Friday, March 23, 2012

Planet Question Time III

Do all planets orbit the equator of their star?
It was once thought that all planets would orbit around the equatorial plane of their star, or at least very close to it. However, as with a majority of exoplanet discoveries, the theorists were sent back to the drawing board.

The angle of a planets orbit relative to the rotation of its host star is called the spin-orbit alignment. This is not an easy thing to measure for a large majority of exoplanets, as it requires high precission measurment of v sin I, which can only be done for small inclinations. If, however, the planet transits the star we are able to measure the projected spin-orbit misalignment angle, λ, in the plane of the sky. This is called the Rossiter-McLaughlin effect (RM effect).
(c) Systemic http://oklo.org/2010/06/20/that-other-angle/


As the planet transits the star small changes in the radial velocity measurment can be observed. The radial velocity is the shift in the spectral lines of a star induced by another body in the system causing the main star to change in position and velocity as they orbit the center of mass of the system. The video on the left shows how the spectral lines shift over as series of orbits (ESO/L. Calçada http://www.eso.org/public/videos/eso1035g/).


Radial velocity observations can also tell us a lot about the orbit of the planet, as they are highly affected by the spin-orbit alignment of the planet-star system (the RM effect). As the star rotates relative to the observer, us on the Earth, half the light is blue shifted as it rotates towards us, while half is shifted toward the red as it rotates away from us. When the transiting planet blocks the blue-shifted light we will see more of the red-shifted light relative to the blue and vice versa when the planet blocks the red-shifted light. By modelling the RM effect, the angle of the planets orbit relative to the rotation of the star can be calculated.

A large number of systems have now been found to be misaligned with their host stars rotation, even to the extent that they rotate in the opposite direction to their star, which has provided a lot of information about exoplanetary system formation.

The RM effect: showing the change in the RV at different angles.
It is important to remember that a theory can be developed using all currently known physical principles. However, without observations it is still just a theory. It is also very important to note that if observations disprove your theory, in this case planet formation, it is not necessarilly a bad thing!

Saturday, March 17, 2012

What EaHS'12 taught me!

“If we can’t prove it, we let the evidence speak for itself.” 

“You can use a probe to probe another probe!”
“If everyone is equally unprepared, then no one will notice ”
“Parameters can have parameters but they are hyper!”
“The more data we have the more we complain that they won’t let us get any more”
“Anything and everything told to you by an Oxford or Cambridge student is inherently biased”
"Small dense things have a smaller amplitude but higher frequency"
"If it is not what we expect, then what you expect is probably flawed"
"Theory is always ahead of observation, but it means nothing without it!"
“A Ravenclaw shooter is disappointingly red, whereas the Slytherin one glows green with pride.”
"Even the most hungover member of the group can introduce a presentation on a subject they have very little knowledge of because no one else does either"
“Betrayal is sudden but inevitable… no wait that was Firefly!”

Exoplanets and their Host Stars Course


Over the last week I have been at the Exoplanets and their Host Stars STFC course in Oxford. Since officially starting my PhD in October this was my first field trip, if you will, to meet with other astrophysicists and get a face to face update on what we are learning and discovering as we work. I was amazed to discover the breath of information we can gleam from one continuous data set, like those obtained by the Kepler mission. From the structure of the interior of the star, to activity on the surface, and out to the planets that orbit it.  
The course was intense; it has been a long time since I had to sit down in lectures all day, however, for the most part with the help of caffeinated beverages I made it through. The key to an engaging presentation, it seems, is pure enthusiasm and love for the work that you do. It is these presentations where I truly feel I have learnt something and in particular during this course, from Don Kurtz and Bill Chaplin who spoke about Asteroseismology, increasing my awe at what we can observe from so far away. If you go on a course like this, which to some extent is specilized, it is important that you do not just focus on those subjects that you specifically work on. This course introduced to me the extent at which our understanding of other physical process appear in our data and how we need to incoroprate all of this knowledge in order to produce the full picture.

We were all lucky enough to have a dinner on the Thursday night at All Souls college in Oxford. Unfortunately the organizer forgot to tell us before that there is a strict dress code, and it was quite an experience to walk into one of the most prestigious colleges at Oxford surrounded by people in jeans and tee shirts. It was a fantastic meal and the tradition of passing around a bottle of port at the end of the meal until it has all gone is a great one. We then headed out to the town and that is where my memory of the, what I am told was a great night, ends. However, some pictures and stories the next day seem to have filled in most of the gaps. 

During the week we also split up into groups to do our own projects which we then had to present to the rest of the course participants. I and a number of others worked with Neale Gibson and Steve Roberts on Gaussian Processes a subject that is still way over my head. I bit the bullet and introduced our presentation hopefully giving everyone a much dumbed down version of what we had been told during a lecture by Steve Roberts earlier in the week. I was then able to hand over to other members of the group who had applied it to their data demonstrating how it could be useful for all participants to look at. I am greatful for the oportunity to work on it for the four hours we were given with people who know it best. I fully intend to use it in the near future, but I think four hours of working on it will never have given me a full understanding, though it was a good start. 

I am now very much looking forward to the National Astronomical Meeting at the end of the month in Manchester where I am presenting a poster.

