Answer: As you probably know, our Sun is just a star. It’s our closest, most familiar star, but it’s still just a star. With a great big Universe out there, populated with countless stars, astronomers have been able to see examples of stars in all shapes, sizes, metal content and ages.
According to their system of classification, the Sun is known as a yellow dwarf star. This group of stars are relatively small, containing between 80% and 100% the mass of the Sun. So the Sun is at the higher end of this group. The official designation is as a G V star.
Stars in the this classification have a surface temperature between 5,300 and 6,000 K, and fuse hydrogen into helium to generate their light. They generally last for 10 billion years.
But there’s more to this question, because G V Stars can experience several different stages. Some are newly forming, others are in their middle ages, and others are nearing the end of their lives.
Our Sun is right in the middle ages, in a time known as the main sequence. It has already lived for 4.3 billion years, and will likely last another 7 billion years or so. At that point, it will balloon into a red giant star, and eventually collapse down into a white dwarf.
The Sun also belongs to the Population I group of stars, which contain relatively large amounts of heavier elements. The first ever stars, made from pure hydrogen and helium are Population III. These exploded as supernovae, producing fusing the lighter elements into heavier and heavier elements. Our Sun, then, contains the metal from previous generations of stars that went supernova.
Some other examples of the yellow dwarf star group include Alpha Centauri, Tau Ceti and 51 Pegasi.
For the quick answer, the Sun is a Population I yellow dwarf star, in the main sequence. Why is the Sun yellow? It’s actually because of the Earth’s atmosphere. If you saw it from space, it would actually look white.
False colour image of Titan's atmosphere. Credit: NASA/JPL/Space Science Institute/ESA
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Titan not only has an atmosphere it has hydrocarbon lakes, oceans, sand dunes and now research has just been published proving Saturn’s moon is sparkling with electrical activity. Scientists are in general agreement that organic molecules, the precursors to life on Earth, are a consequence of lightning in the atmosphere. Now, using data from the Huygens probe that descended through Titan’s atmosphere in 2005 and continued transmitting for 90 minutes after touchdown, Spanish scientists have “unequivocally” proven that Titan has electrical storms too. The presence of electrical activity in the atmosphere is causing much excitement as this could mean that organic compounds may be found in abundance on the Titan surface.
The fruits from the Cassini-Huygens mission are coming thick and fast. Only yesterday, Nancy reviewed the discovery of liquid hydrocarbon lakes by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS). Although possible lakes have been theorized, it is only now that there is observational proof of the existence of such features. Now, three years after the Huygens probe dropped through Titan’s atmosphere, scientists have made another crucial discovery: Titan experiences electrical activity in its atmosphere. Now Titan has all the necessary components for life; it has an atmosphere with electrical activity, increasing the opportunity for prebiotic organic compounds to form, thus increasing the possibility for life to evolve.
“On this moon clouds with convective movements are formed and, therefore, static electrical fields and stormy conditions can be produced. This also considerably increases the possibility of organic and prebiotic molecules being formed, according to the theory of the Russian biochemist Alexander I. OparÃn and the experiment of Stanley L. Miller [who managed to synthesise organic compounds from inorganic compounds through electrical discharges] That is why Titan has been one of the main objectives of the Cassini-Huygens joint mission of NASA and the European Space Agency” – Juan Antonio Morente.
Morente and his team analysed data from Huygens’ Mutual Impedance Probe (MIP) that measured the atmospheric electrical field. The MIP instrument was primarily used to measure the atmosphere’s electrical conductivity but it also acted as a dipolar antenna, detecting the natural electric field. The MIP was therefore able to detect a set of spectral peaks of extremely low frequency (ELF) radio signals (known as “Schumann resonances”). These ELF peaks are formed between the moon’s ionosphere and a huge resonant cavity in which electromagnetic fields are confined.
