The appearing and disappearing feature observed in Titan's Lakes was dubbed "Magic Island". Image: NASA/JPL-Caltech/ASI/Cornell
Saturn’s largest Moon, Titan, is the only other world in our Solar System that has stable liquid on its surface. That alone, and the fact that the liquid is composed of methane, ethane, and nitrogen, makes it an object of fascination. The bright spot features that Cassini observed in the methane seas that dot the polar regions only deepen the fascination.
A new paper published in Nature Astronomy digs deeper into a phenomenon in Titan’s seas that has been puzzling scientists. In 2013, Cassini noticed a feature that wasn’t there on previous fly-bys of the same region. In subsequent images, the feature had disappeared again. What could it be?
One explanation is that the feature could be a disappearing island, rising and falling in the liquid. This idea took hold, but was only an initial guess. Adding to the mystery was the doubling in size of these potential islands. Others speculated that they could be waves, the first waves observed anywhere other than on Earth. Binding all of these together was the idea that the appearance and disappearance could be caused by seasonal changes on the moon.
Titan’s dense, hydrocarbon rich atmosphere remains a focal point of scientific research. Credit: NASA
Now, scientists at NASA’s Jet Propulsion Laboratory (JPL) think they know what’s behind these so-called ‘disappearing islands,’ and it seems like they are related to seasonal changes.
The study was led by Michael Malaska of JPL. The researchers simulated the frigid conditions on Titan, where the temperature is -179.2 Celsius. At that temperature, some interesting things happen to the nitrogen in Titan’s atmosphere.
On Titan, it rains. But the rain is composed of extremely cold methane. As that methane falls to the surface, it absorbs significant amounts of nitrogen from the atmosphere. The rain hits Titan’s surface and collects in the lakes on the moon’s polar regions.
The researchers manipulated the conditions in their experiments to mirror the changes that occur on Titan. They changed the temperature, the pressure, and the methane/ethane composition. As they did so, they found that nitrogen bubbled out of solution.
“Our experiments showed that when methane-rich liquids mix with ethane-rich ones — for example from a heavy rain, or when runoff from a methane river mixes into an ethane-rich lake — the nitrogen is less able to stay in solution,” said Michael Malaska of JPL. This release of nitrogen is called exsolution. It can occur when the seasons change on Titan, and the seas of methane and ethane experience a slight warming.
“Thanks to this work on nitrogen’s solubility, we’re now confident that bubbles could indeed form in the seas, and in fact may be more abundant than we’d expected,” said Jason Hofgartner of JPL, a co-author of the study who also works on Cassini’s radar team. These nitrogen bubbles would be very reflective, which explains why Cassini was able to see them.
The first-ever images of the surface of a new moon or planet are always exciting. The Huygens probe was launched from Cassini to the surface of Titan, but was not able investigate the lakes and seas on the surface. Image Credit: ESA/NASA/JPL/University of Arizona
The seas on Titan may be what’s called a prebiotic environment, where chemical conditions are hospitable to the appearance of life. Some think that the seas may already be home to life, though there’s no evidence of this, and Cassini wasn’t equipped to investigate that premise. Some experiments have shown that an atmosphere like Titan’s could generate complex molecules, and even the building blocks of life.
NASA and others have talked about different ways to explore Titan, including balloons, a drone, splashdown landers, and even a submarine. The submarine idea even received a NASA grant in 2015, to develop the idea further.
So, mystery solved, probably. Titan’s bright spots are neither islands nor waves, but bubbles.
Cassini’s mission will end soon, and it’ll be quite some time before Titan can be investigated further. The question of whether Titan’s seas are hospitable to the formation of life, or whether there may already be life there, will have to wait. What role the nitrogen bubbles play in Titan’s life question will also have to wait.
In 2005, the Future In-Space Operations Working Group (FISOWG) was established with the help of NASA to assess how advances in spaceflight technologies could be used to facilitate missions back to the Moon and beyond. In 2006, the FISO Working Group also established the FISO Telecon Series to conduct outreach to the public and educate them on issues pertaining to spaceflight technology, engineering, and science.
Every week, the Telecon Series holds a seminar where experts are able to share the latest news and developments from their respective fields. On Wednesday, April 19th, in a seminar titled “An Air-Breathing Metal-Combustion Power Plant for Venus in situ Exploration“, NASA engineer Michael Paul presented a novel idea where existing technology could be used to make longer-duration missions to Venus.
To recap the history of Venus exploration, very few probes have ever been able to explore its atmosphere or surface for long. Not surprising, considering that the atmospheric pressure on Venus is 92 times what it is here on Earth at sea level. Not to mention the fact that Venus is also the hottest planet in the Solar System – with average surface temperatures of 737 K (462 °C; 863.6 °F).
Although similar in size and composition to the Earth, Venus has an extremely dense atmosphere with clouds that produce sulfuric acid rain. Credit: NASA
Hence why those few probes that actually explored the atmosphere and surface in detail – like the Soviet-era Venera probes and landers and NASA’s Pioneer Venus multiprobe – were only able to return data for a matter of hours. All other missions to Venus have either taken the form of orbiters or consisted of spacecraft conducting flybys while en route to other destinations.
Having worked in the fields of space exploration and aerospace engineering for 20 years, Michael Paul is well-versed in the challenges of mounting missions to other planets. During his time with the John Hopkins University Applied Physics Laboratory (JHUAPL), he contributed to NASA’s Contour and Stereo missions, and was also instrumental in the launch and early operations of the MESSENGER mission to Mercury.
However, it was a flagship-level study in 2008 – performed collaboratively between JHUAPL and NASA’s Jet Propulsion laboratory (JPL) – that opened his eyes to the need for missions that took advantage of the process known as In-Situ Resource Utilization (ISRU). As he stated during the seminar:
“That year we actually studied a very large mission to Europa which evolved into the current Europa Clipper mission. And we also studied a flagship mission to the Saturn, to Titan specifically. The Titan-Saturn system mission study was a real eye-opener for me in terms what could be done and why we should be doing a lot of more adventurous and more aggressive exploration of in-situ in certain places.”
