Exploring the Planets

Comet Spacecraft Encounters

International Cometary Explorer: ICE Meets Ice
The first spacecraft encounter with a comet occurred in September 1985, when the International Cometary Explorer (ICE) flew through the tail of Comet Giacobini-Zinner.

The International Sun/Earth Explorer 3 (ISEE-3) satellite, launched in 1978, was designed to monitor the interaction between the solar wind, a stream of charged gas emanating from the Sun, and the Earth's magnetic field. Because of this mission, the spacecraft was not equipped with a camera system, but with numerous instruments to measure the characteristics and composition of the solar wind. When the decision was made to change the trajectory for a comet intercept, the spacecraft was renamed the International Cometary Explorer.


Comet Halley Missions
Mission Launch Date Encounter Date Distance from
Number of
Vega-1 Dec. 1984 Mar 1986 10,000 km 13
Vega-2 Dec. 1984 Mar 1986 3,000 km 13
Suisei Aug. 1985 Mar 1986 200,000 km 2
Sakigake Jan. 1985 Mar 1986 10,000 km 3
Giotto Jan. 1985 Mar 1986 596 km 10


Plasma Wave Detector

A Plasma Wave Detector similar to the one pictured here on display in the National Air and Space Museum is aboard the ICE spacecraft, and measured radio waves produced by ionized gases near Comet Giacobini-Zinner over a period of 24 hours. Gift of Fred Scarf, TRW Space and Technology Group.

The Giotto Mission
The Giotto mission, carrying 10 instruments, came closest to the nucleus of Comet Halley. It flew by the comet 596 kilometers (375 miles) from the nucleus, and returned pictures in visible light, as well as other wavelengths. Giotto was guided in its course by data supplied by the Soviet Vega spacecraft and Earth-based tracking from the US Deep Space Network. See Encounters with Comet Halley for imagery from Giotto.

Giotto Space Probe

The Soviet Vega mission consisted of two identical spacecraft (Vega 1 and Vega 2) launched in December of 1984. Each spacecraft deployed a lander and a balloon at Venus in 1985 and then used a gravity assist at Venus to fly by Comet Halley on March 6, 1986.


Orbital Observatories
Spacecraft orbiting Venus and Earth were used to examine the nucleus and tail of Comet Halley. The International Ultraviolet Explorer (IUE) satellite measured variations in ultraviolet light and found times of brightening that were caused by release of carbon dioxide. Also in Earth orbit, the Solar Maximum Observatory (Solar Max) took pictures of the nucleus in ultraviolet wavelengths.

The Pioneer Venus Orbiter, in orbit around Venus from 1978 to 1992, also provided data on Comet Halley. This spacecraft observed the comet at the time the comet and the Earth were on opposite sides of the Sun, and when the comet was closest to the Sun.


Deep Impact
NASA's Deep Impact probe reached Comet Tempel-1 in 2005. It dispatched a heavy copper sphere to strike the comet and then observed the gas and dust released from beneath the surface. This photo shows the comet nucleus about a minute after the impact. The bright area is a cloud of dust released by the impact and strongly reflecting sunlight.


Tempel Alive with Light

Comet Hartley 2
After its encounter with Tempel-1, the Deep Impact spacecraft undertook an extended mission that included a flyby of Comet Hartley 2 in 2010. The comet is about 1.25 miles (2 km) long. It has 2 areas of rough terrain separated by a smooth region that may be covered by fine dust.


Comet Hartley 2

Rosetta Follows a Comet
The European Space Agency's Rosetta is the first spacecraft to follow a comet through the inner solar system. After a decade-long trip, Rosetta began orbiting Comet 67P/Churyumov-Gerasimenko in 2014. The mission also included a lander, called Philae, that landed on Nov. 12, 2014 and collected images and data on the comet's temperature, structure, and surface properties for 3 days.

This artist's view depicts the Rosetta orbiter with its solar panels extended. Because its long path took it out to the distance of Jupiter, Rosetta has solar panels 32 meters (106 feet) across to generate enough power. Rosetta is scheduled to continue monitoring the comet as it moves further from the Sun until September 2016 when it will be impacted onto the surface.


Rosetta Follows a Comet

This photo taken by Rosetta shows the comet's rugged surface and highly irregular shape. The longest dimension is only about 5 kilometers (3 miles). Because the comet has passed through the inner solar system many times, its surface shows the effects of extensive melting and outgassing.



The Philae lander as it approached the comet


The Philae lander

Stardust Captures Dusty Traces of a Comet
NASA's Stardust probe flew through the tail of Comet Wild-2 in 2004 and captured tiny particles in its aerogel collectors. The spacecraft then flew past Earth again, released the capsule containing the collectors, which returned to Earth, and headed off to rendezvous with another comet.

Scientists analyzing the returned particles were excited to discover that rocky material in the comet formed under very high temperatures early in the history of our solar system. These rocky bits were then pushed far beyond Neptune by the energy of the young Sun, where they combined with icy materials to form the comets.

Stardust photographed the 5-kilometer (3-mile) diameter comet as it flew by.


Stardust Captures Dusty Traces of a Comet

Stardust Aerogel
To capture cometary and interstellar dust samples, Stardust used a porous, silicon-based material called aerogel. The lightest solid ever created, aerogel has a spongelike structure that is 99 percent empty space and only slightly denser than air. The cometary particle grid (at the end of the capsule's arm) held 132 aerogel tiles.


Scientists at NASA's Johnson Space Center, Houston, examine the Stardust aerogel grid just after the capsule returned to Earth


Scientists at NASA’s Johnson Space Center