Blanch the fava beans in boiling water for about 2 minutes. Drain and pinch off the skins with your fingers. Set aside in a small bowl.

In a large saucepan, combine the carrot juice, 1/2 cup butter, and carrots. Bring to a boil, reduce heat to a simmer, and stir until the butter is melted. Add the zucchini, cayenne, cinnamon, nutmeg, and fava beans. Simmer until vegetables are tender, 3 to 5 minutes. Add salt. Cover and keep warm over very low heat.

In a large sautè pan or skillet, melt the 4 tablespoons butter over medium-high heat. Pat the scallops dry with a paper towel and add them to the pan one at a time. Sautè until browned on both sides and slightly firm to the touch. Transfer to an ovenproof platter and keep warm in a low oven.

In a large pot of salted boiling water, cook the pasta until al dente, about 10 minutes. Drain well and divide among warmed shallow bowls. Ladle a generous amount of the carrot sauce over each pasta portion and place 3 scallops on top of each serving. Garnish with parsley and serve at once.