The argument that the Moon is a dry, desolate place no longer holds water.
At a press conference today, researchers revealed preliminary data from NASA's Lunar Crater Observation and Sensing Satellite, or LCROSS, indicating that water exists in a permanently shadowed lunar crater. The discovery opens a new chapter in our understanding of the Moon.
On Oct. 9th, the LCROSS spacecraft and a companion rocket stage made twin impacts in crater Cabeus near the Moon's south pole. A plume of debris traveled at a high angle beyond the rim of Cabeus and into sunlight, while an additional curtain of debris was ejected more laterally.
"Multiple lines of evidence show water was present in both the high angle vapor plume and the ejecta curtain created by the LCROSS Centaur impact," says Colaprete. "The concentration and distribution of water and other substances requires further analysis, but it is safe to say Cabeus holds water."
Since the impacts, the LCROSS science team has been analyzing the huge amount of data the spacecraft collected. The team concentrated on data from the satellite's spectrometers, which provide the most definitive information about the presence of water. A spectrometer helps identify the composition of materials by examining light they emit or absorb.
The team took the known near-infrared spectral signatures of water and other materials and compared them to the impact spectra the LCROSS near-infrared spectrometer collected.
"We were able to match the spectra from LCROSS data only when we inserted the spectra for water," Colaprete said. "No other reasonable combination of other compounds that we tried matched the observations. The possibility of contamination from the Centaur also was ruled out."
Additional confirmation came from an emission in the ultraviolet spectrum that was attributed to hydroxyl (OH), one product from the break-up of water (H2O) by sunlight.
Data from the other LCROSS instruments are being analyzed for additional clues about the state and distribution of the material at the impact site. The LCROSS science team and colleagues are poring over the data to understand the entire impact event, from flash to crater. The goal is to understand the distribution of all materials within the soil at the impact site.
"The full understanding of the LCROSS data may take some time. The data is that rich," Colaprete said. "Along with the water in Cabeus, there are hints of other intriguing substances. The permanently shadowed regions of the Moon are truly cold traps, collecting and preserving material over billions of years."
Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color; Mars is sometimes referred to as the Red Planet. (An interesting side note: the Roman god Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing and terraforming Mars may prefer this symbolism.) The name of the month March derives from Mars.
Mars has been known since prehistoric times. Of course, it has been extensively studied with ground-based observatories. But even very large telescopes find Mars a difficult target, it's just too small. It is still a favorite of science fiction writers as the most favorable place in the Solar System (other than Earth!) for human habitation. But the famous "canals" "seen" by Lowell and others were, unfortunately, just as imaginary as Barsoomian princesses.
The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 1997 July 4. In 2004 the Mars Expedition Rovers "Spirit" and "Opportunity" landed on Mars sending back geologic data and many pictures; they are still operating after more than three years on Mars. In 2008, Phoenix landed in the northern plains to search for water. Three Mars orbiters (Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Express) are also currently in operation.
Mars' orbit is significantly elliptical. One result of this is a temperature variation of about 30 C at the subsolar point between aphelion and perihelion. This has a major influence on Mars' climate. While the average temperature on Mars is about 218 K (-55 C, -67 F), Martian surface temperatures range widely from as little as 140 K (-133 C, -207 F) at the winter pole to almost 300 K (27 C, 80 F) on the day side during summer.
Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.
Mars has some of the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular:
Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.
Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.
Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep (top of page);
Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.
Much of the Martian surface is very old and cratered, but there are also much younger rift valleys, ridges, hills and plains. (None of this is visible in any detail with a telescope, even the Hubble Space Telescope; all this information comes from the spacecraft that we've sent to Mars.)
The southern hemisphere of Mars is predominantly ancient cratered highlands somewhat similar to the Moon. In contrast, most of the northern hemisphere consists of plains which are much younger, lower in elevation and have a much more complex history. An abrupt elevation change of several kilometers seems to occur at the boundary. The reasons for this global dichotomy and abrupt boundary are unknown (some speculate that they are due to a very large impact shortly after Mars' accretion). Mars Global Surveyor has produced a nice 3D map of Mars that clearly shows these features.
The interior of Mars is known only by inference from data about the surface and the bulk statistics of the planet. The most likely scenario is a dense core about 1700 km in radius, a molten rocky mantle somewhat denser than the Earth's and a thin crust. Data from Mars Global Surveyor indicates that Mars' crust is about 80 km thick in the southern hemisphere but only about 35 km thick in the north. Mars' relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (iron and iron sulfide).
