John Wood
The planetary scientist who co-created the petrologic types of chondrites and first proposed that the young Moon was covered in a magma ocean.
Key facts
- Born
- 1932
- Nationality
- American
- Field
- Planetary scientist
John Armstead Wood worked for many years at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and taught at Harvard. His research spanned chondrites, the Moon and the formation of the planets.
In 1967, with W. Randall Van Schmus, he published a way of describing how much each chondrite has been changed since it formed. Their scale runs from 1 to 6. Types 3 to 6 record increasing heating inside the parent asteroid, which slowly blurred the chondrules and evened out the minerals. Types 1 and 2 record alteration by water. The number is now part of every chondrite's classification, as in H5 or CM2.
When the first Apollo 11 samples arrived in 1969, Wood found small white fragments of anorthosite, a rock made almost entirely of plagioclase feldspar. He and his colleagues argued in 1970 that these pieces had floated to the top of a deep layer of molten rock covering the young Moon. This magma ocean idea is now the standard picture of how the Moon's crust formed.
Wood also wrote widely on how chondrules might have formed and on the earliest history of the Solar System. He received the Leonard Medal of the Meteoritical Society, and an asteroid is named after him.