The Hubble Space Telescope demonstrated that the best viewing is outside the Earth’s atmosphere. Over the years, a series of new telescopes have been lofted into space, and expanded this view into other wavelengths: Spitzer, Chandra, Compton, etc. Next up is the James Webb Space Telescope, with a mirror 6 times larger than Hubble, due for launch in 2013. But these observatories will pale in comparison when squadrons of space telescopes reach orbit. Both NASA and ESA are working on next generation space-based interferometers. They could answer one of the most fundamental questions of science: is there other life in the Universe?
One of the holy grails of astronomy is to find evidence of life outside the Earth, and one strategy is to find evidence of large quantities of oxygen in the atmosphere of another planet. Oxygen is extremely reactive, so large quantities in the atmosphere would mean some source – life – is continuously replenishing it.
In order to sense the atmosphere of another planet, you need an enormous telescope, with a view unobstructed by the Earth’s atmosphere, and some way to block the overpowering light from the planet’s star. The telescope would need to be huge, at least 30 metres across, and launched into space to get above the atmosphere. Since the cost of a single, huge telescope would be enormous, astronomers have developed a strategy where the light from several smaller telescopes could be combined. This called an interferometer.
Interferometers have made huge advances here on Earth. The twin Keck telescopes atop Mauna Kea in Hawaii are separated by a distance of 85 metres. Even though each telescope is only 10 metres across, their light can be combined to give them the resolving power of an 85 metre telescope. But even with this power, the Kecks and other Earth-based interferometers suffer from the distortions of the Earth’s atmosphere.
To make the best interferometers, you’ve got to get out into space. Both NASA and ESA are working on missions to launch a squadron medium-sized observatories. Connected together in a rigid structure, or flying in formation, they would add their light together to act as a much larger instrument. And without the obscuring effect of the Earth’s atmosphere, they would have unprecedented resolving power.
NASA’s space interferometer will be the Terrestrial Planet Finder. This would consist of 3-4 6.5+ metre telescopes to gather light. This light would then be funneled into another spacecraft that contains a special device – called a coronograph – capable of dimming the light from the central star. With such powerful resolution, and without the light from the central star, dimmer objects, such as Earth-sized planets should be visible.
Unfortunately, the mission has been put on hold indefinitely, as part of recent NASA science cutbacks. Let’s hope it doesn’t get completely canceled, and returns to service.
ESA has a space-based interferometer in development called Darwin. This would be a flotilla of three space telescopes, at least 3 metres in diameter, that could combine their light into a fourth telescope equipped with a coronograph as well. It would be able to dim the light from the central star by a factor of millions or even billions to allow faint objects to show up.
ESA and the European Southern Observatory have already developed a nulling interferometer as part of the Very Large Telescope array, which consists of four 8-metre telescopes and a collection of smaller telescopes. Darwin is scheduled for launch in 2015. Darwin will easily see Jupiters orbiting other stars, and should be able to pick out Earth-sized planets as well.
A recent paper by researchers from the Harvard-Smithsonian Center for Astrophysics and the European Space Agency outlined the different telescope configurations that could be used for Darwin or the Terrestrial Planet Finder.