One of the biggest surprises of the 13-year Cassini mission came in Enceladus, a tiny moon with active geysers at its south pole. At only about 504 kilometers (313 miles) in diameter, the bright and ice-covered Enceladus should be too small and too far from the Sun to be active. Instead, this little moon is one of the most geologically dynamic objects in the Solar System.
A new study has modeled how this activity could be taking place, and what mechanism might power the geysers spewing from ‘tiger stripe’ fissures. While previous studies have indicated some type of unknown internal heat source on Enceladus, the new study infers no heat source would be necessary.
Max Rudolph, from the University of California, Davis and colleagues say that cracks in the ice shell caused by changes in Enceladus’ orbit around Saturn would allow water from the subsurface ocean to leak out. And instead of active cryovolcanism, the researchers propose the water spontaneously boils when it hits the vacuum of space.
Voyager 1 acquired this image of Io on March 4, 1971. An enormous volcanic explosion can be seen silhouetted against dark space over Io’s bright limb. Credit: NASA/JPL.
Cryo-volcanism is a relatively newly found phenomenon, initially discovered by the Voyager missions’ travels to the outer Solar System. Instead of hot, molten lava like volcanoes on Earth, cryo-volcanism spews out water, ice and other materials in environments that can be hundreds of degrees below freezing. For example, temperatures at the surface of Enceladus rarely rise above –200°C (-330 F).
Cryo-volcanism has been observed at Jupiter’s Io and Europa, as well as at Enceladus and other icy moons. While Io appears to be outgassing sulfur dioxide, other moons are erupting with water, methane and ammonia.
Cassini’s view down into a jetting “tiger stripe” in August 2010. Credit: NASA
Rudolph and colleagues said they modeled the orbital and internal evolution of the ice-covered ocean worlds Enceladus and Europa across 100 million years of time. The eccentricity of the moons’ orbits leads to varying thicknesses of their ice shells. As the ice thickens and thins, the team said, thermal stresses in the ice shell and pressure in the underlying ocean will change, promoting the fracturing of the ice shell, creating the tiger stripe fissures.
This takes place as the ice cools and thickens. The pressure exerted on the ocean below would create stress on the ice, since ice has more volume than water. The pressure and stress could cause cracks, and create pathways for fluid to reach the surface, as much as 20-30 kilometers away. The sublimation of the water as it hit the vacuum of space gives the appearance of “jets” when there aren’t any.
Rudolph said in a press release that this is consistent with the appearance of the surface of Enceladus, which doesn’t show any evidence of cryo-lava flows leaking from the cracks on the surface, which are found on Io. Enceladus appears to be unique in that the tiger stripe cracks are not found anywhere else in our Solar System. They are parallel and evenly spaced, about 130 kilometers long and 35 kilometers apart, and they appear to be continually erupting with water ice.
Dramatic plumes, both large and small, spray water ice out from many locations along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. Credit: NASA/JPL/Space Science Institute
But the mechanism identified in this new study of ocean pressure and
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We Should Hit Peak Solar Activity Next Year
You may be familiar with the solar cycle that follows a 22 year process shifting from solar minimum to maximum and back again. It’s a cycle that has been observed for centuries yet predicting its peak has been somewhat challenging. The Sun’s current cycle is approaching maximum activity which brings with it higher numbers of sunspots on its surface, more flares and more coronal mass ejections. A team from India now believe they have discovered a new element of the Sun’s magnetic field allowing them to predict the peak will occur early in 2024.
The Sun is a gigantic sphere of plasma or electrically charged gas. One of the features of plasma is that if a magnetic field passes through it, the plasma moves with it. Conversely if the plasma moves, the magnetic field moves too. This magnetic field is just like Earth and is known as a dipole magnetic field. You can visualise it if you can remember your school science days with a bar magnet and iron filings.
A dipole magnetic field has two opposite but equal charges and at the start of the Sun’s cycle the field lines effectively run from the north pole to the south. As the Sun rotates, with the equator rotating faster than the polar regions, then the plasma drags the magnetic field lines with it, winding them tighter and tighter.
The field lines become stretched causing the magnetic field to loop up and through the visible surface of the Sun. This localised event prevents the convection of super heated gas from underneath and appears as a cooler area of the surface which appears dark. As the solar cycle starts, these sunspots appear around the polar regions and slowly migrate toward the equator as it progresses with peak activity occurring when the sunspots fade away as we head toward the start of another cycle.
Image of sunspots (Credit : NASA Goddard Space Flight Center // SDO)
On occasions the magnetic field of sunspots are disrupted and we can experience flares or coronal mass ejections hurling vast amounts of charged particles out into space. If they reach us here on Earth they give rise to the beautiful aurora displays but they do also have a rather negative impact to satellites, power grids and telecommunications systems.
Deep inside the Sun, a dynamo mechanism is driving all this. It is created by the energy from the movement of plasma and it is this that is responsible for the flipping of the Sun’s magnetic poles where the north pole becomes south and the south pole becomes north which happens every 11 years or so. It’s another aspect of the solar cycle.
It’s been known since the 1930’s that the rate of rise the sunspot cycle relates to its strength with stronger cycles taking less time to reach peak. In the paper published in the Monthly Notices of the Royal Astronomical Society Letters; Priyansh Jaswal, Chitradeep Saha and Dibyendu Nandy from the Indian Institutes of Science Education and Research announced their findings. They discovered that the rate of decrease in the Sun’s dipole magnetic field also seems to relate to the rise of the present cycle.
