Author: Alise Fisher

Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.

We spoke with Kristen McQuinn of Rutgers University, one of the lead scientists on Webb Early Release Science (ERS) program 1334, focused on resolved stellar populations. These are large groups of stars – including stars within the dwarf galaxy Wolf–Lundmark–Melotte (WLM) – that are close enough for Webb to differentiate between individual stars, but far enough for Webb to capture a large number of stars at once.

So, tell us a bit about this galaxy, WLM. What’s interesting about it?

WLM is a dwarf galaxy in our galactic neighborhood. It’s fairly close to the Milky Way (only about 3 million light-years from Earth), but it’s also relatively isolated. We think WLM hasn’t interacted with other systems, which makes it really nice for testing our theories of galaxy formation and evolution. Many of the other nearby galaxies are intertwined and entangled with the Milky Way, which makes them harder to study.

Another interesting and important thing about WLM is that its gas is similar to the gas that made up galaxies in the early universe. It’s fairly unenriched, chemically speaking. (That is, it’s poor in elements heavier than hydrogen and helium.)

This is because the galaxy has lost many of these elements through something we call galactic winds. Although WLM has been forming stars recently – throughout cosmic time, really – and those stars have been synthesizing new elements, some of the material gets expelled from the galaxy when the massive stars explode. Supernovae can be powerful and energetic enough to push material out of small, low-mass galaxies like WLM.

This makes WLM super interesting in that you can use it to study how stars form and evolve in small galaxies like those in the ancient universe.

You arranged to show this image at a planetarium. How did you feel when you saw the image projected on the dome?

It was just inspiring. It really was incredible. I will never look at these images the same again. Seeing this on the dome, it was like looking up at our own night sky – at the Milky Way – from a dark site. I could imagine that we were standing on a planet in the WLM galaxy and looking up at its night sky.

We can see a myriad of individual stars of different colors, sizes, temperatures, ages, and stages of evolution; interesting clouds of nebular gas within the galaxy; foreground stars with Webb’s diffraction spikes; and background galaxies with neat features like tidal tails. It’s really a gorgeous image.

And, of course, the view is far deeper and better than our eyes could possibly see. Even if you were looking out from a planet in the middle of this galaxy, and even if you could see infrared light, you would need bionic eyes to be able to see what Webb sees.

What are you trying to find out by studying WLM?

The main science focus is to reconstruct the star formation history of this galaxy. Low-mass stars can live for billions of years, which means that some of the stars that we see in WLM today formed in the early universe. By determining the properties of these low-mass stars (like their ages), we can gain insight into what was happening in the very distant past. It’s very complementary to what we learn about the early formation of galaxies by looking at high-redshift systems, where we see the galaxies as they existed when they first formed.

The Early Release Science programs were designed to highlight Webb’s capabilities and help astronomers prepare for future observations. How are you supporting other astronomers with this work?

In a few ways. We’re checking the calibration of the NIRCam instrument itself. We’re checking our stellar evolution models. And we’re developing software to measure star brightnesses.

We already studied this exact same field very carefully with Hubble. Now we’re looking at the near-infrared light with Webb, and we’re using WLM as a sort of standard for comparison (like you would use in a lab) to help us make sure we understand the Webb observations. We want to make sure we’re measuring the stars’ brightnesses really, really accurately and precisely. We also want to make sure that we understand our stellar evolution models in the near-infrared.

Our team is also charged with developing a public software tool to measure the brightness of all the resolved stars in the NIRCam images. This is a non-proprietary tool that everyone will be able to use. We are developing and testing the software, and optimizing the parameters used for measurements. This is a bedrock tool for astronomers around the world. If you want to do anything with resolved stars that are crowded together on the sky, you need a tool like this.

About the Author

Kristen McQuinn is an assistant professor in the Department of Physics and Astronomy at Rutgers University, and co-investigator on Director’s Discretionary Early Release Science program 1334.

