advanced concept for the detection of weather hazards on mars€¦ · aimee covert...
TRANSCRIPT
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Advanced Concept for the Detection of Weather
Hazards on Mars
Advanced Concept for the Detection of Weather
Hazards on Mars
Aimee Covert([email protected])
Nilton O. RennoUniversity of Michigan
Aimee Covert([email protected])
Nilton O. RennoUniversity of Michigan
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NIAC Annual MeetingMarch 7, 2006
Introduction
• Study electric behavior of weather-related dust events– Dust devils and dust storms
• Terrestrial• Martian
– Field experiments– Laboratory simulations of dust devils
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NIAC Annual MeetingMarch 7, 2006
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
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NIAC Annual MeetingMarch 7, 2006
Outline
• Research Goals• Electric Theory of Dust Events• Experiments
– Lab Results– Field Results
• Plans for the Future• Conclusions
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NIAC Annual MeetingMarch 7, 2006
Weather Hazards on Mars
• Dust events pose a significant hazard to future missions to Mars– High winds, high dust content could
negatively affect manned missions– Electric activity could negatively effect
robotic landers and manned missions– Electric fields can ionize the air and cause
potentially hazardous chemical reactions
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NIAC Annual MeetingMarch 7, 2006
Research Goals
• To find an effective method for detecting weather hazards on Mars (dust events) at any time of the day or during periods of low visibility– To study microdischarges between colliding dust
particles in the laboratory– To study microdischarges in terrestrial dust devils– To design an instrument to remotely fingerprint Martian
dust events based on their microdischarges
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Electric Theory of Dust Events
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NIAC Annual MeetingMarch 7, 2006
Microdischarges in Dust Events
• Asymmetric rubbing occurs between colliding particles– Causes a net transfer of electrons from larger to
smaller particles– Smaller particles become negatively charged– Large particles become positively charged
• Microdischarges occur when the particles separate from each other, after a collision
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NIAC Annual MeetingMarch 7, 2006
Non-thermal Microwave Emissions
• Microdischarges produce non-thermal microwave radiation [Renno et al., 2004]– Non-thermal emissions can be used to remotely
fingerprint dust events
• To distinguish thermal from non-thermal emissions we look at the probability distribution function of the amplitude of the emissions (pdf)– Gaussian: thermal– Non-gaussian: non-thermal
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NIAC Annual MeetingMarch 7, 2006
Bulk Electric Fields
[Kok and Renno 2006]
• Charge separation occurs when small particles rise in updrafts– The larger particles stay near the
ground• Charge separation produces
large electric fields in terrestrial dust devils and dust storms– Fields in excess of 10 kV/m on
Earth [Renno et al., 2004]
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NIAC Annual MeetingMarch 7, 2006
Applications to Mars
• Martian dust events are significantly larger and dustier than terrestrial dust events.– There is evidence that microdischarges and large
electric fields occur in these dust events [Renno et al., 2003, 2004]
– Lower atmospheric pressure makes electric breakdown easier on Mars
– Higher dust content and larger storms result in more collisions and therefore more microdischarges
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Experiments
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NIAC Annual MeetingMarch 7, 2006
Laboratory Setup
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NIAC Annual MeetingMarch 7, 2006
Particles of InterestMartian Soil Composition
At Viking 1 Landing Site• Experiments with various
materials– Representatitve of the
Martian regolith• Silicon• Iron• Aluminum• Potassium• Magnesium
– Particles of a range of sizes representing those likely to be found in Martian dust events
[http://resources.yesican-science.ca]
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NIAC Annual MeetingMarch 7, 2006
Experimental Setup
• Materials classified by size:– Large particles (~1
mm diameter)– Small particles (~1 to
10 µm)– Mixed particles (half
large particles, half small by volume)
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NIAC Annual MeetingMarch 7, 2006
Experimental Setup
• Used three materials:– Aluminum– Basalt– Hematite (Fe2O3)
• Experiments conducted at various pressures– Ranging from 0.1
to 1 Bar
QuickTime™ and aH.264 decompressor
are needed to see this picture.
