Have you ever looked right into the night sky, and also been lucky sufficient to clues anotherplanet? our solar system has 8 planets, countless with their own moons and also sometimeswith battalions the accompanying asteroids. However how did they all acquire there, and arethey different from ours own residence planet? What makes them different?

We can observe currently active processes in our solar device to release puzzles of how planets were formed. We recognize most about Earth and theprocesses the shaped it, and we can apply this to researches of surface ar features(such as glaciation, volcanism, river and lake features), rock composition,atmospheres and magnetic areas of other planets to offer us a better idea of theirorigin, too as possible future pathways for Earth and other planets.Studies of these planets expose to us hidden secrets, such as that Mercury issimilar come the earth on the inside, Mars is favor the earth that didn"t quitemake it, and also Venus is a variation of the planet gone horribly wrong. So, let"slook at this comparative strategy to planetary geoscience and see what we canlearn about our own residence planet in the process.

First, let’s take it a brief tour of the different species of planet we findin our solar system:

Jovian planets

Jupiter-like, or Jovian planets (gas giants) to be the first to kind manybillions of years ago. Condensation the noble gases (unreactive ones the sit onthe much right that the regular table of elements) and volatile (explosive)elements such together hydrogen or helium came together past the "snow line", apoint in our solar system where it is cold enough for these aspects to formsolid ice cream grains. Together they swiftly grew, gravity became solid enough to holdthe aspects in location and type these massive gas behemoths.

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Rocky (terrestrial) planets

Successive collisions that rocky masses in space formed the rocky planets,such as Earth. These collisions and also sticking together of various objectseventually distinguished into the layers us are acquainted with on planet due tothe various weights the the elements; iron- and also nickel-rich matter sunk come thecentre that planets to form their cores, the lightest rocks formed the exterior crustsof the planets and in between sits the mantle. The asteroid belt between Marsand Jupiter may actually be an example of the failed development of a terrestrialplanet!

Surface features

These frameworks are commonly found on planets include impact craters,evidence of volcanism, tectonics and also erosion.

All of these procedures can additionally be watched on Earth, but evidence ofimpact craters is rarer on earth due to consistent renewal of the surface ar of theplanet by key tectonics and erosion by wind, ice, and water. Bombardment rate(the lot of meteorites the hit planets in a given time) has also slowlydecreased, together most large meteorites have burned up in the settings ofplanets or already affected in the virtually 14 billion year background of ouruniverse.


Craters indicate influence of meteorites top top the surfaces of planets, andare very useful as indicators of geological characteristics such together the extentof volcanism, erosion and tectonics.


The relative eras of various layersof rock within craters have the right to tell us around the quantity of volcanism on a planet -how often do eruptions occur, for example? In addition, we can additionally find outabout exactly how the surface ar of the planet reacts to forces put upon it, dubbed therheology that the rocks, yet for now let’s think that it as elasticity the thesurface of a planet.

On the moon,the crater thickness – the variety of craters in a details area – varies: highlands(on the moon, the ‘highlands’ room the areas near the north and south poles) haveremarkably high number of impact craters compared to the rest of the rockymarble. Mercury has actually lots that craters, however Venus has very couple of craters, due to itsdense environment (containing lots of ‘heavy’ gases), meaning that manymeteorites burn up as result of friction in the atmosphere and never finish theirmission come the planet’s surface. Jupiter’s moons mostly have actually high craterdensities due to the fact that they have actually a solid gravitational pull, yet Europa and Io haverelatively tiny due come their ice cover and also volcanism, respectively.


Volcanisminvolves the melt of a planet’s interior and eruption the molten (liquid) rockat the surface. Too many of warmth is compelled to melt these rocks, which frequently canhave extremely high melting temperatures of up to 1200 degrees Celsius. Thisheat originates from the initial warm of planetary formation, radioactive decay ofelements in ~ the planet, or tidal friction – the gravitational pull thatoccurs between planets and also their moons. Typically, a planet boosts intemperature by around 25 degrees Celsius for each kilometre you descend belowthe surface (called a ‘geothermal gradient’), for this reason magmas kind at countless differentdepths depending on what they’re made from, your chemical composition.

