Scientists studying the Crab Nebula have discovered high energy gamma rays around the rotation-powered pulsar, the neutron star at the center of this enigmatic nebula. Neutron stars accelerate particles to immense energies, typically one hundred times more than the most powerful accelerators on Earth. Scientists have been uncertain exactly how these systems work and where the particles are accelerated. But by using the gamma-ray telescope on the European Space Agency’s INTEGRAL spacecraft orbiting Earth, astronomers have detected polarized gamma-rays emitting from near the pulsar.
The Crab Nebula was created by a supernova explosion which was seen from Earth by early Chinese and Arab astronomers on July 4, 1054. The explosion left behind a pulsar or rotating neutron star with a nebula of radiating particles around it. The Crab Pulsar. This image combines optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).
The neutron star contains the mass of the Sun squeezed into a volume of about 10 km radius, rotating very fast – about 30 times a second – thereby generating magnetic fields and accelerating particles. But until now, astronomers didn’t know exactly where the particles were accelerated.
Looking into the heart of the pulsar with Integral’s spectrometer (SPI), the researchers made a detailed study of over 600 observations to assess the polarization – or the alignment – of the waves of high-energy radiation originating from the Crab.
They saw that this polarized radiation is aligned with the rotation axis of the pulsar. So they concluded that a significant portion of the electrons generating the high-energy radiation must originate from a highly-organized structure located very close to the pulsar, very likely directly from the jets themselves. The discovery allows the researchers to discard other theories that locate the origin of this radiation further away from the pulsar. Credits: NASA/CXC/ASU/J. Hester et al.(for the Chandra image); NASA/HST/ASU/J. Hester et al. (for the Hubble image)
Professor Tony Dean of the University’s School of Physics and Astronomy, and one of the researchers, commented that the discovery of such alignment – also matching with the polarization observed in the visible band – is truly remarkable. “The findings have clear implications on many aspects of high energy accelerators such as the Crab,†he added.
“The detection of polarized radiation in space is very complicated and rare, as it requires dedicated instrumentation and an in-depth analysis of very complex dataâ€, said Chris Winkler, Integral Project Scientist at ESA.
The paper ‘Polarized gamma-ray emission from the Crab’ is published this week in Science.
Atlantis rolls over to the Vehicle Assembly Building. Credit: NASA
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Space shuttle Atlantis was rolled over the the Vehicle Assembly Building after hunkering down in the Orbiter Processing Facility at Kennedy Space Center during Tropical Storm Fay. In the VAB, Atlantis will be attached to its external fuel tank and twin solid rocket boosters. NASA announced that Atlantis will be moved out to Launch Pad 39A next Saturday, August 30 to prepare for launch on the STS-125 mission to service the Hubble Space Telescope one last time, targeted for an Oct. 8 liftoff.
The mobile launcher platform will bring Atlantis to he pad, atop a crawler-transporter. The crawler will travel slower than 1 mph during the 3.4-mile journey. The process is expected to take approximately six hours.
Repairs to Launch Pad 39A’s flame trench wall were completed Aug. 5 after crews installed a steel grid structure and covered it in a heat-resistant material. The pad’s north flame trench was damaged when bricks tore away from the wall during the May 31 launch of space shuttle Discovery.
NASA has several videos about the final Hubble servicing mission. Find them here.
Deep trench dug by Phoenix. Credit:NASA/JPL/Caltech/U of AZ
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The next sample of Martian soil being grabbed for analysis is coming from a trench about three times deeper than any other trench NASA’s Phoenix Mars Lander has dug. On Tuesday, August 26, the scoop on the lander’s robotic arm will pick up a sample of soil from the bottom of a trench called “Stone Soup” which is about 18 centimeters, or 7 inches deep. Tuesday will be the 90th Martian day or sol that the lander has been on the Red Planet, which was the original amount of time set for Phoenix’s primary mission. NASA has extended the mission through September, but the clock is ticking for the plucky little lander and the oncoming winter at Mars’ north polar region.
The soil sample from the deep trench will be delivered into the third cell of the wet chemistry laboratory. This deck-mounted laboratory, part of Phoenix’s Microscopy, Electrochemistry and Conductivity Analyzer (MECA), has previously used two of its four soil-testing cells.
“In the first two cells we analyzed samples from the surface and the ice interface, and the results look similar. Our objective for Cell 3 is to use it as an exploratory cell to look at something that might be different,” said JPL’s Michael Hecht, lead scientist for MECA. “The appeal of Stone Soup is that this deep area may collect and concentrate different kinds of materials.”
Stone Soup lies on the borderline, or natural trough, between two of the low, polygon-shaped hummocks that characterize the arctic plain where Phoenix landed. The trench is toward the left, or west, end of the robotic arm’s work area on the north side of the lander. Deep Dig 3-D. Credit: NASA/JPL/Caltech/A of AZ
When digging near a polygon center, Phoenix has hit a layer of icy soil, as hard as concrete, about 5 centimeters, or 2 inches, beneath the ground surface. In the Stone Soup trench at a polygon margin, the digging has not yet hit an icy layer like that.
“The trough between polygons is sort of a trap where things can accumulate,” Hecht said. “Over a long timescale, there may even be circulation of material sinking at the margins and rising at the center.”
