Year: 2022

One of the James Webb Space Telescope’s four primary scientific instruments, known as the Near-Infrared Imager and Slitless Spectrograph instrument (NIRISS), has concluded its postlaunch preparations and is now ready for science.

The last NIRISS mode to be checked off before the instrument was declared ready to begin scientific operations was the Single Object Slitless Spectroscopy (SOSS) capability. The heart of the SOSS mode is a specialized prism assembly that disperses the light of a cosmic source to create three distinctive spectra (rainbows), revealing the hues of more than 2,000 infrared colors collected simultaneously in a single observation. This mode will be specifically used to probe the atmospheres of transiting exoplanets, i.e., planets that happen to eclipse their star periodically, momentarily dimming the star’s brightness for a period of time. By comparing the spectra collected during and before or after a transit event with great precision, one can determine not only whether or not the exoplanet has an atmosphere, but also what atoms and molecules are in it.

“I’m so excited and thrilled to think that we’ve finally reached the end of this two-decade-long journey of Canada’s contribution to the mission. All four NIRISS modes are not only ready, but the instrument as a whole is performing significantly better than we predicted. I am pinching myself at the thought that we are just days away from the start of science operations, and in particular from NIRISS probing its first exoplanet atmospheres,” said René Doyon, principal investigator for NIRISS, as well as Webb’s Fine Guidance Sensor, at the University of Montreal.

With NIRISS postlaunch commissioning activities concluded, the Webb team will continue to focus on checking off the remaining five modes on its other instruments. NASA’s James Webb Space Telescope, a partnership with ESA (European Space Agency) and CSA, will release its first full-color images and spectroscopic data on July 12, 2022.

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-Thaddeus Cesari, NASA’s Goddard Space Flight Center

-Nathalie Ouellette, Webb outreach scientist, Université de Montréal

 

 

 

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

NASA’s James Webb Space Telescope team continues to work its way through the 17 science instrument modes. This week they checked off numbers (5) NIRCam grism time series and (4) imaging time series, both used to study exoplanets and other time-variable sources; (12) NIRISS aperture masking interferometry mode, for direct detection of a faint object that is very close to a bright one; (11) NIRISS wide-field slitless spectroscopy, for studying distant galaxies; and (9) NIRSpec bright-object time series, for studying exoplanets. That totals seven modes approved to date, with 10 still to go.

This week we are featuring MIRI’s medium-resolution spectroscopy mode and sharing our first spectroscopic engineering data. We asked two of the MIRI commissioning team members – David Law, of the Space Telescope Science Institute (STScI), and Alvaro Labiano, of the Centro de Astrobiologίa (CAB) – to explain this mode to us:

“One of Webb’s most complex instrument modes is with the MIRI Medium Resolution Spectrometer (MRS). The MRS is an integral-field spectrograph, which provides spectral and spatial information simultaneously for the entire field of view. The spectrograph provides three-dimensional ‘data cubes’ in which every pixel in an image contains a unique spectrum. Such spectrographs are extremely powerful tools to study the composition and kinematics of astronomical objects, as they combine the benefits of both traditional imaging and spectroscopy.

“The MRS is designed to have a spectral resolving power (observed wavelength divided by the smallest detectable wavelength difference) of about 3,000. That is high enough to resolve key atomic and molecular features in a variety of environments. At the highest redshifts, the MRS will be able to study hydrogen emission from the first galaxies. At lower redshifts, it will probe molecular hydrocarbon features in dusty nearby galaxies and detect the bright spectral fingerprints of elements such as oxygen, argon, and neon that can tell us about the properties of ionized gas in the interstellar medium. Closer to home, the MRS will produce maps of spectral features due to water ice and simple organic molecules in giant planets in our own solar system and in planet-forming disks around other stars.

“In order to cover the wide 5 to 28 micron wavelength range as efficiently as possible, the MRS integral field units are broken up into twelve individual wavelength bands, each of which must be calibrated individually. Over the past few weeks, the MIRI team (a large international group of astronomers from the USA and Europe) has been focusing primarily on calibrating the imaging components of the MRS. They want to ensure that all twelve bands are spatially well aligned with each other and with the MIRI Imager, so that it can be used to place targets accurately into the smaller MRS field of view. We show some early test results from this alignment process, illustrating the image quality achieved in each of the twelve bands using observations of the bright K giant star HD 37122 (located in the southern sky near the Large Magellanic Cloud).

