Podcaster: Samir Dhurde
Title: Mysterious Outer Solar System Series – The Family of Dwarves 2
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!
We are ready for the next part of the tale of the Sun and its five dwarves. As we came to know last time, the International Astronomical Union currently recognizes Ceres, Pluto, Haumea, Makemake, and Eris as dwarf planets. It is estimated that there are hundreds to thousands of dwarf planets in the Solar System, but all await actual discovery by observation.
Among the five, Ceres isn’t really from the outer Solar system. It is the largest object in the Asteroid belt, which lies between the orbits of Mars and Jupiter. It has been studied well since its discovery right at the beginning of the 19th century. It has been, in the past, tagged as a planet for some time as well as an asteroid. It is about 950 km in diameter and contains a third of the mass of the whole asteroid belt. However, since it has obviously not “cleared the neighbourhood around its orbit”, it is classified as a Dwarf Planet since the 2006 IAU resolution. No less mysterious than the other dwarves, the structure of Ceres appears to be differentiated into a rocky core and icy mantle, and it may even harbour an ocean of liquid water under its surface. In early 2015, this dwarf planet named after the Roman goddess of Agriculture & Fertility, will have the unmanned spacecraft Dawn arrive at and study it.
Getting back to the outer solar system, in the tally of Dwarf planets, after Pluto lies Haumea, a small body having only around 6 % the mass of our Moon. Following the IAU regulation that the Dwarf Planets be named after Mythological Creation Gods, Haumea is named after the Hawaiian goddess of childbirth. It is unique in having an extremely elongated ellipsoidal shape, making it the least spherical of the dwarf planets. Observations suggest that Haumea has a mean diameter of roughly 1,400 km. This would make the elliptical dwarf planet close to the size of Pluto on its longer axis.
This oddly shaped object has an unusually rapid rotation. It completes its “day” in only 3.9 hours. This, along with its high density, and high reflectance of Sunlight, are thought to be the results of a giant collision on a larger parent body, billions of years ago. This left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects and its two known moons, Hi’iaka and Namaka sharing an orbit. This system has an orbital period of 283 Earth years and gets as far as 35 AU from the Sun at perihelion.
In 2009 a dark red spot was discovered on Haumea’s bright white surface which stands out in the possibly crystalline water ice. This spot could be an area of the dwarf planet which has a higher concentration of minerals and carbon rich compounds than the rest of the icy surface. The Haumean moons show a similar surface when their infra red spectrum is studied. This seems to be an evidence of common origin, hence strengthening the collision theory of formation.
About three more AU away is the orbit of the next dwarf, Makemake. With a diameter that is about 2/3 the size of Pluto, it is perhaps the largest Kuiper belt object. It was discovered on March 31, 2005, shortly after the Christian festival of Easter and hence codenamed “Easterbunny”. Makemake happens to be the god of fertility in the mythology of the Rapanui, who are the native people of Easter Island in the southeastern Pacific. Thus, by naming this object as Makemake, the Easter reference was also maintained by the discoverers.
The presence of natural satellites makes it easier for Scientists to measure the mass of a big but distant object. However in the case of this dwarf planet, the situation is further challenging. Makemake was discovered just months after the discoveries of Eris and of Haumea, and all were announced within days of each other. However, as its co-discoverer Michael Brown says, “Makemake has no known satellites, and I’ve looked hard with both the Keck telescope and the Hubble Space Telescope”. This makes it impossible to judge its mass without sending a space probe. However, the size can still be estimated. One of the ways in which this can be done is during Occultations, which happens when Makemake (or any solar system body) passes in front of a star as seen from the earth. When in front of the star, the closer, opaque body essentially makes a shadow of its size on the Earth. The shadow races across the Earth as the body moves across the sky. By measuring the size of the shadow of Makemake, we can actually measure its size.
Finding all the physical properties of these distant objects is no easy job. Even finding the same object again after having observed it once is a challenge. Planets lie in fairly circular orbits mostly confined to the ecliptic. So to estimate their position in the solar system we only need to know their average distance from the Sun. The Earth is at 1 AU, Mars at about 1.5, Jupiter 5, and Saturn, Uranus, and Neptune at about 10, 20, and 30. But Pluto and its friends generally have much more elliptical and inclined orbits. In that case, the average distance from the Sun just isn’t enough information. One needs information about how far away they are now, the shape of their orbit, the current direction of their motion etc. This needs regular followup observations, making it a tough job.
The three new dwarf planets were discovered by the team of Michael Brown, Chad Trujillo, and David Rabinowitz as recently as 2005. The search team had been systematically scanning for large outer Solar System bodies for several years, and had been involved in the discovery of several other large TNOs, including Quaoar, Orcus, and Sedna. Next time we will talk about these smaller objects that add further to the Mystery of the Outer Solar System.
End of podcast:
365 Days of Astronomy
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