Wednesday, May 30, 2012

Scuba diving on an alien world

With good British sunshine, comes good British scuba diving. Well, baring the occasional bout of unpredictable sea fog. During my happy jaunts around the Dorset coast one question came to mind that I could not seem to let go of.

What would it be like to scuba dive on an alien world?

After a number of days struggling with my own PhD work I have turned to this question with an air of relaxation and yet it seems to offer more conundrums than I first thought. We have one fantastic example in our own solar system that offers the details necessary to compute these and a completely alien environment to explore. Titan! 

Titan is the largest moon of Saturn and it is also has the distinction of having the most Earth like qualities of any planet or moon in our solar system or beyond. Don’t get me wrong there are also a large number of qualities it possesses that make it wholly un-earth-like, but it is those that make it the perfect place to start our journey.

JPL, NASA - model of Titans atmosphere (1)
The first close up images of titan were taken by the Pioneer space craft in September 1979, and then later by Voyager 1 in 1980 and voyager 2 in ’81, however, these did not have on-board instruments that could penetrate the hazy atmosphere of the moon. I took a specifically designed spacecraft, Cassini-Huygens; that reached Saturn in July 2004 for the process of mapping Titan to begin. High resolution images were taken by Cassini while the Huygens probe made for a landing on the surface of the moon. Cassini continued to make close fly-bys of the moon collecting radar imagery of the northern and southern poles. It was these radar images that confirmed the proposed hypothesis that bodies of liquid could form on the surface, like those seen on the Earth. However, it is here that the comparison starts to break down as these lakes are not made of water but liquid methane and other hydrocarbons. In fact there is no liquid water on Titan, in its atmosphere or on the surface; this is due to the fact that it is -178°C and any water that may be on the moon is frozen in rocks. Yet, like the Earth most of Titans atmosphere consists of nitrogen though on Titan the majority of the remaining atmosphere is made up of methane, which can condense and form a liquid. It is thought that due to the relative lack of sunlight at the poles methane can accumulate in seas and lakes, however, in the summer seasons intense methane rainstorms can occur with over 100 times the volume of liquid deposited in an area the equivalent size on the Earth (though these flash floods would only occur once in a decade or century).

But what about scuba diving; what would that be like?

Titan may be far smaller than the earth but standing on the surface in your scuba gear would not be made any easier by the decreased gravity. This is because the atmosphere of Titan is so dense that the pressure on the surface is 1.45 times that of the Earth. In fact the atmosphere is so dense that if you were to attach wings to your arms you would be able to fly through it under your own power. 

The spectral images taken by Cassini show that the chemical composition of the lakes can vary, however, most are formed 75% ethane, 10% methane, 7% propane and a series of other heavier hydrocarbons. It was expected that due to the low gravity and detectable surface winds that waves would easily form on the surface, however no evidence has shown this leading scientists to believe that the lakes may be more viscous than expected with tar like qualities. So expect low visibility conditions, in a gloopy custard-like lake. 

Measurements of Ontario Lacus in the southern hemisphere show that it is extremely shallow with a maximum depth between 2.9 and 7.4 m. So you will be able to spend as long as you like under the surface without having to do any decompression stops. In the northern hemisphere however, Ligeia Mare has depths exceeding 8m (the extent of the radar measurement), and given the long northern winter on Titan means that it could still harbour the tons of methane from the last rainfall. I suggest you do a little fly over to get measurements of the depth before heading into this one.

The density of liquid ethane is less than half that of sea water and given the decreased gravity of Titan you will not feel the increased pressure as you go down. In fact to double the atmospheric pressure on Titan you would have to go down to 406m, while on Earth if you go down just 10m you double the atmospheric pressure. This does mean that if you want to get the record for the deepest dive (though I am not sure Guinness world records cover Titan) you will have no trouble dealing with the pressure effects. 

