Kepler was NASA's first space telescope built specifically to hunt for exoplanets, and since its launch in 2009, thousands of planets have been confirmed. But exoplanet researchers want to go beyond just cataloging, and dig deeper to understand the composition and atmosphere of these worlds, and learn whether they harbor alien life.

Most of the rocky, Earth-sized planets have been detected orbiting red-dwarf stars, the smaller, dimmer, and the most common type of stars in our Milky Way galaxy. Such planets are hard to detect and confirm because of their star’s tight habitable zones.

Directly imaging them requires advanced exoplanet coronagraphic technologies which block out the light of the host star. The James Webb Space Telescope’s Near Infrared Camera (NIRCam), Near Infrared Spectrograph (NIRSpec), and Mid-Infrared Instrument (MIRI) have coronagraphic capabilities which helped it directly observe the Earth-size rocky planet, formally known as LHS 475 b. 

The planet's spectrograph couldn't definitively identify its atmospheric composition, however, researchers were able to confirm the absence of Methane and other hydrocarbons. They also observed that an atmosphere composed entirely of carbon dioxide is plausible, as its signature might appear as a flat or featureless spectrum with the current spectrographic capabilities.

With current technology, Webb can detect life-marker elements like Methane, but the mere presence of such elements doesn’t translate to the planet’s habitability. More advanced instruments are needed to draw more definitive conclusions.  

To push exoplanet exploration further, a new eye is needed: NASA's proposed Habitable Worlds Observatory or HWO. Leveraging the technology of Webb and the forthcoming Roman Space telescope, HWO will offer more accurate measurements, potentially distinguishing between types of atmospheric composition.  

“The critical thing when talking about biomarkers is the ratios of these different signatures in the planet's atmosphere, as well as all of the other things that are going on with the planet, like its distance from the star, and the rate of rotation of the exoplanet,” says Dr. Amber Straughn, Deputy Project Scientist for James Webb Space Telescope Science Communications and Associate Director of NASA’s Astrophysics Science Division in an interview with Supercluster.

Dr. Straughn also added that the habitability of a planet is dependent on its host stars. The tighter habitable zones of red dwarfs mean that the planets in such zones are usually pretty close to the star, exposing them to extreme levels of X-ray and ultraviolet (UV) radiation, which can be hundreds of thousands of times more intense than what Earth receives from the Sun, likely rendering these planets uninhabitable.

“Not only the biomarkers in the atmosphere but also the host star is super important in determining habitability. A planet could have an atmosphere with things like methane or oxygen, but if the star is blasting X-rays, there's no way there's going to be life on that surface.”

The HWO concept aims to enable the highest precision exoplanet observations. In addition to the coronagraph, which blocks out starlight, a JPL team proposed a supplementary structure to achieve a one-ten billionth contrast ratio: the Starshade. This deployable, flower-shaped structure is designed to situate itself precisely between the telescope and the star, significantly reducing starlight before it reaches the telescope. The distinct design of the Starshade's petals is optimized to reduce light bending, producing exceptionally dark shadows.

Why utilize two starlight suppression techniques? The answer lies in the distinct advantages and limitations of both the coronagraph and the starshade that are largely complementary. This makes the combined approach in HWO far superior to one that uses either technique exclusively. In tandem, they can observe a spectrum from ultraviolet to near-IR without depending on emerging or untested technologies.

Advanced coronagraphic and spectrographic tools will enhance our understanding of planetary systems. One system that has captivated NASA and the wider scientific community is TRAPPIST-1. TRAPPIST-1 consists of 7 rocky worlds, and all of them hold the potential for water on their surface. Studies have suggested some could harbor more water than the oceans of Earth, either in the form of water vapor for the planets closest to their star, liquid water for others, and ice for those farthest away.

TRAPPIST-1 has been a prime observation focus for Webb and is anticipated to be a key target for future space observatories, including HWO.

The Habitable Worlds Observatory isn't just about exoplanets. As a large-aperture UV to near IR telescope, it promises a wide range of astrophysics research. It will capture the most detailed UV to visible images compared to any existing or planned space telescope. Its capabilities extend to exploring the lifecycle of baryons, probing the universe's origins by observing primordial stars and supernovae, modeling dark matter across galaxies, and mapping auroral activity on gas and ice giants within our solar system. 

Continuing NASA's tradition for flagship astrophysics missions, HWO will not only complement research from telescopes like JWST and Roman but will also allocate half of its primary mission time to the Guest Observer (GO) program, which allows external scientists, researchers at public and private universities and institutions, and sometimes even the general public to propose observations for the space observatory.

The HWO project came together after HabEx (Habitable Exoplanet Observatory) was proposed as a top priority by the Decadal Survey on Astronomy and Astrophysics 2020, a forum for long-term exploration the astronomy community will pursue. Rather than endorsing one specific proposal, the Decadal Survey urged NASA to merge key features of both HabEx and the proposed LUVOIR, the Large Ultraviolet Optical Infrared Surveyor. This fusion, now dubbed the Habitable Worlds Observatory, marks NASA's inaugural mission explicitly designed to seek life signs on planets outside of our Solar System.

NASA is now putting together teams that will reframe the goals set out by the decadal survey. It’s called the START team, which stands for Science, Technology, Architecture, and Review Team.”

