{tab=Rocks from Mercury}

Rocks from Mercury...

     If you are meteorite hunter, you will be surely aware of meteorites originating from Moon and Mars. Henceforth, do not be surprised even if you find a meteorite originating from Mercury! So far, meteorites from Mercury were not at all expected to be found on Earth. But computer studies recently carried out by Brett Gladman and Jaime Coffey (University of British Columbia, Vancouver) show that rocks from Mercury may find their way to Earth. In fact, some geologists believe that ‘angrites’ (a rare group of meteorites) may have originally belonged to planet Mercury.

Angrite meteorite
(Credit: North Arizona University)

     Meteorites coming from Moon and Mars are actualy ejecta produced after the surface of Moon or Mars is hit by a body like asteroid or comet. Although such ejecta from Moon and Mars reach Earth, scientists were skeptical about such a possibility in the case of ejecta from Mercury due to its insufficient velocity. But according to Gladman, earlier calculations were based on wrong assumptions. Mercury, being closest to Sun, moves at a high speed of 48 km/sec in its orbit. Moreover, asteroids or comets crossing the Mercury’s orbit also move with very high speed. This results in an asteroid or comet hitting the Mercurial surface with very high energy. Consequently the velocity acquired by the ejecta is 5 to 15 times that required to overcome Mercury’s gravitation. This makes some of the ejecta from Mercury to land on Earth as meteorites. Gladman and Coffey’s studies show that actual number of Mercurial meteorites reaching Earth is more than one-third of those coming from Mars.

{tab=Martian Amazon}

Martian Amazon...

     Amazon is the largest river on our Earth. It carries about 200,000 cubic meters of water per second. Can you imagine a river four times as big as this? Such a giant river did exist in past on planet Mars! This river had suddenly erupted on Martian surface, flowed for about 20 km and drained into 128 km wide crater. This crater is located in the southern hemisphere of Mars, close to its equator. The draining of water occurred at very high flow rate of 800,000 cubic meters per second. Sand deposits seen on the floor of this crater are formed from the sand carried by the water that had gushed through the adjacent Martian channel. These inferences are based on the similar delta formations seen in the simulation studies carried out by Erin Kraal of Virginia Polytechnic Institute (USA) and her colleagues.

River channel on Mars
(Credit: NASA/JPL/ASU)

     According to Kraal, this river might have existed only for a short period of few decades; but the underground source of its water existed for a long. Most of this underground water was in frozen state. After receiving enough heat from hot magma, the water found its way out to the surface. There may be few more such channels on Mars created by the then flowing rivers. Some of these rivers might have existed for hundreds or even thousands of years.

{tab=Three-in-one asteroid}

Three-in-one asteroid...

     '2001 SN263' is a Near-Earth-Asteroid (NEA). It has proved to be exceptional NEA. Non-NEA triple asteroids are known. Likewise, binary NEAs are fairly common. In fact, one in six NEAs is binary. However, triple NEAs were so far not known to exist. '2001 SN263'  is the first NEA to be established as a triple asteroid. As the designation suggests, this asteroid was discovered in the year 2001. But its multiplicity was discovered only in the last week - on February 11, 2008. This discovery was made by Michael C. Nolan and his colleagues using radar telescope of Arecibo Observatory in Puerto Rico.

(Credit: Arecibo Observatory)

     This asteroid has an orbital period of 2.8 years. Its perihelion (point closest to Sun) and aphelion (point farthest from Sun) distances are 1.0 and  2.9 A.U., respectively.  At present, this asteroid is passing close to us. It is at a distance of about 11 million km. Radar studies revealed that main asteroid has a diameter of about 2 km. Its larger moon is about half of the main asteroid in size. The smaller moon has a diameter of about 400 meters. Shape, surface features and surface properties of this peculiar asteroid will be studied in coming days. Attention will also be paid to accurately determine the orbits of the moons. Accurate knowledge of the orbits will allow the estimation of density of the main asteroid and speculation about type of material of which it is made.

{tab=Food for E-ring}

Food for E-ring...

