From The Space Science Telescope Institute (US): “2021 Volume 38 Issue 02” 

From The Space Science Telescope Institute (US)


Go, Webb, Go!
M. Stiavelli ( and K. Pontoppidan (

These are exciting times for the James Webb Space Telescope [below] mission at STScI.

An Ariane 5 rocket, provided by the European Space Agency, gave astronomers worldwide a marvelous present. A flawless launch on Christmas morning 2021, followed by two successful Mid-Course Correction (MCC1a and MCC1b) burns, sent Webb toward the L2 Lagrangian point with a nominal expenditure of fuel.

LaGrange Points map. NASA.

This ensures that we have enough on-board fuel to support more than 10 years of science operations.

Several busy days followed launch, culminating in the critical deployment and tensioning of the five-layer sunshield, needed to keep the telescope and instruments cold. At the time of writing, the successful deployment of the secondary mirror had taken place. The deployment of the mirror and alignment of the optical telescope element will follow, which leads into instrument commissioning. These activities are planned to take a total of six months and will culminate in the release of the first public images and the start of the Cycle 1 science program. We cannot wait to see what discoveries Webb has in store for us this summer!

HST @ STScI Update
C. Christian (, T. Brown (, H. Jenkner (, and J. Mackenty (

Hubble Science Spotlight

The Hubble Space Telescope [below] continues to be a distinctly powerful observational machine that enables significant advances across a broad range of astrophysics.

For more than three decades, Hubble has yielded unique discoveries, contributed to multi-wavelength investigations, and campaigned to study time-variable phenomena. A few results captured in nearly 1000 refereed papers this year are mentioned here.

Time-Variable Phenomena

A major contribution of Hubble to research has been long- and short-term observations of various astrophysical objects; 31 years of operation have provided unique opportunities for such studies. The refinement of the Hubble constant, a major goal for the observatory, is a prime example benefiting from long-term, consistent, and comparable instrumentation, enabling multiple avenues for measuring the accelerating expansion of the universe, and the precision associated with Hubble observations may be revealing new physics when compared to expectations gleaned from the cosmic microwave background.

A highly visible series of investigations conducted by the OPAL program monitors the gaseous planets in the Solar System. Changes in their atmospheres have been cataloged and analyzed, allowing researchers to precisely trace the evolution of Jupiter’s Red Spot and surrounding winds, examine subtle seasonal variations on Saturn, and study storms on Neptune and Uranus. In the inner Solar System, Hubble’s insight into Martian weather dovetails with missions in situ.

Hubble’s long-term baseline enables unique insights into stellar physics and evolution, such as the 10‑year program to observe brightness variations of Eta Carina, providing evidence for the dynamic interaction of its central stars. The Stingray Nebula has been seen to morphologically change and fade, with a 20‑year baseline of data suggesting variability and outbursts of the central star. Another impressive example of the reliability and precision of Hubble data is the observation of supernovae in lensed cluster fields. In MACS J0138.0–2155, recent re‑analysis of observations of a lensed object seen in 2019 and images found in archival data from 2016 suggested that an additional instance of the object will appear in 2037. This is reminiscent of the earlier study of Frontier Fields MACS J1149.5+2223, in which a supernova, called Refsdal, was discovered and then reappeared later, providing an excellent test of lensing models, laying the ground work for ambitious additional studies.

Figure 1: Something to look forward to. In a 2016 Hubble image (left), three views of the same supernova, called Requiem, appeared embedded in a distant galaxy lensed by the giant galaxy cluster, MACS J0138. In 2019 (right), the SN images are gone. The image is predicted to reappear in 2037.


Hubble has been a perfect platform for Treasury Programs and Observational Campaigns. The Director’s Discretionary program dubbed ULLYSES (Ultraviolet Legacy Library of Young Stars as Essential Standards) was designed specifically to utilize about 1,000 HST orbits to create an ultraviolet spectroscopic library of young high- and low-mass stars in the local universe. The third Data Release, or DR3, of High-Level Science Products (HLSPs) from the program is available now. This release contains 90 new targets and updated data for 137 targets. Updates include new pipeline and calibration improvements, and users are advised to replace older data with the new products available. Several additional companion targets were observed with the STIS long slit toward selected T Tauri stars. New products are also available, such as time-series spectra and drizzled images. In addition, DR3 is making data from the Las Cumbres Observatory Global Telescope (LCOGT) available for that initial subset of ULLYSES T Tauri stars.

