The 2017 Eta Aquarid Meteors.

The Eta Aquarid Meteor Shower will peak before dawn on Friday 5 and Saturday 6 May 2017, with up to 45 meteors per hour at it's peak, radiating from the constellation of Aquarius. The radiant point of this shower does not spend long above the horizon in the Northern Hemisphere at this time of year, but is often a good display in the Southern Hemisphere. The Eta Aquarids are potentially visible between 19 April and 28 May, but are extremely hard to spot away from the peak of activity, which this year falls shortly before the Full Moon on Wednesday 10 May; however the Moon will be setting shortly after midnight, so there should still be some good opportunities for meteor spotting (the Moon sets at the same time no matter where you are on Earth, as it's rising and setting time is caused by its position relative to the Sun).

The radiant point for the 2017 Eta Aquarid meteors. The Leisurely Scientist.

The meteor shower is caused by the Earth passing through the trail of Halley's Comet, where it encounters thousands of tiny dust particles shed from the comet as its icy surface is melted (strictly sublimated) by the heat of the Sun. Halley's Comet only visits the inner Solar System every 75 years (most recently in 1986 and next in 2061), but the trail of particles shed by it forms a constant flow, which the Earth crosses twice each year; in May when it causes the Eta Aquarid Meteor Shower and in October when it causes the Orionid Meteor Shower.

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Recalculating the nature of the planets of thr TRAPPIST-1 system, using data from the Kepler Space Telescope.

M-type Stars (Red Dwarfs) are the most abundant type of stars in the galaxy, and are both smaller and longer lived than other types of stars. A number of recent studies have shown that many such stars are home to planetary systems, making them of great interest to planetary scientists. One recent discovery of particular not is the TRAPIST-1 system (formerly 2MASS J23062928-0502285), comprising a Red Dwarf Star (TRAPPIST-1A) 39.5 light years from Earth in the constellation of Aquarius, that has only 0.08 times the mass of the Sun, but which is surrounded by a system of six known planets (TRAPPIST-1 b, c, d, e, f, and g).

The system discovered in 2016 by the 2MASS (Two Micron All-Sky Survey) project, which combined data from telescopes at the Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona and the Cerro Tololo Inter-American Observatory in Chile, and all six planets estimated to be of approximately Earth-mass, generating  great deal of interest in the system, and therefore a desire on behalf of planetary scientists to gather further data on the system.

In a paper published on the arXiv database at Cornell University Library on 13 April 2017, Songhu Wang of the Department of Astronomy at Yale University, Dong-Hong Wu of the School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics at Nanjing University, Thomas Barclay of the NASA Goddard Space Flight Center, and the University of Maryland, and Gregory Laughlin also of the Department of Astronomy at Yale University describe the results of a study of the TRAPPIST-1 system using data from the Kepler Space Telescope.

The Kepler Space Telescope was launched in March 2009, and was trained on a single area of sky, the Kepler Deep Field until May 2013, when the spacecraft malfunctioned and begun to spin on its axis. This did not however prevent the craft from gathering new data, despite the inability of astronomers to choose the telescope's targets. Between 15 December 2016 and 4 March 2017 the TRAPPIST-1 system fell within Kepler's field of view, enabling the telescope to gather data on this system. 

Wang et al. took the Kepler observation data for the TRAPPIST-1 system and analysed the light curved produced by the system's planets passing in front of the star, in order to produce a new model of the TRAPPIST-1 system.

Based upon this data Wang et al. calculate that the innermost planet, TRAPPIST-1b, has an orbital period of 1.5 days, and orbits the star at an average distance of 0.011 AU, i.e. 1.1% of the distance at which the Earth orbits the Sun. They further calculate that planet has a mass 0.79 times that of the Earth, and a radius 1.086 times that of the Earth. 

The second planet, TRAPPIST-1c, is calculated to have an orbital period of 2.4 days and orbit at an distance of 0.015 AU. This planet is estimated to have a mass 1.63 times that of the Earth, and a radius 1.056 times the Earth's.

The third planet, TRAPPIST-1d, is calculated to have an orbital period of 4.0 days and orbit at an distance of 0.021 AU. This planet is estimated to have a mass 0.33 times that of the Earth, and a radius 0.722 times the Earth's.

 Orbits of the Trappist-1 planetary system. The yellow lines are 1000 planetary orbits drawn randomly from the converged Markov Chain in TTV dynamical ts. The blue points correspond to the location of the planets at the K2 initial epoch 2,457,738.3654. Further photometric transit follow-up is urgently needed to attain a precise understanding of the Trappist-1 system. Wang et al. (2017).