Related Links

• • Zoom in to the Dwarf Galaxy WLM (video)
  • Dwarf Galaxy WLM (standalone NIRCam image)
  • Webb’s First Year of Science
  • NASA’s Webb Telescope Will Show Us More Stars at Higher Resolution — Here’s What That Means for Astronomy

 

The James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) has four observing modes. On Aug. 24, after measuring increased friction in one of the grating wheels used in MIRI’s medium resolution spectrometry (MRS) mode, the Webb team paused science observations using this specific mode. Since then, a team of experts has carried out an in-depth investigation that has reviewed instrument design as well as historical and postlaunch data.

The team concluded the issue is likely caused by increased contact forces between sub-components of the wheel central bearing assembly under certain conditions. Based on this, the team developed and vetted a plan for how to use the affected mechanism during science operations.

An engineering test was executed Wednesday, Nov. 2, that successfully demonstrated predictions for wheel friction. Webb will resume MIRI MRS science observations by Saturday, Nov. 12, starting with a unique opportunity to observe Saturn’s polar regions, just before they become unobservable by Webb for the next 20 years. The team will schedule additional MRS science observations, initially at a limited cadence, following a plan to keep the affected wheel in balance, monitor wheel health, and prepare MIRI MRS for a return to full science operations.

NASA will share a new image or spectrum from the James Webb Space Telescope at least every other week on the mission’s blog. This week, check the blog on Wednesday, Nov. 9 at 11 a.m. EST for a new image highlighting a nearby dwarf galaxy.

In the meantime, learn more about what to expect as Webb observations make their way from raw data to published, peer-reviewed science.

News Media Contacts

Alise Fisher
Headquarters, Washington
202-358-2546
alise.m.fisher@nasa.gov

Laura Betz
Goddard Space Flight Center, Greenbelt, Md.
301-286-9030
laura.e.betz@nasa.gov

Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.

NASA’s James Webb Space Telescope captured its first images and spectra of Mars Sept. 5. The telescope, an international collaboration with ESA (European Space Agency) and CSA (Canadian Space Agency), provides a unique perspective with its infrared sensitivity on our neighboring planet, complementing data being collected by orbiters, rovers, and other telescopes.

Webb’s unique observation post nearly a million miles away at the Sun-Earth Lagrange point 2 (L2) provides a view of Mars’ observable disk (the portion of the sunlit side that is facing the telescope). As a result, Webb can capture images and spectra with the spectral resolution needed to study short-term phenomena like dust storms, weather patterns, seasonal changes, and, in a single observation, processes that occur at different times (daytime, sunset, and nighttime) of a Martian day.

Because it is so close, the Red Planet is one of the brightest objects in the night sky in terms of both visible light (which human eyes can see) and the infrared light that Webb is designed to detect. This poses special challenges to the observatory, which was built to detect the extremely faint light of the most distant galaxies in the universe. Webb’s instruments are so sensitive that without special observing techniques, the bright infrared light from Mars is blinding, causing a phenomenon known as “detector saturation.” Astronomers adjusted for Mars’ extreme brightness by using very short exposures, measuring only some of the light that hit the detectors, and applying special data analysis techniques.

Webb’s first images of Mars, captured by the Near-Infrared Camera (NIRCam), show a region of the planet’s eastern hemisphere at two different wavelengths, or colors of infrared light. This image shows a surface reference map from NASA and the Mars Orbiter Laser Altimeter (MOLA) on the left, with the two Webb NIRCam instrument field of views overlaid. The near-infrared images from Webb are on shown on the right.

The NIRCam shorter-wavelength (2.1 microns) image [top right] is dominated by reflected sunlight, and thus reveals surface details similar to those apparent in visible-light images [left]. The rings of the Huygens Crater, the dark volcanic rock of Syrtis Major, and brightening in the Hellas Basin are all apparent in this image.

The NIRCam longer-wavelength (4.3 microns) image [lower right] shows thermal emission – light given off by the planet as it loses heat. The brightness of 4.3-micron light is related to the temperature of the surface and the atmosphere. The brightest region on the planet is where the Sun is nearly overhead, because it is generally warmest. The brightness decreases toward the polar regions, which receive less sunlight, and less light is emitted from the cooler northern hemisphere, which is experiencing winter at this time of year.