The detection of these signals have led the Spanish researchers to state that it is “irrefutable” evidence of electrical activity on Titan, not dissimilar to static charge that builds up in the terrestrial atmosphere, leading to electrical storms.
[/caption]Greetings, fellow SkyWatchers! Are you ready for today’s eclipse? Be sure to follow Ian’s earlier instructions this week and catch the action for yourself! When the Sun is gone at last, then let’s continue through the New Moon weekend with our globular cluster studies and we’ll take a look at some of the summer’s finest for both binoculars and telescopes. If you’re not afraid of the dark, then follow me…
Friday, August 1, 2008 – Mark your calendar! A total solar eclipse occurs today in northern Canada, the Arctic and Asia. Totality will begin at 09:21:07 UT in Canada, with the path crossing Greenland, the Arctic Ocean, Russia, and Mongolia – ending in China at 11:21:28 UT. Maximum occurs at 10:21:08 UT. For those not in the path, a partial eclipse will be visible over northeastern Canada, most of Asia and Europe, and the Middle East, between 08:04:07 UT and 12:38:28 UT. Be sure to consult with online sources such as Mr. Eclipse for accurate locations of the path of totality. And please…NEVER look at the Sun without taking proper precautions. Wishing you clear skies for this event!
Since tonight is also New Moon, let’s continue our exploration of summer’s globular clusters. These gravitationally bound concentrations of stars contain anywhere from ten thousand to one million members, and attain sizes of up to 200 light-years in diameter. At one time, these fantastic members of our galactic halo were believed to be round nebulae; perhaps the very first to be discovered was M22 in Sagittarius by Abraham Ihle in 1665. This particular globular is easily seen in even small binoculars and can be easily located just slightly more than two degrees northeast of the teapot’s lid, Lambda Sagittarii – Kaus Borealis (RA 18 36 24 Dec -23 54 12).
M22Ranking third amidst the 151 known globular clusters in total light, M22 is probably the nearest of these incredible systems to our Earth, with an approximate distance of 9,600 light-years. It is also one of the nearest globulars to the galactic plane. Since it resides less than a degree from the ecliptic, it often shares the same eyepiece field with a planet. At magnitude 6, the class VII M22 will begin to show individual stars to even modest instruments and will burst into stunning resolution for larger aperture. About a degree west-northwest, mid-sized telescopes and larger binoculars will capture the smaller 8th magnitude NGC 6642 (RA 18 31 54 Dec -23 28 34). At class V, this particular globular will show more concentration toward the core region than M22. Enjoy them both!
Saturday, August 2, 2008 – If you’re out tonight at sunset, be sure to watch the horizon in hopes of catching a glimpse of the very beginning of the Moon’s return. Both Regulus and Venus are nearby!
Tonight, let’s return again to look at two globular giants so we might compare roughly equal sizes, but not equal classes. To judge them fairly, you must use the same eyepiece. Start first by re-locating previous study M4. This is a class IX globular cluster. Notice the powder-like qualities. It might be heavily populated, but it is not dense. Now return to another previous study, M13, which is of class V. Most telescopes will achieve at least some resolution and show a distinct core region. It is the level of condensation that creates the different classes. Judging a globular’s concentration is no different from judging magnitudes, and simply takes practice.
M71Now try your hand at M55 (RA 19 39 59 Dec -30 57 43) along the bottom of the Sagittarius teapot – it’s a class XI. Although it is a full magnitude brighter than the class I cluster M75, can you tell the difference in concentration? For those with GoTo systems, take a quick hop through Ophiuchus and look at the difference between NGC 6356 (class II) and NGC 6426 (class IX). If you want to try one that science can’t even classify? Look no further than M71 in Sagitta (RA 19 53 46 Dec +18 46 42). It’s all a wonderful game and the most fun comes from learning!
