How The James Webb Space Telescope Will Hunt For Exoplanets

When the new James Webb Space Telescope is launched into orbit around our planet later this year, it won’t be just another tool for astronomers to explore the universe. With its cutting-edge spectroscopy technology, it will be able to peer out into the darkness of space and see distant objects in more detail than ever before — far more than its predecessor, the Hubble Space Telescope. It’s going to revolutionize our understanding of exoplanets, and it could even help us to learn about where we came from and where else in the universe might be habitable.

To get the lowdown on how the James Webb Space Telescope will help us study spinning balls of rock trillions of miles away (and why astronomers want to), we spoke to two researchers who will be working with James Webb: Néstor Espinoza of the Space Telescope Science Institute and Antonella Nota of the European Space Agency (ESA).

A giant leap forward

In recent years, researchers have identified planets outside of our solar system using telescopes like TESS (the Transiting Exoplanet Survey Satellite) or the Kepler space telescope. These are able to look at the very brightest stars and see changes in their brightness when a planet passes between them and us using a technique called the transit method. This is an impressive feat of scientific observation, but it doesn’t tell us much about what those planets are like — just their approximate size and mass.

If we want to know what a planet is like — does it have an atmosphere? what is it composed of? are there clouds in the sky? is there water there? — we need to look in much, much greater detail. That’s what Webb is going to do, but it’s a massive technical challenge. That’s why NASA, ESA, and the Canadian Space Agency (CSA) are all working together on this project.

“Webb is a hundred times more sensitive than Hubble, and because of that, Webb will be able to reveal the faintest details in the farthest corners of the very distant universe, with exquisite resolution,” Nota explained.

While Hubble has been used to learn more about exoplanets, Espinoza said, “the view that it gives you is very narrow. It gives you one feature, maybe.” By comparison, he said, Webb is going to be “mind-blowing,” allowing us to see several features at once and to look at smaller planets. “It’s going to be our first change to look at smaller planets in large detail.”

Hubble also works in the visible light wavelength, capturing images in the range of light that we can see. But James Webb will be working in the infrared wavelength, which can pick out different features and peer through obscuring dust, “opening a window into the universe that will be completely new,” as Nota put it.

Hubble and Webb will be able to work together, gathering complementary data on the same targets. So if you love the beautiful images of space captured by Hubble, don’t worry, these won’t be going away. We’ll simply be gaining another tool for even deeper understanding.

“James Webb is going to be revolutionary. Literally revolutionary,” Espinoza said. “It’s going to allow us to see stuff that we’ve been expecting to detect for a long time but haven’t had the technology to see, and I’m pretty sure it’s going to detect stuff that we are not thinking of.”

Updating Hubble’s 1980s technology

Researchers have done a remarkable job finding and learning about exoplanets using currently available instruments, discovering over 4,000 exoplanets so far. However, this field is very recent, with the first planets outside our solar system being identified in the 1990s. That means that many current-generation instruments, like Hubble, were never designed with exoplanet studies in mind.

“Hubble is ’80s technology,” Espinoza said. “Nothing against the ’80s – I love the ’80s, especially the music! – but technology has evolved a ton. The kind of detectors we had back then are nothing compared to the kind of detectors we have now.”

James Webb, on the other hand, has been designed with the specific intent to be used for exoplanet characterization, and that has been at the forefront of its design principles. For example, when Webb is pointing at a star, it will point at a particular pixel with very high precision and it won’t move at all, allowing researchers to very accurately measure any dips in brightness that could give clues to a planet in orbit.

This level of precision allows Webb to perform its most exciting exoplanet-related function: Detecting whether an exoplanet has an atmosphere, and what that atmosphere is composed of. “The little details that matter a ton when you’re trying to detect exoplanet atmospheres,” Espinoza explained.

Investigating exoplanets using infrared light

Although researchers have come up with some very creative ways to detect exoplanet atmospheres, it’s not something that current instruments were designed to do. That’s why Webb’s capabilities will be so revolutionary.

