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Disruptive collisions in the main belt can liberate fragments from parent bodies ranging in size from several micrometers to tens of kilometers in diameter. These debris bodies group at initially similar orbital locations. Most asteroid-sized fragments remain at these locations and are presently observed as asteroid families. Small debris particles are quickly removed by Poynting-Robertson drag or comminution but their populations are replenished in the source locations by collisional cascade. Observations from the Infrared Astronomical Satellite (IRAS) showed that particles from particular families have thermal radiation signatures that appear as band pairs of infrared emission at roughly constant latitudes both above and below the Solar System plane. Here we apply a new physical model capable of linking the IRAS dust bands to families with characteristic inclinations. We use our results to constrain the physical properties of IRAS dust bands and their source families. Our results indicate that two prominent IRAS bands at inclinations [approximately equal to] 2.1[degrees] and [approximately equal to] 9.3[degrees] are byproducts of recent asteroid disruption events. The former is associated with a disruption of a [approximately equal to] 30-km asteroid occurring 5.8 Myr ago; this event gave birth to the Karin family. The latter came from the breakup of a large > 100-km-diameter asteroid 8.3 Myr ago that produced the Veritas family. Using an N-body code, we tracked the dynamical evolution of [approximately equal to] [10.sup.6] particles, 1 [micro]m to 1 cm in diameter, from both families. We then used these results in a Monte Carlo code to determine how small particles from each population undergo collisional evolution. By computing the thermal emission of particles, we were able to compare our results with IRAS observations. Our best-fit model results suggest the Karin and Veritas family particles contribute by 5-9% in 10-60-[micro]m wavelengths to the zodiacal cloud's brightness within 50[degrees] latitudes around the ecliptic, and by 9-15% within 10[degrees] latitudes. The high brightness of the zodiacal cloud at large latitudes suggests that it is mainly produced by particles with higher inclinations than what would be expected for asteroidal particles produced by sources in the main belt. From these results, we infer that asteroidal dust represents a smaller fraction of the zodiacal cloud than previously thought. We estimate that the total mass accreted by the Earth in Karin and Veritas particles with diameters 20-400 [micro]m is [approximately equal to] 15,000-20,000 tons per year (assuming 2 g [cm.sup.-3] particles density). This is [approximately equal to] 30-50% of the terrestrial accretion rate of cosmic material measured by the Long Duration Exposure Facility. We hypothesize that up to [approximately equal to] 50% of our collected interplanetary dust particles and micrometeorites may be made up of particle species from the Veritas and Karin families. The Karin family IDPs should be about as abundant as Veritas family IDPs though this ratio may change if the contribution of third, near-ecliptic source is significant. Other sources of dust and/or large impact speeds must be invoked to explain the remaining [approximately equal to] 50-70%. The disproportional contribution of Karin/Veritas particles to the zodiacal cloud (only 5-9%) and to the terrestrial accretion rate (30-50%) suggests that the effects of gravitational focusing by the Earth enhance the accretion rate of Karin/Veritas particles relative to those in the background zodiacal cloud. From this result and from the latitudinal brightness of the zodiacal cloud, we infer that the zodiacal cloud emission may be dominated by high-speed cometary particles, while the terrestrial impactor flux contains a major contribution from asteroidal sources. Collisions and Poynting-Robertson drift produce the size-frequency distribution (SFD) of Karin and Veritas particles that becomes increasingly steeper closer to the Sun. At 1 AU, the SFD is relatively shallow for small particle diameters D (differential slope exponent of particles with D [??] 100 [micro]m is [approximately equal to] 2.2-2.5) and steep for D [??] 