Macro-level features have been mapped for a while, but even from earth orbit (Hubble) it's not possible to resolve features at high resolution. I'm not sure what the precise limits are, but according to one photo (http://commons.wikimedia.org/wiki/File:Mars_HST_Mollweide_ma...), Hubble's imaging of Mars is at a resolution of approximately 20 km/pixel, which is several orders of magnitude too low to resolve the "hole" here, which is <100m.
Since 2006, there's been a high-resolution camera platform orbiting Mars (http://en.wikipedia.org/wiki/HiRISE), and it's doing this high-res imaging, at up to 30cm/pixel (!), for the first time. Though Wikipedia says that as of 2010, it's only mapped 1% of Mars's surface to that degree.
Since 2006, there's been a high-resolution camera platform orbiting Mars (http://en.wikipedia.org/wiki/HiRISE), and it's doing this high-res imaging, at up to 30cm/pixel (!), for the first time. Though Wikipedia says that as of 2010, it's only mapped 1% of Mars's surface to that degree.