“Once the spatial alignment and image quality of the several bands are well characterized, the MIRI team will prioritize calibrating the spectroscopic response of the instrument. This step will include determining the wavelength solution and spectral resolution throughout each of the twelve fields of view using observations of compact emission-line objects and diffuse planetary nebulae ejected by dying stars. We show the exceptional spectral resolving power of the MRS with a small segment of a spectrum obtained from recent engineering observations of the active galactic nucleus at the core of Seyfert galaxy NGC 6552. Once these basic instrument characteristics are established, it will be possible to calibrate MRS so that it is ready to support the wealth of Cycle 1 science programs due to start in a few short weeks.”

—David Law, AURA associate astronomer, STScI

—Alvaro Labiano Ortega, Telespazio UK  for ESA, CAB (Consejo Superior de Investigaciones Cientificas – Instituto Nacional de Técnica Aeroespacial)

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—Jonathan Gardner, Webb deputy senior project scientist, NASA Goddard

—Alexandra Lockwood, project scientist for Webb science communications, STScI

—Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard

In the lead-up to the release of Webb’s first full-color images and spectroscopic data on July 12, the Webb team is now in the last phase of commissioning the science instruments. The first two instrument modes, NIRCam imaging and NIRISS imaging, have been declared ready for science; watch the “Where is Webb” page as the team works their way through the other 15 instrument modes.

After commissioning is finished, the fun – and discoveries – will start: implementing the hundreds of peer-reviewed science programs that have been selected for Webb’s first year. The area on the sky that Webb can see at any given time is called the field of regard. Deciding which observations to make on which day is a complicated process designed to optimize observational efficiency and manage the observatory’s resources. We asked Christine Chen, science policies group lead at the Space Telescope Science Institute (STScI), to tell us how Webb’s schedule comes together.

“Webb will soon transition from commissioning to regular operations when Webb’s time will be devoted to scientific observations.

“Webb’s first year of observations (Cycle 1) has already been selected. There are three types of scientific programs planned: General Observer (GO), Guaranteed Time Observer (GTO), and Director’s Discretionary Early Release Science (DD-ERS). The GO and DD-ERS programs include scientists from all over the world whose programs were selected in a dual anonymous peer review process. The GTO programs are led by scientists who made key contributions to the development of the observatory.

“All of the observations in approved Cycle 1 programs are available for scheduling at the beginning of regular operations. However, the DD-ERS observations have been given priority during the first five months because the DD-ERS programs are designed to help the scientific community understand Webb’s performance for typical scientific observations as soon as possible.

“Webb’s Long Range Planning Group (LRPG) has created a 12-month+ Observing Plan, including all of the approved observations, with the goal of creating the most efficient plan. Even though a Webb Observing Cycle is defined as a 12-month period, more than one year’s worth of observations have been approved for Cycle 1. This over-subscription will enable a smooth transition between cycles as well as provide a repository of flight-ready observations that can be moved earlier, if a window opens up. At the current time, before the start of Cycle 1, the Observing Plan is not yet completely filled. This allows the schedulers to accommodate late-breaking Targets of Opportunity (ToOs) and Director’s Discretionary (DD) programs. ToOs and DDs typically include ’unplanned for‘ events such as interstellar comets, gravitational wave sources, and supernovae.

“During regular operations, the Short Term Scheduling Group (STSG) will create detailed weekly schedules to be executed by the observatory during the following week. These Short Term Schedules will take into account several factors, including observing constraints, data volume limits for the onboard data recorder, momentum buildup on the observatory’s reaction wheels, etc. At the beginning of each week, the Flight Operations Team will uplink the week’s Short Term Schedule to Webb. At the end of each week, the LRPG will update the Observing Plan to reflect the actual programs that were executed, and to identify priorities for the following week. In this way, the LRPG and STSG work synergistically together throughout the observing cycle to maximize the scientific return from the observatory.”

