Loud cheers and happy faces fill the ATLAS Control Room while the whole detector lights up: protons are back today at the experiment's door, and everybody forgets in a second the long year of waiting for the Large Hadron Collider (LHC) to resume operation.

While no date has been fixed, collisions at 0.9 TeV total energy are expected in the near future. Today's "launch" of the LHC is similar to launching a rocket to Mars with a rover. The excitement on launch day is very high, but the science will begin a few months later when the rover lands and even then it takes some time to collect data.

ATLAS won't be roving through physics for some time, but the champagne cheers reflect the excitement of the launch. (See photos of the ATLAS control room scenes below).

Collisions at an energy of 7 TeV are expected a few weeks into 2010. Today the ATLAS detector lit up as a flood of particles traversed the detector when the beam was occasionally directed at a target near ATLAS (these are called "splash events"). This allows ATLAS physicists to study how well the various components of the detector are functioning in preparation for the forthcoming collisions.

Now, after twenty years of preparation, ATLAS is ready and anticipates incredible discoveries about our Universe in the coming months and years.