On 13 April 2029, the massive asteroid Apophis will sweep within 20,000 miles (approximately 32,000 kilometres) of Earth’s surfaceβpassing closer than standard geostationary broadcast satellites in a rare celestial event that occurs only once every 7,500 years. Stationed in deep space, NASA‘s OSIRIS-APEX spacecraft will capture the flyby from afar as the rocky body glides past the night side of our planet, clearly visible to millions of naked-eye observers across Europe and northern Africa.
APEX and Apophis
Originally deployed under the name OSIRIS-REx, the spacecraft completed its primary objective in September 2023 when it returned a historic sample from the asteroid Bennu. Rather than retiring the craft, mission controllers repurposed the probe to rendezvous with Apophis in late spring 2029, turning a completed voyage into a secondary deep-space pursuit.
Dani Mendoza DellaGiustina
“I think that’s just going to be a really powerful sequence of images to help people understand how vulnerable we are,” said Dani Mendoza DellaGiustina, associate professor at the Lunar and Planetary Laboratory and principal investigator of OSIRIS-APEX.
Repurposing Flight Paths and Observing Earth as an Exoplanet
Reaching Apophis requires navigating a complex trajectory shaped by multiple planetary gravity assists. During these manoeuvres, the craft skims past Earth to borrow orbital energy from the planet, iteratively bending its flight path around the sun to align directly with the asteroid.
These close passes provide distinct calibration benefits. During its approach from millions of kilometres away, the science team turned the onboard suite toward Earth, observing our home planet as if it were an exoplanet orbiting a distant star.
This vantage point allows researchers to gather data on a confirmed habitable world while actively recalibrating sensitive instruments that have experienced gradual operational drift since the probe launched in 2016.
Apophis
Extreme Solar Heat and the “Fig Leaf” Defensive Manoeuvre
Rendezvousing with Apophis forces the spacecraft into an orbit considerably closer to the sun than its original design specifications accounted for. To prevent sensitive systems from overheating, mission engineers developed an improvised protective protocol dubbed the “fig leaf.”
- Repurposed Solar Mounts: Engineers tilt the craft’s solar panels along their wrist-like joints to cast defensive shade across heat-sensitive instruments.
- Legacy Hardware Adaptations: These motorised hinges were originally designed only to raise the panels clear of ground boulders during the Bennu touchdown.
- Survival Through Perihelion: The probe must endure a total of six intense solar flybys using this thermal shadowing technique to survive the journey.
While the solar shield protects the hardware during transit, an entirely different set of physical forces awaits once the probe finally intercepts Apophis.
Core Flight Specifications
| Mission Parameter | Operational Detail |
|---|---|
| Target Asteroid | Apophis |
| Flyby Distance to Earth | Approximately 20,000 miles (c. 32,000 km) |
| Primary Encounter Date | 13 April 2029 |
| Orbital Arrival Window | Late spring 2029 |
| Primary Earth Flyby Visibility | Visible to the naked eye over Europe and northern Africa |
Gravitational Forces and Surface Shaking
A prevalent misconception regarding close near-Earth asteroid passes is that gravitational encounters affect only the trajectory of the body. In reality, Earth’s immense gravitational pull will exert substantial tidal forces on Apophis, warping the asteroid itself as it sweeps past.
Researchers have analysed extensive telescope tracking data to model two key vulnerabilities: shifts in the asteroid’s rotational spin and visible destruction across its surface. The stretching and squeezing caused by terrestrial gravity is predicted to shake Apophis violently.
“OSIRIS-APEX will be in a unique geometry to observe that shaking, which is very cool,” DellaGiustina said.
Because Apophis possesses weak internal gravity, structural vibrations are anticipated to dislodge surface material. Loose dust and rocky debris will likely be thrown upward, causing surface disruptions ranging from millimetre adjustments to multi-metre structural shifts that the high-resolution sensors on OSIRIS-APEX are specifically calibrated to record.
Beyond its planetary science objectives, the programme continues to serve as an operational pipeline for aerospace personnel, expanding its workforce with students and early-career researchers as the late spring 2029 encounter draws near.
π‘ The 2029 encounter presents a rare natural laboratory for observing gravitational tidal disruption in real time.
π High-resolution telemetry gathered during the flyby will provide crucial data on the structural cohesion of hazardous near-Earth objects.
π How closely will you be watching the skies when Apophis becomes visible across Europe and northern Africa?
π Share your thoughts and questions on the OSIRIS-APEX mission below.
