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December 2013: Stormy

December 2013

In the show this time, we talk to Dr Erminia Calabrese about the ACT, Stuart rounds up the latest news and we find out what we can see in the December night sky from Ian Morison and John Field.

The News

This month in the news, the truth about the Chelyabinsk asteroid and NASA's latest journey to Mars.

Asteroids that enter the Earth's atmosphere are notoriously hard objects to study because usually they will arrive unannounced and are visible for only a brief time before either exploding in the atmosphere or impacting the ground. In fact in recent years two of the larger asteroids that exploded in the atmosphere went largely unstudied because the only information which was available came from satellites or distant infrasonic sound stations. Even meteorites that impact the Earth, like the one at Sutton Hill, California, in 2012, can only give a partial picture of the life of an asteroid because we are limited to only studying the chemical composition of the surviving fragments. Such information can be used to imply the origins of a meteorite but without direct observations of the asteroid entering the atmosphere it is impossible to deduce its original trajectory or even original size. So when earlier this year in February an asteroid exploded above the Russian Urals, in skies over the city of Chelyabinsk, and the event was recorded by thousands of cameras on car dashes or on the sides of buildings, scientists had access to an unprecedented wealth of information to investigate the asteroid.

Scientists have now reconstructed the full story of the Chelyabinsk asteroid and last month published the conclusions to their studies in both the journals Science and Nature. By calculating the speed of the of the asteroid, which was measured to be moving at about 50 times the speed of sound upon entering the upper atmosphere, and the brightness of the final detonation, which was briefly brighter than the Sun, they have found that the asteroid had a mass of 12,000 metric tons and was about 19 meters in diameter, or about the size of a house. When it exploded at about 35 Km from the ground, nearly all of this mass was vapourised into dust and gas with the surviving recovered fragments weighing in at a total of less than 800 kg. The largest surviving fragment smashed into the frozen sheets of Lake Chebarkul, 60 Km South-West of Chelyabinsk, and its recovery was mostly thanks to a nearby security camera catching the moment of impact.

All this information about the Chelyabinsk asteroid has revealed one new important finding. By modelling the asteroids entrance into the upper atmosphere we have been able to retrace the trajectory of the asteroid by thousands of years and have found that the asteroid originated from the asteroid belt between Mars and Jupiter. More interestingly though they have found that there is a clear link between the orbit of the Chelyabinsk asteroid and the orbit of a much larger 2.2 Km asteroid which was found in 1999 called 86039. For several millennia both asteroids have shared intersection points at both their closest and furthest approaches to the Sun, the chance of this occurring at random is remote. This implies that perhaps at some point in the past the Chelyabinsk and 86039 asteroids may have been the same object and that the Chelyabinsk asteroid could have been formed by a chance collision between 86039 and some other piece of solar system debris. Using the model of the orbit for the Chelyabinsk asteroid it was possible to deduce how much energy would be required in a collision with 86039 to send a fragment as large as the one above Chelyabinsk on a course towards Earth. The scientists found that it would only require a relatively small push when 86039 was at the periapse of it orbit to produce the Chelyabinsk asteroid. The most important idea to take from all this is that we are now able to confirm the sort of materials that are present in the asteroids that make up the asteroid belt because we now have both the chemical structure of the asteroid, from the meteor in Lake Chebarkul, and the confirmed origin from the videos that captured the asteroids descent through the atmosphere. Since it is thought that the asteroids in the asteroid belt have remained largely unchanged in their properties since the birth solar system knowing exactly what materials lie within the belt help us constrain theories that allow us to deduce the origins of planets like the Earth.

Also in the news last month on Monday the 18th, at about half past six Greenwich Mean Time, the Martian Atmosphere and Volatile Evolution satellite known as MAVEN was launched from Cape Canaveral on board an Atlas V rocket. The primary goal of MAVEN is to measure volatile gases in the Martian atmosphere, such as water, carbon dioxide or nitrogen, and determine the processes involved in Mars losing its atmosphere over the course of the planets long history.

When MAVEN reaches Mars it will enter an elliptical orbit with a period of four and a half hours where it will stay for the year long duration of the mission. MAVEN's orbit will take it both close enough to Mars to experience drag from the atmosphere and far enough away to be able to take images of the entire Martian surface. Over the course of the MAVEN's year long mission it will be utilising its several on board instruments to conduct its investigations of Mars. The primary instrument is the Imaging Ultraviolet Spectrograph, usually referred to by its anagram IUVS, which will be used to map out the different quantities of various volatile molecules within the Martian atmosphere by measuring the unique frequencies of light they emit. However the focus for IUVS will different at each stage of MAVEN's orbit. At the furthest point from Mars, the apoapsis, it will be measuring the overall levels of the molecules in the Martian atmosphere and then as it approaches Mars again and reaches its the nearest point, the periapsis, the instrument is turned to point straight down and measure local variations in the quantities of the molecular construction of the atmosphere. The second instrument is called the Neutral Gas and Ion Spectrometer, or NGIMS, which deals with measuring more stable elements that tend not to form molecules, such as Helium and Argon. NGIMS is not a camera like the IUVS instrument and requires direct contact with the atmosphere to be able to measure its contents, therefore requiring MAVEN to dip down to just 80 Km above the martian surface where the atmosphere becomes ten times denser and NGIMS can start taking atmospheric samples. This maneuver will be done several times over the course of MAVEN's life and the short periods MAVEN spends at these low altitudes will be the most precarious of the entire mission, after the launch on the 18th of last month.The final instrument on board MAVEN is known as the particles and fields package, and is in itself a slew of different tools and instruments. The aim of the particles and fields package is to constantly keep track of the effects of the Sun, how strong the solar winds are and constantly measuring the highly variable and weak Martian magnetic field.

