Monday, 31 October 2016

Anatomy of a Martian Crash

Schiaparelli’s Crash Site
Crash site of the Schiaparelli lander as viewed by  the 
High Resolution Imaging Science Experiment on the
NASA 
Mars Reconnaissance Orbiter,
imaged on October 25th, 2016.

Image Credit: NASA/JPL/University of Arizona



The planet Mars has seen its share of mechanical disasters. An interesting look at this phenomenon is presented in a Universe Today article written just this past April. But never before have we had the capability to scrutinize a distant crash in such detail.

The Schiaparelli Descent and Landing Demonstrator Module (EMD) crashed into the Martian surface on October 19th at approximately 3 pm (Greenwich Mean Time). The crash was viewed by no less than three instruments. Data from the lander’s descent was recorded by the ExoMars Trace Gas Orbiter (TGO), which had travelled to Mars with the Schiaparelli lander. Collection and transfer of data was also assisted by the ESA Mars Express orbiter, which has been parked at Mars since December of 2003, when it too lost its accompanying lander the Beagle 2. In addition, measurements were made from Earth, using the Giant Metrewave Radio Telescope (GMRT), an experimental telescope array located near Pune, India. Scientists and engineers are still poring over this glut of data to determine what happened. However, several details have already become clear.
Farewell Schiaparelli
2013-2016.
Image Credit: ESA – B. Bethge



Schiaparelli’s 6-minute descent through the martian atmosphere was intended to proceed in three stages. The first stage was to be free-fall under the protection of two heat shields, at front and back of the module. In stage two, a parachute (12 meters in diameter) was to be deployed, reducing the lander’s descent speed. In the third and final stage, the parachute and back shield were to be released, so that a set of nine thrusters could fire, further slowing the lander down and bringing it to a soft landing at Meridiani Planum near the martian equator.

Preliminary analysis of the collected data indicates that, for some reason, the thrusters switched off prematurely at a height of 2-4 km above the martian surface. This resulted in a long free-fall for the lander module, much longer than had been planned, and the lander crashed into the surface at speeds of more than 300 km/h. The hydrazine propellant tanks, which fueled the thrusters, are expected to have still been fairly full when the thrusters switched off, so they may have exploded on impact.  The descent data is still being analyzed, so more accurate details may become available in the future.

But monitoring the lander’s descent was not the only observation that was planned for Schiaparelli. Two cameras on NASA’s Mars Reconnaissance Orbiter (MRO) spacecraft were scheduled to image the predicted landing ellipse, a 100 km by 15 km area where the lander was expected to touch down. This allowed the location of the crash to be identified and the aftermath to be studied.

Finding Schiaparelli
Crash site of the Schiaparelli lander as viewed by the Context Camera on the NASA Mars Reconnaissance Orbiter. Image on the left shows the full view, while the image on the right shows a zoomed-in view. Both images toggle between data collected on Oct. 20th, just after the crash, and data collected on May 29th, five months before the crash. The images are located at approximately 2 degrees south latitude and 354 degrees east longitude, are oriented with north towards the top, and have a resolution of 6 m/pixel.
To learn more about this image, go to this ESA website.

Image Credit: NASA/JPL-Caltech/MSSS
MRO’s low-resolution Context Camera (CT) was scheduled to cover the anticipated landing site on Oct. 20th, and so was the first to image the suspected crash site. Scientists compared these images to previous ones, collected by the same instrument less than 5 months earlier, and found exactly where the lander came down. Despite the fatal difficulties, the module landed very close to its intended landing spot, only 5.4 km west and well within the predicted landing ellipse.

The discovery image shows the locations of two distinct components of the lander module. The dark fuzzy patch in the upper part of the image is where the lander crashed, forming an impact crater. The crater itself is fairly small, while the bulk of the dark patch, which is roughly 15 x 40 meters in size, represents surface material that was disturbed by the impact. Below the lander crash site, a small white dot can be seen. This is the module’s jettisoned parachute.

A Closer Look
Higher resolution images of the Schiaparelli lander as viewed by NASA’s Mars Reconnaissance Orbiter HiRISE camera on Oct. 25th.  Zoomed-in views are provided for each identified impact point resulting from module’s crash.
In the image, north is up; west is to the left, and the resolution is 29.5 cm/pixel. The brightness of the zoomed-in sections have been individually adjusted to best reveal the features in question. In addition, the image is corrected to adjust for the fact that HiRISE acquired them at an oblique angle. As a result, the scale bar in the main image is only indicative.
To learn more about this image, go to this ESA website.
Image Credit: NASA/JPL-Caltech/University of Arizona
On October 25th, MRO’s High Resolution Imaging Science Experiment (HiRISE) took a closer look at the crash site.  Close inspection of the resulting image revealed several new insights. At the bottom of the image, the rear heat shield can be seen, still attached to the parachute. At the top right of the image, a new crater was identified and attributed to impact of the front heat shield. Finally, the crater formed by the main lander impact is resolved in the image centre.

The Schiaparelli lander’s impact site consists of a central dark spot, an asymmetrical deposit around the dark spot, and a long dark arc on the north-east side. The dark spot is about 2.4 m across, which is consistent with a crater made by a 300 kg object impacting at a few hundred km/h. The crater is predicted to be about 50 cm deep and it is hoped that more details will be visible in future images. This will be necessary to help explain the enigmatic asymmetric and arc features, which are currently not well understood.

Asymmetrical deposits are not uncommon around impact craters, but such craters are usually formed by meteors travelling at speeds of 40,000 – 80,000 km/h. In such cases, the presence of asymmetric debris around a crater implies that the meteor came in at a low angle (closer to horizontal), so material was ejected from the crater in a preferred direction, with more ejecta material deposited in the direction of travel. However, the Schiaparelli lander is thought to have been travelling at only 300 km/h and descending almost vertically at the time of impact, so directed ejecta would not be expected. Also, the lander entered the atmosphere travelling from west to east. Thus, even if the impact was not vertical, the preferred direction for ejected material would have been to the east of the crater, not to the west as is seen in the HiRISE imagery. It is possible that the module’s propellant tanks exploded in a westerly direction, producing the asymmetrical ejecta, but more analysis is required to confirm this idea.

The long dark arc to the north-east of the crater is also currently unexplained. One suggestion is that an exploding propellant tank may have created this arc by disturbing the surface soil.

Despite many remaining questions, the abundant data from the Schiaparelli EDM crash is allowing us to study an extra-planetary accident in more detail than has ever been possible before. We can only hope that more data will bring more insights into how to avoid such disasters in the future.


Sources:
Mars Reconnaissance Orbiter views Schiaparelli Landing Site.
ESA ExoMars News, Oct. 21, 2016

Detailed Images of Schiaparelli and its Descent Hardware on Mars.
ESA ExoMars News, Oct. 27, 2016

Tuesday, 31 May 2016

Discover the Smithsonian Moon Exhibit On-Line

This February the Smithsonian National Air and Space Museum in Washington D.C. opened an exhibit titled “A New Moon Rises: New Views from the Lunar Reconnaissance Orbiter Camera.” The exhibit, which showcases some of the most spectacular images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) since 2009, is scheduled to run until December 2016. If you live in Washington D.C., or are planning a trip there in the near future, I would encourage you to check out the exhibit, especially since admission to the museum is free.

