LtE in CMO #262

From Dr Konrad DENNERL

To: <cmo@mars.dti.ne.jp>

Sent: Saturday, June 29, 2002 5:20 PM

Subject: Mars images (letter to Y. Morita)

Dear Sir/Madam,

could you please forward the following letter to

Mr. Yukio Morita ? I could not find his e-mail address.

Many thanks for your help!

Sincerely,

many thanks for your quick and detailed response, and the new set of impressive colour images. I will be happy to include one of MORITA's images in the publication of the X-ray results (unfortunately it will probably be reproduced only in black and white).

Here is some quick information to your questions:

As these were the first successful X-ray observations of Mars ever made, we do not know how its X-ray properties were affected by the dust storm. We have only X-ray data from Mars from 4 July, 11:47 - 21:00 UT, which corresponds to central meridians between 167 and 302 degrees. It seems that on 4 July the dust storm had not yet covered the whole planet and was more or less located to the hemisphere which was rotated to Earth at the beginning of the X-ray observation, while we saw more of the undisturbed side at the end. Interestingly, there is no significant difference in the X-ray flux during the whole observation, which implies that the dust storm had not much influence on the X-ray emission.

It is, however, important to know that the X-ray signal from Mars is extremely faint: only about every two minutes an X-ray photon was recorded from Mars! This very low flux limits the sensitivity of detecting subtle changes in the X-ray emission, which might be correlated with the dust storm (the spatial resolution of the X-ray telescope, orbiting around Earth, is below 1 arcsec, so the main restriction is the low number of photons). It is also important to know that the tenuous Mars atmosphere appears quite dense to soft X-rays, which do not reach heights below about 80 km. So we would see only dust which reaches this height in the atmosphere, and only dust particles which are extremely small, so that they can efficiently scatter (solar) X-rays. The X-ray flux which we observe is predominantly caused by fluorescent scattering of solar X-rays on oxygen atoms in the upper CO₂ Mars atmosphere.

This is the current status. I am still in the process of finishing the analysis and of writing the publication. I will be happy to send you a copy of the manuscript as soon as it is available.

Best wishes,　

(1 July 2002 email)

many thanks for your kind e-mail with the sequence of Mars images from Yukio MORITA. This is a most impressive demonstration of how dramatically the appearance of Mars was changed by the dust storm. These images will in fact be very useful for me.

Thanks again, and best wishes,

(9 July 2002 email)

Konrad DENNERL (Garching, Deutchland)

kod@mpe.mpg.de

Max-Planck-Institut für extraterrestrische Physik

Giessenbachstrasse, D-85748 Garching, Germany

phone: +49-89-30000-3862 fax: +49-89-30000-3569

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