2. Sentry

Sensors on the tow-yo confirmed strong petroleum hydrocarbon readings west-southwest of the well site at a depth of about 3,600 feet. Scientists dispatched Sentry, an autonomous underwater vehicle (AUV), to that location, equipped with the TETHYS mass spectrometer to detect chemicals. Sentry zigzagged across the area, with TETHYS detecting where chemicals were and were not. In three dives covering 146 miles between June 23 and 27, Sentry sculpted the shape of the plume. It was more than a mile wide and 600 feet high, and it flowed continuously southwest from Deepwater Horizon at a speed of about 4 miles per day for at least 22 miles.