* Astronomy

Members Login
Post Info TOPIC: Carbonaceous Micrometeorites


L

Posts: 131433
Date:
Zodiacal Light
Permalink  
 


Zodiacal light is a faint, roughly triangular, whitish glow seen in the night sky which appears to extend up from the vicinity of the sun along the ecliptic  or zodiac. Caused by sunlight scattered by space dust, it is so faint that either moonlight  or light pollution renders it invisible. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band completely around the ecliptic.
Read more

__________________


L

Posts: 131433
Date:
Carbonaceous Micrometeorites
Permalink  
 


Title: Cometary Origin of the Zodiacal Cloud and Carbonaceous Micrometeorites
Authors: David Nesvorny, Peter Jenniskens, Harold F. Levison, William F. Bottke, David Vokrouhlicky
(Version v2)

The zodiacal cloud is a thick circumsolar disk of small debris particles produced by asteroid collisions and comets. Here, we present a zodiacal cloud model based on the orbital properties and lifetimes of comets and asteroids, and on the dynamical evolution of dust after ejection. The model is quantitatively constrained by IRAS observations of thermal emission, but also qualitatively consistent with other zodiacal cloud observations. We find that 85-95% of the observed mid-infrared emission is produced by particles from the Jupiter-family comets (JFCs) and <10% by dust from long period comets. Asteroidal dust is found to be present at <10%. We suggest that spontaneous disruptions of JFCs, rather than the usual cometary activity driven by sublimating volatiles, is the main mechanism that librates cometary particles into the zodiacal cloud. Our results imply that JFC particles represent ~85% of the total mass influx at Earth. Since their atmospheric entry speeds are typically low (\approx 14.5 km s^{-1} mean for D=100-200 \mu m with \approx 12 km s^{-1} being the most common case), many JFC grains should survive frictional heating and land on the Earth's surface. This explains why most micrometeorites collected in Antarctic ice have primitive carbonaceous composition. The present mass of the inner zodiacal cloud at <5 AU is estimated to be 1-2 x 10^{19} g, mainly in D=100-200 \mu m particles. The inner zodiacal cloud should have been >10^4 times brighter during the Late Heavy Bombardment (LHB) epoch \approx 3.8 Gyr ago, when the outer planets scattered numerous comets into the inner solar system. The bright debris disks with a large 24-\mu m excess observed around mature stars may be an indication of massive cometary populations existing in those systems.

Read more (206kb, PDF)

__________________
Page 1 of 1  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard