The Mars Polar Lander Spider Encounter

Today we have a post by Dr. Candice (Candy) Hansen, principal investigator (PI) of Planet Four and Planet Four: Terrains. Dr. Hansen also serves as the Deputy Principal Investigator for HiRISE (the camera providing the images of spiders, fans, and blotches seen on the site). She is also a Co-Investigator on the Ultraviolet Imaging Spectrograph on the Cassini spacecraft in orbit around Saturn. Additionally she is a  member of the science team for the Juno mission to Jupiter. Dr. Hansen is responsible for the development and operation of  JunoCam, an outreach camera that will involve the public in planning images of Jupiter.

My first glimpse of a “spider” on Mars was in 1998. The Mars Global Surveyor (MGS) had gone into orbit around Mars, and winter was turning to spring in the southern hemisphere. The Mars Polar Lander was en route to Mars, and we were anxiously waiting for polar night to lift so that we could see our landing site.

The Mars Observer Camera (MOC) onboard MGS started returning images just a few weeks before Mars Polar Lander (MPL) was due to arrive. We would scrutinize long rolls of film, and that was when we realized that the terrain was not exactly what we expected. Dark spidery forms and cracks that resembled caterpillars fascinated us. I was hooked on trying to understand these exotic features.

We now know that if the MPL made it safely as far as the surface it landed in very inhospitable terrain. We use the colloquial term “spiders” to describe an array of interconnected channels on the surface. The branching channels, now formally referred to as “araneiform” terrain, cover the surface where MPL was predicted to land.   They occur in a wide variety of morphologies, from isolated to connected to starburst to lace, with channels that are typically 0.5 – 2 m deep, and ~5m wide.

Image Credit - High resolution image of Spiders at Mars' south pole taken by the HiRISE camera - credit NASA/JPL/University of Arizona

High resolution image of Spiders at Mars’ south pole taken by the HiRISE camera – Image credit NASA/JPL/University of Arizona

We never heard from MPL after it entered Mars’ atmosphere. Any number of things could have gone wrong. Or everything might have gone perfectly and it landed with one leg in a channel and simply tipped over.

Help  identify spiders and other araneiform terrain with Planet Four: Terrains at

Introducing Planet Four: Terrains

Dear Martian Citizen Scientists!

We are excited to introduce to you a new companion citizen science project to Planet Four called “Planet Four: Terrains” built on the Zooniverse’s new platform. You have explored with us here in Planet Four some of the most detailed surface observations ever made in our solar system and many of you have acknowledged and wondered about all the other amazing features visible in these images that we did not ask to be studied, like spiders, networks of channels and weirdly looking craters. (some of you will remember that one of these even led to a re-observation of the same crater with the HiRISE camera).


HiRISE imaged spiders Image Credit: NASA/JPL/University of Arizona

It is an interesting fact that when one decides to make a camera that can resolve a lot of small details, that it will not be able to scan a lot of area. One has to decide, as long as we don’t have infinite data transport capabilities and infinite mission time at other planets and moons in the solar system. That’s why the Mars Reconnaissance Orbiter (MRO), the spacecraft that houses the HiRISE camera that produced all the images in the Planet Four project has a complementary camera system onboard to provide context, appropriately called CTX for ConTeXt camera. It has a lower resolution than HiRISE (approx 5-6 m compared to HiRISE’s 25 to 50 cm) but takes images from a far larger region than HiRISE.


CTX image – Image Credit:NASA/JPL-Caltech/Malin Space Science System

So here is our idea: We confirmed that many of the features you were asking about are still recognizable with the lower resolution images of CTX. Therefore we would like your help in gathering spatial statistics in where around the south pole we can find which kind of patterns on the ground that are related to CO2 ice activities. Your help in classifying CTX data into a set of ground patterns will serve to decide where the HiRISE camera will be pointed next during 2016’s south polar spring season observation campaign. This way your contributions directly improve the scientific output of both CTX and the HiRISE camera and we are very excited to provide to you a way to point the highest resolution camera in the solar system to the most interesting areas of the Martian south pole!

