The next solar eclipse -- a partial one -- will occur on January 26 next year but the phenomenon will be marginally visible from eastern and southernIndia. 
India will witness a partial eclipse of the Sun beginning in the northeast of India on Friday.It will begin at 4:03 pm in Delhi. It will last for about two hours with maximum impact at 5.02 pm. In the rest of the country, the partial eclipse will be visible a few minutes later.However, some parts of the world will witness a rare total solar eclipse -- when the moon will pass directly between the earth and the sun.The eclipse will begin in Arctic Canada and sweep across Greenland, western Siberia, Mongolia and central China.Viewers all across the globe can see the eclipse as it happens on NASA TV and by logging on to www.nasa.gov. The US space agency has made arrangements to telecast live images of the rare celestial event.
Image: Indians will miss this sight -- A total solar eclipse August 01, 2008 According to Nehru Planetarium director Rathnasree, the maximum obscuration of the sun will occur at Sibsagar in Assam..The biggest and last phase of the eclipse will be visible from most parts of the country, except Nagaland and Mizoram, where it ends after sunset, she said.The southern parts of India will see between 20 to 40 per cent of the sun's diameter while the northern parts of the country will see between 40 to 70 per cent of the sun's diameter.
Image: A combo photograph of the partial solar eclipse.August 01, 2008 People must also avoid watching the eclipse through sunglasses, single or multiple layers, smoked glass, colour film or black-and-white film that contains no silver or photographic negatives with images on them.The Nehru Planetarium, in collaboration with the Amateur Astronomers Association, Delhi will be conducting public sky-watch for the eclipse from the Jantar Mantar, the planetarium and the India Gate area.
Image: A multiple exposure photograph shows the progress of a total solar eclipse. The sequence begins at the upper left.
Jupiter's moon Io floats above the cloudtops of Jupiter in this image captured January 1, 2001. The image is deceiving: there are 350,000 kilometers - roughly 2.5 Jupiters - between Io and Jupiter's clouds. Io is about the size of our own moon Jupiter is in the news again, this time because its "Baby Red Spot" - a storm less than a year old - appears to have been swallowed up by the massive storm known as the Great Red Spot. This is good occasion to share some of the best photographs of Jupiter and its larger system of rings and moons, as seen by various probes and telescopes over the past 30 years
This image of Jupiter's moon Europa rising above Jupiter was captured by the New Horizons spacecraft in February just after it passed Jupiter on its way to Pluto and the outer Solar System.
The gibbous phase of Jupiter's moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface.
This view of the icy surface of Jupiter's moon, Europa, is a mosaic of two pictures taken by the Solid State Imaging system on board the Galileo spacecraft during a close flyby of Europa on February 20, 1997. The area shown is about 14 kilometers by 17 kilometers (8.7 miles by 10.6 miles), and has a resolution of 20 meters (22 yards) per pixel. One of the youngest features seen in this area is the double ridge cutting across the picture from the lower left to the upper right. This double ridge is about 2.6kilometers (1.6 miles) wide and stands some 300 meters (330 yards) high.
A composite of several images taken in several colors by the New Horizons Multispectral Visual Imaging Camera, or MVIC, illustrating the diversity of structures in Jupiter's atmosphere, in colors similar to what someone "riding" on New Horizons would see. It was taken near the terminator, the boundary between day and night, and shows relatively small-scale, turbulent, whirlpool-like structures near the south pole of the planet. The dark "holes" in this region are actually places where there is very little cloud cover, so sunlight is not reflected back to the camera.
This image, acquired during Galileo's ninth orbit around Jupiter, shows two volcanic plumes on Io. One plume was captured on the bright limb or edge of the moon, erupting over a caldera (volcanic depression) named Pillan Patera. The plume seen by Galileo is 140 kilometers (86 miles) high, and was also detected by the Hubble Space Telescope. The second plume, seen near the terminator, the boundary between day and night, is called Prometheus. The shadow of the airborne plume can be seen extending to the right of the eruption vent.
A part of the southern hemisphere of Io, seen by the spacecraft Voyager at a range of 74,675 km. In the foreground is gently undulating topography, while in the back-ground are two mountains with their near faces brightly illuminated by the sun. The mountain in the right is approximately 150 km across at its base and its height is probably in excess of 15 km which would make it higher than any mountain on Earth.
This five-frame sequence of New Horizons images captures the giant plume from Io's Tvashtar volcano. Snapped by the probe's Long Range Reconnaissance Imager (LORRI) as the spacecraft flew past Jupiter earlier this year, this first-ever "movie" of an Io plume clearly shows motion in the cloud of volcanic debris, which extends 330 kilometers (200 miles) above the moon's surface. Only the upper part of the plume is visible from this vantage point - the plume's source is 130 kilometers (80 miles) below the edge of Io's disk, on the far side of the moon.
