Friday, March 20, 2015

Water water, everywhere, on earth and in space

The Taklamakan Desert, located in northwest China is the world's second largest shifting sand desert with about 85% made up of shifting sand dunes. It is spread over an area of 337,000 km2 (130,116 sq. mi.). Because it lies in the rain shadow of the Himalayas,Taklamakan is a paradigmatic cold desert climate with almost no rain fall. There is very little underground water in the Taklamakan Desert and it is hazardous to cross even though in recent years, China has constructed a cross-desert highway.

Sven Anders Hedin, (1865 – 1952) was a Swedish geographer and explorer who made an attempt to cross the Taklamakan in spring of 1895 from north to south. On 10th April he left on his expedition with seven camels and three local escorts. He had hoped to find underground water on his way and carried only half as much water as could actually be carried. When he noticed the mistake, it was too late to return. One of his escorts died on way along with seven camels because of thirst. Hedin deserted the caravan and proceeded alone on horseback with his servant. When that escort also collapsed from thirst, Hedin left him behind as well, but at the last desperate moment managed to reach a water source right in the middle of the desert and survived.

The point I am trying to make is that there is water everywhere on earth, even in places, where probability should have been nil. I narrated Sven Hedin experience just to highlight this fact. Earth is a watery place. About 71 percent of the Earth's surface is water-covered, and the oceans hold about 96.5 percent of all Earth's water. Water also exists in the air as water vapor. At any given time, about 12,900 cubic km of water exists in the form of water vapour. Water on surface is in rivers and lakes, in icecaps and glaciers, in the ground as soil moisture and in aquifers, and even in our bodies. About 23,400,000 cubic Km water is underground.

In the recent Hollywood blockbuster “Intersteller,” an imaginary planet from another solar system called “Miller's Planet” is shown to have no land surfaces at all, with water covering its entire surface. Is it only a fragment of imagination? Or there are real planets that are totally water covered? This film depicted planets from other solar systems, but what about our own solar system? Does any other planet other than moon has presence of water on its surface?

Mars with its polar ice caps is perhaps easiest to understand. Both, northern and southern polar caps on Mars primarily contain water ice. Every winter, a surface veneer of frozen carbon-DI-oxide gas or dry ice is formed on its top. Every summer this layer vapourises, exposing the water ice in place.

Let's now come to Earth's moon. India's spacecraft Chandrayaan-1, which was launched by the ISRO in October 2008, did manage to discover water ice on surface of moon when on board impact probe was made to crash land on moon's surface. The scientists now feel that the Moon contains water in various forms. There is water that is locked up in minerals. Water is also scattered throughout the broken-up surface, and, potentially, in blocks or sheets of ice at depth.

The largest planet of our solar system is the gaseous giant Jupiter. It has as many as 67 moons, though the 4 moons discovered in 1610 by Galileo, are the most massive. Largest of these is known as Ganymede. It is the ninth largest object in the Solar System and is actually larger than Mercury. It is the largest moon in our solar system and the only moon with its own magnetic field.

NASA’s Hubble Space Telescope has found strong evidence of a massive saltwater ocean under the icy crust of Ganymede that could potentially support life. This was done by observing a natural phenomenon called aurorae, which is visible even on earth. These are natural light displays seen in polar region, most clearly seen at night against a dark sky. The magnetic field of a planet causes aurorae, which are ribbons of glowing, hot electrified gas, in regions circling the north and south poles.

Since Ganymede has its own magnetic field, observing aurorae caused by this field is not surprising. However what scientists have been able to observe is that the aurorae on Ganymede change, “rocking” back and forth. This phenomenon can be attributed to Ganymede's closeness to Jupiter, because of which, it has got embedded in Jupiter’s magnetic field. When Jupiter’s magnetic field fluctuates or changes, the aurorae on Ganymede also change, “rocking” back and forth.

Scientists say that because of the presence of s saltwater ocean on Ganymede, Jupiter’s magnetic field creates a secondary magnetic field in the ocean that counters Jupiter’s field. This “magnetic friction” suppresses the rocking of the aurorae by a large extent. It is estimated that this ocean is 100 kilometres thick — 10 times deeper than Earth’s oceans — and is buried under a 150-kilometre crust of mostly ice.

With this confirmation, Ganymede joins the ranks of two other moons that are believed to host underground reservoirs of liquid water. Evidence of similar oceans has been detected on Europa, another of Jupiter’s moons, and Enceledus, that orbits Saturn.

The biggest surprise of all is perhaps the discovery made by Nasa's Mercury Messenger spacecraft, which has been orbiting just tens of kilometres from the planet's surface. It is impossible but true that a planet where temperatures soar above 400 C could host water-ice. There are some impact craters at the north pole of Mercury that are always shadowed from the Sun, in this scorching world which turn into cold traps. Scientists feel that Comets smashing into Mercury's surface probably brought both the ice and the dark, carbon-rich (organic) material that is present in these polar cold traps.

Suddenly it seems that there is water everywhere; even on other planets and  on our solar system's moons.

18th March 2015

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