Would a helium balloon float on the moon?

We put this to Phil Rosenberg of the MET Office, Facility for Airborne Atmospheric Measurement

As far as the balloon's concerned you need two things to make a balloon float. First you need an atmosphere for it to float in. The second thing you need is gravity. That's because the reason why a balloon floats is that the balloon itself is less dense than the air around it so gravity pulls on the air around it more than the balloon. The air around it actually tries to push underneath the balloon. That forces the balloon up and makes it float. Unfortunately the moon hasn't got an atmosphere at all. Therefore you're missing one of the two things that you need to make a balloon float. In that case a balloon on the moon wouldn't float at all. It would just land on the floor. However, that doesn't mean you can't have balloons or other bodies in space at all. Actually the Russians launched a space mission in the 80s called Vega. That involves putting a balloon in the atmosphere of Venus which is the second-closest planet to the sun. Balloons in space are possible and have been done in the past. Looking to the future there's a possibility we might be looking at putting balloons on titan which is one of Saturn's moons. Titan has got an atmosphere and it's really cold there. There's obviously gravity there. Therefore you've got all the things you might need to have a balloon on Titan. The reason to do that would be to have atmospheric instruments that you would hang from the bottom of the balloon and they would measure Titan's atmosphere. That's exactly what we've done on Venus with the Vega mission. So unfortunately no balloons on the moon but they do have uses elsewhere in the solar system. Not just on the Earth.