JUPITER VERSUS THE EARTH:
COMPOSITION & STRUCTURE
Randy Gladstone
Southwest Research Institute, San Antonio TX 78238
NASA Space Science Workshop
Explore! Jupiter’s Family Secrets
May 4-5, 2010
Springfield, MO
Solar System Architecture
Warm
Solar Nebula Temperature
Rock
Cold
Ice + Rock
Frost Line
Pluto
Neptune
Ice Dwarf
Uranus
Saturn
Giant Planets
Jupiter
Sun
Mercury
Venus
Earth
Mars
Terrestrial Planets
How Do We Know What’s Inside a Planet?
• 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)
Terrestrial Planet Interiors
Venus (5250 kg/m3)
Mars (3940 kg/m3)
Earth (5520 kg/m3)
Mercury (5420 kg/m3)
Earthquake Waves Probe Earth’s Interior
Inside Earth
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
Earth
Jupiter
(1310 kg/m3)
Saturn
Uranus
Neptune
(690 kg/m3) (1190 kg/m3) (1660 kg/m3)
Jupiter Interior vs. Earth Interior
Inside Jupiter
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