It currently takes Juno 53 days to fly around the solar system's biggest planet, which is almost four times longer than the intended 14-day orbit.

After repeated delays, Nasa decided late last week to forego an engine firing that would have shortened the orbit. Officials said the manoeuvre poses too much of a risk.

Nasa said the quality of science will not be affected, but it will take more time to gather the data, given Juno's longer loops.

The mission will have to be extended at a cost of tens of millions of extra dollars if scientists are to collect everything under the original plan. It is already a billion-dollar mission.

Juno has been circling Jupiter since July.