What is resolved first, an card when-player-summon effect or a summoned card effect?

Question

I'm playing with an Alien deck, and one thing I like to do with this is to activate Planet Pollutant Virus combined with Alien Mars and Alien Psychic.

My question is when my opponent summons a monster that has a effect, which resolves first? E.g.

1. My opponent plays a monster that can destroy another monster when summoned
2. My Planet Pollutant Virus places an A-Counter on it
3. My Alien Mars negates my opponent monster's effect

or

1. My opponent plays a monster that can destroy another monster when summoned
2. My Planet Pollutant Virus places an A-Counter on it
3. My opponent monster's effect is resolved so it destroys my Alien Mars before it's effects are negated

Answer 1

Chain activation 1: Opponent's monster summoned, and tries to destroy your monster. SS1 (SS2 if quick effect)

Chain Activation 2: Planet Pollutant Planet activates SS2

Where is Alien Mars? Because it is a SS1, it cannot be activated in this chain

Chain Resolution 2: An A-Counter is put on your opponent's monster.

Chain Resolution 1: Your opponent destroys your Alien Mars

Therefore, your opponent's monster destroys your monster, but you managed to put an A-Counter on it with your Planet Pollutant Virus.

Answer 2

I think the current answer to this question is wrong. Alien Mars does not activate it's effect because it doesn't have an activated effect; it's effect is continuous. The chain order would be:

Chain link 1: monster is summoned, and it's effect is activated. Note that the summon doesn't start a chain, but the effect does.

Chain link 2: an A-Counter is placed on the opponents monster

On resolution, the counter would be added. Since the opponent's monster has a counter on it, it's effect is negated. This is because the effect of Mars is continuous, and doesn't need its own chain link.