NASA's InSight mission has unlocked the internal structure of Mars, all the way to its core, revealing key differences from Earth. This landmark achievement is detailed in three studies published in the journal Science.
Earth's mantle was first imaged in 1889 using seismic waves from a Japanese earthquake detected in Germany. Our planet's liquid outer core was identified in 1914, and the solid inner core in 1936. The Moon's interior was probed during the Apollo missions. Now, InSight delivers the same for Mars.
Landed in November 2018, InSight captured numerous marsquakes. While most were shallow, some originated deep within the planet. By analyzing shifts in wave speed and direction as they traveled through Mars, mission scientists at NASA's Jet Propulsion Laboratory created this unprecedented internal map.
This breakthrough in planetary seismology offers a vital comparison to the Earth-Moon system, aiding studies of other worlds. "If you're a doctor and you only practice on one patient, you're not going to be a very good doctor," explains Mark Panning, planetary seismologist at NASA's Jet Propulsion Laboratory.
Data confirms Mars' crust is thicker in the southern highlands (up to 72 km) and thinner in the northern lowlands (as low as 24 km), where ancient oceans may have existed. The crust comprises three layers: an upper layer of impact-fractured volcanic rock, a denser mid-layer of volcanic material, and a lower layer with properties still under study.
Mars' mantle dwarfs its crust, much like Earth's. However, the rigid upper mantle—Earth's tectonic plate base—is roughly twice as thick on Mars, potentially explaining the lack of plate tectonics. This rigidity likely prevented crustal fragmentation into plates.
Seismic data indicates Mars' mantle is only half as thick as Earth's, accelerating early heat loss and leaving it cooler today. On Earth, volcanism thrives on internal heat convection; Mars' thin mantle may account for its shift from geologically active to dormant.
This structure also ties to Mars' lost magnetic field. Earth's field arises from liquid outer core convection of iron-nickel alloys. Mars once had similar dynamics, but rapid cooling halted them, stripping its protective shield, atmosphere, and surface water.
InSight sized Mars' core at about 3,670 km in diameter—compressed and less dense than expected, rich in iron and nickel but laced with lighter elements like oxygen, sulfur, and hydrogen.
No quake yet pierced the innermost core, leaving unclear if Mars has a solid inner core like Earth. The mission, extended to December 2022, may yet resolve this.
