What is the black pod on the left wing of a TBM?
That is the front of the housing which encloses the 10" GWX70 Color Weather Radar antenna.
Here are some close up shots of a TBM depicting the weather radome.
Note the lightning diverter strips:
Apart from the simple fact that airborne weather radar is useful, weather radar is a common option due to the equipment requirements imposed on air carriers operating such aircraft. Specifically, in 14 CFR 135.175, the FAA generally prohibits operation without airborne weather radar equipment along routes where thunderstorm activity is forecast.
Many such single engine aircraft include the option for wing-mounted weather radar, as seen on the TBM 900 in the original question. Since weather radar requires a relatively unimpeded area for signal transmission and receipt, the antenna assembly is typically located at the nose of the aircraft, such as on most multi-engine aircraft. In aircraft with nose mounted engines, a mid or outboard wing mounted position makes sense. See the following photos depicting examples of wing mounted weather radar on a Piper PA-46-500TP Malibu Meridian and a Cessna 208B Super Cargomaster, and a nose mounted weather radar on a Beechcraft King Air B200, respectively:
According to the TBM 900 POH, installation of the optional radar system results in a 5 KIAS decrease in maximum cruise performance and a 3 KIAS decrease in long range cruise performance. This change is due to the slight increase in drag from the radar antenna housing.
It is weather radar.
Most multi-engine aircraft have radar in the nose but single engine aircraft mount it on the wing. They have been doing it since WW II, but with night fighter radar.
As stated above, it's a dielectric blister fairing which houses the antenna for the GWX70 weather radar. The single engine requirement for the engine driveshaft and propeller to be mounted on the aircraft centerline as well as interference from the propeller arc required the radar antenna be offset mounted on the wings like this. Wind tunnel studies showed this configuration minimized parasite drag. This is a fairly common WX radar antenna installation for single engine aircraft and similar designs are found on the starboard wingtip of the Pilates PC-12 and the antenna pod on the Piper PA-46 Malibu series.