- 3724 - MARSQUAKES - how they analyze the planet? “Marsquakes” are earthquakes that occur on the planet Mars. Astronomers can measure them just like we measure earthquakes from our orbiting satellites. Astronomers have observed seismic waves propagating along the surface of Mars in the same way.
--------------------- 3724 - MARSQUAKES - how they analyze the planet?
- The “marsquakes” that resulted from two large meteorites that hit Mars were recorded by NASA's ‘InSight lander”. These recordings provided new insights into the structure of the Martian crust, bringing scientists closer to learning how the planet formed and evolved over time.
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- After almost three years of detecting only “body waves” which are seismic waves traveling through the body of a planet, on Mars. The InSight observed surface waves in late December, 2021, when two meteorites collided with the red planet.
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- Data from the Mars Reconnaissance Orbiter confirmed that both meteorites had hypocenters (the point of origin for a quake) on the surface of Mars. Before this, all our knowledge of the Martian crust was based on what was right below the InSight lander.
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- Scientists didn't know if the crust was different in other locations across the planet. With these surface waves, they were finally able to obtain a better understanding of the crust along a big stretch of Mars.
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- A planet's crust, or its outermost solid shell, provides important clues about how that planet formed and evolved over time. Most planetary crusts, including those of Earth and Mars, formed through early dynamic processes in the mantle and were later modified by other events such as volcanism, sedimentation, erosion and impact cratering. Crust analysis can allow researchers to gain a better understanding of the land-shaping conditions of a planet from billions of years ago.
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- They analyzed the velocity of surface waves coming from the two meteorite impacts. They could determine the relationship between surface wave velocity, frequency and depth to estimate the average properties of the crust 3 to 18.6 miles below the surface.
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- On average, the two meteorite impact sites did not vary strongly with depth and had faster seismic velocity than what was previously observed directly below the lander. The faster velocities suggest either compositional differences or reduced porosity in areas traversed by the surface waves.
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- The composition of the crust will determine some of the density, but so will factors like porosity; if you have a lot of holes in the crust, it can also decrease the density of the material.
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- A volcano, with all its intrusions and magma coming up through the crust beneath it, would have also altered the crust density and composition in that region. Mars has a very unique feature, which is the very sharp contrast between its Northern and Southern hemispheres.
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- The southern part is really old, has high topography and is very heavily cratered. Meanwhile, the northern region is volcanic, very low-lying and has comparatively few craters.
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- Researchers have been analyzing the measurements made by the NASA InSight mission's seismometer. The Mars Reconnaissance Orbiter in late December 2021 showed a large impact crater about 3,500 kilometers from InSight. They were also able to pinpoint a meteorite impact at just under 5,000 miles from InSight as the source of a second atypical quake.
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- Because the hypocenter of each earthquake was at the surface, they generated not only seismic body waves similar to previously recorded marsquakes in which the hypocenters were at greater depth, but also waves that propagated along the planet's surface.
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- What makes the seismic surface waves so important to researchers is that they provide information about the structure of the Martian crust. Seismic body waves, which travel through the planet's interior during a quake, have provided insights into Mars's core and mantle, but have revealed little about the crust away from the lander itself.
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- On average, the Martian crust between the impact sites and InSight's seismometer has a very uniform structure and high density. Directly below the lander they detected three layers of crust that implied a lower density.
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- The new findings are remarkable because a planet's crust provides important clues about how that planet formed and evolved. Since the crust itself is the result of early dynamic processes in the mantle and subsequent magmatic processes, it can tell about conditions billions of years ago and the timeline of impacts, which were particularly common in Mars' early days.
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- The speed at which surface waves propagate depends on their frequency, which in turn depends on their depth. By measuring changes in velocity in the seismic data across different frequencies, it is possible to infer how the velocity changes at different depths, because each frequency is sensitive to different depths.
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- This provides the basis for estimating the average density of the rock. The seismic velocity also depends on the elastic properties of the material through which the waves travel. This data allowed the researchers to determine the structure of the crust at depths of between roughly 5 and 30 kilometers below the surface of Mars.
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- Why then was the average speed of the surface waves recently observed considerably higher than would be expected based on the earlier point measurement under the Mars InSight lander? Is this mainly due to the surface rock, or are other mechanisms in play?
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- Volcanic rocks tend to exhibit higher seismic velocities than sedimentary rocks. Also, the paths between the two meteorite impacts and the measurement site pass through one of the largest volcanic regions in Mars' northern hemisphere.
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- Lava flows and the closure of pore spaces from heat created by volcanic processes, can increase the velocity of seismic waves. The crustal structure beneath InSight's landing site may have been formed in a unique way, perhaps when material was ejected during a large meteoritic impact more than three billion years ago. That would mean the structure of the crust under the lander is probably not representative of the general structure of the Martian crust.
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- Ever since the first telescopes were pointed at Mars, it has been known that a sharp contrast exists between the planet's southern and northern hemispheres. While the dominant feature of the southern hemisphere is a plateau covered by meteorite craters, the northern hemisphere consists mostly of flat, volcanic lowlands that may have been covered by oceans in the planet's early history. This division into southern highlands and northern lowlands is called the “Mars dichotomy“.
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- The initial results appear to disprove one of the widespread theories for the Mars dichotomy: the crusts in the north and in the south are probably not composed of different materials, as has often been assumed, and their structure may be surprisingly similar at relevant depths.
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- In May, 2022, InSight observed the largest marsquake to date, with a magnitude of 5.0 It also recorded seismic surface waves generated by this shallow event. This happened just in time, since the InSight mission will soon be coming to an end now that the lander's solar panels are covered in dust, and it is running out of power. An initial analysis of the data confirms findings that the researchers obtained from the other two meteorite impacts.
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- Astronomers had been waiting for so long for these waves, and now, just months after the meteorite impacts, they observed this big quake that produced extremely rich surface waves. These allow us to see even deeper into the crust, to a depth of about 90 kilometers.
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October 29, 2022 MARSQUAKES - how they analyze the planet? 3722
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