The European Space Agency's Herschel Space Observatory snapped these pictures of Apophis on its latest flyover. ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss

Scientists will be keeping a close eye on asteroid Apophis on Wednesday night. The giant space rock will be making a relatively near pass over Earth, coming within about 9 million miles of us.

When Apophis was first discovered in 2004, scientists briefly estimated that there was a 2.7 percent chance it would hit us in 2029. Those estimates were later downgraded to practically zero. But 2029 will still bring a close shave when the asteroid passes within 36,000 kilometers (22,300 miles) of Earth -- closer than the orbits of the Moon and some geostationary satellites.

The next close shave will come in 2036. Scientists aren’t quite sure how close Apophis will skim by Earth then, since the rock’s close flyover in 2029 will probably alter its path due to both tidal forces on Earth and something called the Yarkovsky effect, which is when warmth from the Sun changes the orbit of a rotating object in space.

Getting as many details as we can about Apophis’s size, composition, mass and rotation during this pass could help scientists refine their calculations for those expected close shaves.

“It's very important to learn as much as we can about this object when it gets close enough for physical observations in late 2012 and early 2013,” NASA researcher Lance Benner wrote on the space agency’s website.

At the moment, the data shows that the asteroid has almost no chance of colliding with Earth in 2036 -- the chances are somewhere around 1 in 7,143,000, by NASA’s most recent reckoning. Still, it remains on NASA’s list of near-Earth objects that are potentially threatening.

And already, new data is pouring in. The European Space Agency’s Herschel observatory, currently in orbit around Earth, has already made new observations of Apophis as it approaches Earth.

Previously, scientists had thought the asteroid’s average diameter was something around 270 meters (885 feet); the latest data from Herschel suggests that it’s actually around 325 meters (1,066 feet) across. Apophis also turns out to be brighter than previously estimated, with an albedo of .23, meaning that 23 percent of the sunlight that falls on the asteroid is reflected.

“These numbers are first estimates based on the Herschel measurements alone, and other ongoing ground-based campaigns might produce additional pieces of information, which will allow us to improve our results,” Max Planck Institute researcher Thomas Muller, who is analyzing the new data, said in a statement Wednesday.

Starting at 7 p.m. EST on Wednesday night, there will be live coverage of Apophis’ fly-by, courtesy of the Slooh Space Camera.