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The lost ocean of Mars

Mars' lost ocean. NASA's Goddard Space Flight Center

I’ve probably lost count of the number of ‘Water On Mars’ and related headlines I’ve read over the years. It’s an interesting case study of how a scientific theory gains support as more evidence is collected, until it becomes something ‘that is known’.

But last week we heard evidence that Mars has lost some water – an entire oceans worth in fact.

The history of ‘water on Mars’ is pretty interesting, if we start from the first time that Earth astronomers claimed to have seen features on our neighbour in the 19th century. Know as ‘Canali’ as they were first charted by and Italian astronomer Giovanni Schiaparelli. Speculation was rife for two centuries after as to what had carved these ‘canals’ on Mars, (for instance the eminent Percy Lowell was convinced that they were carved by an intelligent society) - but they were later shown to be an optical illusion.

The map of Martian ‘canali’ as drawn by Schiaparelli Meyers Konversations-Lexikon (German encyclopaedia)

Once we got a closer look of the surface with orbiting spacecraft, it became pretty clear there were no ‘canali’. However, the Mariner 9 craft in 1971 spotted many smaller scale features that could only have been formed from water erosion. This, first direct evidence, prompted the later Viking lander to take a closer look. Since then we have collected quite a lot of evidence about water and its processes on the surface of Mars all the way to Curiosity’s direct evidence that there’s water in the minerals there.

However, recently published results have presented the strongest evidence yet that there used to be much more water on Mars. All from looking at what’s left.

Using entirely Earth based observations a group has even been able to chart where in Mars has lost the most water. This has been done by tracking the water molecule (H2O), and it’s deuterated equivalent HDO.

Deuterium is ‘heavy hydrogen’, an isotope of our lightest element with an extra neutron in its centre. It exists in our own ocean, where about 0.0156 % of the hydrogen atoms in water are actually their heavier counterpart. The ratio between the amount of hydrogen and deuterium on Earth gives a baseline to compare ratios on other terrestrial planets.

Using the appropriately named Very Large Telescope (VLT) and the Keck telescope, the researchers charted the abundance of H2O and HDO over the Mars surface. This then enabled them to map out the deuterium/hydrogen (D/H) ratio mapped across the how of Mars.

ESO’s Very Large Telescope, located in Chile, was used to map water and deuterated water on Mars ESO/H.H. Heyer

Not only did they manage to chart seasonal variations that say much about the movement of water molecules, but also overall they noticed large regions that had a much higher D/H ratio than anticipated. Such enrichment occurs when water is lost, as H2O is more likely to evaporate than HDO.

Using their results on the D/H ratios they estimate that Mars at one point had a layer of water 137 m deep. The thought is that 4.5 billion years ago this amount of water would be enough to fill the Vastitas Borealis, the Northern basin that covers most of the upper hemisphere of the red planet. A great rolling ocean, which would have made up 17 % of Mars’ surface.

Now the big puzzle is, where did all that water go? There’s a number of spacecraft trying to figure this out – including last years’ arrivals MAVEN and MOM. Hopefully, the measurements they are making will show where the water has gone – the likely candidate being a loss through Mars’ tentative atmosphere.

But it does make you think, if Mars still had this ocean, would we have visited the red planet by now? Instead of dry ‘canali’, what if Schiaparelli had seen an ocean? I’m willing to bet that our whole perspective of the red planet would be different. Instead of a place of mystery , we would have perceived it as to a planet a lot like our own – ready to be explored. And given an ocean for 4.5 billion years, it’s rather fun to imagine who or what may have been living there waiting for our visit.

Giant methane storms on Uranus

Most of the times we have looked at Uranus, it has seemed to be a relatively calm place. Well, yes its atmosphere is the coldest place in the solar system. But, when we picture the seventh planet in our solar system invariably the image of a calming blue hazy disc that the spacecraft Voyager 2 took in 1986 comes to mind.

