"By making it easier to see what other news outlets are saying about each topic, we hope that people will feel more informed about the news in their region," Facebook says. "The stories that appear in this section are some of the most popular stories about that topic on Facebook. These stories are determined the same way as the featured headline -- using a combination of factors including the engagement around the article on Facebook, the engagement around the publisher overall, and whether other articles are linking to it."

Any publication is eligible to be featured in the Trending carousel, and Facebook hasn't outlined any new strategies for filtering out unreliable news sources in this section -- a problem the company has faced in the past. In January, Facebook updated its Trending processes in an attempt to filter out fake-news articles. Today's redesign doesn't change the way Facebook finds Trending topics.

The update is live on iPhones in the United States, and it's heading to Android and desktop soon.

Facebook is also experimenting with discoverability on mobile devices. "One of the things we regularly hear from people who use Trending is that it can be difficult to find in the Facebook mobile app," the company says.

A handful of smartphone users will see the top three Trending topics directly in their News Feeds, and Facebook plans to use this test to fine-tune a new mobile layout.