Looking at Mars with the MRO CTX
Posted by Ken Edgett
29-05-2009 12:21 CDT
by Ken Edgett
My time at work is largely divided into three parts: supporting the on-going Mars Reconnaissance Orbiter (MRO) mission, helping to prepare for the upcoming Mars Science Laboratory (MSL, Curiosity) rover mission, and contributing to a lengthy "final report" on the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) investigation. Some weeks, one or the other of these activities may dominate my time, and other weeks, I may be working on proposals for future work. Today, my mind is on MRO.
At Malin Space Science Systems, we are operating two of MRO's cameras -- the Mars Color Imager (MARCI) and the Context Camera (CTX). The MARCI provides daily global views of the planet's weather. Malin Space Science Systems (MSSS) releases a weekly review of the weather here: http://www.msss.com/msss_images/latest_weather.html. The data from MARCI also provide 5-band color spectra at about 1 kilometer per pixel scale, track the coming and going of the seasonal polar caps and changes in albedo patterns, and observe Mars in the ultraviolet to examine daily changes in atmospheric ozone and water vapor distribution.
The other camera, CTX, acquires grayscale images that typically cover an area 30 kilometers wide by up to 313 kilometers long at 6 meters per pixel.
Using CTX, we have imaged about 42% of Mars at full resolution. One might think that, since we've done 42% of Mars since late September 2006, we should be able to cover 100% by sometime in 2013. But full coverage of the planet at 6 meters per pixel is not a current objective of the CTX investigation. The reason: we also like to repeat things. Repeated coverage allows us to obtain stereo pairs and monitor selected areas to see if things are changing. In addition, some repeated coverage is inevitable when you're trying to build up a mosaic of an area -- you want the edges of the images to overlap a bit.
So, what are we doing with CTX?
As the name implies, the first objective of CTX is to provide context for the data being acquired by the other instruments aboard MRO. In particular, we often acquire images at the same time that the HiRISE and CRISM are taking data. HiRISE (High Resolution Imaging Science Experiment) can see objects of about a meter or two across, and CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) is the near-infrared spectral imager which is providing many new clues about minerals on the martian surface. The CTX images allow investigators using HiRISE and CRISM to extend what they learn from those data to the larger areas covered by the wider field of view of the CTX.
We also use CTX to suggest targets for the HiRISE and CRISM teams to image. Each science team selects targets for their instrument on a bi-weekly basis. When we are targeting CTX, sometimes we find that we're going to be able to image something that we think the HiRISE and/or the CRISM instruments should also look at. We target a CTX image to that location, and then we ask the HiRISE and CRISM teams to "ride along" with us so that there will be a nice set of simultaneous observations.
In addition to working with the other instruments on MRO to ensure an exciting and high quality data set, we also are using CTX to investigate Mars in a more general sense. We have made 6 meter per pixel mosaics of huge regions, including both residual polar caps and most of the Valles Marineris (we're still trying to finish that one!). We are also monitoring many regions to look for changes -- new impact craters, changes in mid-latitude gullies, dust devil and wind streaks, defrosting of the seasonal polar caps, and so forth. In addition, we like taking stereo pair images, as you can see from the anaglyphs presented with this article. :-)
Everything we do is geared toward testing some scientific hypothesis. Every time we find something new and interesting, we ask ourselves what other images can we obtain to help test our ideas about that thing? Some of these efforts take a long time