科研之友
微信
新浪微博
Facebook
分享链接
摘要
The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving at the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer (greater than or similar to 10(5) yr at 1 AU) than postulated in the standard collisional models (similar to 10(4) yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5) x 10(11) km(2) and similar to 4 x 10(19) g, respectively, in a good agreement with previous studies. The mass input required to keep the zodiacal cloud in a steady state is estimated to be similar to 10(4)-10(5) kg s(-1). The input is up to similar to 10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes and need to be supplied at a faster rate. The totalmass accreted by the Earth in particles between diameters D = 5 mu m and 1 cm is found to be similar to 15,000 tons yr(-1) (factor of two uncertainty), which is a large share of the accretion flux measured by the Long Term Duration Facility. The majority of JFC particles plunge into the upper atmosphere at <15 km s(-1) speeds, should survive the atmospheric entry, and can produce micrometeorite falls. This could explain the compositional similarity of samples collected in the Antarctic ice and stratosphere, and those brought from comet Wild 2 by the Stardust spacecraft. Meteor radars such as CMOR and AMOR see only a fraction of the accretion flux (similar to 1%-10% and similar to 10%-50%, respectively), because small particles impacting at low speeds produce ionization levels that are below these radars' detection capabilities.
- 出版日期2011-12-20
