A spacecraft launched in 2007 will soon slide into orbit around Vesta, the solar system’s second-heaviest asteroid.

Located 117 million miles from Earth, Vesta has a circumference of 329 miles. When NASA’s Dawn spacecraft arrives over the weekend of July 16, it will be the first human object to visit.

“It has taken nearly four years to get to this point,” said Dawn project manager Robert Mase of NASA’s Jet Propulsion Laboratory in a press release. “Our latest tests and check-outs show that Dawn is right on target and performing normally.”

Dawn navigated toward the asteroid belt, a space rock-rich zone between the solar system’s inner and outer planets, using gravitational energy from Mars and by firing its ion-powered thrusters. Its arrival at Vesta is expected at 1:00 a.m. EDT on July 16.

It will take 10 minutes and 30 seconds — the time it takes light from Vesta to reach Earth — for engineers to know if the operation succeeded.

Once in orbit, Dawn will hover about 9,900 miles above the asteroid’s surface for a year and use two different cameras, a gamma-ray detector and a neutron detector to study the object. Next July, Dawn’s ion thrusters will fire up and slowly propel the spacecraft toward the dwarf planet Ceres, the largest object in the Asteroid Belt.

Planetary scientists know very little about either Vesta or Ceres, but they suspect each has planet-like qualities. Vesta may have once had a molten core that oozed lava before going cold after a few million years. Ceres, meanwhile, may have an icy mantle and active mud volcanoes.

Image: Dawn snapped this photo of Vesta from about 26,000 miles away on July 9, 2011. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Video: NASA

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