The terrestrial planets are the name given to the four planets which are closest to the sun: Mercury, Venus, Earth, and Mars, all of which share a similar composition primarily of silicate rocks or metals.Terrestrial planets are defined by their solid planetary surface, which sets them apart from the outer gaseous planets, Jupiter, Saturn, Neptune, and Uranus.
How Large is Mars Compared to the Terrestrial Planets?
Mars is the fourth of the terrestrial planets and is known for its distinctive reddish-brown color. The planet has a diameter of 4,212 miles or 6,794 km, and in total it roughly measures just over half of Earth’s diameter.
While it’s smaller than Earth and Venus, it’s not the smallest of the terrestrial planets, as Mercury spans just 3,032 miles - a diameter over 1,000 miles shorter than Mars'. However, Mars is only 30% larger than Mercury.
Earth is far larger than Mars, which is equivalent to 15% the volume and 10% the mass of Earth. Compared to Earth, Mars has a gravitational pull that’s 62% weaker than Earth’s. Though surprisingly, because water covers about 70% of Earth’s surface, Mars and Earth actually have a similar landmass.
How Massive are the Terrestrial Planets?
Earth is the largest terrestrial planet and is composed of metals and silicate rocks, an iron core, silicate mantle, and crust. It is the largest of the terrestrial planets, with an average radius of 6,371.0 km (3,958.8 mi). It’s also the densest, with a mean density of 5.514 g/cm3.
Unsurprisingly, Earth also has the greatest mass of the terrestrial planets, boasting a mass of 5.97 x 1024 kg (equivalent to 5,970,000,000,000 trillion metric tons). This results in a surface gravity of 9.8 m/s², or 1 g.
Venus possesses similar qualities to Earth, and for this reason, it’s often known as “Earth’s Sister Planet.” Like the other terrestrial planets, it has a high density, and is actually the third densest in the solar system behind Earth and Mercury, with a density of 5.243 g/cm³.
In terms of mass, Venus is pretty heavy, weighing in at 4.87 x 1024 kg - the equivalent of 4,870,000,000 trillion metric tons. This is also the equivalent of 0.815 Earths, making Venus the second most massive terrestrial planet in the Solar System.
Venus is also comparable to Earth in terms of its gravity, which measures roughly 8.87 m/s², or 0.9 g.
As we mentioned earlier in this article, Mars is the second smallest terrestrial planet and the second smallest planet in the entire Solar System, too. While it is roughly half the size of Earth, it is only one-tenth as massive.
Mars has a mass of 0.642 x1024 kg, which equates to 642,000,000 trillion metric tons, or roughly 0.11 the mass of Earth. Mars has a surface gravity of 3.711 m/s² (or 0.376 g).
Mercury is the smallest of the terrestrial planets, and is also the Solar System’s smallest planet, with an average diameter of 4879 km (3031.67 mi). Contrastingly, it has a high density of 5.427 g/cm3, second only to Earth.
Like the other terrestrial planets, Mercury is composed of silicate rock and minerals, however, in contrast to the others, it has an abnormally large metallic core relative to its crust and mantle.
Mercury has a mass of roughly 0.330 x 1024 kg, which works out to 330,000,000 trillion metric tons - the equivalent of 0.055 Earths! Combined with its density and size, Mercury has a surface gravity of 3.7 m/s² (or 0.38 g).
Other Differences Between the Terrestrial Planets
While Mars is often referred to as one of the most “hospitable” planets, and the most likely to accommodate human life one day, the atmosphere in Mars is 100x thinner than Earth’s, and therefore it cannot retain heat adequately.
On Earth, we can expect average temperatures of approximately 14.6℃ or 58.3℉, however, due to the thinner atmosphere on Mars, temperatures can change drastically.
The extremes in temperatures would be easily felt if you were to stand on Mars with no protective gear, as you could expect a difference in temperature of 15 degrees (in Fahrenheit) between your head and your feet.
The temperature on Mars is notoriously sporadic, and this is what causes the famous sandstorms that can last for months on end.
There is also a huge difference between the temperatures of Venus and Mars. At over 500°C hotter than Mars, Venus is the hottest planet in the solar system.
Mars has an average surface pressure of 6 to 8 millibars. This amounts to under 1% of Earth’s surface pressure at sea level, which is 1,013 millibars.
Venus has a thicker atmosphere than Earth and therefore has a higher surface pressure of 93 bars. This is the equivalent feeling of being deep underwater at a depth of 3,000 feet!
In terms of surface pressure, Mercury differs from the other terrestrial planets entirely. It has a surface pressure of 0.005 picobar - that’s less than one-trillionth of Earth’s.
Mars has an axial tilt of 25.19°, which is comparable to Earth’s at 23.5°. This means both planets experience four seasons. However, Mars orbits the Sun at a slower pace than Earth does, which is why its seasons are twice as long as ours.
On the other hand, Mercury has an axial tilt of 2°, meaning it rotates practically upright and therefore has no seasons. Venus is also only titled at 3°, however, regardless of this, Venus’ temperatures remain high at all times due to the runaway greenhouse effect, and this means it also has no seasons.
We often think of Mount Everest (29,029 feet or 5.5 miles)
as being unsurpassable in size, however Mars’ highest point, the huge volcano Olympus Mons rises about 15.5 miles (25 km) above the planet’s surface, and Venus’s Maxwell Montes is slightly higher than Everest at 6.8 miles (11 km) tall. Contrastingly, Mercury’s Caloris Montes is just 2.8 miles (4.4 km) higher than the surface of this small planet.
We hope you enjoyed learning about the terrestrial planets in this article.
As you can see, these four planets share several similarities in their compositions, however, they also feature a wealth of differences to do with their temperature, axial tilt, mass, and density.