The fourth planet, TRAPPIST-1e, is calculated to have an orbital period of 6.1 days and orbit at an distance of 0.028 AU. This planet is estimated to have a mass 0.24 times that of the Earth, and a radius 0.918 times the Earth's.

The fifth planet, TRAPPIST-1f, is calculated to have an orbital period of 12.4 days and orbit at an distance of 0.045 AU. This planet is estimated to have a mass 0.36 times that of the Earth, and a radius 1.045 times the Earth's.

The sixth planet, TRAPPIST-1f, is calculated to have an orbital period of 6.1 days and orbit at an distance of 0.028 AU. This planet is estimated to have a mass 0.57 times that of the Earth, and a radius 1.127 times the Earth's.

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The Eta Aquarid Meteors.

The Eta Aquarid Meteor Shower will be at a peak on Monday 6 May 2013, with up to 55 meteors per hour at it's peak, radiating from the constellation of Aquarius. This does not spend long above the horizon in the northern hemisphere at this time of year, but potentially could produce good shows before dawn on the 4-6 May, with longer displays in the southern hemisphere.

The radiant point of the Eta Aquarid Meteors. Astronomy Central.

The meteor shower is caused by the Earth passing through the trail of Halley's Comet, where it encounters thousands of tiny dust particles shed from the comet as its icy surface is melted (strictly sublimated) by the heat of the Sun. Halley's Comet only visits the inner Solar System every 75 years (most recently in 1986 and next in 2061), but the trail of particles shed by it forms a constant flow, which the Earth crosses twice each year; in May when it causes the Eta Aquarid Meteor Shower and in October when it causes the Orionids.

Diagram showing the orbit and current path of Halley's Comet relative to the rest of the Solar System. Image created using the JPL Small-Body Database Browser.

See also Connecticut house struck by meteorite, The Lyrid Meteors, Fireball over Wyoming, Fireball over the northeastern United States, and Comet C/2011 L4 (PANSTARRS) to reach its closest point to Earth this week.

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The impossible planets of HU Aquarii.

HU Aquarii is an eclipsing binary system in the constellation of Aquarius, 586.8 light years from Earth. It's principle component (HU Aquarii A) is a White Dwarf stellar remnant with 88% of the sun's mass, a radius of 1% of the sun's and 0.22% of the sun's luminosity, with a surface temperature of 12 500K (compared to 5578K for the sun). This is being orbited by a small Red Dwarf companion (HU Aquarii B) at a distance of 0.0032 AU (0.32% of the distance at which the Earth orbits the Sun, or 0.8% of the distance at which Mercury orbits the Sun), every 2.08 hours. The Red Dwarf companion has a mass 20% of that of the Sun, a radius 22% of the Sun's, 0.52% of the Sun's luminosity and a surface temperature of 3400K. As it orbits the larger star it's outer layer is being stripped of and forming an accretion disk about it. Systems like this are known as cataclysmic binaries.

An artists impression of a Cataclysmic Binary. Dana Berry/Space Telescope Science Institute

In 2011 the discovery of a pair of planets in the HU Aquarii system was announced, based upon perturbations in the orbit of HU Aquarii B; the small star speeds up and slows down as it orbits the larger, which is often indicative of the presence of a planet, or in this model, planets.

In a paper posted on the online arXiv database at Cornell University Library and accepted for publication in the peer-reviewed conference proceedings of the 11th annual Australian Space Science Conference, held in Canberra, September 2011, a team of scientists lead by Jonathan Horner of the Department of Astrophysics and Optics at the School of Physics at the University of New South Wales describe an attempt to build a working computer model of the HU Aquarii system with two planets, based upon the known data.

Horner et al. were unable to build a stable model of the HU Aquarii system based upon the proposed planetary alignments. They then tried a number of other potential planetary alignments, but came to the conclusion that any planetary alignment that could account for the variability in the orbit of HU Aquarii B would be fundamentally unstable. From this they conclude that the irregularity in the orbit of HU Aquarii B is not caused by the influence of a planetary system, but rather by the interactions of the magnetic fields of the two stars as HU Aquarii B is torn apart by its more massive companion. They caution against the assumption that orbital perturbations are always caused by the influence of planets, particularly in extreme or unstable systems such as HU Aquarii.

See also KOI-13b, a big, hot planet not a Brown Dwarf, A new study of XO-2b, a planet in a wide binary star system, Fomalhaut b; not a planet after all? and Exoplanets and Stars on Sciency Thoughts YouTube.