Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope , we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements .
The mid-transit times are 5.6 \sigma earlier than those of the unverified transit-like signals reported in 2011 , and we find no connection between the two sets of events .
The transit depth together with our determined stellar radius ( R _ { \star } = 0.703 ^ { +0.039 } _ { -0.034 } R _ { \odot } ) indicates a 2.34 ^ { +0.18 } _ { -0.15 } R _ { \earth } super-Earth .
When combined with the radial velocity determined mass of 7.86 \pm 0.73 M _ { \earth } , our radius measure allows us to derive a planet density of 3.44 ^ { +0.91 } _ { -0.82 } g cm ^ { -3 } .
Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements .
The star of the HD 97658 system is the second brightest known to host a transiting super-Earth , facilitating follow-up studies of this not easily daunted , warm and likely volatile-rich exoplanet .