Monday, July 29, 2013

Color me cloudy

Clouds of the coast of Brazil from the ISS
We might all despair when we see clouds in the sky but they are playing a vital role in the energy balance of the planet by reflecting and absorbing solar radiation.

But what about other planets?

Every planet in our solar system with an atmosphere has clouds. Some of them are highly reflective like Earths water vapour clouds, while others are absorbers giving the planets the colours that we see.
Like us Venus has strongly reflective clouds, although on Venus these are made of hydrosulfuric acid and would be far more foreboding than any clouds we get on Earth. These clouds reflect almost 75% of the sunlight that falls on them making them completely opaque. If you were to stand on the surface very little sunlight would reach you and at most you would be able to see ~3km, whereas on Earth you can see over 4.7km from eye lever and over 200km from the top of a tall mountain.

Jupiter's cloud patterns
Jupiter and Saturn have very hazy atmospheres. A haze is comprised of very small particles in the atmosphere that absorb radiation and contribute to the colour of the atmosphere. These are almost always photochemical produced, formed by a reaction with sunlight in the upper atmosphere. Jupiter has several different cloud layers of ammonia, ammonia hydrosulphide, and water vapour with deeper cloud decks at higher pressures as you go down through its atmosphere. You can clear see the shapes that the cloud form on Jupiter with the famous Big Red Spot cloud formation which is through to be a hurricane that has been raging in Jupiter's atmosphere for over 400 years.
Saturn has a similar cloud structure to Jupiter with big up ammonia clouds followed by ammonia hydrosulphide, and water vapour clouds as you head towards its interior. It is incredibly windy in Saturn's atmosphere with wind speeds reaching 1,800 Km/h producing storms which can occasionally be seen through the haze and smog in the upper atmosphere that obscures the lower cloud decks. One such storm observed by NASA's Cassini spacecraft orbiting Saturn revealed a giant hurricane, 20 times the size of the Earth, trapped at the planets northern pole with the eye of the storm giving us a look through the cloud layers of the planets atmosphere.
Polar hurricane on Saturn taken by Cassini

The diversity of clouds is enormous - from particle size, vertical extent, cloud composition. From Earths water vapour clouds with particle sizes from 10 to 100 micrometers, to Titans methane clouds, and Jupiter and Saturn's high altitude hazes. Exoplanets are also thought to have a large diversity in cloud composition, position, and composition. The currently accessible atmosphere so hot Jupiter atmospheres through transmission spectroscopy and emission spectroscopy during secondary eclipse are already showing a wide range in detected species, from Sodium and potassium peaks in the optical to water in the infrared. Hot Jupiter's are likely have clouds formed of liquid Iron droplets due to their high temperatures with solid silicates and other high temperature condensates that contribute the haze and colour of these worlds.
A recent study of the exoplanet HD189733b revealed that it would appear a deep cobalt blue if viewed  directly. This is due to silicate hazes in the upper atmosphere which scatter blue light.

Understanding the composition of Exoplanet atmospheres is key to get a look into their formation as well as the energy balance of these atmospheres where high stellar irradiation could play a key part in the production of obscuring hazes. We still do not completely understand where the colour of planetary atmospheres and new observations with ever advancing technology the puzzle pieces are falling into place.
HD189733b - the deep blue dot

What's Next ...

Check out the HD189733b blue planet press releases here are just a few links:
http://sci.esa.int/hubble/52045-hubble-spots-azure-blue-planet-heic1312/
http://www.nasa.gov/press/2013/july/nasa-hubble-finds-a-true-blue-planet/#.UfZxDmj3A1g
http://www.exoclimes.com/paper-outlines/the-colour-of-an-exoplanet/
http://www.exeter.ac.uk/news/featurednews/title_306413_en.html

Also some good links for the Saturn Cassini images:
http://saturn.jpl.nasa.gov/photos/
http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20130429.html#.UfZxjWj3A1g
http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Saturn_s_atmosphere

A lot of the information is from a book by Sara Seager - Exoplanet Atmospheres which is a fantastic read if you want to really get into the details math, physics, and chemistry of planetary atmospheres.

IMAGE CREDITS: Luca Parmitano (@astro_luca) from the ISS, NASA, NASA Cassini, NASA/ESA press release. 

Tuesday, July 9, 2013

NAM 2013


With every coming year comes the Royal Astronomical Societies National Astronomy Meeting, where astronomy and astrophysics groups from every UK University are welcomed to present their work across all fields of astronomy. This year the annual yell of astronomers assemble called us to St Andrew’s, where we were greeted with beautiful sunshine and the guarantee that it was like that all the time, and with the exception of Tuesday it was.

NAM 2013 brought together over 600 astronomers to nearly 40 parallel sessions over the first five days of July. With additional specialized lunches and social events including Scottish whisky tasting and a traditional ceilidh at the Old Course Hotel. There was also some time to have a look around the cathedral, castle, and even having a go on 'The Himalayas' putting green.
The Himalayas putting green - if the aim is to get the highest score I definitely won.


To cater for all fields of astronomy covered across the UK the sessions are run in parallel, with up to 8 running at the same time. Your choice then is, what session to go to. There will normally be at least 3-4 sessions covering a specific field of astronomy, with other having perhaps more tenuous links to your field of study. But when your line of study is not specifically catered for there is always something new and exciting you can learn.

