Sunday, February 16, 2014

What I learnt at Exoclimes III

Over the past week I attened the biannual planetary and exoplanetary climates conference Exoclimes. This year it was held in Davos in the east of Switzerland.


The conference itself brings together experts in the field of planetary atmospheres from our own system and beyond, to exoplanets and brown dwarfs. It also importantly brings together both theorists and observers in an effot to share knowledge, promote understanding, and grow collaborations. 

But as I have done with previous conferences I attened I thought I would share some of the 
"Things I learnt fro Exoclimes III" with you now.

  • In a small community that has a relatively new biannual conference for those in the field some people automatically assume everyone else was at the previous events and remembers exactly what your talk was on 2 years ago
  • Paleoclimatology is a fascinating subject for instance did you know that the spikiness of a leafs edge can tell you what latitude of the earth you are at due to a temperature correlation.
  • If you spend all of your money on a massive conference room then you cut back on the amount spent on coffee, which is not the greatest idea when dealine with over 150 astrophysicists.
  • The exoclimes drinking game this year required you to take a drink each time someone mentioned 'clouds' or 'WFC3'. Let's just say that if we were actually doing this Tuesdays talks would have been liver destroying.
  • The amount of notes that you take during each talk seriously diminishes as the week goes on. Unless you know they are specific to you or broad enough so that you know what they are talking about (generally rare but appreciated).
  • Venus is the biggest problem we have in planetary science. She is also the queen of super-rotation.
  • From the observers: It is important to constrain the C-O ratio. Hot Jupiters with high albedos probably have high reflective clouds. The smaller the star the smaller the planet we can observe. You need as much data as possible; transit+eclipse+RV+phase curve. WE NEED MORE TELESCOPE TIME!
  • Half of known exoplanet atmospheres are cloudy. (Both a bold and unnerving statement)
  • We need models complex enough to fit the data but not so much as to introduce degeneracies.
  • Many enshrouded exoplanetary systems, like WASP-12, may have disintegrating close-in rocky planets leaving a metallic diffuse haze surrounding the inner system.
  • Both Juno (2016) and JUICE (2030) are going to tell us a lot about the atmosphere of Jupiter.
  • There are knowns, known unknowns, and unknown unknowns.
  • If we want to detect the transmission spectrum of an Earth analogue transiting a sun-like star within 40 light years it would take 77 years and a very good telescope.
  • There are many and varied atmospheric retrieval  techniques and all of those involved will happily sit on stage and argue about them with an audience desperately wishing they would stop eating into the one and only coffee break they get in the day.
  • There are still a huge number of questions to both ask and answer - but hey, that's not a bad thing or we would all be out of a job.
  • And finally if you want to wake everybody up at the end of a very long week make sure that the last talk is by Charbonneau. I mean we all still desperately needed a drink at the end, but it helped. 

Overall it was a really great week and I can honestly say I learnt a lot more than just the highlights I have shared above. As my first international conference it was also a fantastic opportunity to meet some collaborators and hopefully make a few more and I am looking forward to being able to go to Exoclimes IV in 2016 (if I can get a post-doc).

I thought I would also leave you with this trailer and feature I made of myself and friends in what I have called the Exoclimes Olympics









Also check out the website for links to most of the talks and the posters http://www.exoclimes.org.

This is mine :D

email hannah@astro.ex.ac.uk for more details.



Saturday, January 25, 2014

Some of the weirdest and most wonderful facts of the universe


Gravitationally speaking the super-massive black hole at the centre of our galaxy has no idea that it is surrounded by over 300,000 stars and those 300,000 stars have no idea that the surround a super-massive black hole with the mass of 10 billion suns


The stars in the centre of our galaxy orbiting the invisible super-massive black hole









Light exists all around us, but in its own frame it is not there at all. If you travel at the speed of light it takes no time at all to get from one side of the universe to the other, even though it would take over 13 billion years from our point of view. To itself, in its own frame, light does not exist.







The cold gas and dust coming together to
form stars and galaxies




    When stars are forming they drop to temperatures close to absolute zero as the gas becomes essentially transparent to radiation before becoming opaque again and heating up to soaring temperatures as the gravitational pressure increases and ignites hydrogen burning.







