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Chapter 15: Problem 42

Comets are generally brighter a few weeks after passing perihelion than a few weeks before passing perihelion. Explain why might this be. (Hint: Water, including water ice, does an excellent job of retaining heat.)

Short Answer

Expert verified
Comets are generally brighter a few weeks after perihelion due to the heat absorbed and stored by the water ice while passing close to the sun. This heat causes increased 'outgassing' of the comet, which increases its brightness after perihelion.

Step by step solution

01

Understanding Perihelion

Perihelion is the point in the path of a celestial body (like a planet, asteroid or a comet) that is closest to the sun. When a comet reaches its perihelion, it is subjected to intense solar radiation and heat due to its proximity to the sun.
02

Role of Water Ice

Comets typically consist largely of water ice. When a comet gets closer to the sun, this ice begins to vaporize. The hint provided in the exercise indicates that water, including water ice, is an excellent retainer of heat. This means that the water ice in the comet absorbs and stores a lot of the solar heat experienced at perihelion.
03

Post-Perihelion Brightness Increase

After perihelion, as the comet moves away from the sun, the retained heat causes more of the water ice to vaporize into a halo of gas and dust particles that reflect sunlight, a phenomenon known as 'outgassing'. This largely contributes to the brightness of the comet. As the process of outgassing is accelerated due to the stored heat, the comet appears brighter a few weeks after passing perihelion than it does a few weeks before.

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