From Sinkholes to Jets

It’s quite a week for solar system exploration news. Pluto (which is way more than a planet!) continues to be on everybody’s mind with the upcoming close flyby of the New Horizons mission.  Dwarf planet Ceres is still getting the once-over from Dawn. And, today we’re starting to get more high-resolution images from the Rosetta mission’s OSIRIS camera as it scans Comet 67P/Churyumov-Gerasimenko.  Check out this latest image, showing sinkholes and pits on the surface. It’s more than likely they play an important role in creating the jets of dust we see flowing away from the nucleus. A number of the dust jets trace back to these pits, and that’s giving mission scientists a peek into the interior processes that drive those outbursts.

Active Pits and Sinkholes

Scientists have found at least 18 pits, sort of circular in shape, across various parts of the cometary nucleus. They range in size from a few tens of meters across to a few hundred meters. The deepest ones are around 210 meters, and their floors seem to be covered in dust. Other images of the comet show dust jets rising up from fractures in the walls of the pits. The fractures mean that there are volatiles (gases and ices) just below the surface. AS those materials get warmed by the Sun, they expand, and that forces cracks into the sinkhole walls. The trapped materials, plus dust, come rushing out of the cracks and out to space, creating the jets we’ve all been seeing emanating from the comet.

The pits likely form as the materials rush out, leaving behind a cavity under the surface. The cavities could also have existed since the comet was formed, or some other heating caused ices to vent out after the upper layers warmed up. However the cavities formed, eventually their ceilings can’t hold up any more, and they collapse, creating the pit.

Comet 67P is due to make its closest approach to the Sun on August 13, 2015. The Rosetta spacecraft is orbiting the comet’s nucleus and will be charting how the comet changes up to, during, and after perihelion. The newly awakened Philae lander may also contribute observations, depending on how well it can communicate with the orbiter. This mission is giving us all a new look at some very old ice as it makes its passage through our part of the solar system.

Want to follow the mission? Check out the Rosetta mission pages for more images and announcements.