Sunday, January 31, 2016

My exoplanet memories

This is what I was doing in 1995.
Conducting, Counting, and at the beach. These weirdly follow my
real life. But those trousers in the middle, what were they thinking.
It is strange, when I think about the discovery of exoplanets, I cannot place the first time when it dawned on me they were real and not just science fiction. When I give talks about exoplanets to young audiences I am always quick to point out that they are the first generations to grow up always knowing that other worlds outside of our solar system exist. But, I fear I have been lying to myself this whole time, and I am actually part of that generation too. 

In 1995 when exoplanets hit the big time, with the discovery of 51 Pegasi b, I was 5/6 years old. I was in year 1/2 at school (kindergarten/1st grade). My memories of that time are limited. I was modeling for children book publisher DK, where my aunt and uncle worked, and dreaming of becoming a farmer with my friends at school where we would have a farm to look after sick animals. The only science fiction we had been introduced to at this time by my mother was Quantum Leap, and Stargate was not due to be made into a TV show for another two years. 

All I recall from the years following 1995 is my interest changed from farm animals to dinosaurs, spurred on by the 1993 release of Jurassic Park, and Jurassic park lost world in 1997. As this was all accompanied by trips to the Natural History Museum in London with the school, and clear memories of my friend being terrified of the animatronic T-Rex ripping apart another dinosaur as I walked past grinning and loving it. 

We were not introduced to Star Trek or Star Wars growing up, because our mother did not watch it so we didn’t.The first experience of epic science fiction journeys to other worlds came in the form of Stargate SG1. When Stargate, a pivotal information source of my future ambitions and endeavors, did reach my consciousness we were already adventurers and explorers. My parents enrolled us in a snorkeling club where we went on big trips to the lake or the coast to explore the world under the waves. My father a amateur historian loved to take us to castles, towns, and museums. By the early 2000’s we were all planning to be Egyptian archeologists or marine biologists.

It was not until 2001/2 that I distinctly remember turning towards space*. My Father used to drive me to the Guildford astronomical society evenings, to listen to talks or look through a real telescope. Every single year our family grabs some bin liners and goes out to the field out the back of the house to lie down and look up at the sky during the Perseid meteor shower, but I don’t remember when that started, it is just something we have always done but quite honestly could be a relatively new tradition. 

*In 2002 the first atmospheric detection was made of a transiting exoplanet (Charbonneau et al. 2002), work which forms the basis for what I do now as a postdoc. 

Samantha Carter (Amanda Tapping)
from Stargate SG1. We had this photo
signed on our bedroom wall for at least
7 years. Then I took it with me to put
on  my wall at Uni.
Since I decided I wanted to be a real life Samantha Carter (Stargate Astrophysicist, adventurer, and all round depended on kick ass woman), I have not turned back. But by then the presence of other alien worlds as the norm was in my head, the new Star Wars prequels were out, we were having lightsaber fights in the science classroom with the meter rulers, and I was going to sic-fi conventions to meet people from Stargate, Lord of the rings, the matrix, and a host of other shows featured in SFX each month. 

When I went to university exoplanets were not yet part of the general curriculum for undergrad classes. I selected my university degree based on how much space I could learn about, and by how far away they could send me for a year. I ended up at the University of Wales: Aberystwyth, the most awkward to get to from my parents home, where they sent me to Svalbard in the Arctic to finish up my MPhys year. It is half way through my time at Aberystwyth that I remember openly talking about exoplanets as a real scientific discovery. We were asked to write an essay about water on Mars or other planets. As we were enrolled in a Planetary and Space Physics degree, most of us had worked on Venus or Martian data, so I remember most of the class writing about that. But, I wrote an essay on exoplanets and the plans for the upcoming Kepler mission to find all of these strange new alien worlds, of course I linked it all back to Stargate in some way. I loved the work I did on the solar system planets, and the impact the Sun’s atmosphere had on our inner solar system, but I knew I wanted to work on exoplanets. I wanted to find an Abydos, or Chulak. I wanted to discover what they were like, was it anything we had seen before. Did Stargate get any of it right?

