Update on the Mars Exploration Rovers

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Update on the Mars Exploration Rovers

• University of Pennsylvania
• Peter Allen

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Outline

• Goals
• Landing Sites
• Getting There
• The Rovers and their Instruments
• Science so far
• The Future

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Goals of the Mission

• To find evidence of previous (or current) liquid
  water on the surface of Mars
• Note NOT looking for life!

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Goals cont.

• Will look for evidence of water by observing and
  dissecting Martian rocks and soils
• Each rover has a suite of instruments (more
  later)
• Also ground observations will provide
  calibrations of orbital observations

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Landing Sites

• Need landing sites that allow us to explore for
  previous water
• Chose two sites on opposites sides of the planet
• Gusev Crater Possible site of an ancient lake
• Meridiani Planum Large Hematite deposits seen
  from orbit

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Landing Sites
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Gusev Landing Site (Spirit)
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Meridiani Site (Opportunity)
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Meridiani Landing Site
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Getting There

• Three general stages
• Launch (Nail biting)
• Cruise (Boring)
• Entry Landing (Nails re-grown over six months
  to bite again)

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Launch

• Each rover had narrow launch windows to arrive at
  their destinations (3 weeks)
• Spirit (launched June 10th 2003) on a Delta-II
• Opportunity (launched July 7th 2003) on a
  Delta-IIH
• Opportunitys later launch date put Mars further
  away hence more energy needed to get there

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Cruise

• Long, cold, and dark (7 months)

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Entry Landing

• Takes about 6 minutes to reach ground
• Enters at 12000 mph and reaches temperatures of
  1500K
• Bounces and rolls for up to a km
• See Movie

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The Rover

• Each rover is 185 kg and roughly the size of a
  small go-kart with a five foot mast
• Solar panels provide a maximum of 140 W at noon
  (cf 16 W on Sojourner)
• Nominal battery recharge lifetime of 90 sols
  (recently upgraded to 180 sols)
• Can travel upwards of 40 m a sol

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The Rover
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Instruments

• PANCAM (Panoramic Camera)
• Pair of high-res CCDs on top of mast
• Allows 3D imaging of surroundings
• Used to scan for interesting sites to visit

Bonneville crater (current site of Spirit Rover)
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Instruments cont.

• Microscopic Imager (MI)
• A microscope with a CCD attached to the end
  (opposite of what we are used to)
• Attached to Rover arm (1 of 4 instruments)
• Provides detailed images of rock and soil
  surfaces
• Determines size and shape of grains and pebbles

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Instruments cont.

• Miniature Thermal Emission Spectrometer
  (Mini-TES)
• Infrared spectrograph mounted in the mast
• Scanning mirror sends light down mast, looks
  where Pancam looks
• Used to determine mineral composition from a
  distance
• Particularly looking for minerals formed by water
  action

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Instruments cont.

• Mossbauer Spectrometer (MS)
• Sensor mounted on rover arm.
• Takes 12 hours to perform a single measurement
• Used to study mineral composition of rocks close
  up
• Particularly looking at iron rich minerals, if
  hydrated might be from water action

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Instruments cont.

• Alpha Particle X-ray Spectrometer (APXS)
• Sensor mounted on rover arm
• Used to study emission from rocks
• Can yield information about composition,
  formation, and weathering
• Usually makes measurements at night (avoid solar
  background?)

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Instruments cont.

• Rock Abrasion Tool (RAT)
• Mounted on rover arm
• Diamond grinding wheels capable of digging a 45mm
  diameter hole 5mm deep in 2 hours
• Used to expose fresh rock surfaces for study
• Important to look at un-weathered rock

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Instruments cont.

• Magnet Arrays (MA)
• Three sets of magnets rover arm, front of rover,
  and rover top
• Used to study air-born magnetic dust
• The freeze-dried remains of water created
  minerals?

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Instruments cont.

