What is the surface of a comet like? That's one of the main questions that motivated Philae's mission to the surface of comet 67P/Churyumov-Gerasimenko. We now know the comet has a rigid crust about 10 to 50 centimeters thick, below which the comet is much more fluffy.
Mars today is a dynamic place. One visually dramatic sign of change on Mars is "mass wasting," more commonly known as "stuff falling downhill". Scientists presented the results of recent laboratory work on Mars mass wasting at last week's Lunar and Planetary Science Conference.
James Tuttle Keane is increasingly famous (among planetary scientists anyway) for his remarkable illustrated notes from conferences. Here's his work from the Division for Planetary Sciences meeting, illustrating both his own and others' research.
Three years ago, on October 19, 2014, comet C/2013 A1 Siding Spring passed within 138,000 kilometers of Mars. At the 2017 meeting of the Division for Planetary Sciences of the American Astronomical Society, we heard a progress report on Mars orbiter imaging of the comet's nucleus.
The team reported two weeks ago that the first attempts at observing 2014 MU69 were unsuccessful. But in their third try, on July 17, astronomers in Argentina saw the telltale sign of MU69's presence: a stellar wink.