Talulah Riley has made her new husband a promise. 'I've told him I'll retire with him to Mars,' she says matter-of-factly. 'If he has colonised it by then.' She smiles, but she is coolly earnest. She was once a starlet from Hertfordshire, but she now moves in interplanetary circles. Her husband is the internet billionaire turned space entrepreneur Elon Musk, and her future home is an environmentally controlled pod on Mars. Elon will zoom around outside on rockets, while she makes their biosphere cosy. 'I'd love to get involved with designing habitat systems on Mars – like housekeeping on a grand scale,' she says dreamily.