Mars (9 p.m., National Geographic) - In the season finale, Lukrum pushes its corporate interests too far and jeopardizes the safety of both colonies. IMSF springs into action to stabilize the situation, but, for some, it will be too late.
Also on tonight . . .
The Great Christmas Light Fight (8 p.m., ABC) - The two-hour season finale features displays in Greeley, Colo.; Ballplay, Ala.; Phoenix, Ariz.; Temecula, Cali.; Escondido, Calif.; Waco, Texas; Bismarck, N.D.; and Ambler, Penn.
Christmas with the Mormon Tabernacle Choir (9 p.m., PBS / UNC-TV) - This Christmas concert in Salt Lake City features Tony Award-winner (and TV star) Sutton Foster. Narrated by Hugh Bonneville.
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Holiday Baking Championship (9 p.m., Food) - In the season finale, three final bakers must create an edible holiday ornament, and later a cake that is decorated like a gift but contains a surprise inside.
Who Do You Think You Are? (9 p.m., TLC) - Two new episodes tonight. First, actress Regina King learns about her maternal family tree. At 10, actor Matthew Morrison discovers ties to the Revolutionary War.
Christmas Cookie Challenge (10 p.m., Food) - The remaining cookie makers have to create cookies that contain at least four shades of a color for the season finale.
Man on Fire (10 p.m., PBS / UNC-TV) - In this Independent Lens documentary, an elderly white preacher self-immolates to protest racism in his hometown of Grand Saline, Texas, in 2014.
2018 In Memoriam (10 p.m., ABC) - Robin Roberts hosts a tribute to some of the icons the world lost in 2018 and the legacies they left behind.