Their main focus was an island nearly a kilometer long in the middle of the channel; Bleacher says this is much larger than islands typically identified within lava flows. To survey the island, the team used differential GPS, which provides location information to within about 3 to 5 centimeters (1.1 to 1.9 inches), rather than the roughly 3 to 5 meters (9.8 to 16.4 feet) that a car's GPS can offer.
"We found terraced walls on the insides of these channels, channels that go out and just disappear, channels that cut back into the main one, and vertical walls 9 meters (~29 feet) high," Bleacher says. "So, right here, in something that we know was formed only by flowing lava, we found most of the features that were considered to be diagnostic of water-carved channels on Mars."
The new results make "a strong case that fluid lava can produce channels that look very much like water-generated features," says Zimbelman. "So, we should not jump to a water-related conclusion when we see such channels on other planets, particularly in volcanic terrain such as that around the Tharsis Montes volcanoes."
Further evidence that such features could be created by lava flows came from the examination of a detailed image of channels from the Mare Imbrium, a dark patch on the moon that is actually a large crater filled with ancient lava rock. In this image, too, the researchers found channels with terraced walls and branching secondary channels.
The conclusion that lava probably made the channel on Mars "not only has implications for the geological evolution of the Ascraeus Mons but also the whole Tharsis Bulge [volcanic region]," says Andy de Wet, a co-author at Franklin & Marshall College, Lancaster, Penn. "It may also have some implications for the supposed widespread involvement of water in the geological evolution of Mars."
Bleacher notes that the team's conclusions do not rule out the possibility of flowing water on Mars, nor of the existence of other channels carved by water. "But one thing I've learned is not to underestimate the way that liquid rock will flow," he says. "It really can produce a lot of things that we might not think it would."
Philip Christensen of Arizona State University is the principal investigator for the THEMIS instrument on the Mars Odyssey orbiter, and Mike Malin of Malin Space Science Systems is the principal investigator for the CTX instrument aboard the Mars Reconnaissance Orbiter. Both missions are managed by NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. MOLA was aboard the Mars Global Surveyor, built by JPL. HRSC is aboard the European Space Agency's Mars Express spacecraft.
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Tuesday, December 23, 2008
Background: Developed in the second-century BCE, by the ancient Chinese, fireworks are the oldest form of rockets and the most simplistic model of a rocket. Originally fireworks had religious purposes in ceremonies but were later adapted for military use during the middle ages in the form of "flaming arrows." During the tenth and thirteenth centuries the Mongols and the Arabs brought the major component of these early rockets to the West: gunpowder. Although the cannon, and gun became the major developments from the eastern introduction of gunpowder, a tickling of rockets also resulted. These rockets were essentially enlarged fireworks which propelled, further than the long bow or cannon, packages of explosive gunpowder. During the late eighteenth century imperialistic wars, Colonel Congreve, developed his famed rockets, which trave range distances of four miles. The "rockets' red glare" (American Anthem) records the usage of rocket warfare, in its early form of military strategy, during the inspirational battle of Fort McHenry. Labels: How a Firework Rocket Works
Function: Gunpowder, a mixture composing of: 75% Potassium Nitrate (KNO3), 15% Charcoal (Carbon), and 10% Sulfur, provides the thrust of most fireworks. This fuel is tightly packed into the casing, a thick cardboard or paper rolled up tube (figure 1.2), forming the propellant-core of the rocket (figure 1.5) in a typical length to width or diameter ratio of 7:1.
A fuse (cotton twine coated with gunpowder) is lit by a match or by a "punk" (a wooden stick with a coal-like red-glowing tip). This fuse burns rapidly into the core of the rocket where it ignites the gunpowder walls of the interior core. One might think that the fuse would burn out once inside of the core, due to the lack of surrounding air but the chemistry of gunpowder solves this point. As mentioned before one of the chemicals in gunpowder is potassium nitrate, the most important ingredient. The molecular structure of this chemical, KNO3, contains three atoms of oxygen (O3), one atom of nitrogen (N), and one atom of potassium (K). The three oxygen atoms locked into this molecule provide the "air" that the fuse and the rocket use to burn the other two ingredients, carbon and sulfur. Thus potassium nitrate oxidizes the chemical reaction by easily releasing it oxygen. This reaction is not spontaneous though, and must be initiated by heat such as the match or "punk."
Thrust is produced once the burning fuse enters the core. The core is quickly filled with flames and thus, the necessary heat to ignite, continue, and spread the reaction. After the initial surface of the core has been exhausted a layer of gunpowder is exposed continuing, for the few seconds the rocket will burn, to produce thrust. The action reaction (propulsion ) effect explains the thrust as produced when the hot expanding gases (produced in the reaction burning of gunpowder)escape the rocket via the nozzle (figure 1.3). Constructed of clay, the nozzle can withstand the intense heat of the flames that pass through.
The original sky rocket used a long wooden or bamboo stick (figure 1.8) to provide a low center of balance (by distributing the mass of the rocket over a greater linear distance) and thus stability to the rocket through its flight. Fins usually three set at 120 degree angles of one another or four set at 90 degree angles of one another, had their developmental roots in arrow feather guides. The principles that governed the flight of an arrow were the same for early fireworks. But fins could be omitted altogether since a simple stick seemed to grant sufficient stability. Only when firework-type rockets became more developed did the fin rocket gain popularity. With fins properly set (in creating a suitable center of balance) the extra mass of the drag (air resistance) creating guide-stick could be removed, increasing rocket performance. Also, as rockets become larger and more powerful the exhaust from the engine would consume the guide-stick, destroying the rockets mode of guidance.
Fireworks have remained popular in today's age due to the spectacle of colors and sounds they are so renown for. The component of a rocket that produces these stars, reports ("bangs"), and colors is typically located just below the nosecone (figure 1.7) section of a rocket. After the rocket engine has consumed all of its fuel an internal fuse is lit that delays the release of the stars, or other effect. This delay allows for coasting time where the rocket continues its ascent. As gravity will eventually pull the firework back to earth, it slows and eventually reaches an apex (highest point: where velocity of the rocket is zero) and begins its descent. The delay usually lasts just before this apex, at an optimum velocity, where a small explosion shoots the firework's stars in desired directions and thus producing a brilliant effect. The colors, reports, flashes, and, stars are analogous to flavor one adds with spices (chemicals with special pyrotechnic properties) to a soup of otherwise bland gunpowder.
Advantages/Disadvantages: Gunpowder's relatively low specific impulse (amount of thrust per unit propellant) limits its capacity of thrust production on larger scales. Fireworks are the simplest of solid rockets and the weakest. Evolution from fireworks brought about more complex solid fueled rockets, which use more exotic and powerful fuels. The low-explosive properties of gunpowder, relative to the high-explosive properties of more advanced solid fuels testify to the "survival of the fittest," as the use of firework-type engines (for purposes other than entertainment or education) has virtually ceased since the late ninteenth century. Yet with all these drawbacks fireworks will continue to maintain their use as a traditional pastime with an on-going history of nearly 5,000 years.
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