Long story.
Terra Nova was supposed to be a massive hit, what with the subject matter and the Spielberg name and the amount of money they've been spending on it. But the debut ratings were far below expectations and have since slipped downward to a level that would put ANY show in jeopardy, especially one as expensive as this one.
To be fair, Terra Nova has had a run of bad ratings luck. One early episode got delayed almost an hour when the baseball playoffs ran long... which dealt a hit to the ratings and even more of a hit to the DVR numbers, when people booted up their DVR's to watch TN and got baseball instead. (a lot of House viewers were equally dismayed when their House recording turned out to be full of Terra Nova.
)
Then the show was pre-empted for a week because Fox was running the World Series. The week after THAT, Terra Nova aired on Halloween night, when their target audience was trick-or-treating, so the ratings were low again (but did recover once DVR views were counted).
Last week's episode was the first in a while that didn't have some extenuating circumstance to blame... and yet the ratings stayed solidly in the "meh" zone. As a result, more than one Nielsen-watching expert has now put the show officially on the endangered list.
But... I dunno. First of all, TN is already airing in several foreign markets. I'm not following the ratings offshore, but if they're significant enough, that could help Terra Nova's chances.
Next - most every show starts the season with a 13 episode order from the network. A key indicator of the network's mood is when - or if - they order the "back nine" episodes for a full-season total of 22. If a new show dies fast enough (Studio 60, Firefly), there's no "back nine" and thirteen episodes is all there ever is. If a show goes the full 22, of course it can still be canceled at the end of the season, but at least the network's given it a full season to find its audience.
But somewhat unusually, Terra Nova will only be 13 episodes in its first season, no matter what, and those episodes have already been shot. That was a decision made long before it ever aired. So there's no "back nine" decision to be made. This is lucky for Fox, because right about now they'd have to be pulling the trigger on the back nine or not. What they've opted to do instead is announce that all the remaining episodes will air in order and without being bumped.
So they won't move the show to another time slot, or pull it off the schedule and then burn the remaining episodes off next spring, or any of the other things that people like to point to later as excuses for how a network ruined a show that otherwise would have been - supposedly - a huge hit.
This all good news for Fox, because they don't have to be bad guys and cancel Terra Nova - instead they can just quietly not renew it later. They'll air the remaining episodes and then they can just say nothing for the rest of the season, if they don't want to. Maybe not even until they announce next year's lineup and wait to see if anyone notices that Terra Nova's not on it.
But there's also the wildcard - Steven Spielberg could step in and throw his weight around and get another season that way. Might have to make some concessions to make it happen (budget cuts for example, but I wouldn't say that's a bad thing). He got a second season out of Amazing Stories even after that turned out to be a not-so-successful venture, too.
My completely-unscientific guess right now is - Terra Nova gets a second season. Everybody involved seemed to think they'd made the Greatest Show Evar - until the debut ratings came back and they realized they'd just shit themselves in public. It's in everyone's interest to keep it on the air - if for no other reason than as a face-saving gesture all around.