A NASA spacecraft that will return a sample of a near-Earth asteroid named Bennu in 2023 allowed the first-ever observation of near-particle plumes emerging from the surface of an asteroid. Bennu also proved to be more robust than expected, challenging the mission team to change their flight and sample collection plans due to rough terrain.
Bennu is the target of NASA's OSIRIS-REx (Origins, Spectral Interpretation, Spectral Identification, Safety-Explorer) mission, which began orbiting the asteroid on December 31st. , may contain unaltered materials since the very beginning of our solar system.
"The discovery of plumes is one of the biggest surprises of my scientific career," said Dante Lauretta, principal investigator of OSIRIS-REx at the University of Arizona, in Tucson. . "And the rugged terrain went against all our expectations, Bennu already surprises us and our exciting journey is just beginning."
Shortly after the particle plumes were discovered on January 6, the mission's science team increased the frequency of observations and then detected additional particulate plumes over the next two months. Although many particles were ejected from Bennu, the team tracked some particles into orbit around Bennu before returning to the surface of the asteroid.
The OSIRIS-REx team first spotted the plume of particles in images as the space shuttle gravitated around Bennu at a distance of about one kilometer. After a safety assessment, the mission team concluded that the particles did not pose a risk to the spacecraft. The team continues to analyze particle plumes and their possible causes.
"The first three months of OSIRIS-REx's thorough investigation of Bennu reminded us of the purpose of the discovery – surprises, quick thinking and flexibility," said Lori Glaze, Acting Director of Planetary Science at Headquarters. from NASA to Washington. "We are studying asteroids such as Bennu to learn more about the origin of the solar system.The OSIRIS-REx sample will help us answer some of the biggest questions regarding our origin."
OSIRIS-REx was launched in 2016 to explore Bennu, the smallest body ever put into orbit by a spaceship. Bennu's study will allow researchers to learn more about the origins of our solar system, the sources of water and organic molecules on Earth, the resources located in the near-Earth space and to improve our understanding of asteroids that may affect the Earth.
The OSIRIS-REx team also did not anticipate the number and size of blocks on Bennu's surface. From observations based on the Earth, the team expects a generally smooth surface with some big rocks. Instead, he discovered that the entire surface of Bennu was rough and dense with rocks.
The higher than expected block density means that the Mission's sample collection plans, also known as Touch-and-Go (TAG), need to be adjusted. The initial design of the mission was based on a safe sampling site with a radius of 25 meters. However, due to the unexpected rugged terrain, the team was not able to identify a site of this size on Bennu. Instead, he began to identify candidate sites whose radius is much smaller.
The sampling site footprint and the larger number of blocks will require more accurate performance from the spacecraft when it descends to the surface compared to initial forecasts. The mission team is developing a new approach, called Bullseye TAG, to accurately target smaller sampling sites.
"During OSIRIS-REx operations near Bennu, our spacecraft and operations team demonstrated that we could achieve higher system performance than design requirements," Rich Burns said. , OSIRIS-REx Project Manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Bennu challenged us to manage his rugged terrain and we are confident that OSIRIS-REx is up to the task."
The initial estimate, made of large blocks, was obtained from both Earth-based observations of Bennu's thermal inertia – or his ability to drive and store the heat – as well as radar measurements of its surface roughness.
Now that OSIRIS-REx has revealed Bennu's surface closely, these expectations for a smoother surface have proven to be wrong. This suggests that computer models used to interpret the previous data do not adequately predict the nature of small rocky asteroid surfaces. The team is in the process of revising these models with Bennu's data.
The OSIRIS-REx scientific team has made many other discoveries about Bennu over the past three months since the arrival of the spacecraft on the asteroid, some of which have was presented on Tuesday at the 50th Global and Planetary Conference in Houston and in a special collection of documents published by the journal Nature.
The team directly observed a change in Bennu's rotational speed resulting from the effect known as Yarkovsky-O 'Keefe-Radzievskii-Paddack Effect (YORP). The uneven warming and cooling of Bennu when rotating it in the sunlight causes an increase in the rotation speed of the asteroid. As a result, Bennu's rotation period decreases by about one second every 100 years.
Separately, two of the spacecraft instruments, the MapCam Color Imager and the OSIRIS-REx Thermal Emission Spectrometer (OTES), detected magnetite on Bennu's surface, reinforcing previous discoveries indicating the interaction of the rock with liquid water on Bennu's parent body.
OSIRIS-REx at NASA
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