The science team had considered two finalist sites as sources for the next sample to be delivered to the wet chemistry lab. This past weekend, Stone Soup won out. “We had a shootout between Stone Soup and white stuff in a trench called ‘Upper Cupboard,'” Hecht said. “If we had been able to confirm that the white material was a salt-rich deposit, we would have analyzed that, but we were unable to confirm that with various methods.”
Both candidates for the sampling location offered a chance to gain more information about salt distribution in the Phoenix work area, which could be an indicator of whether or not liquid water has been present. Salt would concentrate in places that may have been wet.
While proceeding toward delivery of a sample from Stone Soup into the wet chemistry laboratory, Phoenix is also using its Thermal and Evolved-Gas Analyzer to examine a soil sample collected last week from another trench, at a depth intermediate between the surface and the hard, icy layer.
[/caption]Greetings, fellow SkyWatchers! Are you ready for a relatively Moon-less weekend? For telescope observers, we’ll travel south and capture the cosmic firefly – the “Bug Nebula”. If you have binoculars, take them out as we journey back 2000 years in time to look at the magnificent M25. For those who like a challenge? Try your luck at being a “Snake” charmer. Even if you just relax in a lawn chair and stare at the stars, you’re in luck because the Northern Iota Aquarid meteor shower is in town for a visit, too! Step out the back door, face south, and let’s journey into the night…
Friday, August 22, 2008 – With the Moon long gone from early evening skies, let’s have a look tonight at NGC 6302, a very curious planetary nebula located around three fingerwidths west of Lambda Scorpii: it is better known as the “Bug” nebula (RA 17 13 44 Dec -37 06 16).
With a rough visual magnitude of 9.5, the Bug belongs to the telescope – but it’s history as a very extreme planetary nebula belongs to us all. At its center is a 10th magnitude star, one of the hottest known. Appearing in the telescope as a small bowtie, or figure 8 shape, huge amounts of dust lie within it – very special dust. Early studies showed it to be composed of hydrocarbons, carbonates and iron. At one time, carbonates were believed associated with liquid water, and NGC 6302 is one of only two regions known to contain carbonates – perhaps in a crystalline form.
Ejected at a high speed in a bi-polar outflow, further research on the dust has shown the presence of calcite and dolomite, making scientists reconsider the kind of places where carbonates might form. The processes that formed the Bug may have begun 10,000 years ago – meaning it may now have stopped losing material. Hanging out about 4000 light-years from our own solar system, we’ll never see NGC 6302 as well as the Hubble Telescope presents its beauty, but that won’t stop you from enjoying one of the most fascinating of planetary nebulae!
Saturday, August 23, 2008 – Do you remember August 10, 1966 when Lunar Orbiter 1 was launched? Well, on this day in history it made headlines as it sent back the very first photo of Earth as seen from space! While the photographic quality is pretty poor by today’s standards, can you imagine the media stir it caused at the time? Never before had humankind witnessed our own planet. Just think of the advances we’ve in just 42 years!
Sunday, August 24, 2008 – Today in 1966 from an Earth-orbiting platform, the Luna 11 mission launched on a three day trip. After successfully achieving orbit, the mission went on to study lunar composition and nearby meteoroid streams. Also on this date in 2006, 424 members of the International Astronomical Union shocked the world as they officially declared Pluto “to no longer be a planet.” Discovered in 1930, Pluto enjoyed its planetary status for 76 years before being retired. While text books will have to be re-written and the amateur science community will continue to recognize it as a solar system body, it is now considered to be a “dwarf planet.” At least temporarily…
So far in our southern expedition we’ve mined for globular gems, had our heads in the clouds and squashed a bug. What’s left? Let’s head over to the dark side as we take a look at the “Snake”…
Snake NebulaBarnard Dark Nebula 72 is located about a fingerwidth north of Theta Ophiuchi (RA 17 23 02 Dec -23 33 48). While sometimes dark nebulae are hard to visualize because they are simply an absence of stars, patient observers will soon learn to “see in the dark.” The trained eye often realizes the presence of unresolved stars as a type of background “noise” that most of us simply take for granted – but not E. E. Barnard. He was sharp enough to realize there were at least 182 areas of the sky where these particular areas of nothingness existed, and he correctly assumed they were nebulae which were obscuring the stars behind them.
Unlike bright emission and reflection nebulae, these dark clouds are interstellar masses of dust and gas which remain unilluminated. We would probably not even know they were there except for the fact they eradicate star fields we know to be present! It is possible one day they may form stars of their own, but until that time we can enjoy these objects as splendid mysteries – and one of the most fascinating of all is the “Snake.” Put in a widefield eyepiece and relax… It will come to you. Barnard 72 is only a few light-years in expanse and a relatively short 650 light-years away. If at first you don’t see it, don’t worry. Like many kinds of objects, spotting dark nebulae takes some practice.
