Four years ago, an explosion on the Deepwater Horizon oil rig in the Gulf of Mexico led to one of the worst environmental disasters in history, with 5 million barrels of oil gushing into the ocean. Now, scientists hope a research expedition wrapping up today could help them better understand the impact of oil spills.  

And there’s an interesting twist to this ocean mission. Most of the scientists involved aren’t on the ship; they’re back in labs on dry land. WGBH News science editor Heather Goldstone explains.