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Merry Fans of Manhattan

Season’s Greetings. From all of the Planet Four team to all of you on Earth and Mars, we wish you a very merry Earth solstice, Happy Holidays, and a very happy new Earth Year.

 

Image credit: NASA/JPL/University of Arizona

Image credit: NASA/JPL/University of Arizona

Another holiday treat released by the HiRISE team this December was a 3-D image or anaglyph of Manhattan taken in November. You can find the full image here.

If you throw your red and blue 3-D glasses on, you should see the troughs of the spiders channels with fans dotting the surface. With these observations planetary scientists can measure depths of the channels and slopes of terrain. These images are created by combining two images of the same location (called a stereo pair) where HiRISE was oriented at different angles to the surface. You can read about the details here.

And if you’re looking for a cocktail for your new year’s party – check out this year’s Zooniverse cocktail list including a Planet Four themed drink (the last door of the Zooniverse’s advent calendar)

Adding Some Red (Planet) to the Holiday Season

Image Credit: NASA/JPL/University of Arizona   (http://www.uahirise.org/ESP_038510_0985 )

Image Credit: NASA/JPL/University of Arizona (http://www.uahirise.org/ESP_038510_0985 )

Adding more red (planet) to this holiday season, another new HiRISE image of Inca City was publicly released by the HiRISE team this month. This is the 6th image from the sequence taken this fall as part of Season 5 of the seasonal monitoring campaign (We’re currently showing images from Season 4 on Planet Four).  The image sequence was released as part of the public vote we organized with the help from our friends on the HiRISE team. You can find the rest of the sequence here.

Spring 5 in Inca City

The HiRISE camera right has been taking observations looking for activity on the Martian South Pole over the past few months as part of the new monitoring season (Season 5). In August, we partnered with the HiRISE team for a public vote to determine which polar region would have its first observation prepared for public release. The region dubbed ‘Inca City’ won. We have a big surprise. Not just one image, but all currently available observations this season of Inca City were publicly released by the HiRISE team. That’s right 5 brand new images of Inca City were recently released! You can find these images at:

(If you’re looking to make your computer more Planet Four-themed, each of the links above have versions of the images formatted to be computer desktop backgrounds.)

Today, we have a post by  Planet Four Principal Investigator Candy Hansen telling tell you more about these observations:

It is southern spring again, and once again we are taking images of our favorite locations. We return to the same sites so that we can study processes from year-to-year. Do spring processes always play out similarly? Or do the occasional dust storms affect when fans appear and the pace of seasonal activities?

This location is known informally as Inca City. As citizens of Planet Four you already know that a seasonal polar cap composed of CO2 ice (dry ice) forms every winter. In the spring the ice sublimates from the top and the bottom of this layer of ice, and under the ice the trapped gas builds up pressure. Eventually a weak spot in the ice ruptures, and the gas escapes, carrying material from the surface with it. The material is deposited on the top surface of the ice, forming the fans and blotches that you have been measuring.

spring5_inca_city

Inca City has distinctive ridges, one of which is shown at the top of this series of cutouts. The first cutout on the left was the first image to be taken after the sun rose, marking the end to polar night. We label time on Mars by “Ls”, which indicates the position of Mars in its orbit. Spring officially starts on Ls = 180, so at Ls = 174 there is very little sunlight. In spite of the small amount of sunlight seasonal activity has already started, and fans can be seen emerging from “spiders”, known formally as “araneiforms”.

These images have not been map-projected yet, so use the black arrow pointing at one of the spiders to orient the same locations from image to image. In the second image from the left, taken about 2 weeks later, you can see that the fan from that spider has become more prominent. In the araneiforms above so much dust has blown out that the individual fans seen in the leftmost image have begun to merge. The ridge is peppered with small spots where the seasonal ice has ruptured (blue arrow). Near the bottom of the second image there are new fans associated with boulders. Below that, at the bottom of the image, four new rupture sites have fans going in multiple directions.

The differences between the second and third images from the left are not substantial. That is because the time difference between the two is just 6 days, or “sols”. Fans on the ridge have lengthened just a bit, possibly due to fine material sliding downslope. In the fourth image from the left, taken at Ls = 191, the fans covering the araneiforms and on the ridge slope appear grey – are fine particles sinking into the ice? At the bottom of the image distinctive bright bluish fans are apparent.

Look at the boxed area in the 5th image and compare it to that same area in the 4th image, just below the indicated spider. The bland surface in the 4th image is now cracked. Polygonal cracks typically occur at this time in the spring. There are no easily-ruptured weak spots, so the pressure of the gas below the ice simply cracks the large plate of ice. The ice must have thinned to the point at which this pressure can break the ice sheet. Once it has cracked the gas escapes and new fans emerge, aligned along the cracks.

The ice has continued to thin by the time of the 6th image, and the araneiforms have likely defrosted entirely. More small fans emerge from cracks in the ice.

That’s not Mars!

Credit: NASA/JPL/University of Arizona

Credit: NASA/JPL/University of Arizona

The image above taken by HiRISE isn’t of the South Pole of Mars or any region on Mars for that matter. It’s an interloper from the Oort cloud (reservoir of the long period comets) coming in for a close encounter to Mars on its way into the inner Solar System for its closet approach to the Sun. This icy planetesimal originated in the Oort cloud and was perturbed onto an orbit that has slowly brought it into the inner Solar System and on a path that brings the comet close to Mars. So close in fact (87,000 miles away from Mars) that this is closer than any comet has come to Earth since the dawn of modern astronomy. This provided a rare opportunity to study this icy remnant of planet formation up close and personal with the flotilla of spacecraft orbiting Mars.

