In the show this time, we talk to Professor Elisa Resconi about detecting neutrinos with IceCube, Ian Harrison rounds up the latest news and we find out what we can see in the December night sky from Ian Morison and Claire Bretherton.
In the news this month: a comet landing, dodging black holes and dust-free comets.
ESA's Rosetta mission, launched in 2004, rendez-voused with comet 67P/Churyumov-Gerasimenko in August this year. Carried on board Rosetta is the robotic lander Philae, weighing in at 100 kg. On November 12th, Philae became the first man-made object to do a 'soft' touch-down on the surface of a comet nucleus.
It was planned that Philae would use a cold gas thuster to push the robot lander into the surface upon landing, but this system could not be initiated prior to separation. The lander was also equipped with harpoons and screws which would assist the robot in landing on the comet. However, the harpoons did not fire, and the lander bounced twice (since recording, ESA has announced that the lander may have also grazed a crator rim) before coming to rest in its final place on the surface of the comet, about a kilometer from its intended landing site. After successfully landing on the comet, Philae sent out a message to Earth, via Rosetta, which was picked up after the 28 light-minute delay to the delight of mission scientists.
The lander is equipped with a total of ten instruments which were designed to carry out experiments ranging from photographing the surface to analysing the composition and structure of the comet in a variety of ways. Although the lander is equipped with a number of solar panels which the scientists and engineers hoped would power the lander, the on-board experiments were planned for the worst-case scenario where they would only be able to operate for as long as its battery allowed: approximately 60 hours.
As it turns out, the lander came to rest in the shadow of a cliff which did not allow the Solar panels sufficient sunlight to keep the lander charged. As the battery reserves ran low, the lander was instructed to rotate itself and change its angle by 35 degrees in the hope that more light would be cast on its Solar panels in that position once the comet draws closer to the Sun. After 64 hours of data collection, the lander was put into hibernation, with the possibility of re-awakening if the batteries are successfully recharged later in the comet's orbit.
In those 64 hours, every instrument was used and data collected, including a drill that was instructed to dig 25cm into the comet, take samples and analyse them. The data was transmitted back to Earth via the Rosetta Satellite before the lander was put into hibernation. This data is already changing our understanding of comets. The first panoramic pictures showed a rough, debris-strewn landscape, the Multi-purpose Sensors for Surface and Sub-Surface Science found a hard layer of ice about 10-20 cm underneath the initial dusty top layer and the Cometary Sampling and Composition experiment has detected organic molecules on the surface of the comet. It has also been speculated that some of the experiments, such as the Rosetta Magnetometer and Plasma Monitor which will examine the magnetic field of the comet, may have benefited from the lander's bumpy landing.
The success of this historic mission and the subsequent data collection will have a huge impact on the field, which we will only truly see once the data from all the experiments has been analysed.
A team of astronomers, led by Prof. Andrea Ghez of UCLA, used the W. M. Keck Observatory to observe a dusty object on a close approach with the supermassive black hole at the centre of the Milky Way. The object, designated G2, was first identified in 2011 and was found to be on a path which would take it as close as only 3000 times the distance of the event horizon of the black hole, the boundary at which not even light can escape the black hole's gravitational pull.
Initially, the object was thought to be a dusty gas cloud with a mass 3 times that of the Earth. If that were the case, then G2 would have been torn apart as it approached the supermassive black hole. However, as Ghez and her team showed, G2 not only survived but was unaffected by the black hole and has subsequently continued its journey.
Instead of being a dusty gas cloud, Ghez and her team believe that G2 is actually a binary system that merged to form a single star under the influence of the black hole. This star would be surrounded by a large amount of gas and dust, as G2 is. The team also speculates that G2 is not the only object like this and many more may be found in the vicinity of supermassive black holes.
The discovery of two objects in comet-like orbits was announced this month by a team at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society in Tucson, Arizona. What makes these objects unusual is their distinct lack of dust. When a comet's orbit takes it close enough to the Sun, the surface begins to evaporate and a bright tail of gas and dust is formed. However, observations of these two objects only hinted at the existence of very faint tails. Inactive Oort cloud objects had been hypothesised but never seen before.
The object designated C/2013 P2 Pan-STARRS was the first to be discovered. As follow-up observations of its surface were being carried out with the Gemini North Telescope, a second dust-free comet-like object designated C/2014 S3 Pan-STARRS, was discovered and follow-up observations to examine the object's colour were made using the Canada-France-Hawaii Telescope (CFHT) on Mauna kea.
The surface of the first object, C/2013 P2, was shown to be very red and more like that of an ultra-red Kuiper belt object than the surfaces of comets or asteroids. The second, C/2014 S3, has a more blue colour, making it much more like inner Solar System asteroids than outer Solar System objects.
