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The Return of Asteroid Samples: A Journey to Earth and Back


A time-lapse of images taken by OSIRIS-REx during its touch-and-go maneuver, with the spacecraft arm centered in this video.

This week, the OSIRIS-REx mission by NASA, which stands for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer, is coming back to Earth with approximately 250 grams (8.8 ounces) of material collected from an asteroid’s surface.

Dante Lauretta, the principal investigator for OSIRIS-REx and a planetary scientist at the University of Arizona in Tucson, described the mission milestone as causing a strong emotional reaction. He expressed excitement and pride for the team’s success, stating that they have done an incredible and flawless job. He also noted that the spacecraft is currently in excellent condition and performing perfectly.

The return capsule containing samples is set to gently land with a parachute in the Utah desert on September 24th. Researchers anticipate that the asteroid samples will provide insight into the origins of our solar system and the materials that contributed to the formation of early Earth.

A 7-Year Journey

Gray image of a rugged, diamond-shaped asteroid

Bennu’s terrain is rougher than initially predicted by experts. Photo credit: NASA/Goddard/University of Arizona, Public Domain.

In 2016, OSIRIS-REx was launched from Cape Canaveral, Florida. It journeyed for 2 years to reach Bennu, an asteroid rich in carbon that orbits between Earth and Mars. Upon arrival in December 2018, the spacecraft orbited the asteroid for 2 years, gathering data on its mass, density, albedo, surface composition, and particle environment.

During the exploration of Bennu, the team discovered that the asteroid belongs to a rare type that is active, meaning it periodically releases material from its surface. The surface is more rugged than anticipated, containing numerous boulders larger than 10 meters in diameter. The spacecraft’s instruments also revealed that Bennu’s density is lower than expected, with up to 60% of the asteroid being empty space. The surface was found to be covered in hydrated minerals, indicating past water activity, and Bennu’s rotation is increasing, likely due to an interaction with solar radiation known as the Yarkovsky-O’Keefe-Radzievskii-Paddack effect.

“My pulse accelerated significantly. The gravity of the situation suddenly hit me. Our trajectory is towards Earth. Regardless, we will be landing.”

Using pictures captured during the orbiting stage, the team in charge of the mission developed precise charts of the asteroid’s surface to aid in choosing a spot for landing. On October 20, 2020, OSIRIS-REx effectively landed on Bennu, spending a brief moment at a designated site called Nightingale to gather material from the surface. Following a minor issue in securing the sample container resulting in a small portion being released into space, the spacecraft turned back towards Earth and commenced its voyage back in May 2021.

The spacecraft completed its last planned course adjustment on September 10th in preparation for its return. According to Lauretta, there was a slight deviation of 200 kilometers from the Earth as a precautionary measure. When the thrusters were directed towards Earth, Lauretta’s heart rate increased. It suddenly became very real that the spacecraft was heading towards Earth and there was no turning back.

Why Return Samples?

Samples of material have been retrieved and brought back to Earth from comets, asteroids, the solar wind, and the Moon. According to Lauretta, samples obtained directly from their source can provide insights into scientific inquiries that cannot be addressed through remote observations, landers and rovers, or even meteorites that have landed on Earth.

Lauretta clarified that when studying meteorites, it is difficult to determine their geological origins. It is uncertain where they originated from, how frequently they are found, and the likelihood of them reaching Earth in its early stages. However, with the Bennu sample, we have a clear understanding of its source and geological background.

According to Takahiro Hiroi, a planetary spectroscopist at Brown University, the intricacies of a rock can often be lost during a meteorite’s journey through the atmosphere and impact, but can be preserved through a returned sample. This sample can also retain microscopic materials, such as nanophases, that serve as evidence of space weathering or shock events. It can also provide information on elements, isotopes, grain density, and material strength, which can indicate the age of the rock and its exposure to solar wind and radiation.

