Earth usually has more than one moon, according to a team of astronomers from the University of Helsinki, the Paris Observatory and the University of Hawaii at Manoa.
Our 2,000-mile-diameter Moon, so beloved by poets, artists and romantics, has been orbiting Earth for over 4 billion years. Its much smaller cousins, dubbed “minimoons,” are thought to be only a few feet across and to usually orbit our planet for less than a year before resuming their previous lives as asteroids orbiting the Sun.
Mikael Granvik (formerly at UH Manoa and now at Helsinki), Jeremie Vaubaillon (Paris Observatory) and Robert Jedicke (UH Manoa) calculated the probability that at any given time Earth has more than one moon. They used a supercomputer to simulate the passage of 10 million asteroids past Earth. They then tracked the trajectories of the 18,000 objects that were captured by Earth’s gravity.
They concluded that at any given time there should be at least one asteroid with a diameter of at least one meter orbiting Earth. Of course, there may also be many smaller objects orbiting Earth, too.
Over two decades in orbit, the Hubble Space Telescope has made a huge number of observations. Every week, we publish new images on the ESA/Hubble website.
But hidden in Hubble’s huge data archives are still some truly breathtaking images that have never been seen in public. We call them Hubble’s Hidden Treasures — and we’re looking for your help to bring them to light.
We’re inviting the public into Hubble’s vast science archive to dig out the best unseen Hubble images. Find a great dataset in the Hubble Legacy Archive, adjust the contrast and colours using the simple online tools and submit to our Hubble’s Hidden Treasures Contest Flickr group, and you could win an iPod Touch in our Hubble’s Hidden Treasures Competition.
The traditional picture of comets as cold, icy, unchanging bodies throughout their history is being reappraised in the light of analyses of dust grains from Comet Wild2. A team led by the University of Leicester has detected the presence of iron in a dust grain, evidence of space weathering that could explain the rusty reddish colour of Wild2’s outer surface. The results were presented by Dr John Bridges at the National Astronomy Meeting in Manchester on Tuesday 27th March.
The Wild2 grains were collected by the NASA Stardust mission and returned to Earth in 2006. The fast-moving dust grains were collected in arrays of aerogel, a silicon-based foam that is 99 per cent empty space, which slowed the particles from velocities of 6 kilometres a second to a halt over just a few millimetres. Since then, an international team of scientists has been analysing the samples and the carrot-shaped tracks that they left in the aerogel. Microscopic samples dissected from the grains have been analysed at facilities around the UK, and in particular this work was performed at the Diamond Light Source synchrotron in Oxfordshire and Leicester University. Through a range of analytical techniques, scientists in the UK have been able to fully analyse the mineralogy and isotopes of the samples.
Since the NASA / ESA Cassini-Huygens spacecraft arrived at Saturn in 2004, astronomers and space scientists have been able to study the ringed planet and its moons in great detail. Now, for the first time, a team of planetary scientists have made simultaneous measurements of Saturn’s nightside aurora, magnetic field, and associated charged particles. Together the fields and particle data provide information on the electric currents flowing that produce the emissions. Team leader Dr Emma Bunce of the University of Leicester will present the new work at the National Astronomy Meeting in Manchester on 27 March 2012.
Generally, images of the aurora (equivalent to the terrestrial ‘northern lights’) provide valuable information about the electromagnetic connection between the solar wind, the planet’s magnetic field (magnetosphere) and its upper atmosphere. Variations in the aurora then provide information on changes in the associated magnetosphere. But viewing the aurora (best done at a large distance) at the same time as measuring the magnetic field and charged particles at high latitudes (where the aurora is found, best done close to the planet) is hard
In 2009, Cassini made a crossing of the magnetic field tubes that connect to the aurora on the night side of Saturn. Because of the position of the spacecraft, Dr Bunce and her team were able to obtain ultraviolet images of the aurora (which manifests itself as a complete oval around each pole of the planet) at the same time.
A study of galaxies in the deepest far-infrared image of the sky, obtained by the Herschel Space Observatory, highlights the two contrasting ways that stars formed in galaxies up to 12 billion years ago. Dr Georgios Magdis will present the results at the National Astronomy Meeting in Manchester.
Recent results from Herschel show that gas-rich galaxies in the early universe were able to create stars at an intense rate. In the nearby universe, we only see such high rates of star formation when galaxies collide. However, the Herschel data shows that while star-formation in some galaxies in the early universe were triggered by mergers, the majority of star forming galaxies were not undergoing interactions. The formation was driven by the amount of gas present.
Magdis and his colleagues have now carried out a detailed study of an example of a normal and a merging galaxy observed as part of the Great Observatories Origins Deep Survey (GOODS) Herschel programme. GOODS Herschel is led by David Elbaz of CEA/Saclay, France.
Researchers at the Nottingham Trent University have gathered new evidence that a 4000-year-old monolith was aligned to be an astronomical marker. The 2.2 metre high monument, located in the Peak District National Park, has a striking, right-angled triangular shape that slants up towards geographic south. The orientation and inclination of the slope is aligned to the altitude of the Sun at mid-summer. The researchers believe that the monolith was set in place to give symbolic meaning to the location through the changing seasonal illuminations. Dr Daniel Brown will present the findings on Tuesday 27th March at the National Astronomy Meeting in Manchester.
The rare example of a monolith is located at Gardom’s Edge, a striking millstone grit ridge less than an hour’s drive from Manchester. The researchers have carried out a microtopography survey of the surface surrounding the monolith. Their findings indicate the presence of packing stones around the base of the monolith, evidence that it was placed carefully in position. They have also carried out 3-D modelling of illumination of the stone through the seasons, adapting for changes in the Earth’s tilt to the ecliptic plane over four millennia.
The dramatic appearance of Halley’s comet in the night sky has been observed and recorded by astronomers since 240 BC. Now a study shows that the orbital influences of Jupiter on the comet and the debris it leaves in its wake are responsible for periodic outbursts of activity in the Orionid meteor showers. The results will be presented by Aswin Sekhar at the National Astronomy Meeting in Manchester on Tuesday 27th March.
Halley’s comet orbits the Sun every 75-76 years on average. As its nucleus approaches the Sun, it heats up and releases gas and dust that form the spectacular tail. This outgassing leaves a trail of debris around the orbit.
When the Earth crosses Halley’s path – twice per orbit – dust particles (meteoroids) burn up in the Earth’s atmosphere and we see meteor showers: the Orionids in October and the Eta Aquariids in May. Previous research has suggested that Orionid meteoroids have at times fallen into ‘resonances’ with Jupiter’s orbit – a numerical relationship that influences orbital behaviour. Sekhar’s new study suggests that Halley itself has been in resonances with Jupiter in the past, which in turn would increase the chances of populating resonant meteoroids in the stream. The particles ejected during those times experience a tendency to clump together due to periodic effects from Jupiter.