    A cartoon of GJ 436b's interior



    Just 33 light years away from the Earth there is a planet called GJ 436b which is made of hot ice. This Neptune sized planet sits 50 times closer to its star than the Earth does to the Sun heating up its atmosphere to over 700 degrees. Yet compressed lower down in the planet is a shell of solid water ice at temperatures well above freezing but under so much pressure that it has no choice but to maintain a solid state. 







    The Andromeda nebula - the only naked eye
    galaxy in the northern hemisphere



    The universe is so big that reasonably we do not yet understand it all with the matter that makes up you, me and all the planets, stars, and galaxies we observe taking up just 4% of what we know. The rest occupied by dark matter and dark energy of which we know very little. It wasn't until 1923 when Edwin Hubble discovered that a small fuzzy blob called the Andromeda Nebula could not be part of our galaxy the milky way. Revealing for the first time that the universe is actually much, much bigger than our own little collection of stars. 
    And that the Andromeda nebula was not a nebula at all but another distinct collection of stars forming a vast galaxy separate from our own, just one of billions that occupy our universe. 
    The cosmic web of galaxies and dark matter that forms our universe from the millennium simulation



    WHAT'S NEXT?

    Let me know what weird and wonderful facts I have missed in the comments box below



    IMAGE CREDIT:
    Top to bottom: ESO; http://thequantumlife.tumblr.com/; ESA–AOES Medialab; exoplanets.org; NASA; Millenium Simulation, MPA Garching, V. Springel, S. White et al.


    Tuesday, January 7, 2014

    The smallest things make the biggest differences


    It has been a long time since I have written a scientific post but I was intrigued by a discussion we were having the other day about the Deuterium to Hydrogen ratio (D/H) in exoplanet atmospheres and it got me thinking about Venus and its escaping atmosphere and how little attention is paid to its significance in the exoplanet community. 


    Let me expand on my train of thought by first explaining what the D/H ratio is and why we care. 

    Deuterium (D) is an isotope of Hydrogen (H) defined by the addition of 1 neutron to Hydrogen's original 1 proton + 1 electron configuration. Deuterium acts in the same way that Hydrogen does but is more massive or heavier than its original counterpart. Additionally there is a second isotope of Hydrogen called Tritium, which has two additional neutrons in its nucleus. 

    Deuterium can also form water molecules, called heavy water, because it has the same chemical properties of Hydrogen. There is in fact one deuterium atom for every 10,000 Hydrogen atoms, and as there are two isotopes of Hydrogen we can then assume that one in every 5,000 water molecules should have Deuterium in place of Hydrogen. 

    Consider then that all Hydrogen (and its isotopes) that exist in the universe today were created at the very moment of the Big Bang, because while Hydrogen is turned into other elements through nuclear fusion in stars, no new hydrogen or deuterium has been created since the beginning of the universe. This can be seen all around us by the D/H ratio in the Earth, Moon, comets, and even the space between stars which all have very similar D/H ratios ~ 1/1000.


    But here is the puzzling thing, and this is where Venus comes in, Venus has a D/H ratio 100 times that found on the Earth.

    This is not to say that Venus has more Deuterium than the Earth but that it in fact has less Hydrogen. 

    Which takes me onto the escaping atmosphere part. 

    Hydrogen is about half as massive as a Deuterium atom and on average will therefor sit higher up in a planet's atmosphere. This makes the Hydrogen gas, higher up in the atmosphere, more prone to escape than gasses found lower down. 

    But Hydrogen and Deuterium have a natural affinity to form water molecules and would not be prone to escape; and this is where Venus gets interesting.

    While Venus is about 95% the size of the Earth and 82% of its mass, with an iron-nickel core and a rocky crust, it is noting like our fair planet. Venus has a very thick atmosphere almost entirely comprised of Carbon Dioxide. Its cloud filled sky is a bath of sulphuric acid moving at speeds over 200 km/h.

    From a distance the Earth and Venus are remarkably similar, but as always it is the smallest of difference which produce the most potent affects. The small difference in their distance from the sun, the lack of a magnetic field or ozone layer, the tinniest decrease in mass between the two planets, acted as a catalyst for the dramatic differences we see today. 

