[deadbabe]

Why not some helium balloon type craft that could float along with low power for longer periods of times? Could cover vast distances? Descend into fertile plains looking for samples?

[Jabbles]

Helium's lifting capability is proportional to the density of the atmosphere, which is very low on Mars.

[bloopernova]

Is it viable to use vacuum instead of helium?

[nilsherzig]

Wouldn't you need something with some amount of pressure to stop the "shell" you plan to float from collapsing?

[anticensor]

What if we use hydrogen, which is halfway between helium and vacuum?

[deadbabe]

Hydrogen it is.

[M95D]

Hydrogen leaks.