Searching for signs of life in the atmospheres of extrasolar planets orbiting distant stars is like searching for a needle in a cosmic haystack. NASA estimates that in our galaxy alone, there are several billion Earth-sized planets located in the habitable zones of their stars, which have the right temperatures for liquid water to exist on the planet’s surface.

However, scientists have an idea that they should look for and accumulated knowledge about those signs that could potentially indicate the existence of life.

“We want to probe the atmospheres of these exoplanets for oxygen, methane, water vapor and other chemical compounds that may signal the presence of life. We won’t be able to see little green men, but we will be able to see the spectral characteristics of these key chemical compounds – that is, what we call biomarkers,” said Nick Sigler, technical director of NASA’s exoplanet exploration program.

The Habitable Worlds Observatory (HWO) was a major item in the 2020 Astronomy and Astrophysics Decadal Research Plan. In addition to searching for signs of life beyond the solar system and helping astronomers understand the components of planetary systems, the observatory will also play an important role in astrophysical research.

Although the mission is scheduled to launch in the late 2030s or early 2040s, developing and using advanced technologies now can help avoid cost overruns in the future. To deeply study the atmospheres of exoplanets to look for signs of life, HWO will use its ability to block glare from the stars around which these exoplanets orbit.

Blocking out the bright light coming from stars will allow the dimmer star light to be seen reflected off the planets’ atmospheres. Chemical elements and compounds absorb and emit light at unique wavelengths specific to their composition, meaning light passing through a planet’s atmosphere carries fingerprints of the elements that make it up. Scientists study this light using spectroscopy and look for such “fingerprints.” Such chemical fingerprints may include biomarkers indicating chemical compounds inhaled or exhaled by living organisms.

There are two main ways in which HWO can potentially block excess starlight. On the one hand, it can use a large external block to block light, which, once launched, will unfold into a huge sunflower-shaped umbrella.

Or, alternatively, it could use an internal shield called a coronagraph – similar to the instruments scientists use to block light from the sun’s bright photosphere to study its corona. NASA has now decided to focus its work at HWO around the coronagraph technology used on several other telescopes, including JWST and the soon-to-launch Nancy Grace Roman Telescope.

One idea put forward at the recent Caltech meeting to improve blocking of light from a star is to place a mirror inside the coronagraph, the angle of which can be changed to control the light rays.

This technique can help prevent stray light from entering the final image, thereby preventing unwanted starlight flare. An active mirror mechanism of this kind will be built into the Nancy Grace Roman Space telescope, which is scheduled for launch no later than 2027. This launch will be an important milestone towards the more powerful technology that HWO will require.

We will need to suppress starlight by about 100 times more compared to the Roman coronagraph

The entire astronomical community is eagerly awaiting the launch of HWO, which will mark a new era in the quest to unravel the mysteries of the Universe and answer one of humanity’s most fundamental questions.