The newly detected TRAPPIST-1 system , with seven low-mass , roughly Earth-sized planets transiting a nearby ultra-cool dwarf , is one of the most important exoplanet discoveries to date .
The short baseline of the available discovery observations , however , means that the planetary masses ( obtained through measurement of transit timing variations of the planets of the system ) are not yet well constrained .
The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft , and have uncertainties ranging from 30 % to nearly 100 % , with the mass of the outermost , P = 18.8 { d } , planet h remaining unmeasured .
Here , we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission .
Our analysis refines the orbital parameters for all of the planets in the system .
We substantially improve the upper bounds on eccentricity for inner six planets ( finding e < 0.02 for inner six known members of the system ) , and we derive masses of 0.79 \pm 0.27 M _ { \oplus } , 1.63 \pm 0.63 M _ { \oplus } , 0.33 \pm 0.15 M _ { \oplus } , 0.24 ^ { +0.56 } _ { -0.24 } M _ { \oplus } , 0.36 \pm 0.12 M _ { \oplus } , 0.566 \pm 0.038 M _ { \oplus } , and 0.086 \pm 0.084 M _ { \oplus } for planets b , c , d , e , f , g , and h , respectively .