A take-off twelve years in the making, the experimental Solar Impulse 2 plane left Abu Dhabi at 7:12 a.m. local time, bound for Muscat, Oman, on the first leg in a journey that will require 25 days in the air spread over a period of roughly 5 months.

"We are very ambitious in our goal, but modest given the magnitude of the challenge," said co-pilots Bertrand Piccard and André Borschberg in a statement. "This is an attempt, and only time will tell if we can overcome the numerous weather, technical, human and administrative issues."

The two co-pilots will take turns flying the dozen or so legs of the trip that will cover 35,000 kilometers (about 22,000 miles) and two ocean crossings.