All of the planet books she's brought home are from the same series by the same author. The Mercury book, however, had an error in it. It states that Mercury is "the second smallest planet in the Solar System". Uh...no it's not. Mercury is the smallest planet in the Solar System, at least since 2006 when Pluto was changed from a planet to a dwarf planet. I checked the publication date of the book and it was published in 2008. There's even a book in this same series on Pluto that focuses on itss non-planet status.