The flagship mission to Titan was the subject of Paul’s work since joining Penn Sate’s Applied Research Laboratory in 2009. During his time there, he became a NASA Innovative Advanced Concepts Program (NIAC) Fellow for his co-creation of the Titan Submarine. For this mission, which will explore the methane lakes of Titan, Paul helped to develop underwater power systems that would provide energy for planetary landers that can’t see the Sun.
Having returned to JHUAPL, where he is now the Space Mission Formulation Lead, Paul continues to work on in-situ concepts that could enable missions to locations in the Solar System that present a challenge. In-situ exploration, where local resources are relied upon for various purposes, presents numerous advantages over more traditional concepts, not the least of which is cost-effectiveness.
Consider mission that rely on Multi-Mission Radioisotope Thermoelectric Generators (MMRTG) – where radioactive elements like Plutonium-238 are used to generate electricity. Whereas this type of power system – which was used by the Viking 1 and 2 landers (sent to Mars in 1979) and the more recent Curiosity rover – provides unparalleled energy density, the cost of such missions is prohibitive.
What’s more, in-situ missions could also function in places where conventional solar cells would not work. These include not only locations in the outer Solar System (i.e. Europa,Titan and Enceladus) but also places closer to home. The South Pole-Aitken Basin, for example, is a permanently shadowed location on the Moon that NASA and other space agencies are interesting in exploring (and maybe colonizing) due to the abundance of water ice there.
But there’s also the surface Venus, where sunlight is in short supply because of the planet’s dense atmosphere. As Paul explained in the course of the seminar:
“What can you do with other power systems in places where the Sun just doesn’t shine? Okay, so you want to get to the surface of Venus and last more than a couple of hours. And I think that in the last 10 or 15 years, all the missions that [were proposed] to the surface of Venus pretty much had a two-hour timeline. And those were all proposed, none of those missions were actually flown. And that’s in line with the 2 hours that the Russian landers survived when they got there, to the surface of Venus.”
Diagram of a Sterling Engine, part of proposed mission to Europe (“Fire on Europa”). Credit: lpi.usra.edu
The solution to this problem, as Paul sees it, is to employ a Stored-Chemical Energy and Power System (SCEPS), also known as a Sterling engine. This proven technology relies on stored chemical energy to generate electricity, and is typically used in underwater systems. But repurposed for Venus, it could provide a lander mission with a considerable amount of time (compared to previous Venus missions) with which to conduct surface studies.
For the power system Paul and his colleagues are envisioning, the Sterling engine would take solid-metal lithium (or possibly solid iodine), and then liquefy it with a pyrotechnic charge. This resulting liquid would then be fed into another chamber where it would combined with an oxidant. This would produce heat and combustion, which would then be used to boil water, spin turbines, and generate electricity.
Such a system is typically closed and produces no exhaust, which makes it very useful for underwater systems that cannot compromise their buoyancy. On Venus, such a system would allow for electrical production without short-lived batteries, an expensive nuclear fuel cell, and could function in a low solar-energy environment.
An added benefit for such a craft operating on Venus is that the oxidizer would be provided locally, thus removing the need for an heavy component. By simply letting in outside CO2 – which Venus’ atmosphere has in abundance – and combining with the system’s liquified lithium (or iodine), the SCEPS system could provide sustained energy for a period of days.
The Advanced Lithium Ion Venus Explorer (ALIVE), derived from the COMPASS final report (2016). Credit: Oleson, Steven R., and Michael Paul.
Further help came from the Glenn Research Center’s COMPASS lab, were engineers from multiple disciplines performs integrated vehicle systems analyses. From all of this, a mission concept known as the Advanced Lithium Venus Explorer (ALIVE) was developed. With the help of Steven Oleson – the head of GRC’s COMPASS lab – Paul and his team envision a mission where a lander would reach the surface of Venus and study it for 5 to 10 days.
All told, that’s an operational window of between 120 and 240 hours – in other words, 60 to 120 times as long as previous missions. However, how much such a mission would cost remains to be seen. According to Paul, that question became the basis of an ongoing debate between himself and Oleson, who disagreed as to whether it would be part of the Discovery Program or the New Frontiers Program.
As Paul explained, missions belonging to the former were recently capped at the $450 to $500 million level while the latter are capped at $850 million. “I believe that if you did this right, you could get it into a Discovery mission,” he said. “Here at APL, I’ve seen really complicated ideas fit inside a Discovery cost cap. And I believe that the way we crafted this mission, you could do this for a Discovery mission. And it would be really exciting to get that done.”
Artist’s impression of the surface of Venus. Credit: ESA/AOES
From a purely technological standpoint, this not a new idea. But in terms of space exploration, it has never been done before. Granted, there are still many tests which would need to be conducted before any a mission to Venus can be planned. In particular, there are the byproducts created by combusting lithium and CO2 under Venus-like conditions, which already produced some unexpected results during tests.
In addition, there is the problem of nitrogen gas (N2) – also present in Venus’ atmosphere – building up in the system, which would need to be vented in order to prevent a blowout. But the advantages of such a system are evident, and Paul and his colleagues are eager to take additional steps to develop it. This summer, they will be doing another test of a lithium SCEPS under the watchful eye of NAIC.
By this time next year, they hope to have completed their analysis and their design for the system, and begin building one which they hope to test in a controlled temperature environment. This will be the first step in what Paul hopes will be a three-year period of testing and development.
“The first year we’re basically going to do a lot of number crunching to make sure we got it right,” he said. “The second year we’re going to built it, and test it at higher temperatures than room temperature – but not the high temperatures of Venus! And in the third year, we’re going to do the high temperature test.”
Ultimately, the concept could be made to function in any number of high and low temperature conditions, allowing for cost-effective long-duration missions in all kinds of extreme environments. These would include Titan, Europa and Enceladus, but also Venus, the Moon, and perhaps the permanently-shadowed regions on Mercury’s poles as well.
