Could Antimatter Be Powering Super-Luminous Supernovae?


Explosions are almost always cool, and supernovae are some of the most spectacular and violent explosions in the Universe. In 2006, the supernova SN 2006gy wowed scientists with a light show that was 10 times as luminous as the average supernova, challenging the traditional model of exactly how an exploding star creates a supernova. Astronomers suspect that the cause is the repeated production of antimatter in the core of the star.

Supernovae occur when a star nears the end of its life, and the nuclear processes that fuel the star push outward more powerfully than the force of gravity can hold the star together; the type of supernova created depends on the mass of the star. In stars with masses between 95-130 times the Sun, this process can occur more than once, creating a “pulsational” supernova which can happen as many as seven times.

The cause for the multiple explosions may have to do with the production of antimatter particles in the core, which then recombine and release large amounts of energy.

“The pair instability is encountered when, late in the star’s life, a large amount of thermal energy goes into making the masses of an increasing abundance of electron-positron pairs rather than providing pressure,” wrote Dr. Stan Woosley, of the Department of Astronomy and Astrophysics, USCS Santa Cruz.

What happens is this: the first supernova occurs, powered by the antimatter explosions in the core, and ejects a large amount of the star’s material out into space; however, there still remains enough matter near the core for the star to reignite and begin nuclear processes once again. After between a few hundred days and a few years, another supernova occurs by the same mechanism, and when the ejected material collides with the previous shell of ejected material, the interaction gives off enormous amounts of light.

This process only occurs with stars in the 95-130 solar mass range. Stars with solar masses under 95 undergo typical, non-repeating supernovae, while those over 130 solar masses are subject to the pair instability but explode with such force as to leave nothing near the core to recombine and start the process again.

The production of antimatter in the core, as well as the large amount of light given off by the repeated collision of the shells of ejected matter explains very well the otherwise puzzling luminosity of SN 2006gy.

“The model existed before 2006gy happened as well as the prediction of a possible bright supernova of this sort. When we learned of the supernova, we carried out much more detailed calculations specific to 2006gy and found, to our satisfaction, that many of the observed facts were in the model results,” Dr. Woosley said.

There are other possible candidates for this type of repeating supernova, including Eta Carinae, though they unfortunately may not all be as spectacular as SN 2006gy.

Source: Arxiv paper

Seeing Inside the Earth with Neutrinos


You know what it’s like to get an X-ray done: you go to the doctor, get in a large machine, she puts on a lead vest, and X-rays shoot through your body, forming a picture of your skeletal structure. Well, using the IceCube neutrino detector – as well as other neutrino detectors to come – it might be possible to do something very similar to this, but to the Earth.

A collaborative team of physicists and geologists from around the world has proposed that with the construction of IceCube, a neutrino detector at the South Pole, it should be possible to get a very accurate picture of the Earth’s core using neutrinos that stream through the Earth from the other side. Their recent paper is entitled Imaging the Internal Structure of the Earth with Atmospheric Neutrinos.

Neutrinos are particles with very small mass that don’t interact with other types of matter very often. There are trillions of them streaming through your body this very second, but don’t worry: the chance that they will interact with any of the protons or neutrons that make up your body are very, very low. The higher the energy of the neutrino, the more likely it is to interact with a particle that has mass. When this happens a cascade of other particles is created, and a particle called a muon that is produced by this reaction can be detected.

Neutrino telescopes don’t look anything like your average viewing telescopes; rather, they are made up of a huge block of matter, usually water or ice. IceCube is just such a detector, made up of one cubic km of ice at the South Pole. There are small “strings” of detectors placed strategically in the ice to record the presence of muons from neutrino-particle interactions. The large mass of the detector increases the likelihood of finding the collisions between neutrinos and other particles.

The idea to use neutrinos as a way to image Earth’s interior has been around for more than 25 years, but IceCube is the first neutrino telescope with the ability to detect neutrinos at the energies necessary to give an accurate picture of the core.

Using IceCube to view the inside the Earth would increase our understanding of the “core-mantle transition” – where the Earth’s core meets the mantle – because this method is more accurate than methods currently used to estimate what the inside of the Earth looks like.

