In this near-infrared mosaic, the sun shines off of the seas on Saturn's moon, Titan. Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho
See that yellow smudge in the image above? That’s what the Sun looks like reflecting off the seas of Titan, that moon of Saturn that excites astrobiologists because its chemistry resembles what early Earth could have looked like. This image represents the first time this “sunglint” and Titan’s northern polar seas have been captured in one mosaic, NASA said.
What’s more, if you look closely at the sea surrounding the sunlight, you can see what scientists dub a “bathtub ring.” Besides looking pretty, this image from the Cassini spacecraft shows the huge sea (called Kraken Mare) was actually larger at some point in Titan’s past.
“The southern portion of Kraken Mare … displays a ‘bathtub ring’ — a bright margin of evaporate deposits — which indicates that the sea was larger at some point in the past and has become smaller due to evaporation,” NASA stated. “The deposits are material left behind after the methane and ethane liquid evaporates, somewhat akin to the saline crust on a salt flat.”
In this near-infrared global mosaic of Titan, sunglint and the moon’s polar seas are visible above the shadow. Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho
The sunlight was so bright that it saturated the detector on Cassini that viewed it, called the Visual and Infrared Mapping Spectrometer (VIMS) instrument. The sun was about 40 degrees above the horizon of Kraken Mare then, which is the highest ever observed on Titan.
The T-106 flyby Oct. 23 was the second-to-last closeup view Cassini will have of Titan this year. The spacecraft has been circling Saturn’s system for more than 10 years, and is now watching Titan (and Saturn’s) northern hemisphere enter summer.
Titan is covered in a thick, orangey atmosphere that hid its surface from scientists the first time a spacecraft zoomed by it in the 1980s. Subsequent exploration (most especially by Cassini and a short-lived lander called Huygens) have revealed dunes on and near the equator and at higher altitudes, lakes of methane and ethane.
This cloud in the stratosphere over Titan’s north pole (left) is similar to Earth’s polar stratospheric clouds (right). NASA scientists found that Titan’s cloud contains methane ice, which was not previously thought to form in that part of the atmosphere. Cassini first spotted the cloud in 2006. Credit:
L. NASA/JPL/U. of Ariz./LPGNantes; R. NASA/GSFC/M. Schoeberl
During its 2006 flyby of Titan, the Cassini Space Probe captured some of the most detailed images of Saturn’s largest moon. Amongst them was one showing the lofty cloud formations over Titan’s north pole (shown above). Interestingly enough, these cloud formations bear a strong resemblance to those that are seen in Earth’s own polar stratosphere.
However, unlike Earth’s, these clouds are composed entirely of liquid methane and ethane. Given Titan’s incredibly low temperatures – minus 185 °C (-300 °F) – it’s not surprising that such a dense atmosphere of liquid hydrocarbons exists, or that seas of methane cover the planet.
The ALMA array, as it looks now completed and standing on a Chilean high plateau at 5000 meters (16,400 ft) altitude. The first observations with ALMA of Titan have added to the Saturn moon's list of mysteries. {Credit: ALMA (ESO/NAOJ/NRAO) / L. Calçada (ESO)}
A new mystery of Titan has been uncovered by astronomers using their latest asset in the high altitude desert of Chile. Using the now fully deployed Atacama Large Millimeter Array (ALMA) telescope in Chile, astronomers moved from observing comets to Titan. A single 3 minute observation revealed organic molecules that are askew in the atmosphere of Titan. The molecules in question should be smoothly distributed across the atmosphere, but they are not.
The Cassini/Huygens spacecraft at the Saturn system has been revealing the oddities of Titan to us, with its lakes and rain clouds of methane, and an atmosphere thicker than Earth’s. But the new observations by ALMA of Titan underscore how much more can be learned about Titan and also how incredible the ALMA array is.
ALMA’s first observations of the atmosphere of Saturn’s moon Titan. The image shows the distribution of the organic molecule HNC. Red to White representing low to high concentrations. The offset locations of the molecules relative to the poles surprised the researchers led by NASA/GSFC astrochemist M. Cordiner. (Credit: NRAO/AUI/NSF; M. Cordiner (NASA) et at.)
The ALMA astronomers called it a “brief 3 minute snapshot of Titan.” They found zones of organic molecules offset from the Titan polar regions. The molecules observed were hydrogen isocyanide (HNC) and cyanoacetylene (HC3N). It is a complete surprise to the astrochemist Martin Cordiner from NASA Goddard Space Flight Center in Greenbelt, Maryland. Cordiner is the lead author of the work published in the latest release of Astrophysical Journal Letters.