“This will be a big team of scientists that get together and figure out how those high-level goals drive down into more specific goals; how those specific goals will inform what kind of telescope we need to build, with what specifications.”

NASA has invited 56 individuals from diverse segments of the scientific community, encompassing academia, government, and private sectors. These selected individuals will form the backbone of both the START and the Technical Assessment Group (TAG). While START is dedicated to refining HWO's scientific aspirations, TAG will explore various mission architectures and the technologies needed to realize those goals.

While NASA's current focus lies with the Roman space telescope, slated for a 2027 launch, the planning for the Habitable Worlds Observatory is in progress. “These specific goals laid out by START team will drive the engineering of the technology... That’s the whole process that’s playing out right now.”

Dr. Straughn also emphasized that NASA is intensifying efforts to avert substantial cost overruns and prolonged delays in their upcoming flagship missions, aiming to sidestep issues that plagued Webb’s development program.

Proposed during the 2000 decadal survey as the Next Generation Space Telescope, the JWST was envisioned as a revolutionary leap for astronomy. It aimed to do away with moving parts, embracing segmented mirror optics instead. Its development mantra was "faster, better, and cheaper," a slogan championed by then-NASA administrator, Dan Goldin.

Yet, the journey from conceptualization to tangible hardware was fraught with challenges. The scope and objectives of the JWST expanded, and its specifications underwent frequent revisions. The mission's ambition to incorporate nascent technologies, which were yet to be developed, resulted in delays and escalating costs. These setbacks not only hampered the JWST but also had ripple effects across other programs within NASA's Science division.

“One of the big lessons learned from JWST is when we started its development there were like 10 things we had to invent ... that caused a lot of the schedule delays and budget overruns,” says Dr. Straughn

The Habitable Worlds Observatory (HWO) will leverage existing technology to curtail the ballooning costs and protracted timelines typically associated with such flagship missions. This means HWO (and upcoming flagship missions) will only be commissioned once such advanced technologies are developed and matured. 

Heeding the survey's advice, NASA established the Great Observatory Maturation Program (GOMAP). Tasked with nurturing nascent technologies, GOMAP will operate concurrently with NASA's present flagship projects. It will focus on several key early activities to ensure future flagship telescopes, starting with HWO, are developed on a predictable cost and schedule while minimizing the risks of overruns.

GOMAP will crystallize the HWO's mandate, further the technologies pivotal to its groundbreaking scientific contributions, and lay the groundwork for its long-haul readiness. 

All these steps will be set in motion ahead of its actual development and construction, which will commence after Roman’s launch.

In contrast to the JWST, HWO won't be designed from the ground up. The foldable mirrors proposed by LUVOIR have already been tried and tested by JWST. 

The advanced technologies integral to HWO's coronagraph will be tested and refined with the forthcoming Roman space telescope. Roman's Coronagraph instrument, set to be the most powerful exoplanet coronagraph ever launched, boasts the ability to detect planets nearly a billion times dimmer than their host stars.

“We already know about a couple of key technologies that we need for HWO and we are starting to work on those. The Roman’s coronagraph is being worked on by the JPL team. The folding mirrors and their stability are extremely important and we’ve achieved that with JWST’s mirror,” said Dr. Straughn.

“It is more stable than we planned and predicted, but in order to do exoplanet science, we need an even more stable mirror. One of our scientists is working on this technology, building an ultra-stable test bed. It's just incredibly hard engineering. But we’re already working on it.”

HWO's Starshade is also not new to development. It has been under the aegis of JPL for several years as part of NASA’s Exoplanet Exploration program, and its technical readiness parallels that of the coronagraph.

Dr. Straughn also mentioned that NASA will also roll out new management and scheduling protocols. The program will adopt a modus operandi akin to planetary missions, which have tight and limited launch windows that cannot be missed.

“We are going to take the sort of planetary science view of building to schedule. When you're sending a mission to Mars or to another planet, you have a launch window, and if you miss that launch window, you might have to wait another year and a half before you can launch.”

“We’re gonna have a schedule, we’re gonna have a launch date and if the technology problems come up, we’re going to have to reassess.”

The Habitable Worlds Observatory is slated for a mid-2040s launch and will be stationed at the Earth-Sun Lagrange Point 2 (L2) region, joining the ranks of the JWST and Roman observatories. Situated beyond the Earth, Moon, and Sun, the L2 point presents an optimal vantage point for space observatories. Its strategic location ensures that the Sun is always behind the observatory, enabling efficient solar power generation and offering an uninterrupted gaze into the vastness of space.

Taking cues from the Hubble telescope, which greatly benefited from servicing missions, the design of the Habitable Worlds Observatory will incorporate the feature of serviceability. The aspiration is that, by launch time, crewed missions to the L2 region will have become feasible.

“The Habitable Worlds Observatory will be serviceable and we are planning that from the very beginning. It's something that our astrophysics director at headquarters says every time he talks about it that we're gonna plan this one to be serviceable.”

NASA's work with the HWO represents a dual commitment: uncovering insights about habitable planets in distant star systems while refining its own mission development processes. By integrating new managerial and developmental strategies, the agency aims to optimize the way flagship missions are designed and launched.

The ultimate goal? To reveal Earth-like habitable worlds, that may already harbor life.