Drum roll and applause please! At 8:56 a.m. CDT this morning space station astronauts Don Pettit and André Kuipers successfully captured the SpaceX Dragon capsule with the robotic arm while flying 251 miles over northwestern Australia. Once berthed, the astronauts will unload about 1,200 lbs. of food and supplies and re-load Dragon with equipment. The cargo ship is designed to safely return to Earth. The mission is the first private, non-governmental venture to the space station.
Yesterday we met a star that puffs out clouds of carbon soot like a chain-smoker. All carbon ultimately originates from the interiors of stars, where it’s created through the fusion of simpler elements. Released into space, carbon combines with other elements like hydrogen and oxygen to form organic compounds.
One of the simplest organic compounds is methane, composed of one carbon atoms linked to four hydrogens. While cows are prolific methane producers, the gas can form without any assistance from life. All you have to do is wander over to Uranus and Neptune to get a whiff. Both planets owe their blue color to the presence of methane in their atmospheres. So far as we can tell, no cows were involved.
Organic compounds are found in some meteorites, especially in the carbonaceous chondrite group that includes the Sutter’s Mill meteorite fall in California. More than 14,000 different organics including 70 amino acids and sugar have been discovered in the Murchison meteorite that fell in Australia in 1969.
While life depends upon organic compounds for its existence, the carbon-based molecules form naturally in the raw vacuum in space when carbon (in the form of graphite), water ice and other materials stick together to form tiny interstellar dust particles. Gathered in large clouds and acted upon by their own self-gravity, these clouds collapse to form protoplanetary disks.
At their centers, where the density of material is highest, a star forms, while gas and dust in the outer part of the disk grow into individual planets. After a hundred million years of churning, bashing and kneading, a solar system is born.
During the process, ultraviolet sunlight, heat from radioactive element decay and liquid water provided the energy and materials to convert simple molecules into more complicated ones. 4.6 billion years later, occasional hunks of this original material land on Earth as carbonaceous meteorites containing a storehouse of organic compounds.
Meteorites and comets must have rained down constantly in the early days of our planet. The organic compounds they contained, not to mention what remained in the rocks of the early Earth, provided the vital materials needed for matter to make the leap from non-life to life. Exactly how that happened has yet to be answered.
All this serves as an introduction to a recent examination of 11 Martian meteorites by a NASA-funded study. The meteorites span 4.2 billion years of Martian history, and all but one were found to contain large, complex carbon compounds indigenous to Mars. The molecules were enclosed in crystalline grains that formed in cooling magma, indicating they were created by volcanic activity over the planet’s long history.
One might be tempted to feel disappointment at the news. Far more exciting would be organic compounds left behind by Martian life forms. Some day that may come, but in the meantime we can relish the fact that Mars, like the Earth, started with a storehouse of simpler carbon-containing compounds inherited from the knock-around days of the early solar system and hammered out more complex versions once incorporated into the planet. Versions potential life could use as building blocks.
With the Curiosity Rover set to land on Mars this August, the study will help scientists distinguish between carbon molecules formed by non-biological processes from those built by biology.
Matter can’t seem to help itself. Where energy is in abundance, as it is inside stars, collapsing dust clouds and geothermal sources like volcanoes to name a few, simple stuff invariably becomes more complex.
We’ve witnessed this by tracking carbon across the light years. Created within stars by the fusion of helium and released into space by stellar winds, it combines readily with oxygen and nitrogen to form the simplest organic compounds. Further processing during solar system building creates more complex forms which rain down on planets as meteorites and comets. Over the course of geologic time, these link up with other elements into ever more diverse and complex forms, setting the stage for the formation of life. A messy and wonderful business if there ever was.