Guess the Planet 3: Spider-like features

What are these strange, spider-like features sprawled across the surface of another world? On which planet are they found and what do you think might cause them? Tune in on Friday to find out...
Happy Halloween!

The Seas of Titan

As many of you have spotted this week’s guess the planet doesn’t actually come from a planet. This image is from Titan, the largest of Saturn’s moons. We’ll be seeing a few moons and dwarf planets in this series, and maybe the odd asteroid and comet. 

This is quite a famous image, so it’s good that I had a few responses from people who knew it straight away. It shows Ligeia Mare, the second largest of Titans seas. Here is an image of the northern hemisphere of Titan to put these seas into context. The North Pole of Titan is at the centre of the image, which extends out to 50 degrees north. The credit for this image goes to the Cassini Team, NASA/JPL-Caltech/ASI/USGS More information on this area can be found on the Cassini website. The image from Monday's post can be found here.

The result is a detailed map of this strange moon, showing that the northern hemisphere is covered by numerous lakes and seas. This is actually a false colour image, because Titan is shrouded in thick layers of cloud, so it isn’t possible to photograph the surface from orbit as we can with Mars, the Moon, and when the weather permits, Earth. Instead this image was produced using radar. Different materials respond to the radar in different ways, allowing the Cassini team to determine which areas are solid, which are liquid, map the topography of the landscape, and even determine the roughness of the surface. 

Ligeia Mare itself is 420 by 350 km across, so covers a sizable area. It is surrounded by many smaller lakes and may be connected to the other large seas that occupy this part of the Titan’s surface. We are still not certain why this region of Titan has these large bodies of liquid, when other regions do not. 

While it might look like a terrestrial sea, Ligeia Mare wouldn’t be much fun to swim in, since it is composed of liquid hydrocarbons rather than water. It is so cold on Titan that water never thaws and is only found as solid ice. The liquid that makes up these lakes is composed of Methane and Ethane. On Earth we know these chemicals as gasses, but at low temperatures in the outer solar system they exist only in their liquid state. 

Titan is the only body besides Earth to have stable liquid oceans on its surface which makes it a fascinating opportunity to compare how “hydrology” and coastal processes have evolved separately using different materials in two very different temperature regimes.

A brief history of going to Mars (part 2)

The newly arrived Trace Gas Orbiter is just the latest in a long line of Mars probes. Last week we discussed the first decade of the robotic exploration of Mars. I discussed the early attempts by both the Americans and Russians to reach the red planet, culminating in the observations of the Mariner Probes and the short lived landing attempt by Mars 3. 

 

Both space agencies were keen to get more information from Mars, and so several missions were dispatched throughout the 1970s. The USSR didn’t have much luck with its landing attempts. The Mars 6 lander crashed, while Mars 7 missed the planet entirely and is now in orbit around the sun. However the Americans were about to land not one but two probes on the martian surface.

 

Locations of all Mars landing sites past and future, as well as the crash sites of the unsuccessful landers.

The Viking Era

In 1975 the two Viking landers touched down on Mars. These landers survived their descent and remained operational for considerably longer than a few seconds, making Viking 1 the spacecraft to successfully land on Mars. Both Viking missions consisted of a lander and an orbiter. The landers began studying the environment on the surface, while the orbiters recorded thousands of images, produced detailed “mosaics” of the planets entire surface.

The landing sites for the Viking probes were Chryse Planitia, and Utopia Planitia, both in the northern lowlands of Mars. The landers carried a variety of instruments to study the environmental conditions and meteorology of Mars. They also had a life detection experiment, although the results of this proved inconclusive they did give us insights into the chemical processes taking place within the martian soil. The Viking 1 lander remained operational for over two thousand days, setting a record that wouldn’t be surpassed for decades. 

The 80’s and 90’s

Mars missions became less frequent throughout the subsequent decades. The USSR attempted to reach Phobos, Mars’ largest moon twice in 1988, but both missions failed. While the Americans had steadily improved at sending things to Mars the Russian space agency had entered a string of bad luck which endures to this day. Almost a decade later the Russian Mars ’96 probe also met with failure. The Americans had lost contact with their Mars Observer spacecraft in 1993, resulting in a decades long gap between successful Mars missions. 

This sparse period was to end in 1997 which marked the arrival of the next American orbiter; the Mars Global Surveyor (MGS). This spacecraft was designed to map the planet in unprecedented detail. It would remain in operation until 2006, returning far more data than all of the previous missions combined.  MGS provided unprecedented detail of the martian surface, detecting features such as gullies and debris flows which are indicative of very recent geological activity. By building up a global dataset over many years the MGS produced an unprecedented record of martian weather systems. 

The late 90’s also marked the arrival of the Mars Pathfinder mission. This American lander was a major milestone as it was the first time a rover had been landed on Mars. Pathfinder, and its Sojourner rover were intended primarily as a technology demonstration. However like many spacecraft it massively exceeded its mission parameters returning tens of thousands of images. The technology used in the sojourner rover paved the way for the Mars Exploration Rovers of the following decade. 

1998 marked the first time that a country other than NASA and the USSR sent a probe to Mars. the Japanese Nozomi mission was a failure. It had been intended to go into orbit around Mars, but orbital insertion failed.