While you’re out, watch for the peak of the Northern Iota Aquarid meteor shower. Even though the official peak isn’t until tomorrow night, with no Moon to interfere and deep sky to enjoy, you might catch a bright streak! Wishing you clear skies and good luck…
This week’s awesome image are: NGC 6302: The Bug Nebula – Credit: Don Goldman, Lunar Orbiter’s first photo – Credit: NASA, M25 – Hillary Mathis, Vanessa Harvey, REU program/NOAO/AURA/NSF and B 72: The Snake Nebula – Credit: Tom McQuillan/Adam Block/NOAO/AURA/NSF. Thank you!!
If glancing at this image takes your attention immediately, it should. Not only is it ethereally beautiful and aesthetically pleasing – but it’s shrouded in bizarre cosmological coincidences. Not only do we see a dazzling array of multi-colored stars, but within this single area of space is a hidden an ancient planetary nebula, a reflection nebula, a dark dust cloud, a Bok globule, a peculiar low-mass protostar, the edges of a massive X-ray bubble and the fringes of a supernova remnant. Hold on to the light of the Cepheus Flare and let’s step inside Wolf’s Cave…
In the northern fringe of Cepheus lay an enigmatic gathering of cosmic dust clouds that first gained the attention of astronomers in 1908 when Max Wolf and August Kopff first noticed its complex structure. Using a 28-inch reflector, Wolf took a 2.5 hour exposure of the dusty area which he described as a “long, dark lacuna” and positively identified the reflection nebula cataloged as Sh2-155. His assistant, Kopff, using the same photographic plate, was the first to note the Bok globule which later became cataloged by E.E. Barnard as B175.
Those were wonderful years for astronomy – years when poetic descriptions were still acceptable to the general consensus and Wolf dubbed the area the “Cave Nebula”. But this isn’t a spelunker’s dream, because the radiation emitted from the nearby bright, young OB star would would obliterate any explorer into this thick knot of interstellar dust. But there was one traveler, who dared – a main sequence star whose course took it through the dust maul at nearly 12 km per second. Running headlong into the obscuring mass at nearly supersonic speeds, the star slammed into Bok globule B175, sending shockwaves rippling through the structure and producing collisional excitation and ultraviolet pumping. The result of this cosmic crash was, of course, noted by Wolf in 1908 on his photographic records, but it was while searching high above the Milky Way’s galactic plane in 1934 that this dusty molecular cloud was was spied by Edwin Hubble and became known as the Cepheus Flare.
Together, reflection nebula Cederblad 201 and Bok globule B175 are referred to as van den Berg 152, and sometimes called Lynds Bright Nebula 524. Yet, it is Cederblad 201 itself that so interests modern science. Why? According to studies done by Goicoechea (et al) with the Spitzer Space Telescope, “We present the detection and characterization of a peculiar low-mass protostar (IRAS 22129+7000) located 0.4 pc from the Cederblad 201. The cold circumstellar envelope surrounding the object has been mapped through its 1.2 mm dust continuum emission with IRAM 30 m/MAMBO. The deeply embedded protostar is clearly detected with Spitzer. Given the large near- and mid-IR excess in its spectral energy distribution, but large submillimeter-to-bolometric luminosity ratio (it) must be a transition Class 0/I source and/or a multiple stellar system. Targeted observations of several molecular lines from CO, 13CO, C18O, HCO+, and DCO+ have been obtained. The presence of a collimated molecular outflow mapped with the CSO telescope in the CO line suggests that the protostar/disk system is still accreting material from its natal envelope. Indeed, optically thick line profiles from high-density tracers such as HCO+ show a redshifted absorption asymmetry reminiscent of inward motions. We construct a preliminary physical model of the circumstellar envelope (including radial density and temperature gradients, velocity field, and turbulence) that reproduces the observed line profiles and estimates the ionization fraction. The presence of both mechanical and (nonionizing) far-ultraviolet (FUV) radiative input makes the region an interesting case to study triggered star formation.”
Star formation? Not surprising deep inside the cave of a molecular cloud, but – if you’ll pardon the pun – the plot thickens. The entire complex is about 1400 light years away from us at the perimeter of yet another massive molecular cloud and at the same time it is situated on the frontier of a massive X-ray bubble located between the constellations of Cepheus and Cassiopeia. And that’s not all. Thanks to hydrogen-alpha imaging, the whisper thin strands of an ancient supernova remnant near Cederblad 201 have also been detected.
Like a radioactive roomba, the interstellar dust is being swept up as the expanding debris field moves toward where the Cepheus Flare lights the entrance to Wolf’s Cave. These shocked molecular gas filaments were discovered in 2001 by John Bally and Bo Reipurth and belong to SNR 110.3+11.3 – a unfathomably huge supernova remnant positioned only 1300 light years way – one of the closest known. Add to that the output of ancient planetary nebula Dengel-Hartl 5 and the celestial stew thickens even more. It is estimated all the elements will combine in about a thousand years and the product could very well ignite an incredible burst of star formation.
But, a thousand years is merely a blink of an eye in the grand scheme of things, isn’t it? According to the 2007 studies done of the Wolf’s Cave region by Edwin Bergin and Mario Tafalla; “Cold dark clouds are nearby members of the densest and coldest phase in the Galactic interstellar medium, and represent the most accessible sites where stars like our Sun are currently being born. Newly discovered IR dark clouds are likely precursors to stellar clusters. At large scales, dark clouds present filamentary mass distributions with motions dominated by supersonic turbulence. At small, subparsec scales, a population of subsonic starless cores provides a unique glimpse of the conditions prior to stellar birth. Recent studies of starless cores reveal a combination of simple physical properties together with a complex chemical structure dominated by the freeze-out of molecules onto cold dust grains. Elucidating this combined structure is both an observational and theoretical challenge whose solution will bring us closer to understanding how molecular gas condenses to form stars.”