Further work is ongoing to better understand these objects, their origin and how they fit into theories of Solar System formation.
Interview with Prof. Elisa Resconi
Professor Elisa Resconi studies ghostly particles called neutrinos at the Technical University of Munich, using the IceCube detector at the South Pole. She talks about research at the boundary of particle physics and astrophysics, and discusses the mystery of the ultra-high-energy neutrinos that seem to originate far out in the Universe. She describes the instrument, which comprises a cubic kilometre of very pure ice and detectors that pick up Cherenkov radiation, and she talks about the known types of neutrino and the possibility of a sterile neutrino that could constitute dark matter. Prof. Resconi also tells us about the scientists, engineers and doctors who spend winters in Antarctica, operating IceCube while physically isolated from the rest of the world.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during December 2014.
During the later evening, the Great Square of Pegasus is setting towards the west, with the constellation of Andromeda above and to its left. The W-shape of Cassiopeia is higher still, with Perseus just below and the Perseus Double Cluster between them. Below Perseus is Auriga, containing the bright star Capella, while Orion the Hunter is rising in the south-east. The three stars of Orion's Belt point down to Sirius, the brightest night-time star. Taurus the Bull is between Orion and Perseus, hosting the open clusters of the Pleiades and Hyades, as well as the red star Aldebaran, which appears to be part of the Hyades but is actually just lying along the same line of sight from Earth. Gemini is to the left of Orion, with the stars of Castor and Pollux representing the Twins. Rising later are Cancer, home to the Beehive Cluster, and Leo, the current residence of the planet Jupiter.
- Jupiter rises around 22:00 UT (Universal Time) at the beginning of the month, shining at magnitude -2.2 and positioned some 10° up and right of the star Regulus in Leo. It closes to 7° from Regulus on the 9th, and then begins retrograde (westward) motion across the sky. Jupiter rises around 20:00 by month's end, and has a magnitude of -2.4. It reaches a maximum elevation of 53° when due south, which is at about 05:00 at the start of December and two hours earlier at the end. Its disc grows from 40 to 43" during the month, making surface features visible in a telescope.
- Saturn passed behind the Sun last month, and rises an hour before the Sun at the beginning of December and three hours before it at the end. It is in Libra, above the star Antares in Scorpius, with a magnitude of +0.5. As it rises in the south-east, its ring system is visible through a telescope as it is now angled at 24° to our line of sight.
- Mercury passes in front of the Sun on the 8th, rendering it invisible until the very end of the month, when it may just be spotted low in the south-west after sunset. It is then 3.5° to the lower right of Venus, and binoculars may be needed to see it at magnitude -0.8.
- Mars moves from Sagittarius into Capricornus on the 4th. It dims from magnitude +1 to +1.1 during the month, and shrinks from 5.1 to 4.8". It is low in the south-west for around three hours after sunset, its elevation and apparent size making surface details very difficult to see.
- Venus is now an evening object, setting shortly after the Sun at the start of the month and just over an hour afterwards at the end. Shining at magnitude -3.9, it should be easily visible in the south-west in late December, but low elevation and small angular size of around 10" will make its disc appear fuzzy through the Earth's atmosphere - a spectrum of colours may even be seen as it twinkles.
- Jupiter is impressive this month, as it will be for the next few.
- Mars lies just 0.3° from the globular cluster M75 on the evening of the 3rd, and is still less than a degree away the following night.
- The Geminid meteor shower is best seen after midnight UT on the 14th and 15th. The radiant, from which the meteors appear to originate, is in the constellation of Gemini, but a third-quarter Moon will wash out fainter meteors. Unusually, the dust that produces the Geminids comes from an asteroid rather than a comet.
- The Ursid meteor shower peaks around midnight UT on the night of the 22nd-23rd, with its radiant near to the star Kochab in the constellation of Ursa Minor. There may be around 10 meteors per hour, but, by coinciding with new Moon, the shower is easier to spot than in other years.
- The Alpine Valley is a nice lunar feature to observe on the 13th and 29th this month, when it is close to the shadow-line (terminator) separating the Moon's day and night sides. A cleft in the Apennine Mountain chain, it is 7 miles wide and 79 miles long and has a thin rill running along it. The craters Plato and Copernicus become visible over the two nights following the Alpine Valley's appearance.
- Ian highlights two pieces of freely available software that are good for making star trail images during the long nights this month: the image-stacking programme StarStaX and the photo-editing software Adobe Photoshop CS2.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2014.
