It was supposed to be a £12,000 art project in which a helium-filled sculpture of a desert island floated eerily above the heads of spaced-out festival-goers. It has become instead a £12,000 art project in which a helium-filled sculpture of a desert island floats somewhere through the troposphere without anybody actually seeing it, or even knowing where it is.

Let us round up what we do know. At around 3am on 24 July, as Saturday night at the Secret Garden Party in Cambridgeshire was draining away, a group of five boys was seen cutting the tether ropes that secured the Is Land (as it is known) in place. So determined were these vandals, that two of them requisitioned a dinghy in which they rowed out into a lake to cut the final cable. As they did so, the sculpture floated off and has not been seen since. The Civil Aviation Authority and the local airports were informed, but have not reported any sightings.

"It was pretty devastating," says the artist Sarah Cockings, who returned to the site shortly afterwards to find that six months of her work had gone. "Letting thousands of pounds off into the atmosphere is a little bit too rock'n'roll for me. It wasn't something I took very lightly."

Cockings is confident that she could repair the Is Land, to make it ready for a visit to the Burning Man festival in Nevada. Indeed, she is assured that it will, eventually, return to earth. The question is: where? Using meteorological data, a model has been made to show the sculpture's likely path. To the best of anyone's knowledge, it is right now floating somewhere above the Czech Republic.

There is an appealing romance, Cockings admits, in the Is Land's disappearance – even if her feelings are still too raw to appreciate it. And the incident has fed some new dreams, which may yet come true. "In terms of it being a conceptual project, if somebody filmed it on their phone from a plane, or if it landed somewhere really obscure . . ." Her voice tails off wistfully.

Cockings has been active, launching a website to galvanise interest in the search and getting in touch with several Czech newspapers in the hope that something will turn up. Yet she knows it probably won't. "I guess it could be deemed a publicity stunt," she says, "but sadly it's not . . . It's gutting, but it's hopefully something that in six months' time I can feel a little bit more at ease with . . . I mean, how often in your life do you let a £12,000 planet off into the atmosphere?"