Recent observations with the Hubble Space Telescope have revealed that the conditions during the Viking missions may not have been typical. Mars' atmosphere now seems to be both colder and dryer than measured by the Viking landers (more details from STScI).
The Viking landers performed experiments to determine the existence of life on Mars. The results were somewhat ambiguous but most scientists now believe that they show no evidence for life on Mars (there is still some controversy, however). Optimists point out that only two tiny samples were measured and not from the most favorable locations. More experiments will be done by future missions to Mars.
A small number of meteorites (the SNC meteorites) are believed to have originated on Mars.
When it is in the nighttime sky, Mars is easily visible with the unaided eye. Mars is a difficult but rewarding target for an amateur telescope though only for the three or four months each martian year when it is closest to Earth. Its apparent size and brightness varies greatly according to its relative position to the Earth. There are several Web sites that show the current position of Mars (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.
A satellite photo shows the "face" on Mars, one of several of the planet's volcanic surface features.
In addition to volcanoes, another amazing geological feature in the Tharsis area of Mars is a massive canyon system known as Valles Marineris. This geological wonder was formed billions of years ago when pressure within the planet's interior caused the crust to swell and split open, creating immense gashes in the surface. The canyon system is three thousand miles long, five miles deep, and in some places more than four hundred miles wide. If Valles Marineris were on Earth, it would stretch across the entire United States and make the Grand Canyon look like nothing more than a tiny crevice in the ground.
Mystery image of 'life on Mars'
That's a headline of a recent article on BBC News covering this early image from the Spirit rover.
An image of a mysterious shape on the surface of Mars, taken by Nasa spacecraft Spirit, has reignited the debate about life on the Red Planet.
A magnified version of the picture, posted on the internet, appears to some to show what resembles a human form among a crop of rocks.
It goes on to say...
When the robotic rover set down on 24 January 2004, its images disappointed space-watchers hoping for signs of extraterrestrial life.
Now they appear convinced that this image provides the evidence they have been trawling Nasa's photo files for.
The blown-up image seems to resemble a figure striding among the Martian rocks.
The internet has been abuzz with postings offering theories.
One said it was a garden gnome, another that it was the Virgin Mary.
A third suggested Bigfoot, the hairy bipedal mountain beast that appears in various guises in a number of legends around the world.
But the consensus seemed to be that it bore a striking resemblance to the Little Mermaid statue in the Danish capital, Copenhagen.
Here's one of the first raw images of Saturn taken by the Cassini spacecraft just after equinox, on August 12, 2009. The planet sure looks naked without its rings! But not to fear, the rings are still there; we just can't see them very well — only a thin line. That's because the sun was shining directly straight-on at the rings at Saturn's equinox, and the spacecraft was in the right place, too. Equinox occurs every half-Saturn-year which is equivalent to about 15 Earth years. The illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures and some moons to cast long shadows across the rings. The ring shadows themselves have become a rapidly narrowing band cast onto the planet. Below, see another image with the rings visible as the spacecraft changed its angle.
Saturn's rings at equinox. Credit: NASA
Mystery Object Pierces a Saturn's Ring
August 11, 2009—A mystery object that punched through one of Saturn's thin outer rings created a glittering spray of ice crystals and pulled some material along in its wake, as seen in this rare image recently released by NASA's Cassini orbiter.
The puncture, which Cassini snapped on June 11, is among the many marvels that have been revealed in the weeks leading up to Saturn's equinox, which happens today. (Find out how the equinox has helped astronomers find new moons, how it will make Saturn temporarily "lose" its rings, and more.)
Equinoxes occur at the point in a planet's orbit when the sun shines directly on the planet's equator. Earth has two equinoxes each year, one in spring and another in autumn. (See an equinox video.)
Because of Saturn's comparatively long orbit around the sun, the ringed planet has an equinox just once every 15 Earth years.
This celestial alignment lowers the angle at which sunlight strikes Saturn, causing objects higher or lower than the ring plane to cast long shadows—and offering scientists a completely new look at the gas giant and its rings.
"We're finally seeing the rings in three dimensions," said Carolyn Porco of the Space Science Institute in Boulder, Colorado. "This is the fist time in history that we've been there watching as this happens."
