Asteroid Apophis is expected to fly very close to Earth but will not hit us for at most 100 years.
Friday, April 13th, 2029 will see Earth's closest encounter with the asteroid 9942 Apophis. The 1,120-foot (340-meter) tall object will pass within 19,000 miles (31,000 km), of Earth, a distance that is closer than many geostationary satellites.
Apophis' enormous size means that it will be visible from the outside to around 2 billion people. The asteroid will first be visible in the southern part of the sky. It will appear as a bright star that streaks across the sky, passing first over Australia, then over the Indian Ocean, before finally crossing the Equator over Africa.
This historic and spectacular event is not as devastating as scientists thought. Scientists were initially unsure if Apophis' passage would lead to a collision with Earth.
Similar: A huge asteroid Apophis passes by Earth on Friday, 13th of 2029. It's a lucky day for scientists.
Although this risk was eliminated, researchers could still not rule out the possibility of Earth's gravitational influence influencing the asteroid such that it could impact something that was not yet ruled out, Space.com reported previously.
Richard Binzel, professor of planetology at the Massachusetts Institute of Technology (Cambridge), stated that Apophis falls under the Potentially Hazardous Asteroids category. This means that Apophis has an orbit that brings them very near to Earth right now and for many centuries into the future. He said that Apophis is the most dangerous of potentially hazardous asteroids because it will approach Earth the closest large asteroid in a decade.
"But, the most important thing about Apophis is: Apophis will not be able to leave the Earth. Apophis will be without the Earth. Apophis will be missing the Earth."
Although we know Apophis will not strike Earth in the near-term, NASA's Sentry Risk Table and the European Space Agency's "impact risk list" of PHAs have remained at the top for 17 years. Its future visits will make it an object of scientific interest that is only beginning to be of great scientific value.
Related: Asteroid defense - Scanning space for threats
Animation showing Apophis' path in 2029 compared to the orbit of Earth-bound satellites. (Image credit: NASA/JPL-Caltech)
What we know about Apophis
Fabrizio Berni, Fabrizio Berti and Roy A. Tucker discovered Apophis while working at Kitt Peak National Observatory. At the time, it was designated 2004 MN4. Although the team could only observe the asteroid for two consecutive days due to technical problems and adverse weather conditions, additional observations quickly revealed many details about the object.
2005 saw the asteroid renamed "Apophis" to honor the Greek name of an ancient Egyptian serpent representing evil. This serpent, which dwells in darkness, often attempts to devour Ra the sun-god Ra during his nightly journey across the sky.
Binzel was part a team that used telescopic reconnaissance to determine the composition of Apophis' color properties. The asteroid was found to be similar to the "ordinary chondrites" class of meteorites, which are mostly composed of silicates and stone.
According to NASA, Apophis is classified as an "S Type" or stoney-type Asteroid. It also contains a mixture of metals such as nickel and iron. Its shape looks almost like a rocky peanut, with two lobes.
Similar: Meteor showers, shooting stars: Formation facts and discovery
"Apophis" is a fragment of an early solar system solar system planetesimal, a planetary building block that has never coalesced into a planet in our solar system. Binzel stated that the fragment has been kept in the asteroid Belt for 4.6 billion year and could be a fragment from a larger asteroid which was damaged in an asteroid belt collision. The collision could have put the fragment, which we call Apophis, on a trajectory that brought it to Earth.
When researchers calculated how close Apophis' orbit would bring it to Earth, the excitement over Apophis' discovery soon turned to concern.
Researchers calculated that there was a 2.7% chance of the PHA hitting Earth in 2029 using radar astrometry data. Although these estimates might seem low, they were extreme enough to give Apophis highest values on the Torino and Palermo Technical Impact Hazard Scale systems that astronomers use to determine how dangerous an asteroids is to Earth.
Although the likelihood of Apophis striking Earth in 2029 was almost negated by 2006, future impacts, especially in 2068, cannot be ignored. According to Davide Farnocchia (an astrophysicist at NASA Jet Propulsion Laboratory, JPL), the trajectory of Apophis will be determined by how Earth's gravitation changes the asteroid orbit. Farnocchia is currently studying the trajectory. Farnocchia stated that Apophis would pass through certain gravitational keyholes. This would alter its orbit in the right way or the wrong way to cause it to be on a collision course in the future year.
Astronomers could not track Apophis between 2015 and 2019, due to its location too close to the sun, which made it difficult to see. Further progress in ruling out a 2068-related impact was also impossible. The asteroid appeared almost determined to live up its apocalyptic title.
Farnocchia and his crew resolved to address the problem head-on. They could better observe the trajectory of the asteroid and determine if it would hit Earth in 2068.
