The James Webb Space Telescope— It’s Complicated, but so Is Leadership

Matt Mountain, mmountain@stsci.edu

The recent release of NASA’s Independent Comprehensive Review Panel report (the Casani report) on the James Webb Space Telescope (JWST) has understandably caused consternation within the community, and some of our colleagues’ sound-bite quotes decrying the state of space astrophysics were quickly circulated in the press and on the Internet. As the dust has settled, it’s important to step back for a moment to reflect on why we want to build such an audacious telescope. The words of the President of the AAS, Debra Elmegreen, in a recent article in Space News bear repeating, “We all need to recognize that JWST and the initial $5 billion investment cannot be allowed to fail, since so much of future astrophysics research was built upon the foundation it was to provide—as the Casani report concludes, ‘JWST will play a key role in understanding how and when the first galaxies were born, characterizing the planets that are now being discovered around nearby stars, in providing further insights into the nature of the dark energy and dark matter, and into how stars and planetary systems are born. There is no easy path to understanding such complex scientific questions. To do these things at the level needed to advance scientific understanding requires a complex telescope with truly unique capabilities. JWST is that telescope.’” (Space News, “American Leadership in Astrophysics at Risk,” 22 November 2010.)

I came to the Space Telescope Science Institute because of JWST. Even though I helped to build two large ground-based telescopes, I recognized that there are astronomical observations we struggle to do from the ground. For example, even with 8-m or 10-m telescopes it is next to impossible to take the spectra of high-redshift galaxies to understand the star-formation processes a billion years after the Big Bang. The same is true when trying to measure distant (z > 1) supernovae to try and unravel Dark Energy—it’s a really tough measurement from the ground. As is mapping dust emission to uncover telltale trails of young planetary systems; this is proving to be difficult even in the closest systems.  My colleagues who built the Hubble and Spitzer space telescopes similarly realized that to take the next steps in exploring the Universe would require a bigger space telescope. There is no mystery why: observational astrophysics is a photon-limited field, and once you have near perfect detectors (as we do), our only free parameters are either to spend millions of seconds on every observation or to increase the aperture of the telescope. A large-aperture space telescope combined with the low backgrounds found at L2 was the basic design rationale for JWST, and the broad science this telescope enables was compelling enough to make it the highest-priority large space mission of the 2000 Decadal Survey on Astronomy and Astrophysics.

A decade later, even as our scientific expectations have evolved since the original science case was written—as the Casani report itself notes—JWST remains the most scientifically powerful telescope NASA, ESA and CSA will ever have built: “the next Great Observatory to replace the Hubble Space Telescope.” A decade ago, we were just coming to terms with the possibility of Dark Energy. With JWST, we will reach back to the beginning of time to detect very early supernovae and break the possible degeneracy between supernova evolution and Dark Energy.  A decade ago, we had not yet begun to measure the constituents of exoplanetary atmospheres with transit spectroscopy using Hubble and Spitzer. With JWST, we will use the same technique; as the recent 2010 Decadal Survey (New Worlds, New Horizons in Astronomy and Astrophysics; NWNH) recognized, JWST will be “a premier tool for studying planets orbiting stars that are smaller and cooler than the Sun.”  The goal of detecting liquid water on a planet close to the size of Earth, in the habitable zone around another star, may be within the reach of JWST.  As NWNH notes, with JWST the era of study of … cousins of the Earth … is underway.

And this does not include the great unknown territory that will be uncovered when we fly a telescope 100 times more sensitive than Hubble, almost 1000 times more sensitive than Spitzer. Imagine the creative energy unleashed by the roughly 8,000 astronomers who currently use Hubble and Spitzer. According to a White Paper submitted to NWNH (Sembach et al. 2009), over the period 2005–2007, the Spitzer and Hubble programs alone generated over $130M in General Observer grants, and this community published over 3,000 papers based on Hubble and Spitzer data.  JWST is the next Hubble, the next Spitzer—that’s why we are building this ambitious telescope.