Here on Earth, Carbon is found in the atmosphere, the soil, the oceans, and in every living creature. Carbon 12 - aka. C-12, so-named because it has an atomic weight of 12 - is the most common isotope, but it is by no means the only one. Carbon 14 is another, an isotope of carbon that is produced when Nitrogen (N-14) is bombarded by cosmic radiation.
This process causes a proton to be displaced by a neutron, effectively turning atoms of Nitrogen it into an isotope of carbon - known as"radiocarbon". It is naturally radioactive and unstable, and will therefore spontaneously decay back into N-14 over a period of time. This property makes it especially useful in a process known as "radiocarbon dating", or carbon dating for short.
Origin of Radiocarbon:
Radiocarbon enters the biosphere through natural processes like eating and breathing. Plants and animals absorb both C-12 and C-14 in the course of their natural lifetimes simply by carrying out these basic functions. When they die, they cease to consume them, and the isotope of C-14 begins to revert back to its Nitrogen state at an exponential rate due to its radioactive decay.
Comparing the remaining C-14 of a sample to that expected from atmospheric C-14 allows the age of the sample to be estimated. In addition, scientists know that the half-life of radiocarbon is 5,730 years. This means that it takes a sample of radiocarbon 5,730 years for half of it to decay back into nitrogen.
After about 10 half-lives, the amount of radiocarbon left becomes too minuscule to measure and so this technique isn't particularly reliable for dating specimens which died more than 60,000 years ago - i.e. during the late Middle Paleolithic (aka. Old Stone Age) period.
History of Development:
Experiments that would eventually lead to carbon dating began in the 1939s, thanks to the efforts of the Radiation Laboratory at the University of California, Berkeley. At the time, researchers were attempting to determine if any of the elements common to organic matter had isotopes with half-lives long enough to be of value in biomedical research.
By 1940, the half-life of Carbon 14 was determined, as was the mechanism through which it was created (slow neutrons interacting with Nitrogen in the atmosphere). This contradicted previous work, which held that it was the product of deuterium (H², or heavy hydrogen) and Carbon 13.
During World War II, Willard Libby - a chemist and graduate of Berkeley - read a paper by W. E. Danforth and S. A. Korff (published in 1939) which predicted that C 14 would be created in the atmosphere due to interactions between nitrogen and cosmic rays. From this, Libby came up with the idea of measuring the decay of C 14 as a method of dating organic material.
In 1945, Libby moved to the University of Chicago, where he began the work that would lead to the development of radiocarbon dating. In 1946, he published a paper in which he speculated that C 14 might exist within organic material alongside other carbon isotopes.
After conducting experiments, which measured C-14 in methane derived from sewage samples, Libby and his colleagues were able to demonstrate that organic matter contained radioactive C-14. This was followed by experiments involving wood samples for the tombs of two Egyptian kings, for which the age was known.
Their results proved accurate, with allowances for a small margin of error, and were published in 1949 in the journal Science. In 1960, Libby received the Nobel Prize in Chemistry for this work. Since that time, carbon dating has been used in multiple fields of science, and allowed for key transitions in prehistory to be dated.
Limits of Carbon Dating:
Carbon dating remains limited for a number of reasons. First, there is the assumption that the ratio of C-12 to C-14 in the atmosphere has remained constant, when in fact, the ratio can be affected by a number of factors. For instance, C-14 production rates in the atmosphere, which in turn are affected by the amount of cosmic rays penetrating the Earth's atmosphere.
This is itself affected by things like the Earth's magnetic field, which deflects cosmic rays. Furthermore, precise measurements taken over the last 140 years have shown a steady decay in the strength of the Earth's magnetic field. This means there's been a steady increase in radiocarbon production (which would increase the ratio).
Another limitation is that this technique can only be applied to organic material such as bone, flesh, or wood, and can't be used to date rocks directly. On top of that, the addition of Carbon 12 will throw off the ration, thus leading to inaccurate assessments of a sample's age.
This is where anthropogenic factors come into play. Since fossil fuels have no Carbon 14 content, the burning of gasoline, oil, and other hydrocarbons - and in greater and greater quantity over the course of the past century and a half - has diluted the C-14 content of the atmosphere.
On the other hand, atmospheric testing of nuclear weapons during the 1950s and 1960s is likely to have increased the Carbon 14 content of the atmosphere. In fact, research has been conducted which suggests that nuclear tests may have doubled the concentration of C-14 in this time, compared to natural production by cosmic rays.
Nevertheless, it remains the most accurate means of dating the scientific community has discovered so far. Until such time that another method becomes available - and one that produces smaller margins of error - it will remain the method of choice for archeology, paleontology, and other branches of scientific research.
When Elon Musk speaks publicly about SpaceX and their efforts to make space travel less expensive, people listen. He attracts all kinds of scientists and journalists to his presentations. But he also attracts... other types of people. And those people ask some strange questions.
