Sols

Sols is the term used in planetary science to denote a Martian solar day. A sol is the period from one solar noon to the next on Mars and serves as the standard unit of timekeeping in Mars missions and datasets.

One sol has a mean length of 24 hours, 39 minutes, and 35.244 seconds in Earth time, about 1.02749 Earth days. The exact length can vary slightly because Mars' rotation is not perfectly uniform and its orbital geometry changes over the Martian year, causing the solar day to drift by a few seconds.

In practice, mission teams schedule activities by sol and often label data and events with sol numbers. Sol counting usually begins on the landing day, though conventions can vary by mission. Conversions between sols and Earth time are used for coordination with planners on Earth.

Etymology and context: The word sol derives from the Latin word for the Sun and is used to describe a solar day on Mars. The concept is analogous to a solar day on Earth, but it is longer due to Mars’ longer rotation period.

See also: The term sol is part of a broader framework of planetary timekeeping, where each planet’s daily cycle is used to organize activities, data, and communications for exploration programs.