For the rest of us, the Smithsonian has kindly provided an on-line version for us to experience. Like the physical exhibit, the virtual “A New Moon Rises” exhibit is divided into six themes (Global Views, Exploration Sites, Discoveries, Vistas, Topography and Craters), which can be accessed through the menu bar at the top of the page.

Within the virtual exhibit, you will find some truly spectacular images. Some of my favourites are highlighted below.

Unlike the Earth, the Moon’s axis is not tilted very much. This means that sunlight hits the lunar poles at a very low angle (like at sunrise or sunset on Earth) pretty much all of the time. Some high areas, like mountains and crater rims, will get at least some sunlight most of the year, while low areas, like crater depressions, will get effectively no sunlight, ever. This image of the south pole was created by combining thousands of images taken over a lunar year. It shows what percentage of the year each area is hit by sunlight. The shading is scaled so that areas that get sunlight 100 % of the time show up as white, while those that never get sun are black.  The black areas, known as permanently shadowed regions, get very cold and so are believed to be places where water ice is trapped and preserved from evaporation by the hot sun.
Image Credit: NASA/Goddard Space Flight Center/Arizona State University 



Pairs of stereo images from the LROC Wide Angle Camera, along with altimetry data from the Lunar Orbiter Laser Altimeter, allow topography to be determined for the entire lunar globe.  This image shows the topography of the western limb of the Moon, centred on the Orientale basin.  Orientale is the youngest of the large lunar impact basins and has not been flooded by much lava. As a result, its topography is readily revealed, showing multiple impact basin rings. Here, reds and browns denote high elevation, greens and blues represent medium elevation, and deep blues and purples show areas of very low elevation. 
Image Credit: NASA/Goddard Space Flight Center/Arizona State University 


Giordano Bruno is one of my favourite craters (of course, I covered it in one of my earliest Planetary Geolog posts). This image shows the crater from an oblique angle, which highlights the topography of the rim and floor features of the crater. The sunlight also shows off the interesting landslides on the crater walls.
Image Credit: NASA/Goddard Space Flight Center/Arizona State University 

I hope these few examples will inspire you to explore the virtual “A New Moon Rises” exhibit yourself and find your own favourites.


Source: 
A New Moon Rises: New Views from the Lunar Reconnaissance Orbiter Camera. Smithsonian National Air and Space Museum On-line Exhibits, Accessed May 31, 2016.




Thursday, 31 March 2016

Many Small Nuggets from the 47th Lunar and Planetary Science Conference

Tuesday Night Poster Session at the LPSC 2016.
I might be in there somewhere...
Image credit:  Lunar and Planetary Institute. 


This year's Lunar and Planetary Science Conference (LPSC) was another success. I again went as an independent researcher, but this time I was also looking for employment opportunities. I got a few leads, which I will follow up in the next few weeks.

I also rejoined the official LPSC microblogging crew. Some of you may have followed my short posts on Google+ during the conference. As usual, I am reproducing my entire complement of LPSC microblogs, plus appropriate links (if available), here on the Planetary Geo Log. Again, the intent is for you to digest a few small nuggets at a time. I hope to write up some of these in future blogs, so keep an eye out. If you would like to learn more about any of the posted topics, please feel free to make a request in the comments.

Sunday March 20, 2016
1)  Hello folks. I am at the Lunar and Planetary Science Conference again this year and will be microblogging on Google+. I hope you enjoy my observations of the conference.  
(http://www.hou.usra.edu/meetings/lpsc2016/)  

2)  Attended this year's #Microsymposium57 before #LPSC2016. I'll be posting some highlights......
(http://www.planetary.brown.edu/html_pages/micro57.htm)  

3)  David Paige has found that there are more volatiles in low latitude craters at the lunar poles, because those craters catch the poleward-migrating volatiles before they can reach the high latitudes of the poles. #Microsymposium57 before #LPSC2016.    

4)  Barb Cohen is looking for "operationally useful amounts of water" on the Moon, which means large quantities. She proposes this can be done using cube satellites. #Microsymposium57 before #LPSC2016.    

5)  Mahesh Anand tells us that ESA considers the Moon to be the primary target for human exploration after the ISS. #Microsymposium57 before # LPSC2016.    

6)  Tony Colaprete and Jen Heldmann told us about the proposed Resource Prospector mission. It consists of a rover that will take measurements and samples at several locations on the lunar pole. #Microsymposium57 before #LPSC.    

Monday March 21, 2016
1)  Catherine Johnson shows that the magnetic field on Mercury is strongest in the Caloris basin and the magnetic field is at least as old as the Caloris basin.   
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1391.pdf)

2)  L. Hood noted that you need a long-standing magnetic field to explain the magnetic signatures seen at Caloris and Sobkou basins on Mercury. So, Mercury would have had a magnetic dynamo at the time these basins formed.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1301.pdf)

3)  The models of P. James suggest that the lithosphere of Mercurry is 32 (+/-15) km thick.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1992.pdf)

4)  C. Fasset shows that crater degradation on Mercury happens much faster than on the Moon.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1046.pdf)

5)  Robbie Herrick noted that Mercury has more craters <10 km in diameter than would be expected for the number of craters >10 km in diameter. This would be due to a larger number of secondaries. If so, the oldest surfaces on Mercury could be 100 m.y. younger than previously estimated.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2766.pdf)

6)  Congratulations to last year's Dwornik student award winners:
      Robert Jacobson - U Tennessee,
      Hanna Susorney - John Hopkins,
      Johnathan Oulton - Florida State,
      Hank Cole - Colorado School of Mines.   

7)  Alan Stern reported on the New Horizons mission results so far. Although the flyby of Pluto is complete, only half of the data has been transmitted, because lower transmission rates were selected to keep costs down. The other half of the data is still to come. What additional exciting things will we learn about Pluto?    
(PDF Presentation of Alan Stern's Talk)
(Video of Alan Stern's Talk)

8)  Pluto has 4 small satellites in addition to Charon. The outer-most, Hydra, rotates 100 times about its axis for each orbit around Pluto. It's quite mesmorizing in this animation that Alan Stern showed.
(Animation of Pluto's Satellite's Orbits)
Comment on Google+: Wow. Any particular reason for that? (spin:orbit resonances?)
My reply: No, they're not quite sure. Just sat in on a talk by S. Porter, where they discussed the small satellites. All have retrograde rotations, which is odd, so they suspect this may be related to some kind of tidal state.

9)  Pluto's large, bright, smooth plane, called Sputnik Planum, is thought to be an ancient impact basin that is filled with nitrogen ice. This ice shows evidence of glacial flows at the northern edges according to Alan Stern.    