     Cassini scientists knew that Enceladus, the sixth largest moon of Saturn, is feeding material to Saturn's E-ring through the jets released from its surface. But they did not know the mechanism behind these giant jets. These giant geysers on Enceladus are spewing out mixture of water vapour and ice grains. Continuous ejection of ice grains through these geysers demands their continuous creation. And the continuous creation of the grained ice requires liquid water. The temperature of this water should be neither too hot for ice to melt, nor too low for grains to coalesce into bigger particles. Now the scientists know what is the source of these continually produced ice grains. Data collected from multiple instruments onboard Cassini spacecraft have shown presence of huge body of water below the frozen surface of Enceladus. This lake is similar to Lake Vostok of Antarctica, which has liquid water underneath its frozen surface.

Enceladus and Saturn's E-ring
(credit: ESA and NASA)

     Conditions over this 'underground' water reservoir are such that ice, liquid water and water vapour exist together. Juergen Schmidt and other members of the team working on Cassini's Dust Analyser have concluded that temperature of this reservoir is close to zero degree Celsius. Water vapour from this reservoir escapes to the exteriors through the cracks in the ice crust, along with ice grains at a speed of about 300 to 500 meters per second. Most of the ice grains fall back on surface as they lose their energy due to mutual collisions. However, 10% of the grains overcome Enceladean gravity and accumulate into the Saturn's outermost ring i.e. E-ring.

{tab=Passage to the Sun}

Passage to the Sun...

     ESA-NASA solar probe Ulysses is presently propelling over the Sun's North Pole. It is the very first spacecraft to explore polar regions of the solar sphere. Although launched in 1990, it is its only third passage over the poles. Ulysses is not traveling in an ordinary polar orbit as our terrestrial polar satellites do. It is following an highly elliptical path. When closest to Sun, it comes within 1.34 A.U. of Sun. At farthest point, it is at 5.4 A.U., i.e. a point close to Jupiter's orbit. It completes its orbit in 6.2 years. The orbit makes an angle of 80 degrees with the plane of ecliptic. It had its first passage over the poles in 1994-95 and second in 2000-01. In February, 2007, it had its third passage over South Pole of the Sun. On January 14, 2008, it flew over the North Pole. Ulysses Spacecraft had observed solar minimum of 1994-95 and solar maximum of 2000-01 closely. Now it is observing solar minimum of 2007-08.

Ulysses (artist's conception) and its Path
(Click the images to see enlarged path diagram)
(Credit: ESA)

     Polar regions of the Sun show a scenario different from that at solar equator. Ulysses is studying magnetic field as well as solar wind ion composition, solar X-rays, etc. in the polar regions of the Sun. One of the surprising results is the capability of Sun to have energetic outbursts from the polar region, even during the solar minimum. Other interesting fact is that north polar coronal hole showed 7% to 8%  lower temperature compared to that of south polar coronal hole. Preliminary Ulysses mission had actually ended in 1996, but was extended further as the studies are found to be very interesting. Ulysses Project Scientist Ed Smith says "Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be crucial to studies of the solar cycle".

{tab=Cometary Surprise}

Cometary Surprise..!

     NASA's Stardust spacecraft had collected samples of dust, chucked out from the coma of comet 81P/Wild 2 on January 2, 2004. The  samples were returned to Earth on January 15, 2006. These samples were expected to contain primordial dust particles. But to the surprise of our scientists, it is observed that these particles have inner solar system origin rather than being from outer solar system comet.

    
Comet Wild 2 and 'Stardust sample return capsule' landed in Utah (USA)
Credit: NASA

     Research carried out by team led by Hope Ishii from Lawrence Livermore National Laboratory (USA) shows that these particles come from main asteroid belt. Inferences drawn by this team have raised some questions - How could the dust from inner solar system be transported to comet Wild 2? Do all the comets resemble Wild 2 in composition? Or is it that Wild 2 was an asteroid that has run away from the main asteroid belt? We may have to wait to get the answers to these questions till year 2014, when European Space Agency's Rosetta will visit comet Churymov-Gerasimenko.