Mystery that 'splits Mars in two' finally solved after 50 years - thanks to a 'Marsquake'

Recordings of earthquakes on Mars — or “marsquakes” — might have finally solved the mystery surrounding why one half of the planet is drastically different from the other.

Researchers have been aware that Mars has two main areas, known as the Martian dichotomy, since the 1970s. Around one-third of planet’s northern hemisphere is covered by the northern lowlands, while the southern highlands cover around two-thirds of the Red Planet.

There is a difference in elevation and crustal thickness between the northern and southern hemispheres, with the latter being higher in elevation with a thicker crust. There are two main theories about how this came to be — one suggests it was due to a process within Mars’ interior, while the other theory considers the possibility of a massive collision with an object the size of the moon, or multiple smaller rocks.

The ages of the rocks on Mars’ surface, however, suggests that whatever caused the dichotomy occurred in the early days of our solar system, making it hard to define an exact cause.

However we might be closer to an answer. A study published in December 2024 in the journal Geophysical Research Letters which includes analysed data from NASA’s InSight lander which records how seismic waves from marsquakes reverberate within Mars.

InSight is located close to the border between the northern lowlands and southern highlands. This allowed the researchers to compare how seismic waves moved through the mantle below two sites, with one on each side of the divide.

Artist's impression of Mars four billion years agoflickr

The research team worked with the data to see if they could find any evidence of an internal origin for Mars’ dichotomy.

The study authors wrote in The Conversation: “Comparing these two [sites] showed that the waves lost energy more quickly in the southern highlands. The most likely explanation is that the [molten] rock beneath the southern highlands is hotter than in the north."

The team believes a temperature difference between the two halves can be explained by ancient tectonic activity that no longer happens on Mars. They added: “This temperature difference between the two halves of the dichotomy supports the idea that the split was caused by internal forces on Mars, not some external impact."

"At one point, Mars had moving tectonic plates like Earth does," the researchers explained.

"The movement of these plates and the molten rock beneath them could have created something like the dichotomy, which was then frozen in place when the tectonic plates stopped moving to form what scientists call a 'stagnant lid' on the planet's molten interior."

The researchers said more marsquake data, as well as detailed models of how Mars formed, would be needed to conclusively answer the question of why one half of Mars is so different to the other.

Until this happens, marsquake is a fun word to add to your vocabulary.

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