This sounds like the Lear's Daughters series by Marjorie B. Kellogg and William B. Rossow. There were two novels: The Wave and the Flame and Reign of Fire.
I remember the names of some of the members of the science expedition: Megan Levy, Stavros Ibia, Emil Clausen, Veronica McPherson.
The natives of the planet were a race of small humanoids called the Sawls, and the names of the ice and fire goddesses that they worshipped were Valla Ired and Lagri. The were believed to be primitive at first, but in a later scene they show one of the scientists a diagram that turns out to be periodic table of the elements including elements beyond those discovered so far by humans.
A plot summary of The Wave and the Flame from fantasticfiction.co.uk:
The planet Fiix has a climate of bizarre extremes which defies conventional scientific explanation. An expedition from Earth, expecting to find a desert planet, instead finds itself marooned in the middle of a savage winter. The local population, the Sawls, are small and apparently primitive creatures; but while Emil Clausen - mineral company representative in search of profits from the planet's lithium deposits - and planetologist Tay Danforth are missing, presumed dead, after being caught in ferocious floods, other scientists start to learn that the Sawl's have a complex and surprisingly advanced culture. In particular, linguist Stavros Ibia begins to identify with the Sawl's and determines to protect their planet from commercial exploitation, and to gain an understanding of their theological and historical roots.