The object is most likely a small satellite, or moonlet, that is zipping around Saturn on an inclined orbit, said Porco, who leads Cassini's imaging team.
The moonlet appears to be about 0.6 mile (a kilometer) wide, but a comet-like haze of ice crystals and dust surrounding it may be obscuring its true size, Porco added.
Scientists think Saturn's moonlets are fragments of larger moons that were shattered by asteroids or comets eons ago.
It's possible that the object is a small comet or asteroid barreling through the ring, said Nicole Albers, a Saturn-ring scientist at the University of Colorado at Boulder. But such occurrences are rare.
"Since we suspect that there are moonlets in the F ring," Albers said, "it's really not unlikely that it is one."
Temporary Radiation Belt Discovered at Saturn
A new, temporary radiation belt has been detected at Saturn, located about 377,000 km from the center of the planet , near the orbit of the moon Dione. The temporary radiation belt was short-lived and formed three times in 2005. It was observed as sudden increases in the intensity of high energy charged particles in the inner part of Saturn's magnetosphere, in the vicinity of the moons Dione and Tethys, and likely was caused by a change in the intensities of cosmic rays at Saturn.
"These intensifications, which could create temporary satellite atmospheres around these moons," said Dr. Elias Roussos, "occurred three times in 2005 as a response to an equal number of solar storms that hit Saturn's magnetosphere and formed a new, temporary component to Saturn’s radiation belts.”
The discovery was made possible by Cassini's five-plus year mission, allowing scientists to observe and assess changes in Saturn's radiation belts. An international team of astronomers made the discovery analyzing data from the Magnetospheric Imaging instrument (MIMI) on Cassini MIMI’s LEMMS sensor, which measures the energy and angular distribution of charged particles in the magnetic bubble that surrounds Saturn.
The new belt, which has been named “the Dione belt”, was only detected by MIMI/LEMMS for a few weeks after each of its three appearances. The team believe that newly formed charged particles in the Dione belt were gradually absorbed by Dione itself and another nearby moon, named Tethys, which lies slightly closer to Saturn at an orbit of 295 000km.
Unlike the Van Allen belts around the Earth, Saturn’s radiation belts inside the orbit of Tethys are very stable, showing negligible response to solar storm occurrences and no variability over the five years that they have been monitored by Cassini.
Interestingly, it was found that the transient Dione belt was only detected outside the orbit of Tethys. It appeared to be clearly separated from the inner belts by a permanent radiation gap all along the orbit of Tethys.
“Our observations suggest that Tethys acts as a barrier against inward transport of energetic particles and is shielding the planet’s inner radiation belts from solar wind influences. That makes the inner, ionic radiation belts of Saturn the most isolated magnetospheric structure in our solar system“, said Dr Roussos.
The radiation belts within Tethys's orbit probably arise from the interaction of the planet’s main rings and atmosphere and galactic cosmic ray particles that, unlike the solar wind, have the very high energies needed to penetrate the innermost Saturnian magnetosphere. This means that the inner radiation belts will only vary if the cosmic ray intensities at the distance of Saturn change significantly.
However, Roussos emphasized that outside the orbit of Tethys, the variability of Saturn's radiation belt might be enhanced in the coming years as solar maximum approaches. "If solar storms occur frequently in the new solar cycle, the Dione belt might become a permanent, although highly variable, component of Saturn's magnetosphere, which could affect significantly Saturn's global magnetospheric dynamics,” he said.
The new findings were presented at the European Planetary Science Congress in Potsdam, Germany. http://www.nancyatkinson.com/
Uranus
Uranus is much smaller than Jupiter and Saturn, but with a diameter of 51,118 km, it is still over four times that of Earths. It would take 15 of our planet to equal the mass of Uranus.
Though Uranus is the next planet out from Saturn, it is over twice Saturn's distance from the Sun. Being 28.69 x 108 km from the Sun, Uranus is a cold world with an average temperature of -221 C above cloud tops. And clouds are all we have ssen of this distant cold world. Even the Voyager spacecraft could not see beyond those clouds.
Uranus was not known to the ancient astronomers who knew only those planets out to Saturn. Uranus was too distant to be seen with the unaided eye. This planet had to wait until 1781 when the astronomer William Herschel discovered it while hunting for comets.
