For a long time, scientists thought the inside of Mars was fairly even in temperature.
New research has now revealed a large heat anomaly deep within the planet.
An anomaly is something unusual that does not match what we expected.
The study suggests that the southern interior may be hundreds of degrees hotter than the north.
Part of this deep material could even be molten, meaning it is partly melted rock.
Such a big difference in temperature was a real surprise to researchers.
This finding changes how scientists understand the planet's structure and history.
It shows that Mars is far more complex on the inside than we once believed.