— Christine Chen, Webb science policies group lead, STScI,
and David Adler, Long Range Planning Group lead, STScI

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— Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

 

Micrometeoroid strikes are an unavoidable aspect of operating any spacecraft, which routinely sustain many impacts over the course of long and productive science missions in space. Between May 23 and 25, NASA’s James Webb Space Telescope sustained an impact to one of its primary mirror segments. After initial assessments, the team found the telescope is still performing at a level that exceeds all mission requirements despite a marginally detectable effect in the data. Thorough analysis and measurements are ongoing. Impacts will continue to occur throughout the entirety of Webb’s lifetime in space; such events were anticipated when building and testing the mirror on the ground. After a successful launch, deployment, and telescope alignment, Webb’s beginning-of-life performance is still well above expectations, and the observatory is fully capable of performing the science it was designed to achieve.

Webb’s mirror was engineered to withstand bombardment from the micrometeoroid environment at its orbit around Sun-Earth L2 of dust-sized particles flying at extreme velocities. While the telescope was being built, engineers used a mixture of simulations and actual test impacts on mirror samples to get a clearer idea of how to fortify the observatory for operation in orbit. This most recent impact was larger than was modeled, and beyond what the team could have tested on the ground.

“We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our solar system,” said Paul Geithner, technical deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We designed and built Webb with performance margin – optical, thermal, electrical, mechanical – to ensure it can perform its ambitious science mission even after many years in space.” For example, due to careful work by the launch site teams, Webb’s optics were kept cleaner than required while on the ground; their pristine cleanliness improves the overall reflectivity and throughput, thereby improving total sensitivity. This and other performance margins make Webb’s science capabilities robust to potential degradations over time.

Furthermore, Webb’s capability to sense and adjust mirror positions enables partial correction for the result of impacts. By adjusting the position of the affected segment, engineers can cancel out a portion of the distortion. This minimizes the effect of any impact, although not all of the degradation can be cancelled out this way. Engineers have already performed a first such adjustment for the recently affected segment C3, and additional planned mirror adjustments will continue to fine tune this correction. These steps will be repeated when needed in response to future events as part of the monitoring and maintenance of the telescope throughout the mission.

To protect Webb in orbit, flight teams can use protective maneuvers that intentionally turn the optics away from known meteor showers before they are set to occur. This most recent hit was not a result of a meteor shower and is currently considered an unavoidable chance event. As a result of this impact, a specialized team of engineers has been formed to look at ways to mitigate the effects of further micrometeoroid hits of this scale. Over time, the team will collect invaluable data and work with micrometeoroid prediction experts at NASA’s Marshall Space Flight Center to be able to better predict how performance may change, bearing in mind that the telescope’s initial performance is better than expected. Webb’s tremendous size and sensitivity make it a highly sensitive detector of micrometeorites; over time Webb will help improve knowledge of the solar system dust particle environment at L2, for this and future missions.

“With Webb’s mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time,” said Lee Feinberg, Webb optical telescope element manager at NASA Goddard. “Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations and this one more recently that is larger than our degradation predictions assumed. We will use this flight data to update our analysis of performance over time and also develop operational approaches to assure we maximize the imaging performance of Webb to the best extent possible for many years to come.”

This recent impact caused no change to Webb’s operations schedule, as the team continues to check out the science instruments’ observing modes and prepares for the release of Webb’s first images and the start of science operations.

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— Thaddeus Cesari, NASA Goddard.

The Webb team continues to commission the 17 science instrument modes. This week we asked Nathalie Ouellette of the Université de Montréal to give more detail about the modes of the Near-Infrared Imager and Slitless Spectrograph (NIRISS), Canada’s scientific instrument on Webb.

“NIRISS will be able to capture both images and spectra from different types of celestial objects in near-infrared light, at wavelengths up to 5.0 microns. The NIRISS team has developed four instrument modes to collect different kinds of data that are well-suited for different targets and scientific objectives.

Single Object Slitless Spectroscopy (SOSS)

“The SOSS mode on NIRISS allows the Webb telescope to obtain high-precision spectra from one bright object at a time. This mode is optimized to carry out time-series observations, which are ideal for studying a phenomenon that changes over the length of a typically hours-long observation, such as an exoplanet transiting in front of its host star.

“Using a technique called transit spectroscopy, the NIRISS instrument can collect a spectrum of an exoplanet’s atmosphere, which contains different markers that allow astronomers to determine its composition, temperature, potential habitability signatures, and other important characteristics.

