It is vegetable matter, but of a kind unknown on Earth. X-ray testing has revealed the outer shell protects a liquid interior, within which can be discerned the shape of something that appears to have adopted a foetal position.
Even our strongest X-rays fail to produce further results, however, and the exterior of the pod is impervious to our strongest cutting implements, as well as extremes of heat and cold.
What does the pod contain? Only time will tell.