![]() ![]() ![]() While the expansion and contraction is very small, it puts stress on the rock structure, and after repeated trips around the asteroid, the rock develops cracks. When a boulder on the asteroid makes each transition from night to day and back to night, its surface temperature rises and falls by 200 degrees, causing it to expand as it traverses the day side, and contract as it crosses the night side. Since Bennu has no atmosphere to retain heat, when those heated parts of the surface rotate out of direct sunlight, the surface temperature plummets down to a frigid -73☌. Towards the right-hand side is the terminator from day to night.Īs the asteroid rotates, the surface is heated to a blistering 127☌ on the day-side. Towards the left-hand side of the view is the 'sub-solar' point on Bennu - the part of the asteroid that is pointed directly towards the Sun. The view of Bennu in the video above captures the asteroid's rotation, as it spins on its axis, once every 4.3 hours. Watch Below: OSIRIS-REx sees a day go by for 'rubble pile' Bennu If we somehow were able to instantaneously transport Bennu from space to a point just above Earth's surface, it would immediately collapse into a giant pile of rocks. Walking on the asteroid's surface, however, would probably feel like standing on a deep layer of packed gravel. In space, with all the separate components held together by mutual gravitational attraction, Bennu appears vaguely diamond-shaped and reasonably solid. Basically, it is a half-kilometre-wide collection of boulders - some several meters wide - with the gaps between those boulders filled in bu rocks, gravel and dust. It is a special type of asteroid that scientists refer to as a 'rubble pile'. When depicting an asteroid flying through space, artist impressions and media usually present it as one giant chunk of rock or metal. "This is the first time evidence for thermal fracturing has been definitively observed on an object without an atmosphere," Molaro said in a PSI press release. No spacecraft had been able to capture images clear enough to show this, though, until now. This type of weathering is common here on Earth, and scientists believed it could be responsible for the breakdown of materials on asteroids and comets. ![]() Credit: NASA/Goddard/University of ArizonaĪccording to a new study led by Jamie Molaro, a Planetary Scientist with the Planetary Science Institute and NASA's Jet Propulsion Laboratory, thermal fracturing is a process where the repeated heating and cooling of a rock causes cracks to form, widen, and eventually split the rock apart. The top three images show where boulders have broken apart, while the bottom three views show obvious linear cracks in the rocks. ![]() These close-up images from the surface of Bennu show examples of weathering that are linked to thermal fracturing. These boulders, researchers discovered, show evidence of cracks and fractures that pointed to a type of weathering known as 'thermal fracturing'. Taken when the spacecraft passed just 600 meters over the asteroid's surface, these images focus in on boulders jutting out of the asteroid's surface. The latest discovery from the mission came from a close examination of pictures from the OSIRIS-REx Camera Suite (OCAMS). Since New Year's Eve 2018, the OSIRIS-REx spacecraft has been orbiting around asteroid Bennu, collecting images and revealing a variety of scientific discoveries about these ancient objects. Scientists with NASA's OSIRIS-REx mission just made the first discovery of 'thermal fracturing' on an airless asteroid in space. ![]()
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