Wide Field Slitless Spectroscopy (WFSS)

“The WFSS mode on NIRISS allows Webb to obtain spectra but for thousands of objects, such as galaxies, at the same time over the detector’s entire field of view (4.84 arcmin²). The spectra of thousands of galaxies will enable measurement of their distances, ages, and other physical parameters to trace how galaxies evolve over the lifetime of the universe. In the simulated example shown in the figure, the galaxy cluster acts like a cosmic lens that magnifies and stretches the images of faint background galaxies, so they can be studied in even greater detail.

“Since NIRISS can collect so many spectra at a time using the WFSS mode, individual spectra can overlap if their sources are too close. There are thus two orthogonal grisms, GR150C and GR150R, that can produce spectra horizontally and vertically, respectively, which helps to disentangle blended spectra from different galaxies.

Aperture Masking Interferometry (AMI)

“The AMI mode on NIRISS allows Webb to study objects that are very close together on the sky, using a special technique called interferometry. A mask inside the instrument allows light from only certain parts of the primary mirror to pass through. Astronomers can increase the resolution of the telescope by a factor of nearly 2.5 by looking at the patterns created as the carefully chosen beams of light interfere with each other. This allows two objects that are close to each other that would otherwise look like a single blurred point, like an exoplanet orbiting a star, to appear as two distinct points of light in a Webb image. The mask blocks out a large portion of the light, so the observed objects must be bright in order to detect them. The AMI mode will be used to observe exoplanets, brown dwarfs, and protoplanetary disks. This is the first time that such a mask is being used in space.

NIRISS Imaging

“Because of the importance of near-infrared imaging to Webb’s scientific success, NIRISS includes an imaging capability that functions as a backup to NIRCam imaging. This capability can be used in parallel, with NIRCam and NIRISS simultaneously taking images of two closely separated fields of view, imaging a larger area of an extended source.”

— Nathalie Ouellette, Webb outreach scientist, Université de Montréal

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— Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

The Webb team continues to work on commissioning the science instruments, the final step before starting science operations in the summer. We recently saw the beautiful image of the black hole in the center of our Milky Way galaxy, taken by the Event Horizon Telescope. One of the puzzles of modern astronomy is how every large galaxy came to have a giant central black hole, and how some of these black holes are surprisingly large even at very early times. We asked Roberto Maiolino, a member of the Near-Infrared Spectrometer (NIRSpec) instrument science team, to tell us how Webb will help to answer some of these questions.

“One of the most exciting areas of discovery that Webb is about to open is the search for primeval black holes in the early universe. These are the seeds of the much more massive black holes that astronomers have found in galactic nuclei. Most (probably all) galaxies host black holes at their centers, with masses ranging from millions to billions of times the mass of our Sun. These supermassive black holes have grown to be so large both by gobbling matter around them and also through the merging of smaller black holes.

“An intriguing recent finding has been the discovery of hyper-massive black holes, with masses of several billion solar masses, already in place when the universe was only about 700 million years old, a small fraction of its current age of 13.8 billion years. This is a puzzling result, as at such early epochs there is not enough time to grow such hyper-massive black holes, according to standard theories. Some scenarios have been proposed to solve this conundrum. One possibility is that black holes, resulting from the death of the very first generation of stars in the early universe, have accreted material at exceptionally high rates. Another scenario is that primeval, pristine gas clouds, not yet enriched by chemical elements heavier than helium, could directly collapse to form a black hole with a mass of a few hundred thousand solar masses, and subsequently accrete matter to evolve into the hyper-massive black holes observed at later epochs. Finally, dense, nuclear star clusters at the centers of baby galaxies may have produced intermediate mass black hole seeds, via stellar collisions or merging of stellar-mass black holes, and then become much more massive via accretion.

“Webb is about to open a completely new discovery space in this area. It is possible that the first black hole seeds originally formed in the ‘baby universe,’ within just a few million years after the big bang. Webb is the perfect ‘time machine’ to learn about these primeval objects. Its exceptional sensitivity makes Webb capable of detecting extremely distant galaxies, and because of the time required for the light emitted by the galaxies to travel to us, we will see them as they were in the remote past.

“Webb’s NIRSpec instrument is particularly well suited to identify primeval black hole seeds. My colleagues in the NIRSpec Instrument Science Team and I will be searching for their signatures during ‘active’ phases, when they are voraciously gobbling matter and growing rapidly. In these phases the material surrounding them becomes extremely hot and luminous and ionizes the atoms in their surroundings and in their host galaxies. NIRSpec will disperse the light from these systems into spectra, or ‘rainbows.’ The rainbow of active black hole seeds will be characterised by specific ‘fingerprints,’ features of highly ionized atoms. NIRSpec will also measure the velocity of the gas orbiting in the vicinity of these primeval black holes. Smaller black holes will be characterized by lower orbital velocities. Black hole seeds formed in pristine clouds will be identified by the absence of features associated with any element heavier than helium.

