The exoplanets discovered so far have been mostly around relatively nearby and bright stars .
As a result , the host stars are mostly ( i ) in the Galactic disk , ( ii ) relatively massive , and ( iii ) relatively metal rich .
The aim of the SWEEPS project is to extend our knowledge to stars which ( i ) are in a different part of the Galaxy , ( ii ) have lower masses , and ( iii ) have a large range of metallicities .
To achieve this goal , we used the Hubble Space Telescope to monitor 180,000 F , G , K , and M dwarfs in the Galactic bulge continuously for 7 days in order to search for transiting planets .
We discovered 16 candidate transiting extrasolar planets with periods of 0.6 to 4.2Â days , including a new class of ultra-short period planets ( USPPs ) with P < 1.2 Â days .
Radial-velocity observations of the two brightest candidates support their planetary nature .
These results suggest that planets are as abundant in the Galactic bulge as they are in the solar neighborhood , and they are equally abundant around lower-mass stars ( within a factor \sim 2 ) .
The results also suggest that planet frequency increases with metallicity even for the stars in the Galactic bulge .
All the USPP hosts are low-mass stars , suggesting that either close-in planets around higher-mass stars are irradiatively evaporated , or that planets are able to migrate to and survive in close-in orbits only around such old and low-mass stars .