How NASA Decides What To Look At With JWST
The James Webb Space Telescope was designed for an operational lifetime of at least 5 years, however, the agency believes 20 is possible. No matter the result, the time with this next generation space telescope is limited, and every minute counts. This brings up the question of how the agency picks what to observe and when, with practically unlimited options.
In reality, this process involves years of preparation and many proposals from all different types of scientists and astronomers. With thousands of proposals coming in, the agency assings certain individuals who are expects in their respective fields to review and help pick observations. A process that is extremely important based on the lifetime of Webb and the time available to access this technology.
Here I will go more in-depth into the entire decision and process, what Webb has been up to, the current state of the telescope, and more.
Deciding JWST’s Future
In a statement, NASA was quoted saying, “Webb was designed for a mission of at least five years, with a goal of 10 years. However, after a successful launch and the completion of telescope commissioning, the Webb team determined the observatory should have enough propellant to allow support of science operations in orbit for more than a 20-year science lifetime. Other factors may limit mission lifetime, such as the possibility that Webb’s hardware will degrade over time in the harsh environment of space. However, as we’ve seen with missions such as the Hubble Space Telescope and the Chandra X-ray Observatory, spacecraft often continue operating years beyond their designed mission lifetime” they said.
With this in mind, NASA knows that despite the possibility of Webb lasting decades, they need to make use of its time. A few months ago on May 10, the Space Telescope Science Institute (STScI), the science operations center for NASA’s James Webb Space Telescope, announced the scientific program for Cycle 2, the second year of regular operations. This announcement was the culmination of a peer-review process to select the most scientifically compelling programs, which began with the submission of observing and archival proposals on January 27.
For every year of regular operations, the center plans to issue a Call for General Observer and Archival proposals from the international astronomical community to solicit ideas for new observations and archival studies to be executed in the upcoming year. Archival proposals request support to analyze already existing observations, develop theoretical models to interpret observations, and/or develop scientific software to facilitate data analysis. For Cycle 2, a record-breaking 1,600 proposals were submitted by more than 5,450 scientists from 52 countries including the United States, ESA (European Space Agency) member states, and Canada.
The proposals covered all topics in astronomy and astrophysics from solar system bodies, exoplanets, supernova remnants, and merging neutron stars to nearby and distant galaxies, supermassive black holes at the centers of galaxies, and the large-scale structure of the universe. Together, the submitted proposals requested more than 35,000 hours of telescope time, far exceeding the 5,000 hours of telescope time available to be allocated.
To select the programs that will be executed, STScI recruits hundreds of members of the international astronomical community to serve on the Telescope Allocation Committee (TAC). Each reviewer is assigned to a topical panel reflecting their scientific expertise. The peer-review process is carried out such that the proposers don’t know who is reviewing the proposals, and the reviewers don’t know who wrote the proposals, a process called Dual-Anonymous Peer Review (DAPR).
Once the proposals have been submitted, the JWST Science Policies Group sorts the proposals by type and/or size and by scientific category. Very small proposals, are graded asynchronously by external panelists, whereas larger programs are reviewed by discussion panels. Each panel is given an allocation of telescope time, for which it can recommend observing programs.
Reviewers are asked to grade each proposal based on three criteria: (1) impact within subfield, (2) out-of-field impact, and (3) suitability for the observatory. For external panels, proposals are ranked using submitted grades. For discussion panels, proposals are first triaged using submitted grades because there is not enough time to discuss all of the submitted proposals. At the TAC meeting, the discussion panelists review the strengths and weaknesses of all of the proposals that survive triage, and regrade and re-rank the proposals. The highest ranked proposals are recommended for allocation of telescope time and/or funding. For the Large, Treasury, and Legacy Archive proposals, the panel chairs also receive and incorporate expert reviews from the community and from their discussion panels. In addition, reviewers provide feedback for the proposers detailing the perceived strengths and weaknesses.
For this mission, the center director is the allocating official. Therefore, all of the recommendations from the TAC are advisory to the director. Once the director approves the programs, STScI notifies proposers of the outcome for their proposals and begins implementation of the awarded observations. The selected Cycle 2 program that was just announced contains lots of exciting and ground-breaking science. JWST is now poised to build on its first year of discoveries. Selection of the General Observer programs represents a tremendous effort by the ~5,450 investigators who submitted proposals, the 225 community members who served as expert reviewers, the 350 members of the Telescope Allocation Committee, and the JWST teams at STScI and NASA.
New Update
While all of this has been going on, Webb has continued to observe different parts of the universe. Recently on June 25, NASA’s James Webb Space Telescope turned to famed ringed world Saturn for its first near-infrared observations of the planet. The initial imagery from Webb’s NIRCam (Near-Infrared Camera) is already fascinating researchers. Saturn itself appears extremely dark at this infrared wavelength observed by the telescope, as methane gas absorbs almost all of the sunlight falling on the atmosphere. However, the icy rings stay relatively bright, leading to the unusual appearance of Saturn in the Webb image.
This image was taken as part of Webb Guaranteed Time Observation program 1247. The program included several very deep exposures of Saturn, which were designed to test the telescope’s capacity to detect faint moons around the planet and its bright rings. Any newly discovered moons could help scientists put together a more complete picture of the current system of Saturn, as well as its past.
This new image of Saturn clearly shows details within the planet’s ring system, along with several of the planet’s moons. Additional deeper exposures (not shown here) will allow the team to probe some of the planet’s fainter rings, not visible in this image, including the thin G ring and the diffuse E ring. Saturn’s rings are made up of an array of rocky and icy fragments – the particles range in size from smaller than a grain of sand to a few as large as mountains on Earth. Researchers recently used Webb to explore Enceladus, and found a large plume jetting from the southern pole of the moon that contains both particles and plentiful amounts of water vapor – this plume feeds Saturn’s E ring.
Saturn’s atmosphere also shows surprising and unexpected details. Although the Cassini spacecraft observed the atmosphere at greater clarity, this is the first time that the planet’s atmosphere has been seen with this clarity at this particular wavelength (3.23 microns), which is unique to Webb. The large, dark, diffuse structures in the northern hemisphere do not follow the planet’s lines of latitude, so this image is lacking the familiar striped appearance that is typically seen from Saturn’s deeper atmospheric layers. The patchiness is reminiscent of large-scale planetary waves in the stratospheric aerosols high above the main clouds, potentially similar to those seen in early Webb NIRCam observations of Jupiter.
When comparing the northern and southern poles of the planet in this image, the differences in appearance are typical with known seasonal changes on Saturn. For example, Saturn is currently experiencing northern summertime, with the southern hemisphere emerging from the darkness at the end of a winter. However, the northern pole is particularly dark, perhaps due to an unknown seasonal process affecting polar aerosols in particular. A tiny hint of brightening towards the edge of Saturn’s disk might be due to high-altitude methane fluorescence (the process of emitting light after absorbing light), emission from the trihydrogen ion (H3+) in the ionosphere, or both; spectroscopy from Webb could help confirm this.
Missions like NASA’s Pioneer 11, Voyagers 1 and 2, the Cassini spacecraft, and the Hubble Space Telescope have tracked Saturn’s atmosphere and rings for many decades. These observations from Webb are just a hint at what this observatory will add to Saturn’s story in the coming years as the science team delves deep into the data to prepare peer-reviewed results.
Conclusion
NASA and its partners have been very busy deciding exactly what the future of the JWST looks like. With only limited time, every second counts, and Webb should be observing as often as possible. We will have to wait and see how it progresses and the impact it has on the space industry.
