Atmospheric Losses Under Dust Bombardment in the Ancient Atmospheres

Authors: Pavlov A.K.¹; Pavlov A.A.²

Source: Earth, Moon, and Planets, Volume 76, Number 3, 1997 , pp. 157-183(27)

Publisher: Springer

Abstract:

We have considered the new process of atmospheric losses – ``sputtering'' under bombardment by interplanetary dust. It is demonstrated that ``sputtering'' due to collisions with the interplanetary dust is an effective way of atmospheric gas loss (10^-4–10^-3 of the dust particles' accreting mass) and that it changes the composition of the atmospheric gases.

In calculations we have taken that the dust particles collide elastically with the atoms and molecules of the atmosphere. Estimation of the effects of inelastic collisions was also considered. As a result of these collisions a part of the atmospheric atoms and molecules will have ``upward'' velocity and enough energy to escape. It was considered that escaping atoms can collide with the atoms of the ``main'' gas of the upper atmosphere.

The atmospheric gas composition is assumed to be just as in the modern Martian atmosphere – the ``main'' gases in the upper atmosphere were taken to be O and CO_2.

In our computations we pay particular attention to the abundance of noble gases in planetary atmospheres since these gases are very important for theories of atmospheric origin.

We computed that under ``sputtering'' by the interplanetary dust, atmospheres were enriched by the ``heavy'' elements and isotopes in the wide range of the upper atmospheric parameters O/CO_2, T/g (O/CO_2 – on the level of homosphere; T is temperature of the exosphere, g is gravitational acceleration).

However the loss efficiency for ``heavy'' gases is relatively high compared to other known gas loss processes. In the case of noble gases for the specific parameters of the upper atmosphere (small T/g ratio; high O/CO_2 on the level of homosphere) we have got the unique result: despite the diffusion separation in the upper atmosphere the loss efficiency of Xe > Kr > Ar.

The effect of ``sputtering'' of the planetary atmospheres was strongest during the early stages of the planetary evolution – when the rate of the dust accretion was intrinsically higher than now because of collisions of planetesimals. In light of the new escape process, the main peculiarities of the noble gases abundance in the planetary atmospheres could be explained.

Language: English

Document Type: Regular paper

Affiliations: 1: Ioffe Physical Technical Institute, Russian Academy of Sciences; Polytechnicheskaya st. 26; St. Petersburg 194021, Russia; E-mail : pavlov@nspl.ioffe.rssi.ru; Fax: +7 (812) 247 91 67 2: Faculty of Physical Science and Engineering, Department of Space Physics, St. Petersburg State Technical University, Polytechnicheskaya st. 29, St. Petersburg 195251, Russia

Publication date: 1997-01-01

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