Space exploration is always a challenge. Whenever ideas come along that make it possible to peak into more environments, and on a budget to boot, it is time to start researching and developing them!
This composite of 30 images of asteroid 2014 JO25 was generated with radar data collected using NASA’s Goldstone Solar System Radar in California’s Mojave Desert on Tuesday April 18. Credit: NASA/JPL-Caltech/GSSR
Asteroid 2014 JO25, discovered in 2014 by the Catalina Sky Survey in Arizona, was in the spotlight today (April 19) when it flew by Earth at just four times the distance of the Moon. Today’s encounter is the closest the object has come to the Earth in 400 years and will be its closest approach for at least the next 500 years.
Lots of asteroids zip by our planet, and new ones are discovered every week. What makes 2014 JO25 different it’s one of nearly 1,800 PHAs (Potentially Hazardous Asteroids) that are big enough and occasionally pass close enough to Earth to be of concern. PHAs have diameters of at least 100-150 meters (330-490 feet) and pass less than 0.05 a.u (7.5 million km / 4.6 million miles) from our planet. Good thing for earthlings, no known PHA is predicted to impact Earth for at least the next 100 years.
Most of these Earth-approachers are on the small side, only a few to a few dozen meters (yards) across. 2014 JO25 was originally estimated at ~2,000 feet wide, but thanks to radar observations made the past couple days, we now know it’s nearly twice that size. Radar images of asteroid were made early this morning with NASA’s 230-foot (70-meter) radio antenna at Goldstone Deep Space Communications Complex in California. They reveal a peanut-shaped asteroid that rotates about once every 5 hours and show details as small as 25 feet.
NASA radar images and animation of asteroid 2015 JO25
The larger of the two lobes is about 2,000 feet (620 meters) across, making the total length closer to 4,000 feet. That’s similar in size (though not as long) as the Rock of Gibraltar that stands at the southwestern tip of Europe at the tip of the Iberian Peninsula.
“The asteroid has a contact binary structure — two lobes connected by a neck-like region,” said Shantanu Naidu, a scientist from NASA’s Jet Propulsion Laboratory in Pasadena, California, who led the Goldstone observations. “The images show flat facets, concavities and angular topography.” Contact binaries form when two separate asteroids come close enough together to touch and meld as one.
The Goldstone dish dish, based in the Mojave Desert near Barstow, Cal. is used for radar mapping of planets, comets, asteroids and the Moon. Credit: NASA
Radar observations of the asteroid have also been underway at the National Science Foundation’s Arecibo Observatory in Puerto Rico with more observations coming today through the 21st which may show even finer details. The technique of pinging asteroids with radio waves and eking out information based on the returning echoes has been used to observe hundreds of asteroids.
When these relics from the early solar system pass relatively close to Earth, astronomers can glean their sizes, shapes, rotation, surface features, and roughness, as well as determine their orbits with precision.
Because of 2014 JO25’s relatively large size and proximity, it’s bright enough to spot in a small telescope this evening. It will shine around magnitude +10.9 from North America tonight as it travels south-southwest across the dim constellation Coma Berenices behind the tail of Leo the Lion. A good map and 3-inch or larger telescope should show it.
Use the maps at this link to help you find and track the asteroid tonight. The key to spotting it is to allow time to identify and get familiar with the star field the asteroid will pass through 10 to 15 minutes in advance — then lay in wait for the moving object. Don’t be surprised if 2014 JO25 deviates a little from the predicted path depending on your location and late changes to its orbit, so keep watch not only on the path but around it, too. Good luck!
Here on Earth, a year lasts roughly 365.25 days, each of which lasts 24 hours long. During the course of a single year, our planet goes through some rather pronounced seasonal changes. This is the product of our orbital period, our rotational period, and our axial tilt. And when it comes to the other planets in our Solar System, much the same is true.
Consider Neptune. As the eight and farthest planet from the Sun, Neptune has an extremely wide orbit and a comparatively slow orbital velocity. As a result, a year on Neptune is very long, lasting the equivalent of almost 165 Earth years. Combined with its extreme axial tilt, this also means that Neptune experiences some rather extreme seasonal changes.
Orbital Period:
Neptune orbits our Sun at an average distance (semi-major axis) of 4,504.45 million km (2,798.656 million mi; 30.11 AU). Because of its orbital eccentricity (0.009456), this distance varies somewhat, ranging from 4,460 million km (2,771 million mi; 29.81 AU) at its closest (perihelion) to 4,540 million km (2,821 million mi; 30.33 AU) at its farthest (aphelion).
The orbit of Neptune and the other outer Solar planets, as well as the ice-rich Kuiper Belt that lies just beyond it. Credit: NASA
With an average orbital speed of 5.43 km/s, it takes Neptune 164.8 Earth years (60,182 Earth days) to complete a single orbital period. This means, in effect, that a year on Neptune lasts as long as about 165 years here on Earth. However, given its rotational period of 0.6713 Earth days (16 hours 6 minutes 36 seconds), a year on Neptune works out to 89,666 Neptunian solar days.
Given that Neptune was discovered in 1846, humanity has only known about its existence for 171 years (at the time of this article’s writing). That means that since its discovery, the planet has only completed a single orbital period (which ended in 2010) and is only seven years into its second. This orbital period will be complete by 2179.
Orbital Resonance:
Because of its location in the outer Solar System, Neptune’s orbit has a profound impact on the neighboring Kuiper Belt. This region, which is similar (but significantly larger) than the Main Asteroid Belt, consists of many small icy worlds and objects that extends from Neptune’s orbit (at 30 AU) to a distance of about 55 AU from the Sun.
Animated diagram showing the spacing of the Solar Systems planet’s, the unusually closely spaced orbits of six of the most distant KBOs, and the possible “Planet 9”. Credit: Caltech/nagualdesign
So much as Jupiter’s gravity has dominated the Asteroid Belt, affecting its structure and occasionally kicking asteroids and planetoids into the inner Solar System, Neptune’s gravity dominates the Kuiper Belt. This has led to the creation of gaps in the belt, empty regions where objects have achieved an orbital resonance with Neptune.
