Searching for Other Worlds

Here at science made simple we are keen to inspire not only the next generation of scientists but also the next generation of science communicators. Supporting work experience students each year is an important part of what we do.  Our work experience students get a chance to see a range of the activities that science made simple is involved with and we always set them challenge to produce some science communication themselves, whether designing a demo, delivering a short presentation or, in this case, writing a blogpost that includes all of these!

We hope you enjoy this from one of our latest work experience students, Alexandra Wagstaff, we loved having her in the office and think she’s got a promising career ahead of her.

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by Alex Wagstaff

“For every one, as I think, must see that astronomy compels the soul to look upwards and leads us from this world to another.”
~Glaucon, in Plato’s The Republic

Carina Nebula

Carina Nebula
NASA, ESA and the Hubble SM4 ERO Team CC-BY

In all of us exists a certain curious urge, compelling us to look up and out, to experience our universe and unravel its many mysteries. Astronomy has been practiced ever since humans have been able to look up at the night sky and wonder, ‘What’s out there?’ Ancient astrologists and priests believed stars had spiritual powers, star maps were used for keeping time, making calendars and even predicting the future. It is clear that we humans have always been drawn to the sky.

Today this is the job of the planet hunter. Throughout this post we will explore how humanity’s eyes were widened by the discovery of planets in our own solar system, how astronomers of today are hunting for planets of star systems light-years away and how you can get involved in the search yourself.

The Solar System- a Brief History

Today there are eight official planets orbiting our sun. Only two of these, Uranus and Neptune, had an official ‘discovery’ as the other six: Mercury, Venus, Mars, Jupiter, Saturn and of course, Earth, are visible from Earth by the naked eye- so have been observed by people since they first gazed up at the night sky. Venus and Neptune, the furthest planets from the sun require good telescopes and precise astronomy to be seen.

Uranus (the seventh planet from the sun) was discovered by one of the most famous astronomers in history, Sir William Herschel. On March 13th 1781, Herschel pointed his telescope into the sky in search of binary stars (a pair of stars which orbit each other creating a ‘double star’ solar system). He spotted a tiny grey spot, and thinking little of it, was amazed when he realised he had just discovered the furthest know planet in the solar system at the time!  In 2009 a space telescope was launched by ESA called Herschel, in recognition of the work of William Herschel and his sister, Caroline Herschel.

Neptune (the eighth planet from the sun) was discovered by an English astronomer and Mathematician, John Couch Adams in 1846. For years astronomers had noticed Uranus had a strange orbital path so predicted the possibility of a planet beyond disturbing its orbit with its gravitational pull- it was Adams who pin-pointed its location using complex mathematics.

What makes a planet?

The definition of a planet was only agreed on in 2006 by the International Astronomical Union and states that planets must fit into these three criteria:

1. It must orbit the sun

2. It must be big enough for gravity to squash it into a round ball

3. It must have cleared other objects out of its orbital neighbourhood by pulling them into orbit, down to its surface or slingshot them out into deep space.

Solar system

Author: WP  CC-BY  (Sizes to scale; distances and illumination not to scale)

 

This meant that poor Pluto, discovered in 1930, which was considered a planet for 76 years has now been downgraded to a dwarf planet. Pluto is so tiny that some scientists argue that if it were to remain a planet, then the other 43 Kuiper Belt Objects orbiting the sun should also be called planets!

 

Finding Exoplanets

Exoplanets are planets that orbit stars outside of our solar system. The closest known exoplanet orbits the star system Alpha Centauri, about five light-years away. Exoplanets are somewhat harder to find than planets in our own solar system, as you can imagine, but there are some clever and unexpected ways astronomers now search for planets. Here are a few:

Astrometry and Radial Velocity, a.k.a. ‘The Wobble’:

These methods detect planets by observing the ‘wobble’ of a star, caused by the gravitational pull of large objects in its orbit. A series of images are taken of the star, these images are then carefully analysed and compared in a search for any unexpected changes in a stars movement. Astrometry is concerned only with the visible wobble and requires extremely sensitive instruments. This is the oldest method of searching for exoplanets and to this day hasn’t found a single one, but plans for this method to be used on future space crafts provides Astrometry with a hopeful future!

Doppler signature

Diagram by Hilary Wagstaff- All Rights Reserved (By Permission).

Radial Velocity uses a similar idea in a more accurate way- the wobble caused by an orbiting planet can be detected by analysing the star’s changing colour/Doppler signature. When viewed from certain angles, an orbited star can move towards and away from the viewer, causing the Doppler Effect. When a light sources are moving towards a viewer, light waves are compressed, their wavelengths become shorter and the light becomes blue shifted, when the light source moves away, light waves become stretched out, their wavelengths become longer and red shifted. These slight changes can be detected by highly sensitive spectrographs.