However, temperature is not the only factor affecting the amount of 4.3-micron light reaching Webb with this filter. As light emitted by the planet passes through Mars’ atmosphere, some gets absorbed by carbon dioxide (CO₂) molecules. The Hellas Basin – which is the largest well-preserved impact structure on Mars, spanning more than 1,200 miles (2,000 kilometers) – appears darker than the surroundings because of this effect.

“This is actually not a thermal effect at Hellas,” explained the principal investigator, Geronimo Villanueva of NASA’s Goddard Space Flight Center, who designed these Webb observations. “The Hellas Basin is a lower altitude, and thus experiences higher air pressure. That higher pressure leads to a suppression of the thermal emission at this particular wavelength range [4.1-4.4 microns] due to an effect called pressure broadening. It will be very interesting to tease apart these competing effects in these data.”

Villanueva and his team also released Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy.

Whereas the images show differences in brightness integrated over a large number of wavelengths from place to place across the planet at a particular day and time, the spectrum shows the subtle variations in brightness between hundreds of different wavelengths representative of the planet as a whole. Astronomers will analyze the features of the spectrum to gather additional information about the surface and atmosphere of the planet.

This infrared spectrum was obtained by combining measurements from all six of the high-resolution spectroscopy modes of Webb’s Near-Infrared Spectrograph (NIRSpec). Preliminary analysis of the spectrum shows a rich set of spectral features that contain information about dust, icy clouds, what kind of rocks are on the planet’s surface, and the composition of the atmosphere. The spectral signatures – including deep valleys known as absorption features – of water, carbon dioxide, and carbon monoxide are easily detected with Webb. The researchers have been analyzing the spectral data from these observations and are preparing a paper they will submit to a scientific journal for peer review and publication.

In the future, the Mars team will be using this imaging and spectroscopic data to explore regional differences across the planet, and to search for trace gases in the atmosphere, including methane and hydrogen chloride.

These NIRCam and NIRSpec observations of Mars were conducted as part of Webb’s Cycle 1 Guaranteed Time Observation (GTO) solar system program led by Heidi Hammel of AURA.

-By Margaret Carruthers, Space Telescope Science Institute

Editor’s Note: This post highlights images from Webb science in progress, which has not yet been through the peer-review process.

For the first time, astronomers have used NASA’s James Webb Space Telescope to take a direct image of a planet outside our solar system. The exoplanet is a gas giant, meaning it has no rocky surface and could not be habitable.

The image, as seen through four different light filters, shows how Webb’s powerful infrared gaze can easily capture worlds beyond our solar system, pointing the way to future observations that will reveal more information than ever before about exoplanets.

“This is a transformative moment, not only for Webb but also for astronomy generally,” said Sasha Hinkley, associate professor of physics and astronomy at the University of Exeter in the United Kingdom, who led these observations with a large international collaboration. Webb is an international mission led by NASA in collaboration with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

The exoplanet in Webb’s image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could help narrow that down even further. It is young as planets go — about 15 to 20 million years old, compared to our 4.5-billion-year-old Earth.

Astronomers discovered the planet in 2017 using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile and took images of it using short infrared wavelengths of light. Webb’s view, at longer infrared wavelengths, reveals new details that ground-based telescopes would not be able to detect because of the intrinsic infrared glow of Earth’s atmosphere.

Researchers have been analyzing the data from these observations and are preparing a paper they will submit to journals for peer review. But Webb’s first capture of an exoplanet already hints at future possibilities for studying distant worlds.

Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is sufficiently distant from the star that Webb can easily separate the planet from the star in the image.

Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) are both equipped with coronagraphs, which are sets of tiny masks that block out starlight, enabling Webb to take direct images of certain exoplanets like this one. NASA’s Nancy Grace Roman Space Telescope, slated to launch later this decade, will demonstrate an even more advanced coronagraph.

