OSIRIS-REx flies on as OSIRIS-APEX to explore its second asteroid

After seven years in space and more than 4 billion miles traveled, NASA’s OSIRIS-REx mission has successfully collected and delivered America’s first sample from a near-Earth asteroid. Still, after so much time and travel, the spacecraft will not be retired.

Instead, NASA extended the University of Arizona-led mission so the spacecraft could be used to study another near-Earth asteroid called Apophis. The mission was renamed OSIRIS-APEX, which stands for OSIRIS-APophis EXplorer. The mission overview was published in Planetary Science Journal.

OSIRIS-REx Deputy Principal Investigator Dani DellaGiustina is now the Principal Investigator of the OSIRIS-APEX mission.

Twenty minutes after launching the sample high above Earth’s atmosphere on Sept. 24, the spacecraft fired its thrusters to set it on course for a rendezvous with Apophis in 5.5 years — just after Apophis made its closest approach to Earth. This journey includes three Earth gravities and several tantalizingly close orbits around the Sun.

By April 2, 2029, the spacecraft’s cameras will begin collecting data as it approaches the asteroid. Apophis will also be watched closely by ground-based telescopes. But in the hours after the close encounter, Apophis appears in the sky too close to the Sun to be observed by ground-based optical telescopes. This means that any changes induced by the close encounter will be best detected by the spacecraft.

The spacecraft will catch up with the asteroid on April 13, 2029, as the asteroid whizzes by 20,000 miles above Earth’s surface. The scientists will then spend the next 18 months studying the asteroid in detail. They will also disrupt the material on the surface with the spacecraft to reveal what lies just below.

“Apophis is an infamous asteroid,” said DellaGiustina, who is an assistant professor of planetary sciences at the Lunar and Planetary Laboratory in Arizona.

“When it was discovered in 2004, there was a fear that it would hit Earth in 2029, but that risk was quashed. Then there was another scare that it would hit Earth exactly seven years later, in 2036.” but observations combined with modeling now show that Apophis will not pose a risk for at least the next hundred years. Despite this, Apophis still has this role in the psyche of all of us who study these things. While it won’t impact Earth in 2029, it will come very close.”

The 340-meter-wide Apophis is a stony S-type asteroid made of silicate materials and nickel-iron, which differs from C-type asteroids such as OSIRIS-REx’s first target, Bennu, which are rich in carbonaceous material.

Apophis was probably formed by the collision of the parent body in the asteroid belt, which knocked it into the neighborhood of Earth. The asteroid will pass closer than some satellites in Earth’s orbit and one-tenth the distance from the Moon. This is the closest approach of an asteroid of this size in modern history and will be visible to the naked eye in the Eastern Hemisphere.

An asteroid of this size to come this close to Earth is rare, occurring roughly once every 7,500 years.

The mission considered visiting other targets — even Venus — but Apophis was chosen because it was the only object the spacecraft could make a close encounter with, DellaGiustina said. The close approach allows scientists to study interactions with Earth’s gravitational forces, specifically tidal forces, which could disrupt its surface and reveal what lies beneath.

“Apophis is getting close enough that there is some activity on its surface that we expect,” DellaGiustina said. “There can be landslides or particle ejections that create a comet-like tail. Getting up close is a great natural experiment.

“We know that tidal forces and the accretion of debris pile material are fundamental processes that could play a role in planet formation. They could inform how we got from debris in the early solar system to fully developed planets. Our best guess now is that Apophis is indeed a pile of rubble.”

The mission’s science goals are based on what is known about Apophis from ground-based observations, the team’s experience at Benn, and current data for other S-type asteroids. Ultimately, the team hopes to understand the asteroid’s evolution and properties, including Apophis’ material strength, porosity, and density. Everything they learn can inform planetary defense research, especially since most potentially dangerous asteroids are also S-type asteroids like Apophis.

“We learned a lot at Benn, but now we’re armed with even more questions,” said Amy Simon, project scientist for the OSIRIS-APEX mission and principal scientist for planetary atmosphere research in the Solar System Exploration Division at NASA’s Goddard Space Flight Center. .

For example, as deputy scientist for the OSIRIS-REx Visible and near-IR Spectrometer, Simon and colleagues detected clay minerals and organic matter on Bennu, suggesting that the asteroid interacted with water in the past. Scientists predicted they would find them on C-type asteroids like Bennu, but were unable to detect them from ground-based observations.

Simon said she was excited to see Apophis look different from expectations and from the carbonaceous asteroids Bennu and Ryugu, which Japan visited with the Hayabusa 2 probe in 2018.

Getting up close and personal with these asteroids presents a unique opportunity for planetary scientists. Currently, the scientific understanding of the formation of the solar system is heavily influenced by meteorites, which are pieces of other celestial bodies that fall to Earth.

Asteroids are the primary parent bodies of meteorites, but they are usually observed from such a distance that they appear only as points of light in the sky, revealing little about their global properties or surface variability.

The OSIRIS spacecraft’s science instruments were specifically designed to connect our understanding of meteorites with their parent asteroids by placing meteorite-scale rocks into geological context on asteroids and investigating the geological processes of asteroids at Bennu and very soon at Apophis.