Carbonates from the planetary nebula, dust, exciting energy, photoelectric heating, polycyclic aromatic hydrocarbons, molecular gas… Where will it all end? What we do know is massive, bright star clusters are created from the giant molecular clouds. Will the Cepheus Torch one day ignite a brilliant stellar display from the mouth of Wolf’s Cave? I wonder…
The awesome photo for this story was provided by AORAIA member, Kent Wood. We thank you for the use of this splendid image!
This ATK rocket exploded shortly after liftoff on Friday. Credit: Jacob Owen | NASA Wallops Flight Facility
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Update: NASA said at a press conference this morning that launch officials were forced to destroy the rocket less than 30 seconds after it’s 5:10 a.m. launch. The rocket had veered off-course, although they couldn’t say how far, and they had to terminate the flight at about 12,000 feet.
A suborbital rocket carrying experiments conducted by NASA exploded early Friday morning 27 seconds after launch on Wallops Island in Virginia. The ATK (Alliant Tech Systems) rocket lifted off with no apparent problems at 5:10 a.m. NASA said no property damage or injuries have occurred, but there were conflicting reports as to whether debris had been sighted on land. NASA said it believes that most of the debris landed in the Atlantic Ocean.
NASA said the debris potentially could be hazardous. People who spot debris are being asked to call Wallops Emergency Operations Center at 757-824-1300.
“NASA is very disappointed in this failure but has directed its focus on protecting public safety and conducting a comprehensive investigation to identify the root cause,” the agency said in a statement. NASA is assembling a multidiscipline team, along with ATK of Salt Lake City, Utah to begin the investigation promptly.
The payload was a 5-in-1 experiment on hypersonic flight, air breathing engines and a rocket recovery system.
Space Spa on Galactic Suite Hotel. Credit: Galactic Suite
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The space tourism company Galactic Suite already has 38 reservations made by tourists who, the company says, in 2012 will travel on board a magnetically levitated spacecraft to an orbiting luxury hotel, complete with a floating spa, pictured here. The trip, which costs 3 million Euros, will provide four days in orbit 450 kilometers above the earth and includes 18 weeks of training on a Caribbean island for the tourists to prepare for their spaceflight. The Galactic Suite Spaceport is being built on the island and features the first maglev rocket where the spacecraft will accelerate to speeds up to 1,000 km/h (620 mph) in 10 seconds and lift off from a vertical runway.
Galactic Suite Spaceport. Credit: Galactic Suite
After reaching approximately the speed of sound, the spaceship will detach from its maglev carrier and accelerator, and will ascend to orbit using rocket or air-breathing engines. The maglev accelerator will then brake to a stop and return to its starting point for the next launch. The launch track will be about 3 kilometers long.
According to Xavier Claramunt and Marsal Gifra, founders of Galactic Suite, “Maglev launch assist technology will enable space tourists to travel to our space resorts in orbit on a commercial basis. The most expensive part of any space travel to low-Earth orbit is the first few seconds – getting off the ground. This technology is cost competitive with other forms of space transportation, environmentally friendly and inherently safeâ€.
The stay at the hotel will “offer a mixed programme of reflection and exercise to seize the unique physical conditions encountered in space,” said Claramunt.
One of the most innovative experiences that tourists can experience is the bathroom in zero gravity. Galactic Suite has developed the space spa. Inside the spa, tourists can float with 20 liters of water bubbles. According to Galactic Suite materials, “The tourist, already trained to avoid the effects of water in a state of weightlessness, can play with the bubble dividing it into thousands of bubbles in a never-ending game. In addition, the transparent sphere may be shared with other guests.”
Galactic Suite is a private space tourism company, founded in Barcelona in 2006. The company hopes to make space tourism available to the general public and “will combine an intensive program of training astronauts to relax with a programme of activities on a tropical island as a process preparation to space travel.”
The 2.5 meter SDSS telescope at Apache Point Observatory in New Mexico. Credit: SDSS
Recently we’ve had articles on Universe Today that have discussed the outer Milky Way Galaxy, dark matter, and the discovery of a new minor planet. These articles have a common thread: The discoveries all come from the Sloan Digital Sky Survey (SDSS). If you aren’t familiar with SDSS, it encompasses a comprehensive survey lasting more than eight years, which has so far covered more than one-quarter of the sky.
Using a dedicated 2.5 meter telescope equipped with a 125- megapixel digital camera and spectrographs that can observe 640 stars and galaxies at a time, the SDSS has created terabytes of data that include thousands of deep, multi-color images. It’s also measured the distances to nearly one million galaxies and over 100,000 quasars to create the largest ever three-dimensional maps of cosmic structure.
