Simplify the following text for a Grade 14 native English-speaking person.
Original: It is the innermost large 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 discovered was a single asteroid orbiting at a closer mean distance known .
Simplified: 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 .