arthur has given rather precise conjectures on the decomposition of the regular representation l^2(g(f)\\g(a)), where g is a simple lie group over a number field f, with adele ring a. in particular, the irreducible constituents are partitioned into classes called arthur packets. i will discuss the construction of some of these packets when g is the exceptional group $g_2$ and how one can justify that the constructed packets are the right ones.