Within these gaps, objects have a 1:2, 2:3 or 3:4 resonance with Neptune, meaning they complete one orbit of the Sun for every two completed by Neptune, two for every three, or three for every four. The over 200 known objects that exist in the 2:3 resonance (the most populous) are known as plutinos, since Pluto is the largest of them.
Although Pluto crosses Neptune’s orbit on a regular basis, their 2:3 orbital resonance ensures they can never collide. On occasion, Neptune’s gravity also causes icy bodies to be kicked out of the Kuiper Belt. Many of these then travel to the Inner Solar System, where they become comets with extremely long orbital periods.
Neptune’s largest satellite, Triton, is believed to have once been a Kuiper Belt Object (KBO) – and Trans-Neptunian Object (TNO) – that was captured by Neptune’s gravity. This is evidenced by its retrograde motion, meaning it orbits the planet in the opposite direction as its other satellites. It also has a number of Trojan Objects occupying its L4 and L5 Lagrange points. These “Neptune Trojans” can be said to be in a stable 1:1 orbital resonance with Neptune.
Seasonal Change:
Much like the other planets of the Solar System, Neptune’s axis is tilted towards the Sun’s ecliptic. In Neptune’s case, it is tilted 28.32° relative to its orbit (whereas Earth is tilted at 23.5°). Because of this, Neptune undergoes seasonal change during the course of a year because one of its hemispheres will be receiving more sunlight than the other. But in Neptune’s case, a single season lasts a whopping 40 years, making it very hard to witness a full cycle.
While much of the heat that powers Neptune’s atmosphere comes from an internal source (which is currently unknown), a study conducted by researchers from Wisconsin-Madison University and NASA’s Jet Propulsion Laboratory revealed that seasonal change is also driven by solar radiation. This consisted of examining images of Neptune taken by the Hubble Space Telescope between 1996 and 2002.
These images revealed that Neptune’s massive southern cloud bands were becoming steadily wider and brighter over the six year period – which coincided with the southern hemisphere beginning its 40-year summer. This growing cloud cover was attributed to increased solar heating, as it appeared to be concentrated in the southern hemisphere and was rather limited at the equator.
Images taken by Hubble, showing seasonal change in its southern hemisphere. Credit: NASA, L. Sromovsky, and P. Fry (University of Wisconsin-Madison)
Neptune remains a planet of mystery in many ways. And yet, ongoing observations of the planet have revealed some familiar and comforting patterns. For instance, while it’s composition is vastly different and its orbit puts it much farther away from the Sun than Earth, its axial tilt and orbital period still result in its hemispheres experiencing seasonal changes.
It’s good to know that no matter how far we venture out into the Solar System, and no matter how different things may seem, there are still some things that stay the same!
Every planet in the Solar System takes a certain amount of time to complete a single orbit around the Sun. Here on Earth, this period lasts 365.25 days – a period that we refer to as a year. When it comes to the other planets, we use this measurement to characterize their orbital periods. And what we have found is that on many of these planets, depending on their distance from the Sun, a year can last a very long time!
Consider Saturn, which orbits the Sun at a distance of about 9.5 AU – i.e. nine and a half times the distance between the Earth and the Sun. Because of this, the speed with which it orbits the Sun is also considerably slower. As a result, a single year on Saturn lasts an average of about twenty-nine and a half years. And during that time, some interesting changes happen for the planet’s weather systems.
Orbital Period:
Saturn orbits the Sun at an average distance (semi-major axis) of 1.429 billion km (887.9 million mi; 9.5549 AU). Because its orbit is elliptical – with an eccentricity of 0.05555 – its distance from the Sun ranges from 1.35 billion km (838.8 million mi; 9.024 AU) at its closest (perihelion) to 1.509 billion km (937.6 million mi; 10.086 AU) at its farthest (aphelion).
A diagram showing the orbits of the outer Solar planets. Saturn’s orbit is represented in yellow Credit: NASA
With an average orbital speed of 9.69 km/s, it takes Saturn 29.457 Earth years (or 10,759 Earth days) to complete a single revolution around the Sun. In other words, a year on Saturn lasts about as long as 29.5 years here on Earth. However, Saturn also takes just over 10 and a half hours (10 hours 33 minutes) to rotate once on its axis. This means that a single year on Saturn lasts about 24,491 Saturnian solar days.
It is because of this that what we can see of Saturn’s rings from Earth changes over time. For part of its orbit, Saturn’s rings are seen at their widest point. But as it continues on its orbit around the Sun, the angle of Saturn’s rings decreases until they disappear entirely from our point of view. This is because we are seeing them edge-on. After a few more years, our angle improves and we can see the beautiful ring system again.
Orbital Inclination and Axial Tilt:
Another interesting thing about Saturn is the fact that its axis is tilted off the plane of the ecliptic. Essentially, its orbit is inclined 2.48° relative to the orbital plane of the Earth. Its axis is also tilted by 26.73° relative to the ecliptic of the Sun, which is similar to Earth’s 23.5° tilt. The result of this is that, like Earth, Saturn goes through seasonal changes during the course of its orbital period.
R. G. French (Wellesley College) et al., NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
Seasonal Changes:
For half of its orbit, Saturn’s northern hemisphere receives more of the Sun’s radiation than the southern hemisphere. For other half of its orbit, the situation is reversed, with the southern hemisphere receiving more sunlight than the northern hemisphere. This creates storm systems that dramatically change depending on which part of its orbit Saturn is in.
For staters, winds in the upper atmosphere can reach speeds of up to 5oo meters per second (1,600 feet per second) around the equatorial region. On occasion, Saturn’s atmosphere exhibits long-lived ovals, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval).
This unique but short-lived phenomenon occurs once every Saturnian year, around the time of the northern hemisphere’s summer solstice. These spots can be several thousands of kilometers wide, and have been observed on many occasions throughout the past – in 1876, 1903, 1933, 1960, and 1990.
Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed, which was spotted by the Cassini space probe. Given the periodic nature of these storms, another one is expected to happen in 2020, coinciding with Saturn’s next summer in the northern hemisphere.
