Transverse aeolian ridges (TARs) are a type of sand ridge on Mars and are one of the most common landforms on Mars. They are mid-way in height between dunes and ripples; they are not well understood. One possible mechanism for their formation is that larger grains like pebbles are rolled on top of smaller ripples; then, finer dust settles into the cracks, making the TAR larger than typical ripples.
TARs are often seen in low places like valley floors. Currently, they are not moving. TARs are most common near the equator.
In a study reported in the planetary journal Icarus, TAR's seem to be similar to landforms in the Lut desert of Iran. The measurements of length, width, height, and wavelength of the landforms in the Lut Desert and TARs on Mars overlap. Lut bedforms are classified as mega-ripples, hence Martian TARs may also be mega-ripples.
The term "transverse aeolian ridge", or "TAR" was first used by M. Bourke et al. in 2003.