You can find the new project, a more detailed science case description and an awesome spotter’s guide at this address:

Thanks as always for your time and your enthusiasm!


Solar Powered

This year is the United Nation’s International Year of Light and Light-based Technologies, and there are celebrations, events, and programs on-going for the duration of 2015. The purpose of this initiative, quoting the Year of Light’s webpage,  is to

promote improved public and political understanding of the central role of light in the modern world while also celebrating noteworthy anniversaries in 2015—from the first studies of optics 1,000 years ago to discoveries in optical communications that power the Internet today.

Light is actually one of the important parts of the process that creates the fans and blotches that we’re asking you to map in the classification interface. The entire process is solar powered. The fans and blotches that spot the surface of the South Pole in the spring and summer are the direct result of sunlight warming and sublimating a slab of carbon dioxide ice.

When the south pole is in darkness during the winter sols, the atmosphere condenses out to form a slab of carbon dioxide ice mixed with the atmospheric dust. This ice sheet is semi-translucent so you see down to the surface below that’s it’s covering. When the sun returns to the south pole starting in the early spring, sunlight penetrates through to the base heating the regolith below. The ice at the base of the sheet sublimates turning from solid ice to gas. With carbon dioxide gas trapped between the dirt and the ice sheet, it catches some of the loose dirt and soil particles. The gas exploits weaknesses in the ice sheet, breaking out at the surface as geysers or jets.

The dirt and soil is brought up to the surface, and we think that the prevailing winds then blow the particles into the dark fans you see in the images. If there isn’t any wind or it is not bowing very hard you get the blotches instead. The fans and blotches appear dark, even though they’re really the same color as the material below due to the fact that you’re viewing the surface through tinted glasses (the ice sheet is semi-translucent because of the dust). When the ice sheet has sublimated away, the fans and blotches basically disappear blending back in with the soil.

The sols on the south pole are now getting shorter and shorter and the HiRISE seasonal monitoring campaign has ended. The sunlight is waning and soon the cycle will start anew, with the ice sheet forming as the south pole is shrouded in darkness. Around July 2016, the sun will back and the new season of the HiRISE monitoring campaign will begin again as the fans and blotches reappear at the top of the thawing ice cap.

Remote Sensing Missions to Mars

Since Mariner 9’s pioneering first mission to survey the surface of Mars, several have followed with more advanced equipment able to unveil more detail. This was in a bid to better understand the underlying processes that formed the features of the red planet, including aeolian structures such as sand dunes.

Mariner 9 Mission

Launched in 1971, the Mariner 9 mission had two primary objectives. Firstly, to map 70% of the Martian surface (originally the objective of the failed Mariner 8 mission) and to study temporal changes in the Martian atmosphere and surface. In terms of mapping, the mission exceeded expectations, managing to capture images of almost 100% of the surface. This revealed aeolian features and also large canyons, massive volcanoes and ancient riverbeds.

Despite this success, Mariner 9’s wide and narrow angle telescope cameras could only capture so much detail. The images created had at best a resolution of 1km, and with 5% of the surface this accuracy reduces to 100km. Although this is perfectly adequate to discover large geological features and entire aeolian systems, it is not detailed enough to study dunes in any great depth.

The Viking Missions

Viking Orbiter image of  Martian surface sand dunes (

Viking Orbiter image of
Martian surface sand dunes (

NASA’s Viking Mission to Mars was composed of two spacecraft, Viking 1 and Viking 2, each consisting of an Orbiter and a lander. The mission objectives were to capture high-resolution images of the Martian surface, characterise the structure of the atmosphere and surface, and finally to search for signs of life. Launched in 1975, Viking 1 and 2 Orbiter spacecraft orbited Mars at a distance of 300km above the surface for 1400 and 700 rotations respectively, returning images of the entire surface of Mars with a resolution of 150 to 300m. At selected points of interest, this resolution was improved to an impressive 8m.

