Martian (Yargo)

The native inhabitants of planet Mars are a sapient but physically hideous race. Their appearance is similar to a tall (even though curved forward), reptilian gorilla with webbed feet, lizard eyes, a flat nose and a fish-like mouth. As of the 20th century, they don't have spacefaring technology, but do keep themselves in diplomatic contact with the spacefaring Yargonians, who consider the Martians intellectually superior to Earth s humanity.

They are worried that atomic tests on Earth are somehow related to the sun's activities and might cause the star to prematurely expand, destroying all life on Earth and Mars in the process, but since they cannot travel to Earth themselves, have asked the Yargonians to contact Earth authorities about the problem.

Behind the scenes
At the end of the book, it is very strongly implied that the entire science fiction plot was a fantasy caused by mental instability on the protagonist's part; meaning that all alien species described never existed even in-universe.