Comet Wild 2
Introduction
Comet Wild 2, also known as 81P/Wild, is a short-period comet discovered by Swiss astronomer Paul Wild on January 6, 1978. This celestial body is notable for its interaction with the Stardust spacecraft, which collected samples from its coma and returned them to Earth, providing invaluable insights into the composition of comets and the early solar system.
Discovery and Observation
Paul Wild discovered Comet Wild 2 at the Zimmerwald Observatory in Switzerland. At the time of its discovery, the comet was located near Jupiter, which significantly influenced its orbit. Before 1974, Wild 2 had an orbit that kept it at a considerable distance from the Sun. However, a close encounter with Jupiter in 1974 altered its trajectory, bringing it closer to the inner solar system and making it more accessible for observation.
Orbital Characteristics
Comet Wild 2 has an orbital period of approximately 6.41 years. Its perihelion, the point in its orbit closest to the Sun, is about 1.59 AU (astronomical units), while its aphelion, the farthest point from the Sun, is about 5.24 AU. The comet's orbit is moderately inclined at 3.24 degrees to the ecliptic plane. This relatively short orbital period classifies it as a Jupiter-family comet, a group of comets whose orbits are influenced by the gravitational pull of Jupiter.
Physical Characteristics
Wild 2's nucleus is roughly 5.5 kilometers in diameter, making it a medium-sized cometary nucleus. The surface of the nucleus is covered with a layer of dark, carbon-rich material, which is typical of cometary nuclei. The comet's albedo, or reflectivity, is low, indicating that it absorbs most of the sunlight that strikes it.
The nucleus of Wild 2 is highly irregular in shape, with numerous pits, cliffs, and jets. These features are the result of sublimation, where ice transforms directly into gas, creating jets that eject dust and gas into space. This process forms the comet's coma and tail, which are visible when the comet approaches the Sun.
Stardust Mission
The Stardust spacecraft was launched by NASA on February 7, 1999, with the primary mission of collecting samples from the coma of Comet Wild 2. The spacecraft successfully encountered the comet on January 2, 2004, passing within 240 kilometers of its nucleus. During this flyby, Stardust collected particles from the comet's coma using an aerogel collector, a lightweight, porous material that gently captured the high-velocity particles without altering their structure.
The samples returned to Earth on January 15, 2006, in a sample return capsule that landed in the Utah desert. The analysis of these samples has provided significant insights into the composition of comets and the early solar system. The particles collected from Wild 2 contain a mixture of silicates, sulfides, and organic compounds, including amino acids, which are the building blocks of life.
Scientific Findings
The analysis of the Stardust samples revealed that Comet Wild 2 contains a variety of minerals, some of which are formed at high temperatures. This finding was unexpected, as comets are typically thought to contain only materials that formed in the cold outer regions of the solar system. The presence of high-temperature minerals suggests that material from the inner solar system was mixed into the outer regions during the early stages of solar system formation.
One of the most significant discoveries from the Stardust mission was the identification of glycine, an amino acid, in the samples from Wild 2. This discovery supports the theory that comets may have played a role in delivering the building blocks of life to Earth.
Cometary Jets and Activity
Comet Wild 2 exhibits a variety of jets and outgassing activity, which are driven by the sublimation of volatile ices as the comet approaches the Sun. These jets can be highly variable, both in terms of their location on the nucleus and their intensity. Observations from the Stardust mission revealed that Wild 2 has at least 20 active jets, which are responsible for the ejection of dust and gas into the coma.
The jets on Wild 2 are primarily composed of water vapor, but they also contain other volatile compounds such as carbon dioxide and carbon monoxide. The activity of these jets can cause significant changes in the comet's rotation and can even lead to the fragmentation of the nucleus over time.
Surface Features and Composition
The surface of Comet Wild 2 is characterized by a variety of features, including pits, cliffs, and smooth plains. The pits on the surface are thought to be the result of explosive outgassing events, where pockets of volatile ices rapidly sublimate and eject material into space. These pits can be several hundred meters in diameter and are often surrounded by raised rims of ejected material.
The cliffs on Wild 2 are formed by the erosion of the surface as volatile ices sublimate and cause the overlying material to collapse. These cliffs can be several hundred meters high and are often associated with active jets.
The smooth plains on the surface of Wild 2 are thought to be regions where fine-grained dust has settled after being ejected by jets. These plains are relatively featureless compared to the rest of the nucleus and are thought to be composed of a mixture of silicates and organic compounds.
Impact on Solar System Studies
The study of Comet Wild 2 has had a significant impact on our understanding of the solar system. The findings from the Stardust mission have challenged traditional views of cometary composition and have provided new insights into the processes that shaped the early solar system.
The discovery of high-temperature minerals in the Stardust samples suggests that material from the inner solar system was mixed into the outer regions during the early stages of solar system formation. This finding has implications for our understanding of the formation and evolution of the solar system and suggests that comets may contain a more diverse range of materials than previously thought.
The identification of glycine in the Stardust samples supports the theory that comets may have played a role in delivering the building blocks of life to Earth. This finding has implications for our understanding of the origins of life and suggests that comets may have been an important source of organic compounds in the early solar system.
Future Missions and Research
The success of the Stardust mission has paved the way for future missions to comets and other small bodies in the solar system. One such mission is the Rosetta spacecraft, which was launched by the European Space Agency in 2004 and successfully rendezvoused with Comet 67P/Churyumov-Gerasimenko in 2014. The Rosetta mission has provided detailed observations of the comet's nucleus and has collected valuable data on its composition and activity.
Future missions to comets may focus on collecting samples from different regions of the nucleus or from different comets to provide a more comprehensive understanding of their composition and the processes that shape them. These missions may also aim to study the interaction between comets and the solar wind, which can provide insights into the behavior of comets as they travel through the solar system.
Conclusion
Comet Wild 2 has provided valuable insights into the composition and behavior of comets and has challenged traditional views of their formation and evolution. The findings from the Stardust mission have highlighted the importance of comets in understanding the early solar system and the origins of life. Future missions to comets will continue to build on this knowledge and provide new insights into these fascinating celestial bodies.