“I look forward to using Webb’s unprecedented capabilities to search for these black hole progenitors, with the ultimate goal of understanding their nature and origin. The early universe and the realm of black holes seeds is a completely uncharted territory that my colleagues and I are very excited to explore with Webb.”

— Roberto Maiolino, professor of experimental astrophysics and director of the Kavli Institute for Cosmology, University of Cambridge

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— Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

— Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard

As NASA’s James Webb Space Telescope moves through the final phases of commissioning its science instruments, we have also begun working on technical operations of the observatory.  While the telescope moves through space, it will constantly find distant stars and galaxies and point at them with extreme precision to acquire images and spectra. However, we also plan to observe planets and their satellites, asteroids, and comets in our solar system, which move across the background stars of our galaxy. Webb needs to be able to lock on to these objects and track them with sufficient precision to obtain images and spectra. The Webb team recently completed the first test to track a moving object. The test verified that Webb could conduct moving target science! As we move forward through commissioning, we will test other objects moving at various speeds to verify we can study objects with Webb that move throughout the solar system.

Today, we asked Heidi Hammel, Webb interdisciplinary scientist for solar system observations, to tell us about her plans for studying Earth’s nearest neighbors:

“I am really excited about Webb’s upcoming first year of science operations! I lead a team of equally excited astronomers eager to begin downloading data. Webb can detect the faint light of the earliest galaxies, but my team will be observing much closer to home. They will use Webb to unravel some of the mysteries that abound in our own solar system.

“One of the questions I get asked frequently is why we need a powerful telescope like Webb to study our nearby solar system. We planetary scientists use telescopes to complement our in situ missions (missions that we send to fly by, orbit, or land on objects). One example of this is how Hubble was used to find the post-Pluto target for the New Horizons mission, Arrokoth. We also use telescopes when we don’t have in situ missions planned – like for the distant ice giants Uranus and Neptune or to make measurements of large populations of objects, such as hundreds of asteroids or Kuiper Belt Objects (small ice worlds beyond the orbits of Neptune, including Pluto), since we can only send missions to just a few of these.

“The Webb team has already used an asteroid within our solar system to run engineering tests of the ‘moving target’ (MT) capability. The engineering team tested this capability on a small asteroid in the Main Belt: 6481 Tenzing, named after Tenzing Norgay, the famous Tibetan mountain guide who was one of the first people to reach the summit of Mount Everest. Bryan Holler, at the Space Telescope Science Institute, had a choice of about 40 possible asteroids to test the MT tracking, but, as he told our team: “Since the objects were all virtually identical otherwise, picking the one with a name linked to success seemed like a no-brainer.”  We like that sort of thing.

“My role with Webb as an ‘Interdisciplinary Scientist’ means that my program uses all of the capabilities of this forefront telescope! We need all of them to truly understand the solar system (and the universe!).

“Our solar system has far more mysteries than my team had time to solve. Our programs will observe objects across the solar system: We will image the giant planets and Saturn’s rings; explore many Kuiper Belt Objects; analyze the atmosphere of Mars; execute detailed studies of Titan; and much more! There are also other teams planning observations; in its first year, 7% of Webb’s time will be focused on objects within our solar system.

“One exciting and challenging program we plan to do is observe ocean worlds. There’s evidence from the Hubble Space Telescope that Jupiter’s moon Europa has sporadic plumes of water-rich material. We plan to take high-resolution imagery of Europa to study its surface and search for plume activity and active geologic processes. If we locate a plume, we will use Webb’s spectroscopy to analyze the plume’s composition.

“I have a soft spot in my heart for Uranus and Neptune. Indeed, it was the lack of a mission to these very distant worlds that got me involved in Webb so many decades ago. The Uranus team hopes to definitively link the chemistry and dynamics of the upper atmosphere (detectable with Webb) to the deeper atmosphere that we have been studying with other facilities over many decades. I’ve spent the past 30 years using the biggest and best telescopes humanity has ever built to study these ice giants, and we will now add Webb to that list.

