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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.
Complete with tentacles, a supermassive black hole and x-ray emitting gas, a monster of a galaxy has been found by NASA’s Hubble Space Telescope, and is helping astronomers answer a long-standing puzzle. The very active galaxy NGC 1275 has giant but beautiful and delicate filaments influenced and shaped by a beastly-strong extragalactic magnetic field. But how the delicate structures such as those found in this galaxy can withstand the hostile, high-energy environment has been a mystery. But researchers say the beauty and the beast co-exist and are dependent on each other for survival.
One of the closest giant elliptical galaxies, NGC 1275 hosts a supermassive black hole. Energetic activity of gas swirling near the black hole blows bubbles of material into the surrounding galaxy cluster. Long gaseous filaments stretch out beyond the galaxy, into the multimillion-degree, X-ray–emitting gas that fills the cluster. Astronomers thought these delicate filaments should have heated up, dispersed, and evaporated by now, or collapsed under their own gravity to form stars.
These filaments are the only visible-light manifestation of the intricate relationship between the central black hole and the surrounding cluster gas. They provide important clues about how giant black holes affect their surrounding environment.
Using Hubble’s view, a team of astronomers led by Andy Fabian from the University of Cambridge, UK, have for the first time resolved individual threads of gas that make up the filaments. The amount of gas contained in a typical thread is around one million times the mass of our own Sun. They are only 200 light-years wide, are often very straight, and extend for up to 20,000 light-years. The filaments are formed when cold gas from the core of the galaxy is dragged out in the wake of the rising bubbles blown by the black hole.
A new study published in the August 21 Nature magazine proposes that magnetic fields hold the charged gas in place and resist the forces that would distort the filaments. This skeletal structure is strong enough to resist gravitational collapse.
“We can see that the magnetic fields are crucial for these complex filaments – both for their survival and for their integrity,” said Fabian.
Similar networks of filaments are found around other more remote central cluster galaxies. However, they cannot be observed with comparable resolution to the view of NGC 1275. In future observations, the team will apply the understanding of NGC 1275 to interpret what they see in other, more distant galaxies.
It’s Wednesday, so it’s time for another “Where In The Universe” Challenge. Take a look at the image above and try to determine where in the universe this image was taken. Give yourself extra points if you can name the spacecraft responsible for taking this image. As always, no peeking below for the before you make your guess. Our readers have been having a blast with this challenge, and we hope this one will evoke more eruptions of cheers and enjoyment.
This is a small volcano island here on Earth, found in the Aleutian Islands. But tiny Kasatochi Volcano created a big mess in recently by spewing ash and sulfur dioxide over the surrounding area. The volcano erupted with little warning on August 7, 2008. No one was hurt, but two biologists were evacuated from the island just hours before the eruption. According to the Associated Press, the ash forced Alaska Airlines to cancel 44 flights between Alaska, Canada, and the continental United States. Until the eruption, the steep-sided volcano harbored a small lake inside its 314-meter (1000-foot) summit, and vegetation (red in this image) covered the slopes. Cliffs along the shoreline may be the result of erosion from heavy surf, visible as a white fringe around the island. Kasatochi had not erupted in at least 200 years.
This image, composed of near-infrared, red, and green wavelengths of light, was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite in 2003.
Here’s a link to some images showing Kasatochi during the eruption.
NASA image and caption by Robert Simmon, based on data from the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team and found on the NASA Earth Observatory website.
The Daedalus star ship, proposed in the 1970s, would propel itself forward using controlled fusion explosions Credit: Nick Stevens/starbase1.co.uk
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Some sobering news from a recent rocket science conference: It is highly improbable that humans will ever explore beyond the Solar System. This downbeat opinion comes from the Joint Propulsion Conference in Hartford, Connecticut, where future space propulsion challenges were discussed and debated. It is widely acknowledged that any form of interstellar travel would require huge advances in technology, but it would seem that the advances required are in the realms of science fiction and are not feasible. Using current technology would take tens of thousands of years, and even advanced concepts could take hundreds. But above all else, there is the question of fuel: How could a trip to Proxima Centauri be achieved if we’d need 100 times more energy than the entire planet currently generates?