100 [micro]m. Most of the mass at 1 AU, as well as most of the cross-sectional area, is contributed by particles with D [approximately equal to] 100-200 [micro]m. Similar result has been found previously for the SFD of the zodiacal cloud particles at 1 AU. The fact that the SFD of Karin/Veritas particles is similar to that of the zodiacal cloud suggests that similar processes shaped these particle populations. We estimate that there are [approximately equal to] 5 x [10.sup.24] Karin and [approximately equal to] [10.sup.25] Veritas family particles with D > 30 [micro]m in the Solar System today. The IRAS observation of the dust bands may be satisfactorily modeled using 'averaged' SFDs that are constant with semimajor axis. These SFDs are best described by a broken power-law function with differential power index [alpha] [approximately equal to] 2.1-2.4 for D [??] 100 [micro]m and by [alpha] [??] 3.5 for 100 [micro]m [??] D [less than or equal to] 1 cm. The total cross-sectional surface area of Veritas particles is a factor of [approximately equal to] 2 larger than the surface area of the particles producing the inner dust bands. The total volumes in Karin and Veritas family particles with 1 [micro]m < D < 1 cm correspond to D = 11 km and D = 14 km asteroids with equivalent masses [approximately equal to] 1.5 x [10.sup.18] g and [approximately equal to] 3.0 x [10.sup.18] g, respectively (assuming 2 g [cm.sup.-3] bulk density). If the size-frequency and radial distribution of particles in the zodiacal cloud were similar to those in the asteroid dust bands, we estimate that the zodiacal cloud represents ~3 x [10.sup.19] g of material (in particles with 1 [micro]m< D < 1 cm) at [+ or -] 10[degrees] around the ecliptic and perhaps as much as ~[10.sup.20] g in total. The later number corresponds to about a 23-km-radius sphere with 2 g [cm.sup.-3] density. Keywords: Zodiacal light; Infrared observations; Meteoroids; Asteroids; Collisional physics

Space infrared nulling interferometry has been identified as one of the most promising techniques for direct detection of Earthlike extrasolar planets and spectroscopic analysis of their atmospheres in the near future. After a review of various hulling interferometer schemes, we introduce the concept of internal modulation. As an illustration, we describe a two-dimensional array of telescopes that provides full internal modulation capabilities: the Mariotti space interferometer. It consists of six free-flying telescopes positioned on the sides of an equilateral triangle and grouped into three hulling intefferometers. Their hulled outputs are suitably phase-shifted with respect to each other, coherently recombined, and detected. The phase shifts applied between the nullers are periodically changed, providing signal modulation at a frequency that can be selected to minimize instrumental and background noise. The frequency upper limit is set by the read-out noise of the detectors, and turns out to be [10.sup.-1]-[10.sup.-2] Hz for currently available Si:As BIB devices. This 'fast' signal modulation allows much better monitoring of the background and detector drifts than when one relies solely on the external modulation provided by the slow rotation of the whole interferometer (at typical frequencies of 3 x [10.sup.-4]-3 x [10.sup.-5] Hz). Mariotti internal modulation, also known as 'phase chopping,' thus appears as a major step toward the feasibility of the Darwin and TPF space missions. Keywords: Extra-solar planetary systems; Instrumentation: Infrared observations; Zodiacal light; Atmospheric spectroscopy

The position and shape of the Gegenschein's maximum brightness provide information on the structure of the interplanetary dust cloud. We show that the asteroidal dust bands, extended near the anti-solar point, play an important role in determining both the position of the maximum brightness and the shape of the Gegenschein. After removing the asteroidal dust bands from an observation of the Gegenschein on November 2, 1997, it was found that the maximum brightness point shifted -0.4[degrees] in ecliptic latitude, i.e., to the south of the ecliptic plane, at an ecliptic longitude of 180[degrees], in contrast to a latitude value of +0.1[degrees] when the dust bands were included. Furthermore, the part of the Gegenschein to the south of the ecliptic plane was brighter than the northern part at the time of observation. Referring to the cloud model of T. Kelsall et al. (1998, Astrophy. J. 508, 44-73), it can be estimated that the ascending node of the symmetry plane of the dust cloud is [57[degrees].sup.7[degrees].sub.3[degrees]] when its inclination is 2.03[degrees] [+ or -] 0.50[degrees]. Keywords: Asteroids; Dust bands; Zodiacal light; Gegenschein