Neptune
Neptune is a big world, about 49,530 km in diameter, but despite being sometimes referred to as a lesser gas-giant, it’s not a colossus like Jupiter. It’s not even mostly gas. The sphere we see from outside is only the top of a deep, thick atmosphere. About 20% of Neptune’s apparent diameter is air, mostly hydrogen and helium, but with a fair tincture of methane and ammonia, and some more complex organics at trace levels. As one dives into Neptune the outer air starts off very cold. The planet is 30 AU from the Sun, after all. But inside Neptune the heat rises with depth… along with pressure. At a depth where the air is about as dense as what you’re breathing, the temperature is about -200° C, or ~70 Kelvins… but by the time things warm up to room temperature – around 300 Kelvins – you’d be crushed by over 50 atmospheres of pressure. One of those deep-diving suits from the old movies would be required to survive (along with oxygen tanks, of course).
Below that, things get weird. I said there’s no ocean on Neptune, but there is something like an ocean. As pressure climbs during your dive into Neptune, the atmosphere would gradually thicken into something very much like a liquid. True liquid water can’t exist anywhere inside Neptune, because there is too much hydrogen. The hydrogen molecules shove their way in amongst individual water molecules so much that water can’t fully condense into a true liquid. But at the crushing pressures of Neptune’s interior the thick, hot H2O, H2 and He gas compresses to water-like densities… except it’s not liquid water, and the temperature is over 2000° C. Those temperatures are hot enough to melt iron, and are far too hot for any organic compounds to survive. It is decidedly not an abode for life (as we know it, I must add with geeky circumspection).
But what if all that dense quasi-fluid were cooler? Neptune generates 2.6 times more energy in its core than it receives from the Sun, mostly from radioactive decay in its rocky heart. Really, “core” is an odd word to use, because this rocky kernel is more massive than four Earths. For all we know it might have an adorable little metallic iron core all its own, about the size of ours. In any event, heat from below combined with the thin solar light at 30 AU keep Neptune’s water from condensing as rain. But… if Neptune were colder at its cloud tops, and cooler within, its water could drop out to form a massive ocean realm.
What would such a realm be like? Half the planet’s apparent diameter is currently a hot, ionic quasi-liquid right now, but cooled that material would condense into an ocean thousands of kilometers deep. As a comparison, the Mariana Trench is the deepest part of our ocean, at 10 km. Neptune’s ocean would be hundreds of times deeper, and much stranger. If Neptune had a water ocean, its floor wouldn’t be rock, it would be solid ice. Heavy ice… ice VII, or X, or XI, or some other weird crystalline water-lattice that can survive at ten million atmospheres of pressure. Heat would rise from below, from the imprisoned mass of searing rock in Neptune’s center. Volcanic heat from the core mass would bubble up, melting the icy oceanic crust, and inseminating the deep ocean with precious minerals. Could life exist in such an alien environment?
Maybe. If Neptune could cool enough that it supports a liquid ocean, it might also give birth to life. Only when its massive, world-girdling ocean cools to become normal water, instead of a seething ionic mantle, will the conditions be even remotely similar to what conventional life requires. The big question, of course, is… can that happen?
The answer appears to be a qualified yes. Eventually, when its interior furnaces wind down a bit, and its atmosphere can cool enough, seas become possible on Neptune. The only problem… and it’s a fairly big problem, from our perspective… is that before that can happen the Sun has to go away. Specifically, the Sun must live out its long, long life and ultimately wither into a fading white dwarf. The post-solar white dwarf must, in turn, fade from blazing incandescence to a dim sputter. At that point, tens of billions of years from now, Neptune will cool enough to bear oceans. But not until.
There are two ways of looking at this news. From a purely selfish point of view, I’m quite cross that I’ll never be able to see what titans of the deep Neptune’s olympian waters might birth. But from a larger perspective I’m encouraged. Even when the Sun goes dark, it will be possible for life to spawn… or transplant itself and survive… in our solar system. The details will differ from what we’re familiar with today, on Earth, but water in the dim astronomical future will still require fins, and streamlining, to move through, and the animals of any Neptunian ocean of 100 billion years from now will still need to be sleek and smooth and tapered. I don’t have to see them for myself, because I can use chemistry, thermodynamics, geology, and physics to construct a probabilistic prognostication. Or two, or ten… There are many ways the future of Neptune may work out, but among them are highly realistic ways that lead to life, and complexity, and possibly thought… in a future so deep our own biosphere will be an impossibly ancient memory from a time older than the Big Bang is to us.
When will Neptune get oceans?
