The Solar System

This dust particle was collected by

spacecraft above Earth’s atmosphere.

It is almost certainly from a comet.

As the ices in a comet nucleus

vaporize, they release dust particles that

not only form the dust tail, but also spread

throughout the solar system.

The Deep Impact spacecraft released an

instrumented probe into the path of Comet

Tempel 1. When the comet slammed into the

probe at 10.2 km/s as shown at right huge

amounts of gas and dust were released. From

the results, scientists conclude that the nucleus

of the comet is rich in dust finer than the

particles of talcum powder. The nucleus is

marked by craters, but it is not solid rock. It is

about the density of fresh fallen snow.

This dust particle was collected by

spacecraft above Earth’s atmosphere.

It is almost certainly from a comet.

Fragments

A microscopic

mineral crystal

from Comet

Wild 2

Dust particles (arrows) were embedded in the

collector when they struck at high velocity.

Direction

of travel

Visual-wavelength images

Visual

Comet 73P/Schwassmann-Wachmann3 Fragment B

NASA

NASA/JPL-Caltech/UMD

NASA

JPL/ NASA

NASA/ESA/H. Weaver/JHU/APL/M. Mutchler and Z. Levay/STScI

As the ices in a comet nucleus
vaporize, they release dust particles that
not only form the dust tail but also spread
throughout the solar system.

The Deep Impact spacecraft released an
instrumented probe into the path of Comet
Tempel 1. When the comet slammed into the
probe at 10.2 km/s as shown at right, huge
amounts of gas and dust were released. From
the results, scientists conclude that the nucleus
of the comet is rich in dust finer than the
particles of talcum powder. The nucleus is
marked by craters, but it is not solid rock. It is
about the density of fresh-fallen snow.

2

The nuclei of comets are not strong and can break up. In 2006,

Comet Schwassmann-Wachmann 3 broke into a number of fragments

that themselves fragmented. Fragment B is shown at the right breaking into

smaller pieces. The gas and dust released by the breakup made the comet

fragments bright in the night sky, and some were visible with binoculars. As

its ices vaporize and its dust spreads, the comet may totally disintegrate and

leave nothing but a stream of debris along its previous orbit.

Comets most often break up as they pass close to the sun or close to a

massive planet like Jupiter. Comet LINEAR broke up in 2000 as it passed by

the sun. The comet that hit Jupiter in 1994 was first ripped to pieces by tidal

stresses from Jupiter’s gravity. Comets can also fragment far from planets,

perhaps because of the vaporization of critical structural areas of ice.

3

2a The Stardust spacecraft flew past the nucleus of Comet Wild 2 and collected dust particles

(as shown above) in an exposed target that was

later parachuted back to Earth. The dust particles hit

the collector at high velocity and became

embedded, but they can be extracted for study.

Some of the collected dust is made of high-temperature minerals that could only have

formed near the sun. This suggests that material from the inner solar nebula was mixed

outward and became part of the forming comets in the outer solar system. Other

minerals found include olivine, a very common mineral on Earth but not one that

scientists expected to find in a comet.

Only seconds before

impact, craters are visible

on the dark surface.

Images of Comet Tempel 1 from

the flyby probe 13 seconds after

the impact probe hit. Gas and dust

are thrown out of the impact crater.