In a previous article on the Universe Today, I explored how long it would take to travel to the nearest star using the slowest mode of transportation (the ion driven 1998 Deep Space 1 mission) and the fastest mode of transportation (the solar gravitational accelerated 1976 Helios 2 mission) currently available. I also discussed the theoretical possibility of using nuclear pulse propulsion (a series of fusion bombs dropped behind an interplanetary spaceship to give thrust), much like the 1970’s Daedalus star ship concept (pictured top).
Unfortunately, the ion drive option would take a whopping 81,000 years to get to Proxima Centauri, our nearest star, and using the Sun for a gravitational assist would still take us at least 19,000 years to reach our destination. That is 2,700 to 600 generations, certainly a long-term commitment! To put these figures into perspective, 2,700 generations ago, homo sapiens had not developed the ability to communicate by speech; 600 generations ago the Neanderthals had only recently become extinct. The nuclear pulse propulsion option seems far better taking only 85 years to travel to our nearest star. Still, this is a very long trip (let’s hope they’d offer business class at least…).
Already there are huge challenges facing the notion of travelling to Proxima Centauri, but in a recent gathering of experts in the field of space propulsion, there are even more insurmountable obstacles to mankind’s spread beyond the Solar System. In response to the idea we might make the Proxima trek in a single lifetime, Paulo Lozano, an assistant professor of aeronautics and astronautics at MIT and conference deligate said, “In those cases, you are talking about a scale of engineering that you can’t even imagine.”
OK, so the speed simply isn’t there for a quick flight over 4.3 light years. But there is an even bigger problem than that. How would these interstellar spaceships be fuelled? According to Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute, at least 100 times the total energy output of the entire world would be required for the voyage. “We just can’t extract the resources from the Earth,” Cassenti said during his conference presentation. “They just don’t exist. We would need to mine the outer planets.”
For mankind to extend its reach into the stars, we need to come up with a better plan. Even the most advanced forms of propulsion (even anti-matter engines) cannot make the gap seem any less massive. Suddenly the thought of a warp drive seems more attractive…
NASA will add a system engineers equated to shock absorbers to Ares 1 rockets to reduce significant vibrations that could shake the Orion spacecraft and astronaut crews during early stages of the flight. Earlier, engineers had determined that at about 115 seconds into the flight, the Ares rocket would vibrate for about 5 seconds, enough to potentially make it difficult for crews to read console displays. To mitigate what’s called thrust oscillation, engineers have proposed an active tuned mass absorber that would detect the frequency and amplitude of the thrust oscillation with accelerometers and internal pressure sensors, and use battery-powered motors to move spring mounted weights up and down to damp the vibration out. A spring-and-damper ring will separate the first and second stages of the rocket, and 16 actuators that act like shock absorbers will be added to the bell-shaped aft skirt at the bottom of the rocket.
Engineers are also looking to use a passive “compliance structure” which is a spring-loaded ring that would detune the stack by softening the interface between the first and upper stages while preserving lateral stability in the Ares 1 design concept.
This concept is expected to reduce the G-forces on the astronauts from about 5 G’s to .25 G’s.
Computer modeling and early design analyses showed the Ares 1 rocket would shake near 105-115 seconds into the flight after liftoff, subjecting the Orion spacecraft and astronauts onboard to high G forces for only about 5 seconds. But NASA engineers were concerned that astronauts could be injured or critical systems could be damaged during that time of the flight.
The thrust oscillation occurs as solid fuel in the first stage depletes, leaving a long, empty shell that takes on the characteristics of an organ pipe, resonating, at frequencies between 12 and 14 hertz. The second stage of the rocket and the Orion spacecraft atop it will naturally dampen the resulting pressure pulses, which essentially would jackhammer the astronauts and make it difficult for them to read console displays and respond.