“It was really impressive how well the Webb coronagraphs worked to suppress the light of the host star,” Hinkley said.

Taking direct images of exoplanets is challenging because stars are so much brighter than planets. The HIP 65426 b planet is more than 10,000 times fainter than its host star in the near-infrared, and a few thousand times fainter in the mid-infrared.

In each filter image, the planet appears as a slightly differently shaped blob of light. That is because of the particulars of Webb’s optical system and how it translates light through the different optics.

“Obtaining this image felt like digging for space treasure,” said Aarynn Carter, a postdoctoral researcher at the University of California, Santa Cruz, who led the analysis of the images. “At first all I could see was light from the star, but with careful image processing I was able to remove that light and uncover the planet.”

While this is not the first direct image of an exoplanet taken from space – the Hubble Space Telescope has captured direct exoplanet images previously – HIP 65426 b points the way forward for Webb’s exoplanet exploration.

“I think what’s most exciting is that we’ve only just begun,” Carter said. “There are many more images of exoplanets to come that will shape our overall understanding of their physics, chemistry, and formation. We may even discover previously unknown planets, too.”

– Elizabeth Landau, NASA Headquarters 

With giant storms, powerful winds, auroras, and extreme temperature and pressure conditions, Jupiter has a lot going on. Now, NASA’s James Webb Space Telescope has captured new images of the planet. Webb’s Jupiter observations will give scientists even more clues to Jupiter’s inner life.  

“We hadn’t really expected it to be this good, to be honest,” said planetary astronomer Imke de Pater, professor emerita of the University of California, Berkeley. De Pater led the observations of Jupiter with Thierry Fouchet, a professor at the Paris Observatory, as part of an international collaboration for Webb’s Early Release Science program. Webb itself is an international mission led by NASA with its partners ESA (European Space Agency) and CSA (Canadian Space Agency). “It’s really remarkable that we can see details on Jupiter together with its rings, tiny satellites, and even galaxies in one image,” she said. 

The two images come from the observatory’s Near-Infrared Camera (NIRCam), which has three specialized infrared filters that showcase details of the planet. Since infrared light is invisible to the human eye, the light has been mapped onto the visible spectrum. Generally, the longest wavelengths appear redder and the shortest wavelengths are shown as more blue. Scientists collaborated with citizen scientist Judy Schmidt to translate the Webb data into images. 

In the standalone view of Jupiter, created from a composite of several images from Webb, auroras extend to high altitudes above both the northern and southern poles of Jupiter. The auroras shine in a filter that is mapped to redder colors, which also highlights light reflected from lower clouds and upper hazes. A different filter, mapped to yellows and greens, shows hazes swirling around the northern and southern poles. A third filter, mapped to blues, showcases light that is reflected from a deeper main cloud.  

The Great Red Spot, a famous storm so big it could swallow Earth, appears white in these views, as do other clouds, because they are reflecting a lot of sunlight. 

“The brightness here indicates high altitude – so the Great Red Spot has high-altitude hazes, as does the equatorial region,” said Heidi Hammel, Webb interdisciplinary scientist for solar system observations and vice president for science at AURA. “The numerous bright white ‘spots’ and ‘streaks’ are likely very high-altitude cloud tops of condensed convective storms.” By contrast, dark ribbons north of the equatorial region have little cloud cover.  

In a wide-field view, Webb sees Jupiter with its faint rings, which are a million times fainter than the planet, and two tiny moons called Amalthea and Adrastea. The fuzzy spots in the lower background are likely galaxies “photobombing” this Jovian view.   

“This one image sums up the science of our Jupiter system program, which studies the dynamics and chemistry of Jupiter itself, its rings, and its satellite system,” Fouchet said. Researchers have already begun analyzing Webb data to get new science results about our solar system’s largest planet. 

