The Pirate Incursion is a repeating Event in Star Wars the Old Republic that takes place on Dantooine. There are two secret achievements you can earn as a Solo player during the Pirate Incursion event.

“Well That Was Unexpected” is the first achievement and rewards “Dantooine Well” decorations upon completion. To earn this achievement travel to the Farmhouse atop the hill between both Heroic 2+ door phases (marked in the red square number 1).
In the middle of the Farmhouses you should find an open well with a warning sign, jump into the well and you will unlock the secret achievement.

“The Polly Exclusion Principle” is the second secret achievement and is also pretty easy! To earn this one, travel to the island in the middle of the Lake towards the South-East of Dantooine (marked in the red square number 2). When you arrive find Polly and stand infront of her so that she shoots a red laser at you. You’ll then start earning a buff from Polly on your buffs sheet and once Polly buffs you 10 times Polly will surprise you which earns you the second secret achievement!