Mars Time

At August 6, 2012, 05:14:39 UTC SCET (MJD 56145.21850) the Curiosity rover landed in Gale Crater on Mars.  (SCET stands for Spacecraft Event Time, since it took until about 14 minutes later for the data transmission to reach earth.)  In Mars time that was 05:50:16 AMT (MSD 49269.24), about 15:00 local time.  AMT is Airy Mean Time, also known as Coordinated Mars Time (MTC), because it is the Local Mean Solar Time at Airy Crater, which marks zero longitude on Mars.  MSD is Mars Sol Date, and like Modified Julian Dates it is a count of Martian days, which are called "sols", but from December 29, 1873 (MJD 5521.5).

Another sol count is started whenever a craft lands on Mars, so that was on Sol 0 for Curiosity.  There is currently one other craft active on Mars, Opportunity, which was on Sol 3034.  Opportunity is near the Martian Prime Meridian, one hour behind AMT, but Curiosity is on the other side of the planet, 9 hours, 9 minutes and 40 seconds ahead of AMT.

Note that sols are longer than earth days by nearly 40 earth minutes but are divided into 24 Martian hours, so each hour, minute and second is 2.7% longer than those on earth.  Thus, the mission operators start their shifts 40 minutes later each day.  To keep track, they use a Java program call Mars24, which you can download from NASA.  By default it displays AMT and LMST for Curiosity and Opportunity, as well as MJD and MSD with two digits of decimal time.  You can also find more information at Wikipedia.

MJD 56148.377
MSD 49272.317

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