Asteroid Apophis to make close approach to Earth on 13 April, 2029

On 19 June, 2004, astronomers at the Kitt Peak National Observatory in Arizona, USA spotted a 370 metre wide asteroid moving through the constellation of Pisces, provisionally designated as 2024 MN4. The object was classified as a Near Earth asteroid, and quickly gained significant attention because of its size and trajectory. The initial observations indicated a small but alarming chance of a collision with Earth in 2020, estimated to be up to a 2.7 per cent chance. The asteroid was officially designated as 99942 Apophis, named after an Egyptian Serpent God.

Apophis is a really long snake, similar to the Serpent King Vasuki used for the Churning of the Ocean in Indian Mythology. Apophis is depicted as a giant serpent, the eternal nemesis of the Sun God Ra, symbolising the forces opposing order including chaos, destruction and darkness. The asteroid named after Apophis turned out to not be so threatening after all. Follow-up observations by radar instruments and optical telescopes ruled out an impact in 2029, but confirmed a close approach on 13 April 2029, when Apophis will pass within 31,600 kilometres of the Earth, closer than geostationary satellites. The asteroid will be visible to the naked eye from parts of Europe, Africa and Asia during the close encounter.

In march 2021, Apophis approached within 17 million kilometres of the Earth. Observations conducted during this visit confirmed that Apophis did not pose a threat to the planet for at least a few centuries. The close encounter in 2029 will be a rare event of a large asteroid approaching so close to the Earth. Calculations indicate that asteroids of such size come close to the Earth once every 5,000 to 10,000 years. Apophis is 90 per cent larger than all Near Earth Asteroids discovered. After visiting the Earth, Apophis will also make a close approach to the Moon, at a distance of 94,000 kilometres.

A realistic rendering of the encounter without the spectacular nebula in the background and the dramatic lighting. (Image Credit: NASA Eyes on Asteroids). 

Apophis is both a Near Earth Object (NEO), asteroids that cross the orbit of the Earth, as well as a Potentially Hazardous Asteroid (PHA) or large asteroids that can strike the Earth in the distant future. Apophis is made up of silicates, iron and nickel. The asteroid is on the brighter side, and observations have not revealed signs of water, which is consistent with an asteroid from the inner Solar System. The close approach in 2029 will allow scientists to further study the asteroid, which is tumbling wildly through space and is likely to be deformed by the close approach.

After the close encounter with the Earth on 13 April, 2029, Apophis is scheduled for a number of subsequent close approaches. On 31 March, 2036, Apophis will pass within 22.4 million km of the Earth. On 12 April, 2068, it will approach even closer, at 1.95 million km. On April 11, 2116, the asteroid will make a close approach to the Earth again, but the predictions diverge by this time because of orbital uncertainties, that are expected to be amplified by the 2029 flyby. The estimates range from 150,000 km to 15 million km. The precision decreases rapidly as we calculate the trajectory of the asteroid into the future.

The 2029 encounter with Earth will widen the orbit of Apophis, making it change its family from an Aten to an Apollo. Long-term forecasts grow less reliable because of small perturbations, as well as the Yarkovsky effect and potential collision with another asteroid. The Yarkovsky effect is a subtle force that alters the orbit of an asteroid because of uneven absorption of energy from the Sun and its subsequent remission. The radiation is not uniform, and alters the path of the asteroid slightly. Research has indicated that Apophis is not likely to impact the Earth even after a collision with another asteroid.

None of the future encounters will be as dramatic as the 13 April, 2029 flyby. The asteroid will be visible from India as it darts across the sky as an obvious moving point visible to the naked eye. Finding a remote location far away from polluting city lights, and clear skies will improve the conditions for observing the flyby. NASA’s OSIRIS-APEX mission and ESA’s RAMSES mission, both named after Egyptian deities, will be studying the asteroid after the close encounter. A number of ground and space-based observatories will observe Apophis before, during and after the flyby, to understand the impact of the encounter on the asteroid.