Musk must be getting used to it by now. He's one of those public figures that, by virtue of his efforts to bring the future closer, attracts a lot of interest. But some of the questions in the Q&A following his presentation on Sept. 27 were truly bizarre.
Anybody could stand in line at one of the microphones in the audience and ask their question. And ask they did.
One man started off by saying he just recently attended Burning Man in the desert. Mars is like one big desert, he said, with no water to wash away all the sewage. What will future Mars colonists do with all their s**t he asked?
I felt bad for the guy. Here was his chance to ask Musk, who is clearly some sort of hero the guy, any question about space travel. And he chose to ask about poop. It was truly cringe-worthy, but Musk handled it well. He must be used to it.
It's not like it's not a legitimate concern, way down the line, if we ever do establish a city. But good grief. Musk was there to talk about the Interplanetary Transport System, not the nuts and bolts of city planning. It's clear that this gentleman travelled all that way just to ask about sewage. Fail. (Jump to 1:06:30 in the video for that bit of magic.)
Another person asked everyone to give Elon a hand because he "Inspires the s**t out of us!" (At 1:10:35 in the video.) Musk looked uncomfortable. I don't think he likes the hero-worship part of his gig. The guy then tried to give him a comic book about Mars, but complained that security wouldn't let him. Ummmm, yeah.
One person complained that SpaceX won't hire internationally, and how can they claim to be going interplanetary when they won't even hire from other countries? Musk patiently explained that when it comes to rocketry, the government tightly restricts who is allowed to come from other countries to work on projects. Rocketry is governed by the same rules as weaponry, as it turns out. Thanks for explaining, Elon.
There were others. One lady wanted to come upstairs and give him a kiss, on behalf of all the ladies. Another asked if they were going to mathematically determine the most expendable human on Earth, and send them to Mars? That gem is 1:16:45 in the video. BTW, that guy thought it would be Michael Cera. Huh?
The same guy wanted to pitch a comedy video to him after the presentation. He was, unfortunately, turned down.
Another guy, who called himself a "local idiot" asked if Elon himself was planning on going to Mars. The guy said he would've hated to put in all this work and then not go. Musk's answer was, in short, that he would like to go, but only if a good succession plan was in place in case he perished. That way the company's work could continue.
There were some good questions too, of course. Questions about launch site for the craft, where it will be manufactured, and other pertinent questions around who should be the first people to go. Others asked about the journey itself, and how travellers would be kept safe from radiation and other hazards. So the Q&A wasn't a waste of time by any means.
The whole presentation is worth watching, if you haven't already. For those of you who just want to watch the wackiest parts of the Q&A, you're in luck. There's a highlight video.
KENNEDY SPACE CENTER VISITOR COMPLEX, FL - Sending humans on a ‘Journey to Mars’ and developing strategies and hardware to accomplish the daunting task of getting ‘Humans to Mars’ is NASA’s agency wide goal and the goal of many space enthusiasts - including Apollo 11 moonwalker Buzz Aldrin.
NASA is going full speed ahead developing the SLS Heavy lift rocket and Orion crew module with a maiden uncrewed launch from the Kennedy Space Center set for late 2018 to the Moon. Crewed Mars missions would follow by the 2030s.
In the marketplace of ideas, there are other competing and corollary proposals as well from government, companies and private citizens on pathways to the Red Planet. For example SpaceX CEO Elon Musk wants to establish a colony on Mars using an Interplanetary Transport System of SpaceX developed rockets and spaceships.
Moonwalker Aldrin strongly advocated for more commercial activity in space and that “exposure to microgravity” for “many commercial products” is good, he told Universe Today.
More commercial activities in space would aid space commerce and getting humans to Mars.
“We need to do that,” Aldrin told me.
Buzz Aldrin is the second man to set foot on the Moon. He stepped onto the lunar soil a few minutes after Apollo 11 Commander Neil Armstrong, on July 20, 1969 in the Sea of Tranquility.
Aldrin also strongly supports some type of American space station capability “beyond the ISS” to foster the Mars capability.
And we need to be thinking about that follow on “US capability” right now!
“I think we need to have a US capability beyond the ISS to prepare for future activities right from the beginning,” Aldrin elaborated.
Currently the ISS partnership of the US, Russia, ESA, Japan and Canada has approved extending the operations of the International Space Station (ISS) until 2024. What comes after that is truly not known.
NASA is not planning for a follow-on space station in low Earth orbit at this time. The agency seems to prefer development of a commercial space station, perhaps with core modules from Bigelow Aerospace and/or other companies.
So that commercial space station will have to be designed, developed and launched by private companies. NASA and others would then lease space for research and other commercial activities and assorted endeavors on the commercial space station.
