Noah Wyle on Falling Skies season two and Steven Spielberg

Doe-eyed actor Noah Wyle set pulses racing as medical student-turned-doctor John Carter in ER. He started out alongside George Clooney and eventually became the show's longest-serving cast member, reportedly commanding 400,000 dollars an episode.

Now he's graduated from saving lives to saving the world from aliens, playing the lead role in Steven Spielberg's TV series Falling Skies, airing here on digital channel FX.

The 41-year-old actor plays Tom Mason, a history professor who leads the charge against aliens in the apocalyptic landscape of post-invasion America.

Having lost his wife to the aliens - known in the show as 'skitters' - he's charged with looking after his three sons as well as a band of survivors grouped together in a camp they refer to as 2nd Massachusetts.

Although Tom remained level-headed throughout most of the first series, it ended with the hero surprising both his camp mates and the audience by agreeing to board the alien spaceship.

The show is broadcast in more than 75 countries and, with millions of people on tenterhooks after the cliffhanger of the first season finale, Noah Wyle can only give away a few clues as to how the new series will begin.

"When Tom's let off, he's plagued with questions: Why did the aliens let him go? Is he going to be a liability when he finds the group again? Will his kids still be alive?" the star says.

Spielberg's the man

The series is high concept in theme and filmic in style, as you might expect from the man who brought us Jurassic Park, E.T. and Jaws.

"It gives you great confidence to know that your work is being given over to the most masterful storyteller of the 20th century. It's still amazing to me, and incredibly gratifying, that Steven's as involved in every level of production as he is, from shaping the scripts to casting, and spending a lot of time in this place designing."

Although the aliens are fantastical to the usual Spielberg level, Falling Skies has a domestic drama at heart - that of a man trying to save his family, and the relationships between camp mates are a key part of the drama.

Noah Wyle says that in this second season they will be even more strained than before. "I think when Tom gets off the spaceship, he realises there's no peace to be brokered, there's no negotiation to be had and there's no future for anybody until this threat's been eradicated or lifted. So, nobody's harbouring any sense of hope any longer."

It sounds a universe away from the wards of the Chicago Country General Hospital. Speaking of that show, Noah's former co-star George Clooney was in touch recently. Just days before our interview, the Falling Skies man was arrested after taking part in a demonstration against health cuts in Washington.

Clooney, who himself was arrested for taking part in a protest outside the Sudanese embassy in Washington, showed his support in a typically dry way. "He texted me and offered me the bail money," laughs Noah.

Just as working on ER made Wyle more aware of problems in the health system, filming Falling Skies has made him think about his own survival skills.

"It's made me realise how cowardly I really am," he says, shaking his head. But he makes surviving in the stripped-backed world of 2nd Massachusetts look very real.

Falling Skies, season two, airs on FX from 3 July at 9pm