Yes, and a strange question that is. But actually not an unrealistic question. Neptune, now the farthest true planet from the Sun (after Pluto’s demotion), is namesake to the ancient god of the oceans. Neptune is shrouded in layers of icy, dense air laced with enough methane to color the world azure blue… hence the world’s maritime label. But despite its pelagic associations, Neptune has no oceans… though it might have had, with a slightly different composition. And it’s very possible that Neptune will one day be covered in a deep, wine-black sea of cool, liquid water.
The distant, ice-covered world is no longer a true planet, according to a new definition of the term voted on by scientists today.
"Whoa! Pluto's dead," said astronomer Mike Brown, of the California Institute of Technology in Pasadena, as he watched a Webcast of the vote. "There are finally, officially, eight planets in the solar system."
In a move that's already generating controversy and will force textbooks to be rewritten, Pluto will now be dubbed a dwarf planet.
But it's no longer part of an exclusive club, since there are more than 40 of these dwarfs, including the large asteroid Ceres and 2003 UB313, nicknamed Xena—a distant object slightly larger than Pluto discovered by Brown last year.
"We know of 44" dwarf planets so far, Brown said. "We will find hundreds. It's a very huge category."
A clear majority of researchers voted for the new definition at a meeting of the International Astronomical Union (IAU) in Prague, in the Czech Republic. The IAU decides the official names of all celestial bodies.
The tough decision comes after a multiyear search for a scientific definition of the word "planet." The term never had an official meaning before.
What Is a Planet Today?
According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.
Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.
In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.
Mercury
Mercury, the closest planet to the Sun, remains the most mysterious of the Solar System's inner planets. Hiding in the Sun's glare it is a difficult target for Earth bound observers. The only spacecraft to explore Mercury close-up was Mariner 10 which executed 3 flybys of Mercury in 1974 and 1975, surveying approximately 45 percent of its surface. Mariner 10 deftly manuevered to photograph part of the sunlit hemisphere during each approach, passed behind the planet, and continued to image the sun-facing side as the spacecraft receded. Its highest resolution photographs recorded features approximately a mile across. A recent reprocessing of the Mariner 10 data has resulted in this dramatic mosaic. Like the Earth's Moon, Mercury's surface shows the scars of impact cratering - the smooth vertical band and patches visible above represent regions where no image information is available.
Venus
The Brightest Planet
Venus and Earth are similar in size, mass, density, composition, and distance from the sun. There, however, is where the similarities end.
Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and a surface pressure 90 times that of Earth. Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.
Like Mercury, Venus can be seen periodically passing across the face of the sun. These transits occur in pairs, with more than a century separating each pair. Since the telescope was invented, transits have been observed in 1631, 1639; 1761, 1769; and 1874, 1882. On June 8, 2004, astronomers worldwide saw the tiny dot of Venus crawl across the sun; the second in this pair of early 21st-century transits will occur June 6, 2012.
Toxic Atmosphere
Venus's atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the sun's heat, resulting in surface temperatures over 880 degrees Fahrenheit (470 degrees Celsius). Probes that have landed on Venus have not survived more than a few hours before being destroyed by the incredibly high temperatures.
The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's prograde (west to east) rotation. Seen from Venus, the sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating "backwards" on its axis, the cloud-level atmosphere zips around the planet in the opposite direction from the rotation every four Earth days, driven by constant hurricane-force winds. How this atmospheric "super rotation" forms and is maintained continues to be a topic of scientific investigation.
About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 million to 500 million years ago.
Sulfur compounds, possibly attributable to volcanic activity, are abundant in Venus's clouds. The corrosive chemistry and dense, moving atmosphere cause significant surface weathering and erosion. Radar images of the surface show wind streaks and sand dunes. Craters smaller than 0.9 to 1.2 miles (1.5 to 2 kilometers) across do not exist on Venus, because small meteors burn up in the dense atmosphere before they can reach the surface.
Geological Features
More than a thousand volcanoes or volcanic centers larger than 12 miles (20 kilometers) in diameter dot the surface of Venus. Volcanic flows have produced long, sinuous channels extending for hundreds of kilometers.
Venus has two large highland areas: Ishtar Terra, about the size of Australia, in the north polar region, and Aphrodite Terra, about the size of South America, straddling the equator and extending for almost 6,000 miles (10,000 kilometers). Maxwell Montes, the highest mountain on Venus and comparable to Mount Everest on Earth, is at the eastern edge of Ishtar Terra.
