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
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.
- Jupiter rises around 19:30 UT (Universal Time) at the beginning of the month, reaching its highest elevation of 62° when due south at about 03:00. It shines at magnitude -2.6 and has a disc spanning 42", making this a great time to observe it. It lies in Gemini and, in the 10th, passes just 15' from the star Wasat, which has a magnitude of +3.5. It is at its nightly highest point around midnight by the end of December, and you can see its equatorial bands and larger moons, as well as the Great Red Spot at certain times.
- Saturn is a pre-dawn object, rising around 05:00 UT as the month begins, and 03:30 at its end. With a magnitude of +0.6 and a disc 15.5" across, it now shows its rings at 20° to our line of sight, allowing them to be easily observed through a telescope. It reaches only about 20° above the horizon, however.
- Mars has moved from Leo into Virgo and rises soon after midnight early in the month, with a magnitude of +1.2 and an angular size of 5.6". During December, it brightens to magnitude +0.9 and grows to 6.8" in size, allowing surface features such as the polar caps and Syrtis Major to be seen. Towards the end of the month, it approaches the star Porrima.
- Mercury shines at magnitude +0.6 in the pre-dawn sky as December begins, appearing below Saturn. It brightens to magnitude -0.8 by mid-month, but gets progressively lower at dawn and becomes lost in the Sun's glare around the same time. It reaches superior conjunction (behind the Sun in the sky) on the 29th.
- Venus is spectacular, starting December at magnitude -4.9. Although only 15° above the horizon at sunset, it can be observed at a higher elevation for at least an hour before that. It changes significantly during the first three weeks of December, its illuminated fraction decreasing from 30 to 11% even as its angular diameter grows from 38 to 53". It is just 4% illuminated by month's end, but the slender crescent is almost 60" across. By making these observations, you can follow in the footsteps of Galileo, to whom the changing phase of Venus revealed that it must be in orbit around the Sun and not the Earth. The planet will pass in front of the Sun (inferior conjunction) on the 11th of January.
- Comet ISON passed close to the Sun on the 28th of November, before recording of the current Jodcast episode. The progress of its brightness this month remains unpredictable. Despite initial reports of its demise, parts of the comet survived and the tail may yet become visible to the naked eye during early December, below a thin crescent Moon and the planets Saturn and Mercury. It will reach higher in the sky at daybreak as the month goes on, becoming visible before twilight in mid-December. Although its brightness is then expected to decline, it may be seen 5° to the west of the globular cluster M13, in Hercules, on the 22nd. It becomes circumpolar towards the end of the month, lying in the vicinity of Ursa Major.
- The Moon occults the star Epsilon Piscium at about 22:05 UT on the 11th (commencing at 22:07 from Edinburgh and 22:16 from London, for example). The star, shining at magnitude +4.3 in the constellation of Pisces, is at 30° elevation in the south when the waxing gibbous Moon passes in front of it. It will be seen to vanish as the dark limb of the Moon obscures it, emerging less dramatically from the bright side about 13 minutes later.
- The Geminid meteor shower can be observed after midnight around the 14th and 15th, with the radiant (from where the meteors appear to come) near the bright star Castor in Gemini. The gibbous Moon in Aries hinders the view, but after it sets, around 05:00 UT, there should be an hour of darkness in which to spot the meteors. These shooting stars are produced by dust shed from the asteroid 3200 Phaethon, whereas most showers are cometary in origin.
- The Ursid meteor shower is visible after midnight on the 22nd and 23rd, with its radiant not far from the bright star Kochab in Ursa Minor. A gibbous Moon is again present, but poses less of a problem as it is far from the radiant in the sky.
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.
- The annual Phoenicid meteor shower reaches its peak on the 6th. The meteors seem to come from a point called the radiant, which is in the constellation of Phoenix for this shower, near to the bright star Achernar. It is high overhead, well placed for observing.
- The Geminid meteor shower peaks on the 14th. The radiant, near to the star Castor in Gemini, rises at about 03:00 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time), and its low elevation means that only half the meteors are visible. The Moon, becoming full on the 17th, hampers viewing, but the shower is worth seeing a week either side of the peak, and so the beginning of the month may be a good time to observe without the Moon's glare.
- The planet Jupiter also sits in Gemini this month, its larger moons visible through binoculars. It appears as a brilliant white star to the naked eye.
- The summer solstice occurs in the southern hemisphere this month, with the longest day coming on the 21st. The Sun is currently at a peak of activity, with many sunspots visible - but only look at them via a projection or through a dedicated solar telescope, as other methods may damage your eyesight.
- Comet ISON has now left southern hemisphere skies, but brightened to naked eye visibility last month before doing so. It is still visible to those at low southern latitudes early this month.
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.
|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|
|Cover art:||The Southern Lights, or Aurora Australis, seen above the IceCube Lab at the South Pole. CREDIT: Sven Lindstrom/NSF|