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Gravity Waves in Mars’ Atmosphere

Today we have a guest post Dr. Nicholas G. Heavens. He is a Research Assistant Professor of Planetary Science at Hampton University in Hampton, Virginia. He studies the weather of present day Mars, the climate of late Paleozoic Earth, and the atmospheric evolution of Earth-like planets outside the Solar System. He is a member of the Mars Climate Sounder science team.

Dear Explorers of the Fourth Planet,

Chances are, at some point, you have found yourself by a still body of water on a rainy day. Entranced by the smooth surface of this lake or pond, you began to feel the rain fall on your head and shoulders. And as the rain fell on the water, you noticed circular ripples radiating out from each raindrop and moving toward the shore.

Those ripples are a particularly beautiful and elegant example of a type of wave known as a gravity wave (or sometimes buoyancy wave). The raindrop’s impact depresses the surface of the water, upsetting the balance between the force of gravity and the pressure exerted by the water. Water then moves into the hole to restore this balance, creating a further imbalance that spreads the energy of the impact (but not the water itself) outward as circular rings.

Gravity waves in water are a familiar sight in our everyday lives, but gravity waves are common in atmospheres as well, including Mars’s. On average, gravity and air pressure in Mars’s atmosphere are in balance, meaning that less dense air is higher in the atmosphere than more dense air. However, in some situations, denser air can be forced over less dense air, resulting in gravity waves that can propagate to higher altitudes and grow in amplitude as they do so. Some of those waves can be quite inconvenient, since they make up much of aircraft turbulence.

When you look at Planet Four images, you stare at high-resolution, mostly cloudless images of Mars near its poles. What I want to show you today is what might be happening in the atmosphere above, as seen in cloudy, low-resolution images of Mars. It is common to see visible indications of gravity waves in the winter hemisphere around 45 degrees south, but gravity waves are likely active at other times and places.


Circular gravity waves near 45 degrees south late in Mars’s northern summer. This Mars Orbiter Camera Daily Global Map is freely available to download at

 Nearly linear gravity waves near 45 degrees north late in Mars's northern autumn. This Mars Orbiter Camera Daily Global Map is freely available to download at

Nearly linear gravity waves near 45 degrees north late in Mars’s northern autumn. This Mars Orbiter Camera Daily Global Map is freely available to download at

In the first image, do you see circular, whitish ripples near the center of the image? Something analogous to raindrops dropping in a pond has happened there. In the parts of the waves that correspond to rising air, water vapor is cooled and condenses into ice to clouds that trace out the waves.

In the second image, the wave fronts are not strongly curved and appear to be radiating in one direction, probably indicating that a strong wind is affecting the waves. In each case, the wavelength of the waves can be easily measured, around 40 km in the first case and around 20 km in the second case. The source of the first set of waves is unclear (at least to me). The source of the second set of waves is probably the interaction of dense cold air from the pole moving over less dense warmer air at lower latitudes. In some images, the source of the waves can be traced to wind dropping down into a crater.

Studying gravity waves can tell us much about how Mars’s atmosphere works from bottom to top. Future Martian glider pilots also might appreciate knowing when they occur and the conditions they will create. But I will admit that my interest in Mars’s atmospheric gravity waves continues to be fed by the disturbing beauty they bring to Mars’s thin atmosphere.


Why we need Planet Four: Terrains?

Hi there!

I want to talk why we created the new project Planet Four: Terrains if we have Planet Four already.

The very high resolution images of HiRISE camera are really impressive and one might think that there is no reason to use a camera with lower resolution anymore. Wrong!

First, high resolution of HiRISE image means large data volume. To store on-board and to download large data from MRO spacecraft to Earth is slow (and expensive) and this means we are always limited in the number of images HiRISE can take. We will never cover the whole surface of Mars with the best HiRISE images. Sadly. so we use different cameras for it. Some – with very rough resolution and some – intermediate, like context camera (CTX). We can use CTX, for example, to gain statistics on how often one or the other terrain type appears in the polar areas. This is one point why Planet Four: Terrains is important.

Second, because HiRISE is used for targeted observations, we need to know where to point it! And we better find interesting locations to study. We can not say “let’s just image every location in the polar regions!” not only for the reason 1 above, but also because we work in a team of scientists and each of them has own interests and surely would like his/her targets to be imaged as well. We should be able to prove to our colleagues that the locations we choose are truly interesting. To show a low-resolution image and point to an unresolved interesting terrain is one of the best ways to do that. And then, when we get to see more details we will see if it is an active area and if we need to monitor it during different seasons.

