How the James Webb Space Telescope will examine stars for signs of Earth 2.0

In space astronomy, it all comes down to what’s under the hood.

And for Webb, who is about to complete the final stages of commissioning its 17 scientific instrument modes, a device – specifically designed to capture both images and spectra of different types of objects cosmic – has the potential to go beyond detection where extraterrestrial worlds may lie.

Called NIRISS (Near-Infrared Imager and Slitless Spectrograph), the Canadian-built science instrument could reveal Earth 2.0 signals – just by looking at a viable candidate’s host star.

Canada’s contribution to the James Webb Space Telescope

Basically, the NIRISS instrument will competently examine universal phenomena in the near infrared, “at wavelengths down to 5.0 microns,” said Nathalie Ourellette of the University of Montreal, in a blog post. on the NASA website. “The NIRISS team has developed four modes of instruments to collect different types of data well-suited to different targets and scientific objectives.”

NIRISS’ SOSS mode will allow the James Webb Space Telescope to collect highly accurate spectra “of one bright object at a time,” Ourellette added in the post. “This mode is optimized for performing time-series observations, ideal for studying a phenomenon that changes over the course of an observation of several hours, such as an exoplanet transiting in front of its host star.”

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“Using a technique called transit spectroscopy, the NIRISS instrument can collect a spectrum of an exoplanet’s atmosphere, which contains different markers allowing astronomers to determine its composition, temperature, potential habitability signatures and ‘other important features,’ Ourellette explained in the blog post. .

Then there’s the WFSS mode, which will allow the NIRISS to help Webb gather information on thousands of objects, “such as galaxies, at the same time across the detector’s entire field of view” – which is 4.84 minutes of square arc, according to Ourellette. “The spectra of thousands of galaxies will make it possible to measure their distances, their ages and other physical parameters to follow the evolution of galaxies during the life of the universe.”

And there’s more. NIRISS is able to collect information from many spectra at once in WFSS mode, which means that discrete spectra can overlap (if the light sources are too close from our point of view). “So there are two orthogonal grisms, GR150C and GR150R, which can produce spectra horizontally and vertically, respectively, which helps sort out mixed spectra from different galaxies,” Ourellette said.

In SOSS mode, Webb’s NIRISS instrument can examine the atmospheres of extraterrestrial worlds as they transit through their host star. Source: European Southern Observatory / NASA

Webb’s NIRISS Could Reveal New Alien Worlds With Habitable Conditions

Additionally, the NIRISS’ AMI mode will allow Webb to examine nearby cosmic objects (from our vantage point, of course). This will be done with a special technique known as interferometry. “A mask inside the instrument lets light through only from certain parts of the primary mirror,” Ourellette explained. “Astronomers can increase the telescope’s resolution by a factor of almost 2.5 by examining the patterns created when carefully chosen beams of light interfere with each other.”

Using this method, two seemingly close objects can still appear as two distinct bright spots, instead of an absurd blur. However, since the mask blocks a lot of light, the observed cosmic objects must be bright enough for detection to occur. But, with sufficient brightness, the NIRISS instrument’s AMI mode will allow the James Webb Space Telescope to observe brown dwarfs, protoplanetary disks, and even exoplanets themselves. It’s the first time we’ve used such a method to lay our eyes on extraterrestrial worlds, and it’s only a small sliver of the wealth of scientific knowledge in store once Webb begins his science missions in earnest this summer. .

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