I didn't see an explanation in the movie. How many days pass on Earth when one SOL passes on Mars?

I heard a reference of two months passing, but I thought only (counts)....less than 50 SOLs had passed.


1 Answer 1


The physics of Mars in The Martian is identical to the actual physics of the planet, as such, we only need to know the actual length of a Martian sol (in hours/minutes) to know how it compares with an Earth day.

A Martian day is nearly identical to an Earth day. There's only a difference of about 2.7% between the two.

The average length of a Martian sidereal day is 24h 37m 22.663s (88,642.66300 seconds based on SI units), and the length of its solar day (often called a sol) is 24h 39m 35.244147s (88,775.244147 seconds). The corresponding values for Earth are 23h 56m 4.0916s and 24h 00m 00.002s, respectively. This yields a conversion factor of 1.02749125170 days/sol. Thus Mars' solar day is only about 2.7% longer than Earth's.

The number above you're interested in is the solar day - 24 hours, 39 minutes, 35 seconds.

  • 2
    Isn't the number they are interested in 1.02749125170 since they are looking for the ratio? as in 1:1.02749125170
    – Puddler
    Jan 12, 2017 at 5:13
  • 10
    "There's only a difference of about 2.7% between the two." Not to humblebrag, but I had a great opportunity to work on a Mars mission when I was in college (my avatar photo is from this mission). A difference of "only" 40 minutes/day for a 90 sol mission meant that every sol's work begins at 8:00am, then 8:40am, ..., 8:00pm, etc. I lived in 3 straight months of perpetual jet lag. Great experience, but would not want to repeat shifting my schedule daily by 40 minutes!
    – Dang Khoa
    Jan 12, 2017 at 6:45
  • @DangKhoa for some people (most notably 'evening people'), the increased day length is actually beneficial.
    – Glorfindel
    Jan 12, 2017 at 10:30
  • 5
    I need to create calories. And I need enough to last the 1387 sols until Ares 4 arrives. If I don’t get rescued by Ares 4, I’m dead anyway. A sol is 39 minutes longer than a day, so it works out to be 1425 days. - from Chapter 3, LOG ENTRY: SOL 25 Jan 12, 2017 at 11:18

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