Sir

Over the past few weeks I have read with great interest your coverage of the discoveries of the Mars Sojourner1. There have been many fascinating data reported about the mineral constituents of Mars rocks.

At the same time, however, references are made to martian soil without any data to support the existence of this material. Careless use of the term soil is misleading2.

For many in Earth sciences, soil imparts a notion of biological activity for which we have no evidence on Mars. In fact, most definitions of soil are closely linked with plant growth, organic matter or biological activity3,4,5,6.

Although I do not subscribe to all these definitions of soil and I do not want to limit the study of pedology solely to planet Earth, I also do not envisage all martian dust as martian soil. It may well be that with continued advances in planetary studies we need to re-evaluate the definition of soil. In the meantime it may be prudent to refrain from imparting this earthly quality to all planets.