Data from OSIRIS-REx reveals loose surface of asteroid Bennu and early aging of asteroids

Date:
Tue, 26 Jul 2022 16:52:37 +0000

Description:
Recently analyzed data from an asteroid surface-sample collection performed
by NASAs OSIRIS-REx mission has revealed The post Data from OSIRIS-REx
reveals loose surface of asteroid Bennu and early aging of asteroids appeared first on NASASpaceFlight.com .

FULL STORY ======================================================================

Recently analyzed data from an asteroid surface-sample collection performed
by NASAs OSIRIS-REx mission has revealed that asteroid 101955 Bennus surface regolith is much looser than previously thought. Had OSIRIS-REx not fired its thrusters to back away from Bennu after collecting its sample, the spacecraft likely wouldve sunk straight into Bennus surface.

Whats more, additional data from OSIRIS-RExs sample collection revealed that surface regeneration occurs much quicker on asteroids than on Earth.



Bennus loose surface

At 22:13 UTC (6:13 PM EDT) on October 20, 2020, OSIRIS-REx, with its Touch-And-Go Sample Acquisition Mechanism (TAGSAM) sample collection arm extended, successfully touched down on the surface of asteroid 101955 Bennu. Following surface contact, OSIRIS-REx engaged its sample collection system, filling the TAGSAM head with regolith from the surface of Bennu. OSIRIS-REx then fired its thrusters and backed away from Bennu, completing the sample collection process in less than five seconds.

Since its sample collection, OSIRIS-REx has left Bennu and is currently en route to Earth. Just before it flies by Earth, it will release the sample capsule into the atmosphere for retrieval by NASA teams following a touchdown at the Utah Test and Training Range in the United States. However, scientists have been continuously analyzing the data collected by OSIRIS-REx during the sample collection procedure.

In a new study led by OSIRIS-REx principal investigator Dante Lauretta, scientists have discovered that the outer particles of Bennus surface are extremely loose and lightly bound, so much so that if a person were to step onto Bennus surface, they would feel little to no resistance and sink into
the asteroids surface similar to a plastic ball pit on Earth. Our expectations about the asteroids surface were completely wrong" Dante Lauretta, NASAs OSIRIS-REx Mission

Results published today from #OSIRISREx have implications for asteroid Bennu, other 'rubble pile' asteroids, and planetary defense. https://t.co/BuhqGtVlKM pic.twitter.com/855ZP4Vxlm

NASA Solar System (@NASASolarSystem) July 7, 2022



If Bennu was completely packed, that would imply nearly solid rock, but we found a lot of void space in the surface, said OSIRIS-REx scientist Kevin Walsh of the Southwest Research Institute in San Antonio, Texas.

Furthermore to the surprise of the OSIRIS-REx team if the probe had not fired its thrusters to back away from Bennu after collecting the surface sample, it likely would have continued sinking into Bennus surface until it hit a compact object. See Also OSIRIS-REx Mission Updates Atlas V/OSIRIS-REx Updates L2 BEO Section Click here to Join L2

The effect of OSIRIS-RExs sample collection on Bennus surface was also
clearly seen in up-close imagery of Bennus surface taken by the spacecraft after collecting its sample.

What we saw was a huge wall of debris radiating out from the sample site, Lauretta said.

The wall of debris created by the spacecraft was larger than expected and had an unusually high abundance of pebbles and other surface regolith, especially since OSIRIS-REx barely tapped the surface. Additionally, a large eight-meter crater was left on Bennus surface from the sample collection. This
observation was quite bizarre to OSIRIS-REx teams, as every time they had tested the sampling system on Earth, the spacecraft barely made a divot in
the testing area.

Every time we tested the sample pickup procedure in the lab, we barely made a divot, Lauretta said.

Our expectations about the asteroids surface were completely wrong. We were like, Holy cow!

In order to gain a better understanding of the sample collection and what occurred on Bennus surface during the procedure, teams had OSIRIS-REx swing back around to the sample site to gather more imagery of the crater and surrounding areas.

Using images taken before and after the sample collection, scientists were able to determine the volume of debris at the impact site, named Nightingale, before and after OSIRIS-REx collected its surface sample. Scientists also analyzed acceleration data from the spacecraft during touchdown. The data showed that as OSIRIS-REx touched Bennus surface, it experienced very little amounts of resistance and was sinking into Bennus surface by the time the spacecraft fired its thrusters.

By the time we fired our thrusters to leave the surface we were still
plunging into the asteroid, said mission scientist Ron Ballouz of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.



Mission scientists continued to run hundreds of computer simulations based on OSIRIS-REx images and acceleration data to understand the density and
cohesion of Bennus surface. Teams varied the surface cohesion in each simulation until they got a value that closely matched real-life data collected by OSIRIS-REx.

Having precise information on the cohesion and nature of Bennus surface
allows scientists to better interpret asteroid observations, both from Earth and spacecraft. Additionally, the Bennu data could prove useful for
developing upcoming missions to asteroids and methods to protect Earth from possible asteroid collisions. Loose asteroids like Bennu could pose a different kind of threat when entering Earths atmosphere than asteroids that are more solid.

