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The >100-kilogram ( >220-pound) Murchison meteorite landed in Australia in 1969 and has been extensively studied. It contains many types of chemicals that are used by life on Earth. A pebble-sized fragment (less than an ounce or 23 grams) is shown at lower right. Magnified 10 times and seen in polarized light, a thin slice reveals colors that indicate different minerals.
Many meteorites are pieces of asteroids and comets that land on Earth. Others are rocks from Mars or the Moon. Some contain a variety of organic (carbon-containing) chemicals. These include amino acids (the building blocks of proteins) and nucleobases that form the rungs of the DNA ladder (life’s genome). Astrobiologists study these meteorites to discover their chemical content.
COLLECTING EXTRATERRESTRIAL VISITORS: The yearly Antarctic Search for Meteorites (ANSMET) expedition finds and collects meteorites for scientific study.
About 40,000 tons of meteoritic material hit Earth each year. Most of it is dust that burns up in the atmosphere, but larger pieces land all over Earth’s surface. Scientists study collected meteorites, often by crushing them and placing them in hot water to dissolve certain molecules. The resulting “meteorite tea” is analyzed in the laboratory to identify the meteorite’s chemical content.
The amino acid glycine, made of carbon (gray), nitrogen (blue), oxygen (red), and hydrogen (white), is one of the many chemicals essential to life on Earth that are also present in meteorites.
AMINO ACID’S HANDEDNESS: The two mirror-image forms of amino acid molecules are like your hands — they can’t be rotated or flipped to line up with each other. A right hand won’t fit into a left-handed glove, and right-handed amino acids don’t fit into life’s left-handed proteins.
Chemistry usually makes these two forms in equal amounts, but life on Earth uses mostly the “left-handed” type to build proteins. Why? This is a great mystery in science, and meteorites might hold the answer. Some meteorites have more left-handed amino acid molecules than right-handed ones. Scientists are working to understand how this happened, and whether meteorites delivered extra left-handed amino acids to the early Earth. Maybe the first life on Earth used the left-handed molecules delivered by meteorites!
MISSION TO A CARBONACEOUS ASTEROID: In 2020, OSIRIS-REx will collect pristine material from asteroid Bennu (1999 RQ36) and return it to Earth for study in terrestrial laboratories at Goddard and elsewhere.
Goddard scientists identified the amino acid glycine in samples returned from comet Wild 2 by the Stardust spacecraft. OSIRIS-REx will return samples of a carbonaceous asteroid for similar study.
Sample return missions bring pieces of other Solar System bodies to Earth. This material is untouched by Earth’s contaminating environment, and so preserves a true record of its history. Scientists who were not yet born when Apollo astronauts walked the Moon are now studying the lunar rocks brought back to Earth.