10)  Using GRAIL Gravity data from the Moon, Maria Zuber showed that cryptomaria (hidden mare deposits) in the Schiller-Zucchius basin do NOT extend to a depth of 10 km. This is not a surprising result, but it's good to have a confirmation of this.   
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2105.pdf)

11)  Tony Colaprete reported on LADEE data for the thin lunar atmosphere, or exosphere. Titanium and magnesium concentrations in the exosphere are somewhat correlated with mafic deposits on the surface and aluminum deposits are somewhat corelated with surface highlands, though the surface compositions cannot completely explain the exosphere compositions.
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2635.pdf)

12)  The Pluto/New Horizons research articles in Science are all open access!! Enjoy...    
(http://science.sciencemag.org/content/351/6279)

13)  S. Porter tells us that the moons of Pluto are in extremely stable orbits and their surfaces (as far as we can tell with the limited available data) are cratered and old. So, these moons are not new or ephemeral objects, but have been orbiting around Pluto for a long time.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2390.pdf)

14)  NASA Night at #LPSC2016. NASA is looking for community input on how we use NASA data. Foreign input is also welcome. There will be a link posted on the LPSC webpage with instructions on how to submit your input. I will update this microblog post with the link as soon as it goes up.
Instructions for submitting input can be found at: (http://science.nasa.gov/researchers/sara/grant-solicitations/nasa-request-information-assessing-planetary-science-communitys-use-planetary-science-division-facilities/)

15)  NASA Night at #LPSC2016. Cosmoquest was mentioned as one of the organizations that won an Education and Public Outreach grant this year. Congratulations #Cosmoquest!
(https://cosmoquest.org/)

16)  NASA Night at #LPSC2016. Jim Green tells us that the NASA planetary science budget got $270 million more than was requested this year!!
Total budget is $1.63 billion.    

17)  NASA Night at #LPSC2016. This was Jim Green's closing slide for questions.


18)  Really enjoyed meeting old friends and new at the Students Reception.    

Tuesday March 22, 2016
1)  Jeff Plescia told us that impact melt flows on the Moon show evidence of multiple pulses of material from the same impact.   
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2585.pdf)

2)  Jason Cook talked about the distribution of non-volatiles on Pluto. Apparently this means water, which I think of as a volatile. But water does not act like a volatile on Pluto, because of the extremely cold temperatures. Jason finds that water is widely destributed on Pluto, predominantly as fine particles.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2296.pdf)

3)  Misha Kreslavsky found large-scale dendritic patterns, with a topographic range of 20 meters, in parts of the lunar maria.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1331.pdf)

4)  Lisa Gaddis showed that M3 data can be used to identify volcanic pyroclastic deposits on the Moon.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2065.pdf)

5)  Tom Giguere suggests that the floor of Gassendi crater, a floor-fractured crater on the north-west shore of Mare Humorum on the Moon, shows evidence of drained lava lakes.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1884.pdf)

6)  Carl Allen used Diviner data, collected during a lunar eclipse, to show that pyroclastic deposits in the Aristarchus region of the Moon cool faster than other materials in sinuous rills, maria, or mare rays. The thermal inertia of pyroclastic material must, therefore, be lower, possibly due to a much finer grain size.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1309.pdf)

7)  Carolyn van der Bogert showed that the Dark Mantle Deposits of Taurus Littrow are actually older than the surrounding maria, even though they look younger. This is because small craters in the dark mantle deposit are in saturation and have experienced preferential degredation, while the small craters in the nearby maria are still in production, resulting in more craters at that size.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1616.pdf)

8)  Tuesday poster sessions were such a whirlwind, I didn't get a chance to microblog about anything.

9)  30th annual Hawaii Party was it's usual fun. Really enjoyed chatting with Tom Giguere and Steve Ruff.   

Wednesday March 23, 2016
1)  Daniel Moriarty and Makiko Ohtake presented back-to-back competing interpretations for the interior of the South Pole-Aitken basin on the Moon. I confess, I am confused....    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1735.pdf)
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1414.pdf)

2)  Noah Petro presented work that supports the presence of cryptomare deposits in the Bhabha region of South Pole-Aitken basin on the Moon. During the question period, Apollo 17 astronaut Jack Schmidtt noted that one of the flat-floored irregular craters in the region may not be a flooded impact crater, but rather a volcanic caldera related to the cryptomare volcanism period.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2669.pdf)

3)  Paul Spudis identified a number of units around the edges of Mare Crisium on the Moon. These units poke through, and so pre-date, the mare material of the basin. Paul suggests that these may be remnants of the Crisium impact melt sheet and so would make good targets for future sample-return missions.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1463.pdf)

4)  Based on low-angle impact experiments, Pete Schultz proposes that so-called "double impacts", which have been identified in GRAIL gravity data from the Moon, may actually be due to a single low-angle impact. What happens is the approaching bolide hits the surface at an oblique angle, causing the top of the bolide to decapitate and hit the surface in a second location down-range, producing what looks like a double impact.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2931.pdf)

5)  Shared from Stuart Robbins.
Lisa Gaddis: NASA’s Cartography & Imaging Sciences Node contains >850TB of data, growing at ~120TB/yr.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2281.pdf)

6)  Just uploaded the electronic version of my #LPSC2016 poster. You can see it here...    
(http://www.hou.usra.edu/meetings/lpsc2016/eposter/2948.pdf)

7)  Pamela Gay told us about the exciting funding developments happening for the #Cosmoquest project during our Cosmoquest community meeting at #LPSC2016.    

8)  At the #Cosmoquest community meeting (during #LPSC2016), Andrea Jones encouraged us to spread the word about International Observe the Moon Night, happening this year on Oct. 8, 2016. Now is the time to start planning your event. Don't forget to register your local event, whether it's a big museum function or a small neighbourhood get together, so InOMN can highlight how global this celebration truly is! Instructions on how to get involved can be found under the Get Involved tab on the web link below.    
(http://observethemoonnight.org/)
Frustum
Image credit:  Wikipedia. 



9)  New Vocabulary Word from R. Beyer's talk at #LPSC2016. Frustum: A diagram illustrating the angle a camera is pointing towards the target surface.    

10)  Planetary Spatial Infrastructure session at #LPSC2016 was very interesting. Best quote has got to be "Cartography is important to cartography." This means that Cartography, as the manipulation of digital data so that it can be presented in a map, is important to Cartography, the process of creating maps.     
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/sess453.pdf)

11)  LEAG Networking Session at #LPSC2016. A group of young scientists are gathered around Apollo astronaut Jack Schmidtt, soaking up his wisdom.    

12)  Smart people tend to be more prone to unintentional bias. They tend to feel they are immune to this bias, because they are smart. So recognize that you have biases, know what they are, and work to overcome them. #WomenInPlanetaryScience and #LPSC2016.    

13)  Being self-aware of your own biases and working on those is not enough. The culture and institutions in the community need to be changed too, to help overcome this bias problem. Senior and mid-career members, who are less vulnerable, need to take the initiative in this regard. #WomenInPlanetaryScience evening at #LPSC2016.    

14)  Discussion section of the #WomenInPlanetaryScience evening at #LPSC2016. was great.    

Thursday March 24, 2016
1)  Systems engineering is ensuring that you don't design misunderstandings into your system. #NextGenWorkshop Scientists and Engineers: Learning to Work Together at #LPSC2016.    
(Video about system engineering, recommended by the presenter, Lee Graham )

2)  Think of mission requirements as dollars in a different form. You want the minimum necessary requirements to cover the scope and objectives of your entire mission, no more and no less. #NextGenWorkshop Scientists an Engineers: Learning to Work Together at #LPSC2016.    

