What Might I Have Seen?

I’m genuinely curious. I was camping in the Utah desert southeast of Dugway (huuuuge military base/training grounds) and about 15 minutes after sunset I saw a bright gold/orange thing moving horizontally, very very quickly, in the sky above a mountain top. The shape seemed mostly spherical, but it was hard to get a good look. It appeared to be in Class G airspace according to AutoPylot (drone app), but obviously E is a possibility. It was flying east southeast, so away from the nearby restricted airspace. There was no sound at all.

It had to be several thousand feet high due to its position relative to the mountain top and my perspective. It seemed much too large to be a small plane like a Cessna. Way too big to be a meteor that wouldn’t be in the news the next day. Then it disappeared completely, immediately, like someone flipped a light switch. It was in unrestricted airspace as far as I can tell. It had no lights on despite flying after sunset.

My first thought was a large military jet reflecting the sun and I saw it exactly when the sun set at the plane’s altitude, but again, G/E airspace, no lights, no sound, and nothing was visible in its path after it disappeared. It moved VERY fast. Pilot forgot to turn on the lights? Weird military craft? Do military pilots not need to use lights in G or E airspace? If it was a weather balloon, I’m pretty sure it set some balloon speed records. Lemme hear it! I figure someone here knows what objects in the sky might look like what I saw.

PS I’m not saying it was aliens or that I even believe in them. I’m just curious.