For example, Bigelow wants to dock their privately developed B330 habitable module at the ISS by 2020, following launch on a ULA Atlas V. And then spin it off as an independent space station when the ISS program ends - see my story.
Only China has firm plans for a national space station in the 2020’s. And the Chinese government has invited other nations to submit proposals. Russia’s ever changing space exploration plans may include a space station - but that remains to be actually funded and seen.
Regarding Mars, Aldrin has lectured widely and written books about his concept for “cycling pathways to occupy Mars,” he explained.
Watch this video of Apollo 11 moonwalker Buzz Aldrin speaking to Universe Today:
Video Caption: Buzz Aldrin at 'Destination Mars' Grand Opening at KSCVC. Apollo 11 moonwalker Buzz Aldrin talks to Universe Today/Ken Kremer during Q&A at 'Destination Mars' Holographic Exhibit Grand Opening ceremony at Kennedy Space Center Visitor Complex (KSCVC) in Florida on 9/18/16. Credit: Ken Kremer/kenkremer.com
Here is a transcript:
Universe Today/Ken Kremer: Can you talk about the role of commercial space [in getting humans to Mars]. Elon Musk wants to try and send people to Mars, maybe even before NASA. What do you think?
Buzz Aldrin: “Well, being a transportation guy in space for humans - well commercial, what that brings to mind is tourism plus space travel.
And there are many many more things commercial that are done with products that can be fine tuned by exposure to microgravity. And we need to do that.”
“I think we need to have a US capability beyond the ISS to prepare for future activities right from the beginning.”
“And that’s why what has sort of fallen into place is the name for my plan for the future - which is ‘cycling pathways to occupy Mars.’”
“A cycler in low Earth orbit, one in lunar orbit, and one to take people to Mars.”
“And they are utilized in evolutionary fashion.”
Meanwhile, be sure to visit the absolutely spectacular “Destination Mars” holographic exhibit before it closes on New Year’s Day 2017 - because it is only showing at KSCVC.
You can get more information or book a visit to Kennedy Space Center Visitor Complex, by clicking on the website link:
Scott Manley is one of my favorite YouTubers/Twitch Streamers. In case you've never seen him before, Scott is an absolute master of the space game, running instructional videos on EVE Online, Kerbal Space Program and other cosmic simulations.
The planets aligned, and Scott was planning to run a livestream game on his Twitch channel Monday night, so I jumped in and provided colour commentary while Scott constructed all aspects of the mission: a spacecraft capable of carrying 100 Kerbals safely to the surface of the Red Planet (Duna), a monster booster rocket to blast the crew compartment into orbit, and a refueling module that travels on a re-purposed booster.
Today, Elon Musk elaborated on his plans to make humanity a planet-faring species. We've known for a long time that Mars is SpaceX's destination, but the fine details haven't been revealed. In today's talk at the International Astronautical Congress (IAC), Musk revealed a game-changer for travel to Mars, and beyond.
If anyone has ever guessed that Musk's plans involved a refuelling ship, I've never heard them say it out loud. But that's exactly what Musk revealed. SpaceX plans to launch a Mars-bound craft into orbit, then launch a refuelling craft to refill the interplanetary ship's fuel tanks. Only then would the Interplanetary Transport System (ITS) depart for Mars.
SpaceX's proposed system is all about lowering the cost of travel to Mars. Only when the cost is lowered, does a sustained presence there become realistic. And Musk's ITS system will definitely lower the cost.
Traditional space travel would cost $10 billion to get one person to Mars. Musk said that they can get it down to the median cost of a house in the US, about $200,000 US. The idea is that anyone who really wanted to could save up enough money and go to Mars. Musk did acknowledge that it will be tricky to reduce the cost of the Earth to Mars trip by a whopping 5 million percent.
There are four keys to reducing the cost:
refilling in orbit
propellant production on Mars
The ITS would feature reusable boosters, reusable spaceships, and refuelling in orbit. The interplanetary ship would be launched into orbit around Earth and parked there. Fuel ships would make 3 to 5 trips to fill the tank of the interplanetary ship waiting in orbit. From there, Musk thinks that the trip to Mars could take as little as 80 days. In the more distant future, that could be cut to 30 days.
If this whole system isn't shocking enough, and thrilling enough, for you, Musk has more than just one of these craft in mind. He imagines a fleet of them, perhaps 1,000, travelling en masse back and forth to Mars.
The driving force behind all this is, of course, making Mars possible. In his presentation, Musk said we have two paths. One is to stay on Earth and face extinction from some doomsday event. The other is to become an interplanetary species, and use Mars to back up Earth's biosphere. The SpaceX system is designed to make the second path possible.
Musk talked about the need to create a self-sustaining city in its own right. That obviously won't happen right away, but it'll never happen unless transport to Mars, and back, becomes feasible. With the proposed SpaceX system, Mars will be an option. Musk thinks that the ITS could also get us to one of the Jovian moons, if we could create fuel production and depots. In fact, he said we can probably go all the way to Pluto and beyond.
