1. Stardust@home A Distributed, Interactive, Internet-based Search for Interstellar Dust in the Stardust Interstellar Collector Stardust@home is a NASA-funded project operated by the Space Sciences Laboratory at the University of California, Berkeley

2. Interstellar Dust The space between the stars is vast, but not empty. It is filled with gas and dust: The Interstellar Medium (ISM): stuff between the stars. The density of the Interstellar Medium is extremely low:  1 gas atom per cubic centimeter  1 dust particle per 1 cubic kilometer (one dust particle inside a volume equivalent to 250 football stadiums)

3. Light interacts with matter in the ISM in a variety of ways Light from stars or other sources can be scattered (bounced): Light can be emitted: Atoms and Molecules can absorb the energy of light Where ISM is densest, light from background light sources is completely blocked Hydrogen gas around hot young stars can become completely ionized by absorbing ultraviolet light Light can be absorbed: Electrons stripped off by UV light can recombine with protons to form hydrogen and release visible red light – the gas glows red! Warmed dust glows in infrared light Typical size of dust grain: 0.1 microns Size of visible wavelengths of light: 0.4-0.7 microns Blue light is more easily scattered Background light sources are reddened and dimmed Interstellar Dust

4. Cosmic Recycling Supernovas ISM SuperGiant Stars Protostars Stars Planetary Nebula Matter in the ISM condenses to form stars and planets During its life a star generates energy by converting light elements into heavier elements via nuclear fusion At the end, low-mass stars slowly puff off their outer layers back into the ISM High-mass stars blow strong winds of gas back into the ISM and explode in the end Interstellar Dust Interstellar dust particles are created in many different environments: New stars and planets are formed from interstellar dust and gas. Supernova Remnants We are quite literally stardust! Outflows from dying stars Atmospheres of Red Giant stars

5. Interstellar Dust The Ulysses and Galileo spacecrafts detected a flow of interstellar dust through the Solar System coming from the direction of the constellation Ophiuchus

6. Stardust Mission NASA’s Stardust mission launched in 1999 to collect dust from comet Wild 2 and return the samples to Earth. The first ever comet sample return mission. Science objective: to understand the materials and conditions that went into the formation of the Solar System. A very special material was used to collect the dust.

7. Aerogel

8. Stardust Mission Stardust made 3 orbits around the Sun to encounter Wild 2 and then returned home. Along the way, the aerogel collector was opened up and pointed into the interstellar dust stream to collect samples of dust coming from outside the Solar System. Stardust collected interstellar dust twice for a total of 6.5 months

9. Aerogel Collection Grid Sample Return Capsule Stardust Mission Direction of Interstellar Dust The first time interstellar dust such as this was ever collected for return!

10. Interstellar dust impacted the aerogel collector grid with a relative speed of about 20 km/s (45,000 mph) With masses in the picogram regime, the particles should only penetrate about 100 microns into the surface of the 3cm thick aerogel tiles, leaving behind tracks in the aerogel. Dust in the Aerogel The particles are sub-micron in size and are few in number, approximately 45 in the entire collector. The collector itself is about 1,000 cm 2 in area.

11. Ants in a football field An automated microscope at JSC scans through the grid taking digital “focus movies”. The field of view is about 0.5mm on a side. The collector itself is about 1,000 cm 2 in area. There will be nearly 1 million of these. Finding the interstellar dust particles will be like searching for 45 ants in a football field looking one 5cmx5cm square at a time.

12. Finding the dust How do we find 45 microscopic particles somewhere within a million focus movies? The particles themselves are not visible in the movies, only the tracks they leave in the aerogel. Pattern recognition software? We had no knowledge of the condition of the aerogel until it returned, nor do we really know what the particle tracks look like. We would have to first teach the software to recognize particle tracks and differentiate them from other possible features. To do that we would need to find a dozen or so particles! We need people to look through the movies.

13. Stardust@home The task of manually searching through a million focus movies would be overwhelming for a small research group…but not for an army of enthusiastic volunteers. The focus movies are placed online for volunteers to examine. We estimate that it will take 30,000 person-hours to complete the task. We now have over 20,000 people registered. It will take several months to complete the scan of the collector with the automated microscope, that will be limiting time factor. http://stardustathome.ssl.berkeley.edu

14. Virtual Microscope Volunteers use a Virtual Microscope (VM) to examine focus movies. The VM works directly within a web browser, no special software needed, simply an internet connection and a fair amount of RAM. A simple online training session and test are required for volunteers to learn how to use the VM. The first focus movies were made available online on August 1 st, 2006 and the project will continue for several months following.

15. Each focus movie is viewed by many people. Calibration movies are placed into the data stream (movies known to have no particles, etc.) to gauge each volunteer’s sensitivity (find tracks when they are there) and specificity (find no tracks when they are absent). Each user receives an overall score. How It Works Each movie receives a score weighted by the score of the volunteer who flags it as either containing a track or not Scientists at UC Berkeley follow up on movies that receive a high enough score. Stardust Interstellar Dust Collector Scanning Progress as of December 8, 2006

16. Website features a ‘Community’ section where volunteers can communicate with each other via a bulletin board. Website features a list of the volunteers with the top scores. Users achieving a high score receive a certificate of participation. The first to find a track will have the privilege of naming the dust particle. Will also be given co-authorship of scientific papers about the discovery The Volunteers 20,000+ volunteers 20% Female, 80% Male Ages 6 - 99 From over 60 countries on 6 continents Starduster Stats:

17. Educational Resources Using the bulletin board, teachers can discuss lesson plans for students using the Virtual Microscope. Stardust@home Website contains educational materials developed by the Stardust mission E/PO team: Comets, Solar System, Orbits, Aerogel, Building a Spacecraft We also provide professional development for educators about ISM, planetary system formation, and comets.