3)  Totally amazed by the interesting people who stopped by my unconventional planetary poster about using financial modeling techniques for identifying basalt spectra.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2948.pdf)
(http://www.hou.usra.edu/meetings/lpsc2016/eposter/2948.pdf)

4)  The annual Arizona Party was fun, but I was too beat from my poster session to take advantage of the dance floor and DJ. Does anyone know if there was much dancing this year?    

Friday March 25, 2016
1)  Michael Nayak found that magnetic data from the South Pole-Aitken basin suggests the existence of several new magnetic paleo-poles on the Moon, which had not been previously identified.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2506.pdf)

2)  Lon Hood suggested that the absence of magnetization on the rims of large lunar impact basins may be due to their being erased by subsequent volcanic flooding. However, Mark Wieczorek pointed out that his earlier work shows that mare layers cool too quickly for their heat to be able to erase the magnetic signature.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1303.pdf)

3)  Rona Oran used simulations to model the behaviour of the lunar magnetic field during large-scale impact events. Her work shows that the magnetic field is increased all over the Moon during an impact event, not just at the antipode. However this increase is too small to explain observed magnetizations, thus supporting a stable core dynamo as their source.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/3057.pdf)

4)  Mark Wieczorek gave a fascinating talk about the depth of lunar magnetization. Almost the entire Moon is magnetized and most of it has a deep origin. This means that impact magnetization, which only affects the surface, is not the dominant magnetizing process on the Moon. Similarly, volcanic intrusions cannot be used to explain magnetism on the far side, where volcanism is very limited. Therefore, most of the magnetization seen on the Moon must have been accumulated during slow cooling of the primordial crust in the presence of a stable dynamo. Magnetization of the farside crust would have been locked in by 230 million years after the formation of the Moon, so the dynamo must have been in place by then. This is even earlier than the oldest magnetized samples we have from the Moon, which have been dated at 4.25 billion years old (~250 million years after the formation of the Moon).    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/2288.pdf)

5)  D.A. Patthoff mapped two populations of ridges on Enceladus, one old and one recent. Based on these, the following tectonic history was proposed: compression of the crust associated with its formation, followed by a long tectonically quiet period, culminating in a recent period (<100 m.y.) of compression possibly associated with thickening of the crust due to cooling of the underlying ocean. What is not known is what are the implications of this history or the evolution of life and how long before the ocean completely freezes over.
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1772.pdf)

6)  Mike Bland proposes that the grooved terrain of Ganymede is formed when magmatic intrusions heat the overlying crust. This allows convection in the intrusion to push the overlying crust and bunch it up (like a table cloth) to form sets of parallel grooves.    
(http://www.hou.usra.edu/meetings/lpsc2016/pdf/1287.pdf)

7)  Audience request for some Game of Thrones names on Charon.   

8)  We have reached the end of #LPSC2016. Thank you so much for letting me bombard you with my observations. I hope you enjoyed it, I know I did. Until next year....    

Tuesday, 31 March 2015

Many Small Nuggets from the 46th Lunar and Planetary Science Conference

Science talk at LPSC 2015.
I was in the room, but I don't think I'm in this picture.
Image credit:  Lunar and Planetary Institute. 



This year's Lunar and Planetary Science Conference (LPSC) was fabulous. I went as an independent researcher and was pleased to see that this is no longer frowned upon like it used to be in the past. Times are tough and budgets are tight. Many scientist are looking at alternate funding models to pay for their research. So, it was wonderful to get a chance to compare notes on this front.

I also was an independent microblogger this year. For the past three years, LPSC organizers have recruited conference attendees to write short blurbs about the session talks on social media. I didn't join the official microblogging crew, but continued to post to Google+ on my own terms - I wanted to reduce the pressure I put on myself.

And just like last time, I am reproducing my entire complement of LPSC microblogs here on the Planetary Geo Log. Don't feel the need to read it all at once, but rather savour a few small nuggets at a time. I hope to write up some of these in future blogs, so keep an eye out.

Sunday March 15, 2015
1)  I am at the Lunar and Planetary Science Conference again this year and will be microblogging about it. I hope you enjoy.....
(http://www.hou.usra.edu/meetings/lpsc2015/)  

2)  The talks at Sunday's session of Microsymposium 56 were really good! Some highlights below:
     - Ejecta from the Moon-forming impact may have reached the asteroids at very high velocities, producing melts that retain a signature of the event.
     - The Procellarum basin may be a palimpsest, formed in a warm crust and mantle.
     - A Procellarum-forming impact would have melted the underlying mantle to the core and distorted the crust at the antipode, allowing later melts to migrate to the surface.
     - The South Pole-Aitken basin may have precipitated mantle melting and also distorted the the crust at the antipode, allowing melts to come to the surface in the Procellarum region.
     - Early lunar impacts may have formed before the overturn of the olivine cumulate layer in the mantle, explaining why we see so little evidence of olivine on the surface. Alternatively, the composition of the mantle may be heterogeneous.
     - Modelling of crustal relaxation for the lunar basins suggests they must have formed when the crust was warm, which is too early in the Moon's history to be consistent with a late heavy bombardment.
     - Modelling of Orientale and seismic studies of the Chixulub crater show that outer rings of multi-ring basins are associated with multiple faults (some listric) that extend all the way to the Moho.
(http://planetary.brown.edu/html_pages/micro56.htm)

3)  The LRO Data Users Workshop took place on Sunday before the LPSC. Some very useful information on how to access and work with the LRO data was presented. Slides from the individual talks can be downloaded from the workshop website.
(http://lunar.gsfc.nasa.gov/datausersworkshop.html)

4) An impromptu demonstration of the Lunar Mapping and Modelling Portal (pub.lmmp.nasa.gov/LMMPUI/LMMP_CLIENT/LMMP.html) was presented at the end of the LRO Data Users Workshop. This tool lets you view a variety of lunar data layers, all registered together.
     I suggested that the ability to do math between the layers would be a very useful addition to the tools and the presenters seemed very receptive to this idea. Maybe that functionality will be added in the future.

Monday March 16, 2015
1)  The Next Generation Lunar Scientists and Engineers panel on tips and strategies for writing successful scientific papers was very informative. The best tips (in my humble opinion) included:
     - Start with your tables and figures and write around them - use them as your outline.
     - If you are having writer's block, start writing your figure captions.
     - Writing is a two step process: dump your thoughts, then word-smith. If you are word-smithing before you have finished dumping your thoughts, you can loose your train of thought or polish something that doesn't really fit anyway, and so end up wasting lots of time.
     - Make sure your paper has only one major take-away message, since that is all that most people will take way.
     - Have your paper end by outlining the next steps; this can be helpful when applying for grants.
     - Reviewers' comments aren't absolute; you can rebut them, preferably with evidence, when you write your response.
     - Rejections often have more to do with timing - the editor doesn't think you can address the reviewers' comments fast enough for their schedule. Unless the editor encourages you to submit this paper to other  journals, consider this an opportunity to edit and resubmit to the same journal.

2)  Overheard at the Students' Reception on Monday:
"I play the stock market, because I want to be a scientist, but I also want to live in a nice house."
... We need to pay our scientists more.      

