InSight - NASA...2017/12/19 · InSight Marsquakes: How do we detect them, and how do we use them...
Transcript of InSight - NASA...2017/12/19 · InSight Marsquakes: How do we detect them, and how do we use them...
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InSightMarsquakes: How do we detect them, and how do
we use them to understand Mars?
Mark Panning
Research Scientist, Jet Propulsion Laboratory, California Institute of
Technology
Presentation to NASA’s Museum
Alliance and Solar System
Ambassadors, December 19, 2017
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A more basic question: What are earthquakes?
San Francisco, 1906
Obviously, the biggest reason most people think about earthquakes is in the context
of natural hazards, but seismologists use them to learn about the physics of what
cause them, and what the Earth looks like between where the quakes happen and
where we observe them
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3
Earthquakes (and marsquakes) happen on faults
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Quakes make waves
Marsquake visualization from Martin van Driel, ETH Zürich
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Seismometers measure waves
Example output from SeisMac, which makes seismograms from the
seismometer inside a laptop (most laptops and phones have accelerometers,
compared with a seismogram from an earthquake)
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Seismometers measure waves
EQ faulting: ~1 second
Seismogram: ~12 minutes
Example output from SeisMac, which makes seismograms from the
seismometer inside a laptop (most laptops and phones have
accelerometers, compared with a seismogram from an earthquake)
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A seismometer for Mars
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Wherever they are, quakes make the same kind of waves
Body waves go through the interior (or body) of the planet, and can be divided
into two types:
Surface waves travel around stuck to the top of the planet
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P waves
http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
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S waves
http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
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Rayleigh waves
http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
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Why planetary seismology?
• Planetary missions tend to focus on surface
observations, which do not tell us directly about
what’s inside planets
• Most of our detailed knowledge of the interior
structure of the Earth comes from seismology
• Most of what we know about planetary interiors
comes from gravity measurements plus educated
guesses about chemistry
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Earth Mars Moon
Comparing Earth, Moon, and Mars on the same scale
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Planetary interiors, or at least our best guesses
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For the Earth, we know the inside structure very well
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Seismology teaches us planetary structure
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History of planetary seismology
• The “good”: 5 seismometers were placed on Earth’s moon and recorded data (Apollo 11, 12, 14, 15, and 16 missions 1969-1972)
• Data recorded until 1977
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History of planetary seismology
• The “good”: 5 seismometers were placed on Earth’s moon and recorded data (Apollo 11, 12, 14, 15, and 16 missions 1969-1972)
• Data recorded until 1977
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• The “bad”:
• Viking landers included seismometers
1 didn’t “uncage” –no dataThe other primarily recorded the rocking of the lander due to wind
History of planetary seismology
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• The “ugly”: At least 10
other seismometers
have been included in
launched missions
that failed for a variety
of reasons
Mars 96 – failed due to launch vehicle stage failure – never escaped Earth orbit
History of planetary seismology
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InSight
• Launches May 5,
2018 (6 months
travel time)
• Instruments on board
o SEIS
o HP3
o RISE
o Cameras
• Should return data
for ~1 martian year
(about 2 Earth years)
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Seismic networks are pretty cool
• Modern
seismology relies
on networks
o Accurate
locations and
origin times
o Array
seismology
techniques
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What are we going to do with only one station on Mars?
• Having a network on Mars would be
wonderful (and it’s been proposed many
times)
• Having one station allows for an infinite
relative increase in our seismic data, though!
• Two options for how to proceed if we want to
model the interior seismic structure of Marso Techniques that don’t require location information
o Single station location techniques
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Where do we see earthquakes?
Earthquakes, shown as black dots, occur at boundaries of large plates
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Will we see Marsquakes?
Fault map from Martin Knapmeyer, showing faults
observed from orbital images in red and green (no
plate tectonics on Mars, but plenty of faults)
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What will seismograms look like on Mars?
We can use computational techniques to simulate seismograms
through Mars
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What will seismograms look like on Mars?
We can add simulated noise from atmospheric, temperature, and
even tidal variations
Noise Marsquake + noise
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Single station location
• We estimate location
using the timing of 3
orbits of surface waves
(called R1, R2, and R3).
There are 3 unknowns:
Δ, the distance, t0, the
origin time, and U, the
surface wave group
velocity.o U=2π/(R3-R1)
o Δ=π-U(R2-R1)/2
o t0=R1-Δ/U
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Testing with Earth data from a single station
With 7 “big” events With only 5 smaller events
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Summary
• To know about the inside of a planet, nothing’s
better than seismology
• We’re going to land a seismic station on Mars
next year
• We should see marsquakes, and we should be
able to use them to figure out the internal
details of Mars