Yes, there is work going on to achieve that. Airplanes can fly quite well in thinner air, they just have to fly faster or have bigger wings. I don't know about

Yes, there is work going on to achieve that. Airplanes can fly quite well in thinner air, they just have to fly faster or have bigger wings. I don't know about helicopters or balloons, but there is a project which aims to bring a solar-powered airplane to Mars. The main problem are the batteries as they have to hold enough energy to fly trough the night. See e.g.: Noth A., Engel W., Siegwart R. Recent Progresses on the Martian Solar Airplane Project Sky-Sailor In Proceedings of the 9th ESA Workshop on Advanced Space Technologies for Robotics (ASTRA 2006), Noordwick, Netherland, 2006. [http://www.sky-sailor.ethz.ch/docs/Sky-Sailor-ASTRA2006_Noth_(13.10.2006).pdf http://www.sky-sailor.ethz.ch/docs/Sky-Sailor-ASTRA2006_Noth...] Noth, A., Bouabdallah, S., Michaud, S., Siegwart, R. and Engel, W. SKY-SAILOR Design of an autonomous solar powered martian airplane. In Proceedings of the 8th ESA Workshop on Advanced Space Technologies for Robotics, (ASTRA 2004), Noordwick, Netherland,2004. [http://www.sky-sailor.ethz.ch/docs/Sky-Sailor-ASTRA2004_Noth_(4.10.2004).pdf http://www.sky-sailor.ethz.ch/docs/Sky-Sailor-ASTRA2004_Noth...] Noth, A., Engel, W. and Siegwart, R. Flying Solo and Solar to Mars - Global Design of a Solar Autonomous Airplane for Sustainable Flight. IEEE Robotics & Automation Magazine, Volume 13, Issue 3, pp 44-52, Sept. 2006. [http://www.sky-sailor.ethz.ch/docs/Flying_Solo_and_Solar_to_Mars.pdf http://www.sky-sailor.ethz.ch/docs/Flying_Solo_and_Solar_to_...] See http://www.sky-sailor.ethz.ch/ http://www.sky-sailor.ethz.ch/ as well for more.