Science is always looking ahead to the next discovery, even as it answers the questions raised by the last one. Astronomers follow this pattern perfectly, and theirs is a high-stakes game because the instruments they use to push the boundaries of human knowledge are so expensive. That is doubly so for space telescopes, as anyone who has watched the ongoing struggle over the James Webb Space Telescope (JWST) is acutely aware. has labored mightily to maintain support for the gigantic infrared telescope in the face of cost overruns that threatened other valuable science, and schedule slips that have pushed its launch date out to 2018. So it is useful to look at the possibilities the JWST offers for the money.
Matt Mountain is in a unique position to do that as director of the Space Telescope Science Institute in Baltimore, the body which is essentially the eyepiece of the Hubble Space Telescope. He is also the telescope scientist on the JWST, which will be managed by the space telescope institute as well. In a presentation at the recent Goddard Symposium, Mountain outlined just one tantalizing possibility among the list of discoveries the JWST may enable, and argued passionately for thinking about what needs to be done in science, instead of being “limited by what we think is possible.”
The answer lies in technology, Mountain argues. Technologically, Hubble, as a telescope, is in the same family as the Palomar telescope built in the 1930s. It's a big heavy slug of glass, carefully shaped to focus photons caught and reflected by its 2.4-meter (nearly 8-ft.) surface. It has changed science because it orbits outside the atmosphere.
The JWST mirror is 6.4 meters across, its size enabled by a segmented construction that allows it to be unfolded and focused after launch (see illustration). It will be sent to the Sun-Earth L2 point, almost 1 million miles deeper into the solar system than Earth, and shielded with a huge deployable sunshade that will keep its infrared sensors cool enough to see the red-shifted objects and structures of the universe as they lit up after the Big Bang 13.7 billion years ago. But its mirror will also enable observations much closer to Earth with unprecedented resolution and, Mountain avers, with the potential to answer one of the most profound questions—are we alone?
“This might be the moment we can discover life on other planets,” he says.
In the past 5-6 years, the ground-based search for extra-solar planets has revealed there are 100 billion planetary systems in the Milky Way Galaxy, something that was not known before. From its vantage point in space, the Kepler planet-finder has suggested in just the past year that fully a third of those systems may include Earthlike planets. Mountain says the Webb telescope may be able to begin looking for the spectroscopic signatures of life on those planets.
This is where technology comes in. At the distances involved, the signatures of a “living planet” will be found in its atmosphere, Mountain says. A JWST-size telescope probably can get meaningful spectroscopic data from no more than a few tens of the millions of candidate planets within range. That capability can be improved with the addition of a deployable “star shade” between the JWST and its targets to block photons unneeded for the analysis, Mountain says, noting that most of the technology for that is already in hand at a cost comparable to the $550 million Kepler mission price tag.
The observations necessary for the Webb to probe an Earth-like planet for water, ozone and other evidence of life would be difficult, Mountain says, but probably no more so than for the Hubble Deep Field and its successors.
The chances of finding evidence of life would be dramatically increased by fielding larger telescopes in space. An 8-meter telescope could probe hundreds of Earth-like planets, and a 16-meter version could study thousands, Mountain says. And that also isn't outside the realm of possibility. The JWST is based on technology pioneered on the ground-based Keck telescope in the 1980s, and the state of the art has advanced since then.
“We now need to take the technologies that are in use on the ground, the active and adaptive optics, and apply those in space,” Mountain says.
Using new technology also can hold down costs. Great observatories like the Hubble and Webb are comparable in real costs, Mountain argues, with technology enabling the advances in capability. The same can be true for future space-based telescopes. They will be worth the hefty price because of the key questions they can answer, including the big one.
“That will cause the breakthrough that will be remembered across the centuries,” Mountain says. “We will know whether we are alone for the first time in our history.”
With the human exploration of Mars still 30 years off, using deep-space telescopes to look for life in more distant locations can inspire a full generation of humanity in the interim. “We have to dream; we have to think ahead,” says Mountain.