The National Science Foundation’s NOIRLab has shared a great picture of the sky behind the Gemini North Observatory which is located in Maunakea, Hawai’i. The dominant feature is a white large looming cloud, which the team jokes is not a flying saucer.
So not aliens, but a perfectly natural phenomenon known as lenticular cloud. Lenticular means lens-like and you can see why the term is used. These clouds are usually seen around mountains and peaks. You need high, humid winds blustering over mountainous terrain – of which Mauna Kea is an excellent example of being 4,207 meters (13,802 feet) above sea level.
When the humid winds pass over the mountain, the air cools down and with rising altitude there is lower pressure, making this combo an ideal place for water droplets that make a cloud to form. High-altitude air continues to flow while the lower altitude air rush up the mountain to make the cloud. As they meet when the cloud forms, it is carved in the lens-like shape that we see.