The Gemenid Meteors.

The Geminid Meteor Shower is expected to peak on Wednesday 13 December this year (2017) 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 a waning Crescent Moon, with the New Moon falling on Sunday 17 December, so viewing should be fairly good. The meteors appear to radiate from a point in the constellation of Gemini, hence their name.

The relative positions of the radiant point of the Gemenid Meteors (i.e. the point from which the meteors radiate) at 9.00 pm on 13 December 2017. Sky & Telescope.

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.

Image of 3200 Phaethon taken on 20 November 2017 with the Pearl Telescope at the Tenagra Observatory in Arizona The asteroid is the point in the centre of the picture, indicated by the two red lines. The longer lines are stars, their elongation being caused by the telescope tracking the asteroid over the length of the exposure, in this case five exposures, each of 180 seconds. Gianluca Masi/Virtual Telescope/Michael Schwartz/Tenagra Observatory.

 

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. observed two successive perihelions of 3200 Phaeton, in June 2009 and May 2012. On both occasions they were able to observe a faint comet-like dust tail emerging from the body, even though it was apparently reaching temperatures that would rapidly destroy an icy comet. This tail grew rapidly, reaching a length of over 250 000 km within a day of first appearing, and appeared to represent material being lost from the parent body at a rate of about 3 kg per second.

Composite images of 3200 Phaethon in 2009 (top row) and 2012 (bottom row) compared with the projected sun- comet line (white). The Sun is to the upper right in each panel. Insets are 49000 square and show eld stars near to Phaethon to demonstrate the point spread function of the data. Each panel has North to the top, East to the left and shows the median of 30 images taken over a 1 day period. Jewitt et al. (2013).

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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The Geminid Meteors.

The Geminid Meteors peak each year on or around the night 13-14 December radiating from a point in the constellation of Gemini. They are visible from around the globe, but are harder to observe in the southern hemisphere, since Gemini does not rise far above the horizon at this time of year. They were first observed in 1860, and have apparently been gradually getting brighter each year since then, leading some scientists to speculate that the path of the meteor shower might have recently been perturbed by the planet Jupiter, shifting it into the Earth's path.

The point of origin of the Geminid Meteors. Meteor Showers Online.

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 Phaeton 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.

The orbit of 3200 Phaeton. Image created using the JPL Small-Body Database Browser.

See also The Leonid Meteors, Four more asteroids found to be co-orbitals of Neptune, Asteroid 2012 TC4 passes within 95 000 km of the Earth, Comet C/2012 S1 (ISON) to pass within 60 000 000 km of the Earth and The Perseid Meteors. 

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The HATNet project announces the discovery of three new Hot Jupiter type planets.

The HATNet (Hungarian made Automated Telescope Network) project uses eight small (11 cm diameter lens) telescopes located at the  Fred Lawrence Whipple Observatory in Arizona and the Mauna Kea Observatory in Hawaii, to search for exoplanets. Such Earth-based networks are playing an increasingly important role in the search for exoplanets, since while they do not discover the shear number of planets that the space-based telescopes find, the planets they do discover tend to be more amicable to follow-up observations by Earth-based observatories.

In a paper published on the online arXiv database at the Cornell University Library on 13 July 2012, a team of scientists led by Joel Hartman of the Department of Astrophysical Sciences at Princeton University, announce the discovery of three new Hot-Jupiter type planets by the HATNet project. All three planets have been observed both by the light they occlude when they pass in front of their host stars, and by the movement they cause in the star as they orbit about it. This enables scientists to estimate both the volume and the mass of the planets, revealing that all of the planets have lower masses, but higher volumes than Jupiter, which matches predictions that gaseous planets close to stars will expand due to the heat of the star.

The first new planet obits the star GSC 1364-01424; this is the 39th star found to have a planet by HATNet, and the system is therefore renamed HAT-P-39, with the star being HAT-P-39A and the planet HAT-P-39b (naming conventions dictate that stars are given upper case letters and planets lower case letters. 

HAT-P-39A is about 2094 light years from Earth in the constellation of Gemini. It is an F-class star, slightly larger and hotter than our Sun, with a mass 1.4 times the Sun's and a radius 1.6 times the Sun's. It's effective surface temperature is 6430 K, compared to 5778 K for our Sun. The star is thought to be about 2 billion years old.

HAT-P-39b orbits this star at a distance of 0.0509 AU (that is to say 5.09% of the distance at which the Earth orbits the Sun), completing one orbit every 3.54 days (85 hours). It has a mass equivalent to 0.599 times that of Jupiter, but a radius 1.57 times Jupiter's. It is thought to have an average equatorial temperature of 1752 K, compared to 303 K for Earth or 152 K for Jupiter.

Diagram showing the mass of HAT-P-39b compared to the planets of out Solar System. Visual Exoplanet Catalogue.

The second new planet orbits the star GSC 3607-01028, now renamed HAT-P-40A, another F-class star, 1634 light years from Earth in the constellation of Lacerta. HAT-P-40A has a mass 1.5 times that of the Sun, and 2.2 times the Sun's radius. Its effective surface temperature is 6080 K, and it is thought to be about 2.7 billion years old.

HAT-P-40b orbits this star at a distance of 0.0608 AU (6.08% of the distance at which the Earth orbits the Sun), taking 4.46 days (107 hours) to complete one circuit about the star. I has 0.615 times the mass of Jupiter, and 1.73 times the radius. Its average equatorial temperature is 1770 K.

Diagram showing the comparative masses of HAT-P-40b and the planets of our Solar System. Visual Exoplanet Catalogue.

The final new planet orbits GSC 0488-02442, now renamed HAT-P-41A, another F-class star, this one  1014 light years away in the constellation of Aquila. HAT-P-41 A has 1.42 times the Sun's mass and 1.68 times the Sun's radius. It has an effective surface temperature of 6390 K, and is thought to be 1.5 billion years old.

H-band AO image of HAT-P-41. Hartman et al. (2012).

The planet HAT-P-41b orbits this star every 2.69 days (65 hours) at a distance of 0.0424 AU (4.24% of the distance between the Earth and the Sun). It has 0.8 times he mass of Jupiter and 1.68 times Jupiter's radius. It's average equatorial temperature is thought to be 1941 K.

Diagram showing the comparative masses of HAT-P-41b and the planets of our Solar System. Visual Exoplanet Catalogue.

See also A fourth body in the KOI-13 system, Two Hot Jupiters found in the Beehive Cluster, A new study of the Kepler 11 planetary system, The object orbiting GD66 is probably a planet, not a Brown Dwarf and Exoplanets on Sciency Thoughts YouTube.

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