"How far up can a helium balloon go? Could it go out to space?" asks Juliet Gok, aged 9.

This calls for some fieldwork! Adam travels to the Meteorology Department at the University of Reading where Dr Keri Nicholl helps him launch a party balloon and track its ascent. But this experiment doesn't quite go to plan.

Meanwhile, Hannah consults Public Astronomer Dr Marek Kukula, from the Royal Observatory Greenwich, to discover where space begins.

And she decides to take matters into her own hands, with the help of a helium canister and some trusty equations, to help answer Juliet's question.

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Presenters: Hannah Fry, Adam Rutherford