Asteroid Bennu images have for the first time proved space rocks are susceptible to solar radiation, NASA data has revealed Space experts have finally found evidence even a little sunshine can crack rocks on asteroids.
Rocks on asteroid Bennu appear to fracture as sunlight heats them during the day and cool down at night, according to images from NASA's Origins Spectral Interpretation Resource Identification Security-Regolith Explorer (OSIRIS-REx) probe.
The Asteroid’s Mystery
Dr Jamie Molaro of the Planetary Science Institute, lead author of the research paper, said: "This is the first time evidence for this process, called thermal fracturing, and has been definitively observed on an object without an atmosphere.
It is one piece of a puzzle that tells us what the surface used to be like, and what it will be like millions of years from now. Rocks expand when sunlight heats them during the day and contract as they cool down at night, causing stress that forms gradually growing cracks.
Scientists have long suspected thermal fracturing could be an important weathering process on airless objects such as asteroids because many experience extreme temperature differences between day and night, compounding the stress.
Daytime highs recorded on Asteroid Bennu can hit almost 127C (260F), and nighttime lows plummet to about minus 73C (almost minus 100F). However, many of the tell-tale features of thermal fracturing are small, and before OSIRIS-REx got close to Bennu, the high-resolution imagery required to confirm thermal fracturing on asteroids did not exist.
The NASA’s Reaction
Professor Dante Lauretta, OSIRIS-REx principal investigator, said: "Like any weathering process, thermal fracturing causes the evolution of boulders and planetary surfaces over time - from changing the shape and size of individual boulders, to producing pebbles or fine-grained regolith, to breaking down crater walls.
How quickly this occurs relative to other weathering processes tells us how and how quickly the surface has changed. The mission team found features consistent with thermal fracturing using the spacecraft's OSIRIS-REx Camera Suite (OCAMS), which can see features on Bennu smaller than 1cm.
NASA spotted evidence of exfoliation, where thermal fracturing likely caused small, thin layers (1 to 10cm) to flake off of boulder surfaces. OSIRIS-REx also produced images of cracks running through boulders in a north-south direction, along the line of stress that would be produced by thermal fracturing on Asteroid Bennu.
Other weathering processes can produce similar features, but the team's analysis ruled them out. Rain and chemical activity can also produce exfoliation, but Bennu has no atmosphere to produce precipitation.
The Key Scientific Takeaway
Rocks squeezed by tectonic activity can also exfoliate, but Bennu is too small for such activity. And meteoroid impacts do occur on Bennu and can certainly crack rocks, but they would not cause the even erosion of layers from boulder surfaces that were seen.
There is also no indication of impact craters where the exfoliation is occurring. Additional studies of Bennu could help determine how rapidly thermal fracturing is wearing down the asteroid, and how it compares to other weathering processes.
Dr Jason Dworkin, OSIRIS-REx project scientist, said: "We don't have good constraints yet on breakdown rates from thermal fracturing, but we can get them now that we can actually observe it for the first time in situ. Laboratory measurements on the properties of the samples returned by the spacecraft in 2023 will help us learn more about how this process works.
When she's not at her desk absorbing all the latest news and producing fresh content for her audience Carmina loves to spend time at coffe shops and dancing at local music festivals.