A volcanic plume rises over 300 kilometers above the horizon of Jupiter's moon Io in this image from cameras onboard the New Horizons spacecraft. The volcano, Tvashtar, is marked by the bright glow (about 1 o'clock) at the moon's edge, beyond the terminator or night/day shadow line. The shadow of Io cuts across theplume itself. Also capturing stunning details on the dayside surface, the high resolution image was recorded when the spacecraft was 2.3 million kilometers from Io. Later it was combined with lower resolution color data by astro-imager Sean Walker to produce this sharp portrait of the solar system's most active moon.
Jupiter's moon Io, seen by NASA's Galileo spacecraft against a backdrop of Jupiter's cloud tops, which appear blue in this false-color composite.
The first color movie of Jupiter from NASA's Cassini spacecraft shows what it would look like to peel the entire globe of Jupiter, stretch it out on a wall into the form of a rectangular map, and watch its atmosphere evolve with time. The brief movie clip spans 24Jupiter rotations between Oct. 31 and Nov. 9, 2000. The darker blips that appear are several moons and their shadows.
Jupiter's Great Red seen by NASA's Voyager spacecraft. July, 1979 Around the northern boundary a white cloud is seen, which extends to east of the region. The presence of this cloud prevents small cloud vortices from circling the spot in the manner seen in the Voyager 1 encounter. Another white oval cloud (different from the one present in this position three months ago) is seen south of the Great Red Spot. This image was taken on July 6, 1979 from a range of 2,633,003 kilometers. The Red Spot is 20,000 km across.[/I
Awesome Close-Ups of the SunThe sun (not the earth!) is the center of our solar system. Here are some interesting facts of this quintessential planet to live on earth that we so easily take for granted. * Containing more than 99.8% of the total mass of the Solar System, the Sun is by far the largest object in the Solar System.* 109 Earths would be required to even fit across the Sun’s disk, and the Sun’s interior could hold over 1.3 million Earths.* Within the core of the Sun, the temperature (15,000,000 K) and pressure (340 billion times Earth’s air pressure at sea level) of it is so intense that nuclear reactions actually take place.* The Sun’s energy output, produced by these nuclear fusion reactions, is approximately 3.86e33 ergs/second or 386 billion billion megawatts.* This energy, released as heat as well as light, takes a million years to reach the surface.* The Sun also emits low density streams of particles, also known as the solar wind. These winds blow through the solar system at 450 km/sec and consist mostly of electrons and protons.* The Sun consists of the core, photosphere, chromosphere and corona, each with differing temperatures and components.* Existing for about 4 and a half billion years, it has burnt up about half of the hydrogen in its core. This leaves the Sun’s life expectancy to 5 billion more years, at which time, the Sun’s elements will “swell” up, swallow Earth, and eventually die off into a small white dwarf.
The possibility that there were seas of liquid methane on Titan were first suggested based on Voyager 1 and 2 data that showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them, but direct evidence wasn't obtained until 1995 when data from Hubble and other observations had already suggested the existence of liquid methane on Titan, either in disconnected pockets or on the scale of satellite-wide oceans, similar to water on Earth.
The Cassini mission affirmed the former hypothesis, although not immediately. When the probe arrived in the Saturnian system in 2004, it was hoped that hydrocarbon lakes or oceans might be detectable by reflected sunlight from the surface of any liquid bodies, but no specular reflections were initially observed.
The possibility remained that liquid ethane and methane might be found on Titan's poles, where it was expected to be abundant and stable. At Titan's south pole, an enigmatic dark feature named Ontario Lacus was the first suspected lake identified, possibly created by clouds that are observed to cluster in the area. A possible shoreline was also identified at the pole via radar imagery. Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (which are currently in winter), a number of large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole. Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007. The Cassini–Huygens team concluded that the imaged features are almost certainly the long-sought hydrocarbon lakes, the first stable bodies of surface liquid found off Earth. Some appear to have channels associated with liquid and lie in topographical depressions.
Repeated coverage of these areas should prove whether they are truly liquid, as any changes that correspond with wind blowing on the surface of the liquid would alter the roughness of the surface and be visible in the radar. The high relative humidity of methane in Titan’s lower atmosphere could be maintained by evaporation from lakes covering only 0.002–0.02% of the whole surface.
Size comparison of Ligeia Mare with Lake Superior.During a Cassini flyby in late February 2007, radar and camera observations revealed several large features in the north polar region that may be large expanses of liquid methane and/or ethane, including one sea with an area of over 100,000 km² (larger than Lake Superior), and another (though less definite) region potentially the size of the Caspian Sea. A flyby of Titan's southern polar regions in October 2007 revealed similar, though far smaller, lakelike features.
Image of Titan taken during Huygens' descent, showing hills and topographical features that resemble a shoreline and drainage channels.During a close Cassini flyby in December 2007 the visual and mapping instrument observed a lake, Ontario Lacus, in Titan's south polar region. This instrument identifies chemically different materials based on the way they absorb and reflect infrared light. Based on this instrument's observations, scientists concluded that at least one of the large lakes observed on Saturn's moon Titan does in fact contain liquid, that liquid being hydrocarbons, and have positively identified the presence of ethane. This makes Titan the only other object than Earth in the solar system known to have liquid on its surface. This would make Titan a very interesting place to observe and study , to refine weather science, as differing liquid and gaseous materials and temperatures are at play there. This would help refine the science of Earth weather forecasting, allowing for better weather forecasts.