Alex explains the radial velocity method:

This method is by far the most effective technique for planet hunters and is constantly detecting new planets all over the place! The main disadvantages of this technique are that it cannot predict the mass of a planet and cannot detect planets with orbits at all angles to us. If the planet orbits the star parallel to the viewer’s view point, little or no Doppler Effect will occur and the planet is invisible. (See diagram above)

Transit Photometry, a.k.a. ‘The Blink’:

Transit Photometry

Diagram by Hilary Wagstaff- All Rights Reserved (By Permission)

This is a very effective method which finds planets by detecting minute dimming of stars. As planets pass in front of their star, it blocks out some of the light reaching us, this causes a dimming and the degree of dimming can be used to accurately estimate the size of the planet. This technique is very good at finding possibly habitable, Earth sized planets. 

 

 

Gravitational Microlensing, a.k.a. ‘The Blip’:

This technique relies on the chance event that a star passes between the viewer and a distant star. Massive objects in space, like stars, actually bend space-time; this is called the Theory of Relativity dreamt up by Einstein himself. When as the star passes between the viewer and the distant star, it bends the space-time around itself, warping the image of the star we see.

Microlensing image 3

Photography by Alexandra Wagstaff- All Rights Reserved (by Permission)
The centre of the block represents the star mass.

 

This effect can be demonstrated using a piece of transparent material (e.g. perspex or glass) in a shape similar to the base of a wine glass.

 

 

 

 

 

Photography by Alexandra Wagstaff All Rights Reserved (By Permission) Diagram Representing Deep Space

 

Microlensing image 4

Photography by Alexandra Wagstaff- All Rights Reserved (by Permission)

In these images, the Perspex block (representing the travelling star) travels past the images of the stars on the paper, it warps the round shape into a smooth sausage-like shape and eventually into a larger circle.

 

Microlensing image 8

Photography by Alexandra Wagstaff- All Rights Reserved (by Permission)

The flat centre of the perspex represents the star mass warping space-time.

In the first image you can see that the

distant star begins to warp into a smooth sausage shape.

 

The second image represents the situation where the travelling star (the centre of the perspex) and the distant star (the white dot) are perfectly aligned and the star is warped into a large circle surrounding the travelling star.

If a slight ‘blip’ or irregularity is detected, a planet is detected.

 

 

Direct Imaging a.k.a. ‘Pretty Pictures’:

Taking a picture of exoplanets light-years away is extremely difficult if not impossible- orbiting exoplanets will normally be lost in the glare of its star.

Exoplanet 1

Author: ESO CC-BY
An image of the brown dwarf star 2M1207 and the blue Jupiter-like ‘planet’.

In July 2014, a star system of 200 light years away was pictured by the ‘Very LargeTelescope/(VLT)’. An object five times the mass of Jupiter was found orbiting a brown dwarf star named 2M1207. It has been argued that this image is the very first of an exoplanet but many astronomers do not consider it to be a ‘proper planet’ due to its formation, it may be considered to be a failed beginning of a star.

Being able to capture an image of an exoplanet is extremely rare, but there is something truly magical about being able to see a snapshot of a far away world, after all, seeing is believing.

 

 

What is a light-year?

A light-year is a unit of distance used in astronomy. One light-year is the distance which light can travel through space over one whole year- this is equal to just under 10 trillion kilometres.

So when we look up into the stars, we are really looking into the past. The light reaching us is hundreds, thousand even millions of years old and some stars we see are long dead.

Agent Exoplanet: Get involved

If you are interested in this field of work and would like to take your interest further, Why not help with investigating exoplanets yourself? ‘Agent Exoplanet’ set up by Astronomers at Las Cumbres Observatory is a unique opportunity to get involved, follow the link to find out more http://lcogt.net/agentexoplanet/

Possible Monster Planets beyond Pluto

With all this complex technology and constant discoveries of exoplanets thousands of light years away, you’d think we know all about the planets orbiting around our own sun, wouldn’t you? Well perhaps not! A recent discovery has been made of two possible giant planets orbiting beyond our own former-planet Pluto! But how could objects so massive sharing our own solar system cruise by unnoticed?  Well the only answer, really, is that nobody was looking for it. Space telescopes such as NASA’s Kepler Space Telescope wouldn’t have a chance finding a planet so close by. You can read more on this revelation here http://www.newscientist.com/article/dn25711-two-giant-planets-may-cruise-unseen-beyond-pluto.html#.U6P6e-DfCZZ

The Universe is Massive

If you still can’t wrap your head around how little we have explored the universe then read on…

The image below is an ‘eXtreme Deep Field’ assembly of 10 years worth of photographs taken by the NASA Hubble Space Telescope. Astronomers decided to point the telescope into a dark patch of sky with seemingly nothing in it and take the series of photographs to allow maximum exposure. They were amazed at what they found, each one of these dots are whole galaxies.

Galaxies


Author: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team-  Public Domain.

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