Uranus as seen by NASA’s Voyager 2 NASA/JPL-Caltech

However, all we have previously known about the atmosphere of Uranus has been ’thrown to the wind’ with observations made last year.

In August 2014 a group led by Imke de Pater pointed the Keck telescope at Uranus and were a little bit surprised to see storms raging. It wasn’t as though clouds haven’t been seen before, but the clouds they spotted last year were very much brighter than any seen before. The fact that the storms are bright in the methane spectrum isn’t a surprise – Uranus, and its neighbour Neptune, are pretty much just big balls of methane, water and ammonia (but it does make for a snigger-worthy headline).

Light from Uranus, as captured from my backyard in Sydney. The dips in the spectrum mainly correspond to methane (positions of the methane absorption is shown by the blue lines). Andy Casely

The storms are described in a paper recently published in Icarus, with the pre-print available here. After the first observations, the group put out a call to amateur astronomers to see if they could also observed this unusual activity too. They did, and with this information the group built a case to point the Hubble Space telescope at Uranus, which happened in October. Again, they saw large storms, showing that what they had seen in August hadn’t been a one off event - the weather report on Uranus is looking rather unsettled.

The storms on Uranus, as seen from the Keck telescope. Imke de Pater (UC Berkeley), Larry Sromovosky and Pat Fry (U. Wisconsin), and Heidi Hammel (AURA)

Uranus was the first planet to be discovered in the ‘recent’ era of science. All the planets up to Saturn were observed to be different ‘wandering’ stars by many ancient cultures – so we’ll never know who first spotted them. But Uranus was first observed in 1690 by John Flamsteed. He plotted it six times – but didn’t realise it was different from any other star (he catalogued it to be 64 Tauri). The French astronomer Pierre Lemonnier also observed Uranus, but didn’t distinguish it from the other stars he was watching. It was William Herschel who realised, in 1781 after thinking it was a comet, that he’d seen a planet orbiting further from the sun than Saturn.

Despite knowing where it was for over 300 years, we’ve only in the last decade started to take a detailed view of the Northern hemisphere of Uranus. The observations made by de Pater and her team are the first time this giant region of our solar system has been surveyed by modern telescopes from Earth. This is because of the very strange rotation, which makes Uranus pretty unique.

Our Earth rotates on its axis tilted only slightly from being straight up (if we define up as being perpendicular to a planet’s orbital plane). It is this tilt that drives our seasons.

Uranus has the most extreme tilt of axis in the whole solar system, it is inclined 98° from up. This means Uranus has the most extreme seasons – as each hemisphere of the planet faces the sun as it orbits (a cycle that take 84 years). The upshot is that as the Northern hemisphere has been in winter until recently, and from Earth we have been unable to see it. In 2007 Uranus reached it’s equinox, with the equator pointing at the sun and each of the two hemispheres illuminated.

Uranus' strange orbit explained. M. Showalter/M. Gordon/SETI Institute

The group observed Uranus with the Keck telescope as it past equinox seven years ago. They expected to see storm activity, as parts of the planet that haven’t seen the sun in 20 years started to come to light. They thought it has gone quiet again, which is why 2014’s storms took them by surprise. Added to this is the fact the storms are flaring up in the Northern hemisphere, the part of Uranus that is entering its spring, and thought not to have warmed up from its prolonged winter yet.

Where is the energy to drive these storms coming from? That’s the mystery. Storms on the other gas giants are thought to be fed by energy from their dynamic interiors. Voyager 2 saw that Uranus should have a dynamic interior (it has an active magnetic field like Neptune) but that little of this energy is reaching the atmosphere. This is why Uranus is the coldest planet in our solar system, parts of the atmosphere were observed to be a chilly -224°C.

What this observation of these giant storms really does highlight, is just how little we know about our solar system’s giant icy planets Uranus, and its neighbour Neptune. In the light of the fact that missions like Kepler are finding many other similar planets orbiting distant stars, we really need to sort this out. Hopefully knowing more about our ‘local’ planets will mean that we can understand much more about those further away.

