Today I saw something that I have never seen before. Standing outside my house, a 757 on it's approach to DTW (3,000-4,000 feet) had contrails coming out of the engines. Obviously this happens at higher altitudes, but I have never seen this that low. A few minutes later, a CRJ and a DC-9 had the same effect. I thought it was so cool to see that so low. Just a little excitement before the big game today.