The projected PDFs of model NEO orbits for different sources (projected p _j (a, e, i)): ν ₆, 3:1, 5:2, 8:3, 2:1 and JFCs (from top left to bottom right). Higher values are shown by brighter colors. For reference, the red lines show orbits with q = a _Earth, Q = a _Earth, q = a _Venus, and Q = a _Venus, where Q = a(1 + e) is the aphelion distance, a _Earth = 1.0 au and a _Venus = 0.72 au.