The SDSS archive represents a thousand-fold increase in the total amount of data that astronomers have collected to date. But almost equally impressive is the easy-to-use interface that allows anyone in the world to access the SDSS data online. Whether you are a research astronomer looking for information to help solve a cosmological puzzle or an armchair astronomy enthusiast who just likes looking at pretty pictures of the universe, SDSS is at your disposal.
Astronomers gathered in Chicago earlier this week to celebrate the accomplishments and look ahead to the future of SDSS. “What amazes me is the huge range of the discoveries that have come from SDSS data,” said SDSS-II Director Richard Kron, an astronomer at the University of Chicago and Fermilab. “We designed it primarily as a survey to map the distribution of galaxies and quasars, but it’s also had a huge impact on the study of stars, the structure of our own Galaxy, and even solar system objects.”
SDSS has found new dwarf companion galaxies to the Milky Way, confirmed Einstein’s prediction of cosmic magnification, and observed the largest known structures in the universe. The new survey, SDSS-III, will continue to expand our horizons with new studies of the structure and origins of the Milky Way Galaxy and the nature of dark energy.
SDSS was undertaken to update the database of information about the sky with current technology. The previous comprehensive guide to the heavens was the Palomar Sky Survey that was conducted in the 1950’s and used glass photographic plates to store the data.
Not only has SDSS updated the technology, but it has changed the way astronomers do business. Astronomers who are doing research or have a question can look at the existing data in SDSS rather than having to pore through the sky, taking their own data with hard-to-get telescope time.
Dr. Pamela Gay, professor at Southern Illinois University Edwardsville and host of the Astronomy Cast podcast said SDSS not only helps her research, but enhances her work in the classroom. “It’s a wonderful project,” she said. “I’m at a small state university and while I did my dissertation on galaxies, when I landed at a state school, I thought I’d never be able to do this (study galaxies) again because I don’t have access to a large telescope. But because of the Sloan Digital Sky Survey, and because of the easy to use tools where I can say to my undergraduate students, ‘go find all the data on these clusters,’ it’s possible for people at small schools to do amazing, amazing research and explore the entire universe.”
SDSS also powers the popular Galaxy Zoo website, where anyone in the world can help classify galaxies via the internet. From the work done by the public from their home computers, Galaxy Zoo has submitted peer reviewed research articles to astronomical journals.
Visit the SDSS website to take a look at the images and discoveries made possible by this comprehensive survey. The Sky Server interface on the SDSS website provides the tools you need to start perusing the universe, and has educational activities for teachers and students as well.
Jim Gunn, SDSS Project Scientist from Princeton University, who has guided the project since its inception said that more than any single discovery, he is proud of the quality and scope of the SDSS data sets. “Visible light is where we understand the universe best, but when we began the SDSS, there were no sensitive, well characterized, visible-light catalogs that covered a large area of sky,” he said. “Now we have multi-color images of 300 million celestial objects, 3-dimensional maps and detailed properties of well over a million of them, and it’s all publicly available online. That changes everything.”
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The Sun and the Moon are the two objects in the Solar System that influence Earth the most. Let’s take a look at all the different was we experience these two objects, how they’re similar, and how they’re mostly different.
The Size of the Sun and the Moon
In absolute terms, the Sun and the Moon couldn’t be more different in size. The Sun measures 1.4 million km across, while the Moon is a mere 3,474 km across. In other words, the Sun is roughly 400 times larger than the Moon. But the Sun also happens to be 400 times further away than the Moon, and this has created an amazing coincidence.
From our perspective, the Sun and the Moon look almost exactly the same size. This is why we can have solar eclipses, where the Moon passes in front of the Sun, just barely obscuring it from our view.
And this is just a coincidence. The gravitational interaction between the Moon and the Earth (the tides) are causing the Moon to slowly drift away from the Earth at a rate of 3.8 centimeters per year. In the ancient past, the Moon would have looked much larger than the Sun. And in the far future, the Moon will look much smaller. It’s just a happy coincidence that they look the same size from our perspective.
Gravity from the Sun and the Moon
Once again, the Sun is much larger and has a tremendous amount of mass. The mass of the Sun is about 27 million times more than the mass of the Moon. It’s this gravitational interaction that gives the Earth its orbit around the Sun, and the tiny pull of the Moon just causes the Earth to wobble a bit in its movements.
When the Sun and the Moon are pulling on the Earth from the same direction, their gravity adds up, and we get the largest spring tides. And then, when they’re on opposite sides of the Earth, their forces cancel out somewhat, and we get neap tides.
Light from the Sun and the Moon
This is a bit of a trick, since the Sun is the only object in the Solar System actually giving out light. With its enormous mass, the Sun is able to fuse hydrogen into helium at its core, generating heat and light. This light shines in the Solar System, and bounces off the Moon so we can see it in the sky.
Astronomers measure brightness using a measurement called magnitude. The star Vega was considered 0 magnitude, and the faintest star you can see with the unaided eye is about 6.5 magnitude. Venus can get as bright as -3.7, the full Moon is -12.6, and the Sun is -26.73. These numbers sound similar, but it’s a logarithmic scale, where each value is twice the amount of the previous one. 1 is twice as bright as 2, etc.
So the Sun is actually 450,000 times brighter than the Moon. From our perspective.
