Venus is a rocky planet with an extremely dense atmosphere that heats up as a result of a “runaway” greenhouse effect. This explains why Venus’s surface temperature is so much higher than Earth’s.
Mars is a planet with an extremely thin atmosphere that does not warm up as much. This explains why Mars’s average surface temperature is significantly lower than that of Earth.
Size and Mass
Venus and Mars share many similarities, including their terrestrial nature (meaning they have an atmosphere and solid surface) and their close proximity to the Sun. But despite their similarities they are also very different in other ways.
The most obvious difference between the two planets is that Venus is much larger than Mars. While they both have a mean radius of 3,760 miles, Venus is almost twice as large in diameter.
This difference translates into a difference in weight as well, as gravity is an effect of the planet’s mass. Because of this, a 100-pound person on Earth would weigh 38 pounds on Mars.
The size of a planet is not only affected by the distance it is from the sun but also by its rotation. Most planets in the solar system rotate rapidly, so their diameters bulge slightly at the equator and differ from one pole to the other.
Atmosphere
Atmospheres are the chemical compounds that make up the atmosphere of planets. They are the key to keeping a planet warm enough for life.
Our Earth’s atmosphere is mainly carbon dioxide (CO2). This gas was originally in a form that could not support life, but today it has been removed by the processes of plants and animals.
Venus and Mars also have carbon dioxide in their atmospheres, but it is in a different form than on Earth. This is because they have had to go through a process called evolution to get their atmospheres to where they are now.
Early on, Venus and Mars had thicker atmospheres. This was probably due to the delivery of volatiles from asteroids and comets and volcanic outgassing from their rocky interiors.
Surface Conditions
Mars and Venus, two of the planets in our solar system known for their contrasting surface conditions, have more in common than you might expect. Two nearly identical spacecraft around each of these worlds are taking measurements of their atmospheres as they interact with solar radiation.
The Venus Express magnetometer instrument has discovered that the structure of the magnetic field on both planets is surprisingly similar, even though their atmospheres are different. This discovery is based on the fact that both planets have a dense ionosphere at 250 km altitude, which is a shell of charged particles surrounding each planet’s upper atmosphere.
This dense shell of electrically charged particles can act as a barrier between the planets’ surface and the Sun’s magnetic field, causing some to spin faster than others and create storms and other forms of activity. These events help to maintain a weak but robust magnetic field, which drapes itself around each planet and stretches behind the night-side in a long tail.
Temperature
Despite their similar distance from the Sun, Venus and Mars differ in temperature. While Venus is the hottest planet, Mars’s temperature is colder than Earth’s.
The reason for this is that Venus has a thick atmosphere and gets more of the Sun’s heat reflected back to it than does Mars. This is what creates the greenhouse effect.
On the other hand, Mars has a thin atmosphere and very little of the Sun’s heat is reflected back to it. This is why Mars’s temperature is so cold.
Another difference between the two planets is that Venus has a small magnetosphere which helps protect it against solar winds. On the other hand, Mars has no such protective shield and therefore is much more vulnerable to solar storms.
However, it’s not clear why this is so. One possibility is that a small magnetic field was originally present on Mars, but that has since been lost. This may have been a part of the reason why the Martian atmosphere is so thin.