Paper
The Atlas of Mars
Published Aug 16, 2019 · K. Coles, Kenneth L. Tanaka, P. Christensen
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Abstract
Mars is the fourth planet from the Sun and the outermost of the rocky, terrestrial planets that make up the inner solar system. Mars is the second smallest planet; only Mercury is smaller. Surface gravity onMars is 3.71 m s, which is 37.6% that of the Earth. The present atmospheric pressure is low (~0.6 kPa) relative to Earth’s (101 kPa), and the atmosphere is mostly carbon dioxide (95%). The obliquity of Mars (tilt of the axis of rotation relative to the plane of orbit) is presently 25 degrees and may have varied by tens of degrees over the past tens of millions of years and longer (Laskar et al., 2004). The rotational period (sidereal) of Mars is slightly longer than that of Earth, at 24 hours 37 minutes, while the Martian solar day (sol) is 24 hours 40 minutes. The orbit of Mars is more elliptical (eccentricity = 0.093) than that of Earth (0.017), so the seasons vary in length with northern spring being the longest. The sidereal period is 687 days (670 Martian sols), while the synodic period relative to Earth, and the interval between oppositions of Mars, averages 780 days. The progress of the seasons is commonly given by Ls, which is the orbital longitude, or angle in degrees at the Sun measured from the northern hemisphere spring equinox to the position of Mars. Thus, Ls = 90 is the summer solstice in the northern hemisphere and the winter solstice in the south (Carr, 2006 gives additional detail on the motion of Mars).
Mars has a rotational period slightly longer than Earth's, with 24 hours 37 minutes, and its seasons vary in length due to its more elliptical orbit.
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