From the article:
Mars rovers, Spirit and Opportunity, have, by now, spent almost two years on the surface of Mars. They traveled several miles each, frequently stopping and analyzing scientific targets with their cameras, spectrometers and other instruments to uncover evidence of liquid water on Mars in the past. Their mission is a smashing success for NASA.
Read the full article here: SpaceDaily_SailingPlanets.pdf (285 downloads)
MORE ABOUT PLANETARY BALLOONS
Read more about Planetary Balloons here