11 awesome Exoplanet facts

The first exoplanet was discovered in 1992. This discovery was unexpected in many ways, first the

planet is in orbit around a pulsar, a highly magnetized stellar remnant from a supernova event, but also because there were not looking for it. The search for exoplanets had been actively investigated since the late 70’s but no one was looking around dead stars. It was not until 1995 that the first exoplanet was discovered around an ordinary main sequence star and that presented some surprises of its own.

The first exoplanets discovered were labelled ‘Hot Jupiters’. These planets, although similar in radius to Jupiter, orbit their stars so close that they are tidally locked in place with one side in permanent daylight and the other in perpetual darkness. The close proximity to their star means it can get incredibly hot. The hottest thus far is WASP-12b with a dayside temperature of around 2,500°C that is hotter than some stars*. This orbital distance also means that a year on these worlds is just a matter of days allowing us to take multiple measurements of the planet and the star over short periods of time. 

Since 1992 over 870 exoplanets have been discovered. As of today, April 28^th 2013, there are 872 planets in 683 stellar systems (exoplanet.eu/catalog). That is an average of 41.5 new planets
discovered every year for the past 21 years, and that is just in our neighbourhood within a tiny portion of our galaxy. 

There are potentially hundreds of billions of planets in our galaxy. Thanks to surveys like Kepler, WASP and HAT (just to name a few); we can work out how many planets there could be orbiting other stars that we cannot yet detect.  And it comes to a mind-boggling number considering just over 20 years ago our solar system seemed like an anomaly but it is not an easy thing to do.

It’s like looking for a flee passing in front of a street lamp over 1km away. Each of the surveys I mentioned above look for the planet as it transits its star. This means they monitor the starlight over a long period of time and look for characteristic dips in the light, which indicate that there is something periodically blocking out a small part of the star. From this we can determine the radius relative to the star, with the frequency of the transit giving us the orbital period.  

The closest exoplanet to us is Alpha Centauri Bb. Although it orbits the Suns closest star at just over 4 light years away it was not discovered until 2012 as it has such a small influence on its star. Alpha Cent Bb was discovered using radial velocity measurements (link to other blog post) and from this we can calculate its minimum mass to be just slightly higher than that of the Earth and 96% closer to its star. So it is not a potential holiday destination and even with current technology it would take us  years to get there.

The habitable zone of different stars

Just 10 worlds have been discovered where liquid water could exist on their surface. The Planetary habitability laboratory, from the University of Puerto Rico at Arecibo, has been cataloguing those worlds that lie in what is popularly called the goldilocks zone. The region around a star where the temperature is just right for liquid water to be able to survive on the surface, assuming the planet has a ‘surface’ as we know it, and its atmosphere is just right to sustain its presence. We can get some of this information by working out the bulk density of the planet.

The bulk density of exoplanets ranges from Styrofoam to solid lead. If we can measure the minimum mass of the planet through radial velocity, and the radius of the planet through its transit, we can calculate the bulk density of the planet. This allows us to draw some conclusions as to its likely composition; however, we are still just making educated guesses at this point as materials will act differently as you change the conditions. The Earth’s bulk density for instance is 5.5 g/cm³, somewhere between Iron and silicon, which would lead us to conclude that it is a rocky world.   

No exoplanet is exactly like another. Like our solar system there is a wonderful and surprising diversity of different worlds out there. From their radius, mass, and density; to what we have been able to detect in their atmospheres. We have even detected a planet losing some of its atmosphere due to extreme stellar activity**, and planets orbiting multiple stars***. The discovery of exoplanets has really tested each of our imaginations about what is possible. 

Multiple planet systems

Our solar system still holds the record for total number of planets. There are 130 multiple planet systems found so far. The largest have six planets; Kepler-11 (b,c,d,e,f,g), HD 10180 (c,d,e,f,g,h), HD 40307 (b,c,d,e,f,g). And these are just the planets we can detect, with only 20 years of practice and technology development behind us. Imagine what other worlds these systems might hold that we cannot yet see, or any other systems and stars for that matter. 

For your bonus 11^th fact.

Thor - Supreme commander of the Asgard fleet

Aliens are out there. More than just letting the statistics speak for itself, we have found some startling evidence on our own planet to suggest that life is not impossible but probable. New studies are popping up everywhere into astrobiology and the potential for life in the most extreme of environments.

The possibilities appear to be endless. 

 WHAT’S NEXT?

*Red star range in temperature between roughly 800-3500°C

**HD 189733b had a portion of its atmosphere blown off due to an x-ray stellar flare event that was monitored using ESA's XMM-Newton X-ray space telescope, while a transit of the planet was observed in the visual with NASA’s Hubble Space Telescope, showing a large atmospheric tail in the planets wake. (http://arxiv.org/abs/1206.6274)

*** Planet Hunters: Transiting circumbinary planet in a quadruple star system (http://arxiv.org/abs/1210.3612)

Also check out the exoplanet databases:

http://exoplanet.eu/catalog/

http://exoplanets.org/table

and the habitable exoplanet database,

http://phl.upr.edu/projects/habitable-exoplanets-catalog

There is also this gret interactive exoplanet catalog based on the XKCD comic (http://xkcd.com/1071/) where you can find out some things about the diffrent planets. - http://codementum.org/exoplanets/

All the kepler planets detected from astronomy-to-zoology

 

Why is the Sun yellow, the sky blue, and the clouds white?