• Calibration Targets
• Each instrument has internal calibrators
• Pancams is unique it is a working sundial!
• Children designed the artwork on the surface
• Says Mars in sixteen languages
• Original idea by Bill Nye (Yes, the Science Guy)

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Instruments cont.
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Typical Rover Day

• Wake up with Sun
• Perform tasks (spectra integrations, imaging, or
  roving)
• Take naps (power downs to allow solar panels to
  recharge batteries)
• More science
• Power down for the night, also do long MS or APXS
  integrations overnight

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Science with Spirit

• After rolling off the lander Spirit went to the
  rock dubbed Adirondack
• Found olivine, a mineral that doesnt weather
  well
• Soil very sticky, evidence of a lot of salts

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Science with Spirit

• Just as Spirit begins investigating Adirondack it
  ceases communication
• Turned out to be a problem with the flash memory
• Files built up in flash memory causing the rover
  to continuously reboot
• Took 10 days to recover sufficiently to continue
  science operations

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Science with Spirit

• Moved on from Adirondack and dug a hole with its
  front left wheel
• More sticky soil found
• Evidence that soil has expanded and contracted
  repeatedly
• Caused by heating/cooling, freezing/ thawing, or
  salty liquid rising/falling

MI image of area before hole was dug
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Science with Spirit

• Next moved on to new rock Humphrey
• 3/5/04 Spirit too finds evidence of water
• Scratched Humphrey with RAT to reveal bright salt
  crystals

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Science with Spirit

• Humphrey is a volcanic rock with bright crystal
  structures
• Implies water flowed through it
• Either water came with magma that formed it or it
  was submerged later on
• Much less than the water reported from Opportunity

MI image of scratched Humphrey
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Science with Spirit

• Approaching a crater within Gusev, Bonneville
• Currently exploring the crater rim
• Took image of Earth from Mars (A first from the
  surface of any other planet)

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Science with Opportunity

• Experience with Spirit allows Opportunity to get
  off its lander in 7 days (cf 12 w/Spirit)
• Landed in a small crater with layered bedrock
  nearby!

• Bedrock is only 8m away and is 0.5m tall

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Science with Opportunity

• Rolls off lander and examines soil
• Finds spherical grains could be impact,
  volcanic, or water action in origin

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Science with Opportunity

• Next drives up to Opportunity Ledge to survey
  it for more detailed study later
• MI finds similar spherical grains (blueberries)
  embedded in the rock
• Spends 2 weeks surveying

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Science with Opportunity

• Press silence from NASA on rovers between 2/26
  and 3/2
• Then they announce definitive evidence that this
  rock on Mars was once soaked in liquid water for
  long amounts of time
• Investigation centered on the rock El Capitan

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Science with Opportunity

• Many lines of evidence intersect
• The blueberries are uniformly spread through the
  rock, not layered.
• Highest concentrations of salt compounds ever
  found on Mars (particularly sulfur)
• Hydrated iron mineral jarosite found
• Wavy structures in the rock suggest water action
• Vugs cavities left behind when salt crystals
  deposited in rock either erode of dissolve in
  less salty water

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Science with Opportunity
Pancam image of Last Chance. The rippling
structures are too small to have been formed by
wind therefore moving water is the only other
explanation
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Science with Opportunity

• Vugs in El Capitan

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Science with Opportunity

• After spending 2-3 weeks near El Capitan
  Opportunity moves on
• Observes Solar eclipses by both of Mars moons,
  Phobos and Deimos, with Pancam

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Science with Opportunity

• Just after leaving the lander surveyed the crater
  with Mini-TES to look for Hematite (red high,
  blue low
• Now testing soil samples in areas abundant in
  hematite
• Hematite most commonly forms on Earth in liquid
  water

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Science with Opportunity

• Last week took Mossbauer spectrum of the
  blueberries
• Found to have a large percentage of hematite!
• Yet another confirmation of the water soaked
  hypothesis

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The Future of Spirit

• Continue to explore rim of Bonneville crater
• Currently digging in the martian soil and
  studying the rocks around the crater rim

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The Future of Opportunity

• Explore nearby hematite deposits
• Head out onto the hematite rich plain towards
  large crater Endurance (720m)

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The Future of Opportunity
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Lifetime of the Rovers

• Initially capped at 90 sols
• Recently extended to 180 sols because of greater
  than expected performance and less dust settling
  on the solar panels
• Spirit in Sol 80 and Opportunity in Sol 59
• We can expect 3-5 months of more productive
  returns from these rovers