There are a lot of challenges for this system. It's far from a done deal. The system will require newer, more powerful engines. But SpaceX is already working on that. It's called the Raptor, and testing has already begun.
Musk talked about the impressive exploration done on Mars by NASA and other agencies, but stressed that it's time to take things further and aim for a sustained presence on Mars. To that end, SpaceX plans on sending a craft to Mars during every Earth-Mars opposition, which happens about every 2 years. Initially, that will be done with an unmanned Dragon capsule.
The mood at Musk's presentation was one of excitement. The crowd was definitely there to see him. There was one humorous moment when Musk remarked "Timelines. I'm not the best at this sort of thing." This is a nod to the difficulties with creating a timeline for something like the ITS. But really, what agency can adhere to strict schedules when doing something that's never been done before? Especially in the realm of interplanetary travel?
The excitement surrounding Musk's plans for travel to Mars is palpable. That's understandable, considering the magnitude of what he's talking about, and considering how long people have dreamed of going to Mars. The fact that someone with a track record like SpaceX's is starting to lay the groundwork for travel to, and a presence on Mars, is exciting. There's no way around it.
But there are lots of questions. Musk is the first to admit that he doesn't have all the answers. He says up front that he sees his role as developing the transport system. Once that is moving ahead, others will address the challenges of establishing a presence on Mars.
One of the primary questions is around energy, and there are two sides to that. Fuel processing will have to be established quickly on Mars if the ships are to return to Earth.
Musk also talked about the three possible fuel types to be derived on Mars.
The ITS ships will be able to carry a large payload, so it's possible that the parts and pieces for a fuel plant could be pre-built somehow, then sent to Mars. There is an enormous amount of detail missing when it comes right down to it, but human ingenuity being what it is, this may be solvable.
Assuming that a rocket fuel plant could be assembled on Mars, that begs the second energy question. Creating this fuel will in itself require lots of energy. Much more than solar can provide. Musk briefly mentioned the possibility of nuclear energy, but didn't go into detail. That's understandable, because he clearly sees his role as developing the transportation system.
Establishing nuclear energy on Mars would also require a lot of infrastructure. On Earth, uranium processing is an enormous task. How will that be done on Mars? Is there enough uranium in Mars' crust? Conventional atomic reactors use water, lots of it, to produce energy. Where will that water come from on Mars? Will the same amount be needed?
Or will thorium reactors be used? If you're not up on thorium reactors, they are different than uranium reactors and are worth reading about. They use thorium for fuel, not uranium, and are different in other ways. They're safer and produce less waste, but is there sufficient thorium available on Mars? Thorium is much more plentiful in Earth's crust than uranium.
Small Modular Reactors (SMRs) are being developed for use on Earth. They are built in one location, then moved to their operational location. They can be linked together and require less sophisticated operators. Perhaps SMRs using thorium will provide the energy required for the ITS to work.
These questions are all important of course, and they bear thinking about. But one thing that can't be denied is Musk's vision. Anyone that wants humanity to survive, or that grew up reading science fiction, will love what Musk is doing. For that matter, anyone with a sense of adventure will love Musk.
Musk's overall vision of us as a planet-faring species is something that will be a long time coming, I think. Fleets of interplanetary cargo ships plying the solar system, with fuelling depots along the way. An established human presence on Mars, the Moon, and perhaps the moons of the gas giants, and all the way out to Pluto.
It seems like a fanciful dream, but remember what Musk said at the start of his presentation. There are really only two paths. The first is to restrict ourselves to Earth, and die at the hands of some sort of extinction event.
The second path is to head outward and expand throughout the solar system.
It's not science fiction anymore. It's simple survival.
Since it first landed on the surface of Mars on August 6th, 2012, the science team behind the Curiosity rover has conducted some crucial experiments. In the course of collecting rock samples, testing the air, and searching for organic molecules, the rover has revealed some very impressive things about Mars' past.
After months of exploring the slopes around Mount Sharp, which sits in the ancient lake basin known as the Gale Crater, the rover team has been drilling into the formation to see what's hidden beneath. And with drill samples now obtained from Mount Sharp's lower levels, the Curiosity team hopes to learn a great deal more about the planet's ancient history.
For years, scientists have understood that Mount Sharp is essentially a giant mound of sedimentary deposits that were deposited by water billions of years ago. These sediment layers are believed to have been laid down over the course of 2 billion years, and most likely came into contact with the water that filled the crater 3.3. to 3.8 billion years ago.