The Sun, sky and clouds over Birling Gap on
Christmas day 2012

A few weeks ago my 4 year-old nephew asked his mother why the Sun was yellow. Of course this got passed on to me, and I found myself trying to explain the wave nature of light to a bemused toddler in a moving car while turned around in my seat.

To a 4 year-old color is very important, hey it’s still important twenty years later.

To understand why the Sun is yellow, the sky blue, and the clouds white we first need to understand how color works.

The different colors we see are the result of different wavelengths of light being filtered out before reaching our eyes. Red light has longer wavelengths, and blue light has shorter wavelengths. By combining all the wavelengths of light together, red, orange, yellow, green, blue and purple, you get white light.

NASA SDO AIA 304 solar image

Just like waves on the ocean, light will always travel in straight line; that is until something gets in its way. It then has three options,

        Reflected
       Refracted (or bent)

or

     Scattered

Each of these mechanisms can be seen as a result of the Earth getting in the way of the Suns light as it makes its way out across space, but as you will see it is predominantly the scattering of sunlight that produces the colors of the Sun, sky, and clouds as we see them.

If you were to look at the Sun from space without Earth’s pesky atmosphere in the way it would actually look white, shortly before your eyes are burnt out. Even solar astronomers are in denial though coloring the sun yellow or orange in a number of their space based observations. We humans are creatures of habit after all.

Astronaut Sunita Williams holding the white Sun in her hand
whilst on a spacewalk

As light enters our atmosphere it is interrupted on its journey by particles of gas. These particles are much smaller than the wavelength of the light that it is interrupting. This results in something called Rayleigh scattering. Rayleigh scattering resorts in the light being redirected on its path towards the surface and is strongly wavelength dependent. Meaning that the shorter the wavelength, or the more blue the light is, the more it is scattered, while the longer the wavelength, the more red the light is, the less it is scattered. Leaving the sky its beautiful blue color.

That beautiful blue sky is accompanied by a strange yellow orb so bright that you cannot look at it directly even under the protection of our atmosphere. The reason for its vibrant yellow color is directly related to the blueness of the sky. As the atmosphere scatters out the blue light the remaining spectrum of the sun is shifted towards the yellow part. As the Sun moves towards the horizon at sunset the light passes through more and more of the atmosphere. This means that more and more of the shorter wavelength light is scattered away making the Sun appear redder as it sets in the evening.

Setting Sun (image credit Monika Landy-Gyebnar)

If you live in the UK, like I do, you will most likely be disappointed by the amount of time that the bright sunshine and the beautiful blue sky is blocked by big white fluffy looking objects.

No not sheep, but clouds.

Clouds are drops or frozen crystals of water and other chemicals in the Earths atmosphere. These droplets or crystals scatter the light in all directions regardless of the wavelength making them appear white. Dark clouds are created when they pass into the shadow of another cloud, or when the top of that cloud casts a shadow on its own base. They also look darker in contrast to a brighter sky. So a dark cloud will not always mean rain. Though if you are in the UK it is the most likely result.

             

Rainbow over the
University of Exeter

Double rainbow over the
University of Exeter

Other than scattering and reflection, we can also observe the refraction in the atmosphere. As larger droplets of water bend sunlight a rainbow forms. They appear in the sky opposite the sun as the light is bent entering water droplets in the air and then reflected inside the back of the droplet. This refraction, like in a prism, causes the light to be split into different wavelengths and thus different colors; red, orange, yellow, green, blue, indigo, violet.  Reflecting the light multiple times inside the water droplet can create double rainbows, where the order of the colors are reversed.

Although our vision is restricted to just a tiny portion of the whole electromagnetic spectrum the wave nature of light puts on remarkable displays for all to see. So look up and enjoy the show because, hey, even on a cloudy day the light is dancing.

WHAT'S NEXT?

Here are just a few helpful websites and blogs that also answer these questions. 

http://sci.odu.edu/sci/Scire/05Edition/whitecloud.html

http://www.universetoday.com/18689/color-of-the-sun/

http://scienceblogs.com/startswithabang/2010/10/14/why-is-the-sun-yellow/

http://spaceplace.nasa.gov/blue-sky/ 

What I learnt from the EOS exoplanet Workshop

Anzere, Switzerland

Last week I spent some time in Anzere, Switzerland at a small collaboration workshop looking at Exoplanet Atmospheres. We discussed things from stellar variability, to transmission spectra, and model atmospheres.

Like all workshops/conferences/meetings there are some things that you really learn so I thought I would compile some of them for you here. I have also added some of the Pictures I took as it was a truly beautiful place.

• Sierre is close to Anzere as the crow flies, but we have no crow.

• The Swiss really like their cheese.