The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI
Similarly, seasonal changes affect the very large weather patterns that exist around Saturn’s northern and southern polar regions. At the north pole, Saturn experiences a hexagonal wave pattern which measures some 30,000 km (20,000 mi) in diameter, while each of it six sides measure about 13,800 km (8,600 mi). This persistent storm can reach speeds of about 322 km per hour (200 mph).
Thanks to images taken by the Cassini probe between 2012 and 2016, the storm appears to undergo changes in color (from a bluish haze to a golden-brown hue) that coincide with the approach of the summer solstice. This was attributed to an increase in the production of photochemical hazes in the atmosphere, which is due to increased exposure to sunlight.
Similarly, in the southern hemisphere, images acquired by the Hubble Space Telescope have indicated the existence of large jet stream. This storm resembles a hurricane from orbit, has a clearly defined eyewall, and can reach speeds of up to 550 km/h (~342 mph). And much like the northern hexagonal storm, the southern jet stream undergoes changes as a result of increased exposure to sunlight.
Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)
Cassini was able to captured images of the south polar region in 2007, which coincided with late fall in the southern hemisphere. At the time, the polar region was becoming increasingly “smoggy”, while the northern polar region was becoming increasingly clear. The reason for this, it was argued, was that decreases in sunlight led to the formation of methane aerosols and the creation of cloud cover.
From this, it has been surmised that the polar regions become increasingly obscured by methane clouds as their respective hemisphere approaches their winter solstice, and clearer as they approach their summer solstice. And the mid-latitudes certainly show their share of changes thanks to increases/decreases in exposure to solar radiation.
Much like the length of a single year, what we know about Saturn has a lot to do with its considerable distance from the Sun. In short, few missions have been able to study it in depth, and the length of a single year means it is difficult for a probe to witness all the seasonal changes the planet goes through. Still, what we have learned has been considerable, and also quite impressive!
Artist Mark Rademaker's concept for the IXS Enterprise, a theoretical interstellar spacecraft. Credit: Mark Rademaker/flickr.com
Forty years ago, Canadian physicist Bill Unruh made a surprising prediction regarding quantum field theory. Known as the Unruh effect, his theory predicted that an accelerating observer would be bathed in blackbody radiation, whereas an inertial observer would be exposed to none. What better way to mark the 40th anniversary of this theory than to consider how it could affect human beings attempting relativistic space travel?
Such was the intent behind a new study by a team of researchers from Sao Paulo, Brazil. In essence, they consider how the Unruh effect could be confirmed using a simple experiment that relies on existing technology. Not only would this experiment prove once and for all if the Unruh effect is real, it could also help us plan for the day when interstellar travel becomes a reality.
To put it in layman’s terms, Einstein’s Theory of Relativity states that time and space are dependent upon the inertial reference frame of the observer. Consistent with this is the theory that if an observer is traveling at a constant speed through empty vacuum, they will find that the temperature of said vacuum is absolute zero. But if they were to begin to accelerate, the temperature of the empty space would become hotter.
According to the theory of the Unruh effect, accelerating particles are subject to increased radiation. Credit: NASA/Sonoma State University/Aurore Simonnet
This is what William Unruh – a theorist from the University of British Columbia (UBC), Vancouver – asserted in 1976. According to his theory, an observer accelerating through space would be subject to a “thermal bath” – i.e. photons and other particles – which would intensify the more they accelerated. Unfortunately, no one has ever been able to measure this effect, since no spacecraft exists that can achieve the kind of speeds necessary.
For the sake of their study – which was recently published in the journal Physical Review Letters under the title “Virtual observation of the Unruh effect” – the research team proposed a simple experiment to test for the Unruh effect. Led by Gabriel Cozzella of the Institute of Theoretical Physics (IFT) at Sao Paulo State University, they claim that this experiment would settle the issue by measuring an already-understood electromagnetic phenomenon.
Essentially, they argue that it would be possible to detect the Unruh effect by measuring what is known as Larmor radiation. This refers to the electromagnetic energy that is radiated away from charged particles (such as electrons, protons or ions) when they accelerate. As they state in their study:
“A more promising strategy consists of seeking for fingerprints of the Unruh effect in the radiation emitted by accelerated charges. Accelerated charges should back react due to radiation emission, quivering accordingly. Such a quivering would be naturally interpreted by Rindler observers as a consequence of the charge interaction with the photons of the Unruh thermal bath.”
Diagram of the experiment to test the Unruh effect, where electrons are injected into a magnetic field and subjected to lateral and vertical pulls. Credit: Cozzella, Gabriel (et al.)
As they describe in their paper, this would consist of monitoring the light emitted by electrons within two separate reference frames. In the first, known as the “accelerating frame”, electrons are fired laterally across a magnetic field, which would cause the electrons to move in a circular pattern. In the second, the “laboratory frame”, a vertical field is applied to accelerate the electrons upwards, causing them to follow a corkscrew-like path.
In the accelerating frame, Cozzella and his colleagues assume that the electrons would encounter the “fog of photons”, where they both radiate and emit them. In the laboratory frame, the electrons would heat up once vertical acceleration was applied, causing them to show an excess of long-wavelength photons. However, this would be dependent on the “fog” existing in the accelerated frame to begin with.
In short, this experiment offers a simple test which could determine whether or not the Unruh effect exists, which is something that has been in dispute ever since it was proposed. One of the beauties of the proposed experiment is that it could be conducted using particle accelerators and electromagnets that are currently available.
On the other side of the debate are those who claim that the Unruh effect is due to a mathematical error made by Unruh and his colleagues. For those individuals, this experiment is useful because it would effectively debunk this theory. Regardless, Cozzella and his team are confident their proposed experiment will yield positive results.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
“We have proposed a simple experiment where the presence of the Unruh thermal bath is codified in the Larmor radiation emitted from an accelerated charge,” they state. “Then, we carried out a straightforward classical-electrodynamics calculation (checked by a quantum-field-theory one) to confirm it by ourselves. Unless one challenges classical electrodynamics, our results must be virtually considered as an observation of the Unruh effect.”