Tuesday March 17, 2015
1)  Dr. Stuart Robbins gave a fabulous talk explaining the issues with current crater chronology techniques (i.e. figuring out the age of a surface by counting craters). His talk included some amazing animations of plots (of all things) that really helped me to understand some aspects of crater dating that I hadn't before. He's shared these animations with me and I will be posting them on my blog in the near future. Stay tuned.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2629.pdf

 
2)  Using simulations, Dr. Carolyn van der Bogert showed that the crater count-determined model age of a surface depends on the size of your count area. For areas that are less than 100 square kilometers in size, the model age can be incorrect, with smaller areas giving younger ages. Caution should be used when determining the age of very small areas, and multiple regions of the same unit should be aggregated to provide counts over a larger area.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/1742.pdf)

Wednesday March 18, 2015
1) LEAG Town Hall Summary  
     - Planning for a "New Views of the Moon II" is underway. Be ready to contribute to this upcoming volume (whose name is still to be determined). Contributions can also form the basis for white papers in the next decadal survey.
     - Contact your congressman about keeping LRO alive. The Planetary Society  is drafting a letter. Use this as a template for your correspondence, but personalize you letter, because studies show a personalized letter has much more impact than a form letter.
     - The next SSERVI Exploration Science Forum is this July 21-23. There will be talks streamed on the web. (http://nesf2015.arc.nasa.gov/)

2) Dr. Paul Lucey is talking about small lunar craters in the South Pole-Aitken basin. Except he keeps talking about craters in the SPA, pronouncing it "spaa" instead of "es-pee-ay", and all I can think about is getting a massage.
      Okay, I need to add that he found that small craters in SPA were almost exclusively noritic in compositions, which has implications for the composition of the mantle under SPA.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/1655.pdf)

3) Dr. S. Lawrence pointed out that GRAIL lunar gravity data does not support the presence of a basin in the Australe region of the Moon.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2739.pdf)
 
4) Just finished giving my talk on the complexity of cryptomaria in the Mare Humorum area of the Moon. Whew! Now I can get back to microblogging.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2808.pdf)


Thursday March 19, 2015

1) Dr. Aileen Yingst used the MAHLI camera on the Mars Curiosity rover to show that fine grained deposits in Gale crater were formed by settling from suspension. The suspension medium is most likely water, because there are no aeolian features present.
     Dr. Yingst and I talk about this some more later and further concluded that the larger grains that can be seen interspersed among the fine grains could not have been carried by wind processes, again supporting the hypothesis that these materials were deposition by settling in water.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/1378.pdf)

2) Dr. Rebecca Ghent looked at radar data of the lunar regolith and found that rocks on the surface break down and disappear within about 1 billion years. Rocks within the regolith, on the other hand, persist for long periods of time, well beyond their brethren on the surface.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/1979.pdf)  

3) A big thank you to Scott at the JMARS booth, who took time during Thursday's poster session to try and solve my JMARS issues.
(http://jmars.asu.edu/)


Friday March 20, 2015
1) Dr. H. Nekvasil conducted experiments that show how crystallization of plagioclase under high pressures can make the plagioclase more anorthitic with cooling. At low pressures, cooling plagioclase becomes more albite-rich, making it difficult to explain the high anorthite content of the lunar highlands crust. Dr. Nekbasil's work suggests the highland plagioclases could have cooled under higher pressures at depth in the lunar mantle and then been transported to the surface.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/1617.pdf

2)  Dr. Pete Schultz gave an amazing talk about the impact that formed South Pole-Aitken (SPA) basin. First he showed spectacular high speed movies of experimental impacts into glass spheres, which demonstrate the disruption and damage that occurs at the antipode of the impact site. These also showed that the antipode of the impact site is not the same as the antipode of the crater for oblique impacts. Next, Dr. Spudis evaluated geological features of SPA , showing that SPA is an oblique impact and that the antipode of the impact site (but not the crater) coincides with the centre of a system of tectonic features related to Procellarum. He thus concludes that the SPA impact would have disrupted the crust under Procellarum, allowing significant melts to form and migrate into the crust. These melts would have differentiated, forming a KREEP layer that was later exposed by the Imbrium impact event. Wow!
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2416.pdf)

3) One of the themes for the Moon at LPSC this year has been the composition of the lunar mantle. Considering the variety of studies and findings, it is clear that we really don't know what the lunar mantle is made of.

4) Zack Morse is doing some great work mapping the ejecta of Orientale basin on the Moon. This impact has been mapped before, but the last extensive work on this was in 1977. Zack is re-visiting these deposits using more recent data sets like the LROC WAC and NAC images.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2608.pdf)

5) Dr. P. Boehnke pointed out that only about 50% of all lunar impact samples were heated to temperatures hot enough to reset their Ar/Ar ratios during the impact that formed them. Thus, about 50% of Ar/Ar dates from these samples will show ages that are older than the impact event. This needs to be considered.
(http://www.hou.usra.edu/meetings/lpsc2015/pdf/2745.pdf)

6) That's it. The last talk has been given. The last drink at the bar has been drunk. And the last goodbyes with old friends have been said. Farewell #LPSC2015. You were a great conference for me.
Till next year....

Monday, 22 December 2014

The Surface of a Comet

Philae landing
This sequence of images captures the landing location of Rosetta’s Philae lander. The first image in the sequence shows the pre-landing surface, at a resolution of 1.3 m/pixel, acquired 3.5 minutes before first touchdown. The second image in the sequence shows the landing site about 1.5 minutes after first touchdown. The large circle on the left highlights the plume of dust Philae raised when it bounced off the surface on its first touchdown. The smaller circles on the right point out where the Philae lander finally settled after bouncing twice on the surface of the comet. More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/11/Philae_spotted_by_Rosetta_after_first_landing.
Image Credit:  ESA/Rosetta/NavCam
It has been a very exciting summer and fall for planetary exploration, but I have been far too busy with a new job and home renovations to write about it. Finally, I have managed to squeeze out a bit of time, just before the end of the year, to summarize the European Space Agency’s awesome landing on the surface of Comet 67P/Churyumov-Gerasimenko.

Comet Churyumov–Gerasimenko is shaped kind of like a barbell, with one smaller lobe and another larger lobe connected by a narrow “neck”. Detailed images from the OSIRIS (Optical, Spectrocopic and Infrared Remote Imaging System) camera on board the Rosetta spacecraft provided the high resolution images that were needed to understand the comet’s form and to select a target site for the Philae lander. An area on the outer edge of the comet’s smaller lobe, just outside a large, circular depression, was selected as the landing site. The selection criteria considered scientific interest, safety, and operations. This particular site was chosen because it was thought to 1) have a relatively smooth and flat surface (at least locally), providing a safe place to land, 2) receive sufficient sunlight to re-charge Philae’s solar batteries, making the location operationally viable, and 3) be close to active processes and provide access to pristine materials, making it scientifically interesting.

Shape model of comet
Comet 67P/Churyumov–Gerasimenko has a very irregular shape. Images taken by the OSIRIS camera on the Rosetta spacecraft have allowed this 3D shape model to be calculated. Philae landed on the outer edge of the comet’s smaller lobe, just outside of the large, circular depression located there.
More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/10/Shape_model_of_comet.
Image Credit:  ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Active processes on a comet can be considerably different from those on other solid bodies in the solar system, like asteroids, moons, and planets. For one, comets have a high content of volatile material that regularly sublimates every time the comet comes close to the sun (at perihelion). Thus, sublimation is the dominant process operating on comet surfaces, rather than impacts, which tend to dominate the other solar system bodies.

