\tau Ceti ( HD10700 ) , a G8 dwarf with mass 0.78 M _ { \odot } , is a close ( 3.65 pc ) sun-like star where 5 possibly terrestrial planet candidates ( minimum masses of 2 , 3.1 , 3.5 , 4.3 , and 6.7 M _ { \earth } ) have recently been discovered .
We report abundances of 23 elements using spectra from the MIKE spectrograph on Magellan .
We find [ \mathrm { Fe } / \mathrm { H } ] = -0.49 and T _ { eff } = 5387 K. Using stellar models with the abundances determined here , we calculate the position of the classical habitable zone with time .
At the current best fit age , 7.63 ^ { +0.87 } _ { -1.5 } Gy , up to two planets ( e and f ) may be in the habitable zone , depending on atmospheric properties .
The Mg/Si ratio of the star is found to be 2.01 , which is much greater than for Earth ( \sim 1.2 ) .
With a system that has such an excess of Mg to Si ratio it is possible that the mineralogical make-up of planets around \tau Ceti could be significantly different from that of Earth , with possible oversaturation of MgO , resulting in an increase in the content of olivine and ferropericlase compared with Earth .
The increase in MgO would have a drastic impact on the rheology of the mantles of the planets around \tau Ceti .