If the experiments should prove successful, and the Unruh effect is proven to exist, it would certainly have consequences for any future deep-space missions that rely on advanced propulsion systems. Between Project Starshot, and any proposed mission that would involve sending a crew to another star system, the added effects of a “fog of photons” and a “thermal bath” will need to be factored in.
The age of the oceanic crust - red is most recent, and blue is the oldest - which corresponds to the location of mid-ocean ridges. Credit: NCEI/NOAA
If you took geology in high school, then chances are you remember learning something about how the Earth’s crust – the outermost layer of Earth – is arranged into a series of tectonic plates. These plates float on top of the Earth’s mantle, the semi-viscous layer that surrounds the core, and are in constant motion because of convection in the mantle. Where two plates meet, you have what it is known as a boundary.
These can be “divergent” or “convergent”, depending on whether the plates are moving apart or coming together. Where they diverge, hot magma can rise from below, creating features like long ridges or mountain chains. Interestingly enough, this is how one of the world’s largest geological features was formed. It called the Mid-Atlantic Ridge, which run from north to south along the ocean floor in the Atlantic.
Description:
The Mid-Atlantic Ridge (MAR) is known as a mid-ocean ridge, an underwater mountain system formed by plate tectonics. It is the result of a divergent plate boundary that runs from 87° N – about 333 km (207 mi) south of the North Pole – to 54 °S, just north of the coast of Antarctica.
The different types of Tectonic Plate Boundaries, ranging from convergent and transform to divergent. Credit: USGS/Jose F. Vigil
Like other ocean ridge systems, the MAR developed as a consequence of the divergent motion between the Eurasian and North American, and African and South American Plates. In the North Atlantic, it separates the Eurasian and North American Plates; whereas in the South Atlantic, it separates the African and South American Plates.
The MAR is approximately 16,000 km (10,000 mi) long and between 1,000 and is 1,500 km (620 and 932 mi) wide. The peaks of the ridge stand about 3 km (1.86 mi) in height above the ocean floor, and sometimes reach above sea level, forming islands and island groups. The MAR is also part of the longest mountain chain in the world, extending continuously across the oceans floors for a total distance of 40,389 km (25,097 mi).
The MAR also has a deep rift valley at is crest which marks the location where the two plates are moving apart. This rift valley runs along the axis of the ridge for nearly its entire length, measuring some 80 to 120 km (50 to 75 miles) wide. The rift marks the actual boundary between adjacent tectonic plates, and is where magma from the mantle reaches the seafloor.
Where this magma is able to reach the surface, the result is basaltic volcanoes and islands. Where it is still submerged, it produces “pillow lava”. As the plates move further apart, new ocean lithosphere is formed at the ridge and the ocean basin gets wider. This process, known as “sea floor spreading”, is happening at an average rate of about 2.5 cm per year (1 inch).
The Earth’s Tectonic Plates, with convergent and divergent boundaries indicated with red arrows. Credit: msnucleus.org
In other words, North America and Europe are moving away from each other at a very slow rate. This process also means that the basaltic rock that makes up the ridge is younger than the surrounding crust.
Notable Features:
As noted, the ridge (while mainly underwater) does have islands and island groups that were created by volcanic activity. In the Northern Hemisphere, these include Jan Mayen Island and Iceland (Norway), and the Azores (Portugal). In the Southern Hemisphere, MAR features include Ascension Island, St. Helena, Tristan da Cunha, Gough Island (all UK territories) and Bouvet Island (Norway).
Near the equator, the Romanche Trench divides the North Atlantic Ridge from the South Atlantic Ridge. This narrow submarine trench has a maximum depth of 7,758 m (25,453 ft), one of the deepest locations of the Atlantic Ocean. This trench, however, is not regarded an official boundary between any of the tectonic plates.
History of Exploration:
The ridge was initially discovered in 1872 during the expedition of the HMS Challenger. In the course of investigating the Atlantic for the sake of laying the transatlantic telegraph cable, the crew discovered a large rise in the middle of the ocean floor. By 1925, its existence was confirmed thanks to the invention of sonar.
The super-continent Pangaea during the Permian period (300 – 250 million years ago). Credit: NAU Geology/Ron Blakey
By the 1960s, scientists were able to map the Earth’s ocean floors, which revealed a seismically-active central valley, as well as a network of valleys and ridges. They also discovered that the ridge was part of a continuous system of mid-ocean ridges that extended across the entire ocean floor, connecting all the divergent boundaries around the planet.
This discovery also led to new theories in terms of geology and planetary evolution. For instance, the theory of “seafloor spreading” was attributed to the discovery of the MAR, as was the acceptance of continental drift and plate tectonics. In addition, it also led to the theory that all the continents were once part of subcontinent known as “Pangaea”, which broke apart roughly 180 million years ago.
Much like the “Pacific Ring of Fire“, the discovery of the Mid-Atlantic Ridge has helped inform our modern understanding of the world. Similar to convergent boundaries, subduction zones and other geological forces, the process that created it is also responsible for the world as we know it today.
Basically, it is responsible for the fact that the Americas have been drifting away from Africa and Eurasia for millions of years, the formation of Australia, and the collision between the India Subcontinent and Asia. Someday – millions of years from now – the process of seafloor spreading will cause the Americas and Asia to collide, thus forming a new super continent – “Amasia”.
The #MemoriesInDNA project intends to create an archive of human knowledge which will be sent to the Moon. Credit and copyright: John Brimacombe.
When the Apollo astronauts returned to Earth, they came bearing 380.96 kilograms (839.87 lb) of Moon rocks. From the study of these samples, scientists learned a great deal about the Moon’s composition, as well as its history of formation and evolution. For example, the fact that some of these rocks were magnetized revealed that roughly 3 billion years ago, the Moon had a magnetic field.
Much like Earth, this field would have been the result of a dynamo effect in the Moon’s core. But until recently, scientists have been unable to explain how the Moon could maintain such a dynamo effect for so long. But thanks to a new study by a team of scientists from the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center, we might finally have a answer.
