We’re off the moons of Jupiter…in 2022

I’ve been waiting a long time for this and I’m pretty sure all planetary scientists have been waiting a long time for this too. It’s regarded as the most important destination(s) in the solar system. That’s right, we’re finally off to the moons of Jupiter. Well we will be in 2022 anyway.

After a brief competition with two other space mission proposals JUICE (JUpiter ICy moons Explorer) will head off to Jupiter in 2022 and arrive in 2030 and spent a minimum of 3 years studying Jupiter’s moons. And it’s a European mission too!

JUICE and the Jupiter System

Why the moons of Jupiter? Well, the moons here are exceedingly interesting. Io, first of all, is the most volcanic object in the solar system (although Io won’t be studied much with this mission). The other 3 main moons are the really exciting ones though. Callisto is a fairly large moon and its surface is incredibly old, peppered with craters. It’s holding clues as to the formation of the Jupiter system some 4.5 billion years ago. Europa, the most famous of the moons, has a liquid ocean beneath it’s icy surface, and a very bizarre looking surface. Could there be life in the ocean? It’s a distinct possibility. The mission is mainly focusing on Ganymede though, the largest moon in the solar system, so large it’s bigger than Mercury! It generates it’s own magnetic field. How? Through a salty sub-surface ocean or a molten iron core?

Ganymede

The spacecraft itself looks quite interesting too. It’s going to be operating at the limits of what’s possible. It’ll be using solar power where there isn’t much solar power. Previous missions have used nuclear generators which are far more efficient this far out, but there’s a shortage of the plutonium required for such endeavours at the moment. We’re likely to get an advancement in solar power technology through the efforts of this mission though.

In my opinion NASA have really mucked up. With all their budget cuts they’re not planning a mission to launch to study Jupiter’s moons until well into the 2030’s despite having been told it is the utmost priority of planetary science at the moment. There’s a possibility they’ll add some hardware to the JUICE mission, but we’ll have to really wait and see. What we’d like to see is a Europa lander and ocean explorer (as outlined in NASA’s JIMO mission, now cancelled).

There’s one certainty though, we’re going to find out some truly exciting stuff and we’re going to be surprised with what we find!


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My Favourite Places in the Solar System

Here I’m going to show you some of my favourite places in our solar system. They’re in no particular order, partly because I don’t think I can pick out an absolute favourite. I’ll provide some pictures for each and briefly describe why I think they’re interesting places.

  • Pele Volcano, Io – Jovian Moon

Pele Volcano, Io

Io is a pretty interesting place. Due to various gravitational interactions it is the most volcanically active place in the solar system. Because it’s quite small, volcanic plumes can reach 300 odd kilometers high, as opposed to a few 10’s of thousands of feet on Earth. The most notable aspect about this volcano though is the large red/orangey ring surrounding it (as can be seen in the picture). This is the sulphurous fallout from the volcanic plume. Pretty good start, right?

  • North Polar Region, Saturn

Hexagonal Cloud Pattern

No ice caps up on the poles on Saturn, it’s too big. It’s one of the gas giants. It still has a rather unique and interesting feature though. It’s called the ‘north pole hexagonal cloud pattern’. Not very catchy at all, is it? But it’s a truly bizarre feature. Each straight side of the hexagon is about 14,000km long, making them larger than the diameter of the Earth! No one quite yet knows exactly how it formed or how it works, however, although there are plausible theories.

  • 433 Eros, Near-Earth Asteroid

The Asteroid Eros

Eros is only here because I remember the photos coming through, when I was 10, when the NEAR spacecraft landed on its surface. Some of the larger rocks found on the asteroid are all thought to originate from a single crater from a meteor impact about 1 billion years ago. The asteroids got a pretty funky shape too.

  • Olympus Mons, Mars

Olympus Mons

Olympus Mons just had to make it in here. It’s the tallest mountain in the solar system (technically an extinct volcano) that stands a whopping 22km high, that’s 3 times the height of Everest! How does a volcano grow to be so big? It’s mainly thanks to Mars’ lower gravity. Lava doesn’t rush down at such a speed so has longer to cool in a given place. Also, it’s thanks to a mantle plume that used to sit beneath the volcano. This is where magma rises from the deep to the surface. We have these mantle plumes on Earth, but because of plate tectonics they move around and don’t stay in one fixed location, which is partly why we don’t have anything as impressive!

