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Mars' Calendar

Time on Mars is easily divided into days based on its rotation rate and years based on its orbit. Sols, or Martian solar days, are only 39 minutes and 35 seconds longer than Earth days, and there are 668 sols (684 Earth days) in a Martian year.

For convenience, sols are divided into a 24-hour clock. Each landed Mars mission keeps track of "Local Solar Time," or LST, at its landing site, because Local Solar Time relates directly to the position of the Sun in the sky and thus the angle from which camera views are illuminated. The time of day, Local Solar Time, depends upon the lander's longitude on Mars.

Unlike on Earth, there is no leisurely-orbiting moon to give Mars "months," and while there have been many imaginative calendars suggested for Mars, none is in common use. The way that scientists mark the time of Mars year is to use solar longitude, abbreviated Ls (read "ell sub ess"). Ls is 0° at the vernal equinox (beginning of northern spring), 90° at summer solstice, 180° at autumnal equinox, and 270° at winter solstice.

On Earth, spring, summer, autumn, and winter are all similar in length, because Earth's orbit is nearly circular, so it moves at nearly constant speed around the Sun. By contrast, Mars' elliptical orbit makes its distance from the Sun change with time, and also makes it speed up and slow down in its orbit. Mars is at aphelion (its greatest distance from the Sun, 249 million kilometers, where it moves most slowly) at Ls = 70°, near the northern summer solstice, and at perihelion (least distance from the Sun, 207 million kilometers, where it moves fastest) at Ls = 250°, near the southern summer solstice. The Mars dust storm season begins just after perihelion at around Ls = 260°.

The coincidence of aphelion with northern summer solstice means that the climate in the northern hemisphere is more temperate than in the southern hemisphere.  In the south, summers are hot and quick, winters long and cold.

Ls marks the passage of time within a Mars year.  To count up the passage of time from one Mars year to the next, Mars scientists have settled upon the following convention:

For the purpose of this comparison, we use the solar longitude range 0°-360° to define a Mars year and adopt April 11, 1955 (Ls=0°) as the beginning of year 1. In this arbitrary convention, the Mariner 9, Viking, Phobos, and Pathfinder missions occurred in years 9-10, 12-15, 19-20, and 23, respectively. By comparison, the 1992-1999 [Earth-based] millimeter observations extend over years 21-24, and the 1997-1999 [Mars Global Surveyor] TES observations extend over years 23 and 24.