Composition of the Sun and the Moon
Now here’s where the Sun and the Moon differ. The Sun is almost entirely composed of hydrogen and helium. The Moon, on the other hand, was formed when a Mars-sized object crashed into the Earth billions of years ago. Lighter material from the collision collected into an object in orbit – the Moon. The Moon’s crust is primarily oxygen, silicon, magnesium, iron, calcium, and aluminium. Astronomers think the core is metallic iron with small amounts of sulfur and nickel. And it’s at least partly molten.
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We’ve all wondered at some point or another what mysteries our Solar System holds. After all, the eight planets (plus Pluto and all those other dwarf planets) orbit within a very small volume of the heliosphere (the volume of space dominated by the influence of the Sun), what’s going on in the rest of the volume we call our home? As we push more robots into space, improve our observational capabilities and begin to experience space for ourselves, we learn more and more about the nature of where we come from and how the planets have evolved. But even with our advancing knowledge, we would be naive to think we have all the answers, so much still needs to be uncovered. So, from a personal point of view, what would I consider to be the greatest mysteries within our Solar System? Well, I’m going to tell you my top ten favourites of some more perplexing conundrums our Solar System has thrown at us. So, to get the ball rolling, I’ll start in the middle, with the Sun. (None of the following can be explained by dark matter, in case you were wondering… actually it might, but only a little…)
10. Solar Pole Temperature Mismatch
Data from Ulysses (D. McComas)
Why is the Sun’s South Pole cooler than the North Pole? For 17 years, the solar probe Ulysses has given us an unprecedented view of the Sun. After being launched on Space Shuttle Discovery way back in 1990, the intrepid explorer took an unorthodox trip through the Solar System. Using Jupiter for a gravitational slingshot, Ulysses was flung out of the ecliptic plane so it could pass over the Sun in a polar orbit (spacecraft and the planets normally orbit around the Sun’s equator). This is where the probe journeyed for nearly two decades, taking unprecedented in-situ observations of the solar wind and revealing the true nature of what happens at the poles of our star. Alas, Ulysses is dying of old age, and the mission effectively ended on July 1st (although some communication with the craft remains).
However, observing uncharted regions of the Sun can create baffling results. One such mystery result is that the South Pole of the Sun is cooler than the North Pole by 80,000 Kelvin. Scientists are confused by this discrepancy as the effect appears to be independent of the magnetic polarity of the Sun (which flips magnetic north to magnetic south every 11-years). Ulysses was able to gauge the solar temperature by sampling the ions in the solar wind at a distance of 300 million km above the North and South Poles. By measuring the ratio of oxygen ions (O6+/O7+), the plasma conditions at the base of the coronal hole could be measured.
Mars, just a normal planet. No mystery here... (NASA/Hubble)
Why are the Martian hemispheres so radically different? This is one mystery that had frustrated scientists for years. The northern hemisphere of Mars is predominantly featureless lowlands, whereas the southern hemisphere is stuffed with mountain ranges, creating vast highlands. Very early on in the study of Mars, the theory that the planet had been hit by something very large (thus creating the vast lowlands, or a huge impact basin) was thrown out. This was primarily because the lowlands didn’t feature the geography of an impact crater. For a start there is no crater “rim.” Plus the impact zone is not circular. All this pointed to some other explanation. But eagle-eyed researchers at Caltech have recently revisited the impactor theory and calculated that a huge rock between 1,600 to 2,700 km diameter can create the lowlands of the northern hemisphere (see Two Faces of Mars Explained).
Bonus mystery: Does the Mars Curse exist? According to many shows, websites and books there is something (almost paranormal) out in space eating (or tampering with) our robotic Mars explorers. If you look at the statistics, you would be forgiven for being a little shocked: Nearly two-thirds of all Mars missions have failed. Russian Mars-bound rockets have blown up, US satellites have died mid-flight, British landers have pock-marked the Red Planet’s landscape; no Mars mission is immune to the “Mars Triangle.” So is there a “Galactic Ghoul” out there messing with our ‘bots? Although this might be attractive to some of us superstitious folk, the vast majority of spacecraft lost due to The Mars Curse is mainly due to heavy losses during the pioneering missions to Mars. The recent loss rate is comparable to the losses sustained when exploring other planets in the Solar System. Although luck may have a small part to play, this mystery is more of a superstition than anything measurable (see The “Mars Curse”: Why Have So Many Missions Failed?).
8. The Tunguska Event
Artist impression of the Tunguska event (www.russianspy.org)
What caused the Tunguska impact? Forget Fox Mulder tripping through the Russian forests, this isn’t an X-Files episode. In 1908, the Solar System threw something at us… but we don’t know what. This has been an enduring mystery ever since eye witnesses described a bright flash (that could be seen hundreds of miles away) over the Podkamennaya Tunguska River in Russia. On investigation, a huge area had been decimated; some 80 million trees had been felled like match sticks and over 2,000 square kilometres had been flattened. But there was no crater. What had fallen from the sky?