Sunday, August 3 – For SkyWatchers tonight, be sure to catch the tender crescent Moon pairing with lovely Saturn just after sunset! Now, let’s return to earlier evening skies as we continue our studies with one of the globulars nearest to the galactic center – M14. Located about 16 degrees (less than a handspan) south of Alpha Ophiuchi (RA 17 37 36 Dec -03 14 45), this 9th magnitude, class VIII cluster can be spotted with larger binoculars, but will only be fully appreciated with the telescope.
M14When studied spectroscopically, globular clusters are found to be much lower in heavy element abundance than stars such as our own Sun. These earlier generation stars (Population II) began their formation during the birth of our galaxy, making globular clusters the oldest formations an amateur can study. Globulars are distributed in a spherical halo around the galaxy center. In contrast, stars in the disk are mostly much younger, their populations having gone through cycles of starbirth and supernovae, which in turn have enriched the heavy element concentration in nearby star forming clouds. Of course, as you may have guessed, M14 breaks the rules! It contains an unusually high number of variable stars – in excess of 70 – with many of them known to be the W Virginis type. In 1938, a nova appeared in M14, but it went undiscovered until 1964 when Amelia Wehlau of the University of Ontario was surveying the photographic plates taken by Helen Sawyer Hogg. The nova was revealed on eight of these plates taken on consecutive nights and showed itself as a 16th magnitude star – and at its peak was believed to be almost five times brighter than other cluster members. So unlike 80 years earlier with T Scorpii in M80, actual photographic evidence of this event existed. In 1991, the eyes of the Hubble were turned its way, but neither the suspect star nor traces of a nebulous remnant were discovered. But six years later, a rare carbon star was discovered in M14.
To a small telescope, M14 will offer little to no resolution and will appear almost like an elliptical galaxy, lacking any central condensation. Larger scopes will show hints of resolution, with a gradual fading toward the cluster’s slightly oblate edges. A true beauty!
This week’s awesome images are: Total Eclipse – Credit: NASA (Fred Espenak), M22 – Credit: N.A.Sharp, REU program/NOAO/AURA/NSF, M71 – REU program/NOAO/AURA/NSF and M14 – NOAO/AURA/NSF.
Latest panorama from Mars. Credit: NASA/JPL/Caltech/U of Arizona
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The Phoenix Mars lander finally was successful in delivering a fairly fresh sample of Martian soil to the Thermal and Evolved Gas Analyzer (TEGA) oven on Wednesday and a “bake and sniff” test identified water in the soil sample. “We have water,” said William Boynton of the University of Arizona, lead scientist for TEGA. “We’ve seen evidence for this water ice before in observations by the Mars Odyssey orbiter and in disappearing chunks observed by Phoenix last month, but this is the first time Martian water has been touched and tasted.”
The soil sample came from a trench approximately 2 inches deep. When the robotic arm first reached that depth, it hit a hard layer of frozen soil. Two attempts to deliver samples of icy soil on days when fresh material was exposed were foiled when the samples became stuck inside the scoop. Most of the material in Wednesday’s sample had been exposed to the air for two days, letting some of the water in the sample vaporize away and making the soil easier to handle.
“Mars is giving us some surprises,” said Phoenix principal investigator Peter Smith of the University of Arizona. “We’re excited because surprises are where discoveries come from. One surprise is how the soil is behaving. The ice-rich layers stick to the scoop when poised in the sun above the deck, different from what we expected from all the Mars simulation testing we’ve done. That has presented challenges for delivering samples, but we’re finding ways to work with it and we’re gathering lots of information to help us understand this soil.” Phoenix's Workspace on Mars. Credit: NASA/JPL/Caltech/U of Arizona
Also at the press conference announcing the results, NASA also announced a mission extension for Phoenix, through Sept. 30. The original prime mission of three months ends in late August. The mission extension adds five weeks to the 90 days of the prime mission.
“Phoenix is healthy and the projections for solar power look good, so we want to take full advantage of having this resource in one of the most interesting locations on Mars,” said Michael Meyer, chief scientist for the Mars Exploration Program at NASA Headquarters in Washington.
