Peculiar Pale Pebbles

During its recent exploration of the crater rim, Perseverance diverted to explore a strange, scattered field of bright white rocks which sparked the interest of the team scientists.

Perseverance has been climbing up the steep slopes of the Jezero crater rim for over two months now, and ever since approaching the edge of the crater has been spying increasingly diverse and strange-looking rocks. Back in the Jezero inlet channel, Neretva Vallis, Perseverance spotted a whole host of colourful boulders at Mount Washburn, and more recently the science team and internet alike were mesmerised by Freya Castle – a rock striped like a zebra! The crater rim hasn’t finished delivering surprises yet though... Just as we humans were preparing for Halloween back on Earth, a ghostly field of bright white rocks appeared in Perseverance’s view, at the base of a mound in the crater rim termed “Mist Park”, and sparking a new mystery for the science team to unravel.

On Earth, we find white rocks in a wide array of geologic settings, and that’s not surprising given the diverse array of light-toned minerals which can be generated across Earth’s various tectonic settings. On Mars however, with its lack of plate tectonics and a basaltic crust dominated by dark minerals like olivine and pyroxene, white rocks are a rare find. The science team planned several observations using Perseverance’s remote sensing instruments to assess the composition of these peculiar pebbles, including multispectral imaging with Mastcam-Z and zapping them with Supercam’s laser. Hopefully these observations can shed light on how these white rocks formed all the way up here on the crater rim. Unfortunately, none of the rocks were big enough to safely inspect them up close with Perseverance’s robotic arm instruments, but the team are on the lookout for larger blocks or outcrops of this strange lithology as we continue traversing upslope.

Aside from their composition, another mystery is just how these rocks got here. The blocks are all float (float = loose rocks, not in their original location), and scattered over just a few square meters. Perhaps these could be erosional leftovers of some kind of resistant vein or rock layer, where the softer, surrounding lithologies have eroded away? Or could these blocks have tumbled downslope from a more continuous bedrock exposure of enigmatic white material? Who knows, but Perseverance will be keeping its eyes peeled for more of these bizarre blocks as it continues to summit new heights...

Written by Alex Jones, PhD student at Imperial College London