NASA tracks colossal asteroid on a close approach to Earth

The event is considered one of the most significant astronomical moments in recent history. It offers a rare, once-in-millennia chance to observe a large near-Earth asteroid as it moves through Earth’s neighborhood. The asteroid is approximately 350–450 meters across, often likened to being “Eiffel Tower-sized.” It is thought to be about 4.6 billion years old. It consists of primordial material left over from the early Solar System that never coalesced into a planet or moon.

A serpent deity

Apophis was discovered in 2004. Early orbital solutions left a small probability of an impact in future decades. Subsequent tracking, capped by high-precision radar work in 2021, eliminated any risk for at least a century. The asteroid's name, proposed by the discoverers, comes from Apep (Apophis), the ancient Egyptian serpent deity associated with chaos and darkness.

Earth’s gravity is expected to exert tidal stresses that could subtly stretch and compress the body. That could trigger localized landslides, surface shaking, and changes in its rotation and internal structure. Its orbit will be slightly altered, and its spin rate may shift. A pass of this size and proximity by a known large asteroid occurs only once every few thousand years, prompting coordinated observations to capture these responses in real time.

Favorable skies could make Apophis visible to the naked eye in parts of the Eastern Hemisphere, with binoculars improving the view.

Multiple campaigns are underway to closely monitor the asteroid. NASA’s OSIRIS-APEX spacecraft is en route to rendezvous with Apophis, arriving in June 2029 to start an 18‑month mission. It will map the surface in detail, document any changes caused by the Earth flyby, and analyze its chemical composition. The European Space Agency is developing the Ramses mission, slated to launch in April 2028 and arrive in February 2029 to meet Apophis ahead of closest approach. Ramses aims to track how the asteroid’s orbit and structure respond to Earth’s gravitational pull and improve planetary defense models.

Radar facilities on Earth plan high-resolution imaging during the flyby. The Goldstone Solar System Radar and the Green Bank Telescope will work to resolve surface features. They will also refine Apophis’s shape and rotation state.

Proposals by Chinese researchers envisioned placing a pair of small satellites near the Sun–Earth L1 point to monitor Apophis as it approaches. In Russia, the Skobeltsyn Institute of Nuclear Physics at Lomonosov Moscow State University has discussed a potential CubeSat or small-spacecraft mission timed for the 2029 pass. Ground-based optical and infrared campaigns are also planned. Together, these efforts would create a multi-instrument, multi-platform dataset capturing the asteroid before, during, and after the tidal encounter.

By watching how Apophis’s boulders, regolith, and interior respond to a gravitational flyby, researchers expect to infer the cohesion and porosity of rubble-pile asteroids. They will test predictions about seismic propagation in low-gravity environments. They aim to validate theories for how close planetary encounters can refresh or reshape small bodies. These data feed directly into impact-risk assessment and mitigation planning for other near-Earth objects.