Nasa’s Webb telescope could be drastically wrong, experts say

When it comes to studying alien worlds, the James Webb Space Telescope could be drastically wrong, though not for any fault of its own.

That’s the finding of a new study by researchers who looked not at the Webb telescope’s optics, but at the models scientists use to interpret the findings after the telescope has made an observation.

Specifically, the models scientists use to understand opacity, how easily light passes through an atmosphere, are not accurate enough, according to MIT graduate student Prajwal Niraula, a co-author on a new paper published Thursday in Nature Astronomy. And since Webb studies exoplanets — planets around stars other than our Sun – by measuring the wavelengths of light that pass through a planet’s atmosphere using its spectroscopy instrument, the less accurate models could mean Webb telescope observations are off from reality by an order of magnitude.

“Currently, the model we use to decrypt spectral information is not up to par with the precision and quality of data we have from the James Webb telescope,” Niraula said in a press statement. “We need to up our game and tackle together the opacity problem.”

Webb’s spectrometer instrument obtains a “spectrum,” a collection of wavelengths of light shining through an exoplanet’s atmosphere. Since different molecules absorb light at different wavelengths, the unique pattern of a spectrum can tell scientists what compounds are present in what quantities in a planet’s atmosphere, including gasses and organics that could hint at signs of biological activity.

So not solving the opacity model problem, in practice, could mean scientists missing signs of life on an exoplanet, or getting a false positive for potential signs of alien life in an exoplanet atmosphere.

“There is a scientifically significant difference between a compound like water being present at 5 percent versus 25 percent, which current models cannot differentiate,” Julien de Wit, assistant professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences and a study co-author, said in a press statement.

In their study, the researchers created alternate opacity models that altered certain assumptions about how light and matter would interact in an exoplanet atmosphere. They then fed Webb spectra through these models and each produced very different results from one another, but also that each model seemed to fit the data very well; it would be hard for scientists looking at that data to know it was wrong, in other words, unless they knew what to look for.

“We found that there are enough parameters to tweak, even with a wrong model, to still get a good fit, meaning you wouldn’t know that your model is wrong and what it’s telling you is wrong,” Dr de Wit said.

The researchers suggest several ways opacity models could be improved so they can match the accuracy of Webb’s optics, beginning with more laboratory experiments to ground models, refinement of models, and a central database with standardized formatting to help astronomers update their models from spectral data and experiments.

“There is so much that could be done if we knew perfectly how light and matter interact,” Mr Niraula said. “We know that well enough around the Earth’s conditions, but as soon as we move to different types of atmospheres, things change, and that’s a lot of data, with increasing quality, that we risk misinterpreting.”

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