AST 248, Lecture 20

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

November 15, 2018

The Search for Intelligent Life in the Universejames.lattimer@stonybrook.edu

James Lattimer AST 248, Lecture 20

Giant Planets

I Mass, radius, rotation rate and atmosphere aresignificantly larger than Earth’s.

I Overall compositions similar to Sun’s exceptheavy elements are 5–10 times more abundant:71% H, 24% He, 5% C, N, O, Si, S, Fe, etc.

I Gaseous envelope and atmosphere, metallic Hinterior, ice and rock core.

I Surface temperatures around 100 K; Coretemperatures above 10,000 K

I Violent winds correlate with observed beltsand zones.

I Long-lived storms (e.g., Great Red Spot) arecommon. Produced by heat risingfrom below by convection.

I Leakage of more internal heat thangained from solar heating.

I Jupiter has intense magnetic field, dueto large interior region of metallic H.

I Violent winds and lack of a solid sur-face make possibility of life bleak.

James Lattimer AST 248, Lecture 20

Jupiter

James Lattimer AST 248, Lecture 20

Comparison of Giant Planets

James Lattimer AST 248, Lecture 20

Outer Giant PlanetsI Uranus discovered in 1781 by William

Herschel, but it had been observednearly 100 years before.

I Neptune discovered in 1846 by JohannGalle, predicted by Adams and LeVerrier;Galileo observed it in 1632 but didn’trecognize it as a planet.

I Neptune’s mass greater and radius smallerthan Uranus; thus has higher density.

I Uranus tipped due to early cataclysm?I Uranus radiates 1.06 times its received

solar flux; Neptune 2.61 times.

James Lattimer AST 248, Lecture 20

Jupiter’s GalileanSatellites

Name Diameter Mass Period(× Moon) (× Moon) (days)

Io 105 1.20 1.77Europa 0.90 65 3.55

Ganymede 1.50 200 7.15Callisto 140 1.50 16.69

Name Density Gravity Albedo(× water) (g)

Io 3.53 0.183 0.63Europa 3.01 0.134 0.67

Ganymede 1.94 0.146 0.43Callisto 1.83 0.126 0.22

James Lattimer AST 248, Lecture 20

IoI Similar to Moon in mass and size

I Tidally locked in 1:2:4 orbital resonancewith Europa and Ganymede, causesextensive interior heating

I Most volcanically active object in SolarSystem, silicate or sodium volcanos,liquid sulfur lakes

I Less volatile matter, includingH2O, boiled away eons ago

I Highest density of Galilean satellitesTvashtar Paterae

James Lattimer AST 248, Lecture 20

I No impact craters, new crustgrows at rate of 10 cm/yr

I Volcanos blast matter into space;it becomes ionized and trappedin Jupiter’s magnetosphere. Ioacts as a giant generator(400,000 V, 3,000,000 amps) andcreates extensive radio noise.

South polar region

James Lattimer AST 248, Lecture 20

Europa

I Half the mass and 90% of size of IoI Surface extremely flat and icy, with

filled-in cracks and few cratersI Surface resembles sea ice or pack ice.I Tidally heated like IoI Heating may produce 100-km thick

water ocean 10–30 km under icy crustI Are there hydrothermal vents and life?

James Lattimer AST 248, Lecture 20

Evidence for Water

I Youngest fractures due to tidal stressesI Older fractures due to faster surface

rotation compared to subsurface oceanI Induced magnetic field suggests presence of

subsurface conductive layer like salty waterI Dark steaks are rich in salts or sulfuric

acid hydrates deposited by evaporatingwater from within

I NASA funded Europa Clipper mission,inserted into a Jupiter orbit to further inves-tigate its surface, composition and water eruptions.

James Lattimer AST 248, Lecture 20

Ice Floes?

James Lattimer AST 248, Lecture 20

Chaotic Terrain

Wikipedia

James Lattimer AST 248, Lecture 20

Interior Models

Wikipedia

James Lattimer AST 248, Lecture 20

James Lattimer AST 248, Lecture 20

Proposed Europa Lander

Wikipedia

James Lattimer AST 248, Lecture 20

Ganymede

I Largest satellite in Solar System, largerthan Mercury but half its mass.

I Low density: rocky core & icy crustI Half of surface is dark and heavily cratered;

craters are flat due to plastic flow.I Half of surface covered by parallel grooves

and ridges due to tectonic activity.I Evidence of water flooding 3–3.5 Byrs ago;

geologically dead since.

James Lattimer AST 248, Lecture 20

Callisto

I 2/3 of mass and 90% of radius ofGanymede, but with more ice

I Surface dominated by craters, deformedby plastic flow. Geologically dead.

I Valhalla is a relatively young (2-4 Byr)impact basin.

I No Valhalla antipodal surface disruption,indicating presence of subsurface ocean.

James Lattimer AST 248, Lecture 20

Evidence For Impact From Tidally-Disrupted Object

Craters in a line: impact with a tidally disrupted object like Comet SL9.

James Lattimer AST 248, Lecture 20