The God of War is coming: The 411 on near-Earth asteroid Apophis

It sounds like the plot of a Marvel movie, but acolytes are eagerly awaiting the arrival of the Uncreator, the evil serpent that swallows the sun. Don't worry, though: this is asteroid 99942 Apophis, and it's NASA scientists that are counting off the ten years until the near-Earth space rock performs an astonishingly close fly-by. Here's what you need to know.

Okay, reassure me - are we going to get squished?

We'll level with you: at one point, scientists were worried. Back when Apophis was first sighted, partial observations led to some ominous calculations about just how likely an impact could be. Indeed, the initial sums suggested a 2.7-percent chance of an Earth impact in 2029.

Happily that's not actually the case. Subsequent observations and crunching the new math suggests there's less than a 1-in-100,000 chance of an Earth impact. Even than, it wouldn't be for many decades. Before that, though, NASA believes future measurements from repeated passes "can be expected to rule out any possible impacts."

Just who is Apophis, anyway?

The asteroid was first spotted on June 19, 2004, but it was only when its orbit had been sufficiently tracked that it was given the deeply-uninspiring official reference of "99942" in the register. However once an astroid is confirmed, the people who discovered it are allowed to choose its name. Turns out, Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi of the Kitt Peak National Observatory are fans of Stargate SG-1.

Apophis is a regular villain on the show, but also has origins in Greek mythology. There, it's the Greek name of Apep, one of the enemies of Ra, the Egyptian sun-god. As the story goes, Apep lurks in eternal darkness and – as the evil serpent Uncreator – tries to consume Ra when the sun sets. Happily for those who like taking sunrise photos for the Instagram clout, Apep never actually succeeds.

We see asteroids all the time, don't we?

We do, but few of this size, this close. At 1,100 feet across, Apophis is an order of magnitude or two larger than most asteroids that come this near to Earth. At roughly 19,000 miles from Earth as it passes, it'll actually be within the distance of some geosynchronous orbiting spacecraft and satellites. That means it'll have some notable characteristics in 2029.

For a start, it'll be visible to the naked eye. Whereas most asteroid fly-by events require a telescope to observe, Apophis will be large and bright enough to see without any equipment. First it'll be those on the west cost of Australia that get to see it, a star-like point of moving light. It'll then track west, closest to the Earth at just before 6pm EST, where it'll perform a high-speed pass across the Atlantic. An hour later, it will have crossed the US.

What's the big deal?

That combination of size and proximity is a goldmine for scientists studying the rocks we cohabit the universe with. For a start, it'll be an opportunity to figure out the size and shape of the asteroid, which are still relatively unknown. Current estimates peg it as approximately 450 x 170 meters in size and a retrograde rotator, meaning it is rotating in the opposite direction to that of the Sun.

There's a lot more to learn, though. For a start, there'll be attempts to figure out the internal composition of the rock: its make-up could hold valuable information about the origins of the solar system. It'll also be a chance to see how Earth's gravity affects Apophis' orbit.

"We already know that the close encounter with Earth will change Apophis' orbit," Davide Farnocchia, an astronomer at JPL's Center for Near Earth Objects Studies (CNEOS), says of the upcoming event, "but our models also show the close approach could change the way this asteroid spins, and it is possible that there will be some surface changes, like small avalanches."

Perhaps most exciting, though, it might prompt a new mission to actually visit Apophis in the future. If scientists deem the asteroid sufficiently interesting, it could be considered worth sending a spacecraft to. Multiple space agencies are already working on – or have running – such missions to do local investigations on near-Earth objects (NEOs) like asteroids.

We could use the God of War's secrets for our own defense

NASA may be pretty confident that Apophis won't present a risk, but that's not to say all NEOs won't. Indeed, the beliefs among some experts is that a future asteroid impact is a case of when, not if. Considering how that tuned out for the dinosaurs, it's something we probably want to avoid if we can.

"Apophis is a representative of about 2,000 currently known Potentially Hazardous Asteroids (PHAs)," Paul Chodas, director of CNEOS, explains. "By observing Apophis during its 2029 flyby, we will gain important scientific knowledge that could one day be used for planetary defense."

Exactly what form that planetary defense will take, no consensus has been reached upon. Indeed, NASA will run a fake asteroid impact exercise to see how organizations might hold up to the effect of such an incident. Some schemes hope to divert PHAs, while others consider detonating them with nuclear weapons might be the best route. Apophis' welcome will be a little more friendly in 2029, but there's some serious science underpinning the whole thing.