Explanation: What creates these long and nearly straight grooves on Mars? Dubbed linear gullies, they appear on the sides of some sandy slopes during Martian spring, have nearly constant width, extend for as long as two kilometers, and have raised banks along their sides. Unlike most water flows, they do not appear to have areas of dried debris at the downhill end. A leading hypothesis -- actually being tested here on Earth -- is that these linear gullies are caused by chunks of carbon dioxide ice (dry ice) breaking off and sliding down hills while sublimating into gas, eventually completely...