Podcaster: Samir Dhurde
Title: Mysterious Outer Solar System Series – The Others
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:
In our podcasts till now we have explored the Larger bodies of the Outer Solar system. These are important, because some of them, although newly discovered, have made us become more specific in the way we define solar system bodies. Astronomers have even had to introduce the new category – Dwarf Planet – to classify them into. Coming in smaller and smaller sizes, these have given us new challenges to test the limits of astronomical instruments. Lets us see now, what important and mysterious objects exist out there, other than the Dwarf Planets.
The idea of this series came to me when reading about the planetoid 90377 Sedna. This one, named in the honour of Sedna, the Inuit goddess of the sea, is probably the farthest object found in our Solar system. Its highly elliptical orbit takes it as far as 936 AU, or one percent of a Light year, away from the Sun. At its closest however, it can be within just 84 AU from the Sun. It completes one orbit in around 11400 years. Despite this, it is nowhere close to the inner edge of the Oort cloud. Astrophysicists are trying to explain how this Pluto-sized world got to this intermediate distance from the Sun. It has also inexplicably obtained this weird orbit without being in the range of the large planets to affect it. Co-discoverer Mike Brown gives three options to explain the distorted orbit – an undiscovered planet near Sedna’s perihelion position; or a disturbance by a passing star that approached to within several hundred AU of the Sun; or a model relating to the fact that the Sun was born in a star cluster.
At the time of its discovery in 2003, Sedna was at one of the closest points of its orbit to the sun. Luckily for us, this made it easier to spot. Infact, in 2014, astronomers announced the discovery of another smaller body 2012 VP113, whose orbit is also extremely elongated, suggesting that perhaps the same thing perturbed both Sedna and 2012 VP113. It is also to be noted that the two are close to each other right now, both being close to their perihelia, both of which are at around 80 AU!
Is this a coincidence?
Sedna is measured to have a rotational period of about 10 hours. It had earlier been thought to be ~50 days, falsely indicating a gravitational pull of a moon orbiting it. However, like Makemake, Sedna has no known moons and hence determining its mass is currently impossible without sending a space probe.
Some bodies in the outer solar system are large enough to have their own satellites, but they are not designated as Dwarf Planets. So the satellites orbiting them are referred to as moonlets! The moonlet Weywot orbits the planetoid 50000 Quaoar (pronounced “Kwawar”). The number 50000 is not needed to be read as part of the name, but it is what is called the minor planet number. It is not a coincidence that Quaoar has a perfect minor planet number, because such numbers are chosen to commemorate particularly large objects found in the search for a Pluto-sized object in the Kuiper belt. This rocky world orbits a billion kilometers beyond Pluto. Unlike many other objects at such distances, it goes around the sun in a near-perfect circle, every 288 years.
Quaoar was the first trans-Neptunian object (TNO) to be measured directly using the Hubble Space Telescope. It is found to be about 1,300 kilometers wide. Given this diameter, close to one-third that of our Moon, Quaoar is about as massive as Pluto’s moon Charon.
In 2004, scientists found signs of crystalline ice on Quaoar, indicating that the temperatures had at some time risen to at least −160 °C. This is hard to explain in the cold depths of space. Moreover, the planetoid is observed to be red. It is believed that in the distant past it had an atmosphere with carbon monoxide, nitrogen and methane. Since neither water-ice, nor these gases are red, the surface colour (spectrum) was a mystery. The suggested model to explain this is that a fickle atmosphere can let in intense radiation from the sun, which can form hydrocarbon molecule chains called tholins, out of the carbon and hydrogen atoms that make up methane. These chains are known for reflecting much more in red and infrared. Hence the red colour could be explained by them. Other TNO’s also show some organic (carbon-containing) surface material such as tholins in their spectra.
Weywot is named after the son of the creator god Quaoar, who is sacred to the Native American tribe of Tongva. It is possible that this moonlet might just be a fragment of the planetoid, that came off due to some collision. It is probably only 75 Km across and 1/2000th in mass as compared to Quaoar.
In contrast there is another moonlet Vanth, that is almost half the size of its parent body – Orcus. This moonlet was discovered in 2005, orbiting the relatively bright Orcus which itself was found in 2004. The latter has been put in consideration for being classified as a Dwarf Planet. Talking about Orcus brings us back closer to the Sun, where it orbits at distances ranging from 30 to 50 AU in an elliptical orbit. Judging from the brightness & distance of the two object system, Orcus may be a sphere of around 900 km diameter.
Orcus is a KBO, locked in a 2:3 orbital resonance with Neptune. This means that it makes two revolutions around the Sun to every three of Neptune’s. Such objects are also known as “Plutinos”. Another funny nickname used by Astronomers, for outer solar system objects, is “Cubewano”! It just denotes objects like Quaoar, that orbit beyond Neptune and are not controlled by the orbital resonance. These have close to circular orbits and unlike Pluto, do not cross Neptune’s orbit. The name cubewano comes from the name of the first such TNO discovered – 1992 QB1. Similar objects found later were often called “QB1-o’s” and the name has stuck in common use.
QB1 is a tiny object and there has been no effort to name it, as a thousand such other objects are known now. However, 2007 OR10 – a very large planetoid, is the largest known body in the Solar System without an official name. This seems quite unfair as it is approximately the size of Haumea, and was infact dubbed as the “seventh dwarf” planet by its discoverers. It is currently the 2nd furthest known large body from the Sun, after Eris. Its distance has been a hurdle for telescope to resolve direct details about it and hence the decision about its dwarf planet status is pending. It is currently moving away from the Sun and will be farther than Eris by 2045, and will reach aphelion at about 101 AU in 2130. Ofcourse by that time we will have been able to observe multitudes of more mysterious objects. With the giant telescopes like the EELT and the Thirty Meter Telescope set to open their eyes to the universe in a decade from now, the field will be teeming with objects to be researched on. We can then set ourselves to look for the ultimate fantasy goal – Planet X – if it exists. Next time we will talk about the quest for this exciting possibility that has however remained elusive yet.
End of podcast:
365 Days of Astronomy
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