Asteroid Apophis

 

On 13 April 2029, the asteroid Apophis (#99942) will pass less than 32,000 km from Earth’s surface. It will be the closest approach of an asteroid of this size that humans have ever been aware of. Roughly 375 meters across, Apophis will, for a short time, be closer to Earth than satellites in geostationary orbit and visible in the night sky to the naked eye from parts of Europe, Africa, and Asia.

When Apophis was discovered in 2004, the initial observations indicated a small chance that it could impact Earth in 2029, 2036 or 2068. A collision would have been devastating, and so the asteroid was named after the Egyptian god of chaos and destruction.

Later observations ruled out any chance of impact for at least the next 100 years.

Nevertheless, the very close approach of Apophis in 2029 represents a unique opportunity for scientific research and public outreach. Space agencies and scientific institutes around the world are planning to use the fly by to explore Apophis from the ground using telescopes and up-close using spacecraft.

Apophis was discovered on 19 June 2004 at the Kitt Peak National Observatory in the USA. It was soon identified as one of the most potentially hazardous asteroids ever detected. The risk of an impact in 2029 rose as high as 2.7% and saw Apophis achieve the highest ever rating on the ‘Torino scale’ – a method used to evaluate the threat that an asteroid poses to Earth.

Additional observations of the asteroid enabled astronomers to rule out the risk of an impact in 2029 or 2036. However, a small chance of impact in 2068 remained for a number of years.

When Apophis passes Earth in April 2029, the pull of the planet’s gravity will significantly change the asteroid’s orbit around the Sun and amplify our uncertainty about its future trajectory. Using the data available at the time, astronomers believed that there was a chance that the fly by could alter the trajectory of Apophis in a way that would line it up for a collision with Earth in 2068.

However, radar observations of Apophis made by NASA’s Goldstone Deep Space Communications Complex in California and the Green Bank Observatory in West Virginia in March 2021 greatly improved our knowledge of the asteroid’s current orbit and allowed astronomers to finally rule out any chance of Earth impact for at least 100 years.

During the approach, Apophis will be affected by Earth’s mighty gravity. The side of the asteroid nearest Earth will be pulled towards our planet more strongly than the side farther away, resulting in tidal forces that will stretch and squeeze it, perhaps triggering quakes and landslides, and change the way it rotates.

The encounter will also lengthen the asteroid’s orbit around the Sun. Apophis is currently a member of the ‘Atens’ group of asteroids. The Atens cross Earth’s orbit and have orbits around the Sun that are smaller in total width than Earth’s.

As a result of its 2029 Earth fly by, the orbit of Apophis will be widened. As of April 2029, it will become a member of the ‘Apollo’ group, the family of asteroids that cross Earth’s orbit but which have orbits around the Sun that are wider than Earth’s.

Apophis poses no risk to Earth during its 2029 fly by, but it offers a unique chance to study such a large asteroid up close and better prepare a response to any future asteroids that do.

ESA's Rapid Apophis Mission for Space Safety (Ramses) aims to rendezvous with Apophis and accompany the asteroid during the fly by to observe how it is warped and changed by our planet’s gravity. There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the Solar System to study them and perform experiments to interact with their surfaces. For the first time ever, nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis reacts to strong external forces that may reveal new material from beneath the surface.

from esa.int