During the mission extension, the science team will attempt to determine whether the water ice ever thaws enough to be available for biology and if carbon-containing chemicals and other raw materials for life are present.
A full-circle, color panorama of Phoenix’s surroundings was recenlty completed by the spacecraft.
“The details and patterns we see in the ground show an ice-dominated terrain as far as the eye can see,” said Mark Lemmon of Texas A&M University, lead scientist for Phoenix’s Surface Stereo Imager camera. “They help us plan measurements we’re making within reach of the robotic arm and interpret those measurements on a wider scale.”
Artist concept of the first stars. Credit: Harvard Smithsonian CfA
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What were the first stars like that formed shortly after the Big Bang? We don’t know much about the conditions of the early universe 13 billion years ago, but a new computer simulation provides the most detailed picture yet of the first stars and how they came into existence. The composition of the early universe was quite different from that of today, said Dr. Naoki Yoshida, Nagoya University in Nagoya, Japan and Dr. Lars Hernquist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. An article that will be published to the August 1 journal Science describes their findings from the computer model that simulates the early days of the universe, the “cosmic dark ages,” where the physics governing the universe were somewhat simpler. The astronomers believe small, simple protostars formed, which eventually became massive, but short-lived stars.
According to their simulations, gravity acted on minute density variations in matter, gases, and the mysterious “dark matter” of the universe after the Big Bang in order to form the early stages of a star called a protostar. With a mass of just one percent of our Sun, Dr. Yoshida’s simulation also shows that the protostar would likely evolve into a massive star capable of synthesizing heavy elements, not just in later generations of stars, but soon after the Big Bang. These stars would have been up to one hundred times as massive as our Sun and would have burned for no more than one million years. “This general picture of star formation, and the ability to compare how stellar objects form in different time periods and regions of the universe, will eventually allow investigation in the origins of life and planets,” said Hernquist.
“The abundance of elements in the Universe has increased as stars have accumulated,” he says, “and the formation and destruction of stars continues to spread these elements further across the Universe. So when you think about it, all of the elements in our bodies originally formed from nuclear reactions in the centers of stars, long ago.”
The goal of their research is to be able to figure out how the primordial stars formed, as well as predicting the mass and properties of the first stars of the universe. The researchers hope to eventually extend this simulation to the point of nuclear reaction initiation – when a stellar object becomes a true star. But that’s the point where the physics becomes much more complicated, and the researchers say they’ll need more computational resources to simulate that process.
Pictures of all the objects in the Solar System. Image credit: NASA/JPL
3D Deep Space – this is one of the most popular Solar System screensavers out there. There are several separate versions, and you can buy a pack that contains all their different versions for about $50. There are demo versions of each product, but they’ve got nag screens and only work for a limited amount of time.
NASA’s Genesis Spacecraft – This screensaver comes from NASA and teaches you about the Genesis spacecraft, and shows the path it will take through the Solar System.
SOHO – NASA/ESA’s SOHO spacecraft captures images of the Sun. This screensaver lets you display the images on your computer desktop while you’re not using it. It works with PC, and they released a Mac version in 2008.
Red dwarf Gliese 581 and the Earth-like planet Bebo is hoping to contact. Credit: AFP
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Social networking sites are the backbone of “Web 2.0” and now one of the most popular sites, Bebo (popular with a younger demographic), hopes to reach out to extraterrestrial civilizations. Why? Well, the power of social networking sites like Bebo, Facebook and MySpace is that you can keep in touch with friends, make new friends and electronically hang out with people with similar interests. So Bebo will invite its users, celebrities and politicians to post messages that “consider the planet from a fresh perspective” and raise awareness of environmental pressures on Earth. In this day and age of democratically selecting news on the Internet (much like another Web 2.0 phenomenon, social bookmarking; like Digg, StumbleUpon, Reddit etc.), rather than letting mainstream media select “what news is important,” Bebo users will vote the top 500 messages to be transmitted to a small red dwarf star, Gliese 581 in the hope of communicating what really matters to Bebo users. Plus they might extend the Bebo network to some new alien friends…
Transmitting messages to outer space is no new thing. Recently we’ve sent Beatles songs to Polaris and we’ve transmitted “Space Spam” to Ursa Major. But through the power of social networking, Bebo is sending the best 500 messages to a star with an orbiting planet, a possible candidate where life (or indeed an advanced civilization) may have evolved. The planet called Gliese 581c is classified as a “super-Earth” and it is located approximately 20 light years from us. The main point behind this effort isn’t necessarily to contact extraterrestrial civilizations however, it is to raise awareness about the concerns young people have for the environment.
