Mars mission with two-arm-joint Martians from dead civilization

Question

Between 1994-1998, my library carried a sci-fi novel about Mars. I remember the cover being mostly black, somewhat larger format than a usual novel. I was under the impression it was Christian-themed, but I remember the themes as being implicit.

The story follows a somewhat shy man, who initially expresses some frustration at the inability to understand women. He uses some kind of email. He is onboard a ship headed for Mars. When he arrives at Mars, he discovers an alien/Martian, from a long-dead civilization. The Martian has two elbow joints on its arms. The Martian travels with him back to Earth, where they uncover some ancient mystery or conspiracy. The Martians had apparently come to Earth in the past, and were worshipped as Hindu gods.

Answer 1

This bears some similarities to Dream Thief (see covers) by Stephen Lawhead. First published in 1983, it is one of Lawhead's earlier works, and is indeed heavily Christian themed (it turns out Christians and Martians worship the same supreme being).

The protagonist is Spencer Reston, a sleep researcher on a space station called Gotham. In the course of the story he goes to Mars and discovers the one of the last remaining Martians, living amid the ruins of their civilization.

he glanced up and saw a humanoid well over two meters tall watching him from a doorway. The thing gazed at him steadily with keen interest, its long, triple-jointed arms crossed over its narrow chest.

This fits with the description in the question, except that these Martians have triple joints instead of double ones. They voyage back to Earth and uncover a conspiracy involving another Martian, named Ortu, who had been living on Earth for millenia. The alien had originally landed with a group of others, but over the course of time the others had died:

One by one the bright ones died… rsis Atri, Pulastya, Kratu, Vasistha, Pulacha, Marici, Angiras…' The words were familiar to Spence, who remembered that these were the names of the gods of Indian folklore Adjani's father had told them about. These had been Ortu's comrades, now long dead, but still remembered and strangely revered in India's fantastic legends...

As Spence had suspected, the coming of the Martians had given birth to one of the most widespread enduring religions of mankind. Hinduism was founded upon a primitive misunderstanding, a mistake of cosmic proportions.