A visitor from before the sun
On September 28, 1969, at 10:58 AM local time, a fireball tore across the sky above Murchison, Victoria. It broke into several pieces, creating a sonic boom before scattering fragments over a 13 square kilometer area. One 680-gram piece crashed through a barn roof, landing in hay. In total, over 100 kilograms of this extraterrestrial visitor were recovered, making it one of the most studied meteorites in history.
The Murchison meteorite is a CM2 type carbonaceous chondrite, a class of meteorite containing water and organic compounds. Its prompt collection meant that the samples were fresh and largely free from terrestrial contamination. When first collected, witnesses reported that the fragments gave off a strange smell, similar to tar or methylated spirits, a first clue to its unusual chemical makeup. The rock itself is about 4.6 billion years old, having formed in the early solar system. But within it, scientists found something even older.
A recipe for life
Analysis of the Murchison meteorite revealed an astonishing molecular diversity. Scientists have identified over 92 different amino acids, the building blocks of proteins. Only 19 of these are common on Earth, confirming their extraterrestrial origin. Further proof comes from their chirality; the meteorite contains a nearly equal mix of left-handed and right-handed amino acid structures, while life on Earth exclusively uses left-handed versions. In addition to amino acids, the meteorite contains sugars, and nucleobases like uracil and xanthine, which are components of RNA and DNA.
Perhaps most remarkably, the meteorite contains presolar grains, bits of literal stardust. These silicon carbide particles were forged in ancient stars that died long before our own sun existed. In 2020, researchers dated some of these grains and found them to be up to 7 billion years old, making them the oldest solid material ever found on Earth. These ancient grains provide direct samples of long-dead stars, showing how stars formed in our galaxy. The sheer number of organic compounds is vast; a 2010 study identified 14,000 molecular compounds, with estimates suggesting millions of distinct organic structures could be present.