Wednesday, March 7, 2012

Planet Question Time: Part II

Do all planets have an atmosphere?
Once again we take ourselves back to the wonderful diversity of planets we see in our own solar system, and onto the surface of Mercury. The surface temperature on Mercury ranges from 100K in the shade at the bottom of craters, and up to 700K when it is closest to the Sun. This, along with the planets small mass, means that its gravity is not sufficient enough to sustain a permanent atmosphere.
Images from NASA's Messenger Spacecraft
A number of small rocky worlds have also been found orbiting other stars. These exoplanets, such as KOI-961b, c, and d, orbit their stars even closer than Mercury does our Sun, and are also thought to have little or no atmosphere due to their size and the stellar wind effects from their stars. The KOI-961 system hosts the smallest known exoplanet to date, with a radius of 0.67 times that of Earth, and the closes orbiting planet discovered, which orbits its star at 0.006AU that is nearly 70 times closer than the orbit of Mercury.

Does a planet have to orbit a star?
Planets have in fact been found alone in space with no apparent star to orbit. These have been called ‘Free-Floating Planets’. It is thought that these lone worlds first formed around a star but, due to close gravitational interactions with other planets and stars, they were ejected from their solar systems. 
In 2006 and 2007 a joint survey conducted by Japan and New Zealand scanned the center of the Milky Way, it revealed evidence of up to 10 free-floating planets with a similar mass to Jupiter.  This survey supports the ejection scenario suggesting that these planets could be more common than the stars themselves.
(c) NASA
Other observations have shown that there are planet-like objects within star-forming clusters with masses over three times that of Jupiter. These are thought to form more like stars growing from collapsing gas and dust, however, they do not have enough mass to ignite and nuclear fusion cannot begin. These are called Brown Dwarfs and are the focus of many stellar formation studies as they may play an important role in stellar evolution.

If you have any questions about planets or space in general please feel free to comment or tweet me @stellarplanet

Sunday, March 4, 2012

Life, the Universe, and Everything!

(c) NASA
The Universe, be it alone or one of many, is big. Really big! So big in fact, that there is no way that we could ever see it all from our small blue dot no matter how hard we squint.

The history of events in the universe plays a vital role in life here on Earth, or even out there, on one of the vast number of worlds discovered and un-discovered.  In a new paper Marcelo Gleiser, professor at Dartmouth and popular science writer, the history of the universe is divided into four ages.  Each of these stages mark a different era of universal evolution which continues beyond the start of the next stage and well into the future.

The Physical age
“In the beginning there was nothing. Then it exploded.” – Terry Pratchett
The era of cosmic emergence spans from the instant our universal bubble was populated with energy to the formation of stars and galaxies. From the great cosmic soup, interactions governed by gravity, electromagnetism, and the strong and weak nuclear forces, help form the light nuclei and at around 400,000 years, the first hydrogen atoms were formed. Denser regions of material coalesced under gravity and after 200 million years the first supermassive stars were born. The first galaxies soon followed and interacted with each other to form the larger galaxies such as our own each with the chemical ingredients necessary for life to begin.

The Chemical age
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” Carl Sagan
Our galaxy is littered with an array of inorganic and organic molecules created by the stars themselves. The chemical age marks the era between the formation of the heavy elements in the stars to the prebiotic chemical processes that lead to the biological age. Gleiser goes into detail about the synthesis of amino-acids and the network of reactions that govern the replication of molecules necessary for life to begin. The timeline for this, although requires heavier elements, is not restricted to the Earth alone. It could have been sparked long ago on another planet, perhaps in another galaxy far far away.

The Biological age
"An American monkey, after getting drunk on brandy, would never touch it again, and thus is much wiser than most men." Charles Darwin
The age of Darwinian natural selection.The line between the chemical age and the biological one is blurry though the jump between simple biological molecules to a living cell is a good indication that you are in the era of biological development. It is even at the simplest level that Darwinian natural selection gets to work though it is not a fast process. It was not until 1 billion years ago that multi-cellular organisms emerged on Earth and around 400 million years later that the first animals start to appear. After 500 million years of evolution, on Earth at least, the process of natural selection lead to self-awareness and the manipulation of the environment around us bringing us into the cognitive age.


The Cognitive age
"There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened." Douglas Adams
Our ability to think, manipulate the environment to our advantage, and to create art and technology, form the basis for the definition of cognitive intelligence and the most recent age in the lifetime of the universe. This leads us to the ultimate question, of life, the universe, and everything! Are we the exception or are we the rule?
A number of astrobiology studies have been conducted using earth shine on the moon to see what signatures are conducive to intelligent life (http://arxiv.org/abs/1203.0209;http://adsabs.harvard.edu/abs/2009ASPC..420..371S) . Though out of the multiple planetary candidates found thus far none have shown more than the simple potential for organic life to exist. If cognitive lifeforms do exist within our galactic neighbourhood then listen out for their radio signals like the SETI program (SETI @ home: http://setiathome.berkeley.edu/).


Marcelo Gleiser takes something as large as the universe and easily links its origins down to the tiniest of electrical processes that go on inside our brains and our connection to those around us that make us self-aware creatures on our lone rock in a sea of other worlds. He concludes  by saying "Search we must, if only as a directive of our own intelligence and with a quote from Carl Sagan;
"absence of evidence is not evidence of absence".
From the Cosmos to intelligent life: The four ages of Astrobiology http://arxiv.org/abs/1202.5042  

Thanks to NASA for the use of their images.