Could approaching an unknown object in space electrocute you? Say you're out for a spacewalk on the ISS one day, and you see an unknown object floating next to you (ignoring the probability that it somehow matched your orbit perfectly and didn't just plunge straight into Earth's atmosphere). Let's say a bowling-ball sized metallic sphere. 
Given the relative nature of voltage/potential difference, assuming this thing hasn't come into contact with anything else recently and ignoring any other ways a mysterious floating object could kill you, is it possible that the potential difference between you and the object could be so great that contact with it would instantly/almost instantly kill you? Would the situation be any different in an atmosphere, or with a bigger object?
 A: The short answer it is highly unlikely it will cause lethal electric shock. Here is the reason why.
Lethal electric shock requires current of sufficient magnitude and duration to flow through your heart to cause ventricular fibrillation or cardiac arrest. This means there has to be two contacts on the body with the source of current in order to have a current path through the heart. Examples are current paths from chest to back, hand to foot, and hand to hand.
Now, for this unknown object to potentially cause lethal electric shock there are three minimum requirements:


*

*There has to be a potential difference, or voltage, between two points on the object that is  potentially  capable of driving the necessary current through the heart.

*The object has to be capable of delivering the necessary current, which depends on the source impedance and available electrical energy.

*The shape/dimensions of the object having the potential for causing shock has to be such that two simultaneous contacts with it and the body per 1 is possible.
Based upon the above it seems highly unlikely, to me at least, that a spherical metal ball could cause a fatal electric shock. Primarily because it’s unlikely to meet the first requirement above that there will be a potential difference between two points on a metal (conducting) sphere. 

I realize that it wouldn't be able to deliver current in the usual
  sense, but what about charge equalization? Could that produce any
  significant effect, or am I misunderstanding how that works?

The phenomenon you are describing is called electrostatic induction. The static electric field associated with the sphere would not penetrate electrically conductive objects such as the human body. Instead it would induce a surface electric charge on the body. If physical contact is made the charges should combine and the two body become electrically neutral. Generally, the physical sensation of this migration of charge to the surface of the skin is limited to that associated with its interaction with body hair. 
Bottom line: I believe that any internal currents generated in the body during electrostatic induction should be brief and occur at or near the surface of the body and not involve critical organs, notably the heart. Just like the electrostatic discharges (ESD) we experience here on earth, I believe it should be harmless to persons.
Hope this helps.
A: Putting your hands on opposite terminals of a large, high voltage capacitor will do it. They are dangerous. 
