Advances in Planetary Science

This year, NASA's Dawn and New Horizons rendezvoused with Ceres and Pluto, respectively. These worlds, despite their modest sizes, have much to teach us about the accretion of the Solar System and its dynamical evolution.

Planets are no longer the only Solar System bodies sporting ring systems. Two dense rings have been detected encircling a Centaur object — a relatively small, icy interloper from the distant reaches of the Solar System. See Letter p.72

Data obtained by the Cassini spacecraft show that the plume of ice particles at the south pole of Saturn's moon Enceladus is four times brighter when the moon is farthest away from the planet than when it is closest. See Letter p.182

In the second of two essays looking at organic chemistry that can be found in the Solar System, Bruce C. Gibb focuses on the gas and ice giants as well as their satellites — concluding the tour on Saturn's fascinating moon Titan.

Gas-giant planets are widely thought to form from solid ‘cores’ of roughly ten Earth masses; simulations now show that such cores can be produced from ‘pebbles’ (centimetre-to-metre-sized objects) provided that the pebbles form sufficiently slowly, leading to the formation of one to four gas giants in agreement with the observed structure of the Solar System.

Observations of a stellar occultation by (10199) Chariklo, a minor body that orbits the Sun between Jupiter and Neptune, reveal that it has a ring system, a property previously observed only for the four giant planets of the Solar System.

The plume at the south pole of Enceladus is several times brighter when that moon is near the apocentre of its eccentric orbit around Saturn than when it is near its orbital pericentre, showing that more material appears to be escaping from beneath Enceladus’ surface at times when models predict its fissures should be under tension.

Transient streaks that appear seasonally on Martian slopes are consistent with brine flows, but evidence of water or salts has been lacking. Analysis of spectral data reveals hydrated salts associated with the streaks, confirming a briny origin.