The successful launch of NASA's Mars Science Laboratory, or Curiosity, offers a chance to correct a misconception about its imaging systems. You say that these have sufficient magnification and resolution “to see, for the first time, tiny grains of silt ... particles that would bear the history of billions of years of erosion from wind and water” (Nature 479, 446; 2011).

Curiosity's imager will be the first to see silt-sized particles in situ, on the undisturbed surfaces of rocks and soils. But bragging rights for the first images of silt grains (4–62.5 micrometres in diameter) and even some clay-sized particles (smaller than 4 micrometres in diameter) go to the Phoenix Mars Lander, which accomplished the feat in 2008 (P. H. Smith et al. Science 325,58–61; 2009).

Soil samples from trenches on the periglacial landforms surrounding Phoenix were imaged by an optical microscope in the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA), which returned hundreds of colour images of grains as fine as 4 micrometres in diameter (W. Goetz et al. J. Geophys. Res. 115, E00E22; 2010). Imaging grains from diverse substrates enables the microscopic characterization of grain magnetic properties. The MECA atomic-force microscope returned three-dimensional images of particles as small as 0.1 micrometres (M. A. Velbel and A. I. Losiak J. Sed. Res. 80, 771–780; 2010).

When it lands, Curiosity will comprise the most capable suite of instruments delivered to the surface of another planet. But Phoenix has already given us a close look at Mars.