In 1897 the British physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself.The experiment was called Discharged Tube experiment.
In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved. Thomson's last important experimental program focused on determining the nature of positively charged particles. Here his techniques led to the development of the mass spectrograph. His assistant, Francis Aston, developed Thomson's instrument further and with the improved version was able to discover isotopes—atoms of the same element with different atomic weights—in a large number of nonradioactive elements.
He was awarded a Nobel Prize in 1906, "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." He was knighted in 1908 and appointed to the Order of Merit in 1912. In 1914 he gave the Romanes Lecture in Oxford on "The atomic theory". In 1918 he became Master of Trinity College,Cambridge where he remained until his death. He died on August 30, 1940 and was buried in Westminster Abbey, close to Sir Issac Newton.
New images beamed back by the Mars Reconnaissance Orbiter (MRO), which has been circling the Red Planet since 2006, have produced the first compelling evidence of flowing, salty water on the Martian surface. Water may mean biology and biology, of course, would mean Martians.
There's been little doubt in recent years that Mars was once very wet. Mineral deposits, ancient shorelines, dried up lake beds and long-empty waterways all attest to the sloshingly aquatic place the planet once was. Most of the water was lost to space due to Mars's low gravity and tenuous atmosphere. Anything that was left contracted into ice coverings in the northern and southern latitudes and perhaps retreated into the soil. If anything warm and liquid existed deeper underground — serving as a potential stew pot for organisms — there was no way of knowing.
The MRO appears to have changed that. In a paper published this week in the journal Science and announced at a press conference at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, mission scientists revealed the appearance of seasonal streaks at key points on the Martian surface, looking for all the world like the tracks of water rivulets running down-slope, collecting at the base of the incline and then evaporating back into the atmosphere."Since the MRO arrived at Mars our overarching theme has been 'follow the water,'" says mission scientist Mike Meyer. "Now we may be catching Mars in the act. We have found repeated and predictable evidence of water flowing on the surface."
There are a lot of things about the images that make a powerful — if not yet seal-the-deal definite — case for water. For one thing, there's the seasonality. The water appears only in the Martian spring and summer when surface temperatures may range from a low of 10 below zero F to a balmy 80 above (-23 to 27°C) — and only in the planet's mid-latitudes, as opposed to the permanently frozen far north and south.
"These flows occur close to the equator," says MRO team member Phil Christensen. "They're at a latitude at which it's actually possible for water to exist." JPL images also show the events occurring over three full Martian years — a repeatability that only makes the case stronger.
Just as important as the presence of the water is the overwhelming evidence that it's salty — a key feature of the seawater in which Earthly life emerged. Salt exists in deposits and dustings over much of the surface of Mars, which is consistent with a world that was once so watery. What's more, while ordinary water could not flow at temperatures below 32 F (0 degrees C), densely concentrated salt water has a much lower freezing point, making it possible for it to remain liquid deep into the mid-latitude's lower temperature ranges. So concentrated may this Martian brine be that it would actually flow more like syrup than water.
Just what shape the subsurface water deposits might take is impossible to say with certainty, but Lisa Pratt, a mission scientist, thinks there's a lot to learn from the closest Earth analogs we have to this part of the Martian surface: the Siberian permafrost. There, she says, subsurface water collects either in fracture networks or in small pockets called cryopegs. Once the Martian water grows warmer and begins to leak out of these deposits, it would seep up first to what's known as a photic zone, a think film of surface soil where warmth from the sun could allow biological activity to take place.
Not every instrument aboard the MRO agreed entirely with the findings of the cameras. The ship's spectrometer, which would be expected to find the elemental signature of water when it scanned the rivulet zones, came up empty, but that could simply be a matter of timing. Atmospheric pressure on the surface of Mars is just 1% of what it is at sea level on Earth. Even in the biting cold, this would cause fresh water simply to boil away.
"Salty water wouldn't boil," says MRO team member Alfred McEwen, "but it would evaporate very quickly." By the time the spectrometer could take a bead on the streaks, the water that formed them would be gone.