Help us classify terrains visible in CTX images with Planet Four: Terrains at

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

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.

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!

Geometry of HiRISE observations is on Talk!

Good news: our wonderful development team has added new feature that many of our volunteers have asked for! Now you can see north azimuth, sub-solar azimuth, phase angle, and emission angle on the Talk pages directly. You can see an example here. These angles give you information about how HiRISE took the image and where the Sun was at that moment.

To understand what those angles are, here is an illustration for you:


You see how the MRO spacecraft flies over the surface while HiRISE makes an image. The Sun illuminates the surface .

Consider a point on the martian surface P.

Emission angle: HiRISE does not necessarily look at point P straight down, i.e. the line connecting point P and HiRISE has some  deviation from vertical line – it is noted as  angle e on the sketch. This is emission angle. It tells you much we tilted spacecraft to the side to make the image.

Phase angle: Because all the images you see in our project is from polar areas, the Sun is often low in the sky when HiRISE observes. To get an idea on how low, we use phase angle – it is the angle between the line from Sun to the point P and line from point P to the HiRISE. It is noted φ in the sketch. The larger phase angle is, the lower the Sun in the sky, the longer are the shadows on the surface.

Sub-solar azimuth: To understand what is the direction towards the Sun in the frame of HiRISE image, we use sub-solar azimuth. In any frame that you see on our project it is an angle between horizontal line from the center of the frame towards right and the Sun direction. It is counted clock-wise. The notation for it in the sketch is a.

North azimuth: The orbit of MRO spacecraft defines orientations of HiRISE images. North azimuth tells us direction to the Martian north pole. In the frame of an image it’s counted same as sub-solar azimuth, i.e. from the horizontal line connecting center of the frame and its right edge in the clock-wise direction.

I hope this helps you enjoy exploring Mars with HiRISE!


A Different View of Mars


Image Credit: Chris Lintott, Becky Smethurst, Sandor Kruk, Ed Paget, CSO

Okay, so this is not your typical view of Mars. You’re used to the HiRiSE images  we show on the site, but the above figure is Mars too. We’ll it’s a spectrum of the upper atmosphere taken by some of the Galaxy Zoo lot , a little over a week ago. I’m collaborating wit them to look at a sample of blue elliptical galaxies  in the submillimeter using the aptly named Caltech Submillimeter Observatory (CSO) equipped with the Leighton telescope. It’s a 10.4-m single dish telescope located on the summit of Mauna Kea in Hawaii. I’ve observed with it remotely, but Chris Lintott, Becky  Smethurst, and Sandor Kruk from the University of Oxford, and Ed Paget from the Adler Planetarium went up the mountain for this run. Ed’s written an account of the trip that you might be interested in reading: Night 1, Night 2, Night 3, Night 4, Night 5, Night 6.

Leighton telescope at the Caltech Submillimeter Observatory with intrepid observers (left to right): Ed Paget, Sandor Kruk, Chris Lintott, and Becky Smethurst. Image Credit: Ed Paget

As a planetary astronomer I’ve pointed telescopes before, but I’ve observed in the optical and mid-infrared wavelengths using a big hunk of polished glass to collection the photons.  This observing project is the first time I’ve ever observed in the submillimeter and used a dish telescope. The aim of this project  is to look at the carbon monoxide (CO) in blue elliptical galaxies and see what it says about star formation. We’re actually looking at in particular  (2-1) rotational electron transition of the CO molecule. This transition occurs in the rest frame of the gas at 230 GHz, wavelengths where our eyes are not sensitive.

Turns out that the CSO uses Mars as a frequent calibrator and pointing target for the Leighton telescope. The first time I pointed the telescope back last July when we had observing time was the first time I’ve ever observed Mars, and it was just to check the pointing! There’s a lot of carbon dioxide (CO2), as you know.  30% of Mars’ atmosphere condenses out into the slab of  CO2 ice in the winter on the South pole that the geysers (and as a result the seasonal fans) will be spawned from. There’s also a lot of CO. CO in Mars’ atmosphere was detected and observed in the submillimeter.back in the 1960s ad 1970s. The result is  a strong absorption feature when you observe the disk of Mars and its atmosphere. You can use it to step the beam across as you tune the telescope and find the optimized pointing that gives you the strongest signal (and thus best pointing). So nightly the Galaxy Zoo gang were using Mars for calibration observations at the start of their nightly observations. It’s  a very different use for Mars’ atmosphere, but there is useful info in the spectrum you can extract about the state of the Martian atmosphere. The width of the line and depth tell you about the global amount of CO and the global average wind speeds. The guess from the Galaxy Zoo lot that night was that they were seeing something on the order of 10 km/s winds.