Cometary surface processes have been studied in the past, most notably on comet 19/P Borrelly, which was observed in 2001 when the Deep Space 1 mission flew by.  Comet Borrelly is a Jupiter-family comet, like Cheryumov-Gerasimenko, therefore both comets are expected to have similar orbits, periods, and active processes. The most notable observation on comet Borrelly was the complete absence of impact craters, down to the resolution limit of 200 m.  Small depressions of 200-300 meters were observed, but their morphology and distribution argued against an impact origin. Instead, Dr. Dan Britt and his team of researchers, who studies the comet’s surface, proposed that these pits were caused by sublimation. 
Philea landing location – 50 km
This image from Rosetta’s OSIRIS narrow-angle camera, taken from 50 km above the comet’s surface, shows the location of the Philae landing site, just outside a large circular depression on the outer edge of the comet’s smaller lobe.
More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/11/First_touchdown.
Image Credit:  ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Philea landing location – 30 km
In this image from Rosetta’s OSIRIS narrow-angle camera, taken from 30 km above the comet’s surface, more details of Philae’s landing site start to become visible. The lander appears to have touched down on a smooth elevated surface within a rugged terrain.
More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/11/First_touchdown_close-up_1.
Image Credit:  ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

During its perihelion pass around the sun, volatile materials are sublimated from the surface of the comet. Non-volatile materials, in contrast, are left behind, building up an insulating “lag” layer that protects the surface from further sublimation and erosion. If this layer is not too thick, thermal instabilities can cause pits to form, exposing the volatile materials below. Impacts can also do the same for thicker lag deposits. In both cases, the volatiles exposed sublimate away, undermining the protective layer and causing the depressions to grow in size. This kind of growth, over may frequent perihelion passes, is thought produce a very rugged topography, with many flat surfaces and steep slopes.

The surface features that Dr. Britt and his team observed at comet Borrelly support this hypothesis. They saw smooth areas, which were interpreted to represent accumulations of non-volatile materials. They saw pits, which they think are indicative of relatively thin lag deposits. And they saw rugged topography, with many steep slopes interspersed with relatively flat regions, suggesting prolonged erosion of a lag deposit through undermining at steep slopes.

Philea landing location - 40 m
This image, taken by Philae's down-looking descent ROLIS imager from 40 m above the comet’s surface, shows that the landing surface is quite rough at smaller scales, in comparison to its smooth appearance in earlier images. The area is covered by debris, ranging in size from mm to meters, with the big bolder at the top right corner being 5 m in diameter. The black bar in the same corner is a section of Philae’s landing gear.
More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/11/Comet_from_40_metres.
Image Credit:  ESA/Rosetta/Philae/ROLIS/DLR
The topography of comet Cheryumov-Gerasimenko appears to have many similar elements. Philae’s landing area in particular seems to have an abundance of steep slopes with flat surfaces at their tops and bottoms. Upon closer approach, these “flat” areas are shown to be covered by rugged debris, containing many different particle sizes, from fine dust to meter-sized boulders. Although the resolution of the Deep Space 1 images was not sufficient to observe roughness of this size on comet Borelly, photometric analysis of that data did suggest that smooth units were rougher at smaller scales. Thus, even in this respect, comet Borelly and comet Cheryumov-Gerasimenko appear to be similar.

First Views from the lander
This is the first image ever taken from the surface of a comet! Acquired by Philae's CIVA camera, this two-image mosaic shows what appears to be a very rough and rugged cliff, illuminated by the sun. One of the lander’s three feet can be seen in the centre left.
More details about this image can be found at: http://www.esa.int/spaceinimages/Images/2014/11/Welcome_to_a_comet.
Image Credit:  ESA/Rosetta/Philae/CIVA
All of this implies that the surface of Cheryumov-Gerasimenko was probably formed by similar processes as comet Borelly. Thus, the surface of Cheryumov-Gerasimenko most likely represents erosive sublimation processes, where a relatively thin lag deposit was breached, presumably by thermal instabilities from below, creating pits that grew and coalesced to form the rugged terrain we see.
However, it is still not clear how the large circular feature near the Philae landing site was formed. It is possible that this feature represents a pit that grew to a particularly large size. It is also possible that this feature is an old impact crater that was too big to be completely eroded away by sublimation. More work is clearly required to answer this question.

Unfortunately, we may never get any more data from Philae on the surface of the comet. Because of its two bounces, Philae did not stay where it was originally targeted to land, but instead came to rest in the shadow of a cliff.  As a result, the solar panels could not keep the lander operational and at half past midnight (GMT) on Nov 15, 2014 Philae stopped transmitting to the Rosetta spacecraft. There is a slight possibility that when the comet makes its closest approach to the sun on August 13, 2015, Philae’s solar panels may receive enough energy to wake up the lander and re-establish communications. Until then, we will have to be satisfied with orbiter data from the Rosetta spacecraft, which continues to collect data, currently from 20 km above the comet’s surface, but with future flybys planned to approach closer than 8 km. Exciting times, indeed!
Sources:

Britt, D.T. et al. The morphology and surface processes of Comet 19/P Borrelly. Icarus  167, 2004, DOI: 10.1016/j.icarus.2003.09.004.

“J” Marks the Spot for Rosetta’s Lander, ESA’s Rosetta Blog, Nov. 15, 2014.

Pioneering Philae Completes Main Mission before Hibernation, ESA’s Rosetta Blog, Sept. 15, 2014.

Wednesday, 30 April 2014

Is Venus Active?

Hot spot on Idunn Mons
This hot spot on Idunn Mons, a volcano on Venus, was discovered by Suzanne Smredar and her coworkers in 2010. Here, Magellan radar imagery (in brown) is draped over Magellan topographic data, showing off the landscape of the region. The elevation has been exaggerated 30 times in order to highlight the topography. On top of all this, data from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument on board ESA’s Venus Express orbiter, is overlain to show temperature variations. Red colours indicate the warmest places and purple the coolest. This hot spot is thought to indicate the presence of geologically young lava flows, less than 2.5 million years old, but it does not prove the existence of current active volcanism.  
More details and the original image can be found at http://sci.esa.int/venus-express/46816-surface-warmth-on-a-volcano-on-venus/
Image Credit: ESA/NASA/JPL


One of the most interesting things to come out of this year’s Lunar and Planetary Science Conference is the identification of potentially active volcanoes on Venus. Venus has long been known to have lots of volcanoes, but evidence for active volcanism on the planet has been elusive until now.

Venus, despite being similar to the Earth in mass and size, is a very different kind of planet. It is shrouded in a thick atmosphere of carbon dioxide and has clouds of sulfuric acid. As a result of this thick atmosphere, pressure on the surface of Venus is 93 times the atmospheric pressure on the surface of the Earth and temperatures are a sizzling 900 degrees Fahrenheit.

The thick atmosphere also makes it very difficult to see the surface of Venus. Regular cameras that capture visible light can’t see beneath the thick atmosphere. However, radar and infra-red instruments can penetrate the dense atmosphere to let us study the planet’s surface. From 1990-1994, NASA’s Magellan mission mapped the entire surface of Venus using radar. More recently, the Venus Monitoring Camera (VMS) on board the European Space Agency’s Venus Express mission has been gathering data from both the planet’s surface and atmosphere.

