The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 374 2014 April 20
Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/
'GEOLOGICAL CLOCK' HELPS DETERMINE MOON'S AGE
Southwest Research Institute
An international team of planetary scientists thinks that the Moon
formed nearly 100 million years after the Solar System originated. Its conclusion is based on measurements from the interior of the Earth combined with computer simulations of the protoplanetary disc from which the Earth and other terrestrial planets formed. The team simulated the growth of the terrestrial planets (Mercury, Venus, the Earth and Mars) from a disc of thousands of planetary building blocks orbiting the Sun. By analyzing the growth history of Earth-like planets from a lot of simulations, the scientists discovered a relationship between the time the Earth was impacted by a Mars-sized object to create the Moon and the amount of material added to the Earth after that impact. Augmenting the computer simulation with details on the mass of material added to the Earth by accretion after the formation of the Moon suggested a relationship that works much like a clock to date the Moon-forming event, and does not rely on radiometric dating methods. Published literature provided the estimate for the mass accreted by the Earth after the Moon-forming impact. Other scientists previously demonstrated that the abundance in the Earth's mantle of highly siderophile elements, which are atomic elements that prefer to be chemically associated with iron, is directly proportional to the mass accreted after the Moon-forming impact. From such geochemical measurements, the newly proposed clock dates the Moon to 95 +/- 32 million years after the beginning of the Solar System. That agrees with some interpretations of radioactive dating measurements, but not others. DEEP OCEAN DETECTED INSIDE SATURN'S MOON NASA
The Cassini spacecraft and Deep Space Network have uncovered evidence
that Saturn's moon Enceladus harbours a large underground ocean. Researchers theorized the presence of an interior reservoir of liquid water in 2005 when Cassini discovered water vapour and ice spewing from vents near the moon's south pole. The gravity measurements suggest a large, possibly regional, ocean about 10 kilometres deep, beneath an ice shell about 30 to 40 kilometres thick. Cassini has flown near Enceladus 19 times. Three flybys, from 2010 to 2012, yielded precise trajectory measurements. The gravity of a planetary body, such as Enceladus, alters a spacecraft's flight path. Variations in the gravity field, such as those caused by mountains on the surface or differences in underground composition, can be detected as changes in the spacecraft's velocity, measured from the Earth. Changes in velocity as small as 90 microns per second can be detected. With such precision, the flyby data yielded evidence of a zone inside the southern part of the moon with higher density than other portions of the interior.
The south-pole area has a surface depression that causes a dip in the
local gravity. However, the magnitude of the dip is less than expected from the size of the depression, leading researchers to conclude that the depression's effect is partially offset by denser material at depth that compensates for the missing volume -- very likely liquid water, which is 7% denser than ice. The magnitude of the anomaly indicates the size of the water reservoir. There is no certainty that the sub-surface ocean supplies the water plume spraying out of surface fractures near the south pole of Enceladus, but it is a real possibility. The fractures may lead down to a part of the moon that is tidally heated by the moon's repeated flexing, as it follows its eccentric orbit around Saturn. POSSIBLE EXO-MOON NASA/Jet Propulsion Laboratory
Are there moons orbiting planets beyond our Sun? Researchers have
observed the first signs of an 'exo-moon', though they say that it is impossible to confirm its presence. The discovery was made by watching a chance encounter of objects in our galaxy, which can be witnessed only once. The technique, called gravitational micro-lensing, takes advantage of chance alignments between stars. When a foreground star passes between us and a more distant star, the closer one can act like a magnifying glass to focus and brighten the light of the more distant one. Such brightening events usually last about a month. If the foreground star -- or what astronomers refer to as the lens -- has a planet, the planet will act as a second lens. By observing such events, astronomers can estimate the mass of the foreground star relative to its planet.
In some cases, however, the foreground object could be a free-floating
planet, not a star. Researchers might then be able to measure the mass of the planet relative to its orbiting companion (a moon). While astronomers are actively looking for exo-moons -- for example, in data from the Kepler mission -- so far, they have not found any. In the new study, the nature of the lensing object is not clear. The mass ratio of the larger body to the smaller one is 2,000 to 1. That means the pair could be either a small, faint star circled by a planet about 18 times the mass of the Earth -- or a planet more massive than Jupiter coupled with a moon with a mass less than the Earth's. The problem is that astronomers have no way of telling which of those models is correct, without knowing the distance to the object. In the future it may be possible to obtain such distance measurements during lensing events by observations with the Spitzer and Kepler space telescopes, which are far enough away from the Earth to be be used to meassure parallaxes.
Meanwhile, surveys like MOA and OGLE are turning up more and more
planets. Those micro-lensing surveys have discovered dozens of exo- planets so far, in orbit around stars and free-floating. A previous study led by the MOA team was the first to find strong evidence for planets the size of Jupiter roaming alone in space, presumably after they were ejected from planetary systems in course of formation. MONSTER CLUSTER OF GALAXIES Space Telescope Science Institute
The Hubble telescope has found the mass of the largest known galaxy
cluster in the distant Universe. By measuring how much the gravity from the cluster's mass warps images of far-more-distant background galaxies, a team of astronomers has asserted the cluster's mass to be as much as 3 times 10 to the power 15 times the mass of the Sun. A fraction of that mass is in several hundred galaxies that constitute the cluster, and a larger part is in hot gas that fills the entire volume of the cluster; the rest is 'dark matter' of indeterminate character. Though massive clusters, such as the so-called Bullet Cluster, are found in the nearby Universe, nothing like that has previously been seen to exist so far back in time, when the Universe was roughly half of its current age. The unusual size of the cluster was first reported in 2012. Astronomers estimated its huge mass on the basis of observations from the Chandra X-ray observatory and galaxy velocities measured by the VLT in Chile. The estimates are based on the motions of the galaxies in the cluster and the very high temperature of the hot gas between the cluster galaxies. HUBBLE MEASURES DISTANCES TO STARS UP TO 10,000 LIGHT-YEARS AWAY NASA/Goddard Space Flight Cente
Using the Hubble telescope, astronomers can now measure the distances
of stars up to 10,000 light-years away -- ten times further than previously possible. They have developed a technique called spatial scanning, which dramatically improves Hubble's accuracy for making angular measurements. The technique extends the parallax method for finding distances by a factor of ten. It has been successfully used to measure the distances of Cepheid variables approximately 7,500 light-years away in the constellation Auriga. Such measurements will be used to provide a firmer footing for the so-called cosmic distance ladder. The ladder's 'bottom rung' relies on measurements to Cepheids that, because of their known absolute magnitudes, have long been used to find distances. They are the first step in calibrating more distant extra-galactic markers such as Type Ia supernovae. Astronomers have developed a technique to use Hubble to make angular measurements with errors as small as 20 millionths of a second or arc. To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when the Earth was on opposite sides of the Sun. A very small shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide-Field Camera 3. A third exposure was taken after another six months to allow the team to account for the effects of the space motion of the star, with additional exposures used to reduce other sources of error.
Bulletin compiled by Clive Down
(c) 2014 the Society for Popular Astronomy
|
Good Clear Skies
--
Astrocomet
--
Colin James Watling
--
Astrocomet
--
Colin James Watling
--
Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
--
--
Profile: http://www.google.com/profiles/astrocomera
--
--
Lyra Website: https://sites.google.com/site/lyrasociety/
--
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
--
Information
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
--
Information
No comments:
Post a Comment