QUESTION:
What is the pH of Mars?

ANSWER from Albert Yen on June 2, 2000:

Your question is a very good one, but unfortunately, we don't have 
enough data from Mars to give you a good answer.

None of the landers that have been sent to the surface of Mars have 
made direct measurements of the soil pH. Elemental abundances 
quantity of Mg, Ca, S, etc.) have been measured at the Viking and 
Pathfinder landing sites; however, without knowledge of how these 
elements are put together into minerals, we don't know which ions 
will go into solution when water is added. Therefore, we don't have 
good constraints on the likely pH. Some people have argued that the 
presence of large volcanoes on Mars implies an abundance of free 
sulfur, which would suggest an acidic soil. On the other hand, some 
scientists believe that carbonates are dispersed in the soil (even 
though there has not been a conclusive detection), and if this is the
case, the soil pH should be on the alkaline side of neutral. The 
bottom line is: We don't know the pH value of the martian soil.
 
Obviously, a direct measurement of the pH would be very useful in 
understanding the chemical process that occur (or have occurred) at 
the martian surface. The wet chemistry cells on the MECA (Mars 
Environmental Compatibility Assessment) instrument have the ability 
to measure pH. The original plan was to include MECA on the lander 
to be launched in 2001, but there is currently some uncertainty about
the future of MECA because of the restructuring of the Mars 
exploration program. So unfortunately, it may be quite some time 
before a direct measurement of soil pH on Mars will be made. You can
find more information about MECA at the following web site:
 
http://mars.jpl.nasa.gov/2001/lander/meca/index.html