Guess the Planet 19) Round Structures

Here is this week's guess the planet. What are these round structures? why are they so regular? And which planet can they be found on?

Check back on Friday for the answer.

Terrestrial Analogues

This week’s guess the planet image comes from Earth. It shows the Barringer Impact Crater, also known as Meteor Crater in Arizona. This image comes from Google Earth, and appears to be an aerial photograph taken by Google. The crater is approximately 1.186 kilometres across. Roads and tracks can clearly be seen to the north of the crater, which I had to crop out of the original image in Monday’s post.

We find impact craters like this all across the solar system, the surfaces of numerous planets, moons and asteroids are covered with them. Only a handful can be found on Earth. Most are badly weathered and eroded by centuries of exposure to the hostile conditions produced by our planet’s thick atmosphere and prevalence of life. What makes this crater interesting to planetary scientists is how easy it is to get to. Earth has the most geologists of any planet in the solar system, making it much easier, and cheaper to study than any other world.

Luckily for us Earth can tell us a lot about the other planets as well. What I want to talk about this week is the importance of studying “terrestrial analogues” these are places where we can compare features on Earth to those we find on other planets.

One of the main principles of comparative planetary science is that the same fundamental processes shape every planet. They might function slightly differently from one world to another, but the principles, and frequently the results are similar. For example, in previous posts I’ve talked about cryovolcanoes, where the environment is so cold that water ice behaves like rock and liquid water like lava. We don’t have cryovolcanic environments on Earth, but we can compare these landscape on Titan or Europa with a silicate volcano on Earth to form theories about how the alien landscape has formed. This allows us to move beyond describing what a landscape looks like, and start to understand the geomorphic processes which resulted in its formation. Processes which likely have implications for the environment of the planet we are studying.

Some landforms develop through virtually identical processes on different planets, and so have fairly obvious analogues. In other cases it is far more difficult to figure out what the nearest terrestrial equivalent might be. One complication to studying the landscapes of other planets in this manner is a phenomenon called “Equifinality”. This means that multiple processes result in similar looking end results. For example a crater could be formed by a meteor impact, or by volcanic collapse. Both have a similar shape, but there are usually subtle clues with which we can distinguish between the two.

On Earth it is relatively easy to go to a site and make “In Situ” observations. Such measurements can let us limit the variety of processes which could be responsible. Quickly figuring out how something was produced. For example the area around our crater doesn’t have any evidence of volcanism, so it is more likely to be an impact crater than a volcanic one. If we only have satellite data from another planet, then it can be harder to make such a determination.

This is where our analogue studies prove useful. We can identify a range of possible analogues and then study all of them to see which are the best morphological match for the features we are seeing on our other planet. We likely have limited information to work with, so we have to take our terrestrial data and examine it as though we were looking at the other planet, seeing which features would be obvious in our satellite images, and which wouldn’t.

In this way we can identify characteristic features to look for in the planetary data, and get closer to determining which processes shaped the surface of our other world.

Guess the Planet 18) Impact Crater

This Impact crater is quite well known. Which one is it and on which solar system body can it be found? Check back on Friday for the answer.

The icy shell of Europa

 

This week’s guess the planet image comes from Europa. It was acquired by NASA’s Gallileo spacecraft. Europa is one of Jupiter’s four large moons. It is an intriguing world, as it is entirely covered in a shell of ice. On a large scale this gives the moon a very smooth topography, with few high relief features. On the small scale the surface is crisscrossed with cracks and streaks, such as those shown in this image which is 163 km by 167 km. NASA produced the colour image by combining data from two different orbits of the Galileo spacecraft. Credit goes to NASA’s JPL

Beneath the ice there is believed to be a subsurface ocean of liquid water, kept warm by tidal heating from Jupiter. This ocean has long intrigued scientists and the public alike as it could be a good place to look for alien life in the outer solar system. There is more water on Europa than on Earth, and so it would be very interesting to break through the ice into the ocean below. This might be easier said than done however, since the ice layer is believed to be kilometres thick, shielding the water below it from space.

The brown streaks on Europa can be seen quite clearly from orbit, and are evidence that Europa is active. They are believed to consist of hydrated salts, which are extruded onto the surface of Europa when cracks open up in the ice. The description of this image over at the NASA Photojournal suggests that the bright regions of the image are pure, white water ice, while the brown streaks might consist of “magnesium sulfate or sulfuric acid”.

Experiments have shown that salts take on a yellow brown appearance when exposed to the unpleasant radiation environment around Jupiter. This makes them very distinctive, and helps to pick out some of the cracks and fissures which riddle the moon’s surface.

the most interesting regions of Europa are the “Chaos Terrains”, where the surface and subsurface appear to interact. These regions are riddled with fractures like those shown above. The ice is broken up into massive blocks, which look somewhat similar to terrestrial icebergs. It has been suggested that areas of chaos terrain are indicative of pockets of water in the subsurface. These buried lakes aren’t part of the massive ocean itself, but are rather areas of melt further up in the icy crust. Unlike the ocean, they are close enough to the surface to interact with it, causing rifts and fissures to develop above them, through which salty water can flow onto the surface.

While the large ocean might be hard for a spacecraft to reach, it could be more feasible to drill into one of these underground lakes, and look for signs of life.

Image Credits

Europaterrain at NASA PhotoJournal: NASA/JPL-Caltech/SETI Institute.

Europa Globe: NASA/ JPL/ DLR 

 

 

Guess the Planet 17: Brown Band

In this week's Guess the Planet we see a bright region scored with quite straight cross cutting features, and bands of darker brown material. What is this landscape and on which world can it be found. Tune in on Friday for the answer!