Data from telescopes like Webb doesn’t arrive on Earth neatly packaged. Instead, it contains information about the brightness of the light on Webb’s detectors. This information arrives at the Space Telescope Science Institute (STScI), Webb’s mission and science operations center, as raw data. STScI processes the data into calibrated files for scientific analysis and delivers it to the Mikulski Archive for Space Telescopes for dissemination. Scientists then translate that information into images like these during the course of their research (here’s a podcast about that). While a team at STScI formally processes Webb images for official release, non-professional astronomers known as citizen scientists often dive into the public data archive to retrieve and process images, too.

Judy Schmidt of Modesto California, a longtime image processor in the citizen science community, processed these new views of Jupiter. For the image that includes the tiny satellites, she collaborated with Ricardo Hueso, a co-investigator on these observations, who studies planetary atmospheres at the University of the Basque Country in Spain.   

Schmidt has no formal educational background in astronomy. But 10 years ago, an ESA contest sparked her insatiable passion for image processing. The “Hubble’s Hidden Treasures” competition invited the public to find new gems in Hubble data. Out of nearly 3,000 submissions, Schmidt took home third place for an image of a newborn star.  

Since the ESA contest, she has been working on Hubble and other telescope data as a hobby. “Something about it just stuck with me, and I can’t stop,” she said. “I could spend hours and hours every day.” 

Her love of astronomy images led her to process images of nebulae, globular clusters, stellar nurseries, and more spectacular cosmic objects. Her guiding philosophy is: “I try to get it to look natural, even if it’s not anything close to what your eye can see.” These images have caught the attention of professional scientists, including Hammel, who previously collaborated with Schmidt on refining Hubble images of comet Shoemaker-Levy 9’s Jupiter impact. 

Jupiter is actually harder to work with than more distant cosmic wonders, Schmidt says, because of how fast it rotates. Combining a stack of images into one view can be challenging when Jupiter’s distinctive features have rotated during the time that the images were taken and are no longer aligned. Sometimes she has to digitally make adjustments to stack the images in a way that makes sense. 

Webb will deliver observations about every phase of cosmic history, but if Schmidt had to pick one thing to be excited about, it would be more Webb views of star-forming regions. In particular, she is fascinated by young stars that produce powerful jets in small nebula patches called Herbig–Haro objects. “I’m really looking forward to seeing these weird and wonderful baby stars blowing holes into nebulas,” she said.  

– Elizabeth Landau, NASA Headquarters 

To learn more about the Webb mission, visit nasa.gov/webb. For more information about NASA citizen science – and how you can get involved doing real NASA Science – go to science.nasa.gov/citizenscience.

On the heels of Tuesday’s release of the first images from NASA’s James Webb Space Telescope, data from the telescope’s commissioning period is now being released on the Space Telescope Science Institute’s Mikulski Archive for Space Telescopes. The data includes images of Jupiter and images and spectra of several asteroids, captured to test the telescope’s instruments before science operations officially began July 12. The data demonstrates Webb’s ability to track solar system targets and produce images and spectra with unprecedented detail.

Fans of Jupiter will recognize some familiar features of our solar system’s enormous planet in these images seen through Webb’s infrared gaze. A view from the NIRCam instrument’s short-wavelength filter shows distinct bands that encircle the planet as well as the Great Red Spot, a storm big enough to swallow the Earth. The iconic spot appears white in this image because of the way Webb’s infrared image was processed.

“Combined with the deep field images released the other day, these images of Jupiter demonstrate the full grasp of what Webb can observe, from the faintest, most distant observable galaxies to planets in our own cosmic backyard that you can see with the naked eye from your actual backyard,” said Bryan Holler, a scientist at the Space Telescope Science Institute in Baltimore, who helped plan these observations.

Clearly visible at left is Europa, a moon with a probable ocean below its thick icy crust, and the target of NASA’s forthcoming Europa Clipper mission. What’s more, Europa’s shadow can be seen to the left of the Great Red Spot. Other visible moons in these images include Thebe and Metis.

“I couldn’t believe that we saw everything so clearly, and how bright they were,” said Stefanie Milam, Webb’s deputy project scientist for planetary science based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s really exciting to think of the capability and opportunity that we have for observing these kinds of objects in our solar system.”

