In the fourth paragraph he claims that the reason why scientists are discussing further visits is because "Astronomers are fascinated by Venus because it may well once have been the most Earth-like planet in our solar system." The second piece of evidence he provides is that "Venus can sometimes be our nearest option for a planetary visit," alluding to the second paragraph, where he explained that Earth, Venus, and Mars all orbit the sun at different speeds, causing them to vary in the distances they are from each other.