1970

Organic Molecules in Murchison Meteorite

One of the motivators of space exploration is the search for life beyond our home planet. But how do we conduct such a search? One way is to search for the chemical elements that occur in life on our own planet—elements like carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. But these elements occur throughout the cosmos, in many places and environments (such as the insides of stars) that are unlikely to be conducive to life. A more effective strategy might be to search not for specific elements but for certain arrangements of them—molecules—that could reveal evidence for life’s basic chemistry.

Life on earth is based on organic molecules. Some organic molecules are simple, like methane (CH₄), methanol (CH₃OH), or formaldehyde (H₂CO), and others are much more complex, like proteins, amino acids, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA). Over the last half century, astronomers have identified many simple organic molecules in dense interstellar clouds, comet tails, icy moons and rings of the outer solar system, and the atmospheres of Titan and the giant planets.

On September 28, 1969, a meteor and fireball streaked across the daytime sky and crashed to the ground near the town of Murchison in Victoria, Australia. More than 220 pounds (100 kilograms) of meteorite samples were found in the area. After detailed analysis of the samples, scientists announced in 1970 that the meteorite—from the most ancient and primitive class of meteorites, known as carbonaceous chondrites—contained some common amino acids. Later studies found that the Murchison meteorite contained more than 70 kinds of amino acids, plus many other simple and complex organic molecules.

Life as we know it requires liquid water, sources of energy like heat or sunlight, and abundant, complex organic molecules. The discovery of amino acids in Murchison and other meteorites supports the idea that molecules that are critical to life can form nonbiologically in environments such as a solar nebular disk, comet, or planetesimal. Life may or may not be abundant in the cosmos, but the stuff of life appears to be everywhere.

X-ray image of magnesium (red), calcium (green), and aluminum (blue) in the Murchison meteorite, a more than 4.55-billion-year-old carbonaceous chondrite. This ancient rock contains primitive minerals condensed from the solar nebula, water, and complex organic molecules, including more than 70 kinds of amino acids.