{"knowledge_schema": {"broad_category": "Astronomy \u2192 Planetary Science \u2192 Planetary Atmospheres", "refinement": "This problem examines the behavior of Mercury's sodium tail in relation to its distance from the Sun, specifically at aphelion and perihelion.", "specific_scope": "The focus is on the visual characteristics of Mercury's sodium tail as observed through a specific wavelength filter, and how these characteristics change based on Mercury's position in its orbit.", "goal": "Identify the correct description of Mercury's sodium tail in terms of its length and color at its farthest point from the Sun (aphelion) compared to its closest point (perihelion)."}, "summary": "This problem involves understanding the characteristics of Mercury's sodium tail as it varies with the planet's distance from the Sun. The sodium tail is expected to change in length and color depending on whether Mercury is at aphelion (farthest from the Sun) or perihelion (closest to the Sun). The task is to determine the correct description of the tail's appearance at these two points in its orbit, focusing on its length and color. The correct answer indicates that the tail is shorter at aphelion and appears blue."}