Podcaster: Samir Dhurde
Title: Mysterious Outer Solar System Series – The Family of Dwarves 1
Organization: The Inter-University Centre for Astronomy and Astrophysics, Pune, India
Link : http://en.wikipedia.org/wiki/Kuiper_belt, http://nineplanets.org/, http://www.universetoday.com/32515/kuiper-belt/
Description: The last two decades have been filled with a lot of discoveries made by Astronomers, while exploring the outskirts of our Solar neighborhood. In this series, let us talk about the exciting objects and the mysteries of the outer Solar System.
Bio: Samir Dhurde is in-charge of SciPOP, the national outreach programme of the Inter-University Centre for Astronomy & Astrophysics (IUCAA) in Pune, India. He loves working with children, sharing Astronomy with people and is a Radio Astronomer in his free time.
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Transcript:
Hello everyone!
Last time we talked about the Kuiper belt and ended mentioning a KBO called Pluto. Yes, It’s a sad story for Pluto to go to this status from the prestige of being called a Planet for almost 85 years. Pluto was actually discovered by a fortunate accident in 1930, when Astronomer Clyde W. Tombaugh was looking for the ever-elusive Planet X. It was found when astronomers were working on a wrong prediction, provided by a wrong calculation, of a big planet beyond Neptune. However, this small body was found and it was so far from the Sun that it may be in perpetual darkness. This gained it the name of the Roman mythological god of the Underworld – Pluto.
Its largest satellite, Charon was discovered much later in 1978 and studies of their masses then became possible. The mass estimated (1.31×1022 kg) for Pluto is less than about 20 percent of our Moon. Although well known for a long time, an image of Pluto is still a blob of dark and bright even from the best telescopes on Earth. Determinations of Pluto’s size are further complicated by the presence of its atmosphere, and a possible hydrocarbon haze around it. The gassy layer cannot currently be resolved from the hard surface. Hopefully, the mission New Horizons will give us very clear pictures of these two in July 2015.
Although it will take a visit by a spacecraft to get accurate figures, we know that Pluto has a Radius of only 2 times more than its satellite. Charon is quite unusual in that it is the largest moon with respect to its primary planet in the Solar System. Some prefer to think of Pluto/Charon as a double planet rather than a planet and a moon. Pluto is however officially classified as a Dwarf Planet, the most famous one in our solar system. It underwent a well-publicized (and somewhat controversial) reclassification that took away its title as the ninth and most distant planet from the Sun.
In an exciting vote in 2006, the International Astronomical Union (IAU) decided to create a new classification category for solar system objects called dwarf planets. This was brought about by an increase in discoveries of trans-Neptunian objects that rivalled Pluto in size. The actual definition of “dwarf planet” is:
A celestial body that
- is in orbit around the Sun,
- has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
- has not cleared the neighbourhood around its orbit, and
- is not a satellite.
The infamous ‘nemesis’ of Pluto, whose discovery led to its demotion, is another dwarf planet Eris. Eris (aka 2003 UB 313, Xena) is a trans-Neptunian object and a member of the “scattered disc” of the Kuiper belt, a population of high-eccentricity TNOs. These are believed to have been “scattered” from the Kuiper belt into more distant and unusual orbits following gravitational interactions with Neptune as the Solar System was forming.
Its distance from the Sun currently is 96.4 astronomical units (14.42 billion km), roughly three times that of Pluto. Eris has one known moon, Dysnomia. Hence, with the exception of some comets, Eris and Dysnomia are currently the most distant known natural objects in the Solar System. Eris has an orbital period of 557 years. The orbits of the eight planets, all lie roughly in the same plane as the Earth’s, which is also referred to as the Ecliptic. Unlike them, Eris’ orbit is highly inclined: It is tilted at an angle of about 44 degrees to the Ecliptic. Also, with its ellipticity, in about 800 years, Eris will be closer to the Sun than Pluto for some time.
Its diameter is estimated by various observations to be close to 2400 km. Based on the currently accepted value for Dysnomia’s period —15.774 days, Eris has a mass 27% more than Pluto’s. This makes it the most massive dwarf planet. More importantly, it tells us that it is quite dense, which leads astronomers to believe that it is made up largely of rocky material. While Pluto’s surface is moderately red, this distant dwarf planet appears almost white. Pluto has a mottled-looking surface which reflects on average 60% of the sunlight which hits it. A measure of this is called the Albedo of an object. Eris appears essentially uniform and reflects around 86% of the light that hits it. In fact, Eris reflects more sunlight from its surface than any body in the solar system other than Saturn’s moon Enceladus, with the reason still being a mystery! Once again we will need very large telescopes or spacecrafts to help us unravel it with actual images.
Next time we look at the others in the family of outer dwarf planets.
End of podcast:
365 Days of Astronomy
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