Tables of Seasonal Data for Mars

Martian years and start dates of northern hemisphere seasons
Mars yearSpring equinox
(Ls = 0°)
Summer solstice
(Ls = 90°)
Autumnal equinox
(Ls = 180°)
Winter solstice
(Ls = 270°)
01 Apr 11 1955 Oct 27 1955 Apr 27 1956 Sep 21 1956
02 Feb 26 1957 Sep 13 1957 Mar 15 1958 Aug 09 1958
03 Jan 14 1959 Aug 01 1959 Jan 31 1960 Jun 26 1960
04 Dec 01 1960 Jun 18 1961 Dec 18 1961 May 14 1962
05 Oct 19 1962 May 05 1963 Nov 05 1963 Mar 31 1964
06 Sep 05 1964 Mar 22 1965 Sep 22 1965 Feb 15 1966
07 Jul 24 1966 Feb 07 1967 Aug 10 1967 Jan 03 1968
08 Jun 10 1968 Dec 25 1968 Jun 27 1969 Nov 20 1969
09 Apr 28 1970 Nov 12 1970 May 15 1971 Oct 08 1971
10 Mar 15 1972 Sep 29 1972 Apr 01 1973 Aug 25 1973
11 Jan 31 1974 Aug 17 1974 Feb 17 1975 Jul 13 1975
12 Dec 19 1975 Jul 04 1976 Jan 04 1977 May 30 1977
13 Nov 05 1977 May 22 1978 Nov 22 1978 Apr 17 1979
14 Sep 23 1979 Apr 08 1980 Oct 09 1980 Mar 04 1981
15 Aug 10 1981 Feb 24 1982 Aug 27 1982 Jan 20 1983
16 Jun 28 1983 Jan 12 1984 Jul 14 1984 Dec 07 1984
17 May 15 1985 Nov 29 1985 Jun Jan 1986 Oct 25 1986
18 Apr 01 1987 Oct 17 1987 Apr 18 1988 Sep 11 1988
19 Feb 16 1989 Sep 03 1989 Mar 06 1990 Jul 30 1990
20 Jan 04 1991 Jul 22 1991 Jan 22 1992 Jun 16 1992
21 Nov 21 1992 Jun 08 1993 Dec 08 1993 May 04 1994
22 Oct 09 1994 Apr 26 1995 Oct 26 1995 Mar 21 1996
23 Aug 26 1996 Mar 13 1997 Sep 12 1997 Feb 06 1998
24 Jul 14 1998 Jan 29 1999 Jul 31 1999 Dec 25 1999
25 May 31 2000 Dec 16 2000 Jun 17 2001 Nov 11 2001
26 Apr 18 2002 Nov 03 2002 May 05 2003 Sep 29 2003
27 Mar 05 2004 Sep 20 2004 Mar 22 2005 Aug 16 2005
28 Jan 21 2006 Aug 08 2006 Feb 07 2007 Jul 04 2007
29 Dec 09 2007 Jun 25 2008 Dec 25 2008 May 21 2009
30 Oct 26 2009 May 13 2010 Nov 12 2010 Apr 08 2011
31 Sep 13 2011 Mar 30 2012 Sep 29 2012 Feb 23 2013
32 Jul 31 2013 Feb 15 2014 Aug 17 2014 Jan 11 2015
33 Jun 18 2015 Jan 03 2016 Jul 04 2016 Nov 28 2016
34 May 05 2017 Nov 20 2017 May 22 2018 Oct 16 2018
35 Mar 23 2019 Oct 08 2019 Apr 08 2020 Sep 02 2020
36 Feb 07 2021 Aug 25 2021 Feb 24 2022 Jul 21 2022
37 Dec 26 2022 Jul 12 2023 Jan 12 2024 Jun 07 2024
38 Nov 12 2024 May 29 2025 Nov 29 2025 Apr 25 2026
39 Sep 30 2026 Apr 16 2027 Oct 17 2027 Mar 12 2028
40 Aug 17 2028 Mar 03 2029 Sep 03 2029 Jan 28 2030

This table is taken from a 2010 paper by Bruce Cantor, Philip James, and Wendy Calvin: "MARCI and MOC observations of the atmosphere and surface cap in the north polar region of Mars," employing a convention described originally in a 2000 paper by Todd Clancy and several coauthors: "An intercomparison of ground-based millimeter, MGS TES, and Viking atmospheric temperature measurements: Seasonal and interannual variability of temperatures and dust loading in the global Mars atmosphere."

Here are how some major events in Mars exploration shake out, according to this calendar:

Martian Years and Seasons for Significant Mission Events
Earth DateMars
year/Ls
Event
July 14, 1965 6.143 Mariner 4 flyby
August 1969 8.200 Mariner 6 and 7 flybys
November 1971 9.284 Mariner 9, Mars 2, and Mars 3 enter orbit
August 1972 10.64 Mars 2 and 3 shut down
October 27, 1972 10.102 Mariner 9 shuts down
February 1974 11.0 Mars 4 and 5 enter orbit
July 1976 12.88 Viking 1 Orbiter & Lander arrive
September 1976 12.116 Viking 2 Orbiter & Lander arrive
July 25, 1978 13.118 Viking 2 Orbiter shuts down
April 11, 1980 14.91 Viking 2 Lander shuts down
August 17, 1980 14.151 Viking 1 Orbiter shuts down
November 13, 1982 15.226 Viking 1 Lander shuts down
January 29, 1989 19.350 Phobos 2 enters orbit
March 27, 1989 20.18 Phobos 2 shuts down
July 4, 1997 23.142 Mars Pathfinder lands
September 1997 23.173 Mars Global Surveyor enters orbit; Mars Pathfinder shuts down
October 24, 2001 25.258 Mars Odyssey enters orbit
December 14, 2003 26.315 Nozomi flies past Mars
January 2004 26.325 Mars Express, Spirit, and Opportunity arrive
March 10, 2006 28.22 Mars Reconnaisance Orbiter arrives
November 5, 2006 28.130 Mars Global Surveyor shuts down
May 25, 2008 29.76 Phoenix lands
November 2, 2008 29.151 Phoenix shuts down
March 22, 2010 30.67 Last contact with Spirit
August 6, 2012 31.150 Curiosity lands

 

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