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NIAC Annual MeetingMarch 7, 2006
Lab Experiments
• Lab experiments conducted using two different radiometers– First provides time series of emission amplitude
• Look for peaks in the data to identify microdischarges• Sensitive to emission frequencies around 10 GHz
– Second provides a probability distribution function (pdf) of electric field amplitude at small time intervals
• Look for non-gaussian distribution to indicate the presence of non-thermal radiation
• Sensitive to frequencies around 10 GHz
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NIAC Annual MeetingMarch 7, 2006
Sensor of Setup 1
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NIAC Annual MeetingMarch 7, 2006
Setup 1 Lab Results• Observed
microdischarges• Only detected significant
emissions in experiments with aluminum particles
• We might need to look at other frequencies or use more sensitive instruments to detect emissions from other particles
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NIAC Annual MeetingMarch 7, 2006
Equipment of Setup 2
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NIAC Annual MeetingMarch 7, 2006
Setup 2 Lab Results• Positive results with
aluminum particles– Consistent with results
from setup 1• pdf significantly different
from control (blackbody pdf)
• Did not detect emissions in experiments with basalt or hematite
• Did not detect emissions in experiments with only small particles
PDF of electric field (Large aluminum particles)
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Blackbody
1 atm
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NIAC Annual MeetingMarch 7, 2006
Kurtosis of the Emissions
Large aluminum particles
0.29 Bar
Large aluminum particles
1 Bar
• Kurtosis ~3 indicates gaussian distribution.
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NIAC Annual MeetingMarch 7, 2006
Field Experiments
• Searched for microdischarges in terrestrial dust devils
• Conducted in Summer 2005 near Eloy, AZ
• Used radiometer from setup 1– Recoded time series
of the amplitude
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NIAC Annual MeetingMarch 7, 2006
Field Results
•Microwave Emissions from a dust devil on June 11th 2005 at 2:15pm and a corresponding image of it.
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NIAC Annual MeetingMarch 7, 2006
More Field Results
2:28 p.m. MST on June 9, 200512:02 p.m. MST on June 11, 2005
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NIAC Annual MeetingMarch 7, 2006
Plans for the Future
• Field Goals– Develop a more portable data collection system– Distinguish non-thermal from thermal emissions– Correlate emission amplitude with weather data at
a fixed location• Laboratory Goals
– Conduct experiments with additional materials– Try different methods to detect emissions with
hematite and basalt– Calculate pdf of non-thermal emissions by
removing background noise
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NIAC Annual MeetingMarch 7, 2006
Conclusions• Have shown that emissions from colliding particles is
non-thermal• Identified a flight qualified instrument that can
distinguish non-thermal from thermal emissions• Additional lab experiments with different materials are
necessary• Additional field measurements using different data
collection procedures are necessary• Optimal frequencies must be identified• Recommend an instrument to measure electric fields to
be placed on Mars landers
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NIAC Annual MeetingMarch 7, 2006
Acknowledgements
• Dr. Nilton O. Renno, University of Michigan• Dr. Chris Ruf, University of Michigan• Collaborators Kevin Reed and Catalina
Oaida, University of Michigan
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NIAC Annual MeetingMarch 7, 2006
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NIAC Annual MeetingMarch 7, 2006
Addressing Problems with Results
• Why didn’t we detect emissions with basalt and hematite?– Sampling rate may not be fast enough– May need to use a sensor with a different
frequency• In experiments with aluminum we detected
changes in pdf for all but small particles– Small particles tend to coat the inside of the bell
jar, which may interfere with detection of emissions
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NIAC Annual MeetingMarch 7, 2006
Why 10 GHz?
• Very sensitive• Developed for satellite dishes• Inexpensive
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NIAC Annual MeetingMarch 7, 2006
Effects of fan?
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Fan on
Fan off
•No visible difference in pdf of electric field amplitude
•No change in kurtosis
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NIAC Annual MeetingMarch 7, 2006
Charge Transfer by Asymmetric Rubbing
• Solid matter has more empty energy levels than electrons in high energy states.
• During asymmetric rubbing:– There is a net transfer of electrons to the smaller body
because it slides more over the other.– The smaller body becomes negatively charged and the
larger becomes positively charged.
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