“We have been planning for Webb observations for over twenty years, and that has gone into overdrive now that we are launched, deployed, and focused! I’ll note that nearly all of my team’s solar system data will be freely available to the broad planetary science community immediately. I made that choice to enable more science discoveries with Webb in future proposals.

“I am gratified to have been able to work with the team for all this time, and I especially want to give a shout out to the thousands of people who collectively have enabled this amazing facility for the astrophysics and planetary communities. Thank you! Ad astra!”

—Heidi Hammel, vice president for science, Association of Universities for Research in Astronomy (AURA)

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–Stefanie Milam, Webb deputy project scientist for planetary science, NASA’s Goddard Space Flight Center

–Jonathan Gardner, Webb deputy senior project scientist, NASA Goddard

With the telescope optics and instruments aligned, the Webb team is now commissioning the observatory’s four powerful science instruments. There are 17 different instrument “modes” to check out on our way to getting ready for the start of science this summer. Once we have approved all 17 of these modes, NASA’s James Webb Space Telescope will be ready to begin scientific operations!

In this post we’ll describe the 17 modes, and readers are encouraged to follow along as the Webb team checks them off one by one on the Where is Webb tracker. Each mode has a set of observations and analysis that need to be verified, and it is important to note that the team does not plan to complete them in the order listed below. Some of the modes won’t be verified until the very end of commissioning.

For each mode we have also selected a representative example science target that will be observed in the first year of Webb science. These are just examples; each mode will be used for many targets, and most of Webb’s science targets will be observed with more than one instrument and/or mode. The detailed list of peer-reviewed observations planned for the first year of science with Webb ranges from our solar system to the most distant galaxies.

1.  Near-Infrared Camera (NIRCam) imaging. Near-infrared imaging will take pictures in part of the visible to near-infrared light, 0.6 to 5.0 micrometers wavelength. This mode will be used for almost all aspects of Webb science, from deep fields to galaxies, star-forming regions to planets in our own solar system. An example target in a Webb cycle 1 program using this mode: the Hubble Ultra-Deep Field.

2.  NIRCam wide field slitless spectroscopy. Spectroscopy separates the detected light into individual colors. Slitless spectroscopy spreads out the light in the whole instrument field of view so we see the colors of every object visible in the field. Slitless spectroscopy in NIRCam was originally an engineering mode for use in aligning the telescope, but scientists realized that it could be used for science as well. Example target: distant quasars.

3.  NIRCam coronagraphy. When a star has exoplanets or dust disks in orbit around it, the brightness from a star usually will outshine the light that is reflected or emitted by the much fainter objects around it. Coronagraphy uses a black disk in the instrument to block out the starlight in order to detect the light from its planets. Example target: the gas giant exoplanet HIP 65426 b.

4.  NIRCam time series observations – imaging. Most astronomical objects change on timescales that are large compared to human lifetimes, but some things change fast enough for us to see them. Time series observations read out the instruments’ detectors rapidly to watch for those changes. Example target: a pulsing neutron star called a magnetar.

5.  NIRCam time series observations – grism. When an exoplanet crosses the disk of its host star, light from the star can pass through the atmosphere of the planet, allowing scientists to determine the constituents of the atmosphere with this spectroscopic technique. Scientists can also study light that is reflected or emitted from an exoplanet, when an exoplanet passes behind its host star. Example target: lava rain on the super-Earth-size exoplanet 55 Cancri e.

6.  Near-Infrared Spectrograph (NIRSpec) multi-object spectroscopy. Although slitless spectroscopy gets spectra of all the objects in the field of view, it also allows the spectra of multiple objects to overlap each other, and the background light reduces the sensitivity. NIRSpec has a microshutter device with a quarter of a million tiny controllable shutters. Opening a shutter where there is an interesting object and closing the shutters where there is not allows scientists to get clean spectra of up to 100 sources at once. Example target: the Extended Groth Strip deep field.

7.  NIRSpec fixed slit spectroscopy. In addition to the microshutter array, NIRSpec also has a few fixed slits that provide the ultimate sensitivity for spectroscopy on individual targets. Example target: detecting light from a gravitational-wave source known as a kilonova.

8.  NIRSpec integral field unit spectroscopy. Integral field unit spectroscopy produces a spectrum over every pixel in a small area, instead of a single point, for a total of 900 spatial/spectral elements. This mode gives the most complete data on an individual target. Example target: a distant galaxy boosted by gravitational lensing.

