FLUG REVUE June 2002: Pluto probe planned

NEW PLANS FOR PROBES TO MERCURY AND PLUTO

By Matthias Gründer

Technical and funding problems have prevented scientists from approaching the hottest and most distant planets of our solar system up to now. But finally the time has come to allay our human curiosity.

"Division of labour” is the catchphrase. International research teams at NASA and ESA are planning to fathom some of the last remaining secrets of the planets. NASA has its sights set on Pluto, ESA on Mercury. Much more is known about the planets that are closest to the Sun than about those furthest away.

The ancient Sumerians knew about Mercury in 3000 BC or so, while the Greeks had two names for it, Apollo for the morning star and Hermes for the evening star. In the 19th century astronomers discovered its eccentric orbit around the Sun, fluctuating between 46 and 70 million kilometres away from it. It was even suspected for some time that the fluctuations were due to the influence of another planet, to which the hypothetical name of Vulcan was given.

In 1974 NASA caused a sensation when its spacecraft Mariner 10 passed Venus and made the first fly-by of Mercury, which it flew past three times. The photographs transmitted to Earth were of astonishing quality, and the planetologists suddenly had their hands full thinking of names for the thousands of craters and indentations.

Pluto probe

For almost 30 years since then, the planet has only been observed from Earth, but the European Space Agency (ESA) set itself the demanding scientific goal of sending a spacecraft to Mercury as part of its "Horizon 2000” programme. After all, the Mariner photographs covered only 45% of the planet's surface, and scientists also want to find out more about Mercury's magnetic field, possible atmosphere and the composition of the rock material.

The space probe was named Bepi Colombo after the Italian Professor who originally calculated the rendezvous trajectories, without which it would not have been possible for Mariner 10 to get a look at Mercury. The craft is fitted with a small orbiter which will investigate the magnetic field on a separate orbit, and a landing platform that will touch down at the boundary between day and night and reconnoitre the local conditions on the planet. Other equipment to be carried will include cameras, magnetometers and spectrometers.

Meanwhile, scientists at NASA have their sights set on Pluto, the planet that was long suspected and initially referred to as Planet X but was not discovered until 1930 by Clyde W. Tombaugh, and which orbits at the outer limits of our solar system. It was only in 1978 that Pluto's moon Charon was discovered, since when little further information has been gleaned about the pair.

The masses and radii of the two celestial bodies, which are assumed to be made up of water ice, frozen nitrogen and carbon acid ice, have been roughly determined. But that is about all. The planet Pluto, which is smaller than our moon, simply defies all attempts at observation. Even the huge power of the Hubble telescope is unable to pick up more than opaque blotches due to the low level of sunlight reflected by the planet.

The question of whether Pluto should actually be viewed as a planet at all, as opposed to merely being a member of the group of small planets within the huge class of asteroids, was long the subject of hot dispute within the scientific community. In February 1999 the International Astronomical Union was forced to settle one of the disputes that keep flaring up and confirmed yet again, once and for all that Pluto really is a planet.

The rationale was that it has a body shaped by gravitation, an atmosphere and a moon, characteristics that do not apply to the approximately 30,000 known asteroids. But we now have only a few more years to wait before we will be able to find out more about the controversial "planet”.

"New Horizons” is the name of a NASA programme which gives scientists reason to hope once more after work begun some years ago on a Pluto-Kuiper Express mission was stopped due to funding shortages. But the times are changing, and spacecraft are becoming smaller, cheaper and more reliable.

Calculations published only recently showed that, if a spacecraft could be launched within a two-week timeframe in 2006, it could reach Pluto in nine years. The project teams, which are headed by the Southwest Research Institute of San Antonio, Texas, will be pressed to complete work on the development and fitting out of the spacecraft in time. Miniature cameras, a radio wave experiment, UV and IR spectrometers that will still work after the long journey through the depths of the universe have to be installed. The results will be keenly awaited.

From page 48 of FLUG REVUE 6/2002

Last updated 2 May 2002

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