Max Planck Institute for Solar System Research the clouds and winds of Venus. Microwave instruments determine the composition of atmospheres while infrared spectrometers examine surface rocks. A novel laser altimeter on board BepiColumbo will survey the topography of Mercury to within a meter. Further MPS instruments identify the atoms, electrons, and dust that move around the planets and impact their moons. Here the influence of the solar wind on the atmospheric gases is of particular interest. Theoretical studies and intensive computer simulations help to understand the processes both inside and surrounding the planets and to interpret the measured data. Models developed at MPS can describe, for example,
Solar System moons. The centaurs and many short-period comets also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles, such as water, ammonia, and methane than those of the inner Solar System because the lower temperatures allow these compounds to remain solid. The four outer planets, or giant planets (sometimes called Jovian planets), collectively make up 99% of the mass known to orbit the Sun. Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of hydrogen and helium.