ESA Science & Technology - Leonids 2001 Observing Campaigns

Australia campaign

Copyright: 2001 Shigemi Numazawa, Japan Planetarium Laboratory; courtesy Sky & Telescope

In addition to their studies of the meteor shower, the team intends to test a new prototype of an instrument that is being developed for future planetary missions to Mars, Mercury and the Moon.

Over the next few weeks, their adventures and discoveries will be posted on the ESA science web site, so watch this space!

In the meantime, read about why they are going to Australia and what they intend to do there.

Why go to Australia?

"Although Mongolia and China are slightly more attractive when it comes to the best observing conditions for the predicted Leonid peaks, we have decided to go to the Australian desert," said ESA scientist Detlef Koschny.

"We took into account the cloud-free atmospheric conditions, the ease of access and the familiar language," he explained. "But our decision was also driven by the fact that we can combine our meteor campaign with a test programme for a prototype of a new scientific instrument."

Lake Eda

ESA's team of Australian adventurers is made up of four scientists. Detlef Koschny, Joe Zender and André Knöfel will be looking for Leonids, while Roland Trautner will be carrying out trials with a prototype instrument, called the Mutual Impedance probe, and measuring changes in the electric field of the atmosphere. The fifth member of the group, Olivier Witasse, will be supporting their efforts from the European Space Research and Technology Centre (ESTEC).

On arrival in Broome, 1500 km to the north of Perth, the team will collect their four-wheel drive camper cars for the expedition into the outback to their final destination - Lake Eda.

Shooting the Leonids

The campaign to observe the Leonid shower will take place between 15 and 19 November. In order to obtain stereo images of the Leonids, the team will set up two observation sites separated by 50 km.

At each location, the team will continually monitor the incoming Leonids with two image-intensified video cameras. A fifth, wide angle, video camera will obtain an 80 degree 'fish eye' view of the night sky.

"The primary objective of our campaign is to count the meteor trails and measure their brightness," said Koschny. "With the 'normal' cameras, we can record many more meteors than are visible to the naked eye."

"This will eventually enable us to calculate the changing numbers of meteors over the five-day observing period," he said. "We can then use this information to improve existing computer models of the many dust streams that are associated with Comet Tempel-Tuttle."

"We will also learn a lot about the size and type of material that is being incinerated by studying its speed and light curve - how each meteor trail brightens and dims as it burns up in the atmosphere," he said.

"The second video camera at each site will enable us to find out what the particles are made of," he added. "These cameras contain a grating that splits the light from the meteor trails into different colours. By analysing these colours, we can discover their chemical composition."

Electrifying Leonids

While his colleagues concentrate on visual observations of the Leonids, Roland Trautner will be attempting to record tiny changes in the electric field caused by the glowing meteor trails.

"We have a prototype of a sensitive electric field sensor that is very difficult to test in laboratory conditions," explained Trautner. "It is even difficult to use outdoors in the Netherlands because of background electrical 'noise'."

"So we decided to take it Australia, where we can test it without interference from other electrical sources and we can also take the opportunity to try an exciting experiment," he said.

"We hope to confirm or rule out the influence of meteor impacts on the electric field in our atmosphere," he explained. "We expect the brighter fireballs to ionise the atoms in the upper atmosphere. This should cause tiny fluctuations in the electric field. However, it is a very difficult measurement to make. If we succeed, it will be the first time this has ever been done."

Roland Trautner will be equally busy testing another instrument, the Mutual Impedance probe. Like the SESAME instrument on the Rosetta lander, the MI probe is designed to measure how easily electrical current flows through the ground. This is a particularly useful technique for detecting subsurface water or ice, and so has potential for future applications on the Moon, Mars or Mercury.

"During the daytime, I will be trying out a new instrument design and testing the capability of the probe to identify water in the subsoil," he said.

"It must be tested under conditions similar to those which can be found on many planetary bodies, so this region is a suitable place for these tests," said Trautner. "I am not sure when I will sleep!" he added.

Australia report

Figure 1: The team from left to right: Joe Zender, Detlef Koschny, André Knöfel, Roland Trautner.

From their remote encampment in the Australian outback, the four-man team from the European Space Research and Technology Centre in the Netherlands successfully observed many thousands of shooting stars while carrying out some groundbreaking trials of new scientific experiments.

Team leader Detlef Koschny and colleague Roland Trautner happily recounted their successful campaign to capture the Lion's offspring.

Question: Were you able to see the Leonids as you had hoped?

Koschny: We were rather nervous because the night of the predicted maximum was cloudy - the first cloudy night we had in Australia - but, fortunately, the clouds went away and we had three hours of beautiful Leonids. We saw the first Leonid fireballs through holes in the clouds - this led to quite spectacular views, since the clouds were black and basically invisible (an unknown experience to a European observer, where there are always lights to illuminate the clouds).