Doom Mons on Titan

This week’s guess the planet image comes from Titan. Credit for this image goes to the cassini team. Their image description states that there 1 km is 2.85 pixels across, north is towards the top of the image. This is a Radar image, which allows us to peer through the thick haze of atmosphere that surrounds the moon of Saturn. This means that it isn’t as crisp an image as those which are available for many other solar system bodies. However we can still learn a lot about the surface of this small world.

Using Radar gives us the opportunity to look at this image in a different way, which makes the nature of the features much clearer. In this 3d model of the area we can see that the round feature near the bottom of the image above consists of a deep hollow directly adjacent to a large peak.

 

The depressed region is Sotra Patera, and the mountain is Doom Mons. “Patera” means bowl in Latin, so is used as the name for basins and depressions in planetary nomenclature. Choosing names for features on other planets can be quite a complex process. On Earth we have been naming the landscape for millennia. If you live near a mountain you likely have a name for it.

When we look at another world for the first time we have to come up with names for features pretty quickly, otherwise it makes it difficult to talk about what we are seeing or to study the geomorphology. For almost a hundred years the task of deciding what things can be called has fallen to the International Astronomical Union, they have defined a series of latin words such as patera, mons and Planitia, which define various easily identified geographical features. These terms are thus used consistently across every planet except earth, where traditional names of features predominate for cultural reasons. The IAU then approve themes to be used to assign consistent names to specific features. Doom Mons has quite an ominous name for a reason, mountains on titan are named after fictional mountains in Middle Earth. Since this is the largest mountain range on Titan it was assigned the name of the most significant mountain in the Lord of the Rings. A large number of fictional and mythological place names have been used for features across the solar system. More information on planetary nomenclature can be found at this link.

Sotra Patera is the deepest of several craters in the mountain range, which are believed to have formed as volcanic calderas. Unlike its fictional counterpart Doom Mons doesn’t spill molten lava onto the surrounding plains. Rather it is believed to be an icy Cryovolcano. The material erupted form this volcano would not be molten rock, but rather a mixture of water and ammonia, or perhaps similar in composition to the liquid hydrocarbons which are found in Titan’s seas. Despite the radically different material, the morphology of this area is a good match for volcanic terrains on Earth, where peaks and craters form distinctive volcanic landscapes. The same processes are shaping the environment, but the different temperature conditions mean that different materials are involved.

This site is the best example of volcanic morphology on Titan, but other features have also been observed which could be evidence of volcanic events. The Cassini team are particularly interested in flow features, and areas where the landscape seems to change between images, possibly suggesting that volcanism is occurring in the present day. If Titans cryovolcanoes are still active then this could explain why the moon has such a thick atmosphere, as volcanic processes might replenish the gases which are lost to space.

Image Credits

• Doom Mons and Sotra Patera NASA/JPL- Caltech Via Wikipedia
• Map of titan’s mountains NASA/JPL-Caltech/University ofArizona/USGS
• 3D model of area NASA/JPL-Caltech/ASI/USGS/University of Arizona

Guess the Planet 16) Grainy Image

Here is this week's guess the planet. Remote sensing images can often be quite grainy and hard to make out, but you can still get a lot of information out of them. What is this feature, and on which world can it be found?

Tune in on Friday for the answer, and more about this fascinating landscape!

Clouds on Venus

This week’s guess the planet image comes from Venus. It was taken by the Galileo spacecraft in 1990 and credit goes to NASA’s Jet Propulsion Laboratory. The ultimate destination of the Galileo probe was the Jupiter system, and it became the first spacecraft to enter Jupiter orbit. However in order to get there it had to make several flybys of other planets in order to increase its speed. This is called a “gravity assist” or slingshot manoeuvre and is often used to accelerate spacecraft on route to the outer solar system.

This image, from one of the spacecraft’s flybys shows cloud patterns in the atmosphere of Venus. Clearly this is a false colour image. The write up that accompanies this image in the NASA gallery explains that this is to “emphasize the subtle contrasts in the cloud markings and to indicate that it was taken through a violet filter”. False colour images are often used in planetary science, so it is always important to understand what you are looking at, and how the way in which the data were collected and processed influence what you can see.

The atmosphere of Venus is dramatically different to that of Earth. It is composed primarily of carbon dioxide. The clouds visible in this image are made of sulphuric acid. These clouds are largely opaque and make direct observation of the Venusian surface quite difficult. The atmospheric composition has also resulted in a runaway greenhouse effect, leading to temperatures at the surface being much higher than those on Earth. The pressure at the surface is also extremely high, making it a very difficult environment to explore.

The soviet Venera 7 probe was the first spacecraft to land on Venus, or indeed any other planet. It touched down in 1970 although it had a somewhat rocky landing, and was nearly lost.

This image of the surface was captured by the Venera9 lander in 1975. This was the first spacecraft to return images from the planet’s surface. These landers required an extensive cooling system to remain operational on the surface, and had to be built to resist the high pressure.  

The surface of Venus may not lend itself for human habitation, but ironically the upper atmosphere, above the cloud layer, might be far more hospitable. As there is an elevation, around 50 km above the surface of Venus where the temperature and pressure are quite Earth-like. It has been suggested that floating cities could be constructed here. A breathable mix of gasses is less dense than those that make up Venus’ atmosphere, so could be used as a lifting gas in the same way that hydrogen and helium are on Earth. Humans could live inside a balloon, safely above the hellish surface of the planet.

Image Credits:

Galileo image of Venus: NASA JPL

Surface of Venus from Venera 9: USSR Space Program via Wikipedia.