“I understand that in the majority of cases these messages may be naïve, but I also hope that we will receive a creative and fresh look at the subject.” – Dr Alexander Zaitsev
To achieve this, Bebo has teamed up with Oli Madgett of RDF Digital, a subsidiary of RDF Media and will be using the expertise of one of the world’s experts in interstellar radio communication, Dr Alexander Zaitsev. Once the 500 messages have been selected, they will be sent to Gliese 581c via a Ukrainian radio telescope, normally used to identify and track near-Earth asteroids.
The voting will commence on Bebo from August 4th until September 30th and the 500 messages, acting like a digital time capsule (after all, the message will take 20 years to reach its destination), will be transmitted on October 9th.
The British production company will cover the £20,000 ($40,000) bill for the four and a half hour transmission from the National Space Agency in Ukraine.
Although sending radio transmissions to the outer reaches of space may seem like a long-shot when trying to communicate with extraterrestrials, this alternative approach will help to raise awareness for the concerns that young people have for the future of Earth, let alone an increase for interest space exploration. The intent is certainly a positive step toward giving the adults of tomorrow a voice and an opinion.
Project Lucifer. Could the plutonium fuel onboard the Cassini mission cause a nuclear chain reaction on Saturn? Credit: NASA
[/caption] The story: The Lucifer Project is allegedly the biggest conspiracy theory NASA could possibly be involved in. First, back in 2003, the space agency (in co-operation with secret and powerful organizations) dropped the Galileo probe deep into Jupiter’s atmosphere. On board, was a significant quantity of plutonium. As the probe fell though the atmosphere, NASA hoped atmospheric pressures would create an implosion, generating a nuclear explosion thereby kick-starting a chain reaction, turning the gas giant into a second Sun. They failed. So, in a second attempt, they will drop the Cassini probe (again, laden with plutonium) deep into Saturn’s atmosphere in two years time, so this smaller gas giant can succeed where Jupiter failed…
The reality: As investigated briefly in Project Lucifer: Will Cassini Turn Saturn into a Second Sun? (Part 1), we looked at some of the technical problems behind Galileo and Cassini being used as makeshift nuclear weapons. They cannot generate an explosion for many reasons, but the main points are: 1) Tiny pellets of plutonium used to heat and power the probes are in separate, damage-proof cylinders. 2) The plutonium is not weapon grade, meaning the 238Pu makes a very inefficient fissionable fuel. 3) The probes will burn up and break apart, therefore disallowing any chance of lumps of plutonium forming “critical mass” (besides, there is no chance the plutonium could possibly form a configuration to create an implosion-triggered device).
OK, so Galileo and Cassini cannot be used as crude nuclear weapons. But say if there was a nuclear explosion inside Saturn? Could it cause a chain reaction in the core, creating a second Sun?
Thermonuclear bombs The Soviet 50-megaton Tsar Bomba, the largest weapon ever detonated (1961)
Unless nuclear fusion can be maintained within a stellar body, the reaction will very quickly fizz out. So the Lucifer Project proposes Cassini will plunge many hundreds of miles into the atmosphere of Saturn and explode as a crude plutonium-fuelled fission explosion. This explosion will cause a chain reaction, creating enough energy to trigger nuclear fusion inside the gas giant.