The nights are at their shortest on the 22nd and the night sky is dominated by the constellations of Taurus, Orion, Canis Major and Canis Minor. In Greek mythology, Orion the Hunter is the enemy of Scorpius the Scorpion, and so the two appear on opposite sides of the sky. The figure of Orion appears upside-down to southern hemisphere observers. The line of three stars forming his Belt are historically known in Aotearoa (New Zealand) as Tautoru, and his Sword and Belt together are sometimes seen as a pot or saucepan. Prominent in the middle of the Sword is the Orion Nebula, M42, a star formation region that looks like a fuzzy star to the naked eye but a beautiful region of nebulosity and young stars in a telescope or binoculars. At its heart is the Trapezium Cluster, a tight group of stars whose ulraviolet radiation makes the surrounding gas glow. The reflection nebula M78 can also be found in Orion using a small telescope, and the Horsehead Nebula, a dark region in the bright nebula of IC 434, lies south of the star Alnitak in Orion's Belt. The blue-white supergiant Rigel, at the top-left, is the brightest star in Orion, while the aging red giant Betelgeuse, at the bottom-right, is the second-brightest.
Following Orion's Belt to the right leads to Sirius, known to Māori as Takurua, which is the brightest star in the night sky. It is in Canis Major, the larger of Orion's two Hunting Dogs, and Canis Minor, the Smaller Dog is lower down, near the eastern horizon in the later evening. The brightest star in Canis Minor is Procyon, which is actually a binary system consisting of a main-sequence star and a white dwarf companion. To the left of Orion's Belt is the V-shape of stars representing the head and horns of Taurus the Bull. The Hyades Cluster resides here, and is one of the closest open star clusters to the Earth. Continuing around the sky, the Pleiades Cluster is another open cluster full of young, blue stars. In New Zealand it is called Matariki, meaning Little Eyes or Eyes of God, and its first pre-dawn appearance in June marks the start of the Māori year. The Milky Way stretches through these constellations and along the southern horizon, and along this line is the constellation Crux, currently low in the south-east later in the night. Beside it is the dark Coalsack Nebula, an interstellar cloud of gas and dust that obscures the stars beyond. To Māori it is Te Pātiki, the Flounder.
- Mars is fairly high in the west after sunset, and this month Venus joins it, setting in the west-south-west about an hour after the Sun.
- Mercury appears late in the month, just below and left of Venus. Bright, golden Jupiter rises just after 01:00 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time) at the beginning of the month, and is up before midnight by the end.
- Saturn becomes a morning object during December, rising some 2.5 hours before the Sun by the end of the month.
- The Phoenicid meteor shower peaks on the 6th, its radiant in Phoenix being quite close to the star Achernar in Eridanus and well placed all through the night for southern hemisphere observers. Unfortunately, a full Moon will hamper viewing this year.
- The Geminid meteor shower is best seen after midnight on the 14th. The constellation is low in the north, even at its highest point at around 03:00 NZDT, so only around half the visible meteors can be seen from New Zealand.
Odds and Ends
Astronomers have discovered the first multiply-imaged gravitationally lensed supernova. Gravitational lensing is a phenomenon arising from Einstein's General Relativity, in which light is bent around massive objects. In this case, a spiral galaxy is lensed by a cluster of galaxies, producing three images. One of those images has been further lensed by a foreground galaxy, so four images of the supernova could been seen. The path difference between the light rays means there is a time delay between the images. This allows astronomers to measure the amount of luminous and dark matter in the galaxy, and could also potentially allow for an absolute measurement of the Hubble constant. It is predicted that the we will see the supernova in another image of the spiral galaxy in about a year.
A new physics paper has estimated the chances of complex life falling victim to gamma-ray bursts (GRBs). Although somewhat mysterious, long-duration GRBs are thought to originate from supernovae, and are incredibly intense flashes of gamma- and X-rays that last for days but do not recur. Such a burst, even several thousand light-years from a planet, could alter its atmosphere and disrupt the ecosystem enough to cause extinctions of complex life forms. Among other things, the authors suggest that everything within 4 kiloparsecs of the centre of the Milky Way is highly likely to have been subject to a lethal GRB over the last 500 million years, and that even the Earth, at twice that distance from the Galactic centre, had a 50% probability of such an event affecting it over the same period.
A joint venture between the European Space Agency and LEGO has been announced to create a robotics course called ExoPREP. ExoPREP will be focussed on space science and technology specifically related to the ExoMars mission. The course will be available in 2015 across the EU.
|News:||Ian Harrison and Christina Smith|
|Interview:||Prof. Elisa Resconi and Mark Purver|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||Mark Purver, Christina Smith and Hannah Stacey|
|Editors:||Ben Shaw, George Bendo, Claire Bretherton, Monique Henson, Mark Purver and Prabu Thiagaraj|
|Segment Voice:||Tess Jaffe|
|Website:||Christina Smith and Stuart Lowe|
|Cover art:||The IceCube neutrino observatory. CREDIT: Eli Duke|