JWST Moving Target Observations

JWST can track and observe planets, satellites, and nearly all comets and asteroids more than 1 AU from the Sun.  

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JWST offers the capabilities necessary for observing Solar System (moving) targets, with high sensitivity and spatial resolution, through imaging as well as low- and medium-resolution spectroscopy, from 0.6 to 28.5 μm. The large dynamic range afforded by the JWST instruments enables observations of bright Solar System objects like Mars, the giant planets, their satellites, and large main-belt asteroids, as well as smaller and fainter objects like collisional fragments in the main asteroid belt, small irregular satellites, Centaurs, and trans-Neptunian objects in the outer reaches of the solar system. The various instruments and observing modes are capable of making observations useful for, e.g., constraining atmospheric and surface compositions, identifying satellites around minor bodies and characterizing their orbits, determining physical properties through stellar occultations, carrying out deep searches in small areas of sky, and following up on newly discovered objects or transient events as targets of opportunity.

The observatory is in a solar orbit near Earth's L2 point, so scheduling is more flexible and efficient compared to HST (which is in a low Earth orbit). JWST's thermal design only allows Solar System targets to be observed near quadrature; observations at opposition are not feasible. Additionally, these thermal constraints also prevent observations of Solar System objects interior to JWST's own orbit, meaning that the Earth, Moon, Sun, Mercury, and Venus, as well as minor bodies and comets inside the Earth's orbit, cannot be observed at any point. Tracking of moving targets has been demonstrated at rates exceeding 100 mas/s, with a nominal "speed limit" set at 75 mas/s for practical reasons. This tracking rate allows observations of nearly every target found outside of Earth's orbit, including fast-moving near-Earth asteroids and long-period comets. Despite these restrictions, there are still over a million Solar System objects available for study with JWST.


Solar System observations with JWST

An overview of JWST's Solar System capabilities, as well as exploration of some possible science applications can be found in Milam et al. (2016) and Norwood et al. (2016). The following list includes links to flyers on some potential science investigations:

  • General: Overview of JWST's capabilities for observations of Solar System targets

  • Solar System GTO & ERS programs: Details of all Guaranteed Time Observations (GTO) and Early Release Science (ERS) programs targeting Solar System objects

  • Asteroids & near-Earth objects (NEOs): Surface composition, thermal properties

  • Giant planets: Vertical and horizontal cloud structures, global circulation, chemistry and composition, thermodynamics
  • Giant planet satellites: Volcanic activity on Io, satellite atmospheres, plume activity on Europa and Enceladus, irregular satellites
  • Trans-Neptunian Objects (TNOs): Surface composition, diameter/albedo, colors, binarity

  • Mars: Atmospheric composition, evolution of dust storms and clouds

  • Occultations: Minor bodies, rings, mutual events, serendipitous occultations

  • Rings and small satellites: Discovery and characterization, transient phenomena (ring arcs and spokes), composition

  • Titan: Atmospheric composition, clouds and hazes, surface temperature, surface changes

  • Comets: Dust, gas, nuclei, observability

More detailed examinations of 10 science areas, and a summary of JWST capabilities and operations for moving targets, can be found in a January 2016 special issue of PASP.


Example APT files and ETC workbooks

GTO & ERS

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

APT files from the Guaranteed Time Observations (GTO) programs, Early Release Science (ERS) programs, and General Observer (GO) programs can be found on the Approved Programs page.

APT files can also be downloaded from APT using the tool's main menu: File → Retrieve from STScI → Retrieve using Proposal ID, then enter the proposal ID in the pop-up box, and click OK.

JWST demonstration proposals

An example APT file for observations of Solar System objects can be found in the APT tool, from the main menu under File → JWST Demonstration Proposals → Solar System Example. This example file includes observations of minor bodies, comets, satellites, and giant planets using the instruments and modes most suitable for Solar System programs.

ETC sample workbook and example science program

The Exposure Time Calculator (ETC) provides a Solar System Sample Workbook and an example science program that can be retrieved from the Available Workbooks page (see JWST ETC Using the Sample Workbooks for additional information on how to retrieve these workbooks). These example workbooks provide users with a starting point for creating sources and calculations for planning Solar System observations.

The example science program, NIRSpec IFU and Fixed Slit Observations of Near-Earth Asteroids, provides an end-to-end walkthrough of how to create a Solar System proposal, and the associated ETC workbook is described in detail in the Step-by-Step ETC Guide for NIRSpec IFU and Fixed Slit Observations of Near-Earth Asteroids.


Webcasts and presentation packets (2016 - 2019)

Presentation chart packets from JWST workshops and Townhall events at AAS Division of Planetary Sciences meetings are linked below. They cover in considerable detail topics such as using the Astronomer's Proposal Tool (APT) and Exposure Time Calculator (ETC) for planning observations, tracking capabilities of the observatory, and processing data in the pipeline.

October 16-21, 2016: JWST at the 48th Annual Division for Planetary Sciences (Joint with EPSC) Meeting

February 7, 2017: Solar System Community Webinar: JWST Early Release Science Program

February 14, 2017: JWST Community Lecture Series - Observing Solar System Targets with JWST

November 13-15, 2017: Planning Solar System Observations with JWST - STScI venue

December 13-15, 2017: Planning Solar System Observations with JWST - ESTEC venue

February 13, 2018: Planning Solar System Observations with JWST in Cycle 1

October 21-26, 2018: JWST at the 50th Annual Division for Planetary Sciences Meeting

September 15-20, 2019: JWST at the 51st Annual Division for Planetary Sciences Meeting (Joint with EPSC)


List of articles

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Additional resources 

JWST Moving Target Visibility Tool Help

NIRSpec IFU and Fixed Slit Observations of Near-Earth Asteroids


References

Magnum, J., ed. 2016, PASP, 128, 959 
Special Issue: Innovative Solar System Science with the James Webb Space Telescope

Milam, S., et al. 2016, PASP, 128, 959
The James Webb Space Telescope’s Plan for Operations and Instrument Capabilities for Observations in the Solar System
ADS  arXiv 

Norwood, J., et al. 2016, PASP, 128, 960
Solar System Observations with the James Webb Space Telescope
arXiv

JWST Observations in the Solar System flyer



Notable updates


Originally published