A panoramic image of Bennu’s surface with marks showing the locations of notable features on the asteroid’s surface.

The International Astronomical Union has given approval for names of various features on the surface of the asteroid that follow the theme of birds and mythical bird-like creatures. This decision aligns with the asteroid’s avian naming tradition. Credit: NASA/Goddard/University of Arizona, Public Domain.

Hiroi studied specimens brought back from the asteroids Itokawa and Ryugu, which were the main objectives of previous missions by the Japan Aerospace Exploration Agency (JAXA). The Hayabusa spacecraft gathered proof of space weathering on Itokawa, while Hayabusa2 discovered that Ryugu is composed of carbon-rich rocks called carbonaceous chondrites that closely resemble the composition of the Sun. According to Hiroi, the samples from Ryugu showed that the limited number of meteorites with the same classification that have landed on Earth have undergone chemical changes during their journey through space.

Lauretta expressed interest in the particular forms of carbon found on Bennu. He believes that carbon chemistry holds the most fascinating discoveries, as it is often impacted by meteorites and can contain organic molecules important to biology.

Hiroi is intrigued by the precise makeup of Bennu and the insights it can provide into the early materials of our solar system. According to Hiroi, the samples obtained from Bennu may also include various types of meteorites that have landed on its surface. These samples could potentially aid in differentiating authentic asteroid materials from any terrestrial impurities or changes that may have occurred in multiple types of meteorites.

Preparing for the Future

This upcoming mission by NASA will mark their first sample return since the Stardust mission in 2006 and the Genesis mission in 2004. Other nations, however, have successfully retrieved samples from celestial bodies since then. Japan’s Hayabusa and Hayabusa2 missions brought back samples in 2010 and 2020, respectively, while China’s Chang’e 5 mission returned lunar samples in 2020.

A tan and white diamond-shaped capsule descends toward the desert floor suspended from a white and orange parachute.

On August 30th, the team for the OSIRIS-REx mission participated in a practice run for the upcoming retrieval of the sample return. A mock-up of the sample return capsule was used to simulate its descent through the atmosphere towards the Utah Test and Training Range, which is under the jurisdiction of the Department of Defense. Image credit: NASA/Keegan Barber, CC BY-NC-ND 2.0.

Lauretta and her team were conducting field rehearsals in the Utah desert in August to prepare for the final touchdown event on September 24th. A mock sample return capsule was dropped with a parachute onto a specific landing area at the Utah Test and Training Range. The team then practiced quickly retrieving it and transporting it by helicopter to a temporary clean room to prevent contamination from the Earth’s environment.

A person in a pink shirt places flags around a tan and white model of the sample return capsule as it sits on the desert floor. Three other scientists in white don protective gear next to the capsule.

On August 29th, recovery teams from the OSIRIS-REx mission took part in practice exercises to retrieve the sample return capsule at the Utah Test and Training Range, which is operated by the Department of Defense. The credit for this photo goes to NASA/Keegan Barber, and it is licensed under CC BY-NC-ND 2.0.

After the samples are released from the capsule, 25% will be kept by the OSIRIS-REx science team. The Canadian Space Agency will receive 4% for their involvement with the spacecraft’s instrumentation, and JAXA will receive 0.5% in return for samples from both Hayabusa missions. The remaining material will be kept by NASA, who will allocate some to museums in the United States, make some accessible for educational purposes, and store the rest for future research. Certain samples will be conserved for many years, similar to the procedure used with samples from Apollo missions.

Lauretta expressed her hope that when she reaches the age of 102, she will witness young researchers utilizing the same samples. She believes that with their advanced instruments and knowledge, they will be able to make significant scientific discoveries.

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Reference: Cartier, K. M. S. (2023), Return of Asteroid Samples to Earth: A Journey There and Back Again, Eos, 104, https://doi.org/10.1029/2023EO230357. Published on September 21, 2023.

Text © 2023. AGU. CC BY-NC-ND 3.0

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