Across the surface of Mars, features termed‘sinuous ridges’ have the right to be found that are thousands of kilometres in size andhundreds the metres wide. These ridges deserve to be believed of together volcanic river‘trace fossils’. Imagine a fast flowing flow in which many sediment isdeposited ~ above the river bed, including large boulders. This is properties ofany river, from the Thames to the Yangtze! Eventually, the flow dries up andmillions of years of erosion walk by. Alongside the river room soft sediments likeclays and muds, while inside the river are sands and also boulders. The clays andmuds erode away quicker than the bigger flow deposits, so the the old riverbed is now a long hill, similar to a country scale map fossil! this sameridge formats can also kind from lava flows, and also populate the surface ar of Mars!

Mars is additionally home to the largest volcano inthe whole Solar device at 27,000m high – Olympus Mons.

Mars has actually not to be visibly active in our lifetimes, although the is assumed thatthere has actually been recent volcanic task (geologically speaking!). The main formof volcanism is basaltic, but more gas accumulation in the lava than supposed dueto a absence of atmospheric pressure. This means that normally magmas that room runnyand passive on earth can erupt violently on Mars. The lack of heaviness alsomeans the magmas are much less buoyant (do not float), therefore they continue to be in the mantlefor much longer in big magma chambers. So, once the magma at some point gets hotenough to escape, the eruptions last much much longer with bigger volumes that lava(lava is magma that has actually breached a planetary surface). Therefore, v largereruptions, Mars can build larger volcanoes!

Venus hasextensive proof lava flows, with vast plains and also channels indigenous constantfloods the basalt remoulding and also resurfacing the the planet, choose a really hotface mask that doesn’t so lot leave the planet refreshed together excessively burnt.Io is the most volcanically energetic body in the solar system and has constanteruptions of toxicity sulphur dioxide (SO2). These correspond withextremely warm localised surface areas and the feather of erupting SO2are so large they can also be viewed from space.


Plate tectonics

Tectonics isthe procedure that requires the movements of the external crustal layer of rocks ona planet. Tectonics involves lithospheric (Earth’s crust and also uppermost mantle)deformation by interior (volcanic, radioactive) or exterior (meteorite impact)forces and leads come distinctive landscape attributes such together faults, fracturesand wrinkle in crustal and also lithospheric rocks. In this, the planet is probably unique,as we have plenty of tectonic key of different sizes and compositions. Theseinteract follow me plate boundaries, of i m sorry there are three main varieties such ascollisional (where mountains type by plates advertise together), extensional(where oceans type by plates tearing apart) and also conservative (where platesslide past one another) and are composed of the three main rock types: igneous,sedimentary and metamorphic.

Other rocky planetsthat do not have plate tectonics as we know it on earth are smaller, thereforethey cooled quicker and formed a more thick crust. Mercury and also Mars, because ofthis, have faults in rocks – wherein rocks have actually moved in relation to one another– however not key tectonics. Faulting wake up here because there needs to bemovement to accommodate the huge inter-planetary pressures caused bygravitational pull.

Venus is themost comparable to Earth regarding tectonics, however has a very different tectonicstyle due to possible lack of water top top the planet bring about a change in the rheology(elasticity) that the rocks to make them an ext likely to fault than developtectonics. An ext water in the chemical make-up of rocks means the rocks movemore conveniently in solution to pressures upon them, meaning they carry out not break soeasily, and also they are more elastic. Mars has a solitary plate that is special andold however geologically diverse (containing many rock types).

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Decoding the system

The story ofthe advancement of ours solar device is scarred in the encounters of the planets, andhidden in their unfathomable rocky depths. We’re just beginning to see what isout there, yet we room pushing ever before further. It’s just a matter of time until weknow around the advancement of other planets, and also can use this to decipher thegeological past and the future of our own house planet, Earth.

Take a look atthe NASAwebsite, and the satellite pictures taken of variousplanets, including Earth. Deserve to you see any kind of surface frameworks of other planetssuch together Mars comparable to those on Earth? do you think these frameworks werecaused by the same thing? If not, why? What carry out you think is different around thestructures’ formation? leave your ideas in the comment below, and if you havequestions then ask us in the comments or via email or Twitter (Jane, Jon).