Magellan Radar Mosaic of Venus
NASA’s Magellan mission to Venus mapped the entire surface of the planet, using radar instruments to peer beneath the thick atmosphere that otherwise obscures the surface of Venus from view. This image is centred more-or-less on Diana Chasma.  Maat Mons is the purple/pink volcano north east of centre with Ganiki Chasma extending northward nearby. 
This image can be found at http://photojournal.jpl.nasa.gov/catalog/PIA00159
Image Credit: NASA/JPL/USGS
The VMS collects data at four different wavelengths of light. The atmosphere of Venus is transparent to one of these wavelengths, namely the near-infrared wavelength of 1.01 microns (1 micron = 1000 nanometers). The radiation reflected from the surface of Venus at this wavelength is highly dependent on the surface temperature. A team of scientists at the Max Planck Institute for Solar System Research, led by Eugene Shalygin, have been using this fact to study temperature variations on the planet’s surface.

Such data can only be collected at night, when heat from the sun is not a factor, and only when cloud variability is low, to ensure that differences are in fact due to changes at the surface. With these constraints, the team was able to collect data from a total of 36 different orbits of the Venus Express spacecraft, providing a series of observations over time.

From the VMS time series data, Eugene Shalygin and his team observed a number of bright spots, representing an estimated 980-1520 degrees Fahrenheit, well above planet's typical temperatures. Most spectacularly, these bright spots appeared suddenly (after having been absent in preceding orbits), persisted through several orbits, and then disappeared in subsequent orbits. “We were looking for these spots for several years (and) didn't find," anything, said Alexander Bazilevskiy, a senior scientist on the team. The scientists conclude that these transient bright spots must represent some kind of localized process that released hot matter to the surface in a short period of time. In other words, these spots suggest that an active volcanic event occurred right before our eyes!

All of the identified bright spots are located at the edge of Ganiki Chasma, a young rift zone in the vicinity of Maat Mons. Maat Mons is a tall shield volcano that erupted between 10 -20 million years ago, so this region is known to have been volcanically active in the past. The bright spots could, therefore, represent either long lava flows, which stretch for about 25 kilometers (16 miles), or a chain of small cinder cones or volcanic hot spots.
Perspective view of Maat Mons
Maat Mons is a very large shield volcano on the surface of Venus. It is thought to have erupted between 10 -20 million years ago. Potential evidence of current volcanic activity has been found in the vicinity of this large volcano.This image shows a computer-generated perspective view of the volcano, looking from the north.
This image can be found at http://photojournal.jpl.nasa.gov/catalog/PIA00106
Image Credit: NASA/JPL

But, before getting too excited, we should be cautioned that the volcanic nature of the observed bright spots has not yet been confirmed. Shalygin and his team plan to look for more bright spots in the VMS data and also to sift through the historical Magellan radar data to see if they can find additional evidence of volcanic activity.

For more details on the location of the spots and to see an example of the VMS discovery data, check out Lunar and Planetary Science Conference Abstract #2556, where Shalygin and his team first presented their findings.

Sources:

Hall, S. Active Volcanoes on Venus? Sky and Telescope, March 24, 2014.
http://www.skyandtelescope.com/astronomy-news/active-volcanoes-on-venus/

Klotz, I. Active Volcanoes Revealed on Venus, Discovery News, March 18, 2014, Space.com http://www.space.com/25106-venus-volcanoes-active.html

Shalygin, E.V. et al. Bright transient spots in Ganiki Chasma, Venus. 45th Lunar and Planetary Science Conference, Abstract #2556, 2014. http://www.hou.usra.edu/meetings/lpsc2014/pdf/2556.pdf

Sunday, 30 March 2014

The Curious Layers of Mars

It has been an extremely long and hard winter this year in the north-eastern portions of North America and I find myself in need of some cheering up. Nothing is so cheery as pretty pictures of planetary surfaces. So today I am going to talk about some of the beautiful imagery that's been coming from the Curiosity rover on Mars, specifically the lovely layers of sedimentary rocks.

Many Layered Sandstones
Many layers of soft and hard sandstone rocks make these step-like structures on Mars. The Curiosity rover collected this image in Gale Crater on Feb. 25, 2014.
 To learn more about this image, go to the JPL Space Images website.
Image Credit: NASA/JPL-Caltech/MSSS

Curiosity landed in the Gale impact crater on Mars in August of 2012 and has been exploring the floor of that crater ever since. The going is slow though. The rover's average travelling speed is about 30 meters per hour. In comparison, most people can easily walk 3 kilometers (3000 m) per hour. But the rover is actually even slower than its average travelling speed. First, it's goal is to explore Mars, so it makes many stops to gather science data. Second, it needs to pick its path carefully to avoid obstacles. So it's not always following the straightest route. In the early days of the mission, sharp rocks were puncturing the rover's aluminum wheels, but now careful route planning has helped to minimize such damage. But that care takes time. In the end, Curiosity has moved only about 4 kilometers from its landing site in the first 561 martian days of operations (a martian day is about 40 minutes longer than an Earth day).

Topography of Gale Crater
The Curiosity rover landed on the floor of Gale impact crater on Mars, just north of Mount Sharp in the centre of the crater. The landing location is highlighted here by the black oval.
To learn more about this image, go to the NASA mission page: http://www.nasa.gov/mission_pages/msl/multimedia/pia15093b.html#.UzejcYXiiCo.
Image Credit: NASA/JPL-Caltech

The type of terrain Curiosity has been passing through has changed in those 4 kilometers, though. The rover's original landing site was relatively flat with only a scattering of small pebbles on the ground. This is actually a good thing for a landing site, since you wouldn't want your rover to land on a cliff or large boulder.

Landing Site Panorama
The Bradbury Landing site (named after Martian Chronicles author Ray Bradbury) is very flat and shows no evidence of layering. The mountain in the distance at the top centre of this image is Mount Sharp.
To learn more about this image, go to the JPL Space Images website.
Image Credit: NASA/JPL-Caltech/MSSS

Ever since it landed, Curiosity has been steadily making its way to the large mountain in the centre of Gale crater, called Mount Sharp. The base of Mount Sharp, which is about 20 kilometers south from the landing site, is the rover's ultimate destination. This region is of great interest to scientists because it contains a very thick exposure of layered rocks, which may reveal several billion years worth of clues about this region's history. 

Landing to Present Traverse
Ever since arriving at Bradbury Landing, Curiosity has been making its way south to Mount Sharp, stopping at a number of planned waypoints along the way. This image shows exactly where Curiosity has traversed, up to day 561 (March 5, 2014) of the mission. Murray Buttes is thought to be a good entry point to the base of Mount Sharp.
To learn more about this annotated image, go to JPL Curiosity Rover Multimedia website.
Image Credit: NASA/JPL-Caltech/Univ. of Arizona

But, Curiosity did not have to go all the way to Mount Sharp to find layered rocks. Those it found relatively soon after landing. More recently, on Feb. 25, 2014, Curiosity arrived at a location where many different types of layered rocks can be seen in one place (see the image at the top of this post).

