NASA’s James Webb Space Telescope reveals the universe with stunning, unprecedented clarity. The observatory’s ultra-sharp infrared vision has cut through cosmic dust to illuminate some of the earliest structures in the universe, along with previously obscured stellar nurseries and rotating galaxies hundreds of millions of light-years away.
In addition to seeing further into the universe than ever before, Webb will capture the most comprehensive view of objects in our own galaxy – specifically, some of the 5,000 planets that have been discovered in our Galaxy. Astronomers are harnessing the telescope’s light-resolving precision to decipher the atmospheres surrounding some of these nearby worlds. The properties of their atmospheres could provide clues about how a planet formed and whether it harbors signs of life.
But a new MIT study shows that the tools astronomers typically use to decode light-based signals may not be good enough to accurately interpret the new telescope’s data. In particular, opacity models—the tools that model how light interacts with matter as a function of matter’s properties—may need significant revision in order to match the accuracy of Webb’s data, the researchers say.
If these models are not refined? The researchers predict that the properties of planetary atmospheres, such as their temperature, pressure and elemental composition, could be reduced by an order of magnitude.
“There is a scientifically significant difference between a compound like water present at 5% versus 25% that current models cannot differentiate,” says study co-leader Julien de Wit, assistant professor in the Department of Earth, Atmosphere and Planetary Sciences of MIT. (EAPS).
“Currently, the model we use to decipher spectral information is not on par with the accuracy and quality of the data we have from the James Webb telescope,” adds EAPS graduate student Prajwal Niraula. “We need to up our game and tackle the problem of opacity together.”
De Wit, Niraula and their colleagues have published their study in Astronomy of Nature. Co-authors include spectroscopy experts Iouli Gordon, Robert Hargreaves, Clara Sousa-Silva and Roman Kochanov of the Harvard-Smithsonian Center for Astrophysics.
Leveling up
Opacity is a measure of how easily photons pass through a material. Photons of certain wavelengths can pass straight through a material, be absorbed or reflected back depending on whether and how they interact with certain molecules of a material. This interaction also depends on the temperature and pressure of a material.
An opacity model works based on several assumptions about how light interacts with matter. Astronomers use opacity models to derive certain properties of a material, given the spectrum of light the material emits. In the context of exoplanets, an opacity model can decode the type and abundance of chemicals in a planet’s atmosphere, based on the light from the planet captured by a telescope.
De Wit says the current state-of-the-art opacity model, which he likens to a classical language translation tool, has done a decent job of decoding spectral data taken by instruments like those on the Hubble Space Telescope.
“So far, this Rosetta Stone is doing well,” says de Wit. “But now that we’re going to the next level with Webb’s precision, our translation process will prevent us from picking up important subtleties, like those that make the difference between a planet being habitable or not.”
Light, agitated
He and his colleagues make this point in their study, in which they tested the most commonly used opacity model. The team looked to see what atmospheric properties the model would obtain if it were modified to assume certain constraints on our understanding of how light and matter interact. The researchers created eight such “perturbed” models. They then fed each model, including the real version, “synthetic spectra”—light patterns simulated by the team and similar to the precision the James Webb Telescope would see.
They found that, based on the same light spectra, each perturbed model produced broad predictions about the properties of a planet’s atmosphere. Based on their analysis, the team concludes that if existing opacity models are applied to light spectra taken by the Webb telescope, they will hit an “accuracy wall.” That is, they won’t be sensitive enough to tell whether a planet has an atmospheric temperature of 300 Kelvin or 600 Kelvin, or whether a particular gas occupies 5% or 25% of an atmospheric layer.
“This difference is important to constrain planet formation mechanisms and reliably identify biosignatures,” says Niraula.
The team also found that each model also produced a “good fit” to the data, meaning that even though a perturbed model produced a chemical composition that the researchers knew was incorrect, it also produced a spectrum of light from that chemical composition that was close. enough to “match” the original spectrum.
“We found that there are enough parameters to tweak, even with the wrong model, to get a good fit, which means you won’t know that your model is wrong and that what it’s telling you is wrong,” de Wit explains.
He and his colleagues outline some ideas for how to improve existing opacity models, including the need for more laboratory measurements and theoretical calculations to improve the models’ assumptions about how light and various molecules interact, as well as collaborations in various disciplines, and in particular between astronomy and spectroscopy.
“There is so much that could be done if we knew perfectly how light and matter interact,” says Niraula. “We know that pretty well around Earth conditions, but once we move into different types of atmospheres, things change and it’s a lot of data, with increasing quality, that we risk misinterpreting.”
Searching the skies for the building blocks of life in the universe More information: Julien de Wit, The looming challenge of opacity in characterizing exoplanet atmospheres, Astronomy of Nature (2022). DOI: 10.1038/s41550-022-01773-1. www.nature.com/articles/s41550-022-01773-1 Provided by Massachusetts Institute of Technology
This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular website covering news about MIT research, innovation and teaching.
Reference: Study: Astronomers risk misinterpreting planetary signals in James Webb data (2022 September 15) Retrieved September 15, 2022 by
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