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Full details for Task Sheet P1b-2
Beagle 2 and the electromagnetic spectrum
What to do next
Radio waves carrying information from Beagle 2 will travel about 60 million kilometres from Mars to Earth.
Radio waves travel at the speed of light.
Q Calculate how long it will take for radio waves from Beagle 2 to reach a receiver on Earth, using the equation
Speed = distance ¸ time.
(Speed of light = 300 000 000m/s or 3 x 108m/s)
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There are additional factors, which increase the time between transmission and reception of the signal to as much as 4 days. For example, the signal must be sent from Beagle to orbiter, and then from orbiter to Earth. The orbiter may be on the other side of Mars to Earth and to Beagle and unable to receive signals from Beagle or transmit them to Earth, so there is a delay in receiving the signal from the Martian surface. Also, the distance from Mars to Earth varies up to a maximum of 398 million km when the planets are their maximum distance apart, although this delay is always of the order of minutes or tens of minutes.
You cannot control the instruments on Beagle 2, as they gather samples and test them in “real time”. It is not like driving a model aeroplane by remote control, where you press the controls, and the plane responds immediately. Instead, a stereoscopic camera takes pictures of the view from Beagle 2 and sends them back to Earth. Scientists can then see where to direct the corer/grinder, or where to let the mole burrow, for example. Then the instruments will be operated using pre-programmed sequences of command, which will be transmitted from Earth to the lander.
So what is Beagle 2 like? In shape, it is a squashed cylinder, being only 0.95m in diameter. It has 5 foldout solar panels, which can open out and power the instruments –see “photo album” on Beagle 2 website. The PAW (Position Adjustable Workbench) is mounted on the end of a robotic arm, so can be positioned close to the surface of Mars.
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The first four of these instruments detect electromagnetic radiation – signals from the objects around them. These signals, like radio waves, travel at the speed of light. The next part of the worksheet looks at what this means.
Look at a textbook/internet to find out what types of radiation are part of the family of waves we call the electromagnetic spectrum.
Members of the same biological family will resemble one another, but will not usually be identical. For example, they may share the same hair colour or nose shape – the same “characteristics”. These types of radiation are part of the same family, so similarities occur.
Q For example, using the textbook, can you name:
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QWhat characteristics do all these types of radiation share? Each of the four hints should help you to find one characteristic. Here’s one to start with:
They are all waves
Hints:
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You can sometimes see Mars in the sky; it looks like a reddish star, but is of course a planet. Where does its red light come from? (Why does it appear red?)
QApproximately what wavelength is this in m? Use the textbook to help you.
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There may be a scale marked on the diagram of the electromagnetic spectrum, showing the wavelengths. You will notice that the wavelengths gradually increase across the chart.
QWrite down the smallest and largest wavelengths in the electromagnetic spectrum and what type of radiation they are.
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Value in metres |
Type of radiation |
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Smallest wavelength |
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Largest wavelength |
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3. How instruments on Beagle 2 use the electromagnetic spectrum
The instruments on Beagle 2 will make many parts of the electromagnetic spectrum work for us, providing us with vital information about Mars. In whatfollows, some of the instruments mentioned are on the PAW and some are amongst a suite of 7 instruments in the main body of the lander. The next section is about which instrument works in which region.
3(a) Instruments on the PAW
Here, the stereo camera, microscope and x-ray spectrometer are considered.
Stereo camera
When you get photographs printed, you sometimes find that the same scene will appear very different when using a flash camera, compared to without. So that we can gain a reliable idea of what the surface of Mars looks like, the camera will look first at a small picture specially produced by Damien Hirst illuminated using white LEDs.It contains spots, each of a particular colour. Scientists know exactly how this picture appears to the camera on Earth and have “calibrated” the camera. They can compare the response of the camera on Mars to that on Earth (that is, how strong the electrical signal produced in each of the light sensors in the camera is); they can then adjust the Mars picture, which they receive to be the same as the Earth picture. Then they will know that they are seeing the Martian surface as it really is.
QWhat colours of light are “contained” within white light?
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The wavelength, frequency and speed of any wave are related using the equation: speed = frequency x wavelength.
QRearrange the equation to see how to calculate frequency and wavelength or use a triangle, if that is easier.
Frequency = _________________________________________
Wavelength = _________________________________________
Use of filters by camera
Check your knowledge of what a filter does.
A filter will block or “absorb” certain wavelengths.
It will let through or “transmit” certain others.
Choose the right answer:
QFor example, a red filter will (absorb / transmit) red light.
QA red filter will (absorb / transmit) green light.
Stereo camera (continued)
The diagram below shows what happens to the white light from the LEDs after it meets a spot on the picture.
2 3 1
1: White light falls on the spots 2. Light of the colour of the spot is reflected 3. Light of the colour of the filter is transmitted
The colour views from each filter can then be combined, to reconstitute a picture of the surroundings of Beagle 2.
QUse the equation to fill in the spaces in the table below. You are calculating information about the wavelength and frequency of the filters used to view the picture.
R1 is a filter used over right hand lens, whereas L1 is a filter used over the left hand lens. 1nm = 1 x 10-9m. Speed of light = 3 x 108 m/s.
