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The Universe is a big place... and it's getting bigger every day.

Our current model of the Universe, called the Big Bang Model, is that the Universe originated approximately 13.7 billion years ago and has been expanding ever since. It was always assumed that expansion was slowing, with the gravity of the Universe itself applying the brakes. But shortly before the end of the 20th century astronomers got a big surprise: the Universe was not slowing down, it was speeding up, the expansion ever accelerating.

Very little is known about this accelerated expansion, and less is known about its cause. The SuperNova Acceleration Probe, or SNAP, will fill the wide gaps in our knowledge. It will study exploding stars called supernovae, as well as the gentle smearing of the light from distant galaxies due to gravity — called weak gravitational lensing — and put limits on what may or may not be the force driving the outward pull on the Universe. SNAP will investigate over one thousand square degrees of sky — more than 5000 times the size of the full Moon! — with a 500 megapixel camera.

SNAP is being proposed for the Joint Dark Energy Mission (JDEM), which is a cooperative venture between NASA and the U.S. Department of Energy. SNAP could be ready to launch by 2013.