In 2010 myself and a friend convinced our advisor to apply to the Royal Astronomical Society for a summer internship position at the university to search through the first sets of data coming from the Kepler Exoplanet Mission. To link it to our work on the Sun, where we had previously been looking at CME tracking and sunspot evolutions, my friend used the Kepler data as a search for starspots to model their influence on the light curve, while I set about looking for planets transiting them. 

I had my taste of what being an exoplanet explorer could be and I wanted to keep doing it as long as I could get away with it. But looking back there was no eureka moment. No point in time where I sat there and thought, ‘holy shit they are real and people have just discovered them’. They were always just there, be it in science fiction which I did not know was not based on truth yet, or in reality. As my earliest memories of the world stem from a time when they actually did exist despite the fact I was born in a world where they did not, I cannot truly claim to be part of the last generation to grow up with this world changing discovery. 

But I think I am okay with that. Now I am part of the first generation to grow up always knowing we were not a lone solar system drifting at the reaches of our galaxy. Like Pluto I have been reborn.

Me talking about exoplanets, and comparing hot Jupiters to a watermelon.

Monday, December 14, 2015

Clear to Cloudy

As of this morning the NASA Exoplanet archive lists the discovery of 1916 exoplanets. These planets range in size and mass all the way from super Jupiters (over 10 times the mass of Jupiter), to Neptune’s, super-Earths (up to 10 times the mass of the Earth), and potentially Mars-sized or even Mercury-sized worlds. One of the most interesting discoveries in the search for exoplanets is that many of them are nothing like what we have in our solar system.

One such class of planet that was discovered is the hot Jupiter. Hot Jupiters are similar to Jupiter in mass , but can range in size from 0.8 - 2 times as large in their radius. Hot Jupiters also orbit much closer to their host stars than Jupiter in our own solar system, which sits at a cool 5 time the distance from the sun as the Earth, in fact hot Jupiters orbit 20 times closer to their star than we do to the Sun, which is even closer than even Mercury. This means that they are also tidally locked, with one face of their planet in constant daylight and the other in constant night.  

But now the new and exciting stuff...

To get an idea about what these strange new alien worlds are like, an international team of astronomers harnessed the observing power of the Hubble space telescope, and the Spitzer space telescope to conduct the most extensive study thus far to characterise the atmospheres of ten hot Jupiters. By looking at the stars light as the planet transits in front of the star, as Venus does in our solar system, from the perspective of the Earth we can detect the unique fingerprints of different molecules in the planets upper atmosphere as the light is filtered through before reaching our telescopes. This measurement of how the atmosphere absorbed light at different wavelengths is called transmission spectroscopy.

HST/Spitzer transmission spectral sequence
of hot Jupiter survey targets.
The solid lines are the model spectra fit to the measured transmission
spectra of each hot Jupiter in the survey, which are shown as data
points with their measured uncertainties. The spectra are offset and ordered
from top to bottom with low to high values of 
In the past only a small number of well-studied planets (HD 209458b, HD189733b, GJ 1214b) have been analyzed over a small wavelength range between 1.1-1.7 microns, just beyond the red part our eyes can see (Deming et al. 2013; Line et al. 2013; Sing et al. 2014; McCullough et al. 2014; Sing et al. 2015). This is an important wavelength range as it is where water vapor absorbs sunlight. Recent studies have shown that hot Jupiters have much smaller and muted water features than is predicted. The smaller signals could potentially be explained by lower amounts of water than was expected (Seager et al. 2005; Madhusudhan et al. 2014), which is a sign that water is removed somehow from the protoplanetary disk from which a solar system would form (Oberg, Murray-Clay, & Bergin 2011), but it is not clear if this high level of depletion is even possible. Alternatively, the weak signals of water vapor could be the result of clouds or hazes in the hot Jupiters atmosphere which obscure the water signals (Pont et al. 2013; Sing et al. 2014, 2015; Nikolov et al. 2015)

This new study published in Nature shows the measurements of ten hot Jupiter atmospheres from the optical (0.3 microns) all the way out into the mid-infrared (5 microns). This allows us to spectral resolve not only the water feature in the near-IR, but also the optical scattering and the IR molecular absorption features. The result of the study reveal a diverse group of planetary environments from clear atmospheres, which exhibit little to no evidence for high altitude clouds or hazes, revealing broad atomic signatures in the optical to large amplitude water features in the IR, to cloudy and hazy planets, which have strong Rayleigh scattering slopes in the optical and muted or even absent absorption features from water in the IR.

