NRO's Gift to NASA Proposed as WFIRST and the Capabilities Therein

Even though budgets are tight, this is an exciting time for NASA’s astrophysics division. New life has been breathed into NASA’s next flagship-class space telescope, the Wide Field Infra-Red Survey Telescope (WFIRST), thanks to the unbidden “gift” to NASA by the National Reconnaissance Office (NRO) of two Hubble-class telescope mirrors. They appeared on NASA’s doorstep in early 2011 and the agency, to its credit, has not ignored them.

This comes during a time of confusion and angst in the agency concerning plans for astronomy missions after the James Webb Space Telescope (JWST). The Astro 2010 Decadal Survey team had pointed to two top priorities after JWST, namely WFIRST and technology development for an exoplanet direct imaging mission. NASA had made halting progress in fulfilling these objectives in the two years since the Astro 2010 report was issued. NASA had developed a plan for WFIRST, but the scenario of when and how to initiate the mission was a bit murk in the aftermath of JWST’s budget woes. In addition, the exoplanet community has taken a beating in recent years, stunned by the cancellation of the Space Interferometry Mission) and the indefinite suspension of the Terrestrial Planet Finder (TPM). How to proceed was the subject of much debate.

In the year since NASA publicly revealed its NRO gifts, things have begun to fall into place. The agency appointed a Science Definition Team (SDT) to evaluate how WFIRST could utilize one of the 2.4-meter NRO mirrors. Now, the SDT has returned with encouraging news. The team’s final report proposes an amazingly capable design for WFIRST. As a bonus, this new WFIRST will be a bonanza for exoplanet studies. It would incorporate a coronagraph that will produce groundbreaking exoplanet science. In one fell swoop, the way forward for the top two priorities of the Astro 2010 team now seems clear.

The primary mission of WFIRST is the study of distant supernova and galaxies. These targets will be used to determine the effect of dark energy on the structure and fate of the Universe. Earlier WFIRST designs had envisioned 1.2-meter optics. The use of the NRO 2.4-meter mirrors means that WFIRST can produce wide-angle, high-resolution views that will be amazing. They will be comparable to HST’s “deep field” views, but cover an area of the sky 100 times greater. There are a number of other astrophysics fields that will benefit immensely from this capability.

The new WFIRST will be a powerful tool in the search for and study of exoplanets in a number of ways. The first is through microlensing, which takes advantage of the bending of space by massive objects, as first posited by Einstein. An exoplanet that passes in front of a distant background star (not its parent star) will cause the star’s light to be slightly magnified because of this space warp. This microlensing search was part of the original WFIRST mission. However, the use of WFIRST’s large 2.4-meter diameter mirror will allow the collection of three times as much light as its original design. This translates into a richer harvest of exoplanets and an increased ability to detect small terrestrial worlds. Overall, the microlensing survey should be able to detect several hundred exoplanets. Together with the results from Kepler, this information will give us a better understanding of the architecture of other solar systems.