This mystery is still an open case, although researchers are pinning their bets of some form of “airburst” when a comet or meteorite entered the atmosphere, exploding above the ground. A recent cosmic forensic study retraced the steps of a possible asteroid fragment in the hope of finding its origin and perhaps even finding the parent asteroid. They have their suspects, but the intriguing thing is, there is next-to-no meteorite evidence around the impact site. So far, there doesn’t appear to be much explanation for that, but I don’t think Mulder and Scully need be involved (see Tunguska Meteoroid’s Cousins Found?).
7. Uranus’ Tilt
Uranus. Does it on its side (NASA/Hubble)
Why does Uranus rotate on its side? Strange planet is Uranus. Whilst all the other planets in the Solar System more-or-less have their axis of rotation pointing “up” from the ecliptic plane, Uranus is lying on its side, with an axial tilt of 98 degrees. This means that for very long periods (42 years at a time) either its North or South Pole points directly at the Sun. The majority of the planets have a “prograde” rotation; all the planets rotate counter-clockwise when viewed from above the Solar System (i.e. above the North Pole of the Earth). However, Venus does the exact opposite, it has a retrograde rotation, leading to the theory that it was kicked off-axis early in its evolution due to a large impact. So did this happen to Uranus too? Was it hit by a massive body?
Some scientists believe that Uranus was the victim of a cosmic hit-and-run, but others believe there may be a more elegant way of describing the gas giant’s strange configuration. Early in the evolution of the Solar System, astrophysicists have run simulations that show the orbital configuration of Jupiter and Saturn may have crossed a 1:2 orbital resonance. During this period of planetary upset, the combined gravitational influence of Jupiter and Saturn transferred orbital momentum to the smaller gas giant Uranus, knocking it off-axis. More research needs to be carried out to see if it was more likely that an Earth-sized rock impacted Uranus or whether Jupiter and Saturn are to blame.
6. Titan’s Atmosphere
False colour image of Titan's atmosphere. Credit: NASA/JPL/Space Science Institute/ESA
Why does Titan have an atmosphere? Titan, one of Saturn’s moons, is the only moon in the Solar System with a significant atmosphere. It is the second biggest moon in the Solar System (second only to Jupiter’s moon Ganymede) and about 80% more massive than Earth’s Moon. Although small when compared with terrestrial standards, it is more Earth-like than we give it credit for. Mars and Venus are often cited as Earth’s siblings, but their atmospheres are 100 times thinner and 100 times thicker, respectively. Titan’s atmosphere on the other hand is only one and a half times thicker than Earth’s, plus it is mainly composed of nitrogen. Nitrogen dominates Earth’s atmosphere (at 80% composition) and it dominates Titans atmosphere (at 95% composition). But where did all this nitrogen come from? Like on Earth, it’s a mystery.
Titan is such an interesting moon and is fast becoming the prime target to search for life. Not only does it have a thick atmosphere, its surface is crammed full with hydrocarbons thought to be teeming with “tholins,” or prebiotic chemicals. Add to this the electrical activity in the Titan atmosphere and we have an incredible moon with a massive potential for life to evolve. But as to where its atmosphere came from… we just do not know.
5. Solar Coronal Heating
Coronal loops as imaged by TRACE at 171 Angstroms (1 million deg C) (NASA/TRACE)
Why is the solar atmosphere hotter than the solar surface? Now this is a question that has foxed solar physicists for over half a century. Early spectroscopic observations of the solar corona revealed something perplexing: The Sun’s atmosphere is hotter than the photosphere. In fact, it is so hot that it is comparable to the temperatures found in the core of the Sun. But how can this happen? If you switch on a light bulb, the air surrounding the glass bulb wont be hotter than the glass itself; as you get closer to a heat source, it gets warmer, not cooler. But this is exactly what the Sun is doing, the solar photosphere has a temperature of around 6000 Kelvin whereas the plasma only a few thousand kilometres above the photosphere is over 1 million Kelvin. As you can tell, all kinds of physics laws appear to be violated.
However, solar physicists are gradually closing in on what may be causing this mysterious coronal heating. As observational techniques improve and theoretical models become more sophisticated, the solar atmosphere can be studied more in-depth than ever before. It is now believed that the coronal heating mechanism may be a combination of magnetic effects in the solar atmosphere. There are two prime candidates for corona heating: nanoflares and wave heating. I for one have always been a huge advocate of wave heating theories (a large part of my research was devoted to simulating magnetohydrodynamic wave interactions along coronal loops), but there is strong evidence that nanoflares influence coronal heating too, possibly working in tandem with wave heating.
Although we are pretty certain that wave heating and/or nanoflares may be responsible, until we can insert a probe deep into the solar corona (which is currently being planned with the Solar Probe mission), taking in-situ measurements of the coronal environment, we won’t know for sure what heats the corona (see Warm Coronal Loops May Hold the Key to Hot Solar Atmosphere).
4. Comet Dust
Comets - where does their dust come from?
How did dust formed at intense temperatures appear in frozen comets? Comets are the icy, dusty nomads of the Solar System. Thought to have evolved in the outermost reaches of space, in the Kuiper Belt (around the orbit of Pluto) or in a mysterious region called the Oort Cloud, these bodies occasionally get knocked and fall under the weak gravitational pull of the Sun. As they fall toward the inner Solar System, the Sun’s heat will cause the ice to vaporize, creating a cometary tail known as the coma. Many comets fall straight into the Sun, but others are more lucky, completing a short-period (if they originated in the Kuiper Belt) or long-period (if they originated in the Oort Cloud) orbit of the Sun.
