Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/jwst/doc-archive/flyers/JWST-Asteroids-Comets.pdf Äàòà èçìåíåíèÿ: Unknown Äàòà èíäåêñèðîâàíèÿ: Mon Apr 11 05:56:37 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: mare

NASA's James Webb Space Telescope:

NIRSpec & MIRI Obser vations of Asteroids

Spectra obt ained with the MIRI Low Resolution Spectrograph (LRS) of main belt asteroids w ill prov id e s e n si ti v e d e t e r min a tio n o f t h e temperature distribution on their sur faces, as well as compositional information through the s ili c a t e e m i s s i o n f e a t u r e s b r o a d l y c l u s t e r e d around 10 microns. The objects are mainly in t wo groups: A) high-albedo objects near 2.5 AU (S-t ype), and B) low-albedo objects near 3.5 AU (C-t ype). Each target could be obser ved t wice in order to bet ter constrain the thermal iner tia of sur face materials. For objects with large (> 0. 25 mag) rot ational lightcur ve s the t wo obser vations would be timed to coincide with lightcur ve minimum and ma ximum. For objects with smaller lightcur ve amplitudes (0.1 ­ 0.2 mag), JWST of fers a wide range of imaging, spectroscopy and coronagraphic capabilities ( see Tables). NIRSpec medium-resolution spectra in the 0.9 ­ 5 micron region will be used to search for organics, hydrated minerals and water ice for a sample of ~100 small (D < 20km) asteroids in the outer main-belt (3.5 ­ 4 AU). Features from these materials will occur in the 1.5 ­ 5 micron region; spectra in the 0.9 ­ 1.5 micron region will constrain the silicate composition of each body so that a more accurate and complete picture can be drawn of the composition of each body, and of compositional diversit y amongst objects in that region. Current dynamical models for the evolution of the solar system indicate that a fraction of the objects in this region may have originated much fur ther from the Sun, so those objects may be revealed as a distinct compositional class by these data.

Near-Infrared Spectrograph (NIRSpec)
Micro-Shut ter Assembly (MSA) ·4 separate quadrants ·365 (dispersion) x 171 (spatial) shut ters per quadrant ·Obser ver specifies which shut ters to open and close Fixed slits (FS) ·Always open, no overlap with MSA on detectors ·One 0.4'' x 3.8'' slit ·Three 0.2'' x 3.3'' slits (of fset along dispersion a xis) ·One 1.6'' x 1.6'' large aper ture Integral Field Unit (IFU) ·3'' x 3'' field of view (covered when not in use) ·30 image slices, each 0.1'' (dispersion) x 3'' (spatial)

Mid-Infrared Instrument (MIRI)
Direct Imaging ·Nine (9) photometric bands from 5 to 28 µm Coronagraphic Imaging ·Three (3) four-quadrant phase masks (4QPMs) at 10.6 5, 11.4,and 15.5 µm ·Lyot coronagraph at 23 µm Low-Resolution Spectroscopy (LRS) ·5 to ~ 14 µm · l/Dl ~ 100 at 7.5 µm ·0.6'' x 5.5'' slit LRS Slitless Spectroscopy ·E xoplanet studies Medium Resolution Spectrometer (MRS) · l/Dl ~ 2200 ­ 3500 ·4.9 to 28.8 µm, enabled by four Integral Field Units (IFUs) ·3.7'' to 7.7'' field-of-views (wavelength-dependent)

JP L / N A S A


Composition and Activit y of Periodic Comets

The composition and dynamics of dust and gas in the comae can be studied using MIRI and NIRSpec. MIRI LRS data from 5 ­14 µm can be used to characterize the composition of the dust y component of the comae, and will be sensitive to the emission features of silicates, PAHs and other large organic molecules. The LRS data also provide sensitive constraints on the temperature of the dust and its grain-size distribution. MIRI 10-µm images of the comae and near-nucleus dust trails can also be obtained. The images will reveal jet structures in the coma, providing constraints on the rotation state of the nucleus, as well as the dust production rate and velocit y of ejection. Each comet would be obser ved t wice to sample activit y at dif ferent phases in its orbit.

C o m e t H a l l e y 's N u c l e u s : A n O r b i t i n g I c e b e r g
Halley Multicolor Camera Team, Giotto Project, ESA

NIRSpec medium resolution spectra will enable characterization of broad emission lines from H 2 O, CO2 and organic molecules in the gas phase. These spectra will also be highly sensitive to the presence of water ice and silicates in the dust grains of the coma. Spectra will be taken of the region surrounding the comet nucleus to characterize the gas and dust composition before interactions with UV and chemical evolution have taken place, and also at a position of fset from the nucleus to characterize the photochemical processes in the coma. NIRSpec high resolution spectra will be used to measure abundances of higher-order organic molecules, and to measure the D-H ratio of the water in the coma. As with the medium resolution data, spectra will be acquired both on the nucleus and at an offset position.

See more at w w w.s t sci.edu / jws t and jwst.nasa.gov and do your own E TC calculations at jwstetc.stsci.edu/etc

Operated for NASA by AURA

AC SP E TELESCOPE SCIENCE INSTITUTE

Images cour tesy of N ASA