Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/jwst/doc-archive/flyers/JWST-Solar-System.pdf Дата изменения: Unknown Дата индексирования: Mon Apr 11 04:28:44 2016 Кодировка: Поисковые слова: horizon

NASA's James Webb Space Telescope:

JWST Obser vations in the Solar System
NASA's astrophysical obser vatories have provided many significant advances in Solar System exploration. Telescopes like Hubble and Spit zer have led directly to new discoveries and also enhanced the productivit y of planetar y missions. For example, monitoring of Mars has led to insights on ideal landing sites for Mar tian mis sions, and re c ent obser vations have reve aled Kuiper B elt t arget s for the ex tended phase of the New Horizons mission. Sur vey missions such as IR AS and WISE have revolutionized our understanding of broad categories of solar system objects. S cheduled for launch in 2018, the Jame s Webb Spac e Tele scope (JWST ) is poised to revolutionize many areas of astrophysic al research, including Solar System Science. JWST is ~100 times more power ful than the Hubble and Spit zer obser vatories. It has greater sensitivit y, higher spatial resolution in the infrared, and signific antly higher spectral re solution in the mid infrared. Imaging and spectroscopy (both long-slit and integral-field) will be available across the entire 0.6 ­ ~ 28.5 micron wavelength range. "Planetar y systems and the origin of life" is one of the core science themes for JWST. For example within the Solar System, molecular inventories and sur face composition of Kuiper Belt Objects and comets will provide key insight into the dynamic histor y of the Solar System and help constrain current theories. Global scale imaging and spectroscopy of planetar y atmospheres will be used to monitor temporal variations as well as decipher dynamics and chemistr y. A 2014 white paper (Nor wood et al., 2014) provides an over view and representative Solar System science case studies: ht tp://w w w.stsci.edu/jwst /doc-archive/ white-papers. In addition, 10 community-based focus groups are examining JWST capabilities in the areas of: Asteroids, Comets, Giant Planets, Mars, Near Earth Objects, Occultations, Rings, Satellites, Titan, and Trans-Neptunian Objects. The JWST project is providing technical information to these groups to aid in their work. Detailed results from these studies will be published in a series of white papers. In the meantime, the groups are preparing 2-page flyers on their topics, which are (or will be) available from: ht tp://w w w.stsci.edu/jwst /doc-archive/flyers.
N IR S p e c ( 1- 5 m ) a n d M IR I (5-28.5m) of fer modes that provide simult aneous spatial and spectral coverage over fields of view of a few arcseconds. The figure at lef t illustrates the spatial resolution of NIRSpec in such a mode. Spectral resolutions of approximately 3000 are available in both instruments.

JWST will be able to obser ve the outer planets without saturating in at least some modes. This figure shows disk-averaged spectra for the outer planets and the NIRCam saturation limits for subarrays large enough to image all of Jupiter in a single pointing. Smaller subarrays (and higher saturation limits) are available. Spectroscopic modes (with even higher limits) will be needed for Mars.
# Resolution Elements Object Mars Jupiter Saturn Uranus Neptune Pluto Size ('') 7 37 17 3.5 2.2 0.1 Size (km) 6.8e3 1.4e5 1.2e5 5.1e4 5.0e4 2.4e3 2 m PSF 100 530 245 50 31 2 NIRSpec IFU 70 370 170 34 22 1 MIRI IFU (6.4 m) 40 200 94 19 12 0.6

Science Capabilit y Highlights
· Impor tant molecular (e.g. H2O, HDO, CO, CO2, S2, CH4), ice, and mineral spectral features are at wavelengths accessible with JWST but not the ground. · Near-IR spectra or colors (composition), and mid-IR photometr y (albedos, sizes), for any Kuiper belt object known today. · Semi-annual monitoring of planetar y (and satellite) weather and seasonal changes. · Near-simultaneous mapping and spectroscopy of cometar y gas and dust from 0.6 ­ ~ 28.5 µm. · Ver y sensitive spectral maps at R > 2000 over a 3''x3'' field and with 0.1'' spatial resolution.


Obser vator y & Capabilities
Af ter launch, JWST will enter a halo orbit around the Sun-Ear th L2 point. This orbit simplifies planning and scheduling, and minimizes thermal and scat tered light influences from the Ear th and Moon. The 6.5m primar y mirror provides dif fraction-limited per formance (PSF F WHM = 64mas) at 2m. The mirror and science instruments are passively cooled to 40K by remaining in the shadow of the Sunshield; the detectors in the mid-IR instrument are actively cooled to 6.7K. The JWST pointing control system will track objects moving at rates of up to 30 mas/sec (adequate to follow Mars and even most near-Ear th objects). The target ephemeris is represented as a 5th order polynomial, enabling tracking of objects (such as Io) that have large apparent accelerations. Pointing stability (and therefore image quality) for moving targets is expected to be comparable to that for fixed targets. The four science instruments on JWST cover the wavelength range from 0.6 ­ ~ 28.5 m. and of fer superb imaging and spectroscopic sensitivit y (see some additional detail in tables below). Subarray readouts will enable non-saturated obser vations of the giant planets and many bright primitive bodies in a variet y of instrument modes. Scat tered light is a concern for obser ving bright targets such as the planets and brighter asteroids. Accurate scat tered light performance will only be known once on-orbit testing is completed, but the fidelit y of PSF models is being improved by incorporating details of mirror-segment edge figures.
9 A rcmin
Ecl. Pole