But something odd has been found in the dust collected by NASA’s 2004 Stardust mission to Comet Wild-2. Dust grains from this frozen body appeared to have been formed a high temperatures. Comet Wild-2 is believed to have originated from and evolved in the Kuiper Belt, so how could these tiny samples be formed in an environment with a temperature of over 1000 Kelvin?
The Solar System evolved from a nebula some 4.6 billion years ago and formed a large accretion disk as it cooled. The samples collected from Wild-2 could only have been formed in the central region of the accretion disk, near the young Sun, and something transported them into the far reaches of the Solar System, eventually ending up in the Kuiper Belt. But what mechanism could do this? We are not too sure (see Comet Dust is Very Similar to Asteroids).
3. The Kuiper Cliff
The bodies in the Kuiper Belt (Don Dixon)
Why does the Kuiper Belt suddenly end? The Kuiper Belt is a huge region of the Solar System forming a ring around the Sun just beyond the orbit of Neptune. It is much like the asteroid belt between Mars and Jupiter, the Kuiper Belt contains millions of small rocky and metallic bodies, but it’s 200-times more massive. It also contains a large quantity of water, methane and ammonia ices, the constituents of cometary nuclei originating from there (see #4 above). The Kuiper Belt is also known for its dwarf planet occupant, Pluto and (more recently) fellow Plutoid “Makemake”.
The Kuiper Belt is already a pretty unexplored region of the Solar System as it is (we wait impatiently for NASA’s New Horizons Pluto mission to arrive there in 2015), but it has already thrown up something of a puzzle. The population of Kuiper Belt Objects (KBOs) suddenly drops off at a distance of 50 AU from the Sun. This is rather odd as theoretical models predict an increase in number of KBOs beyond this point. The drop-off is so dramatic that this feature has been dubbed the “Kuiper Cliff.”
We currently have no explanation for the Kuiper Cliff, but there are some theories. One idea is that there are indeed a lot of KBOs beyond 50 AU, it’s just that they haven’t accreted to form larger objects for some reason (and therefore cannot be observed). Another more controversial idea is that KBOs beyond the Kuiper Cliff have been swept away by a planetary body, possibly the size of Earth or Mars. Many astronomers argue against this citing a lack of observational evidence of something that big orbiting outside the Kuiper Belt. This planetary theory however has been very useful for the doomsayers out there, providing flimsy “evidence” for the existence of Nibiru, or “Planet X.” If there is a planet out there, it certainly is not “incoming mail” and it certainly is notarriving on our doorstep in 2012.
So, in short, we have no clue why the Kuiper Cliff exists…
2. The Pioneer Anomaly
Artist impression of the Pioneer 10 probe (NASA)
Why are the Pioneer probes drifting off-course? Now this is a perplexing issue for astrophysicists, and probably the most difficult question to answer in Solar System observations. Pioneer 10 and 11 were launched back in 1972 and 1973 to explore the outer reaches of the Solar System. Along their way, NASA scientists noticed that both probes were experiencing something rather strange; they were experiencing an unexpected Sun-ward acceleration, pushing them off-course. Although this deviation wasn’t huge by astronomical standards (386,000 km off course after 10 billion km of travel), it was a deviation all the same and astrophysicists are at a loss to explain what is going on.
One main theory suspects that non-uniform infrared radiation around the probes’ bodywork (from the radioactive isotope of plutonium in its Radioisotope Thermoelectric Generators) may be emitting photons preferentially on one side, giving a small push toward the Sun. Other theories are a little more exotic. Perhaps Einstein’s general relativity needs to be modified for long treks into deep space? Or perhaps dark matter has a part to play, having a slowing effect on the Pioneer spacecraft?
How do we know the Oort Cloud even exists? As far as Solar System mysteries go, the Pioneer anomaly is a tough act to follow, but the Oort cloud (in my view) is the biggest mystery of all. Why? We have never seen it, it is a hypothetical region of space.
At least with the Kuiper Belt, we can observe the large KBOs and we know where it is, but the Oort Cloud is too far away (if it really is out there). Firstly, the Oort Cloud is predicted to be over 50,000 AU from the Sun (that’s nearly a light year away), making it about 25% of the way toward our nearest stellar neighbour, Proxima Centauri. The Oort Cloud is therefore a very long way away. The outer reaches of the Oort Cloud is pretty much the edge of the Solar System, and at this distance, the billions of Oort Cloud objects are very loosely gravitationally bound to the Sun. They can therefore be dramatically influenced by the passage of other nearby stars. It is thought that Oort Cloud disruption can lead to icy bodies falling inward periodically, creating long-period comets (such as Halley’s comet).
In fact, this is the only reason why astronomers believe the Oort Cloud exists, it is the source of long-period icy comets which have highly eccentric orbits emanating regions out of the ecliptic plane. This also suggests that the cloud surrounds the Solar System and is not confined to a belt around the ecliptic.
So, the Oort Cloud appears to be out there, but we cannot directly observe it. In my books, that is the biggest mystery in the outermost region of our Solar System…
