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Imagine That! - By- Vijainder K. Thakur and Divya Thakur Vijainder is a former fighter pilot of the Indian Air Force, currently works as a software system architect in Austin. He lives in perpetual bewilderment and bliss! Bewilderment because he cannot fathom why people pay him to do what he loves to do, and could well do it for free! Bliss because he basks in the bountiful love of his wife and two beautiful daughters.

Perhaps the strongest motivation for research in Astronomy and cosmology emnates from a question that stirs within all of us during childhood - when we first look up at the night sky aware of the fact that the stars we see are indeed distant suns like ours. It is then that we first wonder - Are we alone in this Universe?

Without scientific evidence to decisively answer the question, one way or the other, there exist a multiplicity of opinions on what is the probable answer to the question. However, there is an absolute unanimity on what we hope should be the answer - No, we are not alone. Were it to be otherwise it would make life rather meaningless! Admittedly, what we seek on other worlds is sentient life. However, its logical to begin the quest by first ferreting out primitive life.

A concerted, and rather successful, effort is currently underway to detect the existence of other planetary systems around nearby stars. The logic is that if planets abound, the chances of life existing on some of them would be good. Over 50 extrasolar planets have already been detected proving that planetary systems are commonplace...

Mars

Even while the search for extrasolar life is making a credible begining, tantalizing evidence pointing to the existence of primitive life elsewhere within our own solar system is continuously emerging. Photgraphic mapping of the Martian surface by NASA's Global Surveyor suggests that subsurface water may exist on Mars even today! Liquid water is considered a pre-requisite to the existence of life as we know it. If there is indeed subsurface water on Mars, and earlier evidence of primitive fossilized life on meteorites of Martian origin was correct, then it is possible that some form of life may still exist on Mars!

Mars is not the only place in our Solar System, besides Earth, where water may exist. NASA's Galileo spacecraft has found strong evidence of water on three of Jupiter's moons - Europa, Callisto and Ganymede.

Europa

Europa has a radius of 1565 Kms, a little smaller than our moon. It orbits Jupiter at a mean distance of 670,900 Kms. Nasa's Galileo probe established that magnetic north pole of Europa reverses every 5 1/2 hours! (You wouldn't go very far if you were using a magnetic compass on the surface of Europa!) The flip-flop is best explained by the interaction of Jupiters magnetic fields as it rotates around its axis every 10 hours with conductive liquid, like saltwater, beneath the icy crust of Europa. The presence of subsurface water on Europa is also suggested by other observations of

1. A smooth and active (lightly cratered) icy surface.

2. Cracks in the surface ice with telltale marks that could have been formed by the water beneath coming to the surface.

Nasa has planned to launch an unmanned spacecraft - Europa Orbiter in 2003. The spacecraft should enter into an orbit around Europa three years later and begin mapping the surface using photo and radar equipment. If the mapping establishs the presence of a subsurface ocean and a relatively thin crust of surface ice follow up missions may attempt to send hydrobots to explore the subsurface ocean!

Primitive life forms are known to exist in the pitch darkness and freezing cold found in the depths of Earth's oceans so there is good reason to assume that it could well exist under similar conditions on Europa.

Callisto

Callisto has a radius of 2403 Kms and orbits Jupiter at a mean distance of 1,883,000 Kms. The Galileo spacecraft revealed similar findings on Callisto which, much like Europa, bears a variable magnetic field. Callisto's attenuated atmosphere lacks charged particles sufficient enough to generate its magnetic field; nor could its icy crust serve as a good conductor. But a salty ocean of melted ice beneath the surface could be the likely agent. Lending further credence to the premise of a subsurface ocean, the data showed that electric currents were periodically fluctuating, flowing in opposite directions at different times. This shows that Callisto's response is synchronized with the effects of Jupiter's rotation.

Ganymede

Recently, Galileo has detected a magnetic field that varies in sync with Jupiter's rotation on Ganymede also. Ganymede, with a radius of 2630 Kms is the largest moon in our solar system and is indeed bigger than two planets - Mercury and Pluto. Unlike Europa and Callisto, the fluctuation in Ganymede's magnetic field was more difficult to detect because Ganymede has a magnetic field on its own; which tends to mask the fluctuation resulting from the interaction between Jupiter's magnetic field and its presumed subsurface ocean. Current modelling seems to suggest a ocean neary 100 miles beneath the surface! If this ocean actually exists, it probably holds more water than the oceans on Earth.

Energy Source

Though water is quintessential to the presence of life, energy also plays a key role to its development. Ganymede and Callisto's oceans, if they exist, are probably being heated by radioactive elements, whereas Europa has tidal energy as well, which comes from its greater proximity to Jupiter.

We hope to be back with more facts to stir your imagination next fortnight.

Ref.

Nasa's Europa Orbiter Mission Homepage
Astronomy Magazine May 2001
Galileo:Journey to Jupiter

Pictures courtesy NASA.

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