Science and Exploration

Selecting What The Webb Space Telescope Observes Next

By Keith Cowing
Status Report
May 14, 2023
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Selecting What The Webb Space Telescope Observes Next
James Webb Space Telescope

This week, astronomers around the world are celebrating the announcement of the next cycle of Webb observations.

We asked Christine Chen, associate astronomer and JWST Science Policies Group lead at the Space Telescope Science Institute, to describe the selection process to determine the targets Webb will observe.

“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, STScI 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). STScI instituted DAPR in 2016 in support of the Hubble Space Telescope Cycle 26 TAC and has found that DAPR has decreased a previously-seen disparity in proposal selection rate for male and female investigators and has encouraged many more students to apply for telescope time.

“Once the proposals have been submitted, the STScI 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 STScI 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. You can learn more about the breath of research areas and questions to be answered with Webb observations by reading the abstracts of the selected programs. Eventually, all of the observations in the approved programs will become publicly available in the archive, enabling additional new discoveries that may not have been foreseen by the original proposers.”

About the Author:
Christine Chen is an associate astronomer in the Science Mission Office at the Space Telescope Science Institute. She leads the JWST Science Policy Group that issues Calls for Proposals to the astronomical community to conduct research using Webb and organizes Dual Anonymous Peer Review of the proposals submitted by the astronomical community in response to these calls.

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.