LtE in CMO #247,248

From  William SHEEHAN

@. . . . . . . . . Hope you will forgive the intrusion -- I know you are very busy, but I wanted to pass along my greetings and to thank you for the interest in the Edom flare top which Tom Dobbins and I were able to call the advance attention of the astronomical world, and which Tom and his team of observers were able to verify successfully from the Florida Keys.  It was also a great thrill to see the observations of Saheki and other leading Japanese observers confirmed --  Tom has mentioned that you even had a suspicion of a brightening at Edom in 1954 yourself.  This is a region that will repay close study and I'm not sure even now that we understand it.

 

   I have the greatest respect and admiration for your wonderful work on Mars and that of your colleagues at the OAA.  It will be a privilege if we have the opportunity to meet up sometime.

 

   Meanwhile, I am awaiting word of your observations of Edom now that the critical longitudes are placed in view of yourself and other skilled observers in Japan.

 

   Incidentally, I would be very happy to send you a copy of my Mars books – “The Planet Mars”, published by U of Arizona Press, 1996, and “Mars: the Lure of the Red Planet” (with Stephen James O'Meara), just published, in the event they may be of interest to you and your colleagues.    They do not contain any information about the Edom flares, alas, but may contain other backgrounds about the planet of our predilection.

 

   Kind regards,

 (24 June 2001 email)

@. . . . . . . . . . Dear Masatsugu,

  I sent Tom's images of Edom to Andy Young, a photometry expert at San Diego State U.  His comments follow.

   Kind regards,

    Bill

------------------------------------------

Well!  Isn't that something?  Thanks for sending those pictures -- they
certainly are remarkable.

To begin with, I note that the "flash" is clearly an unresolved
instrumental point-spread function; you can see it's a little broader
on the frame where the seeing is a little fuzzier.  So it's clearly
something on Mars and not some kind of instrumental artifact.

From the contrasty images, I assume these were taken at some fairly
long wavelength in the deep red, though the lack of limb-darkening is
surprising -- can you supply information about the passband used?  And
what was the phase angle?  What kind of processing has been applied to
the image?

The bright spot seems brighter than anything else on Mars, but not by
more than a factor of 2.  So the average brightness of the PSF is about
that of a light gray (say, "white") piece of paper the same size.  As
this is roughly 10^5 times dimmer than an image of the Sun, we can
assume that only something like 10^(-5) of the area is filled by
reflecting objects if they reflect like a perfect mirror.  If they are
ice crystals or mica flakes with a reflection on the order of 10%, then
about 0.01% of the area of the PSF is filled with them.  The PSF is
about 1/20 of the diameter of the planet, so if all the reflectors are
together in a coherent area (unlikely) this area is about 1/20 x 1/100
of the diameter of Mars across, or 1/2000 of 6800 km, or about 3 or 4
km across (assuming ice or mica).  If the reflectors are more spread
out, the peculiar area on Mars is somewhat larger, but of course no
larger than the projected PSF of about 340 km diameter.

These sizes sound about like the diameter of a medium-sized impact
crater; it may turn out to be a funny-looking crater floor?

In the old days we would gladly have read this as the leaves of some
Martian heliotrope-field blowing in the wind; but such an
interpretation today seems highly unlikely.  The most pressing problem
is to understand the short timescale -- much less than the time
required for the solar image to pass across a stationary reflecting
surface.  So salt flats with well-developed crystal faces, and frost on
the ground, are not possible interpretations.  I would be inclined to
favor some temporary alignment of crystals suspended in the air; but
then the problem is to tilt them synchronously over such a large area,
to make the "flash" wink on and off coherently.

Perhaps a Martian geyser is erupting here, and its plume is turning to
ice crystals in a few seconds.  But then it's hard to get the crystals
to grow large enough to have well-developed faces, needed to give the
desired directionality to the reflection.  If it were simply a steam
plume from geothermal -- er, areothermal -- activity, then how do we
get it to cover such a large area (now we are talking about a temporary
white spot some 100 km or more across) and yet to disappear again in a
minute or so?

Might we be dealing with a dust cloud stirred by a major Marsquake?
This might account for the timescale: seismic waves travel a few
km/sec, so in 10 sec or se we can easily shake an area large enough to
make the bright spot.  If the dust is merely stirred a few meters into
the air, it can fall out again on a similar time scale.  Ask the
geologists if the terrain suggest earthquake country.

My own inclination is to favor some such widespread brightening of the
surface, rather than a localized glint of Sun on moving surfaces.  But if
the brightening is mild and spread over many tens or a few hundred km,
a mechanism is needed to synchronize the display over that region, and I
think the speed of sound on Mars (about 200 m/sec) is a bit slow to
accomplish this with an atmospheric driver.  If the phenomenon is
basically atmospheric, then we need something that can appear and
disappear in a few tens of seconds at most.  A steam vent doesn't look
promising at first glance, but maybe there is a way to make it serve.

A very remote possibility is a specular reflection from something in
orbit around Mars.  The problem then is that it has to be over a
kilometer across, and tumbling enough to account for the temporal
modulation.  But then why hadn't it been noticed before, and why hadn't
the physical librations been damped out?

You certainly have a puzzler here!

  -- Andy

(26 June 2001 email)

 

@. . . . . . . . . Wonderful to have your kind comments and to read of your interest in my previous book, “The Planet Mars”.  It shall be a signal honor for me to send you copies of both of these books, with my added inscriptions.  It would be a tremendous satisfaction for me.