To recap, the Earth’s magnetic core is an integral part of what keeps our planet habitable. Believed to be the result of a liquid outer core that rotates in the opposite direction as the planet, this field protects the surface from much of the Sun’s radiation. It also ensures that our atmosphere is not slowly stripped away by solar wind, which is what happened with Mars.
The Moon rocks returned by the Apollo 11 astronauts. Credit: NASA
For the sake of their study, which was recently published in the journal Earth and Planetary Science Letters, the ARES team sought to determine how a molten, churning core could generate a magnetic field on the Moon. While scientists have understood how the Moon’s core could have powered such a field in the past, they have been unclear as to how it could have been maintained it for such a long time.
Towards this end, the ARES team considered multiple lines of geochemical and geophysical evidence to put constraints on the core’s composition. As Kevin Righter, the lead of the JSC’s high pressure experimental petrology lab and the lead author of the study, explained in a NASA press release:
“Our work ties together physical and chemical constraints and helps us understand how the moon acquired and maintained its magnetic field – a difficult problem to tackle for any inner solar system body. We created several synthetic core compositions based on the latest geochemical data from the moon, and equilibrated them at the pressures and temperatures of the lunar interior.”
Specifically, the ARES scientists conducted simulations of how the core would have evolved over time, based on varying levels of nickel, sulfur and carbon content. This consisted of preparing powders or iron, nickel, sulfur and carbon and mixing them in the proper proportions – based on recent analyses of Apollo rock samples.
Artist concept illustration of the internal structure of the moon. Credit: NOAJ
Once these mixtures were prepared, they subjected them to heat and pressure conditions consistent with what exists at the Moon’s core. They also varied these temperatures and pressures based on the possibility that the Moon underwent changes in temperature during its early and later history – i.e. hotter during its early history and cooler later on.
What they found was that a lunar core composed of iron/nickel that had a small amount of sulfur and carbon – specifically 0.5% sulfur and 0.375% carbon by weight – fit the bill. Such a core would have a high melting point and would have likely started crystallizing early in the Moon’s history, thus providing the necessary heat to drive the dynamo and power a lunar magnetic field.
This field would have eventually died out after heat flow led the core to cool, thus arresting the dynamo effect. Not only do these results provide an explanation for all the paleomagnetic and seismic data we currently have on the Moon, it is also consistent with everything we know about the Moon’s geochemical and geophysical makeup.
Prior to this, core models tended to place the Moon’s sulfur content much higher. This would mean that it had a much lower melting point, and would have meant crystallization could not have occurred until much more recently in its history. Other theories have been proposed, ranging from sheer forces to impacts providing the necessary heat to power a dynamo.
Cutaway of the Moon, showing its differentiated interior. Credit: NASA/SSERVI
However, the ARES team’s study provides a much simpler explanation, and one which happens to fit with all that we know about the Moon. Naturally, additional studies will be needed before there is any certainty on the issue. No doubt, this will first require that human beings establish a permanent outpost on the Moon to conduct research.
But it appears that for the time being, one of the deeper mysteries of the Earth-Moon system might be resolved at last.
Illustration of the supermassive black hole at the center of the Milky Way. It's huge, with over 4 times the mass of the Sun. But ultramassive black holes are even more massive and can contain billions of solar masses. Image Credit:
Credit: NRAO/AUI/NSF
For decades, scientists have held that Supermassive Black Holes (SMBHs) reside at the center of larger galaxies. These reality-bending points in space exert an extremely powerful influence on all things that surround them, consuming matter and spitting out a tremendous amount of energy. But given their nature, all attempts to study them have been confined to indirect methods.
All of that changed beginning on Wednesday, April 12th, 2017, when an international team of astronomers obtained the first-ever image of a Sagittarius A*. Using a series of telescopes from around the globe – collectively known as the Event Horizon Telescope (EHT) – they were able to visualize the mysterious region around this giant black hole from which matter and energy cannot escape – i.e. the event horizon.
Not only is this the first time that this mysterious region around a black hole has been imaged, it is also the most extreme test of Einstein’s Theory of General Relativity ever attempted. It also represents the culmination of the EHT project, which was established specifically for the purpose of studying black holes directly and improving our understanding of them.
Simulated view of a black hole. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke/Radboud University
Since it began capturing data in 2006, the EHT has been dedicated to the study of Sagittarius A* since it is the nearest SMBH in the known Universe – located about 25,000 light years from Earth. Specifically, scientists hoped to determine if black holes are surrounded by a circular region from which matter and energy cannot escape (which is predicted by General Relativity), and how they accrete matter onto themselves.
Rather than constituting a single facility, the EHT relies on a worldwide network of radio astronomy facilities based on four continents, all of which are dedicated to studying one of the most powerful and mysterious forces in the Universe. This process, whereby widely-space radio dishes from across the globe are connected into an Earth-sized virtual telescope, is known as Very Long Baseline Interferometry (VLBI).
“Instead of building a telescope so big that it would probably collapse under its own weight, we combined eight observatories like the pieces of a giant mirror. This gave us a virtual telescope as big as Earth—about 10,000 kilometers (6,200 miles) is diameter.”
Combined image of Sagittarius A shown in x-ray (blue) and infrared (red), provided by the Chandra Observatory and the Hubble Space Telescope. Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI
With these arrays, the EHT radio-dish network is the only one powerful enough to detect the light released when an object would disappear into Sagittarius A*. And from six nights – from Wednesday, April 5th, to Tuesday, April 11th, – all of its arrays were trained on the center of our Milky Way to do just that. By the end of the run, the international team announced that they had snapped the first-ever picture of an event horizon.
In the end, some 500 terabytes of data were collected. This data is now being transferred to the MIT Haystack Observatory in Massachusetts, where it will be processed by supercomputers and turned into an image. “For the first time in our history, we have the technological capacity to observe black holes in detail,” said Bremer. “The images will emerge as we combine all the data. But we’re going to have to wait several months for the result.”