LCO map 2017. Map of the Las Cumbres Observatory global network of robotic telescopes.

LCOGT Las Cumbres Observatory 1M Global Telescope Network, Haleakala Hawaii, USA, Elevation 10,023 ft (3,055 m).

Hubble Anomalies Get Quick Attention

The telescope performs remarkably after 31-plus years, but does experience occasional anomalies. While the pointing issues are settling down (HST Update in Newsletter v38 Issue 01), in June 2021, the payload computer in the Science Instrument Command and Data Handling unit (SI C&DH) halted. The deliberate investigation of this issue was a month long, and involved several simulations and tests (for a detailed synopsis see the July 17 press release. After many scenarios were studied and simulated, the observatory was reconfigured to use the other side of the SI C&DH unit. The telescope returned to science July 16, 2021.

In September 2021, a Single Event Upset (SEU) suspended the Cosmic Origins Spectrograph (COS).

National Aeronautics Space Agency (US) Cosmic Origins Spectrograph.

Considering that these have been experienced before, the recovery was fairly quick, and science operations resumed. In October 2021, the telescope operations stopped due to a timing synchronization issue. None of the instruments were endangered, yet all four detected the problem. As usual, the diagnosis and remedy of any event with HST is thorough and cautious, involving entire HST team. A clever idea was to use NICMOS, dormant since 2008 (before the 2009 servicing mission) to characterize this problem without affecting the active instruments; the instrument was brought to boot mode without any issues after more than a decade in safe mode. This strategy worked, yielding additional data to inform short- and long-term mitigation strategies for this apparently intermittent timing issue. Hubble returned to science on November 7, starting with the Advanced Camera for Surveys (ACS), followed by observations with WFC3.

National Aeronautics Space Agency(USA) European Space Agency [Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Hubble Wide Field Camera 3.

By December 6, the observatory was fully operational with all four instruments.

A Wealth of Data—The MAST Facility

As described in a recent article, MAST introduced a new improved HST data search designed with improved accessibility, including color choices, font sizes, and layout. This new form also supports data searches with a web browser or through a programming interface. Many features are available, including real-time coordinate lookups, lists, type-ahead forms, and API improvements. The user can search for both public and non-public data sets, with the latter accessible by authorized team members. The new form and the older form will co-exist for a while for user convenience.

Numerous new High-Level Science Data Products (HLSP) have been updated, including Hubble surveys of nearby spiral galaxies from PHANGS-HST, which has models for star clusters in those galaxies, numerous TESS data products, exoplanet candidate data, and the ULLYSES Data Release 3 products (described above).

On the technical side, MAST announced an encrypted FTPS-S connection, and users are urged to upgrade to a client that supports those connections for retrieving staged data. Users can retrieve both public and exclusive access via this method. Of course, the server also provides access to other MAST data from missions other than Hubble.

Roman Space Telescope Update

J. MacKenty (, and J. Schlieder (The NASA Goddard Space Flight Center (US))

The Nancy Grace Roman Space Telescope [below] carries two scientific instruments, the Wide Field Imager (WFI) and a coronagraph demonstration instrument.

The WFI Instrument

The WFI instrument is designed to accomplish the surveys necessary to achieve the scientific goals for the Roman mission as defined in the Astro2010 decadal survey, and refined during the mission formulation phases. These include wide-field, multi-band, near-infrared imaging, and wide-field, slitless spectroscopic, and time-domain surveys. This instrument will address the scientific goals that motivate the Roman mission, namely precision cosmological measurements to elucidate the nature of dark energy via measurements of supernovae at cosmic distances, baryonic acoustic oscillations, weak lensing, large-scale structure, and the census of longer-period and free-floating exoplanets. Simultaneously, these surveys, combined with a robust General Investigator (GI) program, will enable a broad variety of scientific studies.

Figure 1: WFI filter and spectroscopic element passbands. These also illustrate the overall performance of the Telescope+WFI system using a modeled “effective area” consistent with performance requirements on all elements.

