Mars Section Report No. 1

To 1996 November 1

General

By November 1 a few dozen early observations commencing August 4 had reached the BAA. The disk diameter increased from 4”.2 to 5”.4. I include published OAA data (CMO #179–180) for comparison.

North Polar Region

Large hood to J. Warell (36cm OG) August 4 (Ls = 348 deg.), clearing by September 17 (Ls =10 deg.) to reveal the well-defined N. polar cap, at least under CML = 288 deg. Little visibleshrinkage of cap by October 3 (Ls = 18 deg.). R. Schmude (51cm refl.) on August 14 saw thehood to be visible in blue, but not in orange light. D. Niechoy (20cm refl.) August 19–26 confirmed large bright area in NPR, appearing wavelength-dependent. M. Minami and T. Nakajima (Oriental AS; 20cm OG) on September 10 considered the (‘not so evident’) brighterarea to the N. was still the hood. A CCD image by D.C. Parker (41cm refl.) on September 18 showed the cap in red light but the overlying hood in blue light: the latter reached a lower latitude on the morning side, partly covering M. Acidalium and Tempe under CML = 18 deg. OAA observations on October 5 showed only the ground cap at the same CML. [Thus the hood had cleared at CML = 288 deg. by September 17, but did not clear till later at some other CML.]

Surface features

The smallness of the disk has not yet revealed differences in appearance from 1994–95 (see R.J. McKim, J. Brit. Astron. Assoc., 105, 157–158 (1995)) or 1992–93 (ibid, 105, 117–134 (1995)). Syrtis Major is broad and blunt to the north, Utopia–Casius typical of the last decade, Mare Serpentis darker than the Syrtis (Warell September 17), Solis Lacus visible with difficulty to the south. The surroundings of the NPC, including Mare Boreum, are dark. Other features detected include Mare Acidalium, Mare Sirenum, Mare Cimmerium, Mare Tyrrhenum, Sinus Sabaeus and Phlegra/Styx.

Dust storms (yellow clouds)

HST imaged small storm N. of Propontis I, September 18 (70 deg., 160–200 deg.); OAA observers could watch same CML but did not see storm due to smallness of martian disk. Extent of storm suggests it was already a few days old, [Observations in 1992–93 (McKim, op. cit.) revealed a local storm starting over Cebrenia–Elysium, just NE of the HST event, at a somewhat later season (Ls = 39 deg.) Ebisawa (Mem. Plan. Res. Obs., No. 1, Tokyo (1996) reported polarimetric data on further events in this area during 1994–95.]

White clouds

A general morning limb haze has been noticed, appearing brighter in green and blue light. The following observations (apparently seasonally normal) are very incomplete in temporal and longitudinal coverage: discrete morning cloud, brighter in blue light, detected over the Elysium region by Niechoy (August 26) andSchmude (September 6); Hellas lightish near the CM (OAA September 7, 10, October 12; Warell September 17), Argyre I light along the S. limb (OAA, September 27–0ctober 2); evening cloud, brighter in blue light, over Amazonis and Memnonia to Warell (September 25), over Tharsis to OAA observers (September 18), and around Nox Lux (SW Tractus Albus, near Phoenicus Lacus) to Schmude (October 12). [Activity is expected to increase as the NPC evaporates (its regression is swifter after Ls approx. 50 deg., e.g., from 1996 December).]

Richard McKim, Director

1996 November 4