  • Verona Rupes, Miranda – Uranian Moon

Miranda

Now for one not so well known. We venture much farther out to a moon orbiting Uranus, Miranda. We’ve only had a brief glimpse of Miranda, thanks to the Voyager 2 spacecraft, so not all of it has been imaged. It’ll probably be another 50 or more years before that’s done. But from what we’ve seen it looks like a pretty cool place, it’s got some interesting geological features, in fact it’s the most geologically diverse moon of Uranus. Verona Rupes is the tallest cliff in the solar system, up to 10 km high. Imagine looking all the way up at that! It’s not known how it formed, although it’ll either be from an impact or crustal lifting.

  • Kraken Mare, Titan – Saturnian Moon

Radar Image of Kraken Mare, Titan

Titan ranks as possibly the most interesting place in the solar system. It’s the second biggest moon around (larger than the planet Mercury) and it’s enveloped in a thick atmosphere, thicker than the Earth’s. Titan’s sometimes referred to as a primordial Earth in deep freeze. That’s because it’s thought to resemble how the Earth looked a couple billion years ago, but in deep freeze. The most unique feature though is in relation to its temperature. At  about -175°C methane can remain in 3 different states – a gas, a solid and a liquid, much like water can on Earth. As a result there are large icy patches of frozen methane, a nitrogen atmosphere with many different hydrocarbons and there are large lakes of liquid methane, of which Kraken Mare is the biggest. It’s also the only other place in the solar system where it rains. Not water but methane, which drifts slowly down because of its lower gravity. What an amazing sight that would be!

  • The Rings of Saturn, Saturn

The effects of a moonlet on one of Saturn’s rings

What would this be if we didn’t discuss the majestic rings of Saturn? Made from trillions upon trillions of ice particles, some microscopic some up to a few metres in length, they are so bright because they’re mainly made from water ice and reflect a lot of the Sun’s light. They’re incredibly thin too, no more than a few metres thick! Amazing for such a vast system of rings. It’s thought over time these particles coalesce and then break apart, and the cycle continues. Some of Saturn’s little moonlets cause bizarre gravitational patterns in the rings too, and this is also partly why there are gaps between some of the rings. The moon Enceladus also provides material for one of the rings. More on that shortly though. The biggest question though? No one really knows how the rings go there in the first place.

  • Tycho Crater, The Moon

Central Peak of Tycho Crater

The only reason this one made it in is because of a photo taken by the Lunar Reconnaissance Orbiter a few months ago. It’s quite a young crater (just over 100 million years old), easily seen with the naked eye and a favourite observing point for amateur astronomers. The crater has a central peak. This is where, moments after the impact that created it, material from deep below rebounded forming a small mountainous area in its centre. This is typical of most large impact craters. LRO took a photo of this central peak, and you can see so much detail that you can even make out a large boulder right at the top it. Impressive stuff, huh? (Click on the image to see the bigger, better version)

  • Tiger Stripes, Enceladus – Saturnian Moon

False colour image of the jets from the Tiger Stripes

Enceladus is a pretty special place. It’s a tiny little moon, so tiny in fact that it would nicely fit in the North Sea between the UK and Scandinavia. Like the gravitational interactions that make Io active though, Enceladus is active. Not with volcanism but with cryovolcanism (basically icy volcanoes – counter-intuitive, I know, but it really does happen). The Tiger Stripes are where it’s most active. Heat from inside melts icy products and a phenomena similar to geysers on Earth are produced, launching the icy products out into space. This creates Saturn’s outermost ring, the E ring. Due to the gravitational interactions warming the moons interior up it’s also possible that a liquid water ocean exists beneath the surface!

  • Conamara Chaos, Europa – Jovian Moon

Conamara Chaos, Europa

Another world shaped by cryovolcanism now, Europa, the moon lying slightly further out than Io. Whilst not as active as Io, and a tad cooler too, Europa remains the most exciting place in the solar system for the possibility of life. It has a thick icy surface, below which probably lies a massive liquid water ocean. If this exists, which is quite likely the case, then life, extraterrestrial life, could be there too. Chaos terrain is called as such because it’s pretty chaotic, there’s a lot that has been going on, as can be seen by the image. The area consists of icy rafts that have moved around and rotated, it’s all surrounded by a ‘matrix’ of jumbled up ice blocks too. Pretty hectic indeed!