Right I think we are ready to pick our dive site. Also some things to remember; 
  • it will be a low visibility dive so make sure to bring a torch or an infrared sensor, 
  • the lake is quite viscous so you might want to use a dive scooter to drag you along, 
  • you don’t need to worry about the pressure so stay down as long as you want (up until 406m it is equivalent to diving up to 19m on the Earth) 
  • Oh and also remember that the temperature of liquid ethane and methane on Titan is under -89°C and will probably be colder so perhaps just this once you could convince me to dive in an insulated dry suit, but only for this.
And most of all enjoy your dive, your on another planet for crying out loud! (well it's a moon actually)


Monday, May 21, 2012

Venus Transit 2012

On June 5th and 6th 2012 the final transit of Venus across our Sun in our lifetimes will occur. The previous transit occurred just 8 years ago on the 8th of June 2004, however, due to Venus’ orbit relative to Earth the event is not a common one. 

The orbit of Venus is inclined by 3.39° with respect to that of the Earths (the ecliptic) it is the point when Venus’ orbit crosses the line of the ecliptic in front of the Earth. The orbit of Venus and the Earth cause them to line up every 1.6 years, however, and this is where the orbital inclination comes into play, due to the inclination of their orbits Venus will appear above or below the Sun as viewed from Earth, sometime by as much as 9°. The Transit Motion Applet shows how the orbital motion of Venus results in a 243 year cycle that consists of, two transits 8 years apart a 121.5 year gap and another two transits 8 years apart followed by a gap of 105.5 years before the cycle starts again. 

The last transit pair occurred in 1874 and 1882, 121.5 years ago; this means that it will be a further 105.5 years until the next pair of transits in December 2117 and 2125. 

Throughout history the motion of Venus has held special significance; however, it was not until 1639 that a transit was observed by two British astronomers Jeramiah Horrocks and William Crabtree. The transit of Venus was first predicted by calculations conducted by Kepler that suggested that the transit in 1639 would be a near miss, yet recalculations by Horrocks showed that the transits would occur in pairs 8 years apart. The next transit pair did not occur until 1761 and 1769 where a number of expeditions set out across the Earth with an aim to use the transit to measure the precise distance between the Earth and the Sun. It is a great example of International scientific collaboration (1).  

During this year’s transit scientists will use the Hubble space telescope to observe the transit of Venus by observing the shadow it causes in the reflected light on the moon (using the moon as a mirror). This data will hopefully allow us to determine the structure of Venus atmosphere in an effort to test a technique used in the study of exoplanetary atmospheres. With the knowledge we already have of the atmosphere around Venus this transit could represent a great opportunity to further our knowledge of the observations we make of alien worlds. 

Below is a map of the observation points for the upcoming transit followed by some links for how to observe it. Also check out events in your local area because this is not to be missed unless you know something I don’t know and plan to be alive in 2117 for the next event.


A special Venus Transit event will be held at sunrise on the 6th at the University of Exeter, UK keep an eye out for further information.

Monday, May 14, 2012

Picture this!
Pictures can say a thousand words, and when it comes to science a good picture can explain so much more. The ability to visualise your data, information, and interpretation, is something that I have always felt is hugely important. 

From day to day I sit at my desk surrounded by papers, post-it notes, notebooks, and laptops; each used together in an effort to better understand and document my work. I am currently studying the atmospheres of hot Jupiter’s, giant planets orbiting close to their stars; and even with all of the facts and information in front of me I find it difficult to imagine such worlds.  

Their stars can range between dwarfs and giants, active or quiet, old or young. These giant worlds can have over 20 times the radius of Jupiter and yet lie within the orbit of Mercury. At these distances flares and coronal mass ejections from an active star would throw high density plasma right at the planet if aligned in the same direction. The planet may even cause a tidal bulge on the stars atmosphere due to gravitational forces as the planet is locked in its orbit where its day is as long as its year and a terminator region permanently marks out the region between day and night. 

There are so many factors for each of these hot Jupiter systems that make them different. The slightest difference in their stars, their orbit, their size, their atmosphere, can change what we would see. How can we begin to separate them?

