Density

In the solar system

Density on Earth

Density of water 1.0 g/cm3

Density of air 0.0012 g/cm3 (sea level at 15° C)

Changes in temperature, humidity and salinity can change the density of water and air

Density on Earth

Metamorphic rocksSedimentary rocks

Igneous rocks

Density of rocks 2.2-3.3 g/cm3

Density of Earth

Average Density 5.5 g/cm3

Density of Earth

Density is one of the clues geologists have used to help understand the internal structure of Earth

Inside Earth

Seismic waves from earthquakes passing through Earth provide important information about the size and characteristics of each layer.

15

10

5

Den

sity

g/c

m3

Inside Earth

Using these and other pieces of

evidence, geologists have

been able to create a model of Earth’s internal

structure.

Inside Earth

Seismic waves from earthquakes passing through Earth provide important information about the size and characteristics of each layer.

Inner Core

Outer Core

Mantle

The mass and volume of Earth are much larger than the mass and volume of the Moon.

Comparison of Earth and Moon

What about density?

Earth Average Density

5.5 g/cm3

Moon Average Density

3.4 g/cm3

What can we infer What can we infer about the about the

composition and composition and internal structure internal structure

of the Moon of the Moon based on its based on its

density compared density compared to Earth?to Earth?

Comparison of Earth and Moon

What about density?

Mercury vs. Ganymede

Average Density5.43 g/cm3

Average Density1.94 g/cm3

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Credit: NASA

Mercury vs. Ganymede

Average Density5.43 g/cm3

Average Density1.94 g/cm3

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Credit: NASA

What can we infer about the What can we infer about the compositions of Mercury and compositions of Mercury and

Ganymede based on their Ganymede based on their densities?densities?

Mercury vs. Ganymede

Rock surrounding a large iron core

Image courtesy of Windows to the Universe Credit: NASA

Icy shell surrounding a small rocky mantle and

small metallic core

1 CeresDiameter = 606 miles

4 VestaDiameter = 348 miles

The DAWN spacecraft will determine the mass of Vesta and Ceres by

measuring each asteroid’s gravity.

Vesta arrival: July, 2011Vesta departure: September, 2012Ceres arrival: February, 2015

http://dawn.jpl.nasa.gov/

Calculating average density using the mass will give us information about their internal structure