  • Cantaloupe Terrain, Triton – Neptunian Moon

Triton’s south polar cap and cantaloupe terrain

Well I’ve got include a place that has such a cool name, haven’t I. This terrain on Triton is named Cantaloupe terrain because it looks like the skin on a cantaloupe melon! Triton is Neptune’s largest moon and it has a mysterious past. The moon goes the wrong way around the planet. Could it be a captured Kuiper belt object, now locked into orbit? Or did Neptune devour another planet billions of years ago and steal one of its moons? What is interesting about this place though is that its geologically active, again with cryovolcanism. It has geysers expelling nitrogen. These geysers appear to be powered by solar heating, which is odd because it’s so far away from the Sun, it seems to have a profound effect though! The Cantaloupe terrain itself is thought to have formed by a process called diapirism, similar to how a lava lamp works.

  • Taurus-Littrow Valley, The Moon

Orange soil on the Moon!

Back to the Moon now and the landing site of Apollo 17, the last manned mission to the Moon. This makes it in here because of something very interesting Jack Schmitt found (the only scientist to have been to the Moon). We all think of the Moon as a fairly mundane place. It’s just grey and boring…or so it seems. During Apollo 17, the astronauts came across not grey, but orange soil! This orange soil is made up from volcanic glass beads that erupted and solidified in fire fountains during the areas early formation about 4 billion years ago.

  • Valles Marineris, Mars

Topographic image of Valles Marineris

Another of Mars’ unique landscapes. This is one of the greatest valleys in the solar system. You could fit the Grand Canyon into one of the Valles Marineris’ tributaries! It’s 4,000km long, 200km wide and reaching down to 7km deep! It’s thought that this great valley was created by what’s known as rift faulting – that’s responsible for the rift valley too. Erosion by water in Mars’ earlier days may also have helped too.

  • Cassini Regio, Iapetus – Saturnian Moon

The two halves of Iapetus

And last but not least is Iapetus. This is a moon of two deeply contrasting halves. One side is dark and the other a bright white. There’s also has a strange ridge that runs half way around its equator. The dark part of the moon, known as Cassini Regio, is a thin covering of material, only about 10cm thick, that it thought to come not from Iapetus elsewhere. It’s thought that there is also some residue making it up too that has been left behind by the evaporation of surface ice. The ridge is a great complication as it’s not known how it formed, or why it formed nearly exactly around the equator. What we do know though is that it contains some of the tallest mountains in the solar system!

I’d really like to know some of your favourite places, especially if I haven’t mentioned them. Leave them as a comment below along with a brief reason as to why it’s your favourite. 

What’s going on on Europa?

The bizarre surface of Europa

Europa is an intriguing little place. It’s the second innermost of the 4 Galilean satellites (there are actually more than 60 moons around Jupiter but these are all much, much smaller than the 4 big, Galilean, ones) and it has a very interesting and bizarre surface.

When we look at most moons in the Solar System we find that there are an awful lot of craters on them. Some of these are very small whilst others are very big. What’s useful about this is that through looking at the craters we can tell how old the surface is. When we look at the cratering record on the Moon we find that it is about 4 billion years old. Europa is a different story altogether. In the image above you can see very few craters, if any at all. What this means is that the surface of Europa is very, very young. After careful analysis it appears that the surface of Europa is, on average, only 65 million years old (that’s considered very young in geologic terms). Therefore there must be a process on Europa that is working to erase the evidence of these craters. What could it be?

The secret to Europa’s resurfacing lies in Jupiter’s massive gravitational field and interactions with 3 of the other big Galilean satellites. Through this process (tidal heating) the interior of the inner two moons are kept warm. This leads to the spectacular volcanoes of Jupiter’s innermost moon, Io. Io looks kind of like a pizza and is the most volcanically active body anywhere in the Solar System. Europa is under these same processes but to a lesser extent.

The Galileo mission to Jupiter, launched in 1989, found that Europa had a magnetic field about it. This inferred that Europa either has a salty ocean beneath the ice or that there is motion in its core. It is now accepted that this is probably due to the presence of an ocean. Further evidence for the existence of this ocean comes from one of Europa’s few impact craters, Pwyll. The crater is unusual in that its base isn’t any lower than the surrounding terrain and shows the hallmarks of the impact having been into thin ice (about 20km thick). It would be useful here to note that lots of different models come up with different thicknesses for the ice shell, some as little as 3km and some up to 100km. This is where the problems starts. Some features on Europa are explained by there being a thin ice shell and others only by a thick ice shell.