The NASA Goddard press release states, “At the highest altitudes, the gas pockets appeared to be shifted away from the poles. These off-pole locations are unexpected because the fast-moving winds in Titan’s middle atmosphere move in an east–west direction, forming zones similar to Jupiter’s bands, though much less pronounced. Within each zone, the atmospheric gases should, for the most part, be thoroughly mixed.”
When one hears there is a strange, skewed combination of organic compounds somewhere, the first thing to come to mind is life. However, the astrochemists in this study are not concluding that they found a signature of life. There are, in fact, other explanations that involve simpler forces of nature. The Sun and Saturn’s magnetic field deliver light and energized particles to Titan’s atmosphere. This energy causes the formation of complex organics in the Titan atmosphere. But how these two molecules – HNC and HC3N – came to have a skewed distribution is, as the astrochemists said, “very intriguing.” Cordiner stated, “This is an unexpected and potentially groundbreaking discovery… a fascinating new problem.”
The press release from the National Radio Astronomy Observatory states, “studying this complex chemistry may provide insights into the properties of Earth’s very early atmosphere.” Additionally, the new observations add to understanding Titan – a second data point (after Earth) for understanding organics of exo-planets, which may number in the hundreds of billions beyond our solar system within our Milky Way galaxy. Astronomers need more data points in order to sift through the many exo-planets that will be observed and harbor organic compounds. With Titan and Earth, astronomers will have points of comparison to determine what is happening on distant exo-planets, whether it’s life or not.
High in the atmosphere of Titan, large patches of two trace gases glow near the north pole, on the dusk side of the moon, and near the south pole, on the dawn side. Brighter colors indicate stronger signals from the two gases, HNC (left) and HC3N (right); red hues indicate less pronounced signals. (Image Credit: NRAO/AUI/NSF)
The report of this new and brief observation also underscores the new astronomical asset in the altitudes of Chile. ALMA represents the state of the art of millimeter and sub-millimeter astronomy. This field of astronomy holds a lot of promise. Back around 1980, at the Kitt Peak National Observatory in Arizona, alongside the great visible light telescopes, there was an oddity, a millimeter wavelength dish. That dish was the beginning of radio astronomy in the 1 – 10 millimeter wavelength range. Millimeter astronomy is only about 35 years old. These wavelengths stand at the edge of the far infrared and include many light emissions and absorptions from cold objects which often include molecules and particularly organics. The ALMA array has 10 times more resolving power than the Hubble space telescope.
The Earth’s atmosphere stands in the way of observing the Universe in these wavelengths. By no coincidence our eyes evolved to see in the visible light spectrum. It is a very narrow band, and it means that there is a great, wide world of light waves to explore with different detectors than just our eyes.
The diagram shows the electromagnetic spectrum, the absorption of light by the Earth’s atmosphere, and illustrates the astronomical assets that focus on specific wavelengths of light. ALMA at the Chilean site, with modern solid state electronics, is able to overcome the limitations placed by the Earth’s atmosphere. (Credit: Wikimedia, T.Reyes)
In the millimeter range of wavelengths, water, oxygen, and nitrogen are big absorbers. Some wavelengths in the millimeter range are completely absorbed. So there are windows in this range. ALMA is designed to look at those wavelengths that are accessible from the ground. The Chajnantor plateau in the Atacama desert at 5000 meters (16,400 ft) provides the driest, clearest location in the world for millimeter astronomy outside of the high altitude regions of the Antarctic.
At high altitude and over this particular desert, there is very little atmospheric water. ALMA consists of 66 12 meter (39 ft) and 7 meter (23 ft) dishes. However, it wasn’t just finding a good location that made ALMA. The 35 year history of millimeter-wavelength astronomy has been a catch up game. Detecting these wavelengths required very sensitive detectors – low noise in the electronics. The steady improvement in solid-state electronics from the late 70s to today and the development of cryostats to maintain low temperatures have made the new observations of Titan possible. These are observations that Cassini at 1000 kilometers from Titan could not do but ALMA at 1.25 billion kilometers (775 million miles) away could.