The results from Viking gave us the most complete view of the Martian surface to date. The Orbiter images confirmed the existence of volcanoes’, canyons and aeolian features as well as discovering large cratered regions and even evidence of surface water once existing. It meant that these features could be studied in greater detail, and specific regions of sand dunes and sand dune types were discovered.

Mars Global Surveyor (MGS)

MOC image of  Martian north polar sand dunes (

MOC image of
Martian north polar sand dunes (

Launched in 1996, the Mars Global Surveyor spacecraft was NASA’s first mission to Mars in 20 years. It is still the longest serving mission to date, successfully observing the surface for over nine years until November 2006. It was designed to circle in a polar orbit around the planet (travelling over one pole to the other) twelve times a day collecting images from a height of 400km.

The aim of the mission was to contribute to the four main goals of Martian exploration at the time: determine whether life ever existed on Mars, characterise the climate of Mars, characterise the geology of Mars and prepare for human exploration.

To help achieve this, the surveyor spacecraft was fitted with some of the most advanced instrumentation ever sent into space. Part of this payload was the Mars Orbiter Camera (MOC). This camera had two functions; firstly to take a daily wide-angle image of Mars, similar to the weather photographs seen of Earth, in order to study the climate, and secondly to take narrow-angle images to better understand the geological features.

As with the previous two Martian missions, the Global Surveyor was a great success. The landmark discovery was to be the existence of gullies and debris flow features, suggesting that there could be current sources of liquid water on or near the surface of the planet. This wasn’t to be its only achievement however, as it returned images of the surface down to a resolution of 0.5m. The most detailed so far, they provided new information about the physical nature of the windblown material on the Martian surface and showed that the pre-MGS view was much too simple. In addition to bright dust and dark sand, MOC images show evidence of bright sediment that can be transported by saltation (e.g., sand) and dark material that can be transported in suspension.

Mars Odyssey Mission

THEMIS Image of Bunge Crater Dunes

THEMIS Image of Bunge Crater Dunes

Part of NASA’s ongoing Mars Exploration Program, the Mars Odyssey spacecraft launched in 2001, and is still observing the planet to this day. As with MGS, its aim again is to contribute to the four main goals of exploration, and to do this five mission objectives have been derived: to globally map the elemental composition of the surface, determine the abundance of hydrogen, to acquire high spatial and spectral resolution images of mineralogy, provide information on the morphology of the surface and to characterise the radiation risk to human explorers.

The Odyssey spacecraft was fitted with three main instruments to help achieve its targets. THEMIS (Thermal Emission Imaging System) is a camera used to identify the mineralogy of the planet, by studying the different heat radiation properties present. GRS (Gamma Ray Spectrometer) for determining the presence of 20 chemical elements on the surface including hydrogen, and finally MARIE (Mars Radiation Environment Experiment) for studying the levels of radiation present.

Although at first glance none of these instruments seem suitable for the study of aeolian features such as sand dunes, the THEMIS camera also surveys the surface through the visible spectrum. The resulting images have a resolution of 18m, and to date the camera has taken over 15,000 20x20km shots. This resolution nicely ‘fills the gap’ between the large-scale images of the Mariner and Viking missions and the very-high resolution images of the MGS instrumentation.

Mars Reconnaissance Orbiter (MRO)

HiRISE Image of Polar Dunes (University of Arizona, 2011)

HiRISE Image of Polar Dunes (University of Arizona, 2011)

Launched from Cape Canaveral in 2005, the Reconnaissance Orbiter’s main objective is to search for evidence that water persisted on the surface for a length of time. While previous missions have shown that water flowed across the surface, it remains a mystery whether water ever existed long enough to support life.

