Habitable Worlds Observatory

December 29, 2023

Reading Time: mins

Share article via:

What is the Habitable Worlds Observatory (HWO)?

The main goal of the HWO mission is one of the largest questions which people ponder – are we alone? Has life on Earth resulted from a process which is common in the Universe or was it the result of a unique set of circumstances that means life here on Earth is the only life out there. Answering these questions would be revolutionary!

HWO is a 6m telescope mission, which NASA is planning to search for the signatures of life in atmospheres of extra-solar planets (those outside of our Solar System). This ambitious mission is one of NASA’s next big telescope projects after the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). 

This mission will search for Earth-size planets located in a region around their stars called “The Habitable Zone”. This is a region where the temperature is right to allow for liquid water – essential for all life we know it. HWO will explore the atmospheres of these exoplanets looking for oxygen, methane, water vapour and other chemicals which are key signatures of life – or biosignatures of life. 

Astronomers are currently searching for Earth-like exoplanets, which will make good targets for HWO to observe in the future for these exciting biosignatures. NASA estimates there are several billion Earth-size planets in the habitable zone in our Milky Way alone. Over 5,500 exoplanets have been discovered to date, however none of them are truly Earth-like. Finding planets like Earth is harder than larger planets. This is because planet hunting telescopes are looking for small motions of the parent’s star which has been caused by the planet orbiting the star. The larger the planet the larger the star wobbles, so these larger planets are easier to find. One ground-based telescope searching for Earth-like planets is the Keck Planet Finder (KPF), at Keck Observatory, which has been designed to find Earth-size planets in the habitable zone around small red stars. With these types of stars, the habitable zones are closer in. As the KPF is improved over the coming years there is the potential to detect Earth’s twin. Scientists hope that by the time HWO is launched there will be a list of at least 25 Earth-like planets for HWO to investigate.

In addition to hunting for signs of life on exoplanets, HWO will also investigate a broad range of astrophysics. Including studying the earliest history of the Universe, and investigating the life and deaths of the most massive stars, which supply some of the elements that we know are needed for life like ours.

worlds sm
PIA19830: Pantheon of Planets Similar to Earth (Artist’s Concept). Image Credit: NASA/Ames/JPL-Caltech https://cor.gsfc.nasa.gov/studies/habitable-worlds/hwo.php

What wavelengths of light will HWO observe in?

HWO will use a wide range of light, including Optical (O), near-infrared (NIR) and ultraviolet (UV) light. These different wavelengths of light are used to enable us to learn different astrophysics about the exoplanets. The 6m telescope will carry out high-contrast imaging and spectroscopy (splitting light into its constituent wavelength).

Every chemical element and compound have a unique signature, like a fingerprint, as they absorb and emit light at unique wavelengths. This is due to their atomic structure, therefore star’s light that interacts with the planet’s atmosphere then carries the fingerprints of the elements in the atmosphere. Spectroscopy of these atmospheres can then reveal these fingerprints. One of the most exciting potentials is that some of the chemical fingerprints could include biosignatures – chemical compounds which have been inhaled or exhaled by living things, such as oxygen or ozone.

How will HWO observe exoplanet atmospheres?

habitable worlds 2
An illustration shows the Habitable Worlds Telescope in orbit around Earth and (inset) the kind of exoplanet the project will investigate for tell-tale signs of life. (Image credit: NASA/Robert Lea (Inset) NASA Ames/JPL-Caltech/T.Pyle) https://www.space.com/nasa-habitable-worlds-observatory-exoplanets-alien-life

Additionally, a mirror which can be deformed (shape changed) is being planned for within the coronagraph to stop any stray light entering the image. This will be achieved using thousands of actuators (devices that produce a motion by converting energy and signals going into the system) to move the mirror. The mirrors need to be deformed to a picometer-level (one trillionth (11000000000000) of a metre) of precision! Not possible with the technology currently available.

When will HWO launch?

The mission is planned for the later 2030s or early 2040s. This is because the science goals require advanced technologies, such as the active mirror with very high precision, which still need to be developed. 

Where will HWO go in space?

The HWO, like JWST, will be positioned at the Earth-Sun Lagrange point 2 or L2, 1 million miles away from Earth opposite the Sun. The plan is that, similar to the HST, HWO will be able to be serviceable. They predict that in 10 to 15 years’ time, commercial robotic servicing will easily be taking place at L2 which is significantly further than HST, at a relatively easy to reach distance orbiting just a few hundred miles above Earth. This will mean that the satellite is able to operate for decades, potentially getting better with age. 

What is the current stage of HWO?

HWO is currently in a phase of technology maturation. HWO will build directly on the technology of the JWST’s pioneering segmented mirror, as well as the powerful chronograph that will fly on the Roman Space Telescope (Nasa’s next flagship mission after JWST). It will build on existing technology to minimise risks and cost overruns. 


HWO is trying to answer the age old question: are we alone? It will observe Earth-size exoplanets located in the Habitable zone around their stars. It will observe in multiple different wavelengths, looking for biosignatures in the planet’s atmospheres, to see if there are any signs of life on these far away worlds.

For more detail on space telescopes, sign up for one of our courses today. Space telescopes and their missions feature in Mission Astro ‘The Escape from the Blue Marble’ course and our Certificate in Space Science.

This post was written by Dr Heather Campbell for Mission Astro.

If you have any questions about this post or our services, please email us on [email protected].

Take me to the FREE taster session for Mission Astro!

Follow Mission Astro On:

Website and course built and managed by Web X Design Studio