As Ashwin Vasavada, the Deputy Project Scientist of the Curiosity mission at JPL, explained to Universe Today via email:
"Aeolis Mons, known informally as Mount Sharp, is the central mountain within Gale crater where Curiosity landed. It was chosen as Curiosity’s landing site because the mountain and the nearby plains have evidence for ancient liquid water in the form of channels and debris fans, as well as minerals that form when liquid water interacts with rock. Furthermore, the layers within lower Mount Sharp change in mineralogy in a way that indicates that they may record the drying out of Mars: lower and older layers indicate more water, while higher and younger layers indicate less."
The drilling began late on Wednesday, Sept. 24th, when Curiosity's hammering drill bore about 6.7 cm (2.6 inches) into Mount Sharp and collected a powdered-rock sample. Data and images of the drill sample were then received on the following morning (Thursday, Sept. 25th) at NASA's Jet Propulsion Laboratory in Pasadena, California.
With drill samples now obtained from the lower level of Mount Sharp, Curiosity will soon deposit them into a scoop in the rover's arm. While there, the rock powder will be examined to see if it is safe and of proper quality to be analyzed by Curiosity's internal laboratory instruments, which will determine its chemical and mineralogical properties.
And once that analysis is complete, the Curiosity team hopes to make some more major discoveries of the region, the ultimate purpose of which is to determine if life could have existed in the Gale Crater during its warmer, wetter past. As Vasavada explained:
"Now that water-rich ancient environments have been discovered and studied on the plains and in the lowest layers of Mount Sharp, the team in drilling additional samples from progressively higher and younger layers to see how the ancient environment changed over time.
"The team also is searching for additional evidence of organic molecules that would help them understand whether the raw ingredients of life were present and how they degrade over time. The degradation is important to understand for the M2020 Mars rover mission that will search for signatures of ancient microbial life."
Since September 11th, 2014, Curiosity has been exploring the slopes of Mount Sharp. As of Sept. 19th, 2016, the rover arrived at a area called "Pahrump Hills," a basalt rock outcropping located in the lower region of Mount Sharp (known as the Murray Formation).
On Sept. 22nd, the rover completed a mini-drill test to make sure the rock was suitable for drilling. This took place in an area known as "Confidence Hills", which proved to be soft enough to obtain rock samples. This was the second mini-drill test since last month, the previous one having found that the rock was not stable enough for drilling.
Looking forward, the team plans to drill regularly as the rover climbs higher and higher along Mount Sharp, in the process accessing progressively younger layers of rock. In so doing, they will be able to create a comprehensive picture of how Mars evolved over time to become the dry and cold landscape it is today.
The team will also continue to use the rovers instruments to monitor the modern environment, including the weather and composition of the atmosphere to get a better picture of the planet's meteorology today. Needless to say, this is not the last "taste" Curiosity will get of good ol' Aeolis Mons!
Be sure to check this video too - "A Taste of Mount Sharp" - courtesy of NASA JPL:
Mercury is a fascinating planet. As our Suns' closest orbiting body, it experiences extremes of heat and cold, has the most eccentric orbit of any Solar planet, and an orbital resonance that makes a single day last as long as two years. But since the arrival of the MESSENGER probe, we have learned some new and interesting things about the planet's geological history as well.
For example, images that were recently obtained by the NASA spacecraft revealed previously undetected landforms - small fault scarps - that appear to be geologically young. The presence of these features have led scientists to conclude that Mercury is still contracting over time, which means that - like Earth - it is tectonically active.
In geology, fault scarps refer to small step-like formations in the surface of a planet, where one side of a fault has moved vertically relative to the other. Previously, scientists believed that Mercury was tectonically dead, and that all major geological activity had taken place in the planet's early history.
This was evidenced by features spotted by the MESSENGER and Mariner 10 probes, both of which found evidence of large wrinkle ridges and fault scarps on the surface. The features were reasoned to be the result of Mercury contacting as it cooled early in its history (i.e. billion of years ago).
This action caused the planet's crust to break, forming cliffs up to a kilometer and a half (about 1 mile) in height and hundreds of kilometers long. However, as the MESSENGER team noted, these small scarps were considerably younger, dating to about 50 million years of age.
They concluded that the scarps would have to be this young in order to survive bombardment by comets and meteoroids, a common occurrence on Mercury. They also noted their resemblance to similar features on the Moon, which also has young scarps that are the result of recent contraction.
“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts.”
The findings were made during the last 18 months of the MESSENGER mission, during which time the probe lowered its altitude to get higher-resolution images of the planet's surface. The findings are also consistent with recent findings about Mercury's global magnetic field, which appears to be powered by the planet's slowly-cooling outer core.
As Jim Green, NASA's Planetary Science Director, said of the discovery:
“This is why we explore. For years, scientists believed that Mercury’s tectonic activity was in the distant past. It’s exciting to consider that this small planet – not much larger than Earth’s moon – is active even today.”
