We choose a function for the radius that approaches 1. For example, we could use 1+2*exp(-0.1*\t):
\documentclass[border=10pt]{standalone}\usepackage{tikz}\begin{document}\begin{tikzpicture}\draw [red] (0,0) circle [radius=1];\draw [domain=0:50,variable=\t,smooth,samples=500]plot ({\t r}: {1+2*exp(-0.1*\t)});\end{tikzpicture}\end{document}