Venus has an iron core about 1,200 miles (3,000 kilometers) in radius. Venus has no global magnetic field; though its core iron content is similar to that of Earth, Venus rotates too slowly to generate the type of magnetic field that Earth has.
The Solar System consists of the Sun and those celestial objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the retinue of objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly-flat disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, Jupiter, Saturn, Uranus and Neptune, also called the gas giants, are composed largely of hydrogen and helium and are far more massive than the terrestrials.
The Solar System is also home to two regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these regions, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognised to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.
Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.
Sun
The Sun is the most prominent feature in our solar system. It is the largest object and contains approximately 98% of the total solar system mass. One hundred and nine Earths would be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). This layer has a mottled appearance due to the turbulent eruptions of energy at the surface.
Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level) is so intense that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about .7 percent less massive than the four protons. The difference in mass is expelled as energy and is carried to the surface of the Sun, through a process known as convection, where it is released as light and heat. Energy generated in the Sun's core takes a million years to reach its surface. Every second 700 million tons of hydrogen are converted into helium ashes. In the process 5 million tons of pure energy is released; therefore, as time goes on the Sun is becoming lighter.
The chromosphere is above the photosphere. Solar energy passes through this region on its way out from the center of the Sun. Faculae and flares arise in the chromosphere. Faculae are bright luminous hydrogen clouds which form above regions where sunspots are about to form. Flares are bright filaments of hot gas emerging from sunspot regions. Sunspots are dark depressions on the photosphere with a typical temperature of 4,000°C (7,000°F).
The corona is the outer part of the Sun's atmosphere. It is in this region that prominences appears. Prominences are immense clouds of glowing gas that erupt from the upper chromosphere. The outer region of the corona stretches far into space and consists of particles traveling slowly away from the Sun. The corona can only be seen during total solar eclipses.
The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf -- the final end product of a star like ours. It may take a trillion years to cool off completely.
A comet is a small solar system body bigger than a meteoroid[citation needed] that, when close enough to the Sun, exhibits a visible coma (fuzzy "atmosphere"), and sometimes a tail, both because of the effects of solar radiation upon the comet's nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles, ranging from a few hundred metres to tens of kilometres across.
Comet Swarm Delivered Earth's Oceans?
A barrage of comets may have delivered Earth's oceans around 3.85 billion years ago, a new study suggests.
Scientists have long suspected that Earth and its near neighbors were walloped by tens of thousands of impactors during an ancient event known as the Late Heavy Bombardment.
This pummeling disfigured the moon, leaving behind massive craters that are still visible, preserved for millennia in the moon's airless environment. But it's been unclear whether the impactors were icy comets or rocky asteroids.
Now, based on levels of a certain metal in ancient Earth rocks, a team led by Uffe Jorgensen of the Niels Bohr Institute in Denmark says comets were the culprits.
Whether Earth had oceans before any comets arrived has been intensely debated, Jorgensen noted.
Some experts say enough water could have existed from the moment Earth formed, while others argue that the young planet's heat would have vaporized any liquids.
"It's the kind of subject that can make scientists fight physically with one another," Jorgensen said.
His team thinks early Earth was just too hot to retain large bodies of water. But by the time of the Late Heavy Bombardment, things had cooled down, allowing meltwater from the flurry of comets to become the world's first seas.
"We may sip a piece of the impactors every time we drink a glass of water," the study authors write in their paper, which will be published in an upcoming issue of the journal Icarus.
Comets' Metal
Jorgensen and colleagues arrived at this conclusion after measuring the levels of iridium in surface and near-surface rocks from Greenland—some of the oldest known rocks in the world, dating back to the time of the bombardment.
Iridium is a scarce metal on Earth, but it's relatively common in comets and asteroids.
According to the team's calculations, iridium levels in the rocks around an asteroid impact should be about 18,000 parts per trillion. A comet impact, meanwhile, should leave behind only about 130 parts per trillion. That's because comets would carry less metal, since they're mostly made of loosely packed water ice with some rocky debris.
Comets also strike Earth at higher speeds, because of their longer orbits around the sun.
As a result, "the explosion formed by a comet is more violent than from an asteroid, and the amount of material—including iridium—thrown back into space is larger," Jorgensen said.