All told, these findings have let scientists know that the planet is still alive, in the geological sense. It also means that that there is likely such as thing as Mercury-quakes, something which NASA is sure to follow up on if and when a lander mission (equipped with seismology instruments) is dispatched to the surface of the planet.
Imagine if you will, that you are a human being living in prehistoric times. You look up at the sky and see the Sun slowly being blocked out, becoming a ominous black sphere that glows around the edges. Could you really be faulted for thinking that this was some sort of supernatural event, or that the end of the world was nigh?
Of course not. Which is why for thousands of years, human beings believed that solar eclipses were just that - a sign of death or a bad omen. But in fact, an eclipse is merely what happens when one stellar object passes in front of another and obscures it. In astronomy, this happens all the time; and between the Sun, the Moon, and the Earth, total eclipses have been witnessed countless times throughout history.
The general term for when one body passes in front of another in a solar system is transit. This term accurately describes how, depending on your vantage point, stellar bodies pass in front of each other on a regular basis, thus causing the reflected light from that body to be temporarily obscured.
However, when we are talking about how the Moon can pass between the Earth and the Sun, and how the Earth can pass between the Sun and the Moon, we use the term eclipse. This is also known as a syzygy, an astronomical term derived from ancient Greek (meaning "yoked together") that describes a straight-line configuration between three celestial bodies.
Total Solar Eclipse:
When the Moon passes between the Sun and the Earth, and the Moon fully occults (blocks) the Sun, it is known as the solar eclipse. The type of solar eclipse - total or partial - depends on the distance of the Moon from the Earth during the event.
During an eclipse of the Sun, only a thin path on the surface of the Earth is actually able to experience a total eclipse - which is called the path of totality. People on either side of that path see a partial eclipse, where the Sun is only partly obscured by the Moon, relative to those who are standing in the center and witnessing the maximum point of eclipse.
A total solar eclipse occurs when the Earth intersects the Moon's umbra - i.e. the innermost and darkest part of its shadow. These are relatively brief events, generally lasting only a few minutes, and can only be viewed along a relatively narrow track (up to 250 km wide). The region where a partial eclipse can be observed is much larger.
During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its size is nearly the same as the Sun's when viewed from the Earth. This, of course, is an illusion brought on by the fact that the Moon is much closer to us than the Sun.
And since it is closer, it can block the light from the Sun and cast a shadow on the surface of the Earth. If you're standing within that shadow, the Sun and the Moon appear to line up perfectly, so that the Moon is completely darkened.
After a solar eclipse reaches totality, the Moon will continue to move past the Sun, obscuring smaller and smaller portions of it and allowing more and more light to pass.
Total Lunar Eclipse:
A total eclipse of the Moon is a different story. In this situation, the entire Moon passes into the Earth's shadow, darkening it fully. A partial lunar eclipse occurs when the shadow of the Earth doesn't fully cover the Moon, so only part of the Moon is darkened.
Unlike a solar eclipse, a lunar eclipse can be observed from nearly anywhere in an entire hemisphere. In other words, observers all across planet Earth can see this darkening and it appears the same to all. For this reason, total lunar eclipses are much more common and easier to observe from a given location. A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.
There are three types of lunar eclipses. There's a penumbral eclipse, when the Moon crosses only the Earth's penumbra (the region in which only a portion of light is obscured); followed by a partial, when the Moon crosses partially into the Earth's umbra (where the light is completely blocked).
Last, there is a total eclipse, when the Moon crosses entirely into the Earth's umbra. A total lunar eclipse involves the Moon passing through all three phases, then gradually passing out of the Earth's shadow and becoming bright again. Even during a total lunar eclipse, however, the Moon is not completely dark.
Sunlight is still refracted through the Earth's atmosphere and enters the umbra to provide faint illumination. Similar to what happens during a sunset, the atmosphere scatters shorter wavelength light, causing it to take on a red hue. This is where the phrase 'Blood Moon' comes from.
Since the Moon orbits the Earth, you would expect to see an eclipse of the Sun and the Moon once a lunar month. However, this does not happen simply because the Moon's orbit isn't lined up with the Sun. In fact, the Moon's orbit is tilted by a few degrees - 1.543º between the angle of the ecliptic and the lunar equator, to be exact.
This means that three objects only have the opportunity to line up and cause an eclipse a few times a year. It's possible for a total of 7 solar and lunar eclipses every year, but that only happens a few times every century.
Other Types of Eclipses:
The term eclipse is most often used to describe a conjunction between the Earth, Sun and Moon. However, it can also refer to such events beyond the Earth–Moon system. For example, a planet moving into the shadow of one of its moons, a moon passing into the shadow of its host planet, or a moon passing into the shadow of another moon.
For instance, during the Apollo 12 mission in 1969, the crew was able to observe the Sun being eclipsed by the Earth. In 2006, during its mission to study Saturn, the Cassini spacecraft was able to capture the image above, which shows the gas giant transiting between the probe and the Sun.
