New Jersey, 1999. Surrounded by books (Marie Curie biog, The Greenhouse Effect) Holly Evans, aspiring girl-scientist, launches trays of seedlings into the sky. The aim: “to study the effects of extra-terrestrial conditions on vegetable growth.” So when, weeks later, giant vegetables drift across America the conclusion seems obvious . . . But when exotic veggies like arugula and rutabaga appear, Holly realises that the data no longer fits her hypothesis. So whose giant broccoli is in her backyard?

Not until the last page is the “truth” revealed and the ethos of scientific realism exposed. An Arcturian space ship accidentally jettisons its food supply. The joke comes full circle as the hungry aliens consult a scientific manual on how to turn Holly’s seedlings into mega veggies . . .

“Is this real?” asked my six-year-old reader half way through. “Nah, not real”, she announced at the end. Wiesner brilliantly captures that line where science and sci-fi cross, highlighting the limitations of the scientific approach and its aim of discovering “facts” about the natural world - in the face of a galaxy which largely escapes scientific measurements and about which, perhaps, the visual imagination can be equally perceptive.

Clues to the surprise ending are scattered throughout - from the first picture of Holly’s seedling-trays, attached to balloons, looking just like miniature space-craft, to the discarded tabloid (National Inquirer?) blaring “Man kidnapped by well-dressed space aliens”.

A sophisticatedly sceptical picture book raising pertinent questions about the scientific method.

Pond Year is another picture-book about observing nature, and another placing girls centre-stage. A straightforward record of the changes, over a year, in a shallow, mucky, North American pond is interwoven with a “buddy, buddy” story of the pond’s observers, who promise to be “best friends, pond buddies, scum chums” for ever.

The pond may smell like an old mop but it offers hours of enjoyment - sailing twig rafts and collecting frog-spawn in spring; “dipping” in oozy mud and racing crayfish down mud slides in summer, looking for musk-rats in autumn, skating in winter.

In characteristic learning-through-play fashion, textures of plants and insects are remarked upon. At times a slightly more formal note is introduced, as when the girls use magnifying glasses to examine the detail of “dead bugs” - “up close bug parts are amazing and special - just right for each bug.”

Inset miniatures provide close-ups of pond life - including tadpoles en route to becoming frogs - but sometimes the illustrations hover a little uneasily between reality and design. The salamanders with their elaborately scrolled tails are a little too removed from messiness.