Let's Talk Asteroid Apophis, Planetary Defense and Elon Musk

It's time to talk about Apophis again, I guess. Please calm down first.

The asteroid is about 1,100 feet (340 meters) wide, was discovered in 2004 and will make a reasonably close flyby of Earth on Friday, April 13, 2029. Apophis will not hit Earth during that flyby; more on that later. Nevertheless, it's large and close and has a snappy name, and the internet loves its asteroids.

That's presumably how SpaceX CEO Elon Musk ended up retweeting podcaster Joe Rogan's post of an Express story (lacking any news relevance) about Apophis. "Great name!" Musk tweeted yesterday (Aug. 18). "Wouldn’t worry about this particular one, but a big rock will hit Earth eventually & we currently have no defense."

Infographic: Asteroid Apophis' Close Earth Flyby of 2029 Explained

Let's dissect all this a bit. Musk and Rogan made headlines in September when Musk appeared on the latter's podcast for a three-hour discussion of Tesla and whether the universe is a simulation. During that appearance, Musk infamously smoked marijuana and sipped whiskey, which prompted a NASA review of commercial space partnerships, according to The Washington Post.

It is unclear from his tweet whether Musk is referring to the asteroid's actual name, Apophis, or the "God of Chaos" terminology inserted by the news outlet Rogan cited. 

Asteroid 99942 was first dubbed 2004 MN4 based on a formula marking its discovery and was given a formal name Apophis the next year. According to the International Astronomical Union, which oversees all official names in space, the name Apophis commemorates the "Egyptian god of evil and destruction who dwelled in eternal darkness."

Musk is mostly correct in his assessment of Apophis itself. The rock is dubbed a Potentially Hazardous Asteroid for its relatively large size and relatively close approaches, but it's a very long way from potentially hazardous to actually impacting. Asteroid experts are confident it will not hit Earth at that time: They've calculated a trajectory 7.4 miles (12 kilometers) wide that passes thousands of miles away from our home planet during that close encounter. Scientists have also ruled out a 2036 impact.

Related: Huge Asteroid Apophis Flies By Earth on Friday the 13th in 2029

Apophis is just one of thousands of asteroids that scientists have identified. That includes nearly 900 near Earth objects more than 0.6 miles (1 km) wide and nearly 9,000 of them more than 459 feet (150 m), the class into which Apophis falls. A host of instruments on the ground and in space continue to spot more and more of these objects and gather the data necessary for scientists to calculate the rocks' trajectories.

That said, these scientists can't guarantee Apophis and Earth will never meet. Although they have a very good sense of the rock's current trajectory, the tug of Earth's gravity during its 2029 encounter will likely skew its path, throwing off orbital calculations into the future. Potentially, many many decades from now, humans may indeed need to worry about Apophis.

Other space rocks could also be a problem on that sort of time scale, but right now, NASA hasn't spotted any asteroids with worrying trajectories. "No known asteroid poses a significant risk of impact with Earth over the next 100 years," according to the website of NASA's Planetary Defense Coordination Office.

If that status changes, although it would be scary, it wouldn't mark a new risk in the world, just a new knowledge of our risk; the asteroid would hit us whether or not we had identified it.

Related: Even If We Can Stop a Dangerous Asteroid, Being Human May Mean We Don't Succeed

And that's the entire point of scientists' efforts to find and study asteroids in our neighborhood: If we learn about an approaching asteroid a day in advance, there's nothing we can do, as Musk implies. That was the case, most recently, for the asteroid that exploded over Chelyabinsk, Russia, in 2013. On other short timescales, humans may be able only to mitigate the worst damage, by evacuating people or perhaps using a nuclear explosion to split the asteroid into smaller pieces more likely to break up in Earth's atmosphere.

But say hypothetically that someone spotted an asteroid 10 years before it were to slam into Earth. That's a long enough timescale that humans could realistically muster a response, depending on the particular constraints of the asteroid. Such a mission would knock an asteroid to travel a smidge faster or slower along its orbit in such a way that it would miss its appointment with Earth.

The planetary defense community is already working to develop smarter and more effective responses to the intricacies of an individual asteroid threat through hypothetical exercises.

Related: A Fake Asteroid Headed to Earth Can Really Make You Think

And while humans have yet to launch any planetary defense missions, that will change soon. One of SpaceX's own Falcon 9 rockets is due to launch NASA's Double Asteroid Redirect Test, or DART. In October 2022, the spacecraft will crash into the smaller half of a binary asteroid, then measure the deflection the impact causes. The exercise will help planetary defense experts better calibrate any future necessary missions to the size of the threatening asteroid.

It's also worth pointing out that Musk's statement was made in the context of a retweet of an Express headline and link. Now is probably a good time to remind you that Express is one of several media outlets notorious for overhyping asteroid flybys to draw clicks.

That said, the Express headline does actually make a very good point about the 2029 flyby, intentionally or not. NASA and other experts are certainly preparing for the asteroid's visit — because it's an incredible opportunity for scientists to better understand the asteroids that are all around us.

Scientists believe Apophis matches at least superficially about 80% of the potentially hazardous asteroids they've spotted around Earth to date, and the 2029 close approach will bring it well within reach of a host of instruments. Scientists want to know, for example, how much the flyby stretches and distorts Apophis and how solar radiation warming one side of the space rock affects its orbital path.

And yes, that information, once gathered, will feed into the continuing work of planetary defense experts who have spent years working on the precise problem of predicting and mitigating asteroid impacts. 

•  Death by Asteroid: The Most Likely Ways for a Space Rock to Kill You 
•  Finding 'Spooky': Why Hunting Asteroids Is Hard 
•  7 Great Movies Featuring Earth-Threatening Asteroids 

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.