The discoveries at the poles contrast with the findings of the Huygens probe, which landed near Titan's equator on January 14, 2005. The images taken by the probe during its descent showed no open areas of liquid, but strongly indicated the presence of liquids in the recent past, showing pale hills crisscrossed with dark drainage channels that lead into a wide, flat, darker region. It was initially thought that the dark region might be a lake of a fluid or at least tar-like substance, but it is now clear that Huygens landed on the dark region, and that it is solid without any indication of liquids. A penetrometer studied the composition of the surface as the craft impacted it, and it was initially reported that the surface was similar to wet clay, or perhaps crème brûlée (that is, a hard crust covering a sticky material). Subsequent analysis of the data suggests that this reading was likely caused by Huygens displacing a large pebble as it landed, and that the surface is better described as a "sand" made of ice grains. The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles may be made of water ice and are somewhat rounded, which may indicate the action of fluids.
On February 13, 2008, scientists announced that, according to Cassini data, Titan hosts within its polar lakes "hundreds of times more natural gas and other liquid hydrocarbons than all the known oil and natural gas reserves on Earth." The desert sand dunes along the equator, while devoid of open liquid, nonetheless hold more organics than all of Earth's coal reserves. In June 2008, Cassini's Visible and Infrared Mapping Spectrometer confirmed the presence of liquid ethane beyond doubt in a lake in Titan's southern hemisphere.
Models of oscillations in Titan's atmospheric circulation suggest that over the course of a Saturnian year, liquid is transported from the equatorial region to the poles, where it falls as rain. This might account for the equatorial region's relative dryness.
Impact craters
Radar, SAR and imaging data from Cassini have revealed a relative paucity of impact craters on Titan's surface, suggesting a youthful surface. The few impact craters discovered include a 440 km wide multi-ring impact basin named Menrva (seen by Cassini's ISS as a bright-dark concentric pattern). A smaller 80 km wide, flat-floored crater named Sinlap and a 30 km crater with a central peak and dark floor named Ksa have also been observed. Radar and Cassini imaging have also revealed a number of "crateriforms", circular features on the surface of Titan that may be impact related, but lack certain features that would make identification certain. For example, a 90 km wide ring of bright, rough material known as Guabonito has been observed by Cassini. This feature is thought to be an impact crater filled in by dark, windblown sediment. Several other similar features have been observed in the dark Shangri-la and Aaru regions. Radar observed several circular features that may be craters in the bright region Xanadu during Cassini's April 30, 2006 flyby of Titan.
Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, a small amount of ejecta remains as liquid water within the crater. It may persist as liquid for centuries or longer, sufficient for "the synthesis of simple precursor molecules to the origin of life". While infill from various geological processes is one reason for Titan's relative deficiency of craters, atmospheric shielding also plays a role; it is estimated that Titan's atmosphere reduces the number of craters on its surface by a factor of two.
Cryovolcanism and mountains
Scientists have speculated that conditions on Titan resemble those of early Earth, though at a much lower temperature. Evidence of volcanic activity from the latest Cassini mission suggests that temperatures are probably much higher in hotbeds, enough for liquid water to exist. Argon 40 detection in the atmosphere indicates that volcanoes spew plumes of "lava" composed of water and ammonia. Cassini detected methane emissions from one suspected cryovolcano, and volcanism is now believed to be a significant source of the methane in the atmosphere. One of the first features imaged by Cassini, Ganesa Macula, resembles the geographic features called "pancake domes" found on Venus, and is thus believed to be cryovolcanic in origin.
The pressure necessary to drive the cryovolcanoes may be caused by ice "underplating" Titan's outer shell. The low-pressure ice, overlaying a liquid layer of ammonium sulfate, ascends buoyantly, and the unstable system can produce dramatic plume events. Titan is resurfaced through the process by grain-sized ice and ammonium sulfate ash, which helps produce a wind-shaped landscape and sand dune features.
