INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 33, March 2014 141348_Spatium_33_(001_016).indd 1 19.03.14 13:47 Editorial A sunny spring day. A green On 20 March 2013, Dr. Hermann meadow on the gentle slopes of Boehnhardt reported on the pre- Impressum Mount Etna and a handsome sent state of our knowledge of woman gathering flowers. A stran- Pluto and its cohorts, which is not ger passing by and falling in love so much when compared to the with her. planets in our cosmic neighbour- hood, yet impressively much in SPATIUM Next time, when she is picking view of their modest size and their Published by the flowers again, the foreigner returns gargantuan distance. In fact, ob- Association Pro ISSI on four black horses. Now, he, serving dwarf planet Pluto poses Pluto, the Roman god of the un- similar challenges to watching an derworld, carries off Proserpina to astronaut’s face on the Moon. marry her and live together in the shadowland. The heartbroken We thank Dr. Boehnhardt for his Association Pro ISSI mother Ceres insists on her return; kind permission to publishing Hallerstrasse 6, CH-3012 Bern she compromises with Pluto allow- herewith a summary of his fasci- Phone +41 (0)31 631 48 96 ing Proserpina to living under the nating talk for our Pro ISSI see light of the Sun during six months association. www.issibern.ch/pro-issi.html of a year, called summer from now for the whole Spatium series on, when the flowers bloom on the Hansjörg Schlaepfer slopes of Mount Etna, while hav- Brissago, March 2014 President ing to stay in the twilight of the Prof. Nicolas Thomas, underworld during winter. University of Bern Pluto had become the ruler of the Layout and Publisher underworld and Neptune the gov- Dr. Hansjörg Schlaepfer ernor of the oceans, when Jupiter CH-6614 Brissago had wrested the lordship over the world from their common father Printing Saturn. These Roman gods are not Stämpfli Publikationen AG the only divinities making a fan- CH-3001 Bern tastic appearance on the following pages, rather, they team up with many more, such as Sedna, the venerated goddess of the deep ocean of the Inuit or Makemake, the great creator god ruling the Easter Islands. Most interestingly, a modern as- tronomer’s view of dwarf planet Pluto and its companions is in no way less fantastic: Having all their own peculiarities they circle the Sun at the rim of the solar system in eternal twilight just like the souls in the underworld. SPATIUM 33 2 141348_Spatium_33_(001_016).indd 2 19.03.14 13:47 Pluto and its Cohorts1 by Dr. Hermann Boehnhardt, Max-Planck Institute for Solar System Research in Göttingen/Germany Introduction ments and suggestions. Yet, Clyde astronomer who could operate the does not get the expected com- photographic telescope recently ac- ments, but rather a job there: his quired. That was in 1929 (Fig. 1). drawings are judged so excellent Clyde William Tombaugh2 dreams that the observatory’s director em- Unsurprisingly, Clyde accepts the to become a great astronomer. ploys him instantly as an amateur offer and starts working at the ob- Star-gazing is his passion, like his father’s and his uncle’s, who occa- sionally places his telescope at the youngster’s disposal. At the age of 17, Clyde buys a commercial low- cost 2¼-inch instrument from Sears, which has the advantage of being his own, yet the disadvantage of not fulfilling his expectations. So, he decides to build one himself: he starts grinding mirrors and as- sembling parts of discarded farm machinery and a shaft from his father’s 1910 Buick. To help pay for the material required, father Tom- baugh, a modest farmer in the ru- ral heart of Illinois, takes a second job. The instrument gets finished in 1925, and Clyde doesn’t know that this instrument is to become the first of over thirty telescopes he will build over his lifetime. When time comes to decide on his professional life, Clyde intends to enter the local college to get pre- pared for the studies at the Univer- sity; yet a hailstorm destroys his family’s crops putting a sudden end to his dreams. Not quite, though: he begins us- ing his telescope extensively, makes a lot of meticulous sketches of Jupiter and Mars, and sends them to the astronomers at Lowell Ob- Fig. 1: Clyde William Tombaugh, the discoverer of Pluto in a photo of around servatory humbly asking for com- 1929. (Anonymous author) 1 The present issue of Spatium reports on the lecture given by Dr. Boehnhardt for the Pro ISSI Association on 20 March 2013. The notes were taken by Dr. Hansjörg Schlaepfer. 