David McKay
The NASA scientist who led the 1996 study suggesting that the Martian meteorite ALH 84001 might hold traces of ancient life.
Key facts
- Born
- 1936
- Died
- 2013
- Nationality
- American
- Field
- Planetary scientist
David Stewart McKay spent his career at NASA's Johnson Space Center in Houston. In the 1960s he helped train the Apollo astronauts in geology, and he went on to study lunar soil, the fine powder that covers the Moon's surface.
In the 1990s McKay and a team of colleagues, including Everett Gibson and Kathie Thomas-Keprta, studied ALH 84001, a 4-billion-year-old rock from Mars. Inside its cracks were small orange globules of carbonate minerals, formed when water once seeped through the rock on Mars. In and around them the team found organic molecules, tiny crystals of magnetite like those made by some bacteria on Earth, and shapes that looked like minute fossil microbes.
In August 1996 they announced that, taken together, these clues might be evidence of ancient life on Mars. The announcement caused a worldwide sensation, and the President of the United States spoke about it on television.
Over the following years other scientists showed that each feature could also form without life: the shapes are far smaller than most bacteria, and the magnetite and organics can form through chemistry alone. Most researchers now reject the claim, but the debate inspired a new era of Mars exploration and of the search for life beyond Earth, and sharpened ideas about what would count as proof.
On the timeline
- August 1996Signs of life in a Martian meteorite?