JPL is already planning Earth-based experiments in which soil and brine of similar composition can be studied for clues to exactly what's going on Mars. A European-American Missions set to launch in 2016 will orbit Mars looking for trace gas emissions, particularly methane and oxygen molecules, both of which could be the byproducts of biological processes. The Curiosity rover, a Mars car about the size of an SUV, will launch in November as well, but NASA cautions that it won't be able to investigate the sites up close. Its planned landing site is too far from where the streaks have been seen and it was not built to navigate the steep, 35-degree slopes where the rivulets are forming.
This is the most interesting proof found till date about the presence of water in mars
Report frm September,2008
The universe has many secrets hidden inside we just need to explore them!!!
Earth may have once had two moons, but one was destroyed in a slow-motion collision that left our current lunar orb lumpier on one side than the other, scientists say.Astronomers have long been puzzled by the differences between the side of the moon that always faces Earth—the near side—and the side that always faces away, the far side. The topography of the near side is relatively low and flat, while that of the far side is high and mountainous with a much thicker crust.According to a new computer model, this discrepancy can be explained if a smaller "companion moon" collided with our moon's far side early in its history. Such a collision would have left the far side splattered with especially hard rocky material that now forms the current lunar highlands.
For the theory to work, the smaller moon must have crashed into the larger one at about 4,400 miles (7,081 kilometers) an hour.
At this relatively slow speed, the far-side collision wouldn’t have been energetic enough to melt rock or carve out a crater. But it would have been forceful enough to plaster material from the smaller moon onto the larger moon.
"This is the slowest possible collision the two massive bodies could have if they fell into each other’s gravity," explained study co-author Erik Asphaug, a planetary scientist at the University of California, Santa Cruz (UCSC).
The new theory, by Asphaug and UCSC postdoctoral researcher Martin Jutzi, is detailed in the current issue of the journal Nature.
"It's like a car crash, where you have crumpled bumpers but you don't melt the cars as they're colliding," Asphaug said. "This is the same kind of phenomenon."
According to their model, the two moons coexisted peacefully for about 80 million years, each in its own stable orbit. The moons were the same color and composition, but one was about three times larger than the other, Asphaug said.
This brief period of lunar harmony was shattered, according to the model, when natural gravitational interactions with Earth caused both moons to drift farther away from our planet. The sun's gravitational tug then destabilized the smaller moon’s orbit and caused it to fall into its larger sibling.
"Our moon looked like a big dinner plate in the sky ... and when it set, there was this other moon trailing it by about 60 degrees," he said.
Though not very energetic, the collision would have ejected trillions of tons of lunar debris into space, obscuring both moons for several days.
"When the dust cleared, you had one moon that might have looked similar to our moon today," Asphaug said.
For up to a million years after the event, Earth would have been bombarded by moon bits of various sizes, the biggest of which could have been as much as 62 miles (100 kilometers) across.
"By definition, a big collision occurs only on one side," he says, "and unless it globally melts the planet, it creates an asymmetry."The moon's far side is very different than its near side.
"You'd have meteors raining down all over the sky for a long period of time," Asphaug said, though there probably would have been no life yet on Earth to witness the spectacular sky shows.
Now computer simulations hint a second moon essentially pancaked itself against its larger companion, broadly explaining the differences seen between the near and far sides
For instance, widespread plains of volcanic rock called "maria" (Latin for seas) cover much of the near hemisphere, but only a few maria are seen on the far one. In addition, while the surface of the near side is mostly low and flat, the far side is often high and mountainous, with the lunar surface elevated 1.2 miles (1.9 km) higher on average on the far side.
A comet is an icy, small Solar System body which, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of comet. Comet nuclei range from a few hundredmeters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. Comets have been observed since ancient times and have traditionally been considered bad omens.
