One (serious) Planetary and Space Science paper for May (vol. 259):
Marschall, R. Morbidelli, A. Marrocchi, Y. The refractory-to-ice ratio in comet 67P: Implications on the composition of the comet-forming region of the protoplanetary disk Art. 106061 .2501.17864
To bystanders, the Rosetta mission looked like a hit. We went to a comet! We landed on a comet! To scientists, Rosetta looked like a failure. One of the mission goals, deciphering cometary activity and its origins/pathways, was never reached. That lander failed to send more than trivial data; merely landing was not a mission goal (and even that was botched). And nucleus studies in general got short-changed when mission management prioritized space physics- studies of the far coma and its interaction with the solar wind/interplanetary magnetic field. This is why bystanders’ opinions aren’t binding.
One of the basic nucleus studies was not even observed directly: the nucleus composition. What is Comet 67P/Churyumov-Gerasimenko even made of? From the Giotto mission, plus VeGa 2, Stardust, Deep Impact, etc. we had a broad picture that a nucleus is dust grains, various organics, and a volatile component (water ice, plus other frozen volatiles). After Rosetta, we STILL had that broad picture, and not much narrower results. Estimates of the “ice” (total of frozen components) ranged from below a 1:1 refractory-to-ice ratio (𝜒), to over 10:1. Marschall et al. now throw their paper into the ring. Working backwards from the elements (as sampled by Rosetta’s mass spectrometers), they try to reassemble what the nucleus composition was- an inverse problem. And the ratio 𝜒? Still broad.