HiRISE, is the highest resolution camera sent to to the Red Planet, and the images you see on Planet Four come from it. HiRISE is designed to taken observations staring below at Mars. It’s a push broom camera so it’s using the motion of the spacecraft (Mars Reconnaissance Orbiter, MRO) its aboard  to create the image. To observe a comet requires a whole different way of observing using MRO to point and slew to target the comet. This was no easy feat but the HiRISE team accomplished it, taking images of the comet several days before and shortly before cloest encounter. During the closest part MRO was behind Mars to shield it and its instruments (including HiRISE) from the large amounts of dust entering the Martian atmosphere and could possibly damage or destroy the onboard instruments. This is likely the best optical image of Comet C/2013 A1 Siding Spring, we’ll have. It may look blurry and span only  a few pixels, but observations like this will significantly constrain the size of the nucleus. Congratulations to everyone involved for making these challenging observations successful.

This is the only the second comet imaged by HiRISE. HiRISE has tried this previously observing Comet ISON, a sun-grazing comet that broke up shortly before or during its encounter with the Sun. HiRISE imaged ISON’s nucleus and was able to put the best size constraints on the comet (better than the limits from the Hubble Space Telescope), that placed it around 1 km or smaller. With that size, ISON would be predicted not to survive matching the observations. The cool thing about both Siding Spring and ISON is that these comets were discovered with at least a year’s notice before their closest approach giving astronomers and planetary scientists time to apply for telescope time and mobilize resources (including spacecraft orbiting Mars!) to observe these elusive objects.

You can read more about these HiRISE observations here and here.  If you’re interested in hearing more about observations like this get undertaken by HiRISE and the team behind the camera check out this Planet Four Live Chat where we had discussing the preparations for the Comet ISON imaging with Kristin Block  and Christian Schaller. For a summary of all the Comet Siding Spring observations taken by the spacecraft orbiting Mars check out this blog by the Planetary Society’s Emily Lakdawalla.

An Introduction to HiRISE

Today we have a guest post from Chuhong Mai, an undergraduate student working on Planet Four this summer as part of the ASIAA Summer Student Program.

By now, you may have helped the Planet Four team classified hundreds of thousands of cutouts produced from HiRISE season 1 to 3 products, and you may have voted for a region target for HiRISE to be observe in season 5, however, but how well do you know about this camera that makes the whole Planet Four project possible? And that’s what this blog post is going to talk about.

The High Resolution Imaging Science Experiment (HiRISE) camera is carried on the Mars Reconnaissance Orbiter (MRO) spacecraft and since the spacecraft entered Mars orbit in 2006, HiRISE has produced a large amount of beautiful images in unprecedented detail. It was in a 2-year Primary Science Phase (PSP) during 2006 and 2007, corresponding to season 1 in Planet Four project. Later, it had two 2-year Extended Science Phases (ESP) in 2008-2009 (season 2) and 2010-2011 (season 3). HiRISE continues today to operate under an extended mission taking images of unprecedented detail. So if you notice the images’ names (not the cutouts’ names), you’ll find all of them begin with PSP or ESP, which indicates the mission phase HiRISE were in when a certain picture was taken. The rest of their names tell you some other information of HiRISE’s orbit.

The HiRISE camera mainly consists of a telescope with 50 cm diameter and a focal plane system right behind it. This plane might be one of the most important parts of HiRISE since 14 CCD detectors are installed on it, each with 2 separated output channels and 2048 pixels. 10 of these CCDs are for the Red band (RED0 to RED9), 2 are for the Infrared (IR) band (IR10, IR11) and the rest 2 are for the Blue-Green (BG) band (BG12, BG13). They overlap each other by around 48 pixels. Their positions are shown in Fig.1. So as you see, the red band will cover a much wider range (5.0-6.4 km wide) of Mars surface than the other two bands, but only RED4 and RED5, which locate at the center, can cooperate with IR and BG band to generate color products (1.0-1.3 km wide). The HiRISE team also use Time Delay Integration (TDI) to increase SNR (Signal-Noise Ratio). The basic idea of TDI is to image the same small patch of surface many times and add up together to improve SNR. Different numbers of TDI lines (8, 32, 64, 128) are used under different conditions. In addition, six pixel binning modes can be used to increase coverage and SNR, either. Click here to learn more about how binning works. On the whole, HiRISE is able to reach a high resolution: 0.25m/pixel with low SNR exceeding 100:1. This makes sub-meter surface study of Mars possible.

The three bands are selected to differentiate a broad classes of surface materials like bedrocks, frost or ice, sand, dust and other minerals and to avoid ambiguities between shades and different materials, which is often the case in grayscale products. Typically, frost and ice appear bright white and blue, sand and rocks appear bluer and darker, while the dust are the reddest material in these images. Therefore, with these bands combined together, a final color product you see are usually not a true-color images (like what you see through naked eyes), it is either an IRB product, which combines the 3 bands mentioned above, or a RGB product, which combines the Red, BG and synthetic blue band. The latter one is used by Planet Four to make cutouts for you, as RGB images usually do better in contrasting RED with BG color variations. Note again that these images are false-color products and the true Mars surface appear relatively bland and red. Sorry about that because how beautiful these cutouts are!

fig1

Fig 1. Schematic of the focal plane system on HiRISE (from A.S. McEwen et al [Reference 2])

Fig 1. Schematic of the focal plane system on HiRISE (from A.S. McEwen et al [Reference 2])

 

References:

W. Alan Delamere, and 15 colleagues, 2009. Color imaging of Mars by the High Resolution Imaging Science Experiment (HiRISE). Icarus, 205, 38-52

Alfred S. McEwen, and 14 colleagues, 2007. Mars Reconnaissance Orbiter’s High Resolution Imaging Science Experiment (HiRISE). J. Geophys. Res., 112, E05S02