On Saturday, May 18th, I was a passenger in a car just on the outskirts of Tucson, AZ about 15 minutes past sunset when the driver noticed a large metallic object in the sky out the driver side window. It appeared stationary and so I thought maybe it was a large airplane heading towards us. I didn't see any lights, but it was high enough up that it was still illuminated by the sun. I wasn't able to take a picture, but it showed up on FR24 as a "ball": I couldn't find any news articles that explained the "ball". But, I came across an article, "World View Touts Success, Growth" about a company in Tucson that launches stratospheric balloons for commercial purposes. The article has a picture of one of their balloons. If this is what I saw on Saturday, I'm surprised at how much bigger it seemed to be up in the sky at 67,100 ft (according to FR24) than it appears in the photo in the article.