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 (687 Earth days) in a Martian year.

Your Guide to Mars

Mars, the Red Planet, once had liquid water on the surface and could have supported life. We don't know how it changed to the cold, dry desert-world it is today.

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. (Clancy et al., 2000)

They picked Year 1 to correspond with the year of a global dust storm widely observed in 1956. A more recent paper defined the existence of a Mars Year 0 (starting on May 24, 1953), and defined previous years as having negative numbers (Piqueux et al., 2015).

Here is an online tool for converting dates to Ls.

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°)
01Apr 11 1955Oct 27 1955Apr 27 1956Sep 21 1956
02Feb 26 1957Sep 13 1957Mar 15 1958Aug 09 1958
03Jan 14 1959Aug 01 1959Jan 31 1960Jun 26 1960
04Dec 01 1960Jun 18 1961Dec 18 1961May 14 1962
05Oct 19 1962May 05 1963Nov 05 1963Mar 31 1964
06Sep 05 1964Mar 22 1965Sep 22 1965Feb 15 1966
07Jul 24 1966Feb 07 1967Aug 10 1967Jan 03 1968
08Jun 10 1968Dec 25 1968Jun 27 1969Nov 20 1969
09Apr 28 1970Nov 12 1970May 15 1971Oct 08 1971
10Mar 15 1972Sep 29 1972Apr 01 1973Aug 25 1973
11Jan 31 1974Aug 17 1974Feb 17 1975Jul 13 1975
12Dec 19 1975Jul 04 1976Jan 04 1977May 30 1977
13Nov 05 1977May 22 1978Nov 22 1978Apr 17 1979
14Sep 23 1979Apr 08 1980Oct 09 1980Mar 04 1981
15Aug 10 1981Feb 24 1982Aug 27 1982Jan 20 1983
16Jun 28 1983Jan 12 1984Jul 14 1984Dec 07 1984
17May 15 1985Nov 29 1985Jun Jan 1986Oct 25 1986
18Apr 01 1987Oct 17 1987Apr 18 1988Sep 11 1988
19Feb 16 1989Sep 03 1989Mar 06 1990Jul 30 1990
20Jan 04 1991Jul 22 1991Jan 22 1992Jun 16 1992
21Nov 21 1992Jun 08 1993Dec 08 1993May 04 1994
22Oct 09 1994Apr 26 1995Oct 26 1995Mar 21 1996
23Aug 26 1996Mar 13 1997Sep 12 1997Feb 06 1998
24Jul 14 1998Jan 29 1999Jul 31 1999Dec 25 1999
25May 31 2000Dec 16 2000Jun 17 2001Nov 11 2001
26Apr 18 2002Nov 03 2002May 05 2003Sep 29 2003
27Mar 05 2004Sep 20 2004Mar 22 2005Aug 16 2005
28Jan 21 2006Aug 08 2006Feb 07 2007Jul 04 2007
29Dec 09 2007Jun 25 2008Dec 25 2008May 21 2009
30Oct 26 2009May 13 2010Nov 12 2010Apr 08 2011
31Sep 13 2011Mar 30 2012Sep 29 2012Feb 23 2013
32Jul 31 2013Feb 15 2014Aug 17 2014Jan 11 2015
33Jun 18 2015Jan 03 2016Jul 04 2016Nov 28 2016
34May 05 2017Nov 20 2017May 22 2018Oct 16 2018
35Mar 23 2019Oct 08 2019Apr 08 2020Sep 02 2020
36Feb 07 2021Aug 25 2021Feb 24 2022Jul 21 2022
37Dec 26 2022Jul 12 2023Jan 12 2024Jun 07 2024
38Nov 12 2024May 29 2025Nov 29 2025Apr 25 2026
39Sep 30 2026Apr 16 2027Oct 17 2027Mar 12 2028
40Aug 17 2028Mar 03 2029Sep 03 2029Jan 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." You can find dates corresponding to northern vernal equinoxes for Mars years -184 to 100 in Piqueux et al. 2015, "Enumeration of Mars years and seasons since the beginning of telescopic exploration."

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, 19656/143Mariner 4 flyby
August 19698/200Mariner 6 and 7 flybys
November 19719/284Mariner 9, Mars 2, and Mars 3 enter orbit
August 197210/64Mars 2 and 3 shut down
October 27, 197210/102Mariner 9 shuts down
February 197411/0Mars 4 and 5 enter orbit
July 197612/88Viking 1 Orbiter & Lander arrive
September 197612/116Viking 2 Orbiter & Lander arrive
July 25, 197813/118Viking 2 Orbiter shuts down
April 11, 198014/91Viking 2 Lander shuts down
August 17, 198014/151Viking 1 Orbiter shuts down
November 13, 198215/226Viking 1 Lander shuts down
January 29, 198919/350Phobos 2 enters orbit
March 27, 198920/18Phobos 2 shuts down
July 4, 199723/142Mars Pathfinder lands
September 199723/173Mars Global Surveyor enters orbit; Mars Pathfinder shuts down
October 24, 200125/258Mars Odyssey enters orbit
December 14, 200326/315Nozomi flies past Mars
January 200426/325Mars Express, Spirit, and Opportunity arrive
March 10, 200628/22Mars Reconnaisance Orbiter arrives
November 5, 200628/130Mars Global Surveyor shuts down
May 25, 200829/76Phoenix lands
November 2, 200829/151Phoenix shuts down
March 22, 201030/67Last contact with Spirit
August 6, 201231/150Curiosity lands
September 22, 201432/200MAVEN arrives
September 24, 201432/202Mars Orbiter Mission arrives
October 19, 201633/244ExoMars Trace Gas Orbiter arrives
June 10, 201834/190Last contact with Opportunity
November 26, 201935/112InSight lands
February 202136/0Approximate date of planned arrival for Rosalind Franklin rover, Hope Mars orbiter, China Mars orbiter and rover
February 18, 202136/5Scheduled arrival of Mars 2020 rover