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More early morning frost is showing up on the Phoenix spacecraft. The Surface Stereo Imager (SSI) took several pictures of the “Telltale” on the Phoenix Mars Lander, the device used to measure wind velocities at the landing site on Mars and created a movie of bright specks of frost accumulating on the mirror of the Telltale. The movie was created from a series of images taken by the Surface Stereo Imager (SSI)between 12:54 a.m. and 2:34 a.m. during the 80th Martian day, or sol, of the mission (Aug. 15, 2008 here on Earth). Sorry, we couldn’t load the movie on this page, the file was too big. But follow this link to see it — the frost is very cool (pun intended).
Phoenix’s SSI took these images through a blue filter (450 nanometer wavelength) that is used primarily for viewing items on the spacecraft rather than the workspace or horizon. In order to increase the number of frames, the size of the individual images downlinked from the spacecraft has been reduced. These have been shown superimposed upon a full image of the telltale from Sol 13 for context. The frost on the mirror sparkles in low-angle light from the sun, which is barely above the horizon at this hour.
Via Twitter, the Phoenix spacecraft said not to worry, this type of early morning frost is not a concern for the operation of the spacecraft.
The Telltale experiment is a passive instrument that provides information about winds at the landing site. It consists of a lightweight Kapton tube hanging in Kevlar fibers that will deflect as a result of wind forces. Images of the Telltale obtained by the onboard camera (SSI) using long exposure times provide information on the deflection and dynamics that can be related to wind velocities and turbulence.
During the early-morning period when these images were taken the wind was blowing steadily at about 5 meters per second (about 11 miles per hour) from the northeast, as indicated by the telltale.
The telltale is about 10 centimeters (4 inches) tall and the total mass of the active part is about 10 mg. The experiment was built by the University of Aarhus, Denmark. Phoenix weather summary from Sol 63
Here’s some info on the weather on Mars, although Sol 63 is the latest available from the Mars Weather Station on Phoenix. To learn more about the Weather Station, follow this link.
Google Earth view of the Kennedy Space Center launch pads (Google)
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Topical Storm Fay has made landfall along Florida’s southwest coastline and is working inland. Officials at NASA’s Kennedy Space Center have decided to close down operations for 24 hours as a precautionary measure. Kennedy’s 15,000 staff have been instructed to stay at home, although a small number of emergency personnel remain on site to monitor the storm’s effect on the space complex. The Kennedy Visitor Center has also been closed. Fay had been forecast to make landfall as a much more powerful entity and there were concerns that the winds could reach hurricane force, but fortunately it remained classified as a tropical storm and damage has been limited…
So far Fay hasn’t been the monster some meteorologists thought she could be. Building up energy from the Atlantic Ocean, Fay was beginning to look like she could become a hurricane by the time she hit the Florida peninsula. But no, Tropical Storm Fay did not fulfil the predictions, but she is dumping a lot of rain and sustaining winds of up to 65 miles per hour (105 km/h), causing minor damage and a lot of mess. According to news sources, the southern town of Everglades City suffered minor flooding due to a small storm surge (a localized increase of sea level associated with a low pressure region) and there are some downed trees. Electricity still seems to be supplying the remaining residents and there are no reports of serious injuries.
But what of Kennedy Space Center? There is currently a skeleton crew of 200 personnel called the “ride-out crew” keeping a close eye on any damage to the site. Kennedy managers are expected to meet at 5 pm (EDT) to discuss the situation and assess whether the complex should remain closed for a second day.
As for the three Space Shuttles, they have been secured in their Orbiter Processing Facilities, in a powered down state, behind the protection of their hangers. Other instrumentation such as Hubble Space Telescope parts and International Space Station flight hardware are also protected.