A new theory, published in the journal Nature, sets out to put aside some of these problems and explain how what’s called chaos terrain can form. It was previously suspected that you need a very thin layer of ice for them to form, but this theory explains how shallow sub-surface lakes may be responsible.

Thera Macula (false color) is a region of likely active chaos production above a large liquid water lake in the icy shell of Europa. Color indicates topographic heights relative to background terrain. Purples and reds indicate the highest terrain. Credit: Paul Schenk/NASA

The new theory states that phenomena similar to mantle plumes here on Earth heat the base of the ice. Convection occurs and ice lower in impurities slowly rises and melts forming a lens of water a few kilometers below the surface. This would cause the surface to subside and lead to cracks forming from the top of the lens and surface. Eventually these cracks would end up creating rafts, water would then freeze in between and the lens would slowly refreeze and then causing a dome to form at the surface. This process would take millions of years.

It has been speculated that these lakes would be ideal habitats for life. I’m not so sure though. As these lakes would eventually freeze over the only life they could sustain would be some kind of extremophile. In my opinion it would seem that life would be better off living in the ocean beneath the ice. I don’t know enough on this area of astrobiology though to make a truly sound argument.

Europa is a bizarre, intriguing and beautiful place but the only way we’re going to learn more about it is sending a mission there. A review said a mission to Europa should be NASA’s second highest priority (I guess succumbing only to a Mars sample return mission?). Previous missions have been cancelled, like the Jupiter Icy Moons Orbiter (JIMO). Work going on in Antarctica at Lake Ellsworth and Lake Vostok will help us with a possible lander mission to Europa. These lakes in Antarctica are hidden beneath deep layers of ice, drilling technology being used will help us when we come to drill and venture beneath Europa’s icy shell.

Four step process for building “chaos terrains” on Europa

If I haven’t explained any of this adequately (and I probably haven’t, I’ve been up since 5am) or purely just if you’re interested I’ve put some links below this and also the video from the initial conference explaining the theory.

Links
Video: Jupiter Moon’s Subsurface Ocean of Water

NASA Probe Data Show Evidence of Liquid Water on Icy Europa

Active formation of ‘chaos terrain’ over shallow subsurface water on Europa

References
Greenberg et al (1999)
Schmidt et al (2011)
An Introduction to Astrobiology – C4 Europa – Dr David Rothery (OU study book)

Water: Where did it come from?

I haven’t done a proper science post for a while and I’m sorry for that. I saw a news story pop up on Twitter from the ESA Science Team (@esascience) about the origin of Earth’s water. Just where did it come from?

This is an area that really interests me, in fact I get rather too excited about it. We had a long and detailed question on it pop up in S283 (an OU planetary science course) and I thoroughly enjoyed researching and developing my answer. I leapt at this chance to discuss it further.

The origin of Earth's water?

The origin of Earth’s water?

It’s pretty obvious surely? Comets right? They’re mainly composed of water ice, we know the planets were pummeled by them in the late heavy bombardment about 4 billion years ago, its got to be them hasn’t it?

There has been no way to test this hypothesis until very recently. You need to send a spacecraft to a comet to test it – a very expensive but totally worthwhile test.

Now we’ve finally managed to study 4 comets in detail and the results are interesting. What we need to study is what’s called the deuterium/hydrogen isotope ratio. Deuterium is just basically a slightly heavier version of hydrogen, it has an extra neutron (technically not an extra one because hydrogen doesn’t have any neutrons).

If comets are the origin of the Earth’s water we’d expect there to be a very similar ratio of hydrogen and deuterium to the ratio of these isotopes in ocean water. From the comets that have been studied it turns out that this probably isn’t the case. Comets appear to have twice as much deuterium than ocean water, meaning that comets are an unlikely cause for our waters origins. As we’ve said already though, only a few comets have been analysed in detail. They might not be representative of all comets.

Another theory states that water-bearing grains are responsible. The distance from the Sun at which the Earth formed though casts doubt on this. It would have been so warm that water couldn’t have existed here. Not if they were incorporated within hydrated minerals though. As the planet formed (and after) these hydrated minerals would, over time, degas out into the atmosphere via volcanic eruptions. Eventually, enough was degassed  to form today’s oceans. This has been held as the most plausible explanation.