Pressure-Temperature profiles and condensation curves.P-T profiles were calculated from 1D radiative transfer
models (Fortney et al. 2008). Condensation curves are calculated for
chemical species expected in hot Jupiter atmospheres (Morley et al. 2012).
The presence of a cloud or haze can be predicted by the atmospheres temperature profile with altitude. Models show that as we move higher and higher in the planets atmosphere, decreasing log(pressure), the temperature decreases. Where the temperature and pressure of the atmosphere match the temperature and pressure where a material will change from a gas to a liquid is called the condensation point (Wakeford et al 2015). This will form the base of the cloud in that atmosphere. This is shown in the figure where the colored lines cross the grey dashed lines. Yet strangely the presence of obscuring clouds and hazes in the observations do not match up perfectly with the predictions from the models. So temperature and pressure alone cannot explain the clear to clouds atmospheres observed, suggesting circulation, vertical mixing need to be considered to transport heat and particles around the planet (Showman & Polvani 2011).

In the study we present a metric to distinguish between planetary atmosphere, comparing the difference between the measured planetary radius in the near-IR to that measured in the mid-IR (ΔZJ-LM), and correlate this with the strength (amplitude) of the water absorption feature. We additionally define the difference between the optical and mid-IR (ΔZUM-LM) that compares the strength of scattering in the optical, to the molecular absorption measured by Spitzer.

Transmission spectral index diagram: ΔZJ-LM vs H2O amplitude.The uncertainties represent the 1-sigma uncertainty. The purple and grey lines show model 
trends for cloudy and hazy atmospheres. We also show the clear-atom models with sub-solar
abundances in red. Note: WASP-39b and WASP-6b are missing as they currently have no
HST/WFC3 data. However, we have both scheduled for this coming year.
By plotting our measurements from this broad wavelength study we show that the results favor the obscuration of water by clouds or hazes rather than models where the water abundance is lower. The effect of clouds or hazes in the atmosphere reduces the water absorption amplitude, while raising the level of the near-IR to mid-IR continuum levels, leading to high ΔZJ-LM with low water amplitudes.

Theoretical model transmission spectra.
Model spectra assuming 1200K temperature with gravity of 25 m/s^2.
Models in each panel are compared to a clear, solar metallicity atmo (black).
This has revealed a continuum of hot Jupiter atmospheres from clear to cloudy. With the cloud formation in the atmospheres of these planets being highly sensitive to the temperature and pressure profile such steep gradients in the upper atmospheres, mean changes of just 100 degrees either way can totally change the cloud properties being observed. You can also see the different models that go with these metrics below.

This is the first time a large comparative study has been conducted on exoplantary atmospheres using consistent analysis techniques to combine datasets from different instruments and spacecraft. It is fantastic to finally see them all together in one place so that we can start to unravel the mysteries of these planets from afar.

The exciting part is now with this metric we can attempt to classify such strange alien planets, and the James Webb Space Telescope, Hubble’s successor, will expand our range of planets to study even further. Importantly, with more and more observations we may be able to make our own solar system planets part of this interstellar comparison. 

You can find the full nature paper on the Nature site here 

Also check out all of the press releases on the survey below

Friday, November 20, 2015

Condensate clouds in hot Jupiter atmospheres Poster

please email me if you would like more information.

Saturday, November 14, 2015

What I learnt from DPS15

DPS15 is a conference held by the Division of Planetary Science which is a group within the AAS (American Astronomical Society). This year was their 47th annual meeting, which was hosted at National Harbour, just outside of Washington DC.

This was my first DPS conference and while I intended to take many, many notes, I was swept up by the amazing community on twitter and decided to spend my week throughly tweeting the conference instead.

Here are just a few of the things that I learnt from DPS15 in the form of the tweets they sparked. As such it may be a slightly biased view, but I hope you enjoy. Each of the topics links to a Storify album of tweets so look for yours in there if you joined in with the twitter conversation.

Twitter embargo
The planetary community can get a little snarky when they are told they are not allowed to share their science.

