A few years ago, special balloons (called Aerobot) were used to carry limited astronomical instruments up to the higher strata of atmosphere.
There are made of a waterproof outer covering containing hydrogen or helium. As both these gases are lighter than air, the balloons tend to rise to great heights up to 40,000 mts.
The instruments carried up by these balloons Aerobot help to collect a great deal of information. Hence, these balloons Aerobot today have become indispensable research instruments.
Below Balloon Aerobot info from Wikipedia (Read More):-
An aerobot is an aerial robot, usually used in the context of an unmanned space probe or unmanned aerial vehicle.
While work has been done since the 1960s on robot "rovers" to explore the Moon and other worlds in the Solar system, such machines have limitations. They tend to be expensive and have limited range, and due to the communications time lags over interplanetary distances, they have to be smart enough to navigate without disabling themselves.
For planets with atmospheres of any substance, however, there is an alternative: an autonomous flying robot, or "aerobot" [1][2] Most aerobot concepts are based on aerostats, primarily balloons, but occasionally airships. Flying above obstructions in the winds, a balloon could explore large regions of a planet in great detail for relatively low cost. Airplanes for planetary exploration have also been proposed.
http://en.wikipedia.org/wiki/Aerobot