Dr. Francis Halzen of the University of Wisconsin Department of Physics, one of the co-authors of the research paper proposes, “we can see the transition “directly” and not infer it from some analysis of indirect data, such as data on Earth sound waves. The precision of our mapping is directly related to our angular resolution on the path taken through the Earth by a neutrino.”

Much like in an X-ray, some of the neutrinos coming through the Earth would be blocked by the dense core – like the Earth’s “skeleton” – while those streaming through the mantle, which is less dense, would be detected by IceCube.
Though the IceCube telescope is still under construction, it has already begun taking data, and will only continue to improve as more detectors are added to the ice.

Dr. Halzen said, “An unusual feature of IceCube is that we operate the partially deployed detector while we are constructing it. We have been collecting data relevant to this problem for more than 1 year and hope to run half the detector starting this February, i.e. after another construction season over the Antarctic summer that just started.”

The imaging is expected to be finished anywhere between the next 3 and 10 years.

Source: Arxiv Paper

How to Keep a Venus Rover Cool


In comparison to a mission to Venus, missions to Mars or the Moon are a cakewalk. With temperatures exceeding 450ºC (840ºF) and pressures over 92 times that of the surface of the Earth, landing a rover on the surface of Venus is quite a feat. This, however, is exactly what a research and development team at the NASA John Glenn Research Center hopes to accomplish.

Venus has been explored by a number of different missions, but there is a lot of science yet to be done on the planet.

“Understanding the atmosphere, climate, geology, and history of Venus could shed considerable light on our understanding of our own home planet. Yet the surface of Venus is the most hostile operating environment of any of the solid-surface planets in the solar system,” wrote Dr. Geoffrey Landis of the NASA John Glenn Research Center.

The extreme conditions on Venus make traditional rover technology impossible: the heat and pressure combined wreak havoc on any electronic components, and the atmosphere of Venus, mostly composed of carbon dioxide and sulfuric acid, is highly corrosive on metal parts. And if this weren’t enough, the thick atmosphere makes the light conditions on the surface like a rainy day on Earth, which limits the potential of solar energy.

To solve the problem of putting electronics on the surface, the team will split the mission into two: a rover that will have limited electronic components in pressurized chamber cooled to under 300ºC (570ºF), and an airplane that will fly in the middle atmosphere of the planet, where the temperature is more moderate and the pressure not as great. The airplane will contain most of the more sensitive electrical components like computers, and will assist in relaying all the information back to Earth.

The Russian Venera lander to last the longest on the surface of Venus operated for a mere two hours before being crushed, but the rover for this mission will be designed to last more than 50 days.

Extreme conditions call for extreme technology; the team analyzed the possibility of using a number of different sources of energy, from solar to nuclear to microwave beaming. Solar power just can’t provide the energy necessary to run the rover and cool everything down, and microwave beaming energy from the airplane – which would collect solar energy – isn’t feasible because of how new the technology is.

This leaves nuclear power, something that has been used in past missions such as Galileo, Voyager, the current Cassini probe. To power the rover with nuclear energy, though, there is a twist: the heat produced by bricks of Plutonium will power a Stirling engine, an engine that uses the pressure difference between two chambers to produce mechanical energy with very high efficiency. This mechanical energy can be used to power the wheels directly, or transferred to electrical energy for the electrical and cooling systems, and the technology is being adapted to work on Venus.

“We’ve been working on Stirling technology for many years. The project reported was a project to design a Stirling specifically for Venus – which makes for a very different design in some ways; notably in that the heat rejection temperature is extremely hot – but we are building from existing technology, not developing it from scratch,” wrote Dr. Landis

The airplane would study the atmospheric conditions and Venus’ electric field, while the rover would place seismic stations and study surface conditions. A camera is almost definite on the airplane, and while it would be difficult to put a camera on the rover, it is not entirely out of the question.

When can you expect to see images of the surface, or hear more about the sulfuric acid clouds that envelop the planet?

“It’s a mission concept study so far, not a funded mission, so it’s not actually scheduled to take place. However, there’s a lot of interest in flying it in the 2015-2020 time frame,” said Dr. Landis.

Source: Acta Astronautica

Tunguska Meteoroid’s Cousins Found?


