Randy Gladstone

Southwest Research Institute, San Antonio TX 78238

JUPITER VERSUS THE EARTH:COMPOSITION & STRUCTURE

NASA Space Science WorkshopExplore! Jupiter’s Family Secrets

May 4-5, 2010 Springfield, MO

Terrestrial Planets Giant Planets Ice Dwarf

Mer

cury

Ven

usE

arth

Sun

Mar

s

Jupi

ter

Sat

urn

Ura

nus

Nep

tune Plu

to

Solar System Architecture

Frost Line

Rock Ice + Rock

Solar Nebula TemperatureWarm Cold

• For planets other than Earth, there are only a few ways to determine what’s inside

• From the mean density (the total mass divided by the total volume) it is possible to constrain the internal structure based on models of likely composition• From the gravity field (determined by watching how satellites orbit) it is possible to tell more about how the mass inside a planet is distributed (e.g., whether it has a core, etc.)

• For Earth, most of our knowledge of the interior come from the study of seismic waves (as are generated by large earthquakes)

How Do We Know What’s Inside a Planet?

Earth (5520 kg/m3)

Mercury (5420 kg/m3)Mars (3940 kg/m3)

Venus (5250 kg/m3)

Terrestrial Planet Interiors

Earthquake Waves Probe Earth’s Interior

The major regions in the Earth are the crust, mantle, outer core, and inner core:• The outer crust is relatively thin (~30 km thick in the continents and ~5 km thick in the oceans)• The mantle is ~3000 km thick (almost halfway to the center of the Earth) and is made of a dense rock called peridotite; it has plastic-like properties and its slow overturning drags along the crust, causing plate tectonics (i.e., continental drift)• The liquid outer core is 2300 km thick and is a mixture of iron (90%) and nickel (10%); motions in the liquid give rise to the Earth’s magnetic field• The solid inner core at Earth’s center has a 1200 km radius and is made of iron (90%) and nickel (10%); the temperature at the Earth’s core is ~5700 K and the pressure there is ~3.6 million atmospheres

Inside Earth

Jupiter(1310 kg/m3)

Earth

Saturn(690 kg/m3)

Uranus(1190 kg/m3)

Neptune(1660 kg/m3)

Jupiter Interior vs. Earth Interior

Jupiter is still cooling off (and contracting) from its formation 4.5 billion years ago (it emits 1.7 times as much energy as it receives from the Sun)!• The atmosphere (the outermost ~5000 km at <1 atmosphere) is mostly molecular hydrogen and helium); heavier elements are generally enriched by ~3 times compared to the Sun• The deep atmosphere continues down another ~15000 km to a point where the pressure increases above a few million atmospheres and hydrogen becomes metallic; helium may be raining out near this boundary• The metallic hydrogen layer is ~50,000 km thick and motions in the fluid give rise to Jupiter’s strong magnetic field• The rocky inner core at Jupiter’s center contains between zero and 20 Earth masses; the temperature at the Jupiter’s core is ~20,000 K and the pressure there is ~40 million atmospheres

Inside Jupiter