The layered rocks here are thought to be sandstones. This is a type of rock that is literally made up of sand grains glued together by some kind of cement. If the cement is made up of clay materials, the sandstone is relatively soft and can be easily eroded by wind and water. If the cement is made up of hard quartz minerals, the sandstone is very durable and hard to erode. When layers of hard and soft sandstone occur together, they make step-like structures, where the hard sandstone forms caps protruding over the soft sandstone that is eroding away.

Scientists are not clear on why there would be so many different layers of soft and hard sandstone in this one place, or how they formed. But, they are hoping for some answers soon. About 400 meters away is the planned Kimberly waypoint. This area was identified as a point of interest from satellite images, because four different-looking rock types seem to intersect there. And it is expected that layered sandstones will be found at the Kimberly waypoint. The Curiosity rover will stop there for a time to conduct scientific investigations.

Tuesday, 28 January 2014

Antarctica Beneath the Ice

This winter has been a particularly brutal one in my part of the world (south-eastern Canada), with snow coming earlier than usual, extremely cold temperatures persisting for prolonged periods of time, and brutal ice storms causing massive power outages. With all this cold and snow, I thought it would be appropriate to talk about another cold place on Earth, Antarctica.

Sitting at the southern pole, Antarctica is almost completely (98%) covered by an ice sheet. Reaching thicknesses of up to 3km in places, this glacier flows under its own weight and is estimated to hold more than 50% of the world's fresh water. It is anticipated that melting of this great ice sheet, due to global climate change, will contribute significantly to sea level rise. But it is still not clear exactly how the glacier will react to climate change, because the glacier and the bedrock it sits upon is poorly understood.

Ice / No Ice
Antarctica is almost completely covered by a large ice sheet. A new data set, called Basemap2, uses over 26 million data points to determine the surface elevation of the ice (right image), the thickness of the ice, and the topography of the underlying bedrock (left  image). The vertical scale in these images has been exaggerated 17 times, to make the mountains and valleys easier to see.
To learn more about these data sets, go to the NASA Feature website. There you will also find an interactive map of the two datasets, which lets you switch between them, making them easier to compare.
Image Credit: NASA's Goddard Space Flight Center
 Luckily, scientists have recently produced a new data set that, in addition to revealing the stunning topography hidden beneath the glacier, will help modellers resolve these questions. Led by Dr. Fretwell at the British Antarctic Survey, an international consortium of scientists has released the Bedmap2 dataset. Bedmap2 builds on a previous data set called Bedmap (produced in 2001), providing surface elevation, ice thickness, and bedrock topography for all of Antarctica, south of 60° S.

To produce the new data set, the researchers incorporated an additional 25 million measurements and processed these using modern GIS techniques and hardware, which made manipulation of such large data sets possible. For the earlier Bedmap data set, which used only 1.4 million data points, this number had to be reduced for processing to be manageable. In addition, the more recent data points were collected using modern Global Positioning Satellite (GPS) technology, which helped to pin-point the data more precisely. The original Bedmap data didn't always have this level of precision.

The new data comes from a wide variety of sources, representing 83 different survey campaigns, run by various nationalities, and collected using ground, air, and space platforms. A large part of the data comes from the Operation IceBridge campaign. This airborne mission was flown from Punta Arenas, Chile, collecting laser altimeter and ice-penetrating radar data between 2009 and 2011. The radar instrument, called the Multichannel Coherent Radar Depth Sounder (MCoRDS), was operated by the Center for Remote Sensing of Ice Sheets at the University of Kansas. MCoRDS sent radar signals down through the ice and recorded the returning signals, which gave information on the ice surface, the internal layering within the ice, and the bedrock below. This data was processed to determine the surface elevation of the ice and the ice thickness, which were used to calculate the bedrock topography. However, ice-penetrating radar instruments, which tend to work best in flat areas, don't do so well in steep mountainous regions.  In such areas, surface elevation data from NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) proved useful. The laser data from Operation IceBridge was used to verify the accuracy of the surface elevation data from these sources. In some cases, ground-based data was available, including over-snow radar, seismic sounding, surface elevation, bathymetry, rock-outcrop, grounding line, and ice-extent datasets. Also, when the density of the data was particularly low, satellite gravity data was used to determine ice thicknesses.

The result of all this data is that Bedmap2 provides higher resolution, greater coverage, and improved precision over the original Bedmap product. The large amount of data points allows the data to be interpolated over a 1 km grid, but the uncertainties can be high; up to 130 m in ice surface elevation and up to 1000 m in ice thickness.
  
Even so, Bedmap2 highlights the beauty of the bedrock under the ice. The better resolution shows off smaller features that could never be seen before, revealing the full scale of the mountain ranges, valleys, basins, and troughs. The new data has also found that the deepest bedrock elevation is actually deeper (by 15%) than previously believed. In addition, several other deep points (about 2.5 km below sea level) have now been identified on the Antarctic continent. It is not clear how accurate the numbers for these deep points are, but it is certain that the deepest point for any continent on the Earth is located somewhere in Antarctica. No other continental areas even come close to such depths.

The Bedmap2 data set also tells us a lot about the Antarctic ice sheet. Volumes calculated from the data indicated that 27 million km3 of water are stored in the ice sheet, which can potentially contribute 58 m to sea level rise if the Antarctic glacier should melt. These estimates are very close to the values that were determined from the original Bedmap product, but now our confidence in them is much greater. Also, we now know that the ice sheet is on average 4.6% thicker than was previously believed and that a much greater volume of ice exists below sea level.

Bedmap2 / Bedmap
The Basemap2 data set (right image) builds upon a previous version, called Basemap (left image).  The higher resolution and greater coverage of Basemap2, gives us better precision, making it easier to see the spectacular mountain ranges, valleys, and rugged terrain.
To learn more about these data sets, go to the NASA Feature website. There you will also find an interactive map of the two datasets, which lets you switch between them, making them easier to compare.
Image Credit: NASA's Goddard Space Flight Center
Mapping the thickness, volume, and bedrock of the Antarctic glacier helps us to understand how ice sheets respond to changes in ocean and air temperatures. Specifically, the shape and structure of the bedrock below the ice controls how the ice sheet moves, affecting its shape and thickness. For example, ice will flow faster downhill, be thinner at the top of the hill, and thicker at the bottom. Conversely, uphill slopes and bumpy terrain in the bedrock can slow down an ice sheet, or even hold it in place temporarily. Bedmap2 provides the level of detail that is necessary to understand these effects, allowing researchers to build more realistic and accurate models that simulate ice motion.

But the task in still not quite finished. There are still many places in the Bedmap2 data set where the amount of data is very poor or even completely non-existent. Dr. Fretwell and his colleagues have identified what they call 2 "poles of ignorance", regions where no data exists for several hundred kilometers. Clearly, the need for more data gathering exists. Which means we can all look forward to a Bedmap3 sometime in the future.

Sources:
NASA's IceBridge Mission Contributes to New Map of Antarctica, NASA News, July 4, 2013.

Fretwell, et al. 2013, Bedmap2: Improved ice bed, surface, and thickness datasets for Antarctica, The Cryosphere, 7, 375-393, doi:10.5194/tc-7-375-2013.