Images recovered by the James Webb Telescope projected in New York.
Astronomers have so far discovered more than 5,000 planets outside the solar system. The big question is whether there is any life on these planets. To find the answer, astronomers will need more powerful telescopes than are available today.
I am an astronomer who studies astrophysics and planets around distant stars. For seven years, I led a team developing a new type of space telescope capable of gathering a hundred times more light than the James Webb Space Telescope, the largest space telescope ever built.
Almost all space telescopes, including Hubble and Webb, use mirrors to collect light. Our proposed telescope, the Nautilus space observatory, would replace the large, heavy mirrors with a new thin lens that is much lighter, cheaper and easier to manufacture than glass telescopes. Because of these differences, it is possible to launch several separate units into orbit and create a powerful array of telescopes.
The need for larger telescopes
Exoplanets — planets orbiting stars other than the Sun — are prime targets in the search for life. Astronomers must use giant space telescopes that collect large amounts of light to study these faint, distant objects.
Existing telescopes can detect planets as small as Earth. However, greater sensitivity is required to begin to discern the chemical composition of these planets. Even the web is not powerful enough to search some exoplanets for signs of life, such as 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 until 2045 and is estimated to cost $11 billion. These ambitious telescope projects are always expensive, laborious and create a powerful but highly specialized observatory.
A new type of telescope
In 2016, the space agency Northrop Grumman invited me and 14 other NASA professors and scientists — experts in the search for exoplanets and extraterrestrial life — to Los Angeles to answer a question: What will exoplanetary space telescopes look like in 50 years?
During our discussions, we realized that one of the major obstacles to building more powerful telescopes is the challenge of building large mirrors and placing them in orbit. To avoid these hurdles, some of us came up with the idea of revisiting an old technology called diffractive lenses.
Conventional lenses use refraction to focus light. Refraction occurs when light changes direction as it travels from one medium to another – this is what causes light to bend when it enters water. In contrast, diffraction occurs 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 by French scientist Augustin-Jean Fresnel in 1819 to provide lightweight lenses for headlights. Today, similar diffractive lenses are found in many small consumer optics—from camera lenses to virtual reality headsets.
Thin and simple diffractive lenses are known for their blurred images, so they are not used in astronomical laboratories. But if you can improve their clarity, using diffractive lenses instead of mirrors or refracting lenses can make space telescopes much cheaper, lighter and larger.
A thin, high resolution lens
After the meeting, I returned to the University of Arizona and decided to investigate whether modern technology could produce diffractive lenses with better image quality. Luckily for me, Thomas Milster – one of the world’s leading experts in diffractive lens design – works in the building next door to mine. We formed a team and worked.
Over the next two years, our team invented a new type of diffractive lens that required new manufacturing technologies to etch a complex pattern of tiny grooves into pieces of clear glass or plastic. The specific shape and form of the cups focus the incoming light to a point behind the lens. The new design has near-perfect image quality over previous diffractive lenses.
Focusing on the surface texture of the lens, not the thickness, keeps the lens very thin and light so it can be zoomed in easily. Larger lenses gather more light and lighter weight means cheaper launches into orbit—two attractive features for a space telescope.
In August 2018, our team built the first prototype, a 2-inch (5 cm) diameter lens. Over the next five years, we further improved the image quality and increased the size. We are now completing a 10 inch (24 cm) diameter lens that is 10 times lighter than a conventional refractive lens.
The power of a deflection space telescope
This new lens design rethinks how space telescopes are built. In 2019, our team unveiled the concept of the Nautilus Space Observatory.
Using the new technology, our team hopes to be able to create a 0.2 inch (0.5 cm) diameter lens at 29.5 feet (8.5 meters) in diameter. The lens and substructure of our new telescope weighs about 1,100 pounds (500 kilograms). It is three times lighter than a similarly sized Webb-style mirror and larger than Webb’s 21-foot (6.5 meter) diameter mirror.
The thin lens allowed the team to design a lighter and cheaper telescope, which they named the Nautilus Space Observatory. Daniel Abay/University of Arizona, CC BY-ND
Contact lenses have other benefits as well. First, they are much easier and faster to design than glasses and can be mass-produced. Second, lens-based telescopes work well even if they are not properly aligned, making these telescopes easier to assemble and fly in space than mirror-based telescopes, which are more accurate.
Finally, since a single Nautilus unit is light and relatively cheap to manufacture, dozens can be put into orbit. Our current design is not really a telescope, but a constellation of 35 individual telescope units.
Each individual telescope will be an independent, highly sensitive observatory capable of collecting more light than the Web. But the real power of the Nautilus comes from turning the individual telescopes all toward the same target.
Combining the data from all the units, Nautilus’ light-gathering power is equivalent to a telescope nearly 10 times larger than Webb’s. With this powerful telescope, astronomers can search hundreds of exoplanets for atmospheric gases that could indicate extraterrestrial life.
Although the Nautilus space probe is still a long way from launch, our team has made a lot of progress. We’ve shown all aspects of the technology to work on small-scale prototypes, and now we’re focusing on building a 3.3-foot (1 meter) diameter lens. Our next steps are to send a smaller version of the telescope to the far reaches of space on a high-altitude balloon.
And with that, we’ll be ready to bring a new space telescope to NASA and explore hundreds of worlds in search of signatures of life.