How similar are Mars and Earth? Let’s look at some key facts — and why all of this is closely linked to the Artemis programme.
With the Artemis programme, humanity will return to the Moon for two main reasons: to stay, and to set off again. But set off for where? To go further, towards the next destination with a very clear name: Mars.
A planet rich in science
Whether because of its unusual motion across the sky or its striking bright‑red colour, who knows, what is certain is the starring role that both the astronomical community and the public imagination have long assigned to Mars. Its vivid red hue, reminiscent of blood, made it a central figure in myths and legends passed down through ancient civilisations such as the Maya, Greeks, and Romans, who believed the planet was in fact the god of war (a bit dramatic, perhaps).
Today, however, we know that Mars’ characteristic colour is due to the abundance of iron oxides and hydroxides coating its surface. In other words, we could say that Mars is “rusty”, although scraping just beneath the surface reveals shades ranging from grey to black, with hints of green.
Once it became clear that the planet was peaceful in nature, and that its redness was not caused by rivers of blood, scientists turned their attention to the many geological similarities Mars shares with Earth. These analogies have made it one of the prime candidates in the search for biosignatures: anything that might shout, “Hey, there’s life here!”
How similar are Mars and Earth?
Mars is the fourth planet in the Solar System, with an average distance from the Sun of about 228 million kilometres (1.524 AU), and it sits immediately beyond Earth. This makes the “Red Planet” the first of the outer planets, those orbiting beyond Earth’s orbit.
In terms of size, Mars has an equatorial diameter of 6,787 kilometres (roughly half that of Earth) and shows slight polar flattening (flattening factor 0.009). Its orbit is noticeably elliptical and takes about two Earth years to complete (687 days). Its rotation period, the Martian day, or “sol”, is only slightly longer than Earth’s, at 24 hours, 37 minutes, and 25 seconds. The Martian axial tilt is 25°19’.
Surface temperatures range from –63 °C to 14 °C on average, with recorded extremes of 20 °C and –153 °C. (In short: if you’re planning a holiday on Mars, pack something very warm).
Atmospheric composition
As for its atmosphere, Mars is composed of roughly 95% carbon dioxide, 2.59% molecular nitrogen, and 1.94% argon. The remaining trace components include gases of astrobiological interest such as oxygen and methane.
All in all, Mars certainly shares some similarities with our own planet, but at the same time, many differences remain, highlighting the current challenges for the development and survival of potential life forms.