In July of 2015, when the New Horizons mission passed through the shadow of Pluto, it was able to capture a stunning image of the dwarf planet eclipsing the Sun. The image was taken at a distance of about 2 million km (1.25 million miles), which provided the necessary vantage point to see the disc of the Sun become fully obscured.
On top of that, many other bodies in the Solar System can experience eclipses as well. These include the four gas giants, all of which have major moons that periodically transit between the planet and either Earth-based or space-based observatories.
The most impressive and common of these involve Jupiter and its four largest moons (Io, Europa, Ganymede and Callisto). Given the size and low axial tilt of these moons, they often experience eclipses with Jupiter as a result of transits, relative to our instruments.
A well-known example occurred in April of 2014, when the Hubble Space Telescope caught an image of Ganymede passing in front at of Jupiter. At the time the image was taken, Ganymede was casting its shadow within Jupiter's Great Red Spot, which lent the planet a cyclops-like appearance (see below).
The other three gas giants are known to experiences eclipses as well. However, these only occur at certain periods the planet's orbit of the Sun, due to their higher inclination between the orbits of their moons and the orbital plane of the planets. For instance, Saturn's largest moon Titan has been known to only occult the ringed gas giant once about every 15 years.
Pluto has also been known to experience eclipses with is largest moon (and co-orbiting body) Charon. However, in all of these cases, the eclipses are never total, as they do not have the size to obscure the much larger gas giant. Instead, the passage of the moons in front of the larger celestial bodies either cast small shadows on the cloud tops of the gas giants, or lead to an annular eclipse at most.
Similarly, on Mars, only partial solar eclipses are ever possible. This is because Phobos or Deimos are not large enough (or distant enough in their orbits) to cover the Sun's disc, as seen from the surface of the planet. Phobos and Deimos have also been known to experience lunar eclipses as they slip into the shadow of Mars.
Martian eclipses have been photographed numerous times from both the surface and from orbit. For example, in 2010, the Spirit rover captured images of a Martian lunar eclipse as Phobos, the larger of the two martian moons, was photographed while slipping into the shadow of Mars.
Also, between Nov. 4 and Nov. 5, 2010, the Opportunity rover captured several images (later turned into movies) of a Martian sunset. In the course of imaging the Sun for a total of 17 minutes, Opportunity captured stills of the Sun experiencing a solar eclipse. And on September 13th, 2012 - during the 37th day of its mission (Sol 27) - the Curiosity rover captured an image of Phobos transiting the Sun.
As far as astronomical events go, total eclipses (Lunar and Solar) are not uncommon occurrences. If you ever want to witness a one, all you need to do is keep track of when one will be visible from your part of the world. Some good resources for this are NASA's Eclipse Website and timeanddate.com.
Or, if you're the really adventurous type, you can find out where on Earth the next path of totality is going to be, and then book a vacation to go there. Get to the right spot at the right time, and you should be getting the view of a lifetime!
We have written many articles about the eclipse for Universe Today. Here's a list of articles about specific times when a total Lunar Eclipse took place, and here's a list of Solar Eclipse articles. And be sure to check out this article and video of an Annular Eclipse.
Last week, on Tuesday, September 20th, NASA announced that they had made some interesting findings about Jupiter's icy moon Europa. These were based on images taken by the Hubble Space Telescope, the details of which would be released on the following week. Needless to say, since then, the scientific community and general public have been waiting with baited breath.
Earlier today (September 26th) NASA put an end to the waiting and announced the Hubble findings during a NASA Live conference. According to the NASA panel, which was made up of members of the research team, this latest Europa-observing mission revealed evidence of plumes of saline water emanating from Europa's surface. If true, this would mean that the moon's subsurface ocean would be more accessible than previously thought.
Using Hubble's Space Telescope Imaging Spectrograph (STIS) instrument, the team conducted observations of Jupiter and Europa in the ultra-violet spectrum over the course of 15 months. During that time, Europa passed in front of Jupiter (occulted the gas giant) on 10 separate occasions.
And on three of these occasions, the team saw what appeared to be plumes of water erupting from the surface. These plumes were estimated to be reaching up to 200 km (125 miles) from the southern region of Europa before (presumably) raining back onto the surface, depositing water ice and material from the interior.
The purpose of the observation was to examine Europa's possible extended atmosphere (aka. exosphere). The method the team employed was similar to the one used to detect atmospheres around extra-solar planets. As William Sparks of the Space Telescope Science Institute (STScI) in Baltimore (and the team leader), explained in a NASA press release:
"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it. If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."
When they looked at Europa using this same technique, they noted that small patches on the surface were dark, indicating the absorption of UV light. This corresponded to previous work done Lorenz Roth (of the Southwest Research Institute) and his team of researchers in 2012. At this time, they detected evidence of water vapor coming from Europa's southern polar region.
