Exolunar chaos at the edge of the solar system

Exolunar chaos at the edge of the solar system

Image: NASA / Southwest Research Institute / Alex Parker / Friday

Hubble telescope set its sights on Pluto’s four small moons, which turn out to be eccentrics. Exciting tasks await NASA’s New Horizons spacecraft, which will reach the Pluto-Charon system in July

Astronomers see in Pluto and Charon a kind of planetary system en miniature, because both heavenly bodies revolve around a common gravitational center. The four remaining moons are not unaffected by this close relationship, as two scientists report in Nature. They not only observed the chaotic dance of two moons around Pluto, but were surprised by the characteristics of the quartet of small moons. Hopes are now pinned on NASA’s New Horizons robot, which will soon reach its destination after 9.5 years of flight and study the Pluto-Charon system up close. He was able to confirm the current observations and reveal even more surprising things.

Pluto never played the first violin in the interplanetary concert, not even after its discovery in 1930, when the young astronomer Clyde Tombaugh (1906-1997) located a pale, white dot in the winter sky at the Lowell Observatory in Flagstaff, Arizona, and observed it minutely for a year.

Unofficial ascent to the planet

When it became clear that the dot-shaped structure was moving, it achieved unexpected honors. The celestial body named after the Roman god of the underworld Pluto advanced to the status of a planet and also received the blessing of the Union Astronomique Internationale/UAI) founded in Paris in 1919. From then on, Pluto was the smallest, lowest-mass and farthest-from-Earth planet in the solar system.

For 48 years, the icy world, more than six billion kilometers away and only 2290 kilometers in diameter, was able to defend and maintain its official status as a planet without ever being caught in the crossfire of criticism or being in serious danger of being removed from the planetary orchestra.

But when Charon, the innermost of the five known moons, was detected and studied in 1978, it sparked a debate about the classification of Pluto for the first time. Especially Charon’s diameter heated up the minds of the experts and did not fit into their world view.

Exolunar chaos at the edge of the solar system

Clyde Tombaugh with a photographic plate. He discovered Pluto at Arizona’s Lowell Observatory in Flagstaff. Only a few kilometers away, also in Flagstaff/Arizona, the 1.55-meter Kaj Strand Astrometric Reflector of the USNO (United States Naval Observatory) collected the crucial data in 1978, which James Walter Christy used to track the rough moon of Pluto, Charon, a short time later. Such a meeting can be called a scientific-historical coincidence par excellence. Image: NASA

In fact, Charon, with a diameter of 1207 kilometers, was almost half as large as its planetary companion. Compared to the coarseness of its supposed planet, Charon turned out to be a true giant among the moons. In the depths and expanses of the solar system, this rough relation is still unique.

Chaotic Pluto and Charon

When quantities showed that both objects were located in only 19.300 kilometers distance to each other, which corresponds approximately to the flight distance Rio de Janeiro-Tokyo, the doubts increased with some experts. These were mainly motivated by the astrophysical fact that Charon as the smaller and less massive celestial body does not orbit Pluto, but that both orbit around a common axis, which is located between both objects in empty space.

Pluto and Charon also deviate far from the norm when orbiting the Sun together. Where other planets orbit our home star in approximately circular orbits in a common plane, both present themselves as true chaos. This fact was evaluated by the American science author Jeffrey Kluger in his book already published in 1999 Journey Beyond Selene as follows:

Pluto’s and Charon’s orbit is (…) an asymmetric mess. Like the captured moons of the grosser planets, the ninth planet and its moon chase around the sun at a steep angle, sometimes 17.15 degrees below, sometimes 17.15 degrees above the plane of the sun’s equator.

The chaos became even bigger when scientists located the third transneptunian object after Pluto and Charon in 1992, and shortly thereafter identified four more plutinos. Was it not obvious in view of the spatial proximity to these objects to see in Pluto henceforth no more planet? But despite this urgent question, which more and more astronomers were asking themselves, Pluto again retained the blessing of the International Astronomical Society (IAU) in February 1999 after a heated discussion about its classification:.http://www.iau.org/). In the year of Kluger’s book publication, the IAU once again put its trust in the distant celestial body.

