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 meantGalileo had to use flybys of Venus and Earth to providegravity assists.

Observed Moon, Earth, and Venus.

False-color image of surface (imaged at different wavelengths toprovide a spectral image - different compositions reflectdifferent wavelengths of light)

Blue: Titanium-rich soils, younger basaltRed: Titanium-poor and iron-poor, older lunar highlandsPurple: Apollo 17 landing site, ancient explosive volcanic deposits

The Galileo Mission, cont.

Launched October 1989 by the Shuttle AtlantisWeighed 2380 kg (~pick-up truck)Power system: Radioisotope thermoelectric generators (RTGs), 570 watts

Two spacecraft: orbiter and an atmospheric probeProbe 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, 199420 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 TelescopeShows hot areasWhat is the brightest spot??

Dust from the asteroids absorbs solar uv light, looking like dark spots.

Science Objectives

Probe:Determine composition of Jupiter’s atmosphereCharacterize atmosphere with depth to 10 barsInvestigate cloud particles, location and structure of cloud layersExamine heat balance of JupiterNature of lightningMeasure solar wind flux with depth

Orbiter:Study circulation and dynamics of Jupiter’s atmosphereStudy Jupiter’s atmosphere and ionosphereImage the Galilean satellites, investigate geology and mineralsDetermine gravitational and magnetic fields of Galilean satellitesStudy atmospheres, ionospheres of Galilean satsStudy interaction of Jupiter’s magnetosphere with Galilean satsStudy Jupiter’s magnetosphere and plasma torus

Orbiter Instruments

Solid-state imagerupdated technology from Voyagerbasically a telescope with a very sensitive CCD sensorimages recorded, compressed, sent back to Earthprotected with 1 cm thick tantalum shield

Ultra-violet Spectrometermeasured uv albedo ofVenus (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 aurorasUV emissions from the hot interior of JupiterIo torus (abundance of neutral and charged atoms)

Orbiter Instruments, cont.

Near Infra-red Mapping Spectrometermapped infra-red radiation reflected or emitted from bodiescomposition and cloud structure and temperature

Dust Detectormeasures mass & speed of dust

Heavy Ion CounterMonitored the environment to protect spacecraft electronicsStudied composition of ions around Jupiter, solar flares, cosmic rays.

Magnetometermeasures magnetic fieldson an arm away fromthe spacecraft

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Orbiter Instruments, cont.

Plasma Instrumentmeasure density, T, velocity, composition of plasma

Plasma Wave Subsysteman antenna to measure electrical and magnetic fields of the plasma

Radioperform experiments on celestial mechanics and relativityoccultation with Earth - measures P and T of the atmosphere with depth

Probe Instruments

Atmospheric Structure InstrumentT, P

Mass Spectrometercomposition of atmosphere

Nephelometeruses a laser beam to detect atmospheric particles

Energetic Particle Investigationmeasures electrons, protons, alpha particles, heavy ions from

magnetosphere

Net Flux Radiometermeasures radiation of light from the atmosphere

Lightning and Radio Emission InstrumentHelium Abundance Interferometer

Gaspra

19 km long, rotates every 7 hoursSome regions are brighterBlue: brighter regions, around craters, blue due to the Fe-containing

mineral olivineRed: regolith accumulations

no large cratersabundant smaller craters

likely recent origin fromthe break-up of a largerbody

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 adifferent spectral properties

Made of similar rock types.1.5 km long.

Ida

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 kphFar less lightning activity than anticipated, although they were still

10x EarthHe abundance very similar to the SunExtensive resurfacing of Io since Voyager flybys in 1979.Intrinsic magnetic fields for Io and GanymedeEvidence 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 & CallistoDue to warmth of lower part of the ice shell.Strength of ice is dependent upon T and P.

Ganymede & Callistoscale= 30 kmIce appears thicker

Europascale = 10 kmice appears thinner

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Smaller craters: rim and central peak

>30km:no rims or peakssurrounded by concentric ringslikely 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 beliquid.

If less heat, there may be a layer of softconvecting 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 hydrothermalvents at the bottom of the ocean.

How to Look for Life on Europa

Europa Orbiter/Jupiter Icy Moon OrbiterWas scheduled to arrive on Europa in 2010Mission 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

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One of the world’s largest freshwater lakeLake under 3,700 m of iceLake is ~1 million years oldAre 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 aRussian Research facility.

Drilling Stopped in 1998 toavoid contaminating the lake.

Retrieved a 420,000-year icecore!

Lowest layers of ice is frozenlake water (accreted lake ice). Thisice contained a few microbes.

Lake water is constantly removedby freezing - must be a sourceof freshwater.

animation

Oceans on Ganymede and Callisto

Are likely deep, below 100-200 km of ice.

Probe Discoveries

Entered Jupiter’s atmosphere Dec. 1995Relayed data for 57 minutes to a depth of 156 km

Atmosphere drier than expected.Didn’t detect 3-tiered cloud structure, only found one thin cloud layer

Top: ammonia crystalsMiddle: ammonium hydrosulfideLower: thick layer of water and ice crystals

Significantly lower helium, neon, C, O, SMinimal organic compoundsAbsence of lightning (no water ice)Found extremely strong winds and turbulence, even at depthFound a new radiation belt 31,000 miles above the cloud tops

Entered a cloud-free region - a “hot spot”

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Probe Site

Lecture 32. Titan and its Atmosphere.

reading: Chapter 8