So there’s nothing more to do except sit and wait for Fay to pass over Florida, gradually losing energy further inland until it dissipates over the coming days…
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Currently, launching 1 pound (.5 kilogram) of payload to space costs about $5,000 USD, so every little bit helps if engineers can cut down on the weight of the spacecraft. Scientists from the University of Michigan have patented their ideas for cutting down the size and weight of the thrusters used in space to maneuver and control the spacecraft. Usually these thrusters are fairly big; they can be as big as a refrigerator. But the new thrusters, called nano-thrusters, could be made into flat, low weight sheets and mounted on the sides of spacecraft. The new type of thrusters would save weight and fuel, while having a longer life as well.
Conventional ion thrusters work by accelerating gas ions to generate force in the opposite direction. But, they waste gas and are limited in lifetime because the accelerated ions damage the engine.
But, according to a report in New Scientist, the new nano-thrusters, developed by Brian Gilchrist and colleagues at the University of Michigan in Ann Arbor, US, avoid these problems.
Each consists of a small chamber of fluid with electrodes inside and a vent at the top. Above that vent more electrodes generate a powerful electric field. The fluid contains nanoparticles just tens of nanometres across that are ionized by electrodes in the chamber. Those charged ions are accelerated by the electric field and ejected from the vent, producing thrust.
These nanothrusters can be used in large numbers on flat panels. To control the spacecraft efficiently, they would probably have to cover large areas of spacecraft. But in the drag-free space environment, it be just like having a second skin on the spacecraft. And they would be much more light-weight than conventional thrusters, and would help cut the costs of launching vehicles to space.
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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…
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Remember a few months ago when “space” seemed to be a non-issue for the candidates in this year’s US presidential election? But now space seems to be a hot topic. John McCain was in Florida today where he met with 20 leaders from the space industry for a roundtable discussion, and Barack Obama was in Florida last week, to stump for votes. Perhaps both candidates are recalling the 2000 presidential election that hinged on the Florida vote. Hanging chads aside, an important issue in Florida these days is the projected job losses that will be incurred in the gap after the space shuttle is retired in 2010 and before the Constellation program makes its first flights in about 2015, and both candidates have met with members of NASA’s workforce and other NASA officials to discuss this issue. Also, both McCain and Obama recently updated their positions on their space-related agendas on their websites, with both devoting quite a bit of “space” to space.
If you’re still undecided, or haven’t seen the candidate’s latest views on space, take a look at Barack Obama’s position paper on space and John McCain’s space policy statement. If that’s too much reading for you, the folks at Florida Today.com have outlined the major points of each candidate’s space policies:
• Major points of Obama’s space policy:
1. Re-enacting the National Aeronautics and Space Council to oversee and coordinate the civilian, commercial and military space programs and report to the president.
2. Closing the gap between the retirement of the Space Shuttle and the introduction of its successor through adding another Shuttle flight, accelerating the development of the next generation vehicle, and working with the industry to retain our workforce and technical capabilities.
3. Completing and enhancing the International Space Station so it can host the innovative scientific and technological research projects it was intended to facilitate.
4. Embracing human and robotic space exploration with a goal of sending human missions to the Moon by 2020, as a precursor in an orderly progression to missions to more distant destinations, including Mars.
5. Emphasizing NASA’s research function to study climate change and advance aeronautics research.
6. Expanding public/private partnerships to develop cutting-edge technologies.
7. Inspiring the next generation through expanded education programs.
Major points of McCain’s space policy:
1. Ensure that space exploration is top priority and that the U.S. remains a leader.
2. Commit to funding the NASA Constellation program to ensure it has the resources it needs to begin a new era of human space exploration.
3. Review and explore all options to ensure U.S. access to space by minimizing the gap between the termination of the Space Shuttle and the availability of its replacement vehicle.
4. Ensure the national space workforce is maintained and fully utilized; Complete construction of the ISS National Laboratory.
5. Seek to maximize the research capability and commercialization possibilities of the ISS National Laboratory.
6. Maintain infrastructure investments in Earth-monitoring satellites and support systems.
a. Seek to maintain the nation’s space infrastructure.
7. Prevent wasteful earmarks from diverting precious resources from critical scientific research.
8. Ensure adequate investments in aeronautics research.