To peer out into the universe, Webb has four instruments which will look in the infrared wavelength. They include the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec). Then there’s the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS), which, as their names suggest, will look in the near-infrared band. Finally, there’s the Mid-Infrared Instrument (MIRI), which looks across a wide range in the far-infrared.

But these are sensitive instruments, and they require a carefully maintained environment to work. So the technology around them has to be cutting-edge as well.

“Webb is full to the rim of new, complex technology, from the sensitive IR detectors, to the tennis court-sized, five-layer thin Kapton sunshield that will protect the instrumentation from the solar radiation and will allow the telescope and the detectors to reach the cold temperature necessary to observe in the infrared,” Nota said.

She also pointed out the fine details on the instruments, like NIRSpec’s microshutter array, which is a set of tiny shuttered windows the size of a few human hairs. This will allow the instrument to observe hundreds of objects at the same time. “An absolute first in space astronomy, where spectroscopy is traditionally done one object at a time,” Nota said.

Understanding where we came from

The impetus to see whether a distant planet has an atmosphere isn’t just a scientific flourish, or an idle curiosity about what these far-off places are like. Rather, it’s key to understanding how planets — including our own — are created.

When it comes to understanding how our solar system formed, researchers run models and try to see how we could have ended up with the composition of planets that we see. “But currently we have a sample size of one,” Espinoza pointed out. “Our solar system. That’s it. Now we’re in an era when we can peer into the compositions of other solar systems. And how the planets form defines their chemical composition.”

So when we look at a distant exoplanet’s atmosphere, we learn about how it came to be. And from that, we can build up a picture of how planets and solar systems form based on more cases that just the one in our backyard. “So getting these hints of formation signatures in these exoplanets through the chemistry that we observe in their atmospheres is absolutely fundamental for us to understand how they came to be, and therefore how we came to be,” he said.

Hunting for habitability

Perhaps the most exciting reason to look at exoplanet atmospheres is to understand where else in the universe life might be able to flourish. “One of the key questions that Webb will study is the origins of life,” Nota said. “There are huge varieties of exo-worlds, more than we could have imagined. There are Jupiter-sized gas planets orbiting very close to their star, huge rocky ‘super-Earths,’ and ‘warm Neptunes.’ Some of these might have the right conditions of temperature and the right composition to host life.”

But to determine whether a planet is habitable, Espinoza said, it’s not enough just to know its size and mass. After all, when we find a planet that is Earth-sized and has a similar mass, people often assume it will be an Earth-like place. But Venus and Mars are of roughly similar sizes and masses to Earth, and they have atmospheres that are extremely inhospitable to our form of life. “Venus is the worst place to go on vacation!” he joked, with its immense pressure and toxic atmosphere full of carbon dioxide. Mars isn’t much better, with its extremely thin, unbreathable atmosphere that is only 1% the density of our atmosphere on Earth.

So we need to know about atmospheres to know whether an individual planet is habitable. And even more importantly, to get an estimate of how many habitable planets there could be out there, we need to know what types of atmospheres are typical for planets sized like ours. “Which is the most common atmosphere that nature forms?” Espinoza asked. “It could be Venus-like or Mars-like, and Earth is an outlier.” Or it could be that Earth-like atmospheres are typical, and the number of potentially habitable planets out there is huge.

Reaching out into the unknown

Webb won’t only be looking at exoplanets. It will be performing a huge range of research, from looking back into the earliest phases of the universe to see the first galaxies forming, to watching how stars are born from swirling dust and gas. With its first year of science operations planned out, we’re just scraping the surface of what this new tool could be used for. We’ll have to wait and see what other astronomical marvels it will be able to unravel.

“I think the biggest discovery will be the one that nobody expects,” Nota said. “The one that will change the way we see the universe, the one that will define, maybe once for all, what is our place in the universe.”

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