The MRO spacecraft is one of the most comprehensive missions ever sent to Mars, with a payload of many different types of instrumentation. As well as the numerous spectrometers, radiometers, radars and engineering instruments on board, three cameras have been included to fulfil a variety of objectives. MARCI (Mars Colour Imager) takes large-scale images of the planets atmosphere in order to study clouds and weather patterns. Two other cameras, HiRISE (High Resolution Imaging Science Experiment) and CTX (Context Camera), are able to take images of a much more suitable resolution to study aeolian features in detail.

HiRISE, as the name suggests, takes ultra-high resolution images of the Martian surface in order to reveal details of the geologic structure of canyons, craters and aeolian features. Able to produce results at a 0.5m resolution, it has so far returned some of the most detailed and striking images of the Martian surface ever captured.

CTX was designed to be used in conjunction with HiRISE, providing wide-area views of the areas being studied in order to provide a context for the high-resolution analysis of key areas of the surface. Although predominantly an auxiliary instrument, CTX produces good quality images in its own right, and has currently returned data for over 50% of the planet at a resolution of 6m. Although not matching the detail of HiRISE, they still can still be used to study sand dunes in detail while having a much-improved field of view.

If you have any other questions regarding some of the things you have spotted on Planet Four: Craters, please feel free to ask on Talk, and in the mean time please keep marking on!

Happy new Martian year!

Dear Mars Explorers,

Today, June 18 at about 6pm UTC Mars completes yet another turn around the Sun and its calendar starts with brand new year 33 at Ls=0°!


You might remember that the last New Martian Year was at Earth’s date July 31,  2013. The shift to June 18 is due to the difference of Martian and Earth year length: the Mars year is 687 Earth days, meaning it’s 43 days shorter than 2 Earth years.

New Year on Mars starts with the spring equinox in the northern hemisphere. This means it is fall right now in the southern hemisphere in the areas that you are analyzing. All the ice from previous winter is long gone by now, the surfaces are inactive. The times of darkness become longer and longer and soon come long winter nights. At some locations there will be polar nights, when the Sun stays below the horizon for more than a day. These times are cold and CO2 will start to condense on the surface. First in some record-cold shadowed places and then all over southern polar areas. And it might even snow CO2 flakes!

I leave you with this simulated Martian analemma – the image of the Sun in the Martian sky taken at the same local time during the whole Martian year. Slightly less bright, the simulated Sun is only about two thirds the size as seen from Earth, while the Martian dust, responsible for the reddish sky of Mars, also scatters some blue light around the solar disk. On Earth an analemma is a figure-8, while on Mars it is a tear-drop because of a different relationship between orbit eccentricity and its rotational axis tilt than on Earth (see this excellent blog post by Ethan Siegel explaining analemma details).


(c) Dennis Mammana (Skyscapes) Astronomy Picture of the Day Dec 30, 2006

Right now the Sun on Mars is near the middle of this teardrop and moving towards the narrower tip. In about 1 Earth year the spring will come to Southern hemisphere and the southern polar activity will start again, new fans and blotches will appear giving us more data to investigate!

Thank you for helping us with this investigation!

Let us celebrate by classifying an image or two! Happy New Year!

Goodbye Manhattan, Welcome Back to Ithaca

We’ve been focusing on Manhattan for the past few months, with the aim to finish Season 4 and any remaining images of areas surrounding Manhattan in Season 1. We’ve made a big push in the last few months to finish Manhattan, and thanks to your help, we’ve completed all publicly released seasons of Manhattan.

With four seasons of Manhattan to add to the four seasons of Inca City that you’ve helped classify, we now have a rich dataset to start looking at how  geyser formation evolves over time and how the process of fans and blotch  changes from Mars year to Mars year.

Planet Four is  leaving Manhattan for now, but we’ll be back for Season 5 some time in the future. We’re going back to focus on another target of interest, Ithaca. We started classifying Ithaca Season 1 images last year, and they’re now back on the site for your to map fans and blotches.  You can learn more about Ithaca here. The most telling difference between Ithaca and other areas on Mars’ south pole is the giant fans.

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Dive into Ithaca today at

The Cerberus Fossae


The focus of this post will be on the area of the Martian surface that Planet Four: Craters volunteers have been marking craters on, the Cerberus Fossae.