A mountain range measuring 150 km long, 30 km wide and 1.5 km high was discovered by Cassini in 2006. This range lies in the southern hemisphere and is thought to be composed of icy material and covered in methane snow. The movement of tectonic plates, perhaps influenced by a nearby impact basin, could have opened a gap through which the mountain's material upwelled. Prior to Cassini, scientists assumed that most of the topography on Titan would be impact structures, yet these findings reveal that similar to Earth, the mountains were formed through geological processes
Dark terrain
In the first images of Titan's surface taken by Earth-based telescopes in the early 2000s, large regions of dark terrain were revealed straddling Titan's equator. Prior to the arrival of Cassini, these regions were thought to be seas of organic matter like tar or liquid hydrocarbons. Radar images captured by the Cassini spacecraft have instead revealed some of these regions to be extensive plains covered in longitudinal sand dunes, up to 330 meters high. The longitudinal (or linear) dunes are believed to be formed by moderately variable winds that either follow one mean direction or alternate between two different directions. Dunes of this type are always aligned with average wind direction. In the case of Titan, steady zonal (eastward) winds combine with variable tidal winds (approximately 0.5 meter per second). The tidal winds are the result of tidal forces from Saturn on Titan's atmosphere, which are 400 times stronger than the tidal forces of the Moon on Earth and tend to drive wind toward the equator. This wind pattern causes sand dunes to build up in long parallel lines aligned west-to-east. The dunes break up around mountains, where the wind direction shifts.
The sand on Titan might have formed when liquid methane rained and eroded the ice bedrock, possibly in the form of flash floods. Alternatively, the sand could also have come from organic solids produced by photochemical reactions in Titan's atmosphere. Studies of dunes' composition in May, 2008, revealed that they possessed less water than the rest of Titan, and are most likely to derive from organic material clumping together after raining onto the surface.
Climate
Titan's surface temperature is about 94 K (−179 °C, or −290 °F). At this temperature water ice does not sublimate or evaporate, so the atmosphere is nearly free of water vapor. The haze in Titan's atmosphere contributes to the moon's anti-greenhouse effect by reflecting sunlight away from the satellite, making its surface significantly colder than its upper atmosphere. The clouds on Titan, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze. This atmospheric methane conversely creates a greenhouse effect on Titan's surface, without which Titan would be far colder. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto the moon's surface. In October 2007, observers noted an increase in apparent opacity in the clouds above the equatorial Xanadu region, suggestive of "methane drizzle", though this was not direct evidence for rain. It is possible that areas of Titan's surface may be coated in a layer of tholins, but this has not been confirmed.
Simulations of global wind patterns based on wind speed data taken by Huygens during its descent have suggested that Titan's atmosphere circulates in a single enormous Hadley cell. Warm air rises in Titan's southern hemisphere—which was experiencing summer during Huygens' descent—and sinks in the northern hemisphere, resulting in high-altitude air flow from south to north and low-altitude airflow from north to south. Such a large Hadley cell is only possible on a slowly rotating world such as Titan. The pole-to-pole wind circulation cell appears to be centered on the stratosphere; simulations suggest it ought to change every twelve years, with a three-year transition period, over the course of Titan's year (30 terrestrial years). This cell creates a global band of low pressure—what is in effect a variation of Earth's Intertropical Convergence Zone. Unlike on Earth, however, where the oceans confine the ITCZ to the tropics, on Titan, the zone wanders from one pole to the other, taking methane rainclouds with it. This means that Titan, despite its frigid temperatures, can be said to have a tropical climate.
The number of methane lakes visible near Titan's southern pole is decidedly smaller than the number observed near the north pole. As the south pole is currently in summer and the north in winter, an emerging hypothesis is that methane rains onto the poles in winter and evaporates in summer.
Clouds
In September 2006, Cassini imaged a large cloud at a height of 40 km over Titan's north pole. Although methane is known to condense in Titan's atmosphere, the cloud was more likely to be ethane, as the detected size of the particles was only 1–3 micrometers and ethane can also freeze at these altitudes. In December, Cassini again observed cloud cover and detected methane, ethane and other organics. The cloud was over 2,400 km in diameter and was still visible during a following flyby a month later. One hypothesis is that it is currently raining (or, if cool enough, snowing) on the north pole; the downdrafts at high northern latitudes are strong enough to drive organic particles towards the surface. These were the strongest evidence yet for the long-hypothesised "methanological" cycle (analogous to Earth's hydrological cycle) on Titan.
Clouds have also been found over the south pole. While typically covering 1% of Titan's disk, outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the Titanian summer generate uplift in the atmosphere, resulting in convection. This explanation is complicated by the fact that cloud formation has been observed not only post–summer solstice but also at mid-spring. Increased methane humidity at the south pole possibly contributes to the rapid increases in cloud size. It is currently summer in Titan's southern hemisphere and will remain so until 2010, when Saturn's orbit, which governs the moon's motion, will tilt the northern hemisphere towards the Sun. When the seasons switch, ethane will begin to condense over the south pole.
Research models that match well with observations suggest that clouds on Titan cluster at preferred coordinates and that cloud cover varies by distance from the surface on different parts of the satellite. In the polar regions (above 60 degrees latitude), widespread and permanent ethane clouds appear in and above the troposphere; at lower latitudes, mainly methane clouds are found between 15 and 18 km, and are more sporadic and localized. In the summer hemisphere, frequent, thick but sporadic methane clouds seem to cluster around 40°.
