Earth, Venus, and Mars all show signs of wind erosion today. Particles are blown into waves — from the tiny sand ripples seen by the Mars rovers to giant dunes seen on images from orbiting spacecraft. Dunes are seen on the surfaces of all three planets.

Jupiter formed when rock and ice from the disc of material around the young sun coalesced. The gravity of this dense core then swept up 300 Earth-masses of hydrogen and helium. The rock and ice sank to the centre of the gas giant, but it won’t stay there forever.

Mercury is the smallest of the terrestrial planets. Asteroids are remnants of the early solar system that never came together to form a planet. Why is there little erosion on Mercury’s surface? Mercury doesn’t have an atmosphere.

Yet underneath the top layer of soil and rubble are thousands of hidden glaciers, slowly carving away at the planet, some hundreds of kilometers thick. Even at that rate, Mars’ erosion is still slower than anywhere on earth outside of deep freeze in the Antarctic cold desert.

Reasons for colonizing Mars include curiosity, the potential for humans to provide more in-depth observational research than unmanned rovers, economic interest in its resources, and the possibility that the settlement of other planets could decrease the likelihood of human extinction.

Deposits of up to several micrometers were observed after 10 years of service on the solar panels of the Mir space station. Other sources of problems for structures subjected to outer space are erosion and redeposition of the materials by sputtering caused by fast atoms and micrometeoroids.

Mars has experienced significant bombardment. The southern hemisphere is more heavily cratered than the northern hemisphere. Winds are the main erosional force on Mars and windblown dust and soil erode craters over time.

The moon has almost no erosion because it has no atmosphere. That means it has no wind, it has no weather, and it certainly has no plants. Almost nothing can remove marks on its surface once they are made.

But the surface of Earth, constantly eroded by wind and rain, hides its history. Just 128 confirmed impact craters have been spotted on Earth’s surface.

Vredefort crater

The surface is rich in sulfur, about 20 times richer than the surfaces of Earth, the Moon, and Mars. Messenger also found low surface abundances of titanium and iron. Mercury seems to have formed in conditions much more reducing—i.e., those in which oxygen was scarce—than other terrestrial planets.

No evidence for life has been found on Mercury. Daytime Temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to -180 degrees Celsius (-290 degrees Fahrenheit) at night. It is unlikely life (as we know it) could survive on this planet.

Planet X

This hypothetical Neptune-sized planet orbits our Sun in a highly elongated orbit far beyond Pluto. The object, which the researchers have nicknamed “Planet Nine,” could have a mass about 10 times that of Earth and orbit about 20 times farther from the Sun on average than Neptune.

Venus

It contains the asteroid belt as well as the terrestrial planets, Mercury, Venus, Earth, and Mars. The “gas giants” of course are Jupiter, Saturn, Neptune, and Uranus. So now we have eight planets instead of the nine we used to have.

Neptune

Researchers have discovered a new Earth-sized planet. It’s orbiting a dim red star some 185 light-years away. The planet’s official name is K2-315b. But its nickname is “Pi Earth.” The reason: It orbits its star every 3.14 days.

Venus is the brightest object in the sky after the Sun and the Moon, and sometimes looks like a bright star in the morning or evening sky. The planet is a little smaller than Earth, and is similar to Earth inside. We can’t see the surface of Venus from Earth, because it is covered with thick clouds.