The Cerberus Fossae is a set of west-north-west trending and almost parallel fissures or fractures that cut across the Cerberus plains on Mars. Evidence suggests that the fissures have been formed by faults that pulled the crust apart in the Cerberus region (9°N, 197°W).

Ripples seen at the bottom of the fault are sand blown by the wind. The underlying cause for the faulting was believed to be magma pressure related to the formation of the Elysium volcanic field, located to the northwest. The faults pass through pre-existing features such as hills, indicating that they are a young feature by the standards of those found on the surface.

In fact, this area of Mars has been identified as having the youngest volcanic plains on Mars. Early crater-counting efforts have suggested that the youngest lava surfaces in the area are less than 10 million years old. This is why it is of such interest to future missions to Mars, as a location where seismic activity might still be happening. To help predict the amount of seismic activity to expect, we need your crater markings to make a more accurate estimate of the age of the region.

If you have any other questions regarding some of the things you have spotted on Planet Four: Craters, please feel free to ask on Talk, and in the mean time please keep marking on!


Mark your calendars – 2 months until ZooCon 2015

Today officially marks two months until ZooCon 2015 hosted at the University of Oxford by the UK Zooniverse team.  It’s a day dedicated to volunteers and inspired by Zooniverse projects.

There will be some science team members (physically and virtually) from many of the Zooniverse projects talking about the recent progress and science results coming from your clicks. Some of the core Zooniverse team will be in attendance to give you updates on the latest news in the Zooniverse and where it is heading in the future.

After the afternoon discussions, attendees can later head over to a gathering at a local pub for a social evening. If talks aren’t your thing you can skip them and sign up just for the attending the pub event starting at 5pm, where you can meet  other Zooniverse volunteers and get to know some of the dedicated people who build and run the Zooniverse.

To give you an idea of what ZooCon is like check out this guest post  by our Talk  moderator Andy Martin (wassock), who attended ZooCon13. Also you can find the video of the ZooCon13 and ZooCon 14 Planet Four talks here and here. We don’t know if Planet four will be one of the projects featured (since there’s 30 projects to choose from!), but either way there will be lots of citizen science and Zooniverse happenings to talk about on July 11th.

ZooCon is set for Saturday,  July 11, 2015 from 13:00 to 21:00 (BST).There isn’t a published schedule of talks yet, but whether you’re interested in out of this world Zooniverse projects or ones closer to home, they’d love to have you join them in Oxford, UK. Tickets are free, but there is limited seating, so register if you want to attend. Reserve your spot today here.

Planet Four Season 2 and Season 3 Site Statistics

Are you ever curious to know how people classify on Planet Four? Well today is your day. I’m working on generating the final numbers for the first half of the Planet Four science paper in preparation. The paper is an introduction to the project and will contain the catalog of blotches and fans identified thanks to your help in Season 2 and Season 3. We’re getting closer to having the paper and the final catalog preparation in shape for submission by the end of the summer.

As part of the paper,  I wrote the section that talks about the classification rate and how people classify on the site. So I made a few close-to-final plots and calculated some relevant numbers from the classification database for Season 2 and 3 that will be included in the paper so I thought I’d share them here. These values and figures below are pretty close what will be in the submitted science paper.

We had a total of 3,517,363 classifications for Seasons 2 and 3 combined.  More blotches than fans were drawn, 3,483,724 blotches compared to  2,825,930 fans. With a total of 84604 unique ip addresses and registered volunteers who contributed to Planet Four when Season 2 and Season 3 titles were in rotation.  Most classifiers don’t log in. There is no difference between the non-logged in and and logged-in experience on Planet Four other than that if you classify with your Zooniverse account we can then give you credit for your contributions in the acknowledgement website we’ll make for the first paper, and we can only get your name (if you allow the Zooniverse to print it to acknowledge your effort)  if you classify with a Zooniverse account.