As they indicated in a paper detailing their results - titled "Transient Water Vapor at Europa’s South Pole" - Roth's team also relied on UV observations made using the Hubble telescope. Noting a statistically coincident amount of hydrogen and oxygen emissions, they concluded that this was the result of ejected water vapor being broken apart by Jupiter's radiation (a process known as radiolysis).
Though their methods differed, Sparks and his research team also found evidence of these apparent water plumes, and in the same place no less. Based on the latest information from STIS, most of the apparent plumes are located in the moon's southern polar region while another appears to be located in the equatorial region.
"When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it's pretty similar to what Roth and his team found," Sparks said. "The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work."
Another interesting conclusion to come from this and the 2012 study is the likelihood that these water plumes are intermittent. Basically, Europa is tidally-locked world, which means the same side is always being presented to us when it transits Jupiter. This occus once every 3.5 days, thus giving astronomers and planetary scientists plenty of viewing opportunities.
But the fact that plumes have been observed at some points and not others would seem to indicate that they are periodic. In addition, Roth's team attempted to spot one of the plume's observed by Sparks and his colleagues a week after they reported it. However, they were unable to locate this supposed water source. As such, it would appear that the plumes, if they do exist, are short-lived.
These findings are immensely significant for two reasons. On the one hand, they are further evidence that a warm-water, saline ocean exists beneath Europa's icy surface. On the other, they indicate that any future mission to Europa would be able to access this salt-water ocean with greater ease.
Ever since the Galileo spacecraft conducted a flyby of the Jovian moon, scientists have believed that an interior ocean is lying beneath Europa's icy surface - one that has between two and three times as much water as all of Earth's oceans combined. However, estimates of the ice's thickness range from it being between 10 to 30 km (6–19 mi) thick - with a ductile "warm ice" layer that increases its total thickness to as much as 100 km (60 mi).
Knowing the water periodically reaches the surface through fissures in the ice would mean that any future mission (which would likely include a submarine) would not have to drill so deep. And considering that Europa's interior ocean is considered to be one of our best bets for finding extra-terrestrial life, knowing that the ocean is accessible is certainly exciting news.
And the news is certainly causing its fair share of excitement for the people who are currently developing NASA's proposed Mission to Europa, which is scheduled to launch sometime in the 2020s. As Dr. Cynthia B. Phillips, a Staff Scientist and the Science Communications Lead for the Europa Project, told Universe Today via email:
"This new discovery, using Hubble Space Telescope data, is an intriguing data point that helps lend support to the idea that there are active plumes on Europa today. While not an absolute confirmation, the new Sparks et al. result, in combination with previous observations by Roth et al. (also using HST but with a different technique), is consistent with the presence of intermittent plumes ejecting water vapor from the Southern Hemisphere of Europa. Such observations are difficult to perform from Earth, however, even with Hubble, and thus these results remain inconclusive.
"Confirming the presence or absence of plumes on Europa, as well as investigating many other mysteries of this icy ocean world, will require a dedicated spacecraft in the Jupiter system. NASA currently plans to send a multiple-flyby spacecraft to Europa, which would make many close passes by Europa in the next decade. The spacecraft’s powerful suite of scientific instruments will be able to study Europa’s surface and subsurface in unprecedented detail, and if plumes do exist, it will be able to observe them directly and even potentially measure their composition. Until the Europa spacecraft is in place, however, Earth-based observations such as the new Hubble Space Telescope results will remain our best technique to observe Jupiter’s mysterious moon."
Naturally, Sparks was clear that this latest information was not entirely conclusive. While he believes that the results were statistically significant, and that there were no indications of artifacts in the data, he also emphasized that observations conducted in the UV wavelength are tricky. Therefore, more evidence is needed before anything can be said definitively.
In the future, it is hoped that future observation will help to confirm the existence of water plumes, and how these could have helped create Europa's "chaos terrain". Future missions, like NASA's James Webb Space Telescope (scheduled to launch in 2018) could help confirm plume activity by observing the moon in infrared wavelengths.
As Paul Hertz, the director of the Astrophysics Division at NASA Headquarters in Washington, said:
“Hubble’s unique capabilities enabled it to capture these plumes, once again demonstrating Hubble’s ability to make observations it was never designed to make. This observation opens up a world of possibilities, and we look forward to future missions -- such as the James Webb Space Telescope -- to follow up on this exciting discovery.”
Other team members include Britney Schmidt, an assistant professor at the School of Earth and Atmospheric Sciences at Georgia Institute of Technology in Atlanta; and Jennifer Wiseman, senior Hubble project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Their work will be published in the Sept. 29 issue of the Astrophysical Journal.
And be sure to enjoy this video by NASA about this exciting find: