Where did all of the large craters on Ceres go?

27 Jul 2016

A false-colour image of Ceres' Occator Crater. Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Researchers analysing the data from NASA’s Dawn spacecraft on the dwarf planet Ceres had been mystified by where all of its large craters went, but now they may have found an answer.

Ceres was analysed in detail like never before following the entry of Dawn into the dwarf planet’s orbit in March 2015, but, for scientists now analysing data being sent back, what they see has thrown up more questions than answers.

The biggest question hinged on the fact that the planet has presumably been hit by countless large asteroids over the past 4.5bn years, but Ceres’ surface showed very little evidence of large craters.

Future Human

Simulations suggest enormous craters

Computer simulations of Ceres’ past suggest that it should have up to 15 craters larger than 400km in diameter, and at least 40 craters larger than 100km.

However, Dawn returned images that showed it has only 16 craters larger than 100km wide, the largest of which measures 280km across.

By comparison, our own moon is scarred by the cosmic impacts of billions of tonnes of space debris, with the biggest crater – the South Pole-Aitken Basin – 2,500km across.

Now, in a research paper published in Nature Communications, a team of researchers has tried to solve the puzzle by offering us some likely answers.

A healing dwarf planet

Led by Simone Marchi, the research team’s first suggested reason for a less-than impacted Ceres is that the dwarf planet formed farther out in the solar system and then migrated inwards, but this does not fully explain why it has so few craters.

More plausible suggestions include the fact the dwarf planet’s upper layer likely contains ice – because ice is less dense than rock – and would allow for the surface to smooth out post-impact, if salt dominates the subsurface composition.

Hydrothermal activity beneath Ceres’ surface could have led to salt rising up and contributing to the erasure of craters over time.

Similarly, if Ceres had widespread volatile eruptions of water in the past, the cryogenic nature of this material would have resulted in it flowing over craters and burying the largest.

“Somehow, Ceres has healed its largest impact scars and renewed old, cratered surfaces,” Marchi said.

“Whatever the process or processes were, this obliteration of large craters must have occurred over several hundred millions of years.”

Colm Gorey was a senior journalist with Silicon Republic