    Artists impression of Venus' escaping atmosphere
    The smaller mass would result in less radioactive heat sources inside the planet causing the formation of a hard solid crust with little to no tectonic activity after the heat of radioactive decay ran out. The increased temperature due to is closer proximity to our host star leaves more water in the atmosphere as vapor than is locked up in rocks and oceans causing further solidification and drying out of the surface. This evaporation of liquid water releases the Carbon Dioxide dissolved in its depths locking more heat in to the planets atmosphere via the greenhouse effect until no water can survive as liquid on the surface. 

    Venus' water was hot enough to remain a vapor in the upper atmosphere and without the protection of a magnetic field or ozone layer it was subject to harsh radiation from the Sun. Energetic Ultraviolet light bomb-barded the water molecules causing it to dissociate into Hydrogen and Oxygen, or 1/5000th of the time into Deuterium and Oxygen. These would then be prone to escape through further heating of the gas in the planets upper atmosphere. 

    The thermal escape velocity of Venus' atmosphere is around 10.4 km/s, with Hydrogen's escape velocity at half that and Deuterium's around a third, it would not take much to cause either of them to escape. But again it is the small difference that make everything. Just 1.5 km/s difference in escape velocity means that Venus would loose 99.9% of its hydrogen atoms while only 90% of its Deuterium atoms escaped producing the abnormally high D/H ratio observed by the Pioneer spacecraft.

    So there really is a lesson to learn from the Earth and Venus, while from a distance they are unsuspecting twin rocky worlds in our inner solar system, they are vastly different worlds with many different intricate stories to tell. 

    That and the smallest things can make the biggest difference.


    What's Next?

    There were some great resources that I used for this article and they can be found in the links below so please have a browse.



    IMAGE CREDIT: Earth and Venus - ESA; Hydrogen and Deuterium - Nick Strobel; Venus' escaping atmosphere - ESA

    Tuesday, December 10, 2013

    Observing on Mauna Kea



    Over the past week I have delved into the life of a ground based astronomer in an effort to gain some practical knowledge of the instrumentation involved and an understanding of the observing process.

    Having previously work only with space based data – and as they refuse to send me to see one of those in action – this was my first time seeing a professional telescope.
    During the week I was able to observe with both Subaru and the James Clerk Maxwell Telescope (JCMT), two vastly different telescopes all in one glorious place. That place, Mauna Kea.

    Mauna Kea is one of the worlds leading observatories with 13 telescopes covering the near UV through sub-millimeter out to radio with contributions from 10 different countries it is a true collaborative effort.

    After acclimatizing to the advanced altitude at Hale Pohaku astronomer center, which sits at 2800m on the side of Mauna Kea, you head up to the Summit, a further 1400m above sea level. This altitude gives the mountain ideal conditions for observing sitting above the lower cloud deck and surrounded by cool dry air you get a nearly unobstructed view of the universe.

    Well at least in theory!!

    On my first observing night I joined some of our collaborators on the Japanese Subaru telescope. Subaru is one of the largest telescopes on the mountain and contains the largest single mirror reflector measuring 8.2m across.
    In true Japanese style it is a technological and engineering marvel. Our technician for the night, Daniel Birchall, described it as and over engineered playground for the technicians. As a result it is quite a hands off telescope for visiting observers, apart from the full on tour you can take before the sunsets and you get to see all of the robotic arms and instruments that control this ginormous ‘scope.
    The observations that we were taking with Subaru were not only time dependent, as we were observing the transit of an exoplanet, but also required very high precision measurements. So a clear sky is critical.
    Unfortunately that night the clouds decided to roll in and with exposures of 15 minutes per image any breaks in the cloud would end up being combined with those of a cloud free sky.
    Over the course of the 12 hour observing shift we eagerly checked each of the exposures for the maximum count level hoping that we would collect enough photons to do some science with the data. I think in the end we just about got there, but only just.

    While I was up observing with Subaru another observer with the University of Exeter was heading up to do her own observations on the JCMT, and she kindly offered to let me tag along for a few nights and take a look. While the science they do is not in my specific field of study it is a great idea to get a look in at how they take their data and operate their telescope to expand your understanding of the instruments that can be used for astronomy.

