Aerogel - A Little Bit of Almost Nothing

Catching comet dust is no easy feat! When the spacecraft flies past the comet, the impact velocity of the particles they are captured will be up to 9 times the speed of a bullet fired from a rifle. Although the captured particles will each be smaller than a grain of sand, high-speed capture could alter their shape and chemical composition - or vaporize them entirely.

Dr. Peter Tsou with a sample of Aerogel.
To collect the particles without damaging them, STARDUST will use an extraordinary substance called aerogel - a silicon-based solid with a porous, sponge-like structure in which 99 percent of the volume is empty space. Aerogel is 1,000 times less dense than glass, another silicon-based solid. When a particle hits the aerogel, it will bury itself in the material, creating a carrot-shaped track up to 200 times its own length, as it slows down and comes to a stop - like an airplane setting down on a runway and braking to reduce its speed gradually. Since aerogel is mostly transparent - sometimes called blue smoke - scientists will use these tracks to find the tiny particles.

Aerogel Facts...

  • 99.8% Air
  • 39 times more insulating than the best fiberglass insulation
  • 1,000 times less dense than glass
  • Used on Mars Pathfinder's rover

Photograph courtesy of
Ernest Orlando, Lawrence Berkeley National Laboratory
Learn more about Aerogel from our Aerogel brochure. Available on line in pdf format: AEROGEL BROCHURE

John Glenn Will Conduct Tests With Aerogel On STS-95
Marshall Space Flight Center - October 26, 1998


Collection of Dust Samples using Aerogel

The primary objective of the STARDUST mission is to capture both comet coma samples and contemporary interstellar grains moving at high velocity with minimal heating and other effects of physical alteration. To achieve this a new intact capture technology has been developed over the past decade specifically for comet flyby sample return missions [Tsou 1984] in which hypervelocity particles are captured by impact into underdense, microporous

Aerogel Dust Collector
Under Construction
media known as aerogel [Tsou 1994]. This is not like conventional foams, but is a rather special porous material that has extreme microporosity at the micron scale. Aerogel is composed of individual features only a few nanometers in size, linked in a highly porous dendritic-like structure.

This exotic material has many unusual properties, such as uniquely low thermal conductivity, refractive index, and sound speed, in addition to its exceptional ability to capture hypervelocity dust. Aerogel is made by high temperature and pressure critical point drying of a gel composed of colloidal silica structural units filled with solvents. Over the past several years, aerogel has been made and flight qualified at the Jet Propulsion Laboratory.

The JPL facility will produce the aerogel for the STARDUST mission and provide well controlled media properties and purity. For volatiles collection each

Particle Captured in Aerogel
collector medium will be dopped with selected absorbents. Silica aerogel produced at JPL is a water clear, high purity silica glass-like material that can be made with bulk density approaching the density of air. It is strong and easily survives launch and space environments. JPL aerogel capture experiments have flown [Tsou 1993] and been recovered on Shuttle flights, Spacehab II and Eureca. Examples are shown in these photos of Cometary Dust Particles. For additional technical information about aerogel see, Berekley National Laboratory at

When hypervelocity particles are captured in aerogel they produce narrow cone-shaped tracks, that are hollow and can easily be seen in the highly transparent aerogel by using a stereo microscope. The cone is largest at the
Dust Collector
point of entry, and the particle is collected intact at the point of the cone. This provides a directionality detector and is the basis of our approach of using single slabs of aerogel to collect both cometary and interstellar dust, and being able to differentiate between them because the A side of the collector is exposed in the comet dust impact direction and the B side is positioned toward the interstellar dust stream. After the encounter with Wild 2, the aerogel collector will be retracted into the Sample Return Capsule (SRC) and returned to Earth for detailed analysis by scientists.