The Starbase One Astronomy & Space Collection/STARBASE_ONE.ISO/sl9/nsf1217.txt

Text File | 1994-07-18 | 4KB | 71 lines

Image from the NASA/IRTF using the near-infrared 256*256 array
camera, NSFCAM:

    Two sets of images are shown. The July 12 image set shows
    the typical aspect of Jupiter in 8 different near-infrared
    "colors". On the top row, images are shown taken in colors
    that are progressively more affected by gas absorption
    in the atmosphere (namely, hydrogen and methane, the main
     absorbers of light in the Jovian atmosphere). The gas
     absorption prevents light from reaching deep levels in the
     atmosphere: as that absorption increases (as from left
     to right in the top row images), only higher and higher
     levels of the atmosphere can be viewed. At 2.27 um ,
     the very large absorption allows one to see only the
     stratosphere in any clarity. There, the polar hazes
     (a thin veil of haze thought to be generated by magnetospheric
     ions smashing into the hydrogen- and methane-rich atmosphere and
     therby generating more complex, solid molecules) can be
     seen. However, much more optically-thick condensate clouds (principally
      ammonia ice particles) disappear below the gaseous murk, leaving
      the high-altitude but actually very thin veil of stratospheric polar
    hazes as the dominant reflector.

     The second row shows the polar aurorae in the first three
     pictures. The leftmost picture is taken in an extremely
     absorbing wavelength, where methane wipes out virtually every
     bit of sunlight that strikes the planet. The only light seen
     from Jupiter is light that Jupiter emits itself from very
     high altitudes, i.e, auroral emission from the H3+ molecule.
     The next two images show this aurorae again, but with
     progressively more contribution from cloud reflections of
     sunlight as methane absorption becomes progressively
     less effective, allowing us to see through the "murk" once
     again to underlying clouds. The last image shows five-micron
     radiation generated in the relatively-warm deep atmosphere. At
     this wavelength, the Sun's light is very feeble. The bulk
     of the radiation that is seen from Jupiter is generated by
     Jupiter's own heat. However, overlying clouds above the
     source of heat generation (at about 5 bars pressure) obscures
     much of this radiation. Light is seen emanating only in
     relatively cloud-free (or less cloudy) regions of Jupiter...



     The July 17 set shows the affect of the comet impacts on
     the atmosphere. At wavelengths which allow one to peer
     deep in the atmosphere (such as 1.6 um and 4.0), not much
     affect is seen.  However, at wavelengths which restrict
     deep-atmosphere viewing, the impact sites are more and
     more prominent, in a relative sense to other features
     such as the Great Red Spot (near the right hand side
     of these images). Two impact sites are seen near the
     western limb. Impact Site A is the one nearest the
     center (left of center), here seen having just completed
     its first Jovian "day" or rotation after the impact of
     the A fragment some 12 hours earlier.  Impact Site C, here seen just
     one  hour after impact, is near the limb. In most absorption
     bands (such as 2.27 um), Impact site C is dimmer than A,
     indicating that it has less reflective clouds. However, it is
     quite prominent in the deepest absorption bands (such as 3.4
     um), probably indicating a higher altitude cloudtop than for A,at
     this time. However, its strong prominence in both 3.4 and 3.8-um
     pictures may indicate other effects (such as thermal
     or auroral emission).


        Submitted by Kevin H. Baines for the NASA IRTF Comet
        Science Team.