When NASA\u2019s OSIRIS-REx spacecraft first reached asteroid Bennu, scientists expected to find a sandy, beach-like surface. Instead, the mission uncovered a jagged landscape filled with boulders. Bennu is a rubble pile asteroid about half a kilometer wide, formed from the broken pieces of a much larger parent body.<\/p>\n
The surprise was immediate. \u201cScientists expected some boulders, but they anticipated at least some large regions with smoother, finer regolith that would be easy to collect. Instead, it looked like it was all boulders, and we were scratching our heads for a while,\u201d the mission team recalled.<\/p>\n
This wasn\u2019t the first puzzle Bennu had posed. Back in 2007, NASA\u2019s Spitzer Space Telescope had measured low thermal inertia. It suggested that the surface heats up and cools down quickly, like sand. But the picture was different from the one captured by OSIRIS\u2011REx\u2019s cameras<\/a>. The data showed massive boulders that should have behaved more like concrete, holding heat long after sunset. Something didn\u2019t add up.<\/p>\n The answer began to emerge when OSIRIS\u2011REx delivered 121.6 grams of Bennu\u2019s regolith to Earth in September 2023. Laboratory analysis revealed that the boulders were not solid blocks; they were porous and riddled with cracks.<\/p>\n NASA probe discovered water on Bennu<\/a><\/p>\n \u201cThat\u2019s when things became really interesting,\u201d said Andrew Ryan of the University of Arizona. \u201cThe thermal inertia measured in the lab samples turned out to be much higher than what the spacecraft\u2019s instruments had recorded, echoing similar findings obtained by the team of OSIRIS\u2011REx\u2019s partner mission, JAXA\u2019s Hayabusa\u20112.\u201d<\/p>\n To test the role of cracks, researchers at Nagoya University used lock\u2011in thermography, firing lasers at tiny particles to observe heat ripples.<\/p>\n Meanwhile, at NASA\u2019s Johnson Space Center, samples were sealed in nitrogen\u2011filled glove boxes, scanned with X\u2011ray computed tomography, and digitally archived. \u201cThe sample goes into its own \u2018spacesuit,\u2019 gets a CT scan, and then comes back to its pristine environment, all without having any exposure to the terrestrial environment,\u201d explained Nicole Lunning, OSIRIS\u2011REx sample curator.<\/p>\n