WFIRST coronagraph: Imaging Giant Exoplanets Around Nearby Stars   
       
   Technology Development: The Wide-Field Infrared Survey Telescope (WFIRST) is   
   the highest-ranked recommendation for a large space mission in the NRC 2010   
   decadal survey, New Worlds, New Horizons (NWNH) in Astronomy and Astrophysics.   
   The WFIRST coronagraph instrument (CGI) will be the first high-contrast   
   stellar coronagraph in space. It will enable WFIRST to respond to the goals of   
   NWNH by directly imaging and spectrally characterizing giant exoplanets   
   similar to Neptune and Jupiter, and possibly even super-Earths (extrasolar   
   planets with a mass higher than Earth's but lower than our Solar System's ice   
   giants, Neptune and Uranus), around nearby stars. The WFIRST CGI includes both   
   a Shaped Pupil Coronagraph (SPC) and a Hybrid Lyot Coronagraph (HLC). All   
   three of WFIRST's CGI technology milestones for 2015 were passed successfully.   
   coronograph imaging   
       
   Measured milestone contrasts for the HLC (middle) and SPC (left) in a vacuum   
   testbed in2015, where the milestone target contrast of 10-8 average in the   
   dark hole (the annularand wedge-shaped regions, respectively) was achieved for   
   both coronagraphs, as plannedand on schedule.   
       
   First, the HLC demonstrated a raw contrast (speckle/star intensity ratio) of   
   10-8, using a 10% bandwidth filter in visible light (550 nm), in a static   
   environment. Second, the SPC achieved the same milestone under the same   
   conditions. For both the HLC and SPC, the figure above shows excellent average   
   contrast (blue-green) over most of the field of view, and slight turn-up (red)   
   at the inner and outer radii, as expected. The third milestone was   
   accomplished when the Low Order Wavefront Sensing and Control (LOWFS)   
   subsystem achieved its goal of providing sensing of pointing jitter and   
   control at the 0.4 milli-arc-second rootmean- square (RMS) level, which will   
   keep a target star sufficiently centered on the coronagraph star-blocking   
   mask, when the WFIRST telescope experiences pointing drift and jitter.   
   Masks fabricated for WFIRST coronograph   
       
   Pupil-plane reflective mask for the SPC, 24-mm diameter, black silicon on   
   mirror (left).Image-plane reflective mask for the back-up technology Phase   
   Induced AmplitudeApodization Complex Mask Coronagraph (PIAA-CMC) coronagraph,   
   155-æm diameter,raised elements on silicon (center). Image-plane transmitting   
   mask for HLC, 100-æmdiameter, raised dielectric and metal on glass (right).   
   All masks were fabricated in theMicro-Devices Lab (MDL) at the Jet Propulsion   
   Laboratory (JPL).   
       
   Impact: With achievement of these milestones, NASA is a major step closer to   
   being confident that WFIRST will be able to directly image planets and dust   
   disks around nearby stars. There are at least 15 radial-velocity exoplanets   
   that both coronagraphs will be able to image in their dark hole regions, in a   
   few hours integration time each. The WFIRST coronagraph will enable scientists   
   to see these exoplanets directly for the first time, and the images will be in   
   their true colors (using some of the other color filters in the CGI). A   
   simulation is shown in the figure on page 9, where the blocked star is hidden   
   inside the annulus; a planet is seen at about 5 o'clock, and the star is   
   assumed to have no zodiacal dust around it (left) or a strong dust cloud   
   (right).   
       
   Status and Future Plans: WFIRST successfully completed its Mission Concept   
   Review in December 2015, in preparation for its Phase-A start the following   
   January (which was also successful). The CGI is baselined as a technology   
   demonstration instrument on WFIRST; it does not drive mission requirements   
   beyond those needed for the Wide Field Instrument. However, with one year of   
   allocated observing time out of a six-year mission, NASA expects that it will   
   achieve breakthrough science, and will demonstrate key technology elements for   
   follow-up missions, the next of which could be aimed at finding habitable   
   Earth-like planets around nearby stars.   
   simulated CGI imagery of planet   
       
   Simulation of expected image with CGI on WFIRST of a planet (at about 5   
   o'clock) with nozodiacal dust cloud (left) and with a zodiacal dust cloud   
   (right).   
       
   Sponsoring Organization: This coronagraph technology is jointly funded by the   
   Astrophysics Division's SAT program, in partnership with the NASA Space   
   Technology Mission Directorate (STMD). NASA JPL currently leads the   
   coronagraph development effort, and key contributions of the coronagraph team   
   have been provided by three former SAT PIs: Jeremy Kasdin at Princeton   
   University, John Trauger at NASA JPL, and Olivier Guyon at the University of   
   Arizona.   
       
       
   Regards,   
       
   Roger   
      
   --- DB 3.99 + W10 (1607)   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)