Farnocchia said that JPL's Center of Near-Earth Object Studies, (CNEOS), computes high-precision trajectories for all known asteroids and assesses the possibility of future impacts." Farnocchia enjoyed the challenge presented by Apophis. "That's our daily bread."
Apophis won't hit Earth
It was not an easy task to remove Apophis from various space agency's risk lists. This required better understanding of the orbit of the asteroid. NASA released a statement saying that Farnocchia and his team compiled radar and optical tracking data from late 2020 and early 2021 to create a precise trajectory for Apophis. This data was then combined with years of observation to create a better picture of Apophis' path.
Farnocchia stated that Apophis was extensively tracked by radar and optical telescopes since its discovery. "With the help of data from astronomers around the globe, we can accurately predict Apophis' motion through the April 2029 flyby," Farnocchia said.
It was possible to calculate that Apophis' orbital period, which is the time it takes to orbit around the sun, would be shortened by its encounter with Earth in 2029.
Even more important, the CNEOS crew was able to use data from 2020 observations and 2021 observations to predict how close Apophis would be to the gravitational keyholes which correspond to possible impacts with Earth in 2036 and 2068. Farnocchia stated that the CNEOS team was able to exclude any possibility of an impact in the next 100 years.
Similar: Whew! Apophis, a huge asteroid, won't reach Earth until 2036
These NASA radar images depict Apophis passing within 10.6 million miles (17 millions kilometers) of Earth during a 2021 flyby. NASA captured the views using Deep Space Network antennas. (Image credit NASA/JPL–Caltech and NSF/AUI/GBO
What happens if Apophis reaches Earth?
It is difficult to predict what an impact between our planet's surface and Apophis, an asteroid of the same size, shape and density, would look like. It is not possible to find anything similar in the geological records of Earth. Other impacts, however, have been either much greater or smaller than the Chicxulub impact that occurred 66 million years ago. There are many factors to consider when estimating the potential damage from such a collision. These factors include the size, density, and mass of the asteroid, as well the angle and velocity at the strike.
"We have done simulations of Apophis impact on Earth. However, at 340m across, the outcome of an Apophis impact with Earth is very uncertain," Gareth Collins, a professor at Imperial College London. The main factors are size and speed, but it is also important to consider the location of the impact site. The impact can cause dangerous tsunamis if it occurs in the ocean. However, the dust produced on land is much more potent. The impact on human populations is also important.
Related: A tsunami that swept through the oceans of Earth caused by a dinosaur-killing asteroids
Collins estimates that Apophis would strike Earth at 45 mph (20 km per second) and the energy released from asteroid impacts would be approximately 10 billion, billion Joules (that is 1 followed by 19 zeros). He stated that this is comparable to the explosive yield from the global nuclear arsenal. "Around 100,000 times more energy than that of the Chelyabinsk meteor, and one million times more energy as the bombs dropped upon Hiroshima."
Collins stated that the worst case scenario for an impact of this magnitude would be if it occurred near a large population center, or close to a heavily populated coastline. This would lead to devastating secondary effects such as intense thermal radiation, ground shaking and violent ground shaking.
Collins stated that unless an asteroid like Apophis strikes Earth, we will not be able to measure its consequences. Collins agreed. Closer approaches help us to better understand asteroids, and the likelihood that they will strike Earth in the future.
What can scientists learn from future flybys?
Researchers can now concentrate on collecting scientific information from Apophis flybys, with the threat of Apophis impact being eliminated for a time. Apophis research is only eight years away from its next visit.
Farnocchia and his group will take advantage this unique scientific opportunity to observe how Apophis reacts when it is so close to Earth. Farnocchia stated that Apophis' rotation could be affected by its proximity to Earth. Apophis 2029 observations will help scientists to better determine its size, shape and composition, as well as model its interior.
Binzel stated, "By looking at how Apophis might shake and rattle and roll, even a small amount, we can learn how it is assembled on its inside." Binzel explained that seismic waves travelling through Earth, Mars, and the moon have been used to determine what lies beneath their surface. "Interior structure of a potentially dangerous asteroid is something that we have never measured before. Apophis may just be our chance to have that opportunity.
Apophis is similar to about 80% of all the PHAs so far identified. Scientists could collect data to help them understand how to divert future PHAs from Earth's future.
Binzel stated that "Knowing how PHAs work together could be the most valuable space-physics knowledge ever acquired, in the event that we ever had to use that knowledge to defend our planet against an asteroid impact."
Apophis' passage in 2029, however, is an historic event that should not be missed. Farnocchia stated that objects the size of Apophis are only found once in a thousand years. It's worth waiting for the chance to see it. "I know I won't!"
Additional resources