With Planet Four, we’ll also be getting estimates of the wind speeds on Mars, but from the bottom of the atmosphere at the boundary layer that meets the surface. So we’ll be probing a different regime that what the can be studied in the submillimeter. Assuming a particle size,  the length of the fans can tell us the strength of the wind.  The direction the fan is pointing in gives the direction that the wind is heading in. We’ll be able to compare those velocities and directions we extract from you markings to that produced by global climate models of the Martian atmosphere.

HiRISE’s Beagle 2 Detective Story

On Christmas Day 2003, the British lander Beagle 2 entered Mars’ atmosphere and was never heard from again. It had hitchhiked a ride off of ESA’s Mars Express orbiter. The lander successfully departed Mars Express and then nothing. Mars is hard, and many a spacecraft has ended in demise trying to orbit around or land on the red planet. Beagle 2 never phoned home. Its fate was unknown.

This is before the arrival of Mars Reconnaissance Orbiter (MRO)  and its high resolution HiRISE camera. MRO entered orbit in 2006 and is the highest resolution imager sent to a planet in our Solar System. Now a days it is used to capture the descent of Phoenix lander and Curiosity rover (which is a challenging feat in itself), but that information gives a glimpse of what was going on if something goes awry in those 7 minutes of terror of landing, entry and descent. Later it can be used to to spot the lander on the surface. But the only image of Beagle2 at the time of its’ landing attempt is the separation image from it’s mothership Mars Express.


Departing image snapped by the VMC camera aboard Mars Express after Beagle 2 separated and was on its way to the Martian surface on December 2003 Image Credit: ESA – European Space Agency

For 12 years it’s fate wasn’t known. HiRISE can resolve objects down to the size of a small card table on Mars’ surface. The predicted landing ellipse for Beagle 2 was imaged by HiRISE and scientists scoured the images looking for something in essence not red. They looked for something bright and shiny in the images that could be Beagle 2.  And they succeed. A few days ago, ESA and NASA announced that the Beagle 2 and its used parachute had been found.

The British lander wasn’t found in pieces scattered across the surface. It was intact. It had successfully landed on the surface. A huge accomplishment and success for the United Kingdom. They stuck the landing but the deployment had some hitch preventing Beagle 2 from communicating with Earth.With HiRISE’s resolution, the images reveal the rough outline of the lander. Beagle 2 had a petal design. All the petals had to deploy for the communications antenna to be exposed and able to send/receive signals. It appears that Beagle 2 only partially deployed (a broken cable, an air bag that didn’t inflate or deflate, a rock underneath could be one of the multitude of reasons that could have prevented the final panels from unfurling), with that vital communications antenna blocked it ended the mission.



Beagle_sharpened b_w image_Right_Bright_obj_300percent_sharp_edited-1_labelled
We now know what happened to Beagle 2 that Christmas Day back at 2003. Learning the British spacecraft landed successfully will help engineer future European Mars missions. I also think the ending to this detective story serves as a reminder for how powerful the HiRISE camera is. Of the imagers aboard spacecraft orbiting Mars now and in the past, HiRISE is the only instrument capable of spotting Beagle 2. It’s with its keen eyes that it resolves the hundreds of thousands of fans dotting the South Pole of Mars that we ask for your help to map at

Summer Has Come to the Martian South Pole

Like the Earth, Mars is tilted on its axis which produces seasons: Spring, Summer, Fall, and Winter just like the Earth has.  It’s during the Spring and early Summer in the South Pole (and in dunes in the Northern hemisphere), that the  fans and blotches that you map in the images in the classification interface appear.


Solar insolation over its orbit – Image credit:

Yesterday marked the official start of Summer on the South Pole of Mars and the shortest day of the year in the Martian Southern Hemisphere. The carbon dioxide ice sheet that once covered places like Inca City, Manhattan, and Ithaca should be gone or nearly gone at this point. The dark fans and blotches imaged by HiRISE in August-November of last year (and you can now map those images from Inca City in that sequence on the site) have now disappeared back into the regolith. The days will begin to get shorter and the HiRISE seasonal monitoring campaign will eventually switch to the Northern hemisphere. But the geysers and fans will be back in the South  and so will the HiRISE images starting around mid 2016.

In the meantime, we’ve got plenty of images of fans and blotches needing your help to map at




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)