* Astronomy

Blobrana · L

RE: Comet impacts

Blobrana · L

Cometary airbursts

Blobrana · L

RE: Comet impacts

Blobrana · L

Kansas scientists probe mysterious possible comet strikes on Earth

It's the stuff of a Hollywood disaster epic: A comet plunges from outer space into the Earth's atmosphere, splitting the sky with a devastating shock wave that flattens forests and shakes the countryside.
But this isn't a disaster movie plotline.
An investigation by Melott and colleagues reveals a promising new method of detecting past comet strikes upon Earth and gauging their frequency. The results will be unveiled at the American Geophysical Union's Autumn Meeting, to be held Dec. 14-18 in San Francisco.
Read more

Younger Dryas Impact

Blobrana · L

Title: Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event
Authors: Adrian L. Melott (Kansas), Brian C. Thomas (Washburn), Gisela Dreschhoff (Kansas), Carey K. Johnson (Kansas)
(Version v3)

We find agreement between models of atmospheric chemistry changes from ionisation for the 1908 Tunguska airburst event and nitrate enhancement in GISP2H and GISP2 ice cores, plus an unexplained ammonium spike. We then consider a candidate cometary impact at the Younger Dryas onset (YD). The large estimated NO_x production and O_3 depletion are beyond accurate extrapolation, but the ice core peak is much lower, possibly because of insufficient sampling resolution. Ammonium and nitrate spikes have been attributed to biomass burning at YD onset in both GRIP and GISP2 ice cores. A similar result is well-resolved in Tunguska ice core data, but that forest fire was far too small to account for this. Direct input of ammonia from a comet into the atmosphere is adequate for YD ice core data, but not Tunguska data. An analogy of the Haber process with hydrogen contributed by cometary or surface water, atmospheric nitrogen, high pressures, and possibly catalytic iron from a comet could in principle produce ammonia, accounting for the peaks in both data sets.

Read more (140kb, PDF)

Blobrana · L

An investigation by Adrian Melott, professor of physics and astronomy at the University of Kansas, and colleagues reveals a promising new method of detecting past comet strikes upon Earth and gauging their frequency. The results will be unveiled at the American Geophysical Union's Fall Meeting, to be held Dec. 14-18 in San Francisco.

"Comet impacts might be much more frequent than we expect. There's a lot of interest in the rate of impact events upon the Earth. We really don't know the rate very well because most craters end up being destroyed by erosion or the comets go into the ocean and we don't know that they're there. We really don't have a good handle on the rate of impacts on the Earth" - Adrian Melott, professor of physics and astronomy at the University of Kansas.

The research shows a potential signature of nitrate and ammonia that can be found in ice cores corresponding to suspected impacts. Although high nitrate levels previously have been tied to space impacts, scientists have never before seen atmospheric ammonia spikes as indicators of space impacts with our planet.

"Now we have a possible new marker for extraterrestrial events in ice. You don't just look for nitrates, you also look for ammonia."

Melott studied two possible cometary airbursts with Brian Thomas, assistant professor of physics and astronomy at Washburn University, Gisela Dreschhoff, KU adjunct associate professor of physics and astronomy, and Carey Johnson, KU professor of chemistry.

Source: University of Kansas