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Wavelength (nm) |
Frequency (Hz) |
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L2 (Blue filter |
440 |
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L3 (Green filter) |
530 |
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L4 (reddish) |
750 |
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R6 |
1000 |
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R12 |
670 |
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QWhat part of the e.m. spectrum does L10 let through? ________________
QWhich filter transmits the shortest wavelength? ________________
QWhich filter transmits the longest wavelength? ________________
Microscope
This has sufficient magnification to pick out features as small as 0.004mm across in surfaces which have been exposed by the grinder. This is small enough to observe details which could be bacteria, so can help in the search for life.
This time, instead of white light, coloured diodes are used to illuminate the sample.
The frequencies of the light-emitting diodes used are approximately 7.5 X 1014 Hz, 5.5 X 1014 Hz and 4.3 X 1014 Hz.
Speed of light = 3 x 108 m/s.
QWhat wavelengths are being used?__________________________________
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You may have seen what happens when (invisible) UV light shines on peoples’ clothes. The clothes “fluoresce”, or shine brightly, particularly white clothes. A UV LED will be shone on the rocks, and the microscope used to see whether they fluoresce. A fluorescent material absorbs radiation at one wavelength and gives it out at a longer wavelength, in this case visible light.
A common fluorescent material on Earth is chlorophyll, so if a rock fluoresces, it could indicate life forms or at least compounds containing carbon.
Choose the right answer:
QUV is (shorter / longer) in wavelength than visible light.
X-ray spectrometer
This device contains two sources of x-rays. When the x-rays emitted hit the Martian rock, the atoms in the rock surface will absorb them, then re-emit new x-rays of different wavelengths (ask your teacher if you want this explained.
The particular x-rays emitted are characteristic of the atoms present; every type of atom has its own x-ray “signature”, which can be used to identify it.
The device has a window on the front made of Beryllium. The highest wavelength of x-rays, which this window lets through in sufficient quantity to be able to measure, is 1.24nm. (1nm = 1 x 10-9m).
QWhat is the corresponding frequency? Speed of light = 3 x 108 m/s.
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This device is also calibrated using the Damien Hirst picture. The minerals used in the paints have been carefully selected, hence their “signature” is known.
3 (b) Devices on the main body of the lander
These include a UV detector, the solar panels unfurled around it and a radio transmitter and receiver.
QIn addition to visible light, the Sun gives out UV light. Much of this is stopped by the ozone in the Earth’s atmosphere, which therefore protects us from – what?
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UV has the effect of sterilising surfaces on which it falls – you may notice that shops selling food often use a UV light. If it is present on Mars in large quantities, life on the surface is less likely. This is particularly true of short wave UV (wavelength 200-280nm), which is extremely damaging to biological organisms.
Beagle 2 has UV sensors in the body of the lander, which will enable us to draw conclusions about the Martian atmosphere. The thin CO2 atmosphere there does not have a global ozone layer as on Earth.
The detectors will detect over a range of 200 - 400nm. (1nm = 1 x 10-9m).
QWhat frequency range is this?
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The solar panels which power Beagle 2 absorb wavelengths in the range 300nm - 1100nm.
QWhat parts of the electromagnetic spectrum are involved here?
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QThis is then converted into ________________________ energy, which is used to
power the instruments. About 75W should be produced, about the same as in a mains electric light bulb.
4. Carrying the signal back to Earth: radio transmitter
All these e.m. radiation signals, which carry important information about Mars, are coded into digital signals, and added to the carrier wave. When the signal reaches Earth, the information can be extracted, by subtracting the carrier wave, and decoding the digital signal.
Different frequencies are used to beam the signal up from Beagle2 to the orbiter, and from the orbiter to Earth. QCalculate the wavelengths used and include them in the table below.
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Frequency |
Wavelength (m) |
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From Beagle to orbiter |
402MHz |
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From orbiter to Earth |
7.1GHz |
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You need to know that:
1MHz = 1 000 000Hz
1GHz = 1 000 000 000Hz.
Speed of light = 3 x 108 m/s.
You may know that the band Blur have recorded a ‘call sign’, which will be transmitted back to Earth, as soon as Beagle 2 has successfully landed. This is a simple sequence of notes.
QCould a creature with an ear similar to our own hear the Blur call sign on Mars? Explain.
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Scientists will hear it at the Beagle mission control centre. The call sign will have been used to modify an e.m. radio signal and then decoded at the far end. Here, electrical energy is transferred to sound energy.
Further work
The Mars express orbiter has other instruments, which will look at the surface of Mars from a height. The height of its orbit will vary a lot, as it is very elliptical.
The orbiter carries instruments for:
QSee if you can discover the wavelengths of electromagnetic radiation, which they detect. Don’t worry too much about how they work!
Useful websites:
Official Beagle 2 website: www.beagle2.com
ESA website: www.sci.esa.int/marsexpress
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31033&fbodylongid=663 gives a useful description of the PAW
www.spectrum.ieee.org/WEBONLY/publicfeature/may03/mars.html gives a useful overview of what is on Beagle 2.
http://www.src.le.ac.uk/projects/beagle2/xrs/science.html gives an example of the sort of trace we might get from the x-ray spectrometer on the PAW on Mars.
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