  We present results from an 850-$\mu$m survey of the $\sim$ 5 Myr old
$\lambda$ Orionis star-forming region. We used the SCUBA-2 camera on the James
Clerk Maxwell Telescope to survey a $\sim$0.5-diameter circular region
containing 36 (out of 59) cluster members with infrared excesses indicative of
circumstellar disks. We detected only one object at $>3\sigma$ significance,
the Herbig Ae star HD 245185, with a flux density of $\sim74$ mJy beam$^{-1}$
corresponding to a dust mass of $\sim150$ M$_{\oplus}$. Stacking the
individually undetected sources did not produce a significant mean signal but
gives an upper limit on the average dust mass for $\lambda$ Orionis disks of
$\sim3$ M$_{\oplus}$. Our follow-up observations of HD 245185 with the
Submillimeter Array found weak CO 2--1 line emission with an integrated flux of
$\sim170$ mJy km s$^{-1}$ but no $^{13}$CO or C$^{18}$O isotopologue emission
at 30 mJy km s$^{-1}$ sensitivity, suggesting a gas mass of $\lesssim1$ M$_{\rm
Jup}$. The implied gas-to-dust ratio is thus $\gtrsim50$ times lower than the
canonical interstellar medium value, setting HD 245185 apart from other Herbig
Ae disks of similar age, which have been found to be gas rich; as HD 245185
also shows signs of accretion, we may be catching it in the final phases of
disk clearing. Our study of the $\lambda$ Orionis cluster places quantitative
constraints on planet formation timescales, indicating that at $\sim5$ Myr the
average disk no longer has sufficient dust and gas to form giant planets and
perhaps even super Earths; the bulk material has been mostly dispersed or is
locked in pebbles/planetesimals larger than a few mm in size.

Earth and Planetary Astrophysics;Solar and Stellar Astrophysics