The WFI consists of a large focal plane covering over 0.28 square degrees—200 times the field of view of Hubble’s Wide-Field Camera 3 (WFC3) infrared camera with slightly better sampling (0.11 vs. 0.129 arc seconds/pixel) providing imaging from 0.5–2.3 microns and spectroscopy from 0.8–1.9 microns. This focal plane consists of eighteen 4K × 4K Hawaii-4RG detectors, which also provide the precision-pointing control for the spacecraft. A single element wheel provides eight imaging filters, two dispersive optics (a prism and grism), and a blank for dark calibrations. The filter and spectral passbands are shown in Figure 1. The two dispersive elements provide slitless spectroscopy at low resolution (R ~ 80–180) from 0.8–1.8 microns motivated by the need to classify supernovae found in time-domain searches and at higher resolution (R ~ 500–800). A grism element covering 1.0–1.9 microns is optimized for measuring galaxy redshifts at z ~ 1.

The WFI is expected to provide ~28 magnitude 5σ point-source sensitivity in one hour (26 in the F213 filter). For spectroscopy, one hour should yield 10σ continuum-sensitivity limits of 23 and 21 magnitude for point sources at 1.2 microns, for the prism and grism, respectively.

The focal plane, and especially its detectors, have been the focus of many years of development with final deliveries, testing, and selection of the flight devices recently completed. These detectors, which represent the next generation of devices from Teledyne Imaging Systems, feature 4096 × 4096 10‑micron pixels. They represent the next generation of detectors, which build upon the 1K × 1K device flown on Hubble’s WFC3 and the 2K × 2K devices on Webb’s Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSPEC), and Near-Infrared Imager and Slitless Spectrograph (NIRISS). These devices have excellent quantum efficiency, low noise, and fewer pathologies compared to prior devices, thus reaching the demanding requirements expected for Roman’s precise calibration. Considerable effort has been invested in the characterization of these devices by scientists and engineers at NASA’s Goddard Space Flight Center, the Institute, IPAC at Caltech, and the Roman Science Investigation teams over the past several years. This is essential to the science goals of precision cosmology, which require a detailed understanding of the behavior and calibration needs of these sensors. Figure 2 shows the focal plane Engineering Test Unit (ETU).

Figure 2: Engineering Test Unit for the WFI focal plane consisting of 18 detectors. This ETU is a path finder for the assembly, handling, and cryogenic testing of the flight unit, which is now being assembled. Note the small gaps between detectors and the overall shape of the focal plane, which maximizes the optical quality of the Roman Telescope’s field of view. These factors require careful observing strategies, but are easily accommodated in the context of a survey mission such as Roman.

The WFI is more than just its detectors and optical elements. Goddard and Ball Aerospace are tasked with designing, constructing, and testing the WFI collaboratively. Other key components include custom electronic controllers and signal chains for the detectors (ACADIA devices; the next generation beyond the SIDECAR devices used in Hubble’s Advanced Camera for Surveys after the 2009 repair mission, Webb, and ESA’s Euclid infrared instrument. Also under construction are the structural elements and the necessary cooling systems to maintain the detectors, filters, and spectral elements at their designed cryogenic temperatures. The element wheel itself (a very large component due to the optical-element size needed to achieve Roman’s large field of view) has been fabricated. During 2021, the internal calibration system for the WFI was redesigned for simplicity and programmatic needs. This system provides both flat fields for internal calibration and, most importantly, precise calibration of the count rate non-linearity in the detectors via two distinct methods. Lastly, teams are defining the operations, flight software, and ground- and flight-verification and calibration plans.

Key Milestones Passed

The Roman Space Telescope has also recently passed several other key milestones. The telescope and mission-critical design reviews were held successfully in late September following a long sequence of reviews of the various components of the mission over the prior nine months. These included the ground system critical design review in July covering the relevant work at Goddard (Mission Operations Center), STScI (Science Operations Center), and IPAC (Science Support Center), and a detailed review of the calibration plans for WFI in late July. A “Request for Information” was released seeking community input on the possible early definition of a GI science program—which, if carried out, would be done with community involvement.

Formulation Science Working Group and Science Investigation Teams

The Formulation Science Working Group and associated Science Investigation Teams (SITs) have now disbanded in advance of the upcoming selection of new science teams via the NASA ROSES opportunity expected in early 2022. These teams, after six years of dedicated effort, have provided workshops during October (Roman CGI Workshop) and November (Science with Wide-Field Instrument), documenting their work and providing tools and simulations in support of future studies.

Read more information about the WFI and the Roman Mission at NASA, STScI, and CalTech.

STScI’s 2021 Symposium: Toward the Comprehensive Characterization of Exoplanets: Science at the Interface of Multiple Measurement Techniques

The 2021 STScI Symposium, Towards the Comprehensive Characterization of Exoplanets: Science at the Interface of Multiple Measurement Techniques, was held April 19–23, 2021. The symposium was organized in a fully virtual format and had more than 400 registered participants from 43 countries.