Ground-based observations also reveal seasonal variations in cloud cover. Over the course of Saturn's 30-year orbit, Titan's cloud systems appear to manifest for 25 years, and then fade for four to five years before reappearing again.Prebiotic conditions and possible life
Scientists believe that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan. Many hypotheses have developed that attempt to bridge the step from chemical to biological evolution. The Miller-Urey experiment and several following experiments have shown that with an atmosphere similar to that of Titan and the addition of UV radiation, complex molecules and polymer substances like tholins can be generated. The reaction starts with dissociation of nitrogen and methane, forming hydrocyan and ethyne. Further reactions have been studied extensively.
All of these experiments have led to the suggestion that enough organic material exists on Titan to start a chemical evolution analogous to what is thought to have started life on Earth. While the analogy assumes the presence of liquid water for longer periods than is currently observable, several theories suggest that liquid water from an impact could be preserved under a frozen isolation layer. It has also been observed that liquid ammonia oceans could exist deep below the surface; one model suggests an ammonia–water solution as much as 200 km deep beneath a water ice crust, conditions that, "while extreme by terrestrial standards, are such that life could indeed survive". Heat transfer between the interior and upper layers would be critical in sustaining any sub-surface oceanic life.
Detection of microbial life on Titan would depend on its biogenic effects. That the atmospheric methane and nitrogen are of biological origin has been examined, for example. Hydrogen has been cited as one molecule suitable to test for life on Titan: if methanogenic life is consuming atmospheric hydrogen in sufficient volume, it will have a measurable effect on the mixing ratio in the troposphere.
Despite these biological possibilities, there are formidable obstacles to life on Titan, and any analogy to Earth is inexact. At a vast distance from the Sun, Titan is frigid (a fact exacerbated by the anti-greenhouse effect of its cloud cover), and its atmosphere lacks CO2. Given these difficulties, the topic of life on Titan may be best described as an experiment for examining theories on conditions necessary prior to flourishing life on Earth. While life itself may not exist, the prebiotic conditions of the Titanian environment, and the possible presence of organic chemistry, remain of great interest in understanding the early history of the terrestrial biosphere. Using Titan as a prebiotic experiment involves not only observation through spacecraft, but laboratory experiment, and chemical and photochemical modelling on Earth.
An alternate explanation for life's hypothetical existence on Titan has been proposed: if life were to be found on Titan, it would be statistically more likely to have originated from Earth than to have appeared independently, a process known as panspermia. It is theorized that large asteroid and cometary impacts on Earth's surface have caused hundreds of millions of fragments of microbe-laden rock to escape Earth's gravity. Calculations indicate that a number of these would encounter many of the bodies in the solar system, including Titan.
Conditions on Titan could become far more habitable in future. Six billion years from now, as the Sun becomes a red giant, surface temperatures could rise to ~200K, high enough for stable oceans of water/ammonia mixture to exist on the surface. As the Sun's ultraviolet output decreases, the haze in Titan's upper atmosphere will deplete, lessening the anti-greenhouse effect on the surface and enabling the greenhouse created by atmospheric methane to play a far greater role. These conditions together could create an environment agreeable to exotic forms of life, and will subsist for several hundred million years, long enough for at least primitive life to form.
While the Cassini–Huygens mission was not equipped to provide evidence for biology or complex organics, it did support the theory of an environment on Titan that is similar, in some ways, to that of the primordial Earth.
There are a wide range of options for future missions to Titan that might address these and other questions, including orbiters, landers, balloons etc
The Innermost moons of Neptune
In 1989, Voyager 2 found some small tiny bodies revolving around Neptune closely..They were the 4 innermost moons of Neptunes and Very small in size....
1. Naiad ( "NAY ed" ) is the innermost of Neptune's known satellites:
orbit: 48,200 km from Neptune
diameter: 58 km
mass: ?
The Naiads were the nymphs who lived in and presided over brooks, springs, and fountains.
The last of the satellites discovered in 1989 by Voyager 2.
2. Thalassa ("tuh LASS eh") is the second of Neptune's known satellites:
orbit: 50,000 km from Neptune
diameter: 80 km
mass: ?
Thalassa was a daughter of Aether and Hemera. "Thalassa" is also the Greek word for "sea".
Discovered in 1989 by Voyager 2.
3. Despina is the third of Neptune's known satellites:
orbit: 52,600 km from Neptune
diameter: 148 km
mass: ?
Despina was a nymph, the daughter of Poseidon (Neptune) and Demeter.
Discovered in 1989 by Voyager 2
4. Galatea ("gal eh TEE eh") is the fourth of Neptune's known satellites:
orbit: 62,000 km from Neptune
diameter: 158 km
mass: ?
Galatea was a Sicilian Nereid loved by the Cyclops Polyphemus. (Not related to the maiden who was originally a statue carved by Pygmalion and who was brought to life by Aphrodite.)
Other moons of Neptune Apart from the above quoted moons of Neptune, the next one out, Larissa, was actually discovered in 1981, when it blocked a star. This was attributed to the ring arcs, but later was found to be the moon, being re-discovered by Voyager 2 in 1989.
