Phoenix is on Mars to see if organic materials, crucial for life, could be in the soil.
Why not send a microscope along too, just to snap a photo before they turn the oven on? They have them on the rovers…
. . .and the optical microscope on the Phoenix lander is a heckuva lot better than that on the rovers— ~4 micron resolution compared to (if memory serves) ~30 micron. Neither of which would be useful for seeing bacteria, but the microscope is there. The hope is to study the soil particles for a clue to their history (roundness, sphericity, size, texture, etc.)
Just to be clear, the MECA suite of instruments won’t be analyzing the same soil the oven (TEGA) is since the robotic arm delivers the samples to each, which are separate on the instrument deck.
4 microns is good enough to see large bacteria, which range in size up to about 5 microns.
Well, the resolution is 4 microns/pixel, which doesn’t mean that something 4 microns in size can be actually identified— so I’m not sure that even a large bacterium could be reliably distinguished from any other 2 pixel dark (or light) spot.