The tough-guy documentary genre strikes again with “Toughest Race on Earth: Iditarod” (9 p.m., Discovery), a six-part look at the annual sled-dog race between Anchorage and Nome. The 1,150-mile challenge was begun in 1973 to commemorate a famous event. In 1925, teams of dogs and mushers rushed a diphtheria serum to the stricken town of Nome, saving the people in the Bering Sea outpost.

“Iditarod” has all the stuff of TV drama: tough-guy champions and rookie upstarts, grizzled veterans and a longtime female contender and cancer survivor. One challenger insists on making his own sled. Another braves the race and the Arctic elements despite diabetes.

A former champion competes against his son, and everyone just wants to win – or at least finish. The fastest Iditarod time was a little under nine days. The slowest team to finish took 32 days.

In addition to the macho attitudes and harsh elements, “Iditarod” celebrates something unique: the bonds of dependence between mushers and their dogs. Every sled begins with a team of 16 dogs, super-athletes in their own right and the real stars of the show.

¢ On the eve of the third and final debate, “Frontline” presents “The Choice 2008” (8 p.m., PBS, check local listings), detailed biographical profiles of Sen. John McCain and Sen. Barack Obama. This marks the 20th anniversary of the first “Choice,” which aired back in 1988 during the race between George H.W. Bush and Michael Dukakis.

¢ Sigourney Weaver guest stars as a therapist on the second-season premiere of “Eli Stone” (9 p.m., ABC). Six months after his brain surgery, Eli remains vision-free and isn’t entirely sure how he feels about it. Were the signs and portents a gift or a burden? Eli’s friends and colleagues also wrestle with the shift in his outlook. But all of that changes when his surgeon brother Nate begins to exhibit symptoms suspiciously familiar to Eli’s.

Tonight’s other highlights

¢ “Nova” (7 p.m., PBS, check local listings) recalls the 2003 space-shuttle disaster that claimed the lives of the Columbia crew just 16 minutes before its scheduled landing. The hourlong examination looks at problems in the Shuttle program and NASA itself that may have contributed to the fatal failure.

¢ After his father’s death, House tries to ignore his feelings on “House” (7 p.m., Fox).

¢ Tampa Bay and Boston meet in Game 4 of ALCS (7 p.m., TBS).

¢ Smithy needs a shoulder to cry on “Gavin and Stacy” (7:40 p.m., BBC America).

¢ Surf’s up on “The Mentalist” (8 p.m., CBS).

¢ A man’s ability to channel powerful currents attracts the curious on “Fringe” (8 p.m., Fox).

¢ House politics loom large on “Greek” (8 p.m., Family).

¢ Mike works in a filthy snack factory on “Dirty Jobs” (8 p.m., Discovery).

¢ NeNe holds a grudge on “Real Housewives of Atlanta” (8 p.m., Bravo).

¢ A whistle-blower leaves town on “Without a Trace” (9 p.m., CBS).

¢ An investigation leads to a familiar suspect on “Law & Order: Special Victims Unit” (9 p.m., NBC).

¢ Vic employs an old connection on “The Shield” (9 p.m., FX).

¢ An old mining town becomes the center of a medical specialty in the six-part series “Sex Change Hospital” (10 p.m., WE).