[Ervin]

Если выводить нужно не меньше указанного то -

<input type="text" id="theNumber" value=""></div>

var planetsList = {
        "Mercury": 0,
        "Venus": 0,
        "Earth": 1,
        "Marts": 2,
        "Jupiter": 16,
        "Saturn": 17,
        "Uranus": 14,
        "Neptune": 2,
        "Pluto": 1
     };

function getNumber() {
  var number = +this.value;

  outputPlanets(number);
}

function outputPlanets(num) {
   var list = "";
   
   for(var planet in planetsList) {
       if(num <= planetsList[planet]) {
          list += planet + " ";
       }
   }

   console.log(list);
}

window.onload = function() {
   document.getElementById("theNumber").addEventListener("change", getNumber, false);
};