Find leads on the salarian ark
Find leads on the asari ark
Pathfinder Ryder will receive the e-mail Asari refugees! from Cora Harper explaining that asari refugees have landed on Eos, which starts the mission Cora Harper: Asari Ark. Conversing with Hydaria in Prodromos reveals that the Leusinia jettisoned its transponder over Voeld. This objective is marked complete once the conversation is over.
After landing on Voeld and acquiring the transponder, wait for Cora to decipher it and learn the Ark's present location in the Valay system.
Find leads on the turian ark
Tiran Kandros sends you an email titled Turians on Havarl which starts the mission Turian Ark: Not Dead Yet. Landing on Havarl to help the turians at the Turian Camp will reveal they are survivors from the Natanus. Speak with Avitus Rix to acquire Turian Ark: Lost But Not Forgotten. The mission will be on hold, but Rix will eventually make contact via vidcomm with a lead on the ark. After accepting his request to rendezvous, you will find the Natanus in the Remav system, where H-047c (Habitat 5) is located.