The excess of helium 3 in 8.2 million-year-old sediments, from two sites, indicating that the accretion rate of interplanetary dust suddenly increased by a factor of about 4 and then decreased over about 1.5 million years to pre-event levels.
Researchers have found cosmic dust in ocean sediments that indicate the Earth was enveloped in the debris of an asteroidal collision 8.27 million years ago.
The break-up of a large asteroid caused the biggest cosmic dust storm in the last 80 million years and left a blanket of material on the Earth that may have cooled it by about 0.7°C over a period of 1.5 million years.
The researchers reached their conclusion after tracing back to a common origin the orbits of family of 300 asteroids, and the finding of the extraterrestrial element helium-3 in ocean sediments. Computer models show that the Asteroids were once part of a larger asteroid, dubbed Veritas about 160 kilometres wide, orbiting in the asteroid belt, that broke up – possibly in a collision, 8.3 million years ago. In the January 19 2006 issue of the journal Nature, the scientists report a spike in helium 3 in a layer of sediment dated to that time frame. The event would have created vast amounts of dust, some of which would have been scooped up by our planet. The Veritas Family is located in the outer part of the main belt with an average proper semimajor axis of about 3.17 AU.
"The helium 3 spike found in these sediments is the smoking gun that something quite dramatic happened to the interplanetary dust population 8.2 million years ago. It's one of the biggest dust events of the last 80 million years" - Ken Farley, Caltech geochemist.
Today, about 20,000 tons of interplanetary dust lands on Earth every year. While in space, it picks up helium 3 from the solar wind. At the peak of the ancient shower, about five times as much probably fell on Earth. The dust particles make up much less than less than one part per million of terrestrial sediments. Farley and his colleagues studied sediment from beneath the Indian Ocean and the Atlantic, showing that the same event was recorded at two widely separated locations.
"While asteroids are constantly crashing into one another in the main asteroid belt, only once in a great while does an extremely large one shatter" - William Bottke, Southwest Research Institute.
Title: Recent Origin of the Solar System Dust Bands Authors: Nesvorný, David; Bottke, William F.; Levison, Harold F.; Dones, Luke
Abstract Infrared Astronomical Satellite (IRAS) observations in 1983 revealed the existence of several solar system dust bands. These dust bands are believed to be debris produced by recent disruption events among main-belt asteroids, particularly because dust particles have short dynamical and collisional lifetimes. Using young asteroid families as tracers of recent disruptions in the main belt, we linked the most prominent IRAS dust bands with their sources. We propose that the source regions of the dust bands with inclination 9.35d and 2.1d are the Veritas asteroid family at 3.17 AU and the Karin cluster located inside the Koronis asteroid family at 2.865 AU, respectively. The Veritas family and the Karin cluster formed by collisional disruptions of their ~140 and ~25 km diameter parent bodies at 8.3±0.5 and 5.8±0.2 Myr ago, respectively. Asteroid material from the former source may represent about one-quarter of the interplanetary dust particles that have been collected in the Earth's stratosphere (and that have been extensively studied in laboratories). We were unable to identify a recent collision in the main-belt region that could be responsible for the 1.4d IRAS dust band. The region of the Themis family remains the best candidate for this dust band. We speculate that the (4652) Iannini cluster (~5 Myr old, ~12° inclination) is the source for the J/K dust band and that the (1521) Seinajoki cluster (~15° inclination) is the ultimate source for the M/N dust band. We point out that the dust bands' spatial distributions are consistent with our proposed sources. This, and the fact that many prominent but ancient asteroid families have no associated dust bands, strongly suggests that dust bands are primarily by-products of recent asteroid break-up events that occur throughout the main belt.
