New address: Ithaca, (85.2S, 181.4E), Mars
We have recently started showing you data from a new location! Have you noticed?
This new place is called Ithaca. It is located at lat =-85.2, lon = 181.401. Unlike Inca City (our most recent focus), this is a flat area, no considerable slopes are present here. Ithaca is located in the middle of this elevation map:
You see, that the red area has maximum elevation change of less than 80 meters. In the absence of slopes, we can say more confidently that the fans here are result of interaction of dusty CO2 jets with winds and not gravity simply pulling sand downhill. Winds direct dust and sand particles after they are lifted up into the atmosphere by the jets. It is very striking, that the fans look very similar in several consequent years of HiRISE observations. The usual year in Ithaca looks like this:
This is a mini-series of HiRISE images from early spring (a) progressing to late spring via (b) to (c) and finally to (d). Fist images that HiRISE returns each spring show large dark fans with the similar opening angles and similar directionality every year. This tells us that there is few variation in local weather from year to year.
When spring progresses, fans extend, later blue fans appear, and sometimes they take over most of the surface! Like in figure (c) – whole area is blue apart from really dark fans. This is one of the mysteries of Ithaca – we know from spectrometers, that those blue fans are fresh CO2 frost, but how comes fresh frost appears on the sides of the dark fans? Dark surface is warmer when exposed to sunlight and must prevent CO2 from forming there.
Another Ithaca mystery is its fan sizes. Here the fans grow to be huge: you see the scale bar on the first image? That is 100 m and the fans on the figure (d) are 2-3 times that long. It is larger then in most of other polar locations. For example Inca City, that must be familiar to you by now, has fans of only tens of meters. Currently scientist do not have models that is able to explain how such big fans form.
If you carefully compare left and right frames of the figure below, you can see quite some new fans appearing in the right frame.
Scientists would really like to know, how many of those appear each day and how big are they compared to the old fans. In this example new fans look small, but this is only one tiny area from Ithaca. To make a clear statement we really need to count them and outline their sizes. That is why Ithaca is now waiting for you to get marking!