Scientists were especially eager to see these images because they are proof that Webb can observe the satellites and rings near bright solar system objects such as Jupiter, Saturn, and Mars. Scientists will use Webb to explore the tantalizing question of whether we can see plumes of material spewing out of moons like Europa and Saturn’s moon Enceladus. Webb may be able to see the signatures of plumes depositing material on the surface on Europa. “I think that’s just one of the coolest things that we’ll be able to do with this telescope in the solar system,” Milam said.

Additionally, Webb easily captured some of Jupiter’s rings, which especially stand out in the NIRcam long-wavelength filter image. That the rings showed up in one of Webb’s first solar system images is “absolutely astonishing and amazing,” Milam said.

“The Jupiter images in the narrow-band filters were designed to provide nice images of the entire disk of the planet, but the wealth of additional information about very faint objects (Metis, Thebe, the main ring, hazes) in those images with approximately one-minute exposures was absolutely a very pleasant surprise,” said John Stansberry, observatory scientist and NIRCam commissioning lead at the Space Telescope Science Institute.

Webb also obtained these images of Jupiter and Europa moving across the telescope’s field of view in three separate observations. This test demonstrated the ability of the observatory to find and track guide stars in the vicinity of bright Jupiter.

But just how fast can an object move and still be tracked by Webb? This was an important question for scientists who study asteroids and comets. During commissioning, Webb used an asteroid called 6481 Tenzing, located in the asteroid belt between Mars and Jupiter, to start the moving-target tracking “speed limit” tests.

Webb was designed with the requirement to track objects that move as fast as Mars, which has a maximum speed of 30 milliarcseconds per second. During commissioning, the Webb team conducted observations of various asteroids, which all appeared as a dot because they were all small. The team proved that Webb will still get valuable data with all of the science instruments for objects moving up to 67 milliarcseconds per second, which is more than twice the expected baseline – similar to photographing a turtle crawling when you’re standing a mile away. “Everything worked brilliantly,” Milam said.

–Elizabeth Landau, NASA Headquarters

Yesterday, NASA and its partners, ESA (European Space Agency) and CSA (Canadian Space Agency), released the full set of the first full-color images and spectroscopic data from the James Webb Space Telescope.

The images, which uncover a collection of cosmic features elusive until now, are available at: nasa.gov/webbfirstimages.

Learn more.

Three of the four science instruments on NASA’s James Webb Space Telescope have completed their commissioning activities and are ready for science.

Each of Webb’s instruments has multiple modes of operation, which need to be tested, calibrated, and ultimately verified before they can begin to conduct science. The latest instrument to complete this process, the Near-Infrared Spectrograph, or NIRSpec, has four key modes the team officially confirmed as ready to go.

“We made it: NIRSpec is ready for science! This is an amazing moment, the result of the hard work of so many JWST and NIRSpec people and teams over more than two decades. I am just so proud of everyone,” said Pierre Ferruit, Webb project scientist with ESA (European Space Agency) and principal investigator for NIRSpec. “Now is time for science, and I am eager to see the first scientific results coming from NIRSpec observations. I have no doubt they will be fantastic. Big thanks to all who made this possible across the years – great job!”

The final mode verified for NIRSpec was the multi-object spectroscopy mode, a key capability that allows Webb to capture spectra, or rainbows of infrared light, from hundreds of different cosmic targets at once. In multi-object spectroscopy mode, NIRSpec can individually open and close about 250,000 small shutters, all just the width of a human hair, to view some portions of the sky while blocking others. By controlling this “microshutter array,” Webb can observe multiple specific targets while reducing interference from others.

The confirmation of NIRSpec’s multi-object spectroscopy mode marks the first time this capability has been verified for use from space. It will allow NIRSpec to characterize everything from the faintest objects in the universe to the formation of galaxies and star clusters.

NIRSpec was built for ESA by a consortium of European companies led by Airbus Defence and Space, with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, providing its detector and microshutter subsystems.

