sentence: It is the closest big asteroid: no asteroid closer to the Sun has a diameter above 25 kilometres or two-elevenths that of Flora itself, and not until the tiny 149 Medusa was found was a single asteroid orbiting at a closer mean distance known.
modified: fix grammar: It is the closest big asteroid: no asteroid closer to the Sun has a diameter above 25 kilometres or two-elevenths that of Flora itself, and not until the tiny 149 Medusa were found were a single asteroid orbiting at a closer mean distance known.