0 9

Ecl. Plane

JWST science Instrument and guider fields of view as they project onto the sk y. The ecliptic orient ation shown is for a line - of-sight in the ecliptic plane and in the direction of obser vator y o r b i t a l m o t io n a b o u t t h e S u n . T h e l i n e o f s i g h t is restric ted to elongations of 85° ­ 135° (so that the telescope and instruments always remains in the shadow of the Sunshield). The r e s u l t i n g f i e l d o f r e g a r d e n c o m p a s s e s 3 5% of the sk y; any par ticular pointing falls within the field of re g ard t wic e a ye ar. T he s e pointing r e s t ric tions r e sult in c on tinuous vie w ing window s of about 5 0 days for low-inclination t argets, while a 5° cone at the ecliptic poles is continuously visible.

Standard JWST Imaging Modes*
Mode Imaging Instrument NIRCam NIRCam NIRIS S MIRI A p e r t ur e M a s k Inter ferometr y NIRIS S Wavelength (microns) 0.6 ­ 2 . 3 2.4 ­ 5.0 0. 9 ­ 5. 0 5.0 ­ 27.5 3.8 ­ 4.8 P i xe l S c a l e F i e l d o f (arcsec) View 0.0 32 0.0 6 5 0.0 6 5 0.11 0.0 6 5 2.2 x 4.4' 2.2 x 4.4' 2. 2 x 2. 2 ' 1.23 x 1.8 8' ------

JWST science observations will, for the first 2.5 years, fall into Guaranteed Time Observer (GTO) and General Observer (GO) categories. Director's Discretionary Time will also be available, and the project is considering large-program possibilities as well. GTO target lists will be finalized prior to the GO-1 call for proposals (expected to be in late 2017). GO-1 proposals will be due in early 2018. Science operations, including execution of GO-1 programs, are expected to commence in April, 2019. Mission lifetime goal is 10 years. The fraction of time allocated for Solar System proposals will approximately reflect the fraction of the total available time requested for those proposals. The selection process is expected to be highly competitive. Analysis funding will be made available to successful US-based proposers. The Astronomer's Proposal Tool (APT, developed for the Hubble Space Telescope) is being expanded to support planning and submission of JWST proposals. Some APT enhancements related to planning Solar System observations are under discussion, with a goal of making them available for GO-1 proposers.

JWST Spectroscopy Modes
Mode Slitless G r is m Instrument Wavelength Resolving (microns) Power (l/Dl) NIRIS S NIRIS S NIRCam Single Slit NIRSpec Spectroscopy 1.0 ­ 2.5 0.6 ­ 2 . 5 2.4 ­ 5.0 0.6 ­ 5. 0 150 70 0 2000 100, 1000, 27 0 0 F i eld of V i ew 2. 2 x 2. 2 ' single object 2.2 x 4.4' slits with 0.4 x 3.8'' 0. 2 x 3 . 3 ' ' 1.6 x 1.6'' 0.6 x 5.5'' slit 3.0 x 3.0'' 3.0 x 3.9'' 3.5 x 4.4'' 5. 2 x 6 . 2 ' ' 6.7 x 7.7''

* MIRI and NIRCam are capable of imaging in sub arrays to facilitate observations of bright objects, and coronagraphy of extra-Solar planetary systems.

More Information
M o r e in f o r m a t io n a n d d e t a ils a b o u t J W S T, o b s e r v a t o r y a n d instrument capabilities, and Solar System science with JWST can be found at: jwst.nasa.gov/faq_solarsystem.html w w w.stsci.edu/jwst /science/solar-system Instrument pocket-guides, a JWST primer, and other materials are available from: w w w.stsci.edu/jwst /science/doc-archive A protot ype exposure-time calculator for some instrument modes is here: jwstetc.stsci.edu/etc P S F m o d e li n g s o f t w a r e a n d a P S F li b r a r y c a n b e f o u n d h e r e : ht tp://w w w.stsci.edu/jwst /sof t ware/webbpsf

MIRI IFU NIRSpec MIRI MIRI MIRI MIRI

-9

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5.0 ­ ~14.0 0.6 ­ 5. 0 5.0 ­ 7.7 7.7 ­ 11.9 11.9 ­ 18.3 18.3 ­ 28.5

~10 0 at 7.5 microns 100, 1000, 270 0 3 50 0 28 0 0 270 0 220 0

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