Make movieclip arrays not overlap to each other - actionscript-3

Question

I'm currently working on a game with AS3, wherein the player needs to avoid falling random objects by tilting the phone. These objects uses timer for delay to make them fall one time per row. So I'm working now on the level where there are two objects falling randomly on the screen, which are movieclips "mercury" with class name of planet1 and "venus" with class name of "planet2". The problem is, sometimes they overlapped with each other when falling. I want the two movieclips to not overlap with each other when they start to fall. I had look for scripts and tried it but it doesn't work. I'm beginner in AS3.
Here is the script:
var mercury:planet1;
var mercuryArray:Array = new Array();
var mercuryClock = new Timer(5000, 0);
mercuryClock.addEventListener(TimerEvent.TIMER, spawnMercury);
var venus:planet2;
var venusArray:Array = new Array();
var venusClock = new Timer(2000, 0);
venusClock.addEventListener(TimerEvent.TIMER, spawnVenus);
addEventListener(Event.ENTER_FRAME, onMyEnterFrame);
function onMyEnterFrame(e:Event)
{
galawMercury();
galawVenus();
checkCollision();
}
/*==================PLANET 1=====================*/
function spawnMercury(e:Event)
{
gawaMercury();
}
function gawaMercury()
{
var mercury:planet1 = new planet1();
mercury.x = Math.random() * 400;
mercury.y = 0;
addChild(mercury);
mercuryArray.push(mercury);
}
function galawMercury()
{
for(var ee:int = mercuryArray.length - 1; ee >= 0; ee--)
{
mercuryArray[ee].y += 13;
if(mercuryArray[ee].y > stage.stageHeight)
{
mercuryArray[ee].parent.removeChild(mercuryArray[ee]);
mercuryArray.splice(ee, 1);
}
}
}
/*==================PLANET 2=====================*/
function spawnVenus(e:Event)
{
gawaVenus();
}
function gawaVenus()
{
var venus:planet2 = new planet2();
venus.x = Math.random() * 400;
venus.y = 0;
venus.width = 126;
venus.height = 200;
addChild(venus);
venusArray.push(venus);
}
function galawVenus()
{
for(var yy:int = venusArray.length - 1; yy >= 0; yy--)
{
venusArray[yy].y += 12;
if(venusArray[yy].y > stage.stageHeight)
{
venusArray[yy].parent.removeChild(venusArray[yy]);
venusArray.splice(yy, 1);
}
}
}
function checkCollision()
{
for(var oo:int = mercuryArray.length - 1; oo >= 0; oo --)
{
if(stella.hitStella.hitTestObject(mercuryArray[oo]))
{
keme();
}
}
for(var uu:int = venusArray.length - 1; uu >= 0; uu --)
{
if(stella.hitStella.hitTestObject(venusArray[uu]))
{
keme();
}
}
}
function keme()
{
soundtrackChannel.stop();
soundtrackChannel = stellaDead.play();
removeEventListener(Event.ENTER_FRAME, onMyEnterFrame);
mercuryClock.stop();
venusClock.stop();
score.stop();
stella.play();
blah.text = lbl_iskor.text;
removeObjects();
}
function removeObjects()
{
for each (var mercury:planet1 in mercuryArray)
{
mercuryArray.splice(mercury, 0);
removeChild(mercury);
}
for each (var venus:planet2 in venusArray)
{
venusArray.splice(venus, 0);
removeChild(venus);
}
}