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Mars’s Dichotomy and Its Evolutionary Path
Context:
A recent study published in Geophysical Research Letters has challenged the long-held belief that Mars’s distinct northern and southern hemispheres were formed by giant impacts. Instead, the research suggests that mantle convection is the primary cause of this phenomenon, known as the Martian dichotomy.
Origin of the Dichotomy
- Researchers have debated the origins of this dichotomy, with two main hypotheses:
- Giant impacts (large celestial bodies about 2,000 kilometres in diameter) could have caused the variations in elevation.
- Mantle convection, driven by temperature and density differences in Mars’s interior, might be the primary cause.
- The study published in Geophysical Research Letters seeks to explore these theories, especially focusing on mantle convection as the key driver.
Understanding Martian Dichotomy
- Mars has distinct northern and southern hemispheres, each with unique characteristics:
- The Southern Highlands are older, higher, and more cratered.
- The Northern Lowlands are flatter and less cratered.
- The Southern Highlands’ elevated terrain acts as a barrier to airflow, affecting wind patterns and contributing to localised weather phenomena.
Research Methodology
- Marsquakes (seismic activity on Mars) were studied to gain insights into the internal structure of the planet.
- Using data from NASA’s InSight mission (2018-2022), which recorded seismic waves through a single seismometer, the team analysed the movements of waves from marsquakes in different regions: Terra Cimmeria (Southern Highlands) and Cerberus Fossae (Northern Lowlands).
- The seismic waves helped researchers probe Mars’s crust, mantle, and core, revealing differences in the planet’s internal dynamics.
Key Findings:
- The team found that seismic waves from the Southern Highlands (Terra Cimmeria) weakened more compared to those from the Northern Lowlands (Cerberus Fossae). This difference is known as seismic attenuation.
- The lower quality factor (more wave weakening) in the Southern Highlands suggests that the mantle beneath this region is hotter and more viscous than the Northern Lowlands. Specifically:
- The mantle beneath the Southern Highlands could reach 1,000°C, while beneath the Northern Lowlands, it’s about 800°C or slightly higher.
- The thicker southern crust retains heat more effectively, leading to more vigorous convection in the mantle.
Challenges
- Limited Equipment: Unlike Earth, where thousands of seismometers continuously monitor ground motion, Mars had only one operational seismometer during the InSight mission.
- Low Tectonic Activity: Mars experiences fewer and weaker marsquakes compared to Earth’s earthquakes.
- Noise Interference: Diurnal winds on Mars reduced the signal-to-noise ratio of seismic data, requiring advanced processing techniques to extract meaningful information.
Future Research Directions
- Mars’s Crust: Mars has a thicker crust (~50 km) than Earth’s continental crust (~35 km) or oceanic crust (~10 km). Understanding why Mars’s crust is so thick despite being smaller than Earth could provide insights into its geological history.
- Liquid Water on Mars: Evidence suggests that Mars once had vast oceans, but much of the water may have been lost or sequestered in the crust.
- The researchers plan to use seismological techniques to investigate whether liquid water persists beneath the Martian crust, which could have implications for past or potential future life on Mars.
Implications
- Expanding Seismic Studies: Investigating variations in crustal thickness across Mars to better understand its internal structure.
- Exploring Subsurface Water: Employing advanced seismological techniques to determine whether liquid water persists beneath Mars’s surface.