Figure 2: This striking image showing some Leonid meteors was taken on 19 November 2001 by Andrew Johnson in western Australia. (15 minute exposure using a super wide-angle lens).

Trautner: It was a great show - amazing! The most spectacular view for me was in the morning twilight (on 19 November), when the Sun was painting the sky a cobalt blue, the bright stars and the Milky Way were still visible, and there were brilliant fireballs coming in. It was the most beautiful moment of the whole night.

We were very lucky because we had good weather at the end. There had been cloud and smoke from bush fires earlier in the night. The bush fires last for weeks - the farmers just let them burn. We could see them getting closer until they were burning near the road we would have to use on our return journey. Fortunately, the fire was already extinguished when we made our way back to Broome.

Koschny: The weather was a worry to us. There had been thunderstorms around Perth, and we were told that the weather was also bad around Wolf Crater, so we decided to camp out at a dry lake nearer Broome. We made the right decision.

Question: It sounds as if your observations were successful.

Figure 3: André Knöfel and Roland Trautner preparing the spectrograph camera at nightfall.

Our visual observations were reported via satellite phone to Vladimir Krumov from the International Meteor Organisation, who kindly acted as the coordinator. We obtained about 200 hours of video data from five intensified video cameras. Two of the cameras were equipped with objective gratings, so we were able to successfully record meteor spectra showing both emission and absorption lines, and we can now start to analyse the chemistry of these meteors.

Figure 4: The electric field sensor.

Trautner: We suffered from high temperatures - above 40°C every day. This increased the electric current consumption of the MI probe electronics and blew the fuses. Another problem we encountered was the power supply for our equipment. Fortunately, we were able to recharge our batteries during the day using a solar panel and by linking up to our car batteries and generators. The solar array was very useful - it would have been a disaster if the car batteries had run dry!

After a number of MI probe test runs, the display on the laptop controlling the probe died, so that brought my tests to a sudden end. However, I had run sufficient tests before that to get plenty of useful data. It will be very valuable for assessing the performance of the new instrument architecture.

Question: You mentioned the threat from bad weather, heat and bush fires. Were there any other problems that you had to overcome?

Figure 5: Leonid 2001 observing campaign site in Australia.

We also had to keep a look out for lizards. Some of them were up to 1.5 metres long and they looked like small crocodiles! They were very shy, but if we saw any of these animals, we were very respectful! We also saw a lot of other animals - kangaroos, bush turkeys, emus, etc. There were plenty of insects too - sometimes they were a real plague.

Koschny: All in all, it was a fantastic experience. Especially sitting in the outback, with nighttime temperatures above 20 deg C, three hours away from civilisation, seeing the Magellanic Clouds and the Southern Cross, was something I will never forget.

Contact:

Dr. Detlef Koschny
ESTEC Noordwijk
The Netherlands
Tel: +31-71-565-4828
Email: detlef.koschnyesa.int

Radio observation campaign

From 14-18 November a team of ESA scientists will listen to the sound of Leonid meteors as they silently sweep across the night sky.

Instead of using cameras or simply observing with the naked eye, their aim is to repeat an experiment, first performed during last year's Leonids meteor shower, which uses digital signal processing to make audible the impact of the myriads of shooting stars as they hit the Earth's upper atmosphere.

During the nights of 14 - 18 November, as the annual Leonid meteor shower reaches its peak, the group from ESA's Research and Scientific Support Department at ESTEC in the Netherlands, will be glued to a radio receiver and their computer screens.

"The ionised meteor trails act like mirrors and reflect high frequency radio signals from stations that are below the horizon," explained ESA's Jean-Pierre Lebreton, "so we're going to listen to suitable signals from various radio stations around the world."

"The night time is much less effective in reflecting high frequency signals in the range above 10-20 MHz. The signals at those frequencies escape into space, so the high frequency radio stations are usually shut down after dark. However, meteor trails can also reflect high frequency radio signals for brief periods at night," explained Dr. Lebreton. This means that, at night, instead of no radio reception at all, the team can pick up brief transmissions every time they bounce off a meteor trail.

Figure 1: During the daytime, radio signals transmitted from Earth are reflected back by ionised layers of the atmosphere acting like mirrors. Ionised meteor trails also reflect radio signals, and since they are moving they produce a doppler-shifted signal, an echo. At night-time, the reflecting layers are fewer and less dense, so most of the high-frequency radio signals can escape into space. Echos are still produced by meteors intercepting the radio signals.

"For our experiment during night time, we have come to an arrangement with Merlin Communication, the service provider for the BBC, to continue their transmissions at 17.64 MHz," said Lebreton. "They will switch on one of their transmitters every night between 14 and 18 November. We will then use the short-lived meteor ionisation trails as mirrors to reflect the radio signals. In this way, we hope to be able to count the meteor echoes."

