HIGHER THAN ADVERTISED MARTIAN AIR PRESSURE Part 1: Overview of Pressure Measurement Issues By David A. Roffman, Embry-Riddle Aeronautical University http://DavidARoffman.Com Presented at the 14 th International Mars Society Convention, Dallas, TX August 4, 2011 1
Accepted Average Pressure 6.1 Mbar at Mars Areoid Ar eoid is Mars equivalent of Sea Level. Average Earth sea level pressure = 1013.25 Mbar. 6.1 Mbar is nearly a vacuum (= pressure on Earth at 90,417 feet/27,550 meters) • View from a MIG 25 at 83,600 feet, • Pressure = ~11.3 mbar 2
Why Question Accepted Pressure? Initial stimulus - similarities in Martian & Terrestrial dust devils. http://www.lpl.arizona.edu/~lemmon/mer_dd/dd_enhanced_587a.gif Scope of Research: 2 yr. study, special topics course at ERAU, literature & NASA Ames Archives review, interviews of pressure transducer designers, Viking data audit. 3
Why Question Accepted Pressure? Mars dust devils typically have speeds of 6m/s (~13 MPH), but during an Ames experiment at 10 mbar, a wind speed of 70 m/s (~156 MPH) was needed to form a dust devil. 4
5 Why Question Accepted Pressure?
Why Question Accepted Pressure? 6 • No way to change small dust filters on Vikings, Pathfinder, or Phoenix! Rapid clogging likely.
Only Viking-2 provided published pressure data for over a Martian year 7
8 Problems with Viking Pressures When pressures weren’t stuck, they varied with laws for gases in sealed containers (not in contact with the ambient air of Mars).
First Photo From Mars Shows How Dust Affected Viking 1! Greeley et al. (1992): ”In designing future lander spacecraft for Mars, consideration must be given to the infiltration of fine dust into spacecraft components…” Since dust makes its way in at the air intake tube for the pressure sensor – start there! 9
Why Question Accepted Pressure? Dust storms enormously increase opacity and atmospheric density. Can block 99% of light. 10
11 Dust Storm of July 5, 2011 Phoenix, Arizona Pressure at nearby Luke Air Force Base increased during the dust storm by 6.6 mbar – that’s more than average pressure (6.1 mbar) at areoid on Mars.
12 Why Question Accepted Pressure? Last 4 successful landers long (downrange) by 13.4 - 27 km (request for help from NASA’s Prasun Desai, 2008) 3 landers “lost” might have been short (Mars Polar Lander & Deep Space 2 in 1999; Beagle 2 in 2003)
Why Question MPF Thermal wind sensor 13 Accepted Pressure? MPF anemometers could not be calibrated. Path Pathfinder Windsock mast No anemometer on Phoenix. Telltale could not measure speeds >10 m/s and only had 20 - 40% accuracy for winds <10m/s.
Why Question Accepted Pressure? Snow. Ice particles in clouds an order of magnitude too small for GCMs – 2 μm vs. 20 to 30 μm (Richardson, et al., 2002) 14
DUST DEVILS ARE THE MOST OBVIOUS WEATHER ANOMALY If there is so little air on Mars, how can there be enough Δ p to generate them at all? Over 30 dust devils hit the Phoenix lander in just 150 days. Pathfinder detected ~79 in 86 days. 15
Similarities between Terrestrial and Martian Dust Devils Seasons (summer on Earth, spring and summer on Mars) Electrical properties (0.8 MV for a terrestrial event). Shape & often size (but can be 50 x wider and 10 x higher on Mars) Daily formation times (around noon) 16
Similarities between Terrestrial and Martian Dust Devils wind speed (6 m/s typical) core temperature increase (up to 10 K) dust particle size (1 μm typical). But with low 6.1 mbar pressure, 500 m/s (1,118 mph) wind required to lift 1 μm dust. (Read & Lewis, 2004) 17
Differences between Terrestrial and 18 Martian Dust Devils – mainly Absolute and Relative Pressure Excursions Maximum pressure drop for a Mars dust devil at Phoenix was ~0.0289 mbar. Max drop at Pathfinder was .0477 mbar. Pressure drop for a 1953 dust devil that went directly over a microbarograph was 1.354 mbar (13X greater than Pathfinder event, 21X greater than Phoenix d. d.).
19 SCALE HEIGHT The pressure acquired by a parcel of air moved up or down a certain height at a constant temperature. p = p 0 e -(h/h0) where p = atmospheric pressure, h = height (altitude), P 0 = pressure at height h = 0 (surface pressure), and H 0 = scale height. By scale height math, pressure on Arsia Mons where dust devils occur at 17 km should be about 1.17 mbar. Again, Ames couldn’t produce a dust devil @ 10 mbar .
