The disk around AU Microscopii , an M1 star in the \beta Pictoris Moving Group , is extraordinarily well-suited for comparison to the \beta Pic debris disk ( type A5V ) .
We use far-UV absorption spectroscopy of AU Mic to probe its edge-on disk for small amounts of H _ { 2 } , the primary constituent of gas giant planets .
Our conservative upper limit on the line-of-sight H _ { 2 } column density is 1.7 \times 10 ^ { 19 } cm ^ { -2 } , which is 18.5 times lower than the limit obtained from non-detection of sub-mm CO emission ( 12 ) .
In addition , there is a hint of H _ { 2 } absorption at a column density an order of magnitude or more below our upper limit .
The H _ { 2 } -to-dust ratio in the AU Mic disk is < 6:1 , similar to that in the \beta Pic disk .
This shows that the primordial gas has largely been dissipated in less than about 12 Myr for both disks , despite their very different stellar masses and luminosities .
It is extremely difficult to form a giant planet around AU Mic with current core-accretion scenarios in such a short time .