Sky Tour Radio Presents: Tightening Our Asteroid Belt
April 15th, 2018
In this episode of Sky Tour Radio, we discuss exoplanets Kepler 186f andHD69830 in our weekly roundup, where we explore the possibilities of habitability and wither it can be harnessed by humans or if the process could have already started on its own.
We also finish our previous discussion on the last few types of asteroids, including near Earth objects, Centaurs, Kuiper Belt Objects, Scattered DiscObjects, Sednoids and Oort Cloud Objects.
This discussion leads us to also examine Circumstellar Disks and what theirdiscovery has meant to astronomers, what this data can tell us and what itindicates concerning the future discovery of previously unknown exoplanets.
Kepler-186f is an exoplanet orbiting the red dwarf Kepler-186, about 550light-years from the Earth. It is the first planet with a radius similarto Earth’s to be discovered in the habitable zone of another star.
NASA’s Kepler spacecraft detected it using the transit method, along with fouradditional planets orbiting much closer to the star (all modestly larger thanEarth)
Kepler-186f orbits its star with about 4% of the Sun’s luminosity with an orbital period of 129.9 days and an orbital radius of about 0.40 times that of Earth’s. The habitable zone for this system is estimated conservatively to extend over distances receiving from 88% to 25% of Earth’s illumination andreceives about 32%, placing it within the conservative zone but near the outer edge, similar to the position of Mars in our Solar System.
HD 69830 is a yellow dwarf star located approximately 41 light-years away in the constellation of Puppis. In 2005, the Spitzer Space Telescope discovered a narrow ring of warm debris orbiting the star. The debris ring contains substantially more dust than the Solar System’s asteroid belt.
In 2006, three extra-solar planets with minimum masses comparable to Neptune were confirmed in orbit around the star, located interior to the debris ring.
It has about 86% of the Sun’s mass, 90% of its radius, 62% of its luminosity,and 89% of its iron abundance. The star’s age has been estimated at about 10.6 ± 4 billion years.
In 2005, the Spitzer Space Telescope detected a debris disk in the HD 69830 system consistent with being produced by an asteroid belt twenty times more massive than that in our own system. The belt was originally thought to be located inside an orbit equivalent to that of Venus in the Solar System, which would place it between the orbits of the second and third planets.
The disk contains sufficient quantities of dust that the nights on any nearby planets would be lit up by zodiacal light 1000 times brighter than that seen on Earth, easily outshining the Milky Way.
A circumstellar disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form. Around mature stars, they indicate that planetesimal formation has taken place and around white dwarfs, they indicate that planetary material survived the whole of stellar evolution.
Such a disc can manifest itself in various ways.
According to the widely accepted model of star formation, sometimes referred toas the nebular hypothesis, a young star (protostar) is formed by the gravitational collapse of a pocket of matter within a giant molecular cloud. The infalling material possesses some amount of angular momentum, which results in the formation of a gaseous protoplanetary disc around the young, rotating star.
The former is a rotating circums-tellar disc of dense gas and dust that continues to feed the central star. It may contain a few percent of the mass of the central star, mainly in the form of gas which is itself mainly hydrogen. The main accretion phase lasts a few million years, with accretion rates typically between 10−7 and 10−9 solar masses per year.
The disc gradually cools in what is known as the T Tauri star stage. Within this disc, the formation of small dust grains made of rocks and ices can occur, and these can coagulate into planetesimals. If the disc is sufficiently massive, the runaway accretions begin, resulting in the appearance of planetary embryos. The formation of planetary systems is thought to be a natural result of star formation. A sun-like star usually takes around 100million years to form.
SkyTour Radio explores the Universe in a down to Earth manner explaining the science we know in fun and bite-sized terms. Science is for everyone and people shouldn’t require an advanced degree to understand as long as it is delivered in an easy to follow way. From Black Holes to Extraterrestrial Life, we will explore the Universe like never before. Join us to check out such things as how stars form, how they live and, how our fate is intertwined with theirs. On the extraterrestrial life front, we will be speaking to the UFO and science arena’s top researchers and bring UFOlogy into the 21st century.
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