Proteus is the second-largest moon in orbit around Neptune. It is so close to the planet that Earth-bound telescopes cannot see it.
Triton is next (right), and is one of the strangest moons in the solar system. First, it is one of only three moons in the solar system that has an atmosphere (Jupiter's Io and Saturn's Titan are the other two). It is thicker than Io's, yet much thinner than Titan's. Its pressure is 1/100,000 of Earth's. Triton
Second, Triton has a retrograde orbit, which means that it orbits the opposite way the planet spins. This is a very strong indication that Triton was captured. This in itself is not strange; both of Mars' moons were captured. What is strange is that Triton is two-thirds the size of our moon. When two bodies have a close encounter, one does not automatically capture the other, especially if it is so big. One theory is that Triton must have actually hit Neptune, bounced off the atmosphere, and gone into orbit because it lost all of its momentum. Another way this could have happened is that Triton collided with one of Neptune's moons, smashed it to bits (possibly creating the rings), and lost so much momentum that it couldn't escape Neptune's gravity.
Third, it is only 38 °C (100 °F) above absolute zero (the temperature at which all matter comes to rest). In such frigid a climate scientists did not expect to find active geysers. But, they did. They spew out a gaseous form of nitrogen, which is what creates its atmosphere.
The eighth moon, Nereid, has a highly elliptical orbit that causes it to swing around Neptune at various distances. When closest, it is 1,342,530 km (834,210 miles) from the planet. At the farthest distance, it is 9,667,120 km (6,006,870 miles) from Neptune.
The last five moons were discovered in the first few weeks of and throughout 2003. They have not yet been given official names by the International Astronomical Union. Very little is yet known about them. Data for Neptune's Moons Name Discovery Date Discoverer Distance from Neptune(10^3 km) Mass(10^20 kg) Radius (km) Orbital Period (days)
Naiad (NIII) 1989 Voyager 2 48.227 0.002 29 0.294
Thalassa (NIV) 1989 Voyager 2 50.075 0.0004 40 0.311
Despina (NV) 1989 Voyager 2 52.526 0.02 74 0.335
Galatea (NVI) 1989 Voyager 2 61.953 0.04 79 0.429
Larissa (NVII) 1989 Voyager 2 73.548 0.05 104x89 0.555
Proteus (NVIII) 1989 Voyager 2 117.647 0.5 218x208x201 1.122
Triton (NI) 1846 W. Lassel 354.76 214 1353.4 5.877*
Nereid (NII) 1949 G. Kuiper 5513.4 0.3 170 360.136
S/2002 N1 2002 15,686 0.001 24 1874.8
S/2002 N2 2002 22,452 0.001 24 2918.9
S/2002 N3 2002 22,580 0.001 24 29.82
S/2002 N4 2002 46,570 30 8863.1*
S/2003 N1 2003 46,738 0.0002 14 9136.1*
TITAN, MOON OF SATURN
Titan or Saturn VI is the largest moon of Saturn, the only moon known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found.
Titan is the twentieth most distant moon of Saturn and sixth farthest among those large enough to assume a spheroid shape. Frequently described as a satellite with planet-like characteristics, Titan has a diameter roughly 50% larger than Earth's moon and is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and it is larger by volume than the smallest planet, Mercury, although only half as massive. Titan was the first known moon of Saturn, discovered in 1655 by the Dutch astronomer Christiaan Huygens.
Titan is primarily composed of water ice and rocky material. The dense atmosphere prevented understanding of Titan's surface until new information accumulated with the arrival of the Cassini–Huygens mission in 2004, including the discovery of liquid hydrocarbon lakes in the satellite's polar regions. These are the only large, stable bodies of surface liquid known to exist anywhere other than Earth. The surface is geologically young; although mountains and several possible cryovolcanoes have been discovered, it is relatively smooth and few impact craters have been discovered.
The atmosphere of Titan is largely composed of nitrogen and its climate includes methane and ethane clouds. The climate—including wind and rain—creates surface features that are similar to those on Earth, such as sand dunes and shorelines, and, like Earth, is dominated by seasonal weather patterns. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan is viewed as analogous to the early Earth, although at a much lower temperature. The satellite has thus been cited as a possible host for microbial extraterrestrial life or, at least, as a prebiotic environment rich in complex organic chemistry. Researchers have suggested a possible underground liquid ocean might serve as a biotic environment.
951 Gaspra
951 Gaspra orbits the Sun near the inner edge of the main asteroid belt between Mars and Jupiter.
orbit: 330,000,000 km from the Sun (average)
diameter: 18x11x9 km
Gaspra was named by its discoverer Neujmin for a resort on the Crimean peninsula. Consequently, many of the asteroid's craters have been named for resorts and spas worldwide.
Like 243 Ida, Gaspra is an S-type asteroid, believed to be composed of a mixture of rocky and metallic minerals.
The first of the handfull of asteroids that have so far been observed close-up, Gaspra was encountered Oct 29, 1991 by the Galileo spacecraft on its way to Jupiter (Galileo later visited 243 Ida and NEAR visited 253 Mathilda and 433 Eros).
