Far-Side of The Moon

March 2nd, 2009 by Evan Finnes

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.

 

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Fast As A Speeding Star

March 2nd, 2009 by Bellatrix

Using the Hubble Space Telescope, NASA scientists have discovered stars doing something very interesting: speeding around through the interstellar medium.  This came as quite a surprise especially since they were not even looking for them. This is not usual behavior for stars and brings up many new questions about what these stars are doing and why.

The scientists discovered 14 of these crazy runaway stars.  Because of their movement it was harder to gather information about them but scientists were able to deduce some facts about the stars. The stars appear to be young, maybe only about a million years old.  This was deduced from looking a their strong stellar winds. Most stars only have such winds when they are quite young or very old. The nebulae around the stars do not math that of those typically seen around old dying stars. And only very massive stars have winds throughout their lifespan, but these stars could not be that massive because they do not have glowing clouds of ionized gas around them. They are estimated to be about 2 to 8 solar masses.

These stars plow through regions of dense interstellar gas creating brilliant arrowhead shaped glowing bow shocks and trailing tails of glowing gas. These bow shocks are created when the strong winds coming from the stars slam into the surrounding dense gas. It’s difficult to tell their exact distance from Earth but depending on the distance these bow shocks could be 100 billion to a trillion miles wide. By studying these bow shocks we can tell that the stars are moving very quickly, about 180,000 km/hr.  All stars are moving as they are orbiting around the galaxy but not nearly at these speeds, the sun for comparison moves through the galaxy at only about 13,000 km/hr.  Assuming this “young” phase lasts only a million years the stars would have traveled about 160 light years.

The scientists have hypothesized that these stars were likely kicked out or ejected from massive star clusters.  There’s two possible ways this expulsion could have happened.  One way is if a binary system, consisting of two stars orbiting each other, had one star go supernova the explosion would eject the companion star.  The other possibility would be if two binary systems or a binary and a third star collided one of the stars could have used he energy from the interaction to escape the system.

Runaway stars have been observed before, the first being found in the late 80s. However, those stars produced much larger bow shocks meaning they were probably more massive with larger stellar winds.  Scientists think these new objects, the medium size stars, are probably more common since medium sized stars are more common in general and because they would be more susceptible to being ejected.  These objects are difficult to find and observe because one doesn’t know where to find them or where to look for them. 

Follow up studies are planned to look for more of these objects, called interlopers, and to study these recently discovered ones. Further studies will tell us more about the effects these speed demons have on the environments they pass by or interact with. Theorists and modelers will have to set to work on looking at the origins of the objects and the causes of their ejections. Pretty interesting to think about these stars being expelled from their homes now doomed to zoom around the galaxy alone. 

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The Search For Earth-like Planets

February 27th, 2009 by William Reynolds

Looks like we’re in the market for a change in scenery.  Since it appears we might be moving in the not-so-distant future, can I break open those cases of Right Guard I hoarded just before the EPA cracked down on fluorocarbon emissions? What about the styrofoam drink cups I got stashed up in the rafters of my garage – are those back in play as well?  

http://www.nasa.gov/mission_pages/kepler/main/index.html

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Methane on Mars: Extremophiles or Geothermal ?

February 9th, 2009 by Evan Finnes

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.        

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