It’s a cosmic whodunit: a meteorite exploded in the air near a remote part of Russia called Tunguska in 1908, and the meteorite that caused the event all but disappeared. Where did it come from? Was it an asteroid or part of a comet? Astronomers have taken up the case, using mathematical simulations to track down the perpetrator. They even think they might even know a few of its siblings.

Tadeusz J. Jopek and his team at the Astronomical Observatory UAM in Poland – in collaboration with the Observatoire de la Côte d’Azur in France – looked for the possible origins of the Tunguska meteor by essentially running the explosion backwards, and mathematically simulating where the parent object of the event would have been before the impact.

By taking the existing forensic evidence of the impact to estimate the velocity and impact angle of the Tunguska meteorite, the team was able to simulate the possible orbit and speed of the object before it hit the earth. In doing this, they created 3311 virtual “particles” as possible origins of the object.

They then analyzed the orbits of near-earth objects that lie in the most likely region for the past 20,000 years to find possible matches with their simulated particles. It is still unclear exactly where the Tunguska meteor came from, and there are over 130 suspects.

“We believe that TCB originated as the result of a breakup of a single body : a comet or an asteroid. In our study we concluded that it is more probable that it was an asteroid. We cannot point to which one; instead we have found several candidates for the Tunguska parent, and the asteroid 2000 WK63 is an example of it,” Dr. Tadeusz said.

This is a hard case to solve indeed, as there remains little physical evidence of the original object near Tunguska, and the only tools astronomers have to work with are mathematical and statistical simulations. The question still remains whether the parent was a comet or asteroid, and indeed if the near-earth object it came from has been discovered yet.

“Such statistical conclusion gives no absolute sure [sic] that one of the presently known asteroids was indeed the Tunguska cosmic body parent. Therefore it is possible that still, the real Tunguska parent body is undiscovered.” Dr. Tadeusz said.

Source: Earth, Moon, and Planets Journal

The Tiger Stripes and Geysers are Linked on Enceladus


Saturn’s moon Enceladus is one of the most peculiar objects in the Solar System. We now know there are geysers of water ice blasting from its southern pole; a place marked with long gashes that researchers have dubbed “tiger stripes”. Ever since the geysers were first discovered, scientists have been puzzling out their source. Now they understand how the geysers and tiger stripes are linked.

New research by the Cassini imaging team, CICLOPS, shows that the jets of Enceladus emanate from its southern pole, pouring out of four of the tiger stripes. The researchers have named them Alexandria, Cairo, Baghdad and Damascus. Of the four, Baghdad and Damascus are the most active and Alexandria is the least.

By taking Cassini’s two-year observations of the jets that spray from the surface, and combining this with thermal imaging of the stripes, the team was able to determine that the jets were spraying vertically out of the stripes, which are cracks on the surface of Enceladus.

The water sprays through the cracks because the gravity of Saturn pulls and pushes on Enceladus, and this motion – called a tidal force – heats up the frozen water underneath the surface. Much like geysers on Earth, the water is heated and expands below the surface, and follows the easiest path it can find to escape; this path happens to be right through the tiger stripes on the surface.

The researchers noted that when the tidal pull of Saturn was compressing this region of Enceladus, the geysers were not very active, if at all. But when the tides pulled and created tension, they began to erupt. Also, the hotter the region was, the stronger and larger the jet plume tended to be.

There may be other areas of Enceladus capable of producing jets, and now that the origins of the geysers are confirmed, more thermal and digital imaging of the surface could reveal other geysers in the future.

The researcher paper, entitled “Association of the jets of Enceladus with the warmest regions on its south-polar fractures” was published in the October 11th edition of the journal Nature.

Source: Nature

Japan’s Mission to the Moon Blasts Off


If you think the Americans are going to be dominating lunar exploration, think again. Many countries are considering our heavenly companion, helping to unlock its secrets. The next mission to head off is the Japanese lunar probe Kaguya, which blasted off from the Tanegashima space center at 10:31:01 Japan Standard Time (01:31:01 UTC) on September 14th – after an initial delay due to weather. The spacecraft is currently in Earth orbit, and will leave for the moon on October 3rd. It’ll start making scientific observations on October 21st.

