If a planet becomes too hot then that planet cannot sustain life, and mercury is close to the Sun, and is extremely hot. Given these facts, mercury cannot sustain life because it is among the following options:
- too close to the Sun
 - harmful substances
 - dormant state
 - major threat to health
 - too cold
 - has little gravity
 - scarce resources
 - too small


 

 too close to the Sun        