A spanner seems to have been thrown in the works though, the debate has been reignited. The Herschel infrared space observatory has been looking at comet Hartley 2 and has found that its deuterium/hydrogen ratio is pretty much exactly the same as Earth’s oceans. This comet is suspected to originally have been a trans-Neptunian object flung into the inner solar system have a gravitational tug of war. These comets, forming under different conditions to those that formed between Jupiter and Saturn, probably have slightly different compositions, specifically the deuterium/hydrogen ratio.

A recent study shows that there was likely a 5th giant planet in the solar system, but after gravitational encounters with other planets was flung out of the solar system, stirring up all the trans-Neptunian comets on its way. Is this the reason for the late heavy bombardment? It lends weight to comets being the origin of Earth’s water.

I’m still sceptical though. This is only one comet. We’re going to need to study many, many more before we reach a definitive conclusion. From what I’ve studied, hydrated minerals seem to fit best with the available evidence, but as more comes in I’m willing to change my mind.

The report from the ESA science can be read here
The report on a possible 5th giant/ice giant can be read here 

New moon discovered around Pluto

Hubble’s still turning up surprises, even today. Whilst focusing her gaze at Pluto, doing some extra research in preparation for the New Horizons flyby in 2015, Hubble has found an extra blob in its vicinity. That’s right Pluto has a new moon.

New Moon 'P4' Discovered Around Pluto

Pluto already has 3 moons. Charon is the biggest at over 1000km across and is the largest moon in the solar system when compared to the size of its companion, Pluto. There’s also Nix, Hydra and now P4, although that isn’t it’s official name just a nickname for the time being.

The new moon could be between about 10-40km across, making it Pluto’s smallest moon. It’s difficult to judge its size initially. It’s probably a very icy body, like most things out this far – 5.9 billion km – meaning that it’d have a fairly icy surface. If this is the case the moon reflects a lot of the light from Sun and that’ll mean it’d be on the smaller side of things. If it’s reflecting a small amount of light though, meaning it’s a darker body (this could be due to radiation effects) then it’d be on the larger side of things.

The Pluto System

P4 fits nicely between the orbits of Nix and Hydra. It’s thought that the moons were created in a large impact event much like the theory behind our own moons formation where a large body hit the planet, flung material into space and then re-coalesced to form the moon.

We’ll be finding out more about this intriguing, unexplored part of the Solar System when New Horizons flies by in 4 years time. It’s a pretty exciting mission where we’ll be looking in detail at Kuiper Belt Objects for the first time.

More information on this discovery from NASA, the BBC and New Scientist

A New World – Dawn approaching Vesta

Dawn – The journey to the beginning of the Solar System! It’s a fairly ambitious mission, as are most of NASA’s missions at the moment. Firstly the spacecraft uses ion propulsion, a technology tested on Deep Space 1 but never before used for a dedicated science mission. Secondly Dawn has not one but two targets. The large asteroid or even protoplanet, Vesta and then the dwarf planet Ceres. The spacecraft will go into orbit around Vesta, happily do some science for a while, break orbit and then go to orbit Ceres!

Launch of Dawn on a Delta II Rocket

Dawn launched back in September 2007 atop a Delta II rocket. It’s been in the cruise ever since, giving short bursts of ion propulsion to refine it’s orbit. Now after nearly 4 years she’s almost arrived, ready to hop into orbit.

Vesta is the largest asteroid in the Solar System (Ceres is larger but is termed a dwarf planet) it’s about 530km across and is estimated to contain 9% of the mass of the asteroid belt, so it’s a pretty hefty object. It’s thought to be differentiated, that is it’s so big so that heavier elements, like iron, fall towards the centre and lighter elements are found nearer the surface. This is the same way that Earth’s core formed.

We already know a fair bit about Vesta surprisingly. About 1 billion years ago Vesta was hit by an asteroid that’s left a small crater. This threw out lots and lots of debris, and quite a bit of this has fallen to the Earth. These meteorites have the fancy name of Howardite-Eucrite-Diogenite (HED) meteorites. Evidence from these meteorites show that Vesta is between 4.43 and 4.55 billion years old and reveals that Vesta has a history of extensive igneous processes. Infact the meteorites are very similar to magmatic rocks found on the Earth.

The mission at Vesta is to develop our understanding of how the Solar System formed and in particular what role water played in planetary evolution. Vesta and Ceres both reflect what the early Solar System was like, something we can’t figure out here on Earth because of all the geological activity the Earth is still going through. Continue reading