First plot shows the distribution of  the classifications for each tile in Season 2 and Season 3. You can see the impact of BBC Stargazing. Most of our classifications for Season 2 and Season 3 came from the period during and the few months after BBC Stargazing live and the site was getting lots of classifications and attention so we retired titles after more classifications than now. Currently a tile needs 30 classifications before we retire it, a number that better suits our current classification rate. You can see that nearly all of the Season 2 and Season 3 have 30 classifications or more, with a range of total classifications that we have to take into account when doing the data analysis and identifying the final set of blotches and fans from your markings since some tiles will have significantly more people looking at it than others.


The next plot shows the distributions of classifications for logged-in and non-logged in (without a Zooniverse account) classifiers combined for Season 2 and Season 3. We have a way to track roughly the number of classifications a non-logged in session does so I count them as a separate ‘volunteer’ in this plot (note I cut the plot off at 100 classifications for visibility). 

You can see that most people only do a few classifications and leave and there is a distribution and a tail of volunteers who do more work. That’s typical of the participation in most websites on the Internet About 80% of our classifications come from people who do more than 50 classifications, typical of many Zooniverse projects.  Both the people that contribute a few clicks and those that contribute more are valuable to the project and help us identify the seasonal features on Mars. So thanks for any and all classifications you made towards Season 2 and Season 3, and if you have a moment to spare today there’s many more images waiting to be classified at


Tiles and Full Frame Images

I thought I’d go into a bit more into detail about what exactly you’re seeing when you review and classify an image on Planet Four.  On the main classification site we show you images from the HIRISE camera, the highest resolution camera ever sent to another planet.  Looking down from the Mars Reconnaissance Orbiter, HiRISE is extremely powerful. It can resolve down to the size of a small card table on the surface of Mars. The camera is a push-broom style where it uses the motion of the spacecraft it is hitching a ride on to take the image. During the HiRISE exposure,  MRO moves 3 km/s along in its pole-to-pole orbit , which creates the length of the image such that you get long skinny image in the direction of MRO’s orbit. The camera can be tilted to the surface as well, which can enable stereo imaging.

The HiRISE images are too big to show the full high resolution version in a web browser at full size. The classification interface wouldn’t quickly load, as these files are  on the order of ~300 Mb! – way too big to email.  But the other reason is that the full extent of a HiRISE full frame image is too big and zoomed-out for a  human being to review and accurately see all the fan and blotches let alone map them. So to make it easier to see the surface detail and the sizes of the fans and blotches,  we divide the full frame images into bite-sized 840 x 648 pixel subimages that we call tiles.


An example Planet Four Tile

For the Season 2 and Season 3 monitoring campaign, a typical HiRISE image is associated with 36-635 tiles When you classify on the site, you’re mapping the fans and blotches in a tile. Each tile is reviewed by 30 or more independent volunteers, and we combine the classifications to identify the seasonal fans and blotches. To give some scale, for typical configurations of the HiRISE camera, a tile is approximately 321.4 m long and 416.6 m wide. The tiles are constructed so that that they overlap with their neighbors. A tile shares 100 pixels overlap in width and height with the right and bottom neighboring tiles.  This makes sure we don’t miss anything in the seams between tiles .

If you ever want to see the full frame HiRISE image for a tile you classified, favorited, or just stumbled upon on  Talk, there’s an easy way to do it. On the Talk page for each tile we have a link below the image called ‘View HiRISE image’ which will take you to the HiRISE team public webpage for the observation, which includes links to the full frame image we use to make tiles plus more (note= we use the color non-map projected image on Planet Four). Try out this example on Talk.

So next time you classify an image and recall how detailed it is, remember that although it’s just a small portion  of the observation, your classifications are hugely important. Without them we wouldn’t be able to study and understand everything that’s happening in the HiRISE observations. It’s only with the time and energy of the Planet Four volunteer community that we are able to map at such small scales and  individually identify the fans and blotches., which is crucial for the project’s science goals. So thank you for clicks!


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