MAVEN's goal, as stated earlier, is to track Mars' atmospheric decay at the present time. It will do this by measuring what is there now from the ultraviolet emission using IUVS and physically using NGIMS. Then by keeping track of how the atmosphere changes over the course of the year long mission, and especially how it changes in relation to solar activity, it is hoped that MAVEN will uncover some of the unknowns about Mars' atmospheric past. For how quickly did Mars lose its atmosphere when the magnetic field stop protecting Mars from the powerful solar winds? Or what sort of atmosphere we could expect to find on Mars when it was young, with oceans and continents and whether or not it was ever like our own planet.

Interview with Erminia Calabrese

We talk to Dr, Erminia Calabrese about detecting the cosmic microwave background(CMB) with the Atacama Cosmology Telescope (ACT). She tells us the importance of ACT in constraining cosmology. We also learn about the weird and wonderful extensions to the standard model that experiments like ACT can test. We then go on to discuss the future of ACT.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during December 2013.

Pegasus and Andromeda are setting towards the west after nightfall, and you can find the galaxies M31 and, given a dark sky, M33, in this part of the heavens. Aries and Taurus are over to the east, the latter containing the Pleiades and Hyades star clusters. The red star Aldebaran appears to be within the Hyades, but is actually closer to us. Orion rises a little later, and you can follow the three stars of his Belt down to the brightest night-time star, Sirius, in Canis Major. Beneath the Belt is the fuzzy glow of the Orion Nebula, a stellar nursery which is a rewarding sight in binoculars. Gemini, the constellation of the Twins, is nearby. High overhead are Cassiopeia and Perseus, with the picturesque Double Cluster between them.

The Planets

Highlights

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2013.

The evening sky is dominated in the north by the constellations of Taurus, Orion, Canis Major and Canis Minor. The Milky Way stretches through them and along the southern horizon, its pattern of light and dark regions dimmer than in the winter, but still impressive. It comprises many distant stars in our galaxy, combined with patches of obscuring dust. M42, the Orion Nebula, appears as a bright cloud within Orion the Hunter. Upside-down in the southern hemisphere, Orion is sometimes called the Cooking Pot, his Belt of three blue giant stars marking its base. Orion's Sword, containing M42, is one of the Pot's sides. The nebula is part of a large cloud of interstellar material, and a telescope reveals patterns, while photographs show different colours. Beneath the Pot is Betelgeuse, a red giant star which forms one of Orion's shoulders, while above is the blue-white giant Rigel, one of his feet. Rigel has a companion star that can be seen in medium-sized telescopes. The upside-down V-shape of Taurus is to the west of Orion, forming the head of Taurus the Bull. The bright star Aldebaran marks the Bull's eye, while the more distant Hyades Cluster is part of the head. The Bull's back is marked, a little further west, by the Pleiades Cluster, which to Māori are known as Matariki, or the Little Eyes. At least seven stars of the Pleiades can be seen by eye on a dark night, and binoculars reveal many more.

Crux is low in the south-east in the evening, with the dark Coalsack Nebula beside it. The darkness is caused by clouds of material which may one day collapse under gravity and form stars. The Large and Small Magellanic Clouds (LMC and SMC) appear as bright clouds in the southern hemisphere sky, and are satellite galaxies of the Milky Way. The LMC is near to the bright star Canopus in the south-east, and binoculars or a small telescope can be used to find many star clusters and nebulae within it. The SMC is not far away and is close to the globular cluster 47 Tucanae, which looks like a hazy star to the unaided eye but can be seen to be a round group of stars through binoculars. NGC 362 is another nearby globular cluster, but a telescope is needed to observe it well.

Highlights

Odds and Ends

Scientists have come closer to understanding why Jupiter's Great Red Spot is still going strong.The spot, visible through a small telescope, is in fact a giant storm of gas almost twice the size of the Earth. Up till now, it has not been clear why the Great Red Spot hasn't simply blown itself out - but scientists have described a new fluid dynamic model for the spot that could explain where it gets the energy to sustain itself from.

The IceCube neutrino telescope, located at the South Pole, has detected 28 incredibly high energy neutrinos. Such high energy neutrinos can only have been created outside of the vicinity of the Earth, most likely of extra-galactic origin. This means that these nearly massless particles which only very weakly interact with other matter have travelled vast distances before being detected on Earth. The ICEcube experiment uses detectors in embedded 1.5 to 2 kilometers below the surface in the Antarctic ice to capture the flashes of light neutrinos make when they do interact with matter.

Finding such high energy neutrinos of intergalactic origin seems to be opening up a new field of astronomy using fundamental particles other than the photon.

Comet Ison, dubbed by some as the "comet of the century" is due to pass close to the sun on the 28th November. If it doesn't get destroyed as it passes the sun, it should brighten and be spectacular in the night sky from the 3rd of December. STEREO has also made a movie of observations taken over two days of the comet.

Show Credits

News:Stuart Harper
Interview:Chris Wallis and Erminia Calabrese
Night sky:Ian Morison and John Field
Presenters:Adam Avison, Indy Leclercq and Christina Smith
Editors:Indy Leclercq, Francesca Lucini and Mark Purver
Segment Voice:Mike Peel
Website:Indy Leclercq and Stuart Lowe
Producer:Indy Leclercq
Cover art:The Southern Lights, or Aurora Australis, seen above the IceCube Lab at the South Pole. CREDIT: Sven Lindstrom/NSF

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