Size of earth vs mars
Pro Research Analysisby 
Searched over 200M research papers
Comparative Analysis of Earth and Mars: Size and Formation
Size Comparison: Earth vs. Mars
Mars is significantly smaller than Earth. Mars has an average diameter of 6,792 km, which places it between the size of Earth and the Moon, making it the seventh smallest planet in the Solar System. In terms of surface area, Mars has approximately 144,798,500 km², which is about 28% of Earth's surface area and roughly equivalent to the area of Earth's dry land.
Formation and Growth: Viscous Stirred Pebble Accretion (VSPA)
The size difference between Earth and Mars has puzzled scientists for a long time. Traditional planet formation models have struggled to explain why Mars is so much smaller than Earth. However, the Viscous Stirred Pebble Accretion (VSPA) model offers a compelling explanation. This model, which has been used to explain the formation of gas giants, suggests that Mars's growth was stunted due to the inefficiency of pebble accretion beyond approximately 1.5 astronomical units (AU) from the Sun. This inefficiency prevented Mars from accumulating mass at the same rate as Earth, resulting in its smaller size.
Mars as a Planetary Embryo
Another hypothesis is that Mars is a stranded planetary embryo. Terrestrial planets, including Earth, are thought to have formed through collisions between large planetary embryos. Mars, however, may have escaped these collisions and mergers, which allowed it to remain smaller. Studies using the 182Hf-182W decay system in Martian meteorites suggest that Mars accreted very rapidly, reaching about half of its present size in just a few million years. This rapid growth supports the idea that Mars is a planetary embryo that did not undergo significant further collisions.
Water Content and Accretional Histories
The differences in water content between Earth and Mars also provide clues to their accretional histories. Earth's mantle contains significantly more water than Mars's mantle. This disparity is partly due to Earth's plate tectonics, which recycle water into the mantle. Mars, lacking such tectonic activity, has a much drier mantle. Additionally, the smaller size and greater distance from the Sun may have prevented Mars from melting during its formation, limiting the incorporation of water into its interior. Instead, Mars's water likely remained as a surface veneer, consistent with its geologic history of a wet surface but a dry interior.
Conclusion
In summary, the size difference between Earth and Mars can be attributed to several factors, including the inefficiency of pebble accretion beyond 1.5 AU, Mars's status as a stranded planetary embryo, and differences in their water content and accretional histories. These insights not only explain the smaller size of Mars but also enhance our understanding of planetary formation in our Solar System.
Sources and full results
Most relevant research papers on this topic