The shear variety of research covered by conferences like NAM give new researchers a great opportunity to present their work without as much pressure as you might get at a more specialized conference. This relaxed atmosphere also welcomes public astronomers to specialized outreach sessions allowing them to share their hard work and innovative ideas about getting the word out that astronomy is awesome.

So with the Exoplanet sessions confined to the last two days of the week to accommodate those in Europe at another meeting I had three days to scoot around the other sessions and see what I could learn.

During the week I the took the opportunity to sit in on some sessions where my friends were presenting their work, from galactic population studies with GalaxyZoo, computer simulations of forming stars in large molecular clouds, to a detailed look at events on our own sun. That doesn’t even cover the array of topics covered by friends and colleagues during the four exoplanet sessions held across Thursday and Friday.

The view across St Andrew's from the top of the tower at the Cathedral

The one thing that sticks out in my mind still, due to the punchline it presents was, “The sun is round,” or rather that stars sometimes are not. Due to the spin rate of some stars and the fluid nature of the plasma stars can be flattened out like the bulge of a spinning top with the radius at the equator nearly 50% larger than that toward the poles. So if you want a flat Earth we would have to rotate over 800 times faster about our axis, reducing our day down to 1.8 minutes, not very likely we would survive that one.

I also took the Tuesday to sit in on the public outreach sessions where armature astronomers and professionals join together with one goal, introducing astronomy to a wider public audience. There was also a brilliant presentation by two young students from The Langton Star Center in Kent who will no doubt one day be presenting their research at NAM in the future. http://www.thelangtonstarcentre.org/
Here is a list of some public outreach events and opportunities across the UK:
The Jodcast a podcast from students and staff at Jodrell bank observatory - http://www.jodcast.net/
Bradfordbury observatory - http://bayfordbury.herts.ac.uk/
Visions of the Universe exhibition at the Royal Museums Greenwich - http://www.rmg.co.uk/visit/events/visions-of-the-universe
Ogden Trust: making physics matter - http://www.ogdentrust.com/
Faulkes Telescope Project - http://www.faulkes-telescope.com/
HM Nautical Almanca Office - http://astro.ukho.gov.uk/nao/online/


NAM 2014 is going to be held at Portsmouth so I might see you there.

So have fun and always remember to look up.



Monday, July 1, 2013

Water in the atmosphere of HAT-P-1b


Water is a remarkable molecule; it makes up ~55% of our body weight, covers 75% of the Earth’s surface, and has been found in the farthest reaches of our universe in some of the most ancient galaxies.

Water also plays a key role in the atmospheres of hot-Jupiters with its detection gaining us insight into the nature of their environments. There is just one problem. Water is so abundant in our own atmosphere, playing a pivotal role in the life cycle of all living species on Earth, that it gets in the way. Leaving us one option.

 To space we must go!

And thanks to the crew of STS-125 HST servicing mission 4 in 2009, after a total of 36 hours and 56 minutes over five EVA’s, an instrument was successfully installed on the Hubble Space Telescope that is able to help us, Wide Field Camera 3.

The fact sheet of HAT-P-1 and our observations.
Using its infrared channel and low-resolution grism (a stepped prism) we were able to obtain the spectrum of the planet-hosting star HAT-P-1 giving us the first definitive evidence for water in the upper atmosphere of its transiting planet HAT-P-1b.

As the planet passes in front of its star, relative to us, a small portion of the starlight shines through the planets upper atmosphere before reaching us. Imprinted on that light, as weak absorption lines, are the tale-tale signatures of various gasses. By measuring the amount of light received by the telescope over a range of different wavelengths you can build up a transmission spectrum of different chemical species to reveal what is in the atmosphere of the exoplanet.

Water has a strong fingerprint centered at 1.4 microns, which lies in the center of Wide Field Camera 3’s wavelength range. To determine if our planet, HAT-P-1b has a significant amount of water in its atmosphere we separated each of the exposures of our observed stellar spectrum into a number of different wavelength bins. From this we are able to measure the change in planetary radius relative to that of the star caused when starlight is absorbed by water in its atmosphere. We then compared our results to models of hot Jupiter atmospheres tailored for HAT-P-1b to determine the significance of the water absorption feature seen in our transmission spectrum. Our measurements revealed that HAT-P-1b has a water-dominated atmosphere at its limb with temperatures cooler than that seen on the dayside of the planet.  

This observation, combined with other planetary transmission spectra from our large HST program and other published work, has revealed a startling diversity of close-in giant exoplanet atmospheres. Showing that water plays a key role in defining the nature of these strange new worlds.
 
Left - the transmission spectrum of HAT-P-1b with a planetary-averaged HAT-P-1b specific model plotted in blue. This model has a greater than 5-sigma significance over a flat atmosphere corresponding to a straight line through the average planetary radius. Right - The Temperature-Pressure profile of the model compared to two models at constant temperature. 
WHAT'S NEXT?
My poster on this work is being presented at the Royal Astronomical Society National Astronomy Meeting in St Andrews this week (2013July 1st-5th) and can be downloaded by clicking on this link – Water in the atmosphere of HAT-P-1b poster.

There is also a paper that is under review for publication in the Monthly Notices for the Royal Astronomical Society (MNRAS) so watch this space for an official link.