Comets have a wide range of orbital periods, ranging from a few years to hundreds of thousands of years. Short-period comets originate in the Kuiper belt, or its associated scattered disc,which lie beyond the orbit of Neptune. Longer-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies in the outer Solar System. Long-period comets plunge towards the Sun from the Oort Cloud because of gravitational perturbations caused by either the massive outer planets of the Solar System (Jupiter,Saturn,Uranus and Neptune), or passing stars. Rare hyperbolic comets pass once through the inner Solar System before being thrown out into interstellar space along hyperbolic trajectories.
Comets are distinguished from asteriods by the presence of a coma or a tail. However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaurs has blurred the distinction between asteroids and comets.
As of January 2011 there are a reported 4,185 known comets of which about 1,500 are Kreutz Sungrazers and about 484 are short-period. This number is steadily increasing. However, this represents only a tiny fraction of the total potential comet population: the reservoir of comet-like bodies in the outer solar system may number one trillion. The number visible to the naked eye averages roughly one per year, though many of these are faint and unspectacular.Particularly bright or notable examples are called "Great Comets"
NASA has ended operational planning activities for the Mars rover Spirit and transitioned the Mars Exploration Rover Project to a single-rover operation focused on Spirit's still-active twin, Opportunity.
This marks the completion of one of the most successful missions of interplanetary exploration ever launched.
Spirit last communicated on March 22, 2010, as Martian winter approached and the rover's solar-energy supply declined. The rover operated for more than six years after landing in January 2004 for what was planned as a three-month mission. NASA checked frequently in recent months for possible reawakening of Spirit as solar energy available to the rover increased during Martian spring. A series of additional re-contact attempts ended today, designed for various possible combinations of recoverable conditions.
"Our job was to wear these rovers out exploring, to leave no unutilized capability on the surface of Mars, and for Spirit, we have done that," said Mars Exploration Rover Project Manager John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Spirit drove 4.8 miles (7.73 kilometers), more than 12 times the goal set for the mission. The drives crossed a plain to reach a distant range of hills that appeared as mere bumps on the horizon from the landing site; climbed slopes up to 30 degrees as Spirit became the first robot to summit a hill on another planet; and covered more than half a mile (nearly a kilometer) after Spirit's right-front wheel became immobile in 2006. The rover returned more than 124,000 images. It ground the surfaces off 15 rock targets and scoured 92 targets with a brush to prepare the targets for inspection with spectrometers and a microscopic imager.
"What's really important is not only how long Spirit worked or how far Spirit drove, but also how much exploration and scientific discovery Spirit accomplished," Callas said.
One major finding came, ironically, from dragging the inoperable right-front wheel as the rover was driving backwards in 2007. That wheel plowed up bright white soil. Spirit's Alpha Particle X-ray Spectrometer and Miniature Thermal Emission Spectrometer revealed that the bright material was nearly pure silica.
"Spirit's unexpected discovery of concentrated silica deposits was one of the most important findings by either rover," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for Spirit and Opportunity. "It showed that there were once hot springs or steam vents at the Spirit site, which could have provided favorable conditions for microbial life."
The silica-rich soil neighbors a low plateau called Home Plate, which was Spirit's main destination after the historic climb up Husband Hill. "What Spirit showed us at Home Plate was that early Mars could be a violent place, with water and hot rock interacting to make what must have been spectacular volcanic explosions. It was a dramatically different world than the cold, dry Mars of today," said Squyres.
The trove of data from Spirit could still yield future science revelations. Years of analysis of some 2005 observations by the rover's Alpha Particle X-ray Spectrometer, Miniature Thermal Emission Spectrometer and Moessbauer Spectrometer produced a report last year that an outcrop on Husband Hill bears a high concentration of carbonate. This is evidence of a wet, non-acidic ancient environment that may have been favorable for microbial life.
"What's most remarkable to me about Spirit's mission is just how extensive her accomplishments became," said Squyres. "What we initially conceived as a fairly simple geologic experiment on Mars ultimately turned into humanity's first real overland expedition across another planet. Spirit explored just as we would have, seeing a distant hill, climbing it, and showing us the vista from the summit. And she did it in a way that allowed everyone on Earth to be part of the adventure."