I can see where this idea has come from, even though it is inaccurate. The fusion bomb (or “thermonuclear weapon”) uses a fission trigger to kick-start an uncontrolled fusion reaction. The fission trigger is constructed to explode like a normal fission bomb much like the implosion device described in Part 1 of this series. When detonated, huge quantities of energetic X-rays are produced, heating the material surrounding the fusion fuel (such as lithium deuteride), causing the phase transition to a plasma. As very hot plasma is surrounding the lithium deuteride (in a very confined and pressured environment) the fuel will produce tritium, a heavy hydrogen isotope. Tritium then undergoes nuclear fusion, liberating huge quantities of energy as the tritium nuclei are forced together, overcoming the electrostatic forces between nuclei and fusing. Fusion releases large quantities of binding energy, more-so than fission.
How does a star work? A comparison of the size of Jupiter, a brown dwarf, a small star and the Sun (Gemini Observatory/Artwork by Jon Lomberg)
The point that needs to be emphasised here is that in a thermonuclear device, fusion can only be attained when immense temperatures are reached within a very confined and pressurized environment. What’s more, in the case of a fusion bomb, this reaction is uncontrolled.
So, how are nuclear fusion reactions sustained in a star (like our Sun)? In the thermonuclear bomb example above, tritium fusion is achieved through inertial confinement (i.e. rapid, hot and energetic pressure on the fuel to cause fusion), but in the case of a star, a sustained mode of confinement is required. Gravitational confinement is needed for nuclear fusion reactions to occur in the core. For significant gravitational confinement, the star requires a minimum mass.
In the core of our Sun (and most other stars smaller than our Sun), nuclear fusion is achieved through the proton-proton chain (pictured below). This is a hydrogen burning mechanism where helium is generated. Two protons (hydrogen nuclei) combine after overcoming the highly repulsive electrostatic force. This can only be achieved if the stellar body has a large enough mass, increasing gravitational containment in the core. Once the protons combine, they form deuterium (2D), producing a positron (quickly annihilating with an electron) and a neutrino. The deuterium nucleus can then combine with another proton, thus creating a light helium isotope (3He). The outcome of this reaction generates gamma-rays that maintain the stability and high temperature of the star’s core (in the case of the Sun, the core reaches a temperature of 15 million Kelvin).
The proton-proton chain that fuels nuclear fusion inside the core of our Sun. Credit: Ian O'Neill
As discussed in a previous Universe Today article, there are a range of planetary bodies below the threshold of becoming a “star” (and not able to sustain proton-proton fusion). The bridge between the largest planets (i.e. gas giants, like Jupiter and Saturn) and the smallest stars are known as brown dwarfs. Brown dwarfs are less than 0.08 solar masses and nuclear fusion reactions have never taken hold (although larger brown dwarfs may have had a short period of hydrogen fusion in their cores). Their cores have a pressure of 105 million atmospheres with temperatures below 3 million Kelvin. Keep in mind, even the smallest brown dwarfs are approximately 10 times more massive than Jupiter (the largest brown dwarfs are around 80 times the mass of Jupiter). So, for even a small chance of the proton-proton chain occurring, we’d need a large brown dwarf, at least 80 times bigger than Jupiter (over 240 Saturn masses) to even stand the hope of sustaining gravitational confinement.
There’s no chance Saturn could sustain nuclear fusion? Saturn, seen by Cassini. Image credit: NASA/JPL/SSI
Sorry, no. Saturn is simply too small.
Implying that a nuclear (fission) bomb detonating inside Saturn could create the conditions for a nuclear fusion chain reaction (like the proton-proton chain) is, again, in the realms of science fiction. Even the larger gas giant Jupiter is far too puny to sustain fusion.
