Stardust: The mission that forever changed our understanding of comets
AD: Can you tell us about your experience recovering the sample collector?
Brownlee: It was the middle of the night in a very remote place in Utah [the capsule was recovered in Dugway, Utah, in the west desert near the Great Salt Lake]. The entrance to the capsule was a wonder. It was [a] glowing fireball with a luminous tail coming from the west. It was descending and getting closer, but seen from Ground Zero, it was oddly rising in the sky. People nearby [the town of] Wendover heard the sonic boom and a NASA plane got spectacular footage, as did a Japanese film crew on the ground. I was outside to see the fireball, then inside to watch the images from the tracking devices. He landed in the dark and it took several hours to find him. He was found by our helicopter crew and returned to a special clean room prepared for him where he was inspected and prepared for [a] flight the next day to Johnson Space Center in Houston.
AD: What did the analysis of comet dust particles tell us? What were the main conclusions?
Brownlee: The main finding is that the rocky components of the comet, most of its total mass, formed at scorching temperatures. The formation of comets included fire and ice. Some of the ice formed at temperatures near absolute zero, but the rocky material formed under white heat conditions. Many materials from the comet have also been found in meteorites. Comet Wild 2 is a broader mix of components suggesting that material from a wide range of locations was transported past Pluto where the comet formed. The rock materials primarily formed at temperatures above 1832 degrees Fahrenheit (1000 degrees Celsius) and could not have ice or organic material on them at the time of their formation. The comet’s rock silicate materials first formed, then came together with ice and organics in a considerably colder location. This proved that the formation of cometary dust and ice was clearly decoupled. The samples proved that the outer solar system was not isolated from the inner solar system and that materials clearly mixed in regions near the Sun to regions beyond Pluto’s orbit.
AD: Looking back on the mission all these years later, what are your fondest memories of the experience?
Brownlee: Launch: A totally amazing experience when it comes to your own mission. I watched the launch from a mile away, it was so clear we could see the 4 solid rocket motors separate and fall with the naked eye.
The overview: The tension was just incredible. As careful as you are, space exploration involves risks and unknowns, you are involved in a strange game of Russian roulette. Throughout the mission, [I] felt like a soldier on the beach on d-day [in World War II]. Bullets whiz around you and you hope they don’t hit you.
Atmospheric Entry and Recovery: The launch was so impressive that many had tears in their eyes. It had nothing to do with the fireball entering the Sample Return Pod in the middle of the night, in the middle of the desert with a glowing glowing tail behind it.
Opening the collector: We opened the collector in a special clean room at the Johnson Space Center. Mike Zolensky and I were the only ones close by and when the airgel array was finally exposed we were watching it from the back. We couldn’t see the impacts and the airgel looked even better than before launch. We wondered if the collector had actually opened. We were nervous, but we felt like we were seeing capture trails, but [were] not sure because we were looking through the back of about 1.6 inches (4 centimeters) of airgel. When the collector was raised, we could instantly see the catch tracks clearly.
Probably my biggest thrill of the mission was presenting the first results of the sample analysis at the annual Lunar and Planetary Science Conference, just 3 months after landing. When I showed the results to 600 people crammed into the room, you could hear gasps and see jaws drop. We had gone to see a type of body famous for its ice, a body whose dust was believed to be dominated by solids formed around other stars. We had discovered that it contained the hottest material that could have existed in the solar system. Finding such material in a comet was revolutionary. Our modest mission had sent samples back to Earth that taught us things about comets that we could never. [have] known by remote sensing methods.
Doug Adler is the co-host of The good companion podcast and book co-author: From the Earth to the Moon: The Companion to the Miniseries