Not only will this technique enable the scientists to make an accurate count of meteors, but it will provide information on the winds in the upper atmosphere.

"Because upper atmospheric winds move the `mirror' a little bit, it induces a very small Doppler shift in the signal we receive," explained Lebreton. "These minute changes in the signal frequency allow us to separate the reflection from the meteor and the main signal. The fixed frequency of the high frequency carrier wave and the small changes caused by the reflection will be automatically recorded as dynamic spectrograms - in other words we will have a visual record of the audio signals."

Figure 2: Meteor activity is hard to miss! In these images the central horizontal line is the carrier radio frequency. 'Blips' on the graph represent the echos which are caused by reflections of radio signals by the meteor clouds. From left to right: low meteor activity during the daytime, high meteor activity during the daytime, and high meteor activity at night.

This recording of the 2000 Leonids shower was made by Jean-Pierre Lebreton and his colleagues.

"Anyone tuning in their radio to the BBC frequency can try this experiment for themselves," said Lebreton. "It should be possible to pick up the echoes - each lasting a few seconds - from all over Europe. This is the best way to learn about meteor showers - it works day and night, and in all weathers. It should be possible to listen to the radio broadcast and hear echoes that will last for more than a few seconds. During the peak activity on 18 November, we may even be able to listen continuously to the radio programme!"

"We will analyse the signals in real time, and also record them on digital audio tape so that we can analyse them later," said Lebreton. "Last year we were also able to record the sound of the Leonids shower."

So why are they going to all this trouble?

"We're hoping to complement the optical observations that are planned by some of our colleagues," said Lebreton. "And we wanted to do something that would be of interest to the public. One of the advantages of radio observing is that meteors can be detected when skies are cloudy or during daylight. Radio observing has some advantages at night, too. The human eye can only see shooting stars brighter than 6th magnitude, but radio methods can detect meteors that are at least 5 times dimmer."

"There are also some other scientific applications of this technique, but for the moment we are concentrating on fine-tuning our technique," Lebreton concluded.

Other scientists from ESA's Research and Scientific Support Department who will be involved in this radio campaign are: Trevor Sanderson, Udo Telljohann, Olivier Witasse and Andrea Toni.

How to tune in to the shooting stars

The experiment

The Doppler method can be tried by anyone with a good shortwave receiver and a PC. Suitable software and a description of the method can be downloaded from the related link to "Instructions for Doppler experiment" at the Portugese Centro de Observação Astronómica no Algarve. The software uses the sound card of the PC to analyse the signal. All that is needed is a connection from the headphone output of the receiver to the PC's sound card input. Download the software, install, read the help file and you are ready to go. Tune to a station around 500 km or so away. Switch to SSB mode, and start the software. All you need now are the Meteors!

A simpler experiment

For this you use your FM receiver with an external aerial. Try to find a station a long way away (that's the difficult bit, as usually a nearby station gets in the way). Under normal circumstances the transmission should be difficult or impossible to detect, but when a meteor intervenes the signal jumps over the horizon and a brief fragment of the transmission can be heard. Depending on the type of transmission, it might sound like a tone, a fragment of music or voice, or simply noise. Contact lasts for as long as the meteor train persists, usually from 100 milliseconds to a few seconds.

Carribean report

Every year the Earth ploughs through the trail of tiny dust particles left in space by Comet Temple-Tuttle. These dusty motes collide with the Earth's atmosphere where they meet a fiery fate - to burn up as meteors in the upper layers.

This year the best places to observe the Leonids shower were either from North and Central America or East Asia and Australia. A team of ESA scientists travelled to the Australian outback to carry out scientific observations during what was predicted to be a spectacular meteor storm. In the meantime, our correspondant Stuart Clark was on a cruise liner in the Caribbean watching as the storm began in the early hours of Sunday morning, 18th November.

Leonid meteor crossing the sky

By 1 a.m. the show was well underway with a bright meteor bursting across the sky every five to ten minutes. At first the meteors were slow moving, burning a deep orange and leaving ephemeral green trails that were swiftly lost to the wind. As Leo ascended into the sky, however, the rate of meteors increased, as did the speed with which they burnt up. Gradually, subsequent meteors were whiter and whiter until at 2.45 a.m the first fireball exploded in front of the ship with a searing bright glow.

Over the course of the next two hours, a further half dozen of these tremendously bright meteors were seen. One exploded behind those gathered on deck, casting shadows like the flashgun on a camera. Whirling around, observers could see the vapour trail hanging in the sky to show where the meteor had passed.

Around 3.30 a.m. the frequency of faint meteors rose precipitously and for brief periods of time one meteor every few seconds shot across the sky. The peaks and lulls in activity could be seen until sunrise, when the display continued on across Central America and on to the Pacific.