BlueJeans was used for the talk platform, (Figure 1) was used to host the poster sessions and social interactions, and Slack was used for interaction and questions not answered during the live sessions.

The symposium brought together the exoplanet community to address some of the most outstanding questions in the field, such as:

How do we combine techniques to have a more complete census of exoplanets?
Which sets of observed quantities best enable holistic planetary characterization?
How do the observed architectures of exoplanet systems compare to our solar system?
How does the atmospheric chemistry of exoplanets correlate with the physical properties and compositions of their host stars?
How do planets form and evolve?
What are emerging areas in exoplanet science?

Following the recommendation of the Science Organizing Committee of the 2020 STScI symposium, the abstract selection process was completely anonymous to avoid any potential biases the reviewers might have had. The submissions were processed through a Google form and abstracts were randomly assigned to members of the SOC for reviewing. This resulted in a diverse program with a gender balance that was representative of the submitted abstracts.

The symposium consisted of five days, with six hours each day of talks and poster sessions. There were a total of 63 talks: 5 invited (30 minutes each, including questions), 58 regular (15 minutes each, including questions), and 123 posters.

Each day had a poster session before and after the talks to facilitate participants across multiple time zones. To begin each day’s talks, an invited speaker spoke on the topic of that day.

On the first day, the focus was on the current status of combining measurement techniques, including an invited talk from Matthias Nowak of the University of Cambridge about closing the gap between direct and indirect methods. Several talks were given covering various exoplanet detection techniques from transits to radial velocities and imaging to astrometry.

The second day centered on multi-techniques to understand the demographics of exoplanets, including an invited talk from Jessie Christiansen of Caltech/IPAC-NASA Exoplanet Science Institute about building an exoplanet demographics ladder. The focus of demographics was presented in the context of microlensing, astrometry, stellar hosts, and multiplicity.

The third day addressed combining characterization techniques to understand exoplanetary atmospheres, with an invited talk from Laura Kreidberg of the Max Planck Institute for Astronomy about exoplanet atmosphere characterization with multiple observatories. The studies of exoplanet and brown dwarf atmospheres were presented, including new software to analyze these observations and future prospects.

Day four was all about looking toward the future of multi-techniques, with an invited talk from Chris Stark of NASA Goddard Space Flight Center about the future overlap of exoplanet detection and characterization methods. This day focused on innovative techniques to combine various measurement methods, including probabilistic deep learning, vortex fiber nulling, and reflected-starlight observations.

The focus of the final day was future missions and upcoming facilities that will enable comprehensive characterization of exoplanets, with an invited talk from Knicole Colon of NASA Goddard Space Flight Center about the landscape of exoplanet missions in the 2020s and beyond. Expected exoplanetary science outcomes from upcoming facilities, including JWST, were presented, as well as mission concepts, upcoming surveys, and results from the Roman Exoplanet Imaging Data Challenge.

The use of for the poster session brought a unique aspect to the virtual setup of the STScI symposium. is an online platform that allows you to create an avatar and navigate a virtual environment designed to imitate the spontaneous interactions of an in-person conference. The virtual conference space was set up to resemble the Muller building, with five poster rooms organized by topics scattered throughout the virtual building.

At the end of the symposium, we asked the participants to fill out a survey and received 41 responses. The majority of the participants reported that the video and audio connections were excellent or good, and the schedule being an appropriate length. We also received lots of positive feedback about the use of to interact with colleagues.

As the chair, I would like to personally thank all of the members of the SOC, the Event Planning Group, and IT staff at the Institute who made this symposium a huge success.

See the full article here .

We are the Space Telescope Science Institute [STScI] in Baltimore, Maryland, operated by the Association of Universities for Research in Astronomy. We help humanity explore the universe with advanced space telescopes and ever-growing data archives.

Association of Universities for Research in Astronomy

Founded in 1982, we have helped guide the most famous observatory in history, the Hubble Space Telescope.

National Aeronautics and Space Administration(US)/The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Hubble Space Telescope.

National Aeronautics Space Agency(US)/European Space Agency [Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope(US) annotated, finally launched December 25, 2021, ten years late.

National Aeronautics and Space Administration(US) Nancy Grace Roman Space Telescope [WFIRST] depiction.