I think that the focus seems to be towards theoretical astrophysicists when it comes to data visualisation, with their brilliant simulations and movies. Or in the public eye with beautiful observations and graphics, something which NASA triumphs in, that makes it accessible to the general viewer. But one thing trumps them all, and it may sound boring and make you groan but sometimes all you need is a good graph!

The title image of this post is part of the ESO public archive and is a fantastic example of the combination of each of these ways to visualize data and it also shows that graphs can look pretty too. A few more of my favourites are shown below as well. 

Each of these different ways to visualise facts and data has one goal in mind, how can I make you see what I see in the clearest possible way. Stripping away the jargon yet leaving the core science behind in all its glory.
 And one proud moment where exoplanets got their face onto SNL.
SNL weekend update 2005

Monday, May 7, 2012

Messenger of the gods: a tour of Mercury and its majesty from the surface
You open your eyes and stumble backwards sending grey dust and rocks cascading down in front of you, with a steading breath you take a step forwards again. Take a look! You are standing on the precipice of a colossal mountain range; nearly 2 km below you and stretching out over 1500 km in front of you is the Caloris basin, “The basin of heat”. Though the Sun is noticeably absent, the sky is not completely black, but littered with the light of millions of stars left un-obscured by Mercury’s lack of permanent atmosphere. This of course also means that it is also intolerably cold, with temperatures reaching as low as -200°C. 

You shut your eyes again and when you open them you are transported to an icy plane. You are now in a region of the planet permanently shrouded in darkness. Standing at the base of this icy polar crater, an ancient scar left by impacts deep in the planets past, the stars above you rotate with the seasons.  Yet with no atmosphere to weather a storm, no surface activity to effect change, and little axial tilt to alter the solar irradiation through the seasons the landscape around you does not change and no sunlight ever reaches your feet. 

In a blink of your eye, you are once again transported across the planet to the edge of vast a canyon, you look up and in the distance you can just see the enormous mountain range on which you started your journey. You are now inside “the basin of heat” and about to witness the reason for its namesake, for every two Mercurian years the Suns light floods the basin for over 50 Earth days.
With no atmosphere to scatter the sunlight above your head in a welcoming glow alerting you to the coming day, there is no advanced warning as the Sun begins to rise over the eastern horizon. The Sun is a bright sliver of fire above the distant mountain ridge slowly edging its way into full view. Once it is above the horizon you can fully appreciate the sheer size of it as it illuminates the blackness of space and obscures the once visible array of stars. But this time of year is special, the planet is approaching perihelion, its closest approach to the Sun, and as it does the speed at which it proceeds through its orbit increases by one and a half times. The consequence of this happenstance is what you are about to witness, and it is one of pure astronomical wonder. As the Sun rises above the mountain ridge headed toward the western sky it momentarily stops and makes its way back towards the eastern horizon. The orbital motion causing the Sun to appear to move from west to east has overcome the rotational motion that causes it to move from east to west. As the planet continues on its journey past the perihelion point the rotational motion takes over bringing the sun once again back up above the horizon to make its full journey across the sky. You have just witness the only double sunrise in our solar system.

As you fast-forward through the day you will see the Sun appear to shrink in the sky, by nearly one and a half times, as you move towards aphelion, the point in the orbit farthest from the Sun. It is over six Earth weeks until the Sun is at the midday point over the center of the Caloris basin, and with the Sun un-obscured during its total daytime trip from eastern to western horizon the surface can reach temperatures of over 400°C. That is a temperature range of over 600° from coldest to hottest and is the most extreme in the solar system. 

You have just fast forwarded through a year on Mercury; that is 88 earth days, on the fastest planet in the solar system. You have witnessed the unchangeable seasons, the extremes of temperature, and the wonder of a double sunrise, and with a blink of your eye you are back on terra ferma ready for the next adventure. 

Where would you like to go next?
 For more information on Mercury check out some of these link:
  • Bob the Alien is a fun one for kids and is full of fantastic facts