The team found that the Greenland rocks contained about 150 parts per trillion of iridium, supporting the idea that comets were the main players in the Late Heavy Bombardment.
All that ice from the comet swarm then thawed to create a global ocean more than half a mile (about a kilometer) deep, the team calculates.
The moon, meanwhile, lacks an ocean because its gravity is much weaker than Earth's, so most if not all of the debris from a comet strike would be thrown back into space, Jorgensen said.
But Nicolas Dauphas, a geophysicist at the University of Chicago, isn't yet convinced that the bombardment featured comets, not asteroids.
The new study, he said, relies on too many estimates—such as the predicted amount of iridium deposited following an impact.
"I am afraid [they have] stretched their conclusions too far," Dauphas said.
Accidental Life?
Chandra Wickramasinghe, an astrobiologist at Cardiff University in the U.K. not involved in the new study, also supports the theory of an ancient comet bombardment.
And he thinks it's possible that comets seeded Earth not only with water but with life.
According to some controversial studies, the oldest evidence for life on Earth dates back to about 3.85 billion years ago, around the time of the Late Heavy Bombardment, he noted.
Asteroid
Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are smaller than planets but larger than meteoroids. The term "asteroid" has historically been applied primarily to minor planets of the inner Solar System, as the outer Solar System was poorly known when it came into common usage. The distinction between asteroids and comets is made on visual appearance: Comets show a perceptible coma while asteroids do not.
Asteroid Impact
There have been many Asteroid Impact videos but not one is as beautiful and scary as this one. If you realise this could indeed happen some day it makes you wonder will mankind be on outer space in time or will we all die when this happens? Check out this HD CGI footage by Discovery Channel about an Asteroid the size of the moon hitting planet earth.
Meteorites
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids. When it enters the atmosphere, impact pressure causes the body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting/falling star. The term bolide refers to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface.
More generally, a meteorite on the surface of any celestial body is a natural object that has come from elsewhere in space. Meteorites have been found on the Moon and Mars.
It's amazing what a rover can find laying by the side of the road. The Mars Exploration Rover Opportunity has found a rock that apparently is another meteorite. Less than three weeks ago, Opportunity drove away from a larger meteorite called "Block Island" that the rover examined for six weeks. Now, this new meteorite, dubbed "Shelter Island," is another fairly big rock, about 47 centimeters (18.8 inches) long, that fell from the skies. Block Island is about 60 centimeters (2 feet) across and was just 700 meters (about 2,300 feet) away from this latest meteorite find. At first look, the two meteorites look to be of a similar makeup; Opportunity found that Block Island was is made of nickel and iron.
Meteorites that are recovered after being observed as they transited the atmosphere or impacted the Earth are called falls. All other meteorites are known as finds. As of mid-2006, there are approximately 1,050 witnessed falls having specimens in the world's collections. In contrast, there are over 31,000 well-documented meteorite finds.
Meteorites have traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites are largely composed of metallic iron-nickel; and, stony-iron meteorites contain large amounts of both metallic and rocky material. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy.
Astronomers think that there are hundreds of billions galaxies in the universe, however the exact number is not known. But astronomers should know how many galaxies we've actually seen and discovered, right?
Well, not necessarily.
“We don’t know,” says Ed Churchwell, professor of astronomy at the University of Wisconsin-Madison. “We know it’s a very large number.”
In just one image for example, the Hubble Ultra Deep Field, above, there are about 10,000 galaxies visible.
In our own galaxy, There are between 4 billion 100-300 billion stars in the Milky Way. At most, 8,479 of them are visible from Earth. Roughly 2,500 stars are available to the unaided eye in ideal conditions from a single spot at a given time.
But the number of galaxies will keep growing as our telescopes get better and can look out and back farther in time.
“To count them all, you have to be able to look far enough back in time or deep enough in space to see when galaxies were formed,” Churchwell says. “We haven’t reached that point yet. It’s not a well-determined number, but at some point we’re going to reach it.”
The estimate of how many galaxies there are in the universe is done by counting how many galaxies we can see in a small area of the sky. This number is then used to guess how many galaxies there are in the entire sky.
For the time being, the hundreds of billions in the tally are extrapolated from the Hubble Ultra Deep Field, taken over a time period in 2003 and 2004. Pointed at a single piece of space for several months — a spot covering less than one-tenth of one-millionth of the sky — Hubble returned an image of galaxies 13 billion light years away.