I think were still at the beginning of understanding what these bodies are, because they behave in very counterintuitive ways, said OSIRIS-REx scientist Patrick Michel, director of research at the Centre National de la Recherche Scientifique at Cte dAzur Observatory in Nice, France.

Lauretta et al.s research on Bennus surface was released on July 7 in the journals Science and Science Advances.

Early aging of asteroids

The Lauretta et al. study isnt the only recent study to use high-resolution up-close imagery from OSIRIS-REx to uncover the many secrets of asteroid evolution. A new study led by Marco Delbo of Universit Cte dAzur, CNRS, Observatoire de la Cte dAzur, Laboratoire Lagrange in Nice, France, has revealed that asteroids regenerate their surfaces much faster than Earth does
meaning asteroids age faster.

Using up-close imagery of the surface of Bennu, scientists were able to determine that the heat from the Sun can fracture rocks on Bennus surface in just 10,000 to 100,000 years much quicker than scientists previously
thought.

We thought surface regeneration on asteroids took a few millions of years. We were surprised to learn that the aging and weathering process on asteroids happens so quickly, geologically speaking, said Delbo.

Though jarring and enormous natural disasters such as volcanic eruptions, landslides, and earthquakes can rapidly change a landscape on Earth, widespread changes to Earths surface happen gradually, typically by wind, temperature changes, and water. These natural occurrences can change and
shape Earths surface extensively over the course of a few million years as they erode surface layers gradually. A great example of this occurrence is
the Grand Canyon in the United States, which was shaped, molded, and layered by flowing rivers and other bodies of water, meaning that its top layers are its youngest while its lowest layers are around 1.8 billion years old. Don't forget to wear sunscreen.

Some asteroids are aged early by the Sun, with surface rocks fracturing in just 10,000-100,000 years. Analysis of images from our #OSIRISREx mission revealed a weathering process that happens fast, geologically speaking: https://t.co/EupmNjFsKe pic.twitter.com/gFfkIhQXgV

NASA (@NASA) July 24, 2022



On Bennu, quick temperature changes create internal stress, causing fractures to form in its surface rocks, leading to the rocks being broken down after further stress.

So just how quickly does the temperature change on Bennu?

Every 4.3 hours, the Sun rises on Bennu. The sunlit side of Bennu can reach temperatures of nearly 127 C, with the night side experiencing temperatures
as low as -23 C. The rpid change in temperature every 4.3 hours is what
causes the internal stress and rock fractures on Bennu.

When first investigating the OSIRIS-REx images of fractured rocks, Delbo et al. immediately noticed the temperature shock signature in the fractured
rocks imaged by the spacecraft.

A distinct signature that temperature shocks between the day and the night could be the cause (was seen in the rock images), said Delbo.

Delbo et al. then measured the length and angles of more than 1,500 rock fractures in rocks seen in the OSIRIS-REx images. Interestingly, the size of the fractures varied immensely, with some being as small as a tennis racket and others being as large as a tennis court. The group of researchers found that the rock fractures mainly align in the northwest-southwest direction, which is a major indication that they were formed by the Suns heat
confirming that the Sun is a primary force in shaping the landscape of Bennu.

If landslides or impacts were moving boulders faster than the boulders were cracking, the fractures would point in random directions, said Delbo. In this image from OSIRIS-REx, deep, dark, and long fractures can be seen in rocks, with some major fractures being outlined in red. (Credit: NASA/Goddard/University of Arizona)

In addition to hand-measuring the fractures seen in the images, Delbo et al. developed computer simulations to model how the fractures formed over time. Using the computer simulations and the OSIRIS-REx images, they were able to calculate the 10,000 to 100,000-year timeframe needed for the thermal rock fractures to propagate and split the rocks.

The thermal fractures on Bennu are quite similar to what we find on Earth and on Mars in terms of how they form. It is fascinating to see that they can exist and are similar in very exotic physical conditions [low gravity, no atmosphere], even compared to Mars, said co-author Christophe Matonti of Universit Cte dAzur, CNRS, Observatoire de la Cte dAzur, Goazur, Sophia-Antipolis, Valbonne, France.

Though new rocks and surface features form relatively quickly (geologically speaking), its important to remember just how old these asteroids are and why we study them.

Keep in mind, the topography of Bennu is young, but the rocks on the
asteroids are still billions of years old and hold valuable information about the beginning of the solar system, said OSIRIS-REx mission scientist Jason Dworkin of NASAs Goddard Space Flight Center in Greenbelt, Maryland.

Delbo et al.s research was published in June in the journal Nature
Geoscience.

(Lead image: Artists illustration of OSIRIS-REx performing its sample collection on Bennu. Credit: NASA)

The post Data from OSIRIS-REx reveals loose surface of asteroid Bennu and early aging of asteroids appeared first on NASASpaceFlight.com .



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Link to news story: https://www.nasaspaceflight.com/2022/07/osiris-rex-bennu-aging/


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