The first images from the JWST have dazzled the world, but someone is always looking for the next challenge. An even larger space telescope will require a significant upgrade on humanity's current launch capacity. Instead, a new generation of giant Earth-based telescopes are on their way, along with smaller space telescopes optimized for specific purposes. Some of the monster instruments under construction are expected to begin operations in just a few years and their immense scale is hard to grasp.
Sometimes Size Does Matter
Over the next three centuries after Galileo's first astronomical telescope apertures grew more than 100-fold, allowing them to collect more than 10,000 times as much light as the original. Then progress stalled.
From 1949 to 1976 the largest telescopic mirror belonged to the 5.1 meter-wide (200 inches) Hale Telescope, known as the “Glass Giant of Palomar”. After the partial failure of the larger BTA-6 telescope, many astronomers ruefully concluded the limit for telescopes operating in the optical wavelengths had been reached. To see deeper into the universe we would have to put telescopes above the atmosphere.
The capacity to use active optics to operate smaller mirror segments as a single mirror, seen in the JWST's 18 hexagonal segments, restarted the race. The current record-holder, the Gran Telescopio Canarias, has a collecting area of 74 square meters, more than four times that of Hale (the combined size of the Large Binocular Telescope's mirrors are somewhat greater). That, however, is small compared to what is to come.
In the next decade, three giant instruments are expected to experience first light: the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT), and the Extremely Large Telescope (ELT). These will have respectively collecting areas of 368, 655, and 978 square meters – in the largest case almost 30 times greater than Hale.
By contrast, the JWST has a collecting area of 25.4 m2. Being in space is an immense advantage, of course, but not an infinite one. The ELT in particular is expected to exceed even the JWST's capabilities for many tasks, such as the direct spotting of Earth-sized planets around nearby stars.
Delays are not just for space telescopes; controversy over the location of the TMT telescope atop Mauna Kea in Hawai'i has led to construction being suspended. The GMT and ELT could strike problems of their own. Nevertheless, they are expected to see first light between 2027 and 2029, although in the GMT's case this will be with only four of its eventual seven mirrors, each of which takes several years to make.
Before then we can expect the Vera Rubin telescope – slightly smaller than the largest existing telescopes, but whose enormous field of view will allow it to photograph the entire sky at its location every few nights. First light is anticipated for next year, with full survey operations in 2024.
Don't Forget About Radio, Too
Telescopes that operate at radio wavelengths need to be much larger than those that collect light our own eyes can see, although fortunately they don't need the same precisely smoothed mirrors. The largest single-dish radio telescope in the world today is the Five-hundred-meter-Aperture Spherical radio Telescope (FAST). Radio-telescope arrays, such as the Very Large Array combine multiple dishes to have even larger collecting areas.
Here too, instruments are on their way that will far exceed anything currently in existence. The Square Kilometer Array (SKA) will be made up of thousands of instruments in Australia and South Africa whose combined collection area is in the name.
South Africa's core will be made up of large dishes in the Meerkat National Park, while the Australian counterpart will use 130,000 low frequency antennas Murchison in Western Australia. Predecessor telescopes have already been built at both sites. The sites have been chosen for their “radio quiet”. With these telescopes operating at frequencies that include those used by FM radio, it's important not to drown out signals from billions of light-years away. Additional stations will be dotted across Africa and Australia, making the arrays able to operate for some purposes as if they were a single continent-sized dish.
The SKA will test general relativity with currently impossible precision, explore the universe before the first stars, map a billion galaxies, and advance the search for dark matter. They will also investigate a number of recently discovered radio sources we can't explain and provide us with our best chance of detecting signs of alien civilizations.
Filling In the Niches
Big telescopes are expensive – the giants under construction all have budgets of billions of dollars; some may eventually exceed the JWST's $10 billion cost. Once built, demands on their time far exceed what is available. An alternative approach is to build smaller, cheaper telescopes carefully honed to do quite specific tasks.
An extreme example of this is the TOLIMAN telescope, which has just one job: to find out if Alpha Centauri A or B have habitable planets. As comfortably the closest stars that resemble the Sun, planets orbiting this pair would be prime targets for the search for life, but none have yet been confirmed. The telescope's designer told IFLScience there was a possibility the instrument would prove useful for a handful of other nearby binary systems, but in reality, it was being launched to study “just two stars”. It will, however, cost thousands of times less than the JWST.
The Huntsman telescope, now in the tuning phase, is cheaper still. It combines 10 Canon telephoto lenses and it is expected to discover planets on distant orbits that TESS, NASA's planet hunter, has missed and answer questions about the formation of galaxies and individual stars.
The Nancy Grace Roman telescope is far more expensive and ambitious than these, but still significantly smaller, and hopefully cheaper, than the JWST. However, its wide field of view will allow it to explore large areas of the skies in infrared much more quickly than the JWST, particularly useful for exploring dark energy and conducting an exoplanet census.
Right now, the JWST is exploring space like nothing else humanity has ever built, but soon this multitude of telescopes, with all their different functions, will contribute to our understanding of the cosmos like never before, and we can't wait.