The Apollo missions of the 1970’s can be credited with many great discoveries–the most notable of which, were the six missions that sent twelve astronauts to the moon.  During these manned missions to the Moon, rock samples were collected and returned to the Earth.  The analysis of these samples led to the current hypothesis of lunar formation.  This hypothesis suggests that the Moon was formed by a catastrophic collision between Earth and Mars-sized planetesimal.  After this collision, the Moon would have been covered by a thick blanket of magma, which cooled to form a crust much different from the Earth’s crust.   Then 3.8 billion years ago, during the late heavy bombardment, the Moon’s surface was pounded by meteor impacts, leaving the surface deformed and heavily cratered.  New data gathered by the Japanese mission, SELENA, may offer new insights into the formation of the moon.

SELENA focused on the differences between the near and far side of the moon, such as: compositional, gravitational, topographical, and tectonic differences.   However, it is difficult for spacecrafts to relay information from the far side of the Moon, due to the fact that the Moon is tidally locked to the Earth.  SELENA was able to surmount this obstacle by using a companion satellite positioned in an elliptical orbit at a higher altitude.  This companion satellite was then able to relay information between Earth and SELENA. 

Because the Moon is a homogeneous body, there are several differences between the near (Earth facing) and far-side of the Moon.  The nearside of the Moon is covered by dark basaltic plains, (the very features that Galileo once mistook for seas).  The far side of the Moon is much more heavily cratered, and the higher elevations are composed of a bright material. These compositional differences are accompanied by differences which are intrinsic properties of the materials that make up each side of the Moon, such as crustal thickness and density.  Other differences between lunar faces include volcanic activity and surface age.

Another key difference between the lunar faces is the gravitational anomalies found on either side of the Moon.   These differences in gravitational anomalies can be used to deduce possible density differences of the interior.  Positive gravitational anomalies on the nearside of the Moon have been known about for several years and are associated with the large areas of basaltic planes.  These planes are referred to as mascons (mass concentrations).    These mascons could be the result of basaltic magma filling basins after basin formation, or they could be the result of mantle uplift that could have occurred during a large impact event.  SELENA was able to map the gravitational anomalies of the lunar far-side for the first time.  What SELENA discovered was that the far-side mascons have small central positive gravitational anomalies that are surrounded by a wide ring of negative anomalies.  These differences in gravitational anomalies observed on either side of the Moon could suggest that the far-side of the Moon may have had much cooler and rigid conditions in its early history.  

SELENA also used a Lunar Radar Sounder to map subsurface stratigraphy beneath the nearside basaltic basins.  The results of this experiment show that the thickness of the most recent volcanic flows may have been deformed compressive stresses that occurred during a period of global cooling, and not entirely because of the stresses which occurred during mascon formation.

The terrain camera onboard SELENA was able to photograph volcanic flows on the lunar far-side.  These photos were then used to estimate the age of the far-side basalts using cratering statistics. Based on the cratering statistics, the age of the lunar far side was found to be much younger than the lunar nearside, with volcanic activity continuing to make fresh surface until approximately 2.5 billion years ago.

Although the data gathered so far is not enough to paint a clear picture of lunar evolution, it has become clear that the mascons formed much differently on either side of the Moon during late heavy bombardment.  To help interpret these discoveries, new data will be on its way as China, India, and the United States all have orbiters slated for lunar observation in the next couple of years.  In the meantime we are left to wonder, are these differences due to external processes such as a giant impact, or are they due to internal processes such as core formation, and crustal differentiation?  One thing seems clear, the difference in surface age on either side of the Moon will be an important variable when devising a model for lunar evolution.

Could the detection of methane on Mars be an indication of microbial life, or is a geologic process causing this chemical anomaly?    Prior to 2003, no methane was observed in the Martian atmosphere, beginning on 2003 methane was detected using three ground-based infrared spectrometers.  This Methane was then observed over a three year period (seven Earth years).  The largest plumes were observed during the summer months, the largest contained approximately 19000 metric tons of methane.

The Martian atmosphere is composed of 95% carbon dioxide, 2.7% nitrogen, .07% carbon monoxide, .13% oxygen, 1.6% argon, and trace amounts of water vapor.   Small amounts of methane may be produced due to atmospheric processes but would be relatively short lived due to the ionization of the compound, caused by UV radiation.  Therefore any large amounts of methane present in the atmosphere would have to be the result of the release of a subsurface reservoir.  The origin of such methane reservoirs is unknown, but could be due to biologic or natural processes. 

