  Abell 1689 is a galaxy cluster at $z=0.183$ where previous measurements of
its mass using various techniques gave discrepant results. We present a new
detailed measurement of the mass with the data based on X-ray observations with
the European Photon Imaging Camera aboard the XMM-Newton Observatory,
determined by using an unparameterized deprojection technique. Fitting the
total mass profile to a Navarro-Frenk-White model yields halo concentration
$c=7.2^{+1.6}_{-2.4}$ and $r_{200}=1.13 \pm 0.21 h^{-1} \mathrm{Mpc}$,
corresponding to a mass which is less than half of what is found from
gravitational lensing. Adding to the evidence of substructure from optical
observations, X-ray analysis shows a highly asymmetric temperature profile and
a non-uniform redshift distribution implying large scale relative motion of the
gas. A lower than expected gas mass fraction $f_{gas}=0.072 \pm 0.008$ (for a
flat $\Lambda$CDM cosmology) suggests a complex spatial and/or dynamical
structure. We also find no signs of any additional absorbing component
previously reported on the basis of the Chandra data, confirming the XMM low
energy response using data from ROSAT.

Astrophysics