Transcript Lecture31

Lecture 31. Galileo Mission.
reading: Chapter 8
The Galileo Mission
Originally proposed to be a direct mission to Jupiter, Challenger
accident and cancellation of Centaur rock program meant
Galileo had to use flybys of Venus and Earth to provide
gravity assists.
Observed Moon, Earth, and Venus.
False-color image of surface (imaged at different wavelengths to
provide a spectral image - different compositions reflect
different wavelengths of light)
Blue: Titanium-rich soils, younger basalt
Red: Titanium-poor and iron-poor, older lunar highlands
Purple: Apollo 17 landing site, ancient explosive volcanic deposits
The Galileo Mission, cont.
Launched October 1989 by the Shuttle Atlantis
Weighed 2380 kg (~pick-up truck)
Power system: Radioisotope thermoelectric generators (RTGs), 570 watts
Two spacecraft: orbiter and an atmospheric probe
Probe weighted 335 kg
Trajectory: VEEGA (Venus-Earth-Earth Gravity Assist)
Unprecedented observations.
First close-up observations of 2 asteroids Gaspra and Ida
Watched Shoemaker-Levy 9 Impact Jupiter
July 16-22, 1994
20 fragments impacted at 60 km/sec - largest was 2 km.
Sent plumes thousands of km high.
Left hot bubbles of gas in the atmosphere.
Dark scars that lasted for months.
Impact was just out of the view from Earth.
Imaged fragment W:
Infrared image - Mauna Kea Telescope
Shows hot areas
What is the brightest spot??
Dust from the asteroids absorbs
solar uv light, looking like dark spots.
Science Objectives
Probe:
Determine composition of Jupiter’s atmosphere
Characterize atmosphere with depth to 10 bars
Investigate cloud particles, location and structure of cloud layers
Examine heat balance of Jupiter
Nature of lightning
Measure solar wind flux with depth
Orbiter:
Study circulation and dynamics of Jupiter’s atmosphere
Study Jupiter’s atmosphere and ionosphere
Image the Galilean satellites, investigate geology and minerals
Determine gravitational and magnetic fields of Galilean satellites
Study atmospheres, ionospheres of Galilean sats
Study interaction of Jupiter’s magnetosphere with Galilean sats
Study Jupiter’s magnetosphere and plasma torus
Orbiter Instruments
Solid-state imager
updated technology from Voyager
basically a telescope with a very sensitive CCD sensor
images recorded, compressed, sent back to Earth
protected with 1 cm thick tantalum shield
Ultra-violet Spectrometer
measured uv albedo of
Venus (measures SO2, H, O, C, and CO)
Earth & Moon (ozone, lunar atmosphere)
asteroids (compare to Moon)
Jupiter’s clouds (hazes and aerosols, variability, hydrocarbons)
Jupiter’s auroras
UV emissions from the hot interior of Jupiter
Io torus (abundance of neutral and charged atoms)
Orbiter Instruments, cont.
Near Infra-red Mapping Spectrometer
mapped infra-red radiation reflected or emitted from bodies
composition and cloud structure and temperature
Dust Detector
measures mass & speed of dust
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Heavy Ion Counter
Monitored the environment to protect spacecraft electronics
Studied composition of ions around Jupiter, solar flares, cosmic rays.
Magnetometer
measures magnetic fields
on an arm away from
the spacecraft
Orbiter Instruments, cont.
Plasma Instrument
measure density, T, velocity, composition of plasma
Plasma Wave Subsystem
an antenna to measure electrical and magnetic fields of the plasma
Radio
perform experiments on celestial mechanics and relativity
occultation with Earth - measures P and T of the atmosphere with depth
Probe Instruments
Atmospheric Structure Instrument
T, P
Mass Spectrometer
composition of atmosphere
Nephelometer
uses a laser beam to detect atmospheric particles
Energetic Particle Investigation
measures electrons, protons, alpha particles, heavy ions from
magnetosphere
Net Flux Radiometer
measures radiation of light from the atmosphere
Lightning and Radio Emission Instrument
Helium Abundance Interferometer
Gaspra
19 km long, rotates every 7 hours
Some regions are brighter
Blue: brighter regions, around craters, blue due to the Fe-containing
mineral olivine
Red: regolith accumulations
no large craters
abundant smaller craters
likely recent origin from
the break-up of a larger
body
Ida
Asteroids have Moons!
