The Lander 1 footpad #2 sensor is under a drift, buried in Martian soil when the lander touched down. The temperature was measured by what was the "entry and descent" thermocouple sensor, meant to take data only while the Viking Lander was entering the Martian atmosphere. It was not designed to measure temperature accurately on the surface of Mars and was not necessarily expected to survive. It is not strictly a "soil temperature" measurement, since the footpad and leg structure modify the soil temperature, and the lander shades the area: the latter changing with the season. However, it provides the only soil temperature measurements, other than experiments with the soil sampler arm thermometer. It is included here to provide some comparison with Earth-based soils.
The data is divided into Sols. A Sol is a Martian day and is equal to about 24 hours and 37 minutes. The data given here is for Sols 1519-1524, 1542, and 1543 which represent the number of Sols since Lander 1 landed.
Footpad Data: Sols 1519-1524,1542,1543
Plot of footpad soil data, Sol 1520 (8K)
Plot of footpad data, Sols 1519-1524 (9K)