Posts Tagged ‘planets’

Could life exist on Super-Earths?

Wednesday, January 7th, 2009 by Evan Finnes

The search for extraterrestrial life within our solar system has mainly been focused on Mars, and there has been speculation that some the moons of the outer solar system may also be a good place to look for life. Outside of our solar system, planet hunters and astrobiologists have been searching for Earth-like planets to help answer one of mankind’s most profound questions, “are we alone?” To date, no such planets have been discovered, so a team of scientists have now set their sights on a relatively abundant group of extrasolar planets known as “super-Earths”.

The term “super-Earth” is slightly misleading because the only thing that these planets have in common with the Earth is the fact that they are terrestrial. A super-Earth is typically classified as a terrestrial planet with a mass of 5 to 10 Earth masses. Thus far, Super Earths have not been found within the habitable zone of their host star, with orbits much too far or much too close to sustain life as we know it. The super-Earths with orbits far from their host star are the places that astrobiologists now believe could harbor some form of life.

It is estimated that one-third of all solar systems contain super-Earths, and some scientists believe that it may be possible to find some that have liquid water either on the surface, or below a thick layer of ice. This water could theoretically exist on a super-Earth if one of three conditions were met. 1) If the planet had a thick enough atmosphere it may be possible that enough solar radiation could be by greenhouse gases to prevent water from completely freezing. 2) If the planet was massive enough or young enough, there may still be enough primordial heat available to sustain some amount of liquid water.

Currently, the best technique for discovering super-Earths is by using gravitational microlensing. This phenomena occurs when an object in the foreground has enough mass, its gravitational field will bend the incoming light of a much more distant object. This results in the magnification of the distant object, no matter how faint it may seem.

It is not unfathomable to predict that an extrasolar super-Earth outside of its host stars habitable zone could contain water, at least as ice. Much of the ice in our own solar system is located outside of the habitable zone. There is no super-Earth in our solar system, but there are icy bodies that could contain liquid oceans. It is hypothesized that Jupiter’s moon, Europa, may have enough heat due to tidal flexing to permit a liquid ocean.

Traveling amongst the stars and exploring extrasolar planets is unfortunately not in the near future, but we can test hypothesis such as this one by exploring the planets within our solar system, and isn’t it about time we send a probe to Europa?

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Plate Tectonics May Have Begun 4.4 Billion Years Ago.

Wednesday, December 3rd, 2008 by Evan Finnes

A new study suggests that the Earth’s tectonic activity may have begun as many as 4.4 billion years ago. The evidence stems from tiny minerals called zircons found in rocks of the Jack Hills region of Western Australia. Zircons, or zirconium silicate (ZrSiO4), are amazing minerals because of the fact that they are very widespread, and can exist in igneous, sedimentary, or metamorphic rocks.

By analyzing tiny mineral inclusions found inside seven of the zircon crystals found in Western Australia ( seven out of 400 found) scientists were able to determine that there was tectonic activity in the earliest eon of our planet, the Hadean. These inclusions allowed the scientist to determine the temperature and pressures at which the zircons formed. Six of the seven bits of zircon contained inclusions composed of the mineral muscovite (KAl2(AlSi3O10)(OH)2). The Silicon to Aluminum ratio in these muscovite inclusions suggest that the rocks formed at depths of about 25 km beneath the Earth’s surface. Because of the amount of Titanium atoms present in the zircons, the scientists were able to determine that temperature of crystallization was between 665 and 745 degrees Celsius. The seventh inclusion consisted of a mineral known as hornblende ( (Ca,Na)2-3(Mg,Fe,Al)3Si6(Si,Al)2O22(OH)2) ). After analyzing the hornblende inclusions, (using methods similar to the above methods), scientists were able to confirm the determined results of the muscovite. However, because this discovery is based only on seven samples, there is some healthy criticism.

These temperatures and pressures indicate that the temperature flux during the zircon crystallization was approximately 75 mW/m2. This flux is slightly higher than what is observed on Earth today. Because the Earth was so much hotter during its first six hundred million years, a higher paleo-flux is expected. However, the calculated flux was also determined to be about 1/5 lower than the expected flux of the hadean eon. It is because of this abnormally lower than average flux of the hadean eon zircons, that it was determined that the plate tectonics had to have begun so early in Earth’s history.

On Earth today, fluxes much lower than average occur above subduction zones, where one plate subducts beneath another. It is hypothesized that these zircons were formed as the descending plate subducted, bringing liquid water with it, where it cooled the surrounding mantle enough for the zircons, and the inclusion minerals, to crystallize out of solution. Zircon contains uranium isotopes, which allowed the year of this crystallization to be calculated using radiometric dating techniques.

This could be an important discovery because it will help us understand the evolution of terrestrial planets. Plate tectonics play a very important role in recycling the gasses which make up our atmosphere, and therefore directly affect the ability of a planet to sustain life. With the right atmospheres, Venus and Mars could have been within the habitable zone of our solar system, however neither planet is believed to have developed plate tectonics.

Besides providing clues to the development of plate tectonics, the zircons also contain oxygen isotopes that suggest that water was also present on the Earth some 4.4 billion years ago. These Western Australian zircons are the oldest minerals on Earth, and have provided us with great insight into the dawning hours of our planet.

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