There are two earthquakes in Pokemon Platinum. The first one is in Pastoria City, but you then don't have to fight him. The second one is at Lake Valor (you're in Canalave City then). Commander Saturn is in the cave at Lake Valor
Saturn
Commander Saturn is at spear pillar in Pokemon pearl.
Go to Canalave City, where you will meet your rival and Prof Rowan and his assistant (in the library). Then there will be a massive earthquake and, when you go outside, a sailor will run up to you and say, "YO, OLD DUDE AND KIDS! SOMETHING BIG HAPPENED AT LAKE VALOR." Prof Rowan tells you to go to Lake Valor, and when you get there, there is no water, and a ton of Team Galactic Grunts. Go to the cave in the middle where you'll have to battle Commander Saturn. Then pretty much go along with the plot from there.
After defeating the Galactic Team Leader Cyrus and Team Galactic Commander Saturn in Team Galactic HQ of Veilstone City, they permit you to set them free by pressing a button to unlock all the capsules. You can meet the trio again in their home lakes after encountering Dialga.
Go into Mt. Coronet from the Hearthome side and go up to Snowpoint City. You get to watch your rival lose to Jupiter.
You see her in the eterna city team galactic building
Commander Saturn is at spear pillar in Pokemon pearl.
Saturn
by knocking out all his/her Pokemon
After you beat Commander Saturn and help your rival you fly to Velistone city and free the three legendary Pokemon. Then after that you go to Mt. Corenet and go to Spear Pillar.
You continue training and then go to gamefaqs.com and check a guide.
In Pokemon Platinum, the player has to defeat several Galactic Grunts and Commander Saturn to get them to leave Lake Valor. This happens after Team Galactic uses a bomb to dry up the lake.
She goes to the Team Galactic HQ in Veilstone City.
comander mars comander jupitar comander saturn comander charon (new guy)
commander Saturn is found at lake valor and galactic HQ in veilstone city
Go to the Pokemon spa there for 365 days in a row. On the 364 day Commander Saturn will be there and ask you to join team galactic!
First you must defeat Commander Saturn at Lake Valor , Fly to Twinleaf Town and defeat Commander Mars at Lake Verity , Then you go to Mt.Cornet & the Team Galatic men will not be there.