... solar system . ... Earth's magnetic field provides vital protection . ... Using the European Space Agencyт??s (ESA) Cluster and Mars Express missions to provide data from Earth and Mars, respectively, scientists compared the loss of oxygen from the two planetsт?? atmospheres as the same stream of solar wind hit them. ... Venus will provide an important new perspective on the issue because, like Mars, it has no global magnetic field, yet it is similar in size to Earth and has a much thicker...