    Now in contrast to the over engineered telescope of Subaru the JCMT is a different kind of engineering marvel. There is something beautifully British about the whole thing and it is one of a kind in the sun-millimeter astronomy world. JCMT is a 15m dish sitting inside an enormous dome in what is called sub-millimeter valley on the summit of Mauna Kea. From the giant dish to the control room that rotates along with the telescope it appears as if it is from a different time and has a fantastic cobbled together space junk feel to it, like something out of Firefly.
    Now unlike Subaru’s measurements clouds would not be too much of a factor for JCMT, however, what we got over the next two nights was. Humidity.
    The top of Mauna Kea was shrouded in fog! And with the humidity over 95% we could not even open up the dome.
    On the second night our support astronomer, Will, lit up the inside of the dome and walked me through how they take measurements but setting up a mock observation. This let me see how the entire place rotated along with the telescope and how the instruments are all aligned with the dish by moving the secondary reflectors. The best thing about it was that I now had a better understanding of the work my old office mate does and after 2 years of learning about it from her the final pieces clicked into place.

    I think the Brit in me liked the industrial feel of the JCMT, but I certainly look forward to getting to use the Subaru telescope for transit observations in the future. Hopefully with better weather conditions.



    Wednesday, October 9, 2013

    The Birth of Our Solar System

    Artists impression of the late heavy bombardment
    of our solar system

    4.5 billion years ago, long before Homo habilis first picked up a pointed stone and used it as a tool, something truly spectacular occurred that would change the space around it forever. The Sun was born!

    Imbedded in a fluffy cloud of gas and dust compressed under its own gravitational pull the core of the Sun burst into existence igniting a fusion reaction that would and will continue to fuel it for over 10 billion years.

    At the start of its life a star rotates very quickly, while there is no way to really know how fast the Sun's early rotation rate was the impact that it would have had on the surrounding disk is also hard to determine. We do, however, know that over time a star will loose its angular momentum through outflows and winds reducing its angular rotation over time, or 'spinning-down'. Using a technique called Gyrochronology we can estimate that at the age of 100 million years the Sun would have been rotating over 10 times its current ~25 day rotation period, so we can only assume that in the lifetime of solar system formation or disk dissipation the Sun had a much faster rotation rate.

    This large rapidly rotating mass at the center of the cloud spins the material surrounding it causing it to flatten into a disk – like spinning out a pizza base from a ball of dough. By observing other pre-main-sequence stars and measuring the dust emission in the infrared and mm wavelengths we can estimate what the Sun might have looked like shrouded by its protoplanetary disk.
    From observations it is estimated that it takes around 7-10 million years for the protoplanetary disk to dissipate potential forming a planetary system invisible to our current instruments.

    The evolution of solids in the protoplanetary disk is a multi-stage process:
    First the gas and dust of the disk condense to form micron-sized particles, 100 times smaller than the thickness of a sheet of paper, to cm sized oxide and silicate grains. Over the next few million years evaporation and recondensation will be the dominant process in the disk.
    From studies of meteorites and asteroids it is estimated that this high-temperature nebula process lasted between 3-5 million years before larger asteroid like bodies formed.
    These asteroid-like bodies would have then later formed bodies capable of retaining their own heat or substantial radioactive material. Over the next 2-3 million years through collisions and gravitational interactions planetesimals emerged. Followed by a chaotic period of ‘shock processing’ or ‘heavy bombardment’ where the material fought its way into stable orbits or was chucked out of the solar system entirely – potentially forming some of the comets that come back to visit their original home every few hundred years.  

    Theoretical models of protoplanetary disks to early solar systems help us understand how material is likely to behave within the disk and the likelihood of forming planetary systems that are stable like our own. With the discovery of such systems over the last few decades an increased effort has been applied to such simulations to determine if we really are the exception to the rule, which thus far appears very different to our own.

    The nature of the very early solar environment is still largely a mystery but scientists are working with renewed vigor from analysis of meteorite to observations and simulations of young protoplanetary disks. In an effort to answer the question; where did it start and how did we get here? 

    A time line of the protoplanetary disk and its different stages
    What’s next?

    Ian Czekala from the astrobites team has a good review article on Protoplanetary disks and their evolution - http://astrobites.org/2011/03/11/review-article-protoplanetary-disks-and-their-evolution/

    If you want to know a bit more about gyrochronology and the methods used here is the paper written by Sydney Barnes explaining in detail the technique used
    Gyrochronology: S. Barnes 2007 -  http://arxiv.org/abs/0704.3068


     Title image: ART BY DANA BERRY; SOURCES: HAROLD LEVISON AND DAN DURDA, SWRI.