The success of Mars Pathfinder was followed by a string of failures for NASA, with the loss of the Mars Climate Orbiter and Mars Polar lander spacecraft. Despite constant improvements in technology and expertise, getting to Mars is still extremely difficult.

The 21^st century

The early 2000s got off to a good start with the launch of the American Mars Odyssey orbiter in 2001. 2003 then saw the launch of both the European Space Agency’s Mars Express and the NASA Mars Exploration Rovers. These four missions have proved to be some of the most successful in the history of Mars exploration. Both MER rovers were intended to operate on the surface for 90 “sols”. A sol is a martian solar days and these are 24 hours and 39 minutes long, so the mission was supposed to last for several months. This would have allowed the rovers to travel up to a kilometre and survey a much larger area than a stationary lander would have been able to. 

Both MER rovers massively exceeded these expectations. The MER Spirit rover operated until 2010, traveling almost eight kilometres. The MER Opportunity Rover is still operational at the time of writing, and has currently traveled 43,436.19 metres according to the mission website. These rovers, and the instruments they carry have provided years of information about the geology of the regions through which they have traveled and provided an invaluable array of “ground truth” observations. This has provided vital context for the analysis of more numerous satellite images. 

And the satellite data has become extremely numerous. Mars odyssey is expected to continue to function until at least 2025, and is currently serving a communications relay for the Curiosity Rover, as well as returning data from its remote sensing instruments. Mars Express is also still operational, and played a key role in last week’s landing attempt.

Several more missions have followed over the last decade. The mars reconnaissance Orbiter was launched in 2005 and continues to survey the martian surface, being heavily involved in landing site selection for future surface missions. The Phoenix lander was launched in 2007 and landed high on the northern plains. It returned lots of valuable information about the composition of martian ground ice at the high northern latitudes. 

The Mars Science Laboratory Curiosity Rover was landed in 2012 and has so far traversed more than 11 kilometre. It has studied the geology of its landing site in unprecedented detail and will continue to do so for some time. More recent arrivals include the American Mars Atmosphere and Volatile Evolution (MAVEN) Mission and the Indian Mars Orbiter Mission, both of which arrived at Mars in 2014. The Mars Orbiter mission is India’s first interplanetary craft, and makes them the fourth space agency to reach Mars successfully.

We really are living in a golden age of Mars exploration. 

Many of the more recent probes will continue to operate for years to come, returning valuable information about the environment, geology and weather of the red planet. With each new mission the range and variety of instruments we have around Mars increases and more landing sites are added to the list of places which have been visited by our machines. 

A lot of people are keen to send humans to Mars, and this would be a useful thing to do. But I’d argue that the best thing we can do is keep new satellites and landers coming, so that as the older instruments are retired we continue to have good coverage of the red planet, and can continue the important work of trying to understand this fascinating world.  

References and Further Reading

NASA's Timelines of Mars exploration can be found here and here.

Viking missions

Mars Global Surveyor

Mars Pathfinder

Mars Odyssey

Mars Express

MER Rovers

Mars Reconnaissance Orbiter

Phoenix Lander

Curiosity

MAVEN

Mars Orbiter Mission

Trace Gas orbiter

Map of all Mars landing sites, including failed attempts andplanned missions. By Emily Lakdawalla, Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Guess the Planet 2: Dark Region

Here is our second guess the planet image. This remote sensing image shows a dark area with kind of fractal edges, within an area of yellowish looking terrain. So what is it and what planet are we looking at? As before I'll post the answer on Friday along with more detail about this image.

Ice filled fractures on Mars.

 Now to reveal the answer to our first guess the planet post...

Here is another view of the features I posted on Monday, this time with the proper context information. North is to the top left, and the image is over a kilometre across. The sun symbol indicates that illumination in this image is coming from the bottom left corner, although in this case that doesn't have too great an effect on how the features look.

 

This image comes from Mars and its location is indicated by the star in the inset context map. It is a section of HiRISE image PSP_007571_2490 and the credit goes to NASA/JPL/ University of Arizona. Their High Resolution Imaging Science Experiment, or HiRISE instrument, on the Mars Reconnaissance Orbiter (MRO) produces the most detailed images of Mars. The Pixels on HiRISE images can be as small as 25 centimetres across. So they have comparable resolution to the air photos you see in Google Earth. This means that metre scale objects can be “resolved”, in other words those are the size of feature which you can reliably tell are present. This means that HiRISE images give us a great view of the landscape. 

This image shows heavily fractured ground in the high northern latitudes. Cracks have opened up in the ground, forming a massive network of cracks which covers many kilometres of the planets surface. These cracks have become filled with bright ice, which makes them stand out from the ground around them. This landscape has resulted from the seasonal temperature changes on Mars. Although it has a cold, dry climate there is actually a lot of seasonal variation in temperature on Mars. This has some interesting effects on ice rich soil.

Changes in temperature result in very small amounts of expansion and contraction of solid materials. As the temperature drops the material that makes up the ground will contract slightly and this will induce tensile stress. If the tensile stress due to contraction exceeds the tensile strength of the material then cracking will occur, releasing the tension and deforming the ground surface. Once small cracks form they start to fill with ice, and these ice wedges will force the fractures open even further, until wide fractures like these are formed. The pattern covers several kilometres of the surface, and some of the fractures are several metres across.

You can see the full image at this link, although full resolution HiRISE images are huge file sizes. http://www.uahirise.org/PSP_007571_2490