Terrestrial Planets

There are four Terrestrial Planets in our Solar System. These Planets happen to be our closest neighbors and the closest to our Sun. They are also known as the Inner Planets. They are Mercury, Venus, Mars, and of course our home Earth. Scientists think that during the formation of our Solar System there were more than likely more Terrestrial Planetoids but that they either merged with each other or were destroyed.

Characteristics of a Terrestrial Planet:

  • Surface conditions may vary but they are made up of rocks or metals with a hard surface.
  • They have heavy metal cores.
  • None of the Terrestrial Planets in our solar systems have rings.
  • They have topological features like craters, valleys, and volcanoes.
  • They have shorter orbits around the Sun as they are closer to it.
  • They rotate slowly.
  • Have very few or no Moons. Earth has one, Mars has two.
Mercury – Photograph © NASA
Venus – Photograph © NASA


Named after the God of Commerce and Messengers (Roman). The first planet from our Sun and the smallest planet in our Solar System. He orbits the Sun every 88 Earth Days. Although he is close to the Sun, radar imaging has reviled highly reflective surfaces at both the poles which indicates the presence of ice in these areas. How is this possible? There are craters at both poles that are permanently in shadow which means that they are cold enough for ice to exist. His surface temperatures can vary wildly from an average of 430 degrees Celsius during the day to -180 degrees Celsius at night. This is because Mercury has a low surface gravity and solar winds constantly hit the Planet which means it doesn’t have much of an atmosphere so it can’t retain the heat at night.


Named after the Goddess of Love and Beauty (Roman). She is the second Planet from the Sun. Even though she is the Second Planet from the Sun, Venus is the hottest planet in our Solar System. Her temperature on average is 462 degrees Celsius. No matter where you are on Venus the temperature remains the same. Her atmosphere is essentially a greenhouse, it has an extremely high level of Carbon Dioxide which traps the heat. Other than our Moon, Venus is the brightest object in our night sky. It’s only not her being one of our neighbors that causes this. When light from the Sun hits a Planet some of it is reflected back. Because Venus’s clouds are highly acidic seventy percent of the light that hits her is reflected back


Home, the blue marble, the third rock from the Sun. Named after the ground we walk on. It is the only planet we know of, that life exists on, a place where millions of different organisms survive. Seventy percent of our planet is covered in water, with our oceans being on average 2.5 miles deep. Her atmosphere is made up of seventy-eight percent nitrogen, twenty once percent, and the last one percent of other gases like water vapor, carbon dioxide, and argon. This atmosphere helps to protect the very life that depends on it by ensuring that many of the meteorites that head our way burn up, by blocking dangerous UV solar radiation, or by keeping our Planet at a temperature suitable for life to thrive.


Named after the God of War (Roman). He is the fourth planet from our Sun. Next to Earth, Mars is the most explored planet in our Solar System. The USA, UEA, China, India, and Russia to name but a few have sent a variety of spacecraft to explore the Planet. The next couple of decades will probably see the first manned missions to Mars. Mars has two small Moons Phobos and Deimos. Interestingly Phobos is so close to Mars, that Mars gravity is slowly pulling the Moon closer. This means that millions of years from now, Phobos will be close enough to Mars to be pulled apart. His beautiful red color is caused by the rusty iron oxide found in the rocks and soil. In the past it appears that Mars had water just like Earth, he has river valleys, lakebeds, and rocks/minerals on the surface that can only exist if there had been liquid water on the surface.

Astronomy with EcoTraining

Astronomy is the scientific study of celestial objects, space, and the physical universe as a whole.

Are you curious with a deep desire to understand some of the grandest and most beautiful phenomena in the universe?

EcoTraining is including modules on Astronomy as part of our On-Demand courses.

Here you go! A sneak preview of what you can look forward to as part of our On-Demand courses soon to be launched!!

About The Author

Written by Emma Summers

Emma Summers is an EcoTraining Camp Manager at Selati Game Reserve.