Asteroid named after ESA astronomer, as a reward for his discoveries
16 February 1999
If you want an asteroid named after you, make a valuable scientific contribution to the study of these rocky mini-planets of the Solar System. That is what 32 year old ESA astronomer Thomas Müller did, and now the International Astronomical Union has rewarded him by giving the name 'Thomasmüller' to asteroid number 8793."It's been a great surprise", Müller said. He is part of the team working at ESA's Infrared Space Observatory (ISO) Data Centre at Villafranca, Spain, and his research is mostly based on ISO data.
Müller's scientific work has proved to be crucial in describing the physical properties of an asteroid. But that is not all: it will improve the performance of the next millennium's infrared space telescopes, since these instruments will be able to check the accuracy of their observations by using the new data on asteroids. Müller has therefore shown that asteroids can be very useful tools for astronomy.
"Many astronomers tend to look at asteroids as boring objects. I've always disagreed. Take the infrared sky: if our eyes were able to see in the infrared, and of course if we could get rid of the Earth's atmosphere which is opaque to most infrared radiation, we would see hundreds of asteroids sparkling and very few stars. I love this idea", he says.
Thomas got his reward for his dedication on 10 December, when his collaborator Johan Lagerros, of the Astronomiska Observatoriet in Uppsala, Sweden, surprised him with the news about Thomasmüller. "I didn't expect it, I didn't even know I had been proposed!", the ESA astronomer exclaimed.
The proposal to the International Astronomical Union (IAU) came from astronomer Claes-Ingvar Lagerkvist, also at the Astronomiska Observatoriet, who is entitled to name the 47 asteroids he has discovered throughout his life. Asteroid 8793 was one of them. The name Thomasmüller was immediately accepted by the IAU.
There are at present almost 10 000 asteroids with a known orbit, of which a few hundred are named after a living astronomer. The orbit is the minimum every discoverer needs to know to get an object catalogued, and often it is all that is known about an asteroid. That is the case with Thomasmüller.
"It puzzles me the fact that we know nothing about Thomasmüller but its orbit and luminosity, although it was discovered in 1979 and it has been observed 43 more times", Müller confessed.
A hard task
It has been precisely this scarce knowledge on asteroids that has added value to the work of Müller and Lagerros. They have developed a very accurate model to predict the brightness of asteroids at any given time, a type of data that will be useful in the calibration of future infrared space telescopes such as ESA's Herschel mission(scheduled for launch in 2007).
Predicting the brightness of an asteroid is a very hard task. Asteroid sizes range from a few to one thousand kilometres. They have very irregular shapes and spin quickly, approximately once every five to ten hours. Their infrared brightness is caused by heating due to sunlight, and this heating strongly depends on the surface material and the surface structures, like craters, and the irregular shape. So, to know the infrared brightness of an asteroid at any given time, one has to find out which face it is showing to the Sun and to the observer, as well as its internal thermal behaviour and its distance to the Earth.
The researchers set up a large database with 650 individual observations, including those from the spectrophotometer ISOPHOT on board ISO, of the top-ten main asteroids. They were then able to model the egg-like shape of the ten asteroids, and to predict exactly how much energy they would be emitting at any given time. They could then derive the brightness with a very high accuracy.
The model has been tested against ISO observations. As Müller explains, "We compared hundreds of observations and predictions one by one, and all test cases confirmed the quality of our model. We can now predict flux densities from mid infrared to submillimetre wavelengths for all ten asteroids, including thermal and lightcurve effects."
A further application of this work is that it is now possible to infer diameters and albedos (the ability to reflect light) for all asteroids observed by the infrared with unprecedented accuracy.
The model applications are not only limited to ISO observations: all infrared measurements from ground, airborne or space telescopes can now be used to improve our knowledge about asteroids.
The description of the model and the technique has been published in the scientific journal Astronomy and Astrophysics:
MÜLLER, T. G. and LAGERROS, J. S. V. "Asteroids as far-infrared photometric standards for ISOPHOT" Astronomy & Astrophysics, Vol 338, p340-352, 1998
