Darksteel Juggernaut

• WOTC Official Reminder Textofficial rules
  Indestructible — Effects that say "destroy" don't destroy this permanent. A creature with indestructible can't be destroyed by damage.

• WWizards of the Coast2011-01-01
  Official Ruling
  Lethal damage and effects that say "destroy" won't cause Darksteel Juggernaut to be put into the graveyard. However, it can be put into the graveyard for a number of other reasons. The most likely reasons are if its toughness is 0 or less or it's sacrificed.
• WWizards of the Coast2011-01-01
  Official Ruling
  The first ability works in all zones.
• WWizards of the Coast2011-01-01
  Official Ruling
  Since Darksteel Juggernaut is itself an artifact, its power and toughness will always be at least 1 while it's on the battlefield (unless a spell or ability somehow changes its card type).
• WWizards of the Coast2011-01-01
  Official Ruling
  If, during your declare attackers step, Darksteel Juggernaut is tapped, is affected by a spell or ability that says it can't attack, or is affected by "summoning sickness," then it doesn't attack. If there's a cost associated with having Darksteel Juggernaut attack, you aren't forced to pay that cost, so it doesn't have to attack in that case either.

Rulings via Scryfall