I know the Enterprise-D carries all sorts of shuttlecraft. But - what's the fastest a vessel carried by the Enterprise - work-pod, shuttle, Captain's yacht, probes, whatever - which has a meaningful ability to scan astronomical phenomena, and perhaps search the surface of a planet for life forms - can go? In terms of warp speed?
PS - Yes, I know warp speeds are very shifty w.r.t. their translation to actual speed.
The Enterprise carries a complement of spatial probes including Class 8 probes which are capable of sustained warp flight at warp 9. Note that this object doesn't contain a warp engine, but rather a warp 'sustainer', meaning that it can only travel at the speed at which it was fired.
Class VIII Medium-Range Multimission Warp Probe
Modified photon torpedo casing.
Delta-v limit: Warp 9.
Powerplant: Matter/antimatter warp field sustainer engine; duration 6.5 hours at Warp 9 + MHD power supply tap for sensors and subspace transceiver.
Sensors: Standard pallet plus mission-specific modules.
Telemetry: 4,550 channels at 300 megawatts.
Additional data: Applications vary from galactic particles and fields research to early-warning reconnaissance missions.
I think we can reasonably assume that the 'standard pallet' of sensors is capable of lifeform scanning as well as looking at various weird spacey stuff.
Purely for the record, workpods and the Captain's Yacht are both incapable of warp flight and the Enterprise' standard complement of shuttles (e.g. those seen in the show and mention in the various manuals) are only capable of achieving Warp 3.
If we're sticking strictly to TNG canon, that would have to be a runabout
In Federation starship classification, a runabout was the designation of a type of vessel smaller than a starship but larger than a shuttlecraft. Runabouts were equipped with limited weapons and drive systems, but offered additional living space and the ability to be configured to mission-specific cargo capacities. They had a larger operational range and better weapons capability compared to shuttles, and were capable of speeds of up to warp 5.
Shuttlecraft in general don't get a lot of screen time before DS9 made them the main ship for several seasons. I don't think any prior shuttlecraft were shown to be warp capable. The Type 15 shuttlepod was not warp capable, and no other canon shuttles in the TNG list are shown to have warp capabilities. And saying "sensor-bearing" isn't much of a limitation (all shuttles seemed to have ample sensors).
Presumably the Enterprise could carry a Class C shuttlecraft (from ST:Discovery), which would be the fastest canon shuttlecraft-sized craft available to the TNG era (max warp 7). The Delta Flyer was after TNG canon.