Gaspra is a member of the Flora family of asteroids.
Gaspra's surface is covered with impact craters. From the number of small craters on its surface, we can estimate that Gaspra is about 200 million years old
243 Ida and Dactyl
243 Ida is a Koronis asteroid orbiting the Sun between Mars and Jupiter:
orbit: 428,000,000 km from the Sun (average)
size: 58x23 km
Ida was a nymph who raised the infant Zeus (Jupiter). Ida is also the name of a mountain on the island of Crete, the site of a classic shrine and the cave where Zeus was said to have been reared.
The second of the small number asteroids that have so far been observed close-up, Ida was encountered Aug. 28, 1993, by the Galileo spacecraft on its way to Jupiter.
Ida has a satellite! (It's the small spot to the right in the picture above.) It is the first natural satellite of an asteroid ever discovered. Provisionally designated "1993 (243) 1", it received the name Dactyl (and the permanent designation "(243) Ida I") in September 1994. The name is derived from the Dactyli, a group of mythological beings who lived on Mt. Ida and protected the infant Zeus. Other accounts are that the Dactyli are the children of the nymph Ida and Zeus.
Dactyl is about 1.6 x 1.2 km, surprisingly round for such a small body. It orbits Ida at approximately 90 km.
The discovery that one out of two asteroids observed up close is in fact a binary system has reinvigorated an old debate about the frequency of binary asteroids. But more data is needed before the controversy can really be resolved.
The application of Kepler's third law to Dactyl's orbit gives a rough estimate of Ida's mass and therefore its density. That value is somewhere between 2.2 and 2.9 grams/cm3 (or perhaps a bit higher), a loose range because Dactyl's orbit is only crudely known.
Ida was originally thought to be an S-type asteroid, like Gaspra, composed of nickel-iron and some silicates. But a density of 2.9 is too low for that. Instead, Ida could well have a composition like that of ordinary chondrite meteorites, which are primitive and largely unaltered.
Interestingly, while the spectra of Ida and Dactyl are very similar they are nevertheless distinctly different; Dactyl is not simply a chunk of Ida. It is thought that the binary system may have formed during the collision and breakup that created the Koronis family.
The surfaces of Ida and Dactyl are heavily cratered and therefore apparently quite old. But dynamical calculations indicate that the whole Koronis family is relatively young. Such calculations also indicate that objects the size of Dactyl may not be to survive for more than 100 million years or so. Perhaps the heavy cratering took place at the time of the breakup that created the Koronis family rather than the 4 billion years ago as is usually the case for such surfaces.
Galileo measured variations in the solar magnetic field as it passed by Ida (a similar effect was found at Gaspra). This indicates the Ida must contain some magnetic material, though its density is far too low for it to be similar in composition to an iron or stony-iron meteorite.
It seems that many other asteroids are also accompanied by tiny moons. 3671 Dionysus also apparently has a moon as does 45 Eugenia and 762 Pulcova as well as many smaller near-Earth asteroids.
253 Mathilde
253 Mathilde is a main belt asteroid with a relatively small perihelion (1.94 AU)
orbit: 394,000,000 km from the Sun (average)
size: 59 x 47 km
Mathilde was discovered in 1885 by Johann Palisa. The name is thought to honor the wife of astronomer Moritz Loewy, then the vice director of the Paris Observatory.
The spacecraft NEAR made a flyby of Mathilde on 27 June 1997; NEAR's main mission to orbit the asteroid 433 Eros.
The most of the asteroids that have so far been encountered by spacecraft such as 433 Eros, 243 Ida and Gaspra are S-type asteroids; Mathilde is our first look at a C-type. C-type asteroids are believed to be the source of carbonaceous chondrite meteorites.
Mathilde has at least 5 craters larger than 20 kilometers in diameter (and we only got to see a little more than half its surface). Ida and Gaspra do not have such large craters. It is not clear how such large craters can be produced on such a small body.
Mathilde's density is only 1.4 gm/cm^3. It is probably very porous, somewhat like styrofoam. This may help account for the large craters.
It's albedo is only 4%. Furthermore, its surface color is very uniform despite the deep craters. This indicates that its interior is homogeneous, perhaps a pristine sample of the early solar system.
Another oddity is that Mathilde's rotation rate is very slow, 17.4 days. Perhaps this is somehow due to the many large impacts it obviously suffered
433 Eros
433 Eros is an S-type asteroid orbiting the Sun mostly between the orbits of Earth and Mars.
orbit: 172,800,000 km from the Sun (average)
size: 33x13x13 km
Eros was the Greek god of love and desire.
At a press conference on February 17, 2000, mission scientists for the Near Earth Asteroid Rendezvous mission exuded the air of kids in a candy shop as they discussed the latest results from asteroid Eros. After less than a week in orbit, NEAR has already returned dazzling pictures that have surprised and delighted researchers.