Part of the reason for the wait is the fact that the recorded data obtained by the South Pole Telescope can only be collected when spring starts in Antarctica – which won’t happen until October 2017 at the earliest. As such, it won’t be until 2018 before the public gets to feast its eyes on the shadow region that surrounds Sagittarius A*, and it is not expected that the first image will be entirely clear.
As Heino Falcke – an astronomers from Radbound University who now chairs the Scientific Council of EHT (and was the one who proposed this experiment twenty years ago) – explained in a EHT press release prior to the observation being made:
“It is the challenge of doing something, that has never been attempted before. It is the start of an adventurous journey towards a black hole… However, I think we need more observation campaigns and eventually more telescopes in the network to make a really good image.”
Despite the wait, and the fact that repeated attempts will be needed before we can get our first clear look at a black hole, there is still plenty of reason to celebrate in the meantime. Not only was this a first that was a long time in he making, but it also represents a major leap towards understanding one of the most powerful and mysterious forces of nature.
Given time, the study of black holes may allow for us to finally resolve how gravity and the other fundamental forces of the Universe interact. At long last, we will be able to comprehend all of existence as a single, unified equation!
Artist's concept of a large asteroid passing by the Earth-Moon system. Credit: A combination of ESO/NASA images courtesy of Jason Major/Lights in the Dark.
Missed us… a concept image of a large asteroid passing by the Earth-Moon system. Credit: A combination of ESO/NASA images courtesy of Jason Major/Lights in the Dark.
It’s a shooting gallery out there. The spattered face of Earth’s Moon and large impact sites such as Meteor Crater outside of Flagstaff, Arizona remind us that we still inhabit a dangerous neck of the solar neighborhood. But despite the inevitable cries proclaiming the “End of the World of the Week” this coming weekend, humanity can breathe a collective sigh of relief next Wednesday on April 19th, when asteroid 2014 JO25 passes safely by the Earth.
To be sure, lots of smaller space rocks pass by the Earth closer than the Moon (that’s an average of 240,000 miles distant) on a monthly basis. Take for example 4-meter asteroid 2017 GM, which passed just 16,000 kilometers distant on April 4th. What makes 2014 JO25 special is its size: measurements from NASA’s NEOWISE mission suggest that 2014 JO25 is about 2,000 feet (650 meters) along its longest axis, about twice the length of a Nimitz-class aircraft carrier. 2014 JO25 is passing 1.1 million miles (1.8 million kilometers) or 4.6 times the Earth-Moon distance on Wednesday, the closest large asteroid pass since 5-km Toutatis in September, 2004. The next predicted large asteroid pass near Earth is 1999 AN10, set to pass 1 LD (lunar distance) from the Earth in 2027.
4179 Toutatis as seen from China’s Chang’e 2 spacecraft. Credit: CNSA
This is also the closest passage of 2014 JO25 near the Earth for a 900 year span.
Discovered on May 5th, 2014 by the Catalina Sky survey, asteroid 2014 JO25 orbits the Sun once every three years, taking it from a perihelion of 0.237 AU (interior to Mercury’s orbit) out to an aphelion of 3.9 distant in the asteroid belt, interior to Jupiter’s orbit.
The orbit of NEO asteroid 2014 JO25. Credit: NASA/JPL.
Finding 2014 JO25 at its Closest Approach
With an estimated albedo (surface brightness) about twice that the lunar surface, 2014 JO25 will reach magnitude +10 to +11 on closest approach on Wednesday. Currently low in the dawn sky in the Square of Pegasus asterism, asteroid 2014 JO25 passed perihelion sunward as seen from the Earth at 1.015 Astronomical Units (AU) distant on March 11th. At its closest to the Earth on April 19th at 12:24 Universal Time (UT)/6:24 AM EDT, asteroid 2014 JO25 will skim the jagged Draco-Ursa Minor border below the bowl of the Little Dipper, moving at a whopping three degrees per hour. Sitting just 25 degrees from the north celestial pole on closest approach, catching sight of 2014 JO25 at favors western North America and northeastern Asia, though the eastern half of North America and Europe have a shot at the asteroid a few hours prior to closest approach in the early morning hours of April 19th. North American viewers get another shot at catching the fleeting asteroid later the same evening 13 hours after closest approach as the asteroid sails through the galaxy-rich constellation Coma Berenices.
The 24 hour path of asteroid 2014 JO25 from midnight UT April 18th through April 19th. (note: hourly time hacks are in Eastern Daylight Saving Time EDT UT-4). Credit: Starry Night Education software.
At +11th magnitude, you’ll need a telescope of at least 6” aperture or larger and a good star chart to nab 2014 JO25 as it glides against the starry background. Fellow Universe Today contributor Bob King has some great star charts of the pass over at Sky & Telescope. The Moon will be at Last Quarter phase on the morning of the 19th, providing moderate light pollution.
Plans are also afoot for NASA to ping asteroid 2014 JO25 using Arecibo and Goldstone radar… expect stunning animations to follow next week.
And if you’re out hunting for asteroids on the coming mornings, there are currently two bright binocular comets in the dawn sky to keep you company: Comet C/2017 E4 Lovejoy in the constellation Andromeda and Comet C/2015 ER61 PanSTARRS in Aquarius. Both are currently performing above expectations at about magnitude +7.
A busy neighborhood: Known asteroids as of April 1st, 2016. Credit: NASA/JPL.
“What if” an asteroid the size of 2014 JO25 hit the Earth? Well, the Chelyabinsk meteor was an estimated 20 meters in size; the impactor that formed Meteor Crater in Arizona was about 50 meters in diameter. The Chicxulub event off the Yucatan peninsula 66 million years ago was an estimated 10 kilometer-sized impactor well over ten orders of magnitude bigger than 2014 JO25. While the impact of a 600 meter asteroid would be a noteworthy event and a bad day locally, it would pale in comparison to an extinction level event.
All something to consider, as you watch the faint dot of asteroid 2014 JO25 pass harmlessly by the Earth and through the news cycle for the coming week.
