We've been to Pluto! The New Horizons mission flew past Pluto this week. On the way it made scans, took photos, and ran several different experiments. As New Horizons is 5.3 billion kilometres away, getting the data back home is no easy task.
Receiving the data is NASA's Deep Space Network, made of three communications sites around the world. The first site to receive these images was the Canberra Deep Space Communication Complex, operated by CSIRO. Each site has several dishes to receive signals and send instructions.
"When we're sending commands to the spacecraft, we shout," says Glen Nagle from the Canberra Deep Space Communication Complex. "New Horizons replies with a whisper. Its transmitter runs at about 20 watts of power, about half the power it takes to light the bulb in a fridge."
That whisper has a long way to go, and as the signal travels it spreads out and gets thinner. By the time we hear it back on Earth, it is amazingly quiet – about 0.000 000 000 000 000 000 04 watts.
When listening for something that quiet, it helps to look in the right direction. Scientists do plenty of calculations to work out exactly where to point the dish. "It takes four and a half hours for a signal to get back to Earth," says Glen. "So when we're pointing our antennas, we have to calculate not where New Horizons is, but where it was."
The universe is a noisy place, and even with a big dish it can be hard to hear. It takes some clever algorithms to filter out the noise from distant galaxies and remove interference closer to home. The signals themselves are specially designed so small errors can be picked up and corrected without asking the spaceship to resend the message.
New Horizons is sending us superb pictures of Pluto from far away, and there's a lot of maths making sure we can receive the messages, loud and clear.
New close-up images of Pluto's surface reveal mountains 3500 metres high. Image: NASA/JHU APL/SwRI
Science essay competition
What's the most amazing experiment you've ever seen or done? Have you ever levitated an orb or turned milk into plastic? The UNSW Bragg Student Prize is now open. Students in years 7–10 are invited to submit an essay of up to 800 words on the topic of mind-blowing experiments.
The winner will receive $500 and have their essay published inDouble Helixmagazine, plus be invited to the book launch ofThe Best Australian Science Writing 2015in Sydney. Two runners-up will receive a voucher worth $250.
Place the cups at a distance to each other so that each cup looks half the height of the previous cup.Measure the distance from the tape line to each cup.
You will need
5 white disposable cups
Marker
Ruler
Masking tape
Tape measure
A long corridor or large room
A partner to help
What to do
Measure the height of a cup.
Draw a thick line halfway up each cup.
Stick a strip of masking tape to the floor at one end of the corridor or room.
Measure 30 cm from the masking tape and place a cup.
Lie down on the floor and put your chin on the masking tape line.
Ask your partner to put a second cup on the ground about 60 cm away. Get them to move the cup back or forward until the second cup looks half the height of the first cup.
Take a third cup, and ask your partner to place it even further back so that it looks half the height of the second cup.
Keep putting out cups in this way until you run out of cups or reach the end of the corridor.
Measure the distance from the tape line to each cup. Can you find a pattern in your results?
What's happening?
Far away things look smaller than close things, but not everyone knows exactly how much smaller they look. In this activity, each cup looks half the height of the previous one when it is twice as far away.
The maths of distance and perspective were developed in the fifteenth century. It influenced art, and paintings became more realistic.
Radio signals experience a similar effect. As a spaceship goes further away, the signals it sends become weaker. When the distance doubles, the signal strength drops to one quarter. If the distance triples, the signal drops to one ninth.
"A good mathematical joke is better, and better mathematics, than a dozen mediocre papers." – J E Littlewood
Brainteaser answer
Half the ice melts every hour. So for every hour early she is, the amount of ice left doubles. If she were one hour early she would have 2 kilograms of ice. If she got home two hours earlier, she would have 4 kilograms of ice left.