"Você olha para isso e dizer, 'Como muitas galáxias posso ver?" Churchwell explica. “And that turns out to be a very large number.” "E isso acaba por ser um número muito grande."
“Then you take that number of galaxies from that postage-stamp-sized piece of the sky and multiply it by the number of postage-stamp-sized pieces of sky,” Churchwell says. "Então você pega o número de galáxias do que um selo de tamanho pedaço do céu e multiplicá-lo pelo número de um selo pedaços do céu", Churchwell diz. “And that turns out to be a much larger number.” "E isso acaba por ser um número muito maior."
In the first Hubble Deep Field image , taken in 1995, there are about 3,000 galaxies visible in the image. Na primeira imagem do Hubble Deep Field, tomada em 1995, existem cerca de 3.000 galáxias visíveis na imagem.
Source: UW-M
Cosmic mystery
Researchers propose a new explanation for why some tiny galaxies have more than their fair share of dark matter.
Literally cloaked in darkness, the faintest galaxies in the universe have remained a mystery since their discovery more than two decades ago. Now a team of theorists has come up with a new explanation for the origin of these dim bodies. Known as dwarf spheroidal galaxies, these ancient stellar groupings not only serve as fossil remains of the early universe but have the highest known ratio of dark matter to ordinary, visible matter.
In the most widely accepted model of galaxy formation, an exotic type of invisible material, known as cold dark matter, provides the gravitational glue that draws together stars and gas and keeps galaxies, along with galaxy clusters, from flying apart. It would seem that all galaxies ought to have about the same ratio of dark matter to visible matter, because gravity builds all galaxies in the same way. Yet dwarf spheroidals are the most dark matter–dominated galaxies known, with 10 to 30 times the ratio of dark to visible matter as large galaxies including the Milky Way.
That’s the puzzle that Elena D’Onghia of the University of Zurich and the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and her colleagues set out to solve in a study posted online July 16 (http://arxiv.org/abs/0907.2442) and in an upcoming Nature.
Like other researchers, she and her collaborators assume that dwarf spheroidals were born with a lower, more typical ratio of dark to visible matter, but that much of the visible stuff somehow got pulled out.
Previous models suggest a complex, two-step process to explain the high ratio. But these models require a dwarf spheroidal to lie close to a galaxy as large as the Milky Way. In reality, some spheroidals lie far from such galaxies. Also, these models don’t easily explain the spherical shape of these galaxies or the diversity of their dark matter ratios.
In contrast, the new model proposed by D’Onghia’s team relies on the assumption that stars and gas rotate in fledgling galaxies, a property which the underlying dark matter model of formation requires.
If the rotation and orbit of stars in a dwarf spheroidal are in sync with the rotation of a slightly larger, nearby galaxy — possibly even just another dwarf spheroidal — the gravitational influences of the two galaxies on each other are enhanced, D’Onghia says.
Within 2 to 3 billion years, the gravitational pull would remove many stars from the lower-mass dwarf, D’Onghia says. Because dark matter does not rotate, it would be left behind in the dwarf galaxy. Depending on how closely the rotation of stars and gas aligns in neighboring galaxies, the dwarf spheroidals would end up with varying, but always high, ratios of dark to visible matter.
The proposed interaction could account for dwarf spheroidals, such as the recently discovered galactic duo Leo IV and Leo V, that don’t reside close to a large galaxy like the Milky Way, D’Onghia asserts.
“Certainly this is an idea that needs to be taken very seriously,” comments theorist James Bullock of the University of California, Irvine. “I bet some of the [dwarf spheroidals] formed this way, but I’m not sure if the numbers work out to explain all of them,” he adds.
D’Onghia and her collaborators simulate only the interaction of stars, not gas, cautions Rosemary Wyse of Johns Hopkins University in Baltimore, Md. But D’Onghia says that the rotating gas in a dwarf spheroidal, although more difficult to model than the stars, ought to be removed in a similar manner.
Jorge Peñarrubia of the University of Cambridge in England takes a contrarian view. “In my opinion, the whole problem may be a theoretical misconception,” due to uncertainties about star formation in galaxies, he says. Although dark matter models require that stars form in rotating disks, star-forming regions in the Milky Way indicate that most stars form in clusters instead. If stars in dwarf spheroidals don’t form in rotating disks, the scenario proposed by D’Onghia and her collaborators wouldn’t provide an explanation, he says.
