Scientists have discovered that Mars has an interior structure similar to Earth's. Results from NASA's InSight mission suggest that the red planet has a solid inner core surrounded by a liquid outer core, potentially resolving a longstanding mystery.

The findings, which are published in Nature, have important implications for our understanding of how Mars evolved. Billions of years ago, the planet may have had a thicker atmosphere that allowed liquid water to flow on the surface.

This thicker atmosphere may have been kept in place by a protective magnetic field, like the one Earth has. However, Mars lacks such a field today. Scientists have wondered whether the loss of this magnetic field led to the red planet losing its atmosphere to space over time and becoming the cold, dry desert it is today.

From residual magnetization in the crust, we think that Mars did once have a magnetic field, possibly from a core structure similar to that of Earth. However, scientists think that the core must have cooled and stopped moving at some point in its history.