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Recently, other theories have been made about the inner composition of the planet and the history of the two celestial bodies. There are two main theories about Pluto. The first theory states that Pluto has an iced crust of 230 km with a silicate rock nucleus inside. The second theory states the addition of an organic material layer. The history of the Pluto may have begun as a very big asteroid or Neptune’s satellite which stabilized its own orbit around the Sun. Later in time there may have been a collision with another asteroid which chipped pieces from the giant asteroid and finally a big boom brought those pieces and fragments to join together and form Charon.

Voyager and Pioneer space-probes, which have visited all the planets outside Earth’s orbit, are not capable of going to Pluto so we haven’t discovered the deepest mysteries of the Solar System. Hubble space-probes are working to give astronomers more data through pictures taken from outside the Earth’s atmosphere but without physical evidence, theories will remain theories.

Many scientists are working to prepare missions in hopes to land on Pluto. From 1991 to 2000, a team of scientists worked to build a space-probe which could travel to Pluto, Agreeing with NASA’s philosophy “faster, better, cheaper” they created the spacecraft with an enormous amount of advanced technologies. The mission, called “Pluto-Kuiper Express”, was to leave in 1999, but was cancelled after a delay in 2000. Another possible mission might be “New Horizons”, which is expected leave before the year 2020.

However, the Solar System does not end with Pluto and Charon. As Kuiper guessed, in 1992 a huge asteroid belt was discovered. The first celestial body discovered was “1992 QPI” (later called Smiley), discovered by David Jewitt and Jane Luu’s teams in Mauna Kea, Hawaii. The belt closest to Pluto was called Kuiper Band, while a farther band of comets was called Oort Cloud. Up to now, hundred of celestial bodies have been discovered and scientists believe that millions more are still waiting to be discovered.

The latest theory states that a Sun has a partner that exists beyond Oort Cloud. This celestial body might be a star, called Nemesis. Scientists Davis, Piet Hut and Richard Muller guess that the Sun is a double star and that it has a smaller twin which has a revolution time of about a billion years. The twin, Nemesis, might be a red dwarf of magnitude between 7 and 12. It is not possible to find its exact location yet, but the search has been limited to a grid of about 3000 stars. Anyway, the theory has proved itself correct after many studies about mass extinctions of many living families (like the dinosaurs). These extinctions occurred on a regular basis, maybe caused by the movement of a big celestial body inside the Oort Cloud which made the comets draw nearer to the Sun and take on an elliptical orbit (such as Halley’s comet). This theory was published in “Nature” in 1984, but it’s only a hypothesis. Nowadays, scientists are studying the sky, looking for the last pieces to complete this huge puzzle.

Bibliography

• Piero Bianucci and Walter Ferreri, Atlante dell’universo, UTET, Torino 1997
• Piero Angela, Viaggio nella scienza, la Repubblica, Novara 1997
• Nicholas Booth, Il Sistema Solare, De Agostini, Novara 1995
• Rossana Rossi, Scoprire i Pianeti, AMZ edizioni, Milano 1987
• AA.VV., l’Universo, De Agostini, Novara 1998
• Susan Watanabe - www.jpl.nasa.gov/ice_fire/pkexprss.htm, last update in 2000
• Richard Muller - muller.lbl.gov/pages/lbl-nem.htm, last update in 2001

Iconography

• Black and white pictures, from Scoprire i pianeti, page 190;
• Couple in colour, from Il Sistema Solare, page 158;
• composition, from l’Universo, 1 volume, page 302;
• Pluto alone, from l’Universo, 1 volume page 306.

Acknowledgement

Special thanks to the teacher Gianfranco Faillaci and to my friend Jonathan Holman.

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