InSight Discoveries That Changed Our View of the Red Planet

How InSight Measures Marsquakes — Explained

Overview

NASA’s InSight lander studies seismic activity on Mars to reveal the planet’s interior structure. The mission uses sensitive instruments to detect ground vibrations (marsquakes), distinguish seismic sources, and translate those signals into models of the crust, mantle, and core.

Key Instruments

How SEIS Works

1. Very low-noise seismometer: SEIS is isolated from lander noise by a leveling and mounting system, then covered with a wind and thermal shield to minimize environmental interference.
2. Broadband and short-period sensors: SEIS contains multiple sensors that record a wide range of frequencies, allowing detection of both long-period signals (deep interior) and high-frequency signals (near-surface sources).
3. High dynamic range and sampling: Continuous, high-resolution sampling captures tiny ground motions (down to nanometer-scale), enabling identification of small marsquakes.

Detecting a Marsquake

1. Continuous monitoring: SEIS records background vibrations and transient events — both natural (marsquakes, meteoroid impacts) and environmental (winds, thermal flexing).
2. Signal filtering and stacking: Engineers filter out known noise sources (lander operations, wind) and stack repeatable signals to boost quake signatures.
3. Event classification: Seismic events are classified by waveform shape, frequency content, and duration to separate quakes, impacts, and atmospheric signals.

Locating and Characterizing Quakes

• Arrival times of seismic phases: Analysts identify primary (P) and secondary (S) wave arrivals in waveforms. The time difference between P and S gives distance to the source.
• Back-azimuth estimation: With only one seismometer on Mars, back-azimuth (direction) is estimated using particle-motion analysis and comparisons across frequency bands.
• Magnitude and depth estimation: Amplitude and frequency content constrain quake magnitude; depth is inferred from waveform characteristics and modeling.
• Use of complementary data: RISE radio tracking constrains internal structure, and HP3 heat data helps interpret mechanical properties affecting wave speeds.

From Waveforms to Planetary Structure

• Velocity profiles: Seismic wave speeds depend on material composition, temperature, and state (solid vs. liquid). Measured travel times are inverted to produce depth-varying velocity models.
• Core detection: Long-period signals and observations of surface waves help determine whether the core is solid or liquid and estimate its size.
• Crust and mantle: Seismic arrival times and waveform dispersion reveal crustal thickness, mantle layering, and potential discontinuities.

Challenges and Solutions

• Single-station limitation: With only one seismometer, location accuracy is limited. InSight overcomes this using detailed waveform modeling, surface wave analysis, and correlations with impact detections via orbital imaging.
• Environmental noise: Wind and thermal effects produce noise. The wind shield, careful instrument placement, and data filtering reduce contamination.
• Small seismicity: Marsquakes are generally weaker than Earthquakes. SEIS’s extreme sensitivity and long-duration monitoring allow detection of small events over time.

Major Findings to Date

• Mars experiences frequent low-magnitude seismic events concentrated in specific regions.
• The crust is thicker than initially predicted in some areas; the mantle shows layering.
• Evidence indicates a liquid outer core, providing constraints on core size and composition.

Why It Matters

Seismic measurements are the most direct way to probe planetary interiors. InSight’s data refine models of Mars’ formation and thermal evolution, inform comparative planetology, and guide future exploration strategies.

Further Reading

• NASA InSight mission pages and SEIS instrument papers provide technical details and ongoing results.