The surprisingly dominant role of gluons in nuclei that are viewed by a high-energy probe has been found in experiments at HERA. Their density grows rapidly when one probes gluons which carry smaller fraction of the proton's momentum, x, until it is believed they become saturated at small enough values of x. In contrast, much less is known about the gluon distribution in nuclei. This is important for heavy-ion physics at RHIC and LHC energies where measurements at mid- and forward-rapidity probe partons at low-x where gluons play a dominant role in particle production (e.g. jets and heavy-flavour). In order to interpret the physics results, it is important to understand the initial conditions. One of the most promising methods is though studying DIS collisions on nuclei in e+A reactions which allow us study parton distributions in nuclei and, through the nuclear oomph factor, also allow us to effectively probe protons at smaller x.
Since the closure of HERA, no such facility exists to undertake this programme of study. However, a number of future accelerators are being proposed such as eRHIC at Brookhaven National Lab in the US which will add an electron beam to the current ion-machine, allowing for both e+A collisions and polarised e+p collisions to elucidate the spin of the proton. In this talk I will describe the physics case for eRHIC as well as feasibility studies which have so far been performed as well as an update on the machine design and the project status.