The team have looked back through archives and have shown how the observation of the dipole decrease rate along with observations of sunspots can predict the peak of activity with better accuracy than before. They conclude the current cycle is expected to peak somewhere between early 2024 and September next year. Being able to better predict the peak of activity will help understand the likely intensity of space weather events here on Earth providing us more warning to be able to prepare.
Source : Solar activity likely to peak next year, new study suggests
The post We Should Hit Peak Solar Activity Next Year appeared first on Universe Today.
The Solar Radius Might Be Slightly Smaller Than We Thought
Two astronomers use a pioneering method to suggest that the size of our Sun and the solar radius may be due revision.
Our host star is full of surprises. Studying our Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization.
Now, a new study, titled The Acoustic Size of the Sun suggests that a key parameter in modern astronomy and heliophysics—the diameter of the Sun—may need a slight tweak.
The study out of the University of Tokyo and the Institute of Astronomy at Cambridge was done looking at data from the joint NASA/ESA Solar Heliospheric Observatory (SOHO’s) Michelson Doppler Imager (MDI) imager. The method probes the solar interior via acoustics and a cutting edge field of solar physics known as helioseismology.
A cutaway diagram of the Sun. NASA/ESA/SOHO
‘Hearing’ the Solar Interior
How can you ‘hear’ acoustic waves on the Sun? In 1962, astronomers discovered that patches on the surface of the Sun oscillate, or bubble up and down, like water boiling on a stove top. These create waves that ripple in periodic 5-minute oscillations across the roiling surface of the Sun.
A view of the Sun, courtesy of SOHO’s MDI instrument. Credit: NASA
What’s more, astronomers can use what we see happening on the surface of the Sun to model the solar interior, much like terrestrial astronomers use seismic waves traveling through the Earth to model its core. Thanks to helioseismology, we can even ‘see’ what’s going on on the solar farside, and alert observers of massive sunspots before they rotate into view.
Solar farside modeling using helioseismology. Credit: NSF/GONG
The study looked at p-mode waves as they traversed the solar interior. Previous studies relied on less accurate f-mode waves, which are surface waves considerably shorter than the solar radius.
The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement. This is only smaller by a few hundredths of a percent, or 100-200 kilometers.
An artist’s conception of SOHO in space. Credit: ESA/SOHO
The solar radius is a deceptively simple but crucial factor in astronomy. The Sun is a glowing ball of hydrogen and helium plasma without a distinct surface boundary. The photosphere—the glowing visible layer we see shining down on us on a sunny day—is what we generally refer to as the surface of the Sun.
The Solar Radius: A Brief
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If Warp Drives are Impossible, Maybe Faster Than Light Communication is Still on the Table?
I’m sure many readers of Universe Today are like me, fans of the science fiction genre. From the light sabres of Star Wars to the neuralyzer of Men in Black, science fiction has crazy inventions aplenty and once science fiction writers dream it, scientists and engineers try and create it. Perhaps the holy grail of science fiction creations is the warp drive from Star Trek and it is fair to say that many have tried to work out if it is even possible to travel faster than the speed of light. To date, alas, to no avail but if the warp drive eludes us, what about faster than light communication!
Let’s start with the warp drive. The concept is a drive that can propel a spacecraft at speeds in excess of the speed of light. According to the Star Trek writers, the speed was described in factors of warp speed where they are converted to multiples of the speed of light by multiplication with the cubic function of the warp factor itself! Got it! Don’t worry, it’s not crucial to this article. Essentially ‘warp 1’ is equivalent to the speed of light, ‘warp 2’ is eight times speed of light and ‘warp 3’ is 27 times the speed of light and so it goes on! Therein lies the problem; achieving faster than light travel.
In attempts to try to understand this, numerous experiments have been undertaken, of note Bill Bertozzi at MIT accelerated electrons and observed them becoming heavier and heavier until they couldn’t be accelerated any more! Once at the speed of light, it takes an infinite amount of energy to accelerate an object further! The maximum speed he achieved was the speed of light. In other experiments, synchronised atomic clocks were taken on board airliners and found that, after travelling at high speed relative to a reference clock on Earth, time had run slower! The upshot is that the faster you go, the slower time passes and at the speed of light, time stops! If time stops, so does speed! hmmmm this is tricky.
The science of faster than light travel aside, In a number of potential warp drive designs have surfaced like the Alcubierre Drive proposed in 1994. However, the common factor to provide the faster than light travel is something called negative energy which is required in copious amounts. The study of quantum mechanics shows that even empty space has energy and anything that has less energy than empty space has ‘negative energy’. The problem (among many) is that no-one knows how to get negative energy in huge amounts to power the warp drives.
Two-dimensional visualization of an Alcubierre drive, showing the opposing regions of expanding and contracting spacetime that displace the central region (Credit : AllenMcC)
It seems the warp drive is some time away yet but what about faster than light communication, could that work? Accelerating macroscopic objects, like spacecraft requires high amounts of negative energy but communication, as a recent paper explains, which operates at much smaller scale requires less energy. Quite a bit less in fact, less than is contained inside a lightning bolt. Perhaps more tantalising is that we may just be able to create small amounts of negative energy using today’s technology.
One of the ways this can be achieved is to ensure the proper configuration and distribution of negative energy to channel communication. The paper proposes a tubular distribution of negative energy in so called hypertubes to enable the acceleration and deceleration of warp bubbles for superluminal communication. Achieving this for long distance communication will require special devices to be designed and built but as the papers author Lorenzo Pieri concludes “it is tantalising to consider the fabrication of microchips capable of superluminal computing”. Yes, that is an exciting proposition but the thought of firing messages out to the cosmos at speeds faster than that of light.. Just wow!
Source : Hyperwave: Hyper-Fast Communication within General Relativity
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