2 Clyde William Tombaugh, 1906, Streator, Illinois – 1997, Las Cruces, New Mexico, US American astronomer. SPATIUM 33 3 141348_Spatium_33_(001_016).indd 3 19.03.14 13:47 servatory that was founded and ground. Hence, in August 2006, full-time. During his years at Low- sponsored by Percival Lowell3, a Pluto is re-classified as a dwarf ell, the former farm boy Clyde member of a wealthy Boston planet by the IAU4. One of the writes astronomical history discov- family, in 1894. Lowell, based on criteria set up to this end is that a ering hundreds of new variable careful analyses of the irregular or- planet must be able to clean its stars, hundreds of new asteroids bits of Uranus and Neptune, had orbital environment from smaller and two comets. He finds new star predicted a so far unknown “Planet bodies, which is the case with all clusters, clusters of galaxies includ- X”, which could explain the odd eight planets but not for Pluto and ing one super cluster of galaxies. behaviour of the planets. Clyde’s its uncountable consorts. In all, he counts over 29,000 job is now to photograph one small galaxies. piece of the night sky at a time and Clyde Tombaugh enters the Uni- to carefully examine and compare versity of Kansas in 1932 where he On 17 January 1997, Clyde Wil- the photos in an effort to search for earns his Bachelor of Science de- liam Tombaugh dies at the age of a tiny moving point of light that gree in 1936. He signs up for a basic 91 while Pluto quietly continues might be the mysterious “Planet astronomy course, but is rejected orbiting the Sun. Since then, the X”. He takes pictures of most of on the grounds that his discovery dwarf planet has revealed many as- the sky, and spends thousands of of Pluto has already made him one tonishing facts, and with improv- hours examining the images. Af- of the world’s most famous astro- ing observational means further ter ten months often working nomers, and it would be absurd to surprises will certainly come up. through the whole night in the un- accept such a personality for an in- heated dome, on 18 February 1930 troductory class. He continues In contrast to the planets, Pluto cir- he discovers an enigmatic object working at Lowell Observatory cles the Sun on an eccentric orbit he names Pluto. That lonely night during the summers and after grad- that brings it at its perihelion nearer makes Clyde a great astronomer. uation, he starts working there to the Sun than neighbouring Pluto orbits the Sun in a mean dis- tance of some 5.9 billion km which is equivalent to 39.2 Astronomical Units. It takes it two and a half earthly centuries to complete one single orbit around the Sun. For many years, Pluto is considered the ninth planet in our solar system. However, as astronomers learn more about the planets and also about a new group of objects, dis- covered as of 1992 and known to- day as the Kuiper Belt objects, it Fig. 2: The orbit of Pluto as compared to the planetary orbits in the solar system. becomes clear that Pluto is more The orbits of all planets are more or less confined to the ecliptic plane defined by the Earth’s orbit around the Sun. In contrast, Pluto orbits the central star in a plane like the larger objects in that belt tilted by 17°. Again in contrast to nearly all planets, Pluto’s axis of rotation lies prac- than the eight planets in the fore- tically within its orbital plane, similar to Uranus. (Credit: NASA) 3 Percival Lowell, 1855, Boston – 1916, Flagstaff, Arizona, USA, US-American astronomer, founder of the Lowell Observatory. 4 The International Astronomical Union (IAU) was founded in 1919 with its headquarters in Paris. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. SPATIUM 33 4 141348_Spatium_33_(001_016).indd 4 19.03.14 13:47 planet Neptune. That was the case planetary system – accompanied by They concentrate in a zone from the last time in February 1979. A some minor satellites. some 30 to 50 Astronomical Units. further peculiarity of Pluto is its 2:3 This is the region at the edge of the orbital resonance with Neptune: Pluto is the brightest, but not the planetary system, called the Kuiper this means that while Neptune or- largest trans-Neptunian object Belt honouring Gerard Peter Kui- bits the Sun three times, Pluto com- (TNO), see Fig. 3. The term TNO per5 who in the forties de veloped pletes exactly two orbits. The rep- (or equivalently Kuiper Belt ob- theoretical foundations allowing etition of a similar orbital geometry ject) designates a body whose mean him to speculate on the existence between Neptune and Pluto helps orbital radius is larger than that of of a “comet belt” where most of stabilize the orbit of the smaller Neptune.