• Even if. Correct that. Especially if you have submitted a paper we can find new things to change/throw a spanner in the works.

  

  Before I badly hurt my knee

• Skiing is a dangerous sport, if you are me, but that won't stop you from trying.

• Our solutions aren't perfect, they are just better than yours. 

• Cheap Swiss Co-Op beer is okay to drink if it is three times cheaper than the good stuff.

• In Englishman, Irishman, Scotsman jokes, the French always loose.

• Even if it is beautiful outside the curtains will be closed so that science can happen. 

• The jokes stop when you find out the kids throwing the rocks are from your country.

And last but not least,

It is not personal, it's SCIENCE!

The view from the chalet in Anzere, Switzerland after a night of snow.

Geneva, Switzerland

Sion, Switzerland

The view from the chalet in Anzere, Switzerland on the last morning

NOTE: All of the photos were taken by myself and all observations are either paraphrased or my own.

Made from the stars

Stages in Star and planet Formation

From star-stuff, to stars to us. As the saying goes,

‘We are all made from star-stuff,’

 but how did we get that way?

The universe is a vast and sparsely populated place. Even within our galaxy things are spread out. The closest star to us is over four light years away with little else occupying the space in between. Yet that gap is not entirely empty the space between the stars, the interstellar medium, is filled with gas and dust at densities lower than the vacuums we can create on Earth. This gas and dust is mostly hydrogen and helium, some of which was left over from the big bang, but it also contains heavier elements like oxygen, carbon, and nitrogen, formed in ancient stars then spread out across space in the explosive event of their death.

This gas and dust can come together under its own gravity to for slightly denser regions called giant molecular clouds that can be seen throughout our galaxy. You can even see some of them in the night sky with the naked eye.

Orion's sword

Just below the Belt of Orion on the left is Orion’s sword, where the central region is the Orion nebula. This massive molecular cloud complex is the birthplace of stars and future planetary systems and yet it is a trillion times less dense than our own atmosphere and thinner than the wispiest clouds observed on the Earth.

These clouds are so cold, just 10 degrees above absolute zero, allowing the atoms to clump together into molecules. Winds and turbulence in the clouds can cause bigger clumps to form in knots. Due to the low temperatures the clumps can grow and grow, and as they acquire more mass they attract more and more clumps. This process can take around 10 million years eventually forming a clump so large that the pressures at the center heat it up forming a proto-star at the heart of the collapsing cloud. These regions are dense enough to block any optical light; millimeter and sub-millimeter observations have helped to reveal how this process occurs searching for the emission from the in-falling material that makes up the proto-star.

The proto-star begins gathering more dust and gas, spinning and collapsing further.  After a few million years of accretion the central mass becomes dense enough to ignite the core, fusing hydrogen into helium. Strong stellar winds erupt from the poles; blasting away the gas and dust of the surrounding cloud, halting the in fall of mass to the star.

The rings of Saturn form distinct bands of material

That stars fate is now sealed in the mass it managed to accumulate and is at the start of its journey along the main sequence. Surrounding the star is a disk of accreted matter that forms the proto-planetary disk. It is here that a stellar system can form and our journey from star-stuff to life can begin.

The gravity of the star pulls on the particles in the disk. As they make their journey in towards the star they hit each other and in some cases join together forming grains. Over several thousand years they grow in size and mass turning into pebbles and rocks orbiting in a plane around the central star. These clump into irregular objects forming bands around the star. Much like the structures seen in the rings orbiting Saturn.

It not until a series of violent mergers and collisions between these rocks, over millions of years, that large terrestrial worlds emerge capable of holding onto any gasses to form an atmosphere. The final fate of these strange new worlds will depend upon the temperature and type and quantity of material in the forming region.

In the last few decades our theory of planet formation has been taken down and shook up. With the discovery of extra-solar giant planets in places contrary to those in our own solar system we have been forced back to the drawing board. Determining how the surrounding environment during formation impacts the resultant system is a major topic in astrophysics with many groups of scientists scratching their heads and imagining anew.

So keep watching this space, reality always has a new way of surprising us.

WHAT’S NEXT?

There are some great links that I found very useful so I have included them here for you to explore.

Whispers from the cosmos -http://archive.ncsa.illinois.edu/Cyberia/Expo/bima_nav.html

National Radio Astronomy Observatory –

http://www.nrao.edu/

University of Exeter - Astrophysics group - star formation -

http://emps.exeter.ac.uk/physics-astronomy/research/astrophysics/research-interests/star-formation/

NASA astrophysics – Stars –

http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/

What to do when your PhD supervisor is gone?

Apart from submit a paper, start a new project, register for a conference, and sleep in until nine. The only thing left to do is play around on photoshop.

Thought I would just post up some I made up last night whilst the code on my new project is running.

Hug the Sun

Pale blue dot, on a moat of dust, suspended in a sunbeam

Fighter Pilot Snoopy taking on space

Mr Fredrickson goes Up on Tatooine

The Clanger living it large

Second star on the right and straight on to morning

Hey you found Nemo

Ninjas!

I hope you all have a good week.

Just keep asking. What's Next?