Figure 4.1

The estimated sensitivities of various ground-and space-based facilities likely to play roles in studies of trans-neptunian objects in the next 10 to 15 years. The current capabilities of the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) are plotted relative to those of the 8-meter Gemini telescope currently under construction in Hawaii, and the Space Infrared Telescope Facility scheduled for launch in 2001. Also shown are two different concepts for NASA's proposed Next Generation Space Telescope (NGST). The 6-meter NGST is in a heliocentric orbit at 3 AU, i.e., in the outer portion of the asteroid belt where the zodiacal emission is 30 to 100 times lower than it is at 1 AU. The 8-meter NGST is in a heliocentric orbit at 1 AU. Gemini (outfitted with low-order adaptive optics), NICMOS, SIRTF, and NGST will readily detect the reflected sunlight from Pluto (off scale) and a typical KBO out to wavelengths of ~5 microns. Pluto's thermal emission should be detectable by either of the two NGST concepts at wavelengths greater than ~15 microns. The thermal emission from the KBO, however, appears to be beyond the capability of any of the facilities in the wavelength range illustrated. SIRTF will, however, be able to detect such a KBO at wavelengths greater than 35 microns (not illustrated). The capabilities indicated assume a 10,000-sec integration, a 10-σ signal-to-noise ratio, and a wide bandpass of λ/Dl = 3. The Kuiper Belt object is taken to have a radius of 100 km and is located at 35 AU. Its temperature is 35 Kelvin; it has a visual magnitude of 22.0 and a V-K color index of 2.0 (i.e., the red color characteristic of some, but not all, trans-neptunian objects). Pluto is assumed to have a diameter of 1,200 km and a temperature of 40 Kelvin, and to be located at its current distance from the Sun. Adapted from The Next Generation Space Telescope: Visiting a Time When Galaxies Were Young, H.S. Stockman, ed., Space Telescope Science Institue, Baltimore, Maryland, 1997, with information on Pluto and the KBO courtesy of D.P. Cruikshank.

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