The first session of DPS15 was a look at some of the mazing science discoveries the New Horizons team have made about the Pluto system. However, we were informed at the start of the session that all of the information we would hear for the next 2 hours was under embargo until the press conference at 12pm. Naturally the room got a little mad. This is how planetary scientists fight back.

Here are just a small selection of the tweets that were posted during the embargoed Pluto session.

NASA brought along a massive model of Saturn's 6th largest moon Enceladus to the DPS15 exhibit hall, which included live plumes of steam bursting forth from it's surface.

Naturally this got a lot of people excited and snap happy, including myself.

Dr. Paddack the P in YORP presented at #DPS15 to a packed room, and I learnt what YORP was.

There were a few excited scientists in the room tweeting, which helped spread the excitement, as I was actually in another session at the time.

Scroll through to learn what YORP is and why it matters.

Clouds are a big thing with planetary scientists. They appear everywhere a persistent atmosphere is observed. As an exoplaneteer it is time we start to use that to our advantage.

Here are a few tweets from across our solar system talking about the cloudy nature of planetary science.

I am biased toward the exoplanet community so I will start there, but never fear clouds were everywhere at this years DPS so just keep scrolling through.

and last but by no stretch of the imagination least.

Mesursky award talk on Harassment
The Mesursky award for service to the planetary science community was awarded to Dr. Christina Richey for her work in the community to combat harassment and discrimination. Normally the Mesursky winner does not get a talk, however, this year Christina asked to be able to address the whole community about an issue she is passionate about, and which needs to be spoken out loud.

Dr. Christina Richey addresses the whole conference in a magnificent show of strength about harassment in the community and how we can all become better allys. Here are just a selection of the tweets during and after her talk which show you the response from the community.

It was fantastic to meet and talk to so many people over the course of the week and make sure you look up #DPS15 for the full story.

See you next year!

Tuesday, September 22, 2015

What I learnt from CCTP2

At the beginning of September I attended the Comparative Climates for Terrestrial Planets II conference at NASA AMES Research Center. 

The conference aimed to foster a series of interdisciplinary conversations on a wide range of planetary climates. this years theme was "Understanding How Climate Systems Work." As an exoplanet researcher I was the outsider attending  a rocky planet conference but I learnt a lot and was hopefully also able to put the current observation capabilities of exoplanets into context.

But as I have done with previous conferences I attend I thought I would share some of the "Things I learnt from CCTP2" with you now.

Old zeppelin hangers are really really big, even without the skin on them.
 - The habitable zone is the hunting zone for planets. It is just giving you the greatest possibility of finding a planet with surface liquid water.

Come to NASA they have cookies.

 - Terrestrial planet scientists don't like the idea of their rock being molten, and especially don't like to think of it floating in the atmosphere of a giant planet.

     - Sometimes you just need to present your crazy idea on what controls global dust storms on Mars. But test it out on other planets first.

     - Weather is not the climate, but sometimes the climate can be weather.

     - New horizons got to Pluto just in time. Any later and the atmosphere might have all been condensed out for the winter.
    You also get to give from a
    fancy lectern. 

     - A planet can be considered 'occasionally habitable' if the climate has strong feedback on the atmosphere where you move from a snowball to a warm planet in a cyclical process.

     - The only way to take N2 out of the atmosphere is with biology.

     - There is the same amount of CO2 locked in rocks on Earth as there is causing the runaway greenhouse in Venus' atmosphere.

     - A dune planet could is the zombie afterlife of a habitable world.

     - Volcanoes are cool.

     - While more planets may be in the habitable zone of M-dwarfs they will be receiving much more UV flux from their star which will affect the chemistry of the atmosphere.

     - There could be more tidally locked planets than earth like planets in our galaxy because there are more small stars where the habitable zone is closer to the star so could have dynamically locking.

     - We all need to be asking the question at conferences; "what can we investigate in our field to potentially inform yours?"

     - Give a group of early career researchers some frozen yogurt then leave them with  a coloring book and pens they will really geek out on you.

     - It is a really small world, and Stargate really is the greatest show.
    The result of the early career researchers evening out, featuring MAVEN, Dr Who, Hitchhikers Guide to the Galaxy,
    Godzilla/Alien, planetary weather systems, and most importantly a Stargate mid KAWOOSH!


    And my talk on Cloud condensates in hot Jupiter atmospheres can be found at this link -