If 90% of Earth’s methane is produced by life forms, could the methane on Mars also be produced biologically?  Extremophiles could live deep below the surface of Mars where they could use hydrogen as an energy source; this energy could be produced when water exposed to radiation is dissociated into H₂ and oxygen.  This reaction also reduces carbon dioxide to methane, which could accumulate in subsurface reservoir s.  If these reservoirs are connected to the surface along faults or fractures, seasonal variations could result in the opening of such cracks which could lead to the release of any methane accumulations.  Extremophiles of this type can be found 3 km below the Witwatersrand Basin of South Africa. 

Another possible source of the methane deposits could be of geologic origin.  Such processes could include the production of magma, or the serpentinization of basalt.  Either of these possibilities could also result in the buildup of subsurface methane deposits.  Much like the extremophile scenario, these deposits could also be released due to the temperature variations that occur with seasonal changes.

The methane appears in highest concentrations at three regions:  Arabia Terra, Nili Fossae, and the South-East corner of Syrtis Major.  The Mars Reconnaissance Orbiter and Mars Express observed that the outcrops in the Nili Fossae region are rich in hydrated minerals.  This suggests that this area resides above a magma chamber.  The largest plume was observed over shield volcano located between Sytris Major and Nili Fossae.  This further suggests that the area is above a magma chamber, and that the production of magma, or the serpentinization of basalt is responsible for the release of the methane plumes, and are probably not the result of the presents of Martian extremophiles.        

On Friday the 13th, of April 2029 an asteroid approximately 330 meters in diameter will transverse the Earth’s orbit, coming nearer to the Earth than any other known asteroid in recorded history. Apophis was discovered in 2004 and after six months of optical and radar observations it was concluded that this asteroid will pass within 35700 km of the Earth, which is an altitude less than that of our satellites in geocentric orbit. Apophis will once again return on 2036, and astronomers say that if the asteroid’s center of mass passes through a small gravitational keyhole in the Earth’s atmosphere in 2029, Apophis’2 2036 orbit could be redirected into the Earth. Astronomers currently rank this asteroid has having little chance of impact, and is 0 on the Torino Scale.

The Torino scale is a scale from 0 to 10 that indicates the threat level of Near Earth Objects (NEO). A zero indicates that there is either no threat of impact, or that the object is too small to penetrate the atmosphere. A ten indicates that the object is likely to impact catastrophically. A NEO is assigned an integer value on the 0 to 10 scale based on impact probability and its kinetic energy. On December 23, 2004, Apophis had been given 1 in 233 chance of impact and a 2 on the Torino scale (Apophis is the first asteroid to have a value larger than 1 on the Torino scale). Later that day the odds of impact were increased to 1 in 64 with a 4 on the Torino scale. By 2006 the chance of impact has been reduced to 1 in 45,000 with a zero on the Torino scale.

In April 2008, a thirteen year old from Germany calculated the chances of collision to be 1 in 450 by factoring changes in the Asteroid’s orbit due to collisions with one or more geosynchronous satellites. To eliminate rumors that NASA and the ESA confirmed these calculations, NASA released a statement saying that the angle of approach relative to Earths equator, and the relatively small size of the satellites leave little or no chance of a satellite-asteroid collision.

Even though NASA has placed a low probability of impact, the threat is real enough that NASA plans on somehow deflecting the asteroid away from the tiny keyhole to prevent a future impact scenario. Some of these plans include nuking the asteroid, painting one half of it white, or by tugging it away using the gravitational pull of a probe. Nuking the asteroid has basically been ruled out because that may just result in showering us with several asteroid segments instead of one large one. Painting half of the asteroid white would result in the painted half of the asteroid reflecting more photons and thus pushing the asteroid in the desired direction, but this solution is impractical. Even if a good plan is developed it will do little good without precise and accurate details and calculations of the asteroid.

In 2008 the Planetary Society developed a $50,000 competition for the best mission designed to track the asteroid, and perform trajectory calculations for a year with an unmanned probe. The goal of the competition is to help Earth’s governments decide whether or not the probe should be deflected. The Planetary Society received 37 entries from 20 countries. The winning entry was designed by an Atlanta based company called Spaceworks Engineering. This plan called ‘foresight’ is planned to launch in 2012, after 5 months of travel it will rendezvous with Apophis, orbit it for one month while taking measurements with a multi-spectral imager. Once the orbiting phase is complete, the probe will follow Apophis around the sun for 10 months while it takes careful measurements of the asteroids orbit.

On Friday the 13th, in April of 2029, Apophis will be observable with the naked eye as it passes over the Earth at a distance of approximately 1/10 that of the moon. If you happen to be watching as the large asteroid come closer to the Earth than any other large asteroid in human history, remember one thing: even though calculus is perfect, the people who use it are not.

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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