Astronomers have so far discovered more than 5,000 extrasolar planets. The big question is whether there is life on any of these planets. To find the answer, astronomers will probably need more powerful telescopes than they do now.
I am an astronomer who studies astrobiology and planets around distant stars. For the past seven years, I’ve co-led a team developing a new kind of space telescope that can collect 100 times more light than the James Webb Space Telescope, the largest space telescope ever built.
Almost all space telescopes, including Hubble and Webb, collect light using mirrors. Our proposed telescope, the Nautilus Space Observatory, would replace large, heavy mirrors with a new, thin lens that is much lighter, cheaper, and easier to produce than mirrored telescopes. Because of these differences, it would be possible to launch many individual units into orbit and create a powerful network of telescopes.
The need for larger telescopes
Exoplanets – planets orbiting stars other than the sun – are important targets in the search for life. Astronomers must use giant space telescopes that collect massive amounts of light to study these dim and distant objects.
Existing telescopes can detect exoplanets as small as Earth. However, it takes much more sensitivity to learn about the chemical composition of these planets. Even Webb is barely powerful enough to search certain exoplanets for evidence of life, namely gases in the atmosphere.
The James Webb Space Telescope cost more than $8 billion and took more than 20 years to build. The next flagship telescope is not expected to fly before 2045 and is estimated to cost $11 billion. These ambitious telescope projects are always expensive, labour-intensive and result in one powerful, but highly specialized observatory.
A new kind of telescope
In 2016, aerospace giant Northrop Grumman invited me and 14 other professors and NASA scientists – all experts on exoplanets and the search for extraterrestrial life – to Los Angeles to answer one question: what will exoplanet space telescopes look like in 50 years ?
During our discussions, we realized that a major bottleneck preventing the construction of more powerful telescopes is the challenge of making larger mirrors and getting them into orbit. To get around this bottleneck, a few of us came up with the idea of revisiting an old technology called diffractive lenses.
Conventional lenses use refraction to focus light. Refraction is when light changes direction as it moves from one medium to another – it’s the reason light bends when it enters the water. Diffraction, on the other hand, is when light bends around corners and obstacles. A cleverly arranged pattern of steps and angles on a glass surface can form a diffractive lens.
The first such lenses were invented in 1819 by French scientist Augustin-Jean Fresnel to provide lightweight lenses for lighthouses. Today, similar diffractive lenses can be found in many small consumer lenses, from camera lenses to virtual reality headsets.
Thin, simple diffractive lenses are notorious for blurry images, so they’ve never been used in astronomical observatories. But if you could improve their brightness, using diffractive lenses instead of mirrors or refractive lenses could make a space telescope much cheaper, lighter and bigger.