The Jewish Calendar on Mars

A plausible set of recommendations:

• The Martian day is the day used and the Martian year is the year used. The Sabbath is celebrated every seven days. The first spaceship carrying Jews to land on Mars sets the day. If the ship lands on a Wednesday (Earth time) that Martian day is declared to be a Wednesday.
• The International Date Line is exactly opposite the landing site.
• Rosh Chodesh is celebrated starting at the sunset after Deimos rises. Phobos has a period of about seven hours. Deimos has a period of about thirty hours. Celebrating Rosh Chodesh for Phobos would be exhausting. Deimos is a bit better since the apparent period of revolution is several days.
• Passover is celebrated at the vernal equinox in the Northern Hemisphere. Shavuot is celebrated seven weeks later. Rosh Hashanah is celebrated at the autumn equinox in the Northern Hemisphere, Yom Kippur ten days later, and Succoth five days after that.

A different recommendation:

• Wait until the Pope decides on the Martian Easter and then plagiarize something.