The 4.5-billion-year-old secrets hidden inside a comet's porous shell
In short: Comets are the solar system's ultimate time capsules, preserved since their formation over 4.5 billion years ago. By crashing an impactor into one and performing high-speed flybys, NASA's EPOXI mission revealed that these celestial bodies are not just solid rocks, but complex, porous structures driven by internal chemistry.
The Deep Impact (EPOXI) mission was designed to look beneath the surface of comets, a feat previous missions like Vega, Giotto, and Stardust could not achieve. In 2005, NASA launched a spacecraft weighing 1,430 pounds, which carried a specialized 820-pound impactor. The primary objective was to probe the internal composition and structure of Comet Tempel 1 by deliberately colliding the impactor with it on July 4, 2005.
The mission yielded significant structural and chemical insights. It determined that a comet's surface layer is highly porous and discovered that 'hyperactive' comets are primarily driven by carbon dioxide (CO2). During the flyby of Comet 103P/Hartley 2 in November 2010, the spacecraft traveled at 27,000 mph, passing at an altitude of about 435 miles. This proximity allowed scientists to observe the comet's nucleus, which is small, dark, and exhibited a rapidly changing rotation period that shifted from approximately 16.4 hours to near 19 hours in a matter of months.
While Hartley 2 shares similar volatile and isotope ratios with other Jupiter-family comets, its CO2-driven activity near perihelion is a distinct characteristic. Additionally, data showed a massive ring of water-ice particles encircling the nucleus during its closest approach to the sun. These findings provide a deeper understanding of how these ancient remnants behave as they interact with the sun, offering a window into the materials that formed our solar system.
The mission concluded in September 2013 after nearly nine years in space, having returned approximately 500,000 images of celestial objects. It successfully bridged the gap between surface observation and internal analysis, proving that the dynamics of comets are governed by complex internal pressures and porous architectures.
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Sources
- Summary by Intellect · source: EPOXI's Comet Encounter Produces Revealing Data
- Also: Deep Impact (EPOXI) - NASA Science
- Also: EPOXI: Comet 103p/Hartley 2 Observations from a Worldwide Campaign - NASA Technical Reports Server (NTRS)
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