Once near the moon, Kaguya will split into three satellites; a 3-ton main orbiter which will orbit the planet at an altitude of 100km, and the smaller Relay and VRAD Satellites, which will orbit and gather information about the poles.

There are three main goals for the mission:

Kaguya will be on the moon to study how it evolved and where it came from by looking at the topography and the abundance of elements in the lunar soil, and measuring the Moon’s gravity and weak magnetic field. Hopefully, it’ll help explain the question: was the Moon captured by the Earth, did it solidify out of the same material and at the same time as our planet, was it somehow fissioned or secreted by the Earth, or is the result of a massive collision by another object.

It’ll also study the plasma, energetic particles and electromagnetic field surrounding the Moon. This will be valuable information, when humans arrive back at the Moon, decide to colonize, or utilize it as a base for other operations. Unlike the Earth, the Moon has no strong magnetic field to shield the surface from harmful radiation from the Sun, and if we are to travel there it will be essential to know what kind of protection we will need to bring along. The polar orbiters will also scope out possible sites for an astronomical observatory on the surface.

Finally, the probes will turn their electromagnetic eyes towards our planet to study the plasma surrounding the Earth, and allow us to better understand how our own magnetosphere and ionosphere protect us from the deadly radiation of the solar wind. One of the neatest aspects of the Kaguya mission is its inclusion of a High Definition Television camera to send back movies of the Earth from the Moon. This means that we will be able to see the Earth-rise from the Moon’s horizon!

Kaguya is the start of exciting times for Earth’s satellite, and for the continued exploration of our solar system. The launch of Kaguya kicks off the International Lunar Decade, ten years of lunar exploration that will end when humans once again land on the Moon. The International Lunar Decade is a project of The Planetary Society to foster international cooperation in studying the moon and invigorate the public about space exploration. Other missions in the spirit of the project include China’s lunar orbiter, Chang’E, which is set to launch sometime in 2007, and India’s Chandrayaan-1 mission, scheduled to launch this month.

Source: Japan Aerospace Exploration Agency

Mars Has Had Many, Many Ice Ages


The polar ice caps on Mars have been there for a long time; although, they haven’t always stayed the same size, or shape. They cover the surface between the poles and approximately 60° latitude today, but Norbert Schorghofer of the Institute for Astronomy and NASA Astrobiology Institute in Hawaii has shown that Mars has had at least forty major ice ages during the past five million years.

The Martian ice caps are divided into three layers: a massive bottom sheet, a porous middle layer and a thin, dry, dusty top layer. The makeup and extent of the ice coverage has varied over its long history due to both precipitation of water vapor from the atmosphere, and the diffusion and condensation of water from pores in the ice.

“Although neither of the two mechanisms by itself could simultaneously account for the mass fraction and latitudinal boundary of the observed ice, their combination provides just enough ice at the right places,” Schorghofer said.

Unlike the Earth, Mars doesn’t have a Moon to keep its tilt in check. Instead, the planet is able to tilt as much as 10-degrees from its current angle. This can create tremendous variation in the size of its ice sheets.

Earlier studies of the ice showed that the shifting of the ice was due largely to Mars’ varying tilt (obliquity), and thus changes in global and local temperatures affecting the humidity levels of the entire planet. Schorghofer used computer modeling that takes into account thermal and atmospheric conditions, as well as the growth and retreat of the ice sheets. His research shows that the transfer of water vapor from the ice into the atmosphere, and the condensation of this water back into the ice profoundly altered the way in which the ice caps melted and re-froze.

Closer to the poles, the amount of ice changes very little over time. But near the edges of the sheets, the volume of ice has varied by as much as 100,000 cubic km during each ice age. Mars’ icy love handles have each also shrunk an overall depth of 60cm over the past 2.5 million years.

Understanding the cause for ice ages on Mars may help us learn more about the climate history of other planets, including Earth.

“The dynamic nature of the ice sheets makes Mars an ideal system in which to test and expand our knowledge of astronomical climate forcing. A great deal could be learned about terrestrial ice ages from the study of Martian ice stratigraphy – a longer, cleaner and simpler record than Earth’s,” Schorghofer said.

When the Phoenix Mars Lander arrives at the Red Planet in 2008, it might just see the different kinds of ice layers that Schorghofer is predicting.

Original Source: IfA