Out of 17 total instrument modes across Webb’s four instruments, only one mode remains to be verified, for the Near-Infrared Camera (NIRCam). When the team confirms this remaining mode, the months-long process of preparing Webb for science will formally be complete.

Webb’s commissioning process culminates on July 12, with the release of the telescope’s first full-color images and spectroscopic data, and the official beginning of its science mission.

The Webb team has now approved 10 out of 17 science instrument modes; since last week we added (14) MIRI imaging, (2) NIRCam wide-field slitless spectroscopy, and our final NIRISS mode, (10) single-object slitless spectroscopy. As we ramp down the final commissioning activities, some openings in the schedule have appeared. The team has started to take some of the first science data, getting it ready to release starting July 12, 2022, which will mark the official end of commissioning Webb and the start of routine science operations.

This week we asked Tracy Beck, Tony Keyes, and Charles Proffitt, all NIRSpec instrument scientists at the Space Telescope Science Institute (STScI), to tell us about how Webb gets the targets lined up for observation with the NIRSpec instrument.

“The Near-Infrared Spectrograph (NIRSpec) is the instrument on the Webb telescope that observes spectra of astrophysical and planetary objects at near infrared wavelengths. The NIRSpec Grating Wheel Assembly (GWA) uses diffraction gratings or a prism to separate the wavelengths of incoming light into a spectrum. Study of the intensity or brightness of light across the wavelengths can provide key diagnostic information about the nature of various objects across the universe – from extrasolar planets around distant stars, to faint galaxies at the edge of the universe, and objects in our own solar system. NIRSpec will observe them all.

“In addition to the gratings and a prism, the NIRSpec GWA also has a mirror that is primarily used to ‘acquire’ targets – to image them and place them at the proper locations in the instrument to observe a spectrum.  NIRSpec has two methods for target acquisition (TA): the Wide Aperture Target Acquisition (WATA) and the Micro-Shutter Assembly (MSA) -based Target Acquisition (MSATA).

“The WATA process takes an image of a single astrophysical target through the wide ‘S1600A1’ fixed slit to determine its position on the sky as seen through the instrument. The software on-board the Webb telescope autonomously calculates an offset to move the telescope and accurately position either this target or another nearby target at the optimal location in NIRSpec to spread the light into a spectrum. During instrument commissioning, the excellent performance of WATA has been demonstrated on the sky for all four of the NIRSpec observing modes: integral field unit imaging spectroscopy, fixed slit spectroscopy, bright object time series, and multi-object spectroscopy.

“NIRSpec includes the multi-object spectroscopy (MOS) mode, where spectra of dozens to hundreds of science targets will be observed at one time. This requires specialized apertures that can be configured by opening and closing specific tiny doorways (microshutters) of the 250,000 total that are arranged in a rectangular grid in the MSA, allowing individual targets to be observed with little contamination from nearby objects or background light.

“During MSATA, a set of target acquisition reference stars are imaged through open microshutters. The stellar positions are calculated autonomously by Webb’s on-board software and used to correct the initial spacecraft pointing and position angle (rotation). To allow accurate correction of the observed spectra for the centering of each source in its shutter, this process must place the MOS science targets across the full span of the NIRSpec field of view with an accuracy of 1/10^th of a NIRSpec shutter width – or just 20 milli-arcseconds on the sky (the approximate size of a bumblebee, 1.5 cm, viewed from 150 km away!).

“The recent confirmation of NIRSpec target acquisition and additional work on the four science modes primes the NIRSpec team for our last activities of commissioning. We cannot wait to see the first NIRSpec science observations coming this summer!

“NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and microshutter subsystems.”

–Tracy Beck, AURA Observatory and Webb NIRSpec Instrument Scientist, STScI; Tony Keyes AURA Scientist and Webb NIRSpec Instrument Scientist, STScI; and Charles Proffitt, AURA Observatory and Webb NIRSpec Instrument Scientist, STScI

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Jonathan Gardner, Webb deputy senior project scientist, NASA Goddard
Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard