We report the discovery of HAT-P-17b , c , a multi-planet system with an inner transiting planet in a short-period , eccentric orbit and an outer planet in a 4.8 yr , nearly circular orbit .
The inner planet , HAT-P-17b , transits the bright V = 10.54 early K dwarf star GSC 2717-00417 , with an orbital period P = 10.338523 \pm 0.000009 d , orbital eccentricity e = 0.346 \pm 0.007 , transit epoch T _ { c } = 2454801.16945 \pm 0.00020 ( BJD Barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time ( UTC ) ) , and transit duration 0.1691 \pm 0.0009 d. HAT-P-17b has a mass of 0.530 \pm 0.018 M _ { J } and radius of 1.010 \pm 0.029 R _ { J } yielding a mean density of 0.64 \pm 0.05 g cm ^ { -3 } .
This planet has a relatively low equilibrium temperature in the range 780–927 K , making it an attractive target for follow-up spectroscopic studies .
The outer planet , HAT-P-17c , has a significantly longer orbital period P _ { 2 } = 1798 _ { -89 } ^ { +58 } d and a minimum mass m _ { 2 } \sin i _ { 2 } = 1.4 _ { -0.4 } ^ { +1.1 } M _ { J } .
The orbital inclination of HAT-P-17c is unknown as transits have not been observed and may not be present .
The host star has a mass of 0.86 \pm 0.04 M _ { \sun } , radius of 0.84 \pm 0.02 R _ { \sun } , effective temperature 5246 \pm 80 K , and metallicity [ Fe / H ] = 0.00 \pm 0.08 .
HAT-P-17 is the second multi-planet system detected from ground-based transit surveys .