Meanwhile, while we in Australia may have past our summer – think of the Southern hemisphere of Uranus where a 20-year winter is coming….

Going a long way to do a quick data collection

Like many a scientist before me, I have spent this week trying to grow a crystal. I wasn’t fussy, it didn’t have to be a single crystal – a smush of something would have done – just as long as it had a bit of long-range order. But no. Hours spent staring at a screen as the sample I wanted to study failed to sort out its atoms into something I could work with.

Look it is pretty, but it’s not the crystal I was looking for. Author

Sitting, staring at an experimental failure rather does make you think about and question many things. Moving on from the “why did I have this stupid idea in the first place” (which is a bit of a running theme in weeks like this), you try and put your experiments in context.

I’m leaving Japan tomorrow, with a stack of lovely fresh data (and probably some excess baggage fees). Some of my experiments worked, some didn’t - that’s the nature of the beast. No amount of planning and preparation for my three months here would have probably changed that.

Actually three months of experiments (or at least access to equipment) has been a massive luxury for me. Most of my data collections are from central facility instruments, like those offered at the Australian Synchrotron and the Bragg Institute.

Access to these instruments can take a lot of preparation, starting with a peer-reviewed proposal. Then, if you’re fortunate enough to be granted time; months of planning, risk assessments and gathering of equipment go into perhaps 24 hours of precious time on the instrument of your desire.

But what if you’ve put in YEARS of planning, and then had to wait YEARS for a tiny window of results? What if, rather than heading to Japan, you’ve had to journey to Pluto for them? How excited would you be that your tiny window of observation was just coming up?

It’s a good job I’m not on the science team for New Horizons, NASA’s mission to Pluto, as I couldn’t quite image how I’d sleep from now until July when it’s due to make it’s closest approach.

How far away is Pluto? Very. Image taken from NSW, Australia Andy Casely

I feel a bit of affinity with New Horizons, as we’re both about the same amount of time into our research careers (after probably a similar amount time of building/planning for New Horizons and growing/educating for me). When it launched in January 2006 I was few months into my PhD, and at that point I probably felt that I was being propelled at nearly the velocity New Horizons' was.

New Horizons did get to see a bit of the solar system on its journey, in 2007 while winding up it’s speed in a gravity assist orbit, it did a tour of Jupiter. There it took some rather wonderful images of the gas giant planet and it’s rings, and even caught an eruption of the Tvashtar volcano on Io. But since then it’s largely been in hibernation, waiting for 2015 for it’s time to shine.

Picture of Jupiter and its moon Io taken by the New Horizons spacecraft’s flyby in early 2007. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Goddard Space Flight Center

(I, on the other hand, have not been asleep since 2007 I should point out!)

When New Horizons reaches its closest approach to Pluto some of its instruments will only have a matter of hours to observe the surface of the icy dwarf. How do you possibly prepare for a window like that?

Well we have some idea, ESA’s Philae lander had a similarly restricted timeline and like New Horizons' years of planning from vast teams of scientists and engineers will have gone into the small observation window. Even once the observations are done, planned down to the seconds, it will be a nervous wait for the results. Not wanting to waste a second of observation, New Horizons will wait until it is past Pluto to send its data bounty back to Earth, a process that will take months after it has flown by.

But, like for me in Japan, the Pluto flyby will only be a step in New Horzions science journey. From there it will continue to fling its way out of the solar system and the hope is that it will encounter a number of other Kuiper belt objects.

We really don’t know much about the whole class of icy dwarf planets, and for me the excitement lies in what new icy geology is there to be explored. I can’t wait to see what materials and in what situations New Horzions turns up on the surface of Pluto and its moon Charon. That’ll be the start of my next (hopefully more successful) experimental adventure.