Ida covered with regolith.
Bright regions near craters.
Compositional differences in Fe-bearing
minerals.
Rotates every 4.5 hours, 56 km long.
Dactyl is a different color - has a
different spectral properties
Made of similar rock types.
1.5 km long.
Discoveries
An intense interplanetary dust storm!
Lasted 3 weeks, counted 20,000 dust particles/day
(Normal: 1 particle/3 days)
Traveling 90,000-450,000 mph!
May have:
-come from Io
-from Jupiter’s thin rings
-from comet Showmaker-Levy 9
Discoveries, cont.
Jovian wind speed of 600 kph
Far less lightning activity than anticipated, although they were still
10x Earth
He abundance very similar to the Sun
Extensive resurfacing of Io since Voyager flybys in 1979.
Intrinsic magnetic fields for Io and Ganymede
Evidence for liquid water oceans underneath Europa and Ganymede
(induced magnetic fields).
How Thick Is Europa’s Crust?
We don’t really know.
Examine impact craters.
Shapes of largest craters different than those on Ganymede & Callisto
Due to warmth of lower part of the ice shell.
Strength of ice is dependent upon T and P.
Ganymede & Callisto
scale= 30 km
Ice appears thicker
Europa
scale = 10 km
ice appears thinner
Smaller craters:
rim and central peak
>30km:
no rims or peaks
surrounded by concentric rings
likely melted the icy crust
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There Are 2 Main Models
Crust thickness estimated to be 20-30 km.
If there is a lot of heat, the ocean may be
liquid.
If less heat, there may be a layer of soft
convecting ice.
Magnetometer data suggests it is liquid.
(But is not proof).
If we could melt through the ice,
we could explore the ocean below
(IF it is liquid).
Predict there should be hydrothermal
vents at the bottom of the ocean.
How to Look for Life on Europa
Europa Orbiter/Jupiter Icy Moon Orbiter
Was scheduled to arrive on Europa in 2010
Mission has been repeatedly bumped.
As of February:
Missing from the President’s 2007 budget.
Proposing a nuclear reactor to power ion thruster engines (Prometheus)
Mike Griffin, NASA Administrator, told a Senate subcommittee that
the mission was too ambitious, and was not well-formed.
Now launch date is 2015 (??).
Radar will map the thickness of the ice crust.
Determine if there is a liquid ocean.
Map the surface and measure topography.
Try to detect signs of recent geologic activity.
How to Look for Life on Europa, cont.
Do we have the 5 things you need for life??
Surface T of Europa is -160˚C
Lake Vostok, Antarctica
One of the world’s largest freshwater lake
Lake under 3,700 m of ice
Lake is ~1 million years old
Are over 145 similar lakes under the ice
What Lake Vostok! looks like:
Coldest Recorded T on Earth: -89˚C
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Lake Vostok, Antarctica
Drilling of the ice began at a
Russian Research facility.
Drilling Stopped in 1998 to
avoid contaminating the lake.
Retrieved a 420,000-year ice
core!
Lowest layers of ice is frozen
lake water (accreted lake ice). This
ice contained a few microbes.
Lake water is constantly removed
by freezing - must be a source
of freshwater.
animation
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Oceans on Ganymede and Callisto
Are likely deep, below 100-200 km of ice.
Probe Discoveries
Entered Jupiter’s atmosphere Dec. 1995
Relayed data for 57 minutes to a depth of 156 km
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Atmosphere drier than expected.
Didn’t detect 3-tiered cloud structure, only found one thin cloud layer
Top: ammonia crystals
Middle: ammonium hydrosulfide
Lower: thick layer of water and ice crystals
Significantly lower helium, neon, C, O, S
Minimal organic compounds
Absence of lightning (no water ice)
Found extremely strong winds and turbulence, even at depth
Found a new radiation belt 31,000 miles above the cloud tops
Entered a cloud-free region - a “hot spot”
Probe Site
Lecture 32. Titan and its Atmosphere.
reading: Chapter 8