Arsia Mons & other Martian Mountains, 20 Valleys, Landers, and Methane Plumes .
Spiral Clouds on Arsia Mons (only) look like 21 Hurricane Eye Walls. 1.17 mbar seems too low. These clouds extend 15-30 km above the mountain, where scale height calculations indicate pressures of 0.29 to 0.07 mbar. This is like what’s seen for Earth at >34.9 km (>21 miles) above sea level.
NASA web site now does not post the same pressures as in 1970s . ( http://nssdc.gsfc.nasa.gov/planetary/mars/mariner.html ) – Mariner 4 flyby: 4.5 to 9 mbar (old) or 4.1 to 7.0 mbar (new) – Mariners 6 flyby and 7 flyby: 3.8 to 7.0 mbar (new). However SP-4212 On Mars: Exploration of the Red Planet 1958-1978 (page 243) states of these flyby craft that the: “occultation experiment indicated that the atmospheric pressure at the surface of Mars ranged from 4 to 20 millibars, rather than 80 millibars as estimated earlier.” 22
Occultation by Mariners missed high points (Olympus Mons) and low points (Hellas Basin). 23
24 Mars Lander Pressure Sensors Only 4 landers could measure pressure in situ . None could measure above 18 mbar (and 2 were limited to 12 mbar). Limited pressure ranges based on previous radio occultation measurements. 24
Viking & Pathfinder Pressure Sensitivity Ranges 3 Tavis pressure sensors sent by NASA: Viking 1 & 2 Range: 0 to 18 mbar Pathfinder : Only 0 to 12 mbar A 1,034 mbar sensor was also ordered (Tavis CAD 10484 – 1 , but Tavis rep says it remained on Earth) 25
5 to12 Mbar Range Phoenix Dust Filter A Finnish Meteorological Institute report (2009) States that, "We should find out how the pressure tube is mounted in the spacecraft and if there are additional filters etc.“ FMI designed the sensor . 26
International Traffic in Arms Regulations (ITAR ) “ After Phoenix landed it appeared that the actual thermal environment was worse than the expected worse case… Information on re-location of the heat source had not been provided initially due to ITAR restrictions.” (Taylor, P.A., et al, 2009) 27
International Traffic 28 in Arms Regulations (ITAR) “That we at FMI did not know how our sensor was mounted in the spacecraft and how many filters there were shows that the exchange of information between NASA and the foreign subcontractors did not work optimally in this mission!” (Kahanpää [FMI] Personal communication, December 15, 2009) 28
29 Data Too Similar Year to Year? 55% of same days each year for 4 years VL-1 Pressure was identical.
PRESSURES DERIVED BY SPECTROMETER Similar to VL-1; but don’t work with ice clouds and frost at poles (Spiga et al., 2007). Pressure readings published for only 9 days 30
31 COMPARISON OF MARS EXPRESS SPECTROSCOPY AND VIKING 1 PRESSURES
Occam's Razor (1) Entities must not be multiplied beyond necessity. (2) The simplest solution is usually the correct one. The Razor suggests that repeatable Viking pressure data should be believed. However, the consistent Viking-Pathfinder-Phoenix pressures may only exist because they all had pressure sensor air access tubes clog in similar fashion . 32
Why Trash Occam? OVERALL Viking pressures vary in inverse proportion to ambient temperature and in direct proportion to heat required by RTGs to keep internal temperatures stable. Viking 1 Pressures for Year 1 are 98.19% in agreement with predictions based on Gay- Lussac’s Law. This implies the transducer only measured internal, not external pressures. 33
Why Trash Occam? Weather doesn’t match low pressure values – Dust Devils – Dust Storms – Eye walls on huge storms over Arsia Mons 34
Why Trash Occam? No way to change Viking, MPF and Phoenix dust filters that could clog. Viking data suspicious due to exact repeat over 4 yrs. Audit of Viking data shows huge patterns of exactly the stuck pressures for up to 6 days (see Part 2 Presentation). Data shows no justification for continuing the pressure curves. 35
WHY TRASH OCCUM? MRO AEROBRAKING “ At some points in the atmosphere, we saw a difference in the atmospheric density by a factor of 1.3, which means it was 30% higher than the model, but … around the south pole we saw an even larger scale factor of up to 4.5, so that means it was 350% off of the Mars GRAM model . ” Han You, Navigation Team Chief for MRO. 36
WHY TRASH OCCAM? MGS Dynamic Pressure Spike @ 121 km Due to Dust Storms. Pressure Doubles in 48 Hours, Up 5.6 Fold in 4 Weeks. 37
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