9.  NIRSpec bright object time series. NIRSpec can obtain a time series spectroscopic observation of transiting exoplanets and other objects that change rapidly with time. Example target: following a hot super-Earth-size exoplanet for a full orbit to map the planet’s temperature.

10.  Near-Infrared Imager and Slitless Spectrograph (NIRISS) single object slitless spectroscopy. To observe planets around some of the brightest nearby stars, NIRISS takes the star out of focus and spreads the light over lots of pixels to avoid saturating the detectors. Example target: small, potentially rocky exoplanets TRAPPIST-1b and 1c.

11.  NIRISS wide field slitless spectroscopy. NIRISS includes a slitless spectroscopy mode optimized for finding and studying distant galaxies. This mode will be especially valuable for discovery, finding things that we didn’t already know were there. Example target: pure parallel search for active star-forming galaxies.

12.  NIRISS aperture masking interferometry. NIRISS has a mask to block out the light from 11 of the 18 primary mirror segments in a process called aperture masking interferometry. This provides high-contrast imaging, where faint sources next to bright sources can be seen and resolved for images. Example target: a binary star with colliding stellar winds.

13.  NIRISS imaging. Because of the importance of near-infrared imaging, NIRISS has an imaging capability that functions as a backup to NIRCam imaging. Scientifically, this is used mainly while other instruments are simultaneously conducting another investigation, so that the observations image a larger total area. Example target: a Hubble Frontier Field gravitational lensing galaxy cluster.

14.  Mid-Infrared Instrument (MIRI) imaging. Just as near-infrared imaging with NIRCam will be used on almost all types of Webb targets, MIRI imaging will extend Webb’s pictures from 5 to 27 microns, the mid-infrared wavelengths. Mid-infrared imaging will show us, for example, the distributions of dust and cold gas in star-forming regions in our own Milky Way galaxy and in other galaxies. Example target: the nearby galaxy Messier 33.

15.  MIRI low-resolution spectroscopy. At wavelengths between 5 and 12 microns, MIRI’s low-resolution spectroscopy can study fainter sources than its medium-resolution spectroscopy. Low resolution is often used for studying the surface of objects, for example, to determine the composition. Example target: Pluto’s moon Charon.

16.  MIRI medium-resolution spectroscopy. MIRI can do integral field spectroscopy over its full mid-infrared wavelength range, 5 to 28.5 microns. This is where emission from molecules and dust display very strong spectral signatures. Example targets: molecules in planet-forming disks.

17.  MIRI coronagraphic imaging. MIRI has two types of coronagraphy: a spot that blocks light and three four-quadrant phase mask coronagraphs. These will be used to directly detect exoplanets and study dust disks around their host stars. Example target: searching for planets around our nearest neighbor star Alpha Centauri A.

— Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

NASA’s James Webb Space Telescope is aligned across all four of its science instruments, as seen in a previous engineering image showing the observatory’s full field of view. Now, we take a closer look at that same image, focusing on Webb’s coldest instrument: the Mid-Infrared Instrument, or MIRI.

The MIRI test image (at 7.7 microns) shows part of the Large Magellanic Cloud. This small satellite galaxy of the Milky Way provided a dense star field to test Webb’s performance.

Here, a close-up of the MIRI image is compared to a past image of the same target taken with NASA’s Spitzer Space Telescope’s Infrared Array Camera (at 8.0 microns). The retired Spitzer telescope was one of NASA’s Great Observatories and the first to provide high-resolution images of the near- and mid-infrared universe. Webb, with its significantly larger primary mirror and improved detectors, will allow us to see the infrared sky with improved clarity, enabling even more discoveries.

For example, Webb’s MIRI image shows the interstellar gas in unprecedented detail. Here, you can see the emission from “polycyclic aromatic hydrocarbons,” or molecules of carbon and hydrogen that play an important role in the thermal balance and chemistry of interstellar gas. When Webb is ready to begin science observations, studies such as these with MIRI will help give astronomers new insights into the birth of stars and protoplanetary systems.

 

In the meantime, the Webb team has begun the process of setting up and testing Webb’s instruments to begin science observations this summer. Today at 11 a.m., Webb experts will preview these next two months of instrument preparations in a teleconference for media. Listen to the audio stream live at nasa.gov/live.