"At first I was stunned speechless by the beauty of this asteroidal landscape," said Mark Robinson, a member of the NEAR imaging team from Northwestern University. "Once I got over that, the geology took over." The first images from NEAR showed that Eros has an ancient surface covered with craters, grooves, layers, house-sized boulders and other complex features. "This is not just another rock floating out in space," continued Robinson. "There's a lot of neat geology going on." "There are tantalizing hints that the asteroid has a layered structure, like a sheet of plywood." said Andrew Cheng, of the Applied Physics Laboratory at Johns Hopkins University, who serves as the NEAR mission's lead scientist. "These layers appear to be very flat and appear to run end-to-end. This could come about if Eros was once part of a larger body, perhaps a fragment of a planet."
This idea fits the general picture that scientists have of asteroids. Most are concentrated in a belt between the orbits of Mars and Jupiter. Asteroids are likely to be leftover pieces of a planet that tried to form 4.6 billion years ago when the solar system was young, but couldn't because of nearby Jupiter's disruptive gravitational field. Eros might be a fragment from a planetoid that coalesced long ago and later broke apart as a result of collisions with other asteroids. With NEAR in orbit, scientists now know that Eros's density is 2.4 grams per cubic centimeter -- about the same as the density of Earth's crust.
"With this new data, it now looks like we have a fairly solid object," says radio science team leader Dr. Donald Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, CA. "There is no strong evidence that it's a rubble pile like Mathilde," the large asteroid NEAR passed and photographed in 1997, and which we just talked about.
Eros has a giant gouge which was of interest. Here's a close-up image. 
Here is one of the final images:
The landing was a gentle one, cruising to the asteroid's surface at less than 4 mph. Afterwards the NEAR Shoemaker spacecraft was still communicating with the NEAR team at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.
And here is the final image:
Meteor showers can be very impressive. Samuel Taylor Coleridge's famous lines from The Rime of the Ancient Mariner:
The upper air burst into life!
And a hundred fire-flags sheen,
To and fro they were hurried about!
And to and fro, and in and out,
The wan stars danced between
And the coming wind did roar more loud,
And the sails did sigh like sedge;
And the rain poured down from one black cloud;
The Moon was at its edge
may have been inspired by the Leonid meteor shower that he witnessed in 1797.
Meteorites are bits of the solar system that have fallen to the Earth. Most come from asteroids, including few are believed to have come specifically from 4 Vesta; a few probably come from comets. A small number of meteorites have been shown to be of Lunar (23 finds) or Martian (22) origin.
One of the Martian meteorites, known as ALH84001 (left), is believed to show evidence of early life on Mars.
Though meteorites may appear to be just boring rocks, they are extremely important in that we can analyze them carefully in our labs. Aside from the few kilos of moon rocks brought back by the Apollo and Luna missions, meteorites are our only material evidence of the universe beyond the Earth.
A very large number of meteoroids enter the Earth's atmosphere each day amounting to more than a hundred tons of material. But they are almost all very small, just a few milligrams each. Only the largest ones ever reach the surface to become meteorites. The largest found meteorite (Hoba, in Namibia) weighs 60 tons.
The average meteoroid enters the atmosphere at between 10 and 70 km/sec. But all but the very largest are quickly decelerated to a few hundred km/hour by atmospheric friction and hit the Earth's surface with very little fanfare. However meteoroids larger than a few hundred tons are slowed very little; only these large (and fortunately rare) ones make craters.
A good example of what happens when a small asteroid hits the Earth is Barringer Crater (a.k.a. Meteor Crater) near Winslow, Arizona. It was formed about 50,000 years ago by an iron meteor about 30-50 meters in diameter. The crater is 1200 meters in diameter and 200 meters deep. About 120 impact craters have been identified on the Earth, so far (see below).
A more recent impact occurred in 1908 in a remote uninhabited region of western Siberia known as Tunguska. The impactor was about 60 meters in diameter and probably consisting of many loosely bound pieces. In contrast to the Barringer Crater event, the Tunguska object completely disintegrated before hitting the ground and so no crater was formed. Nevertheless, all the trees were flattened in an area 50 kilometers across. The sound of the explosion was heard half-way around the world in London.
There are probably at least 1000 asteroids larger than 1 km in diameter that cross the orbit of Earth. One of these hits the Earth about once in a million years or so on the average. Larger ones are less numerous and impacts are less frequent, but they do sometimes happen and with disastrous consequences.
The impact of a comet or asteroid about the size of Hephaistos or SL9 hitting the Earth was probably responsible for the extinction of the dinosaurs 65 million years ago. It left a 180 km crater now buried below the jungle near Chicxulub in the Yucatan Peninsula (right).
Calculations based on the observed number of asteroids suggest that we should expect about 3 craters 10 km or more across to be formed on the Earth every million years. This is in good agreement with the geologic record. It is more difficult to compute the frequency of larger impacts like Chicxulub but once per 100 million years seems like a reasonable guess