 

   I have reread your comments about the 1954 observations and apologize for not comprehending them fully at first -- they are perfectly clear as you stated them.  I am gratified to learn of your having observed the planet as early as July 1954.

 

   I returned to the comments I had made about Herschel's Mars observations. He made the observations of Mars in 1777 at Datchet, before he moved to Bath.  The later oppositions were observed from the southward-facing garden. I do have a copy of his Mars publication in the Philosophical Transactions of the Royal Society before me, which refers to his various drawings of the planet.  His reference to bright spots -- I am looking at his drawing now -- is to polar patches; but you are right to query this.  It seems he made out the south polar cap and a bit of the cloudy haze which can sometimes be seen at the same time over the north cap.  His drawing is less clear than his inference from it.  Certainly he did observe Mars and some of his beloved double stars on March 13, 1781 -- this would indeed have been *after* he first caught sight of Uranus.  I was fascinated to find out that he proceeded with his routine work so soon after making the amazing discovery -- clearly, at that moment, he did not have any suspicion of what he had found in that fateful patch of sky between M35 and M1.

 

   Herschel's observation on this occasion was made well before opposition.

 

   As for your other points.  I do think the "blue clearing" is really little more than an opposition effect.   E. C. Pickering was the older brother of W. H. Pickering, director of the Harvard College Observatory for many years and a leading spectroscopic student of the stars.  I shall be gratified to try to answer any other questions you may wish to put to me.

 

   Once again, my heartfelt salutations! -- I am honored to be in communication with one of the greatest of living Mars observers, whom I have long admired from afar.  I am impressed also by the high level of accomplishment of Japanese observers of Mars generally.  Perhaps oneday I shall have reason to revise one or the other of the Mars books and include a fuller account of your important work -- ideally after having a chance to meet and discuss Mars with you in Okinawa!

 

    The books go out first thing tomorrow!

 

    Your fellow MARTIAN,

 (25 June 2001 email)

 

@. . . . . . . . . . The books went out yesterday.  Meanwhile, thanks much for the news of the recent dust-storm.  I'll begin to monitor.

 

   Regarding the flashes on Mars, you may find this of interest.  A comment from Walter Haas about Percival Lowell logging thousands of hours and not seeing anything jogged my memory. Now I'm sure you will find this of compelling interest, and we ought to mention it in our paper.  Percival Lowell, in *Mars*, pp. 86-87: "An interesting phenomenon occurred in the cap on June 7, 1894 {Note the date!!-W.S.).  On that morning, at about a quarter of six (or, more precisely, on June 8, 1 h. 17m, G.M.T.), as I was watching the planet, I saw suddenly two points like stars flash out in the midst of the polar cap.  Dazzlingly bright upon the duller white background of the snow, these stars shone for a few moments and then slowly disappeared.  The seeing at the time was very good.  It is at once evident what the other-world apparitions were,--not the fabled signal-lights of Martian folk, but the glint of ice-slopes flashing for a moment earthward as the rotation of the planet turned the slope to the proper angle; just as, in sailing by some glass-windowed house near set of sun, you shall for a moment or two catch a dazzling glint of glory from its panes, which then vanishes as it came.  But though no intelligence lay behind the action of these lights, they were none the less startling for being Nature's own flash-lights across one hundred millions of miles of space.  It had taken them nine minutes to make the journey; nine minutes before they reached Earth they had ceased to be on Mars, and, after their travel of one hundred millions of miles, found to note them but one watcher, alone on a hill-top with the dawn."

(27 June 2001 email)

 

@. . . . . . . . . Won't detain you long -- I'm sure you're unbearably busy.  Have been following your reports of the spreading dust clouds now covering the hemisphere of Mars visible from the Orient. On July 5, I looked with my 12 1/2 cm and 30 cm Schmidt- Cassegrains at 2:30 GST. Mars was near the full Moon and it was striking to compare the two side by side -- the Moon seen with the naked-eye, Mars in the telescope.

The Syrtis Major was clearly visible; the north extension was quite dark, the rest faded. The region extending from Hellas to S. Mare Tyrrhenum/Cimmerium were faded, except the northern fringe. The main cloud was located east of the handle of Syrtis Major and lay over Hesperia; it was a brilliant calotte at the limb, lemony-yellow. The whole hemisphere of the planet appeared as if viewed through gauze.  Very strange!

  Hard to say -- but even with the naked-eye I have thought the planet appears to be more yellow than it seemed in early June before the dust began to make its appearance.

  Hope to make more observations tonight.

 (8 July 2001 email)

 

@ . . . . . . . .We continue to follow the dust storms on the Occidental hemisphere of the planet.  Today I wrote up (for the Astronomical Society of the Pacific's journal *Mercury*) something on the Martian flare observations.  Please comment if you would. Best, 

(9 July 2001 email)

 

@. . . . . . . I have made some changes to the article (The Flare from Mars Seen Round the World) in the light of your fascinating and kindly response.  I know you are highly pressed at the moment -- but I wanted to thank you at once.  Perhaps I shall one day visit Japan -- such places as you describe with so much vigor.  We can observe Mars together!

 

Best wishes,

(10 July 2001 email)

  Bill SHEEHAN  ( MN USA )

sheehans@tds.net

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