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hat is the core of a comet? How does the dirty snowball model reveal its mystery?
How many secrets does the core of a comet, the solid center once called a "dirty snowball," hold? Scientists believe that the core of a comet is mainly composed of rocks, dust and frozen gases. As it approaches the sun, the gas sublimates to produce an atmosphere surrounding the core, which is called the coma. Why can these celestial bodies that attract our attention form such amazing comet tails under the influence of the sun's radiation pressure and solar wind?
Consistent observations show that the comet's nucleus has a reflectivity of about 0.04, which is darker than coal, probably due to its dusty surface.
Scientists have observed that comet 67P/Churyumov-Hrasmenko has no magnetic field in its core, suggesting that magnetism may not be important in the early stages of planet formation. As scientists conduct in-depth analysis of comets, they gradually advance the concept of the "dirty snowball" model. They find that the core of a comet is not just a refrigerator of ice and other volatile substances, but a structure containing organic compounds.
On July 30, 2015, scientists reported that the Philae lander had detected at least 16 organic compounds on Comet 67P for the first time, including previously undiscovered components such as acetamine, acetone and propionaldehyde.
The core structure of comets has always been a hot topic for astronomers. Historically, the understanding of comets has evolved from the "flying sandpile" model to the "dirty snowball" theory and then to the current "ice ball" model. These models gradually revealed the complexity and diversity of comets: they are not just icy chunks surrounding a solid core, but crucially, how these cores change as comets approach the sun.
"Comet nuclei are not only ice, but also contain many other components, from organic matter to minerals, showing that their structure is far richer than we thought."
In the study of comets, multiple exploration missions since the 1970s have shown that the structure of comets is quite fragile. These studies not only provide information on the density of comet grains, but also reveal the porosity of the structure and the ratio of ice to dust. Pillard's observations indicate that the dust layer of Comet 67P can be up to 20 centimeters thick, while its base is made of hard ice, and the porosity increases gradually with depth inside the comet.
While modern observational techniques such as the Rosetta mission are providing data that are rigorously testing previous theories, many questions remain, such as how and when these comets formed. How will their composition affect the history of the solar system?
"Their formation and current activity undoubtedly have important implications for our understanding of the evolution of the solar system."
The legendary story of comets is not only about observing their movement trajectories, but also a window for humans to explore the universe. From ancient times to the present, the appearance of comets has aroused people's endless imagination. As space exploration technology advances, we are able to get closer to these mysterious celestial bodies and ask more profound scientific questions.
Whenever we look up at the starry sky, can certain twinkling comets once again inspire us to have the courage to explore the depths of the universe and make us rethink the wonderful connection between comets and the Earth?