I have also seen arguments claiming that Saturn consists of the same gases as our Sun (i.e. hydrogen and helium), so a runaway chain reaction is possible, all that is needed is a rapid injection of energy. However, the hydrogen that can be found in Saturn’s atmosphere is diatomic molecular hydrogen (H2), not the free hydrogen nuclei (high energy protons) as found in the Sun’s core. And yes, H2 is highly flammable (after all it was responsible for the infamous Hindenburg airship disaster in 1937), but only when mixed with a large quantity of oxygen, chlorine or fluorine. Alas Saturn does not contain significant quantities of any of those gases.
Conclusion
Although fun, “The Lucifer Project” is the product of someone’s lively imagination. Part 1 of “Project Lucifer: Will Cassini Turn Saturn into a Second Sun?” introduced the conspiracy and focused on some of the general aspects why the Galileo probe in 2003 simply burned up in Jupiter’s atmosphere, scattering the small pellets of plutonium-238 as it did so. The “black spot” as discovered the next month was simply one of the many dynamic and short-lived storms often seen to develop on the planet.
This article has gone one step further and ignored the fact that it was impossible for Cassini to become an interplanetary atomic weapon. What if there was a nuclear explosion inside Saturn’s atmosphere? Well, it looks like it would be a pretty boring affair. I dare say a few lively electrical storms might be generated, but we wouldn’t see much from Earth. As for anything more sinister happening, it is highly unlikely there would be any lasting damage to the planet. There would certainly be no fusion reaction as Saturn is too small and it contains all the wrong gases.
Oh well, Saturn will just have to stay the way it is, rings and all. When Cassini completes its mission in two years time, we can look forward to the science we will accumulate from such an incredible and historic endeavour rather than fearing the impossible…
Update (Aug. 7th): As pointed out by some readers below, molecular hydrogen wasn’t really the cause of the Hindenburg airship disaster, it was the aluminium-based paint that may have sparked the explosion, hydrogen and oxygen fuelled the fire.
Artist's concept of the liquid lake on Titan. Credit: NASA/JPL
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NASA’s Cassini mission has detected liquid hydrocarbons on Saturn’s moon Titan, in a large, glassy lake near the moon’s south pole. Before the Cassini mission began, scientists thought Titan would have global oceans of methane, ethane and other light hydrocarbons. But after more than 40 close flybys of Titan by Cassini, data showed no global oceans exist. However hundreds of dark, lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material. Using Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), which identifies the chemical composition of objects by the way matter reflects light, a liquid ethane lake 235 kilometers (150 miles) long was detected. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.
“This is the first observation that really pins down that Titan has a surface lake filled with liquid,” said Bob Brown of the University of Arizona, Tucson, leader of the VIMS instrument.
Scientists had deduced through earlier observations that there was likely liquid on Titan, but this is the first incontrovertible evidence. (Emily Lakdawalla at the Planetary Society explains this excellently.)
“Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan,” said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey. “The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan’s atmosphere, raises expectations for exciting future lake discoveries by our instrument.” The dark area near the top is Ontario Lacus. Credit: NASA / JPL / Space Science Institute
Titan’s hazy, nitrogen and methane atmosphere makes it difficult to study the moon’s surface. The liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.
The VIMS instrument observed a lake, called Ontario Lacus, in Titan’s south polar region during a close Cassini flyby in December 2007. The lake is roughly 20,000 square miles (7,800 square miles) in area, slightly larger than North America’s Lake Ontario.
The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen. At Titan’s surface temperatures, approximately 300 degrees Fahrenheit below zero, these substances can exist as both liquid and gas. Titan shows overwhelming evidence of evaporation, rain, and fluid-carved channels draining into what, in this case, is a liquid hydrocarbon lake.
Earth has a hydrological cycle based on water and Titan has a cycle based on methane. Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline. Cassini also observed a shelf and beach being exposed as the lake evaporates.
“During the next few years, the vast array of lakes and seas on Titan’s north pole mapped with Cassini’s radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan’s lakes,” Soderblom said.
