Depressing economic times inevitably cast a pall over our space plans. That makes it important to keep our eyes on the big picture — what we hope to accomplish — rather than succumbing to the fatigue induced by seeing good science pushed back on the calendar year after year. Will we get a terrestrial planet finder off in the next fifteen years? Will we get back to the Jupiter system some time before 2030? I don’t know, but times like these require persistence, patience, and continued hard thinking.

I was musing about this while looking through a paper Dave Moore passed along recently. It’s a discussion of where we need to go now that we’ve got missions like CoRoT and Kepler in space and the James Webb Space Telescope in the picture for 2014. Tom Greene (NASA Ames) and colleagues from various institutions are looking at a space telescope with relatively modest aperture in the 1.4-meter range, one that would use a coronagraph to block the light of central stars to allow direct imaging of planets all the way down to the habitable zones.

Why do we need such a mission? The JWST, able to take high quality spectra on transiting gas giants, is going to have trouble with low mass dust disks near habitable zones, and the same problem extends to small planets in those zones and planets that do not transit. An instrument like the one detailed here would be able to detect planets down to one to two Earth radii in the habitable zones of about two dozen of the nearest stars, looking for spectral features like H20, O2 or other molecules we believe necessary for life.

From the paper:

Our simulations show that any small planets in or near habitable zones of 20 of the nearest stars would have a 20% chance of detection in 6 – 12 hours of integration time with a moderate aperture space coronagraph. Thus there would be a 90% chance of detecting each one in a total of 10 uncorrelated visits. Therefore a complete survey and repeat followup characterization could be completed in about a year of real time. These observations will likely include short term monitoring for variation with rotation and longer term monitoring for seasonal effects (perhaps snow), phase effects in atmospheric scattering, and constraining orbits.

Add in what would be learned about giant planets and circumstellar debris disks over a wider range of target stars and the mission stacks up as a prudent one for our times, relatively modest in scope but capable of extending our knowledge significantly while affecting the design of future, more expansive projects. Kepler’s field of view doesn’t include the nearby F, G and K-class stars envisioned as targets for this hunt and ground-based radial velocity studies won’t be able to produce the detail of this mission, which would be capable of directly imaging many planets that are so far only inferred from our data.

The paper is Greene et al., “Discovering and Characterizing the Planetary Systems of Nearby Stars,” prepared for the Planetary Systems and Star Formation science frontier panel of the Astro2010 Subcommittee on Science (abstract).