Nearly 30 new programs were placed on the fall primetime schedule by the broadcast nets last week, but none may have a bigger impact than two that Fox first announced last year.

“Terra Nova,” the dino-sized thriller that counts Steven Spielberg and Peter Chernin among its exec producers, could make Fox a terror at 8 p.m. Mondays, while Simon Cowell’s ballyhooed talent show “The X Factor” may make the network as tough as it has ever been in the fall on Wednesdays and Thursdays at 8.

Thursdays, in fact, offer interesting new battles the entire night, with CBS debuting its high-testing “Person of Interest” at 9 p.m., followed by NBC launching its “Prime Suspect” adaptation at 10. at four of the Here’s a look at four of the key timeslot tangos in the coming TV season:

Monday 8 p.m.

Originally scheduled for the same kind of spring sneak peek that whetted appetites for “Glee” two years ago, “Terra Nova” instead will launch full force in autumn. While that means it will vie for attention amid the onslaught of other new series, none figures to stand out more. “Terra Nova” has all the heft of a smallscreen “Avatar,” with that film’s Stephen Lang as a major character as well.

The potential of “Terra Nova,” which allowed Fox to push the aging “House” to 9 p.m., figures to provide the biggest challenge in some time to ABC unscripted hit “Dancing With the Stars.” Both shows also have to contend with “Monday Night Football” on ESPN, depending on the time zone (and whether the sport’s ongoing labor dispute affects the season).

Meanwhile, the other networks have hardly surrendered the hour. CBS’ “How I Met Your Mother” still has its fans, many of whom figure to stay tuned for freshman comedy “2 Broke Girls” at 8:30 p.m. NBC’s “The Sing-Off” has performed well in short-term December exposure the past two years, and the CW has a recognizable series in “Gossip Girl.”

Wednesday 8 p.m.

Performance anxiety isn’t unusual among network execs — as in anxiety over whether viewers will finally tire of unscripted performance shows. But “The Voice” overcame skeptics to score big in its spring launch for NBC, and “American Idol” kept chugging along even without the presence of Cowell, considered by many to be its most indispensable cog.

So while some think Cowell’s “X Factor” is at risk of disappointing, it’s hard to imagine X won’t mark the spot for several million viewers at the very worst. And that gives Fox a much bigger presence at 8 p.m. Wednesdays than a year ago, when now-canceled “Lie to Me” started in the slot before hurriedly moving to Mondays to replace “Lone Star.” (“Human Target,” also a goner, replaced “Lie to Me.”)

This sets up a two-show battle for timeslot honors with CBS’ “Survivor,” in its second year on Wednesdays after spending most of the century on Thursdays. Three freshman laffers will try to steal some 18-49 demo love: ABC’s “Suburgatory” (which follows third-year comedy “The Middle”) and NBC newbies “Up All Night,” with Christina Applegate and Will Arnett, and “Free Agents,” with Hank Azaria.

Thursday 9 p.m.

CBS has reloaded in one of TV’s most competitive hours, moving “CSI” to the much tamer timeslot of 10 p.m. Wednesdays. The bigger surprise is that instead of moving “The Mentalist” from 10 p.m. Thursdays to 9, the Eye had enough confidence in new drama “Person of Interest,” with Jim Caviezel, Michael Emerson and Taraji P. Henson, to throw it up against ABC’s “Grey’s Anatomy,” NBC’s “The Office” and Fox’s “Bones.”

Typically a demo darling, “The Office” may begin to decline now that Steve Carell has left, especially if new cast member(s) aren’t considered up to snuff. (Rookie comedy “Whitney” follows at 9:30 p.m.) “Grey’s Anatomy” is coming off what many said was a resurgent season creatively but faces the same issues any series entering its eighth season would. Even the unheralded “Bones” is entering season seven.

That leaves room for “Person of Interest” to make a big first impression, with Emerson’s “Lost” pedigree perhaps helping the show score bigger in adults 18-49 in a time period that has become enticingly unpredictable.

Thursday 10 p.m.

With Fox dropping out of the picture (not to mention the CW), any 10 p.m. slot figures to be less heated than its nightly predecessors. Nevertheless, Thursdays at 10 is worth keeping an eye on.

NBC, which ruled the hour for so long with “ER,” has been adrift ever since. “Prime Suspect,” starring Maria Bello, may not propel NBC back to first place against “The Mentalist,” but it could at least up the Peacock’s perf in the same way that “Parenthood” has improved the net’s fortunes on Tuesday.

At a minimum, fifth-year vet “Private Practice” won’t be the only female-lead show in the hour, and though it benefits significantly from any firstrun “Grey’s Anatomy” as a lead-in, it could be challenged even on its best nights if “Prime Suspect” builds a fanbase.