Asteroid Apophis: OSIRIS-APEX New Mission

NASA has successfully repurposed one of its most successful spacecraft for a new, high-stakes assignment. After delivering a historic sample from the asteroid Bennu to Earth in September 2023, the probe formerly known as OSIRIS-REx has been renamed OSIRIS-APEX. Its new target is the near-Earth asteroid 99942 Apophis, widely known as the “God of Chaos,” which will make an incredibly close approach to Earth in 2029.

From Sample Return to Apophis Explorer

The OSIRIS-REx mission made headlines for years as it mapped, orbited, and eventually touched the surface of asteroid Bennu. After dropping its sample capsule into the Utah desert, the main spacecraft did not retire. Instead, NASA engineers fired its thrusters to place it on a long trajectory toward Apophis.

This mission extension comes with a new name: OSIRIS-APEX, short for OSIRIS-Apophis Explorer. This is a cost-effective move for NASA. By utilizing hardware that is already in space and fully functional, the agency can study a second asteroid for a fraction of the cost of launching a new mission. The price tag for this extended mission is approximately $200 million, compared to the billion-dollar investment required for a new launch.

The spacecraft is currently in a “cruise phase.” It will perform several close passes of the Sun to adjust its trajectory before finally catching up with Apophis in April 2029.

The Target: Why Apophis Matters

Asteroid 99942 Apophis has held the attention of astronomers since its discovery in 2004. It is named after the ancient Egyptian demon serpent who embodied chaos, a fitting name given the initial panic it caused. Early calculations suggested a small but alarming probability that it could impact Earth in 2029 or 2036.

Thanks to a radar observation campaign in March 2021 at the Goldstone Deep Space Communications Complex in California, NASA has officially ruled out any impact risk from Apophis for at least the next century. However, the 2029 encounter remains historically significant for scientific reasons.

Here are the specific dimensions and details of the target:

  • Size: Apophis is approximately 340 meters (1,100 feet) wide. For context, this is roughly the height of the Empire State Building.
  • Composition: Unlike Bennu, which was a carbon-rich “rubble pile,” Apophis is an S-type asteroid. This means it is “stony” and composed primarily of silicate materials and nickel-iron.
  • Discovery Date: June 19, 2004, by astronomers at the Kitt Peak National Observatory.

The 2029 Flyby Event

The encounter slated for April 13, 2029, is unprecedented. Apophis will pass within 20,000 miles (32,000 kilometers) of Earth’s surface. This is closer than our ring of geostationary weather and telecommunications satellites.

Most asteroids of this size pass at much safer distances, usually millions of miles away. A flyby this close, by an object this large, only happens once every 7,500 years. The proximity means that observers in Europe, Africa, and parts of Asia will be able to see Apophis with the naked eye as a point of light moving across the sky.

The OSIRIS-APEX spacecraft will enter orbit around Apophis shortly after this closest approach. The timing is intentional. NASA wants to see how Earth’s gravity affects the asteroid. The gravitational pull from our planet is expected to alter the asteroid’s orbit, change its spin rate, and potentially trigger surface landslides or “asteroid quakes.”

Mission Objectives and Science

The mission is led by Principal Investigator Dani DellaGiustina of the University of Arizona. Under her guidance, the probe will spend 18 months operating in the vicinity of Apophis. The scientific goals are distinct from the Bennu mission because the asteroid type and the circumstances are so different.

Studying Tidal Forces

The primary question is physical integrity. As Apophis passes Earth, tidal forces will stretch and squeeze the rock. OSIRIS-APEX will document any physical changes to the surface, such as shifting boulders or the exposure of fresh material from beneath the dust. This provides a real-time laboratory to study how planetary gravity disrupts small bodies.

The Thruster Maneuver

While OSIRIS-APEX cannot collect a sample to return to Earth (the return capsule is already gone), it will perform a daring maneuver similar to the one performed at Bennu. The spacecraft will descend to within 16 feet of the asteroid’s surface and fire its gas thrusters downward.

This maneuver aims to stir up rocks and dust. By blasting away the weathered top layer, the probe will reveal the pristine material underneath. Onboard instruments, including spectrometers and cameras, will analyze the chemical composition of this subsurface material immediately.

Planetary Defense

Understanding S-type asteroids is vital for planetary defense. These stony asteroids are the most common type found in the inner solar system and represent the most likely class of impactors we might face in the future. Data gathered by OSIRIS-APEX will help scientists understand the density and porosity of these objects. If humanity ever needs to deflect an S-type asteroid using a kinetic impactor (like the DART mission), knowing the internal structure is essential for calculating the necessary force.

Technical Challenges

The mission faces significant hurdles. The spacecraft has already exceeded its original design life. By the time it reaches Apophis, the hardware will have been in the harsh environment of space for over 12 years.

One specific challenge is thermal management. To reach Apophis, the probe must venture closer to the Sun than it was originally designed to go. Engineers have developed a strategy to keep the spacecraft’s photovoltaic arrays positioned to shadow its sensitive components, preventing them from overheating during these solar passes.

Frequently Asked Questions

Will Apophis hit Earth in 2029? No. Extensive radar observations have confirmed that Apophis will miss Earth by about 20,000 miles. While this is geologically close, it is a safe distance for humanity. NASA has removed it from the Sentry Impact Risk Table.

Can I see the asteroid without a telescope? Yes, but it depends on your location. On April 13, 2029, it will be visible to the naked eye as a moderately bright star moving quickly across the sky for viewers in Europe, Africa, and Western Asia. Viewers in North America will likely need binoculars or a small telescope as the timing of the closest approach favors the Eastern Hemisphere.

What is the difference between OSIRIS-REx and OSIRIS-APEX? They are the same physical spacecraft. The name changed to reflect the new mission phase. OSIRIS-REx stood for “Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer.” OSIRIS-APEX stands for “OSIRIS-Apophis Explorer.”

Why didn’t they launch a new spacecraft? Cost and timing. Designing and building a new probe takes years and costs hundreds of millions of dollars. Since the OSIRIS spacecraft was still healthy and had remaining fuel after leaving Bennu, redirecting it was the most logical and economical solution to capture this once-in-a-lifetime event.