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On 10 July, the European Space Agency's Rosetta spacecraft will fly within a few thousand kilometres of 21 Lutetia, a main belt asteroid that orbits the Sun between Mars and Jupiter. Lutetia is an unusual object. It is classified as an M-type asteroid, which are thought to be made mainly of nickel and iron. However, Lutetia's spectrum does not seem to show any evidence of metals. In fact, exactly what Lutetia is made of puzzles astronomers. That's partly why it was chosen for the fly by. So come July, astronomers should know the answer to this conundrum. But in the run up, they're indulging in a little fun. The game they've invented is to see how good a prediction they can make about what Rosetta will find. Today, Irina Belskaya at the Observatoire de Paris and a few friends take a stab. They make several detailed predictions about Lutetia based partly on observations dating back to the 1960s but mostly on data taken since 2004, when interest picked up after the asteroid was chosen as a flyby target. So what do they think Rosetta will find?

This week, Mercury is emerging from the glare of the sun and making a beeline for Venus. By week's end, the two planets will be just 3o apart, an eye-catching pair in the deep-blue twilight of sunset. The best nights to look are April 3rd and 4th. Go outside at the end of the day and face west. Venus pops out of the twilight first, so bright it actually shines through thin clouds. Mercury follows, just below and to the right: April 3April 4 Venus is an old friend to most sky watchers; Mercury, less so. The first planet from the sun spends most of its time wrapped in painful sunlight. Seeing it so easily, and in the beautiful company of Venus no less, is a rare treat indeed. The next apparition this good won't come until Nov. 2011. By that time, however, we'll have much better view of Mercury all the time. NASA's MESSENGER probe is en route to Mercury now, and in March of 2011 it will become the first spacecraft to orbit the planet. During a year-long science mission, MESSENGER will beam back a stream of high-resolution pictures and data obtained using seven instruments designed to operate in the extreme environment near the Sun. This kind of coverage of planet #1 is unprecedented.

Imagine you're a Brontosaurus1 with your face in a prehistoric tree top, munching on fresh leaves. Your relatives have ruled planet Earth for more than 150 million years. Huge and strong, you feel invincible. You're not. Fast forward about 65 million years. A creature much smaller and weaker dominates the Earth now, with brains instead of brawn. Its brain is a lot larger relative to its body size – plenty big enough to conceive a way to scan the cosmos for objects like the colossal asteroid that wrought the end of your kind. Right: An artist's concept of NASA's Wide-field Infrared Survey Explorer (WISE). [more] The creature designed and built WISE, NASA's Wide-field Infrared Survey Explorer, to search for "dark" objects in space like brown dwarf stars, vast dust clouds, and Earth-approaching asteroids. WISE finds them by sensing their heat in the form of infrared light most other telescopes can't pick up.