The Geminid Meteor Shower is expected to peak at about 2.00 am on Monday 14 December this year (2020) with potentially up to 120 meteors per hour being visible in areas of the Northern Hemisphere with a clear sky. This year peak activity for the shower coincides with the New Moon, also on Monday 14 December, so viewing should be good. The meteors appear to radiate from a point in the constellation of Gemini, hence their name.
Oddly for a meteor shower, the Geminids do not appear to be related to a comet, but instead are associated with an object called 3200 Phaethon, which is classed as an Apollo Asteroid (an asteroid with an orbit that crosses that of the Earth). 3200 Phaethon has a highly elliptical orbit, which takes it in as close as 0.14 Au (14% of the distance between the Earth and the Sun, more than twice as close as Mercury) and out as far as 2.4 AU (2.4 times as far from the Sun as the Earth or 1.6 times as far as Mars). 3200 Phaethon does not appear to produce any sort of halo (a cloud of material produced by the evaporation of gas ice from the surface of a comet, thought to be the source of most meteor showers); rather it appears dark in colour an is classed as a B-type Carbonaceous Asteroid, thought to have a surface covering of anhydrous silicates, hydrated clay minerals, organic polymers, magnetite, and sulphides.
Asteroid 3200 Phaethon is a 5 km body with a highly eccentric orbit similar to that of a comet, which takes it closer to the Sun than any other named Asteroid. It appears to be the parent body of the Geminid Meteors, which share essentially the same orbit as it, as well as a group of larger bodies known as the Phaethon-Geminid Complex. Such meteor showers typically form from the tail of a comet; as the comet approaches its perihelion (the closest point in its orbit to the Sun), ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice, which continue to follow essentially the same path as the comet, creating a meteor shower every time the Earth passes through this stream. However, 3200 Phaethon, which has a 1.43 year orbital period in which it reaches 0.14 AU from the Sun (14% of the distance between the Earth and the Sun, or less than half the distance at which Mercury orbits) is thought to regularly suffer surface temperatures in excess of 1000K, making it highly unlikely that it has ice on its surface, which calls its potential role as the parent body to the Geminid Meteors into question. 3200 Phaethon is classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, it is also classified as a Potentially Hazardous Asteroid.
In a paper published on the arXiv online database at Cornell University Library on 17 June 2013, David Jewitt of the Department of Earth and Space Sciences and Department of Physics and Astronomy at the University of California Los Angeles, Jing Li of the Department of Earth and Space Sciences at the University of California Los Angeles, and Jessica Agarwal of the Max Planck Institute for Solar System Research, describe the results of a study of 3200 Phaeton using the NASA STEREO Spacecraft.
Jewitt et al. suggest that at it's perihelion 3200 Phaethon is
being heated to such a degree that hydrated minerals at its surface
could be thermally fractured and desiccated, leading to the ejection of
dust particles.
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