| This close pass of Mars provided an unprecedent opportunity for high spatial resolution telescopic observations from HST. At its closest, HST was able to resolve features as small as about 10 miles (15 km) apart on the Martian surface. This is by far the best resolution ever obtained from a Earth-based telescope, and is the same kind of resolution that was being obtained from Mars spacecraft flybys and orbiters in the 1960s and 1970s!. Additionally, HST's high quality digital cameras can obtain images and scientifically important wavelenghts that are not being studied by any of the past or present MArs sapace missions, thus filling an important gap in color coverage and substantially enhancing the scientific return of those missions. HST is, in effect, another NASA mission to MArs just in a very, very high orbit !.
Here I present a color composite of some of the images obtained by HST on June 26, 2001, when Mars was very near its closest approach point to Earth. The composite consist of images obtained through blue (410 nm), green (502 nm), and red (673 nm) filters as well as several others with the Planetary Camera detector on the WFPC2 instrument. The colors have been balanced to provide an approximate representation of "true color" as would be seen through a backyard telescope, altough the contrast of the clouds, hazes and ices visible primiraly at blue wavelenghts have been enhanced slightly for better visibility.
The Hubble images and resolution at this opposition are spectacular. A number of interesting surface and atmospheric phenomena are visible, and they remind us that Mars, like the Earth, is a dynamic and ever-changing world. To first order, the surface is divided into bright reddish and darker grayish regions. The reddish color is caused by the presence of oxidized iron minerals (rust) on the Martian surface. Smaller, blue/wither areas are seen near the poles(top and bottom in this color composite) and the limbs (left and right sides). These kind of markings have been observed in roughly this same pattern for at least the last 300 years, since serious telescopic observations of Mars began. However, the markings are known to change with time. Bright regions have been seen to darken, and dark regions to brighten, and many changes have been observed specially along the boundaries between bright and dark regions