Una nube insolita sul terminatore marziano

[Acronauta]

Questa fa il paio con le macchie che stanno apparendo su Giove....

Richard McKim, direttore della Mars Section BAA, ha diramato il seguente bollettino (ne riporto solo gli stralci più significativi):

"An unusually high cloud at the martian morning terminator has been spotted on amateur webcam images taken during 2012 March 19-21 [...] it appeared as a nearly detached cloud lying along the terminator, anchored at the S. end. The cloud was visible in red, green and blue images, so it would seem that suspended dust is involved. There are doubtless many other images of this feature in the Director’s unopened emails and posted on various websites, but it seemed more important to send out this alert now, before trying to assess them all. Certainly there are other records of a small feature in the same location captured by many European observers some ten days earlier, but its sudden increase in size on March 20 and 21 (Ls = 85-86) was really remarkable. Marc Delcroix recorded it on March 12 (CM = 152-155), for example. He has measured the images of Mar 20 to obtain a current position of lat. -45, long. 193, placing it at the border between Electris and Eridania.

Terminator projections due to both white cloud and suspended dust have been reported by many past observers, particularly when using large telescopes visually, and when the planet was close to quadrature so that the phase defect was at a maximum. It is therefore unusual for such a prominent projection to be visible just weeks after opposition, though the direction of maximum phase defect does lay within the S. following quadrant of the planet’s disk as we can see from the ephemeris for P (the position angle of the aerographic N. pole) and Q (the position angle of the greatest defect of illumination) from the BAA Handbook:

Date P Q
2012 Mar 14 16 128
2012 Mar 24 14 119

Recall that position angle is measured eastwards from the north point.

Terminator projections due to dust activity have been described at some length in the BAA report on the 2003 opposition, for example, which is readily available as a pdf document at our website:

http://www.britastro.org/mars

[...] Given that there exist previous observations of terminator projections at this location it is very unlikely that they have arisen as the result of planetoidal impact, although there has already been some discussion of this possibility on the internet. [...]

Observers are requested to scrutinise the region carefully [...]."

Alcune immagini si possono vedere seguendo questi link:

http://www.astrosurf.com/planetessaf/ma ... UT-DPa.jpg
http://exosky.net/exosky/?p=1606