Exolunar chaos at the edge of the solar system

This photo of Charon and Pluto was taken in July 2013 by the LORRIE instrument of NASA’s New Horizons research probe. The central female coarser object seen here (in both images) is Pluto. The faintly appearing pixel on the upper left – at 11 o’clock position – is Charon. Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Chaos in the Kuiper belt

69 years after its discovery, there was finally clarity about its true status, many thought. But things were to turn out quite differently. Only a short time later the critics were heard again, who thought Pluto to be a moon escaped from Neptune or a direct descendant of the Kuiper belt.

The Kuiper belt is a disk-shaped region extending behind Neptune’s orbit, at a distance of five and six billion kilometers from the Sun. They also include the so-called trans-Neptunian and trans-Plutonian objects, hundreds of which follow their eccentric orbits and are part of the Kuiper belt. Although so far only 700 objects could be tracked in the Kuiper belt, there are estimates that probably at least 70 objects can be found there.000 Trans-Neptunian Objects (TNO) with a diameter of more than 100 kilometers or much larger are drifting. So it is not surprising that most of the scientists ame Pluto’s place of origin in this region.

One of the cruder TNO is Sedna. Roughly 1000 kilometers in diameter, the dwarf planet approaches the Sun to within 76.4 astronomical units (1 AU = 150.000.000 kilometers). Image: NASA, ESA and M. Brown (Caltech)

Planetary forced descent

When astronomers then tracked down a celestial body even coarser than Pluto in 2003, its fate seemed finally sealed. Concerns reached their peak three years later when the 26. The IAU’s first general assembly in Prague scientifically redefined the term planet and subsequently banned Pluto from the illustrious circle of eight other planets. An unyielding panel of astronomers demoted Pluto to a dwarf planet and gave it the minor planet number 134340. The newly defined classes of plutoids and plutinos were named after it.

That in the same year that New Horizons began its long journey, the IAU passed its legendary verdict, expelling Pluto from planetary Olympus, therefore seems like an irony of scientific history. Above all because the first space probe with the distant goal Pluto before the sensors, the planet earth fell in love at a time, when Pluto was still traded as a wash planet.

Exolunar chaos at the edge of the solar system

24.08.2006 – IAU vote in Prague. The ladies and gentleman, who lift here the yellow document, decided straight against the planet status of Pluto. Image: International Astronomical Union/Lars Holm Nielsen

Nevertheless, there is still uncertainty about the once last and at the same time smallest planetary vagabond of our solar system, whether, contrary to the verdict of the IAU, it perhaps does not deserve the qualifier planet after all. This was most strongly expressed two and a half years after Pluto’s forced descent, when the Illinois State Senate gave it another planetary accolade by decree, and the 13. Marz partout to the "Pluto Day" . On that day in 1930, Illinois native Clyde Tombaugh famously discovered the distant world at the edge of the solar system – and became the first American to discover a planet at all.

Study in preparation for New Horizons

Whatever one may think about the planetary or non-planetary status of Pluto, the distant chunk of ice is a magnet for scientific curiosity. That Pluto is still a highly interesting object of research is proven by the paper penned by Mark R. Showalter and Doug P. Hamilton-originated paper published in the British scientific journal Nature (vol. 522, S. 45-49, 04.06.2015) has been published.

It shows that the duo has succeeded not only in taking a closer look at Pluto and Charon, but also in studying the characteristics of Pluto’s smaller moons Nix, Hydra, Kerberos and Styx in more detail. To accomplish this, the researchers drew on data compiled by NASA’s Hubble Space Telescope (ESA) from 2005 to 2012.

As early as 1994, the Hubble Space Telescope transmitted an unusually sharp photo of Pluto and its moon Charon to Earth. At that time, both celestial bodies were 4.4 billion kilometers away from Earth. Image: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA

This happened also in view of the NASA research robot New Horizons, whose camera LORRI photographed for the first time all so far detected moons of Pluto. Using Hubble and LORRI data, researchers can review and revise scientific objectives and, if necessary, redefine mission goals. Last but not least, the current bits and bytes are used to explore all risk factors during the probe’s audacious Pluto flyby and to initiate appropriate precautionary measures or, to be on the safe side, to program an avoidance maneuver. Finally, the Pluto system could also have a ring system, in which myriads of ice crystals and dust particles vagabond, which could permanently damage the electronics of the spacecraft.

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