The 130 ton German Antenna Dish Transporter, nicknamed Otto. The ALMA transporter vehicle carefully carries the state-of-the-art antenna, with a diameter of 12 metres and a weight of about 100 tons, on the 28 km journey to the Array Operations Site, which is at an altitude of 5000 m. The antenna is designed to withstand the harsh conditions at the high site, where the extremely dry and rarefied air is ideal for ALMA’s observations of the universe at millimetre- and sub-millimetre-wavelengths. (Credit: ESO)
The prototype ALMA telescope was tested at the site of the VLA in New Mexico in 2003. That prototype now stands on Kitt Peak having replaced the original millimeter wavelength dish that started this branch of astronomy in the 1980s. The first dishes arrived in 2007 followed the next year by the huge transporters for moving each dish into place at such high altitude. The German-made transporter required a cabin with an oxygen supply so that the drivers could work in the rarefied air at 5000 meters. The transporter was featured on an episode of the program Monster Moves. By 2011, test observations were taking place, and by 2013 the first science program was undertaken. This year, the full array was in place and the second science program spawned the Titan observations. Many will follow. ALMA, which can operate 24 hours per day, will remain the most powerful instrument in its class for about 10 years when another array in Africa will come on line.
This colorized mosaic from NASA's Cassini mission shows the most complete view yet of Titan's northern land of lakes and seas. Saturn's moon Titan is the only world in our solar system other than Earth that has stable liquid on its surface. The liquid in Titan's lakes and seas is mostly methane and ethane. Image credit: NASA/JPL-Caltech/ASI/USGS
There’s a very early-stage NASA concept to take a submarine and dive into a lake of Titan, that moon of Saturn that has chemistry that could prove to be a similar precursor to what eventually formed life on Earth. The moon has weather and a hydrological system and an atmosphere, making it an exciting location for astrobiologists.
Luckily for scientists, the Cassini spacecraft beams back regular updates on what it sees at Titan. And this week comes yet another opportunity, as the machine whizzes by the moon to look for “mirror-like surface echoes” in a lake-filled region in Titan’s northern sector.
Principal among the targets will be Kraken Mare, a liquid hydrocarbon sea that is about five times the size of Lake Superior in North America. It’s an astounding 154,000 square miles (400,000 square kilometers). On this pass, Cassini is going to sail over the eastern area of the sea.
“Measurements of the absolute strength of the echo and its polarization properties, when detectable, yield important information about the surface status (liquid/solid), surface reflectivity, surface dielectric constant and implied composition, and surface roughness,” Cassini’s website says in a description of the T-106 flyby, which will take place Thursday (Oct. 23).
Saturn’s moon Titan with Tethys hovering in the background. Image taken by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute
This is the second-to-last flyby Cassini will have of Titan in 2014, with the last one coming Dec. 10. In that case, the focus will be learning more about Titan’s atmosphere to learn more about measurement differences obtained by instruments on Cassini.
This past week, meanwhile, Titan has been busy looking at Saturn. It examined a northern aurora, looked at the planet’s F ring, and also searched for small satellites.
Scientists have been working at Saturn for the past 10 years with the Cassini mission, which is now entering a new phase as Saturn enters northern summer. This is expected to produce more changes on Titan, such as winds picking up, as more sunlight strikes the surface and atmosphere.
A false-color view of Saturn's moon Hyperion taken during a Cassini flyby in September 2005. Credit: NASA/JPL-Caltech/Space Science Institute
Ever taken a balloon and rubbed it against your hair? That’s an example of electrostatic charging, which you see as the balloon briefly attracts strands of hair against your head. Turns out a similar process is taking place on Saturn’s moon Hyperion. More astounding, it wasn’t until recently that scientists saw a curious effect on the Cassini spacecraft in 2005.
As the machine whizzed by the small moon, Cassini was blanketed in electrons from Hyperion’s electrostatically charged surface. It’s the first time scientists have seen static electricity in effect on any airless body outside of the Moon.
The charge comes partly from massive Saturn’s magnetic field, which hits Hyperion’s spongy surface constantly with electrons and ions. The Sun also plays a role, sending ultraviolet light that also strikes the moon’s surface. Scientists found out this happens while studying old data on the Cassini spacecraft, when they discovered “something unexpected” during a close flyby of Hyperion in September 2005.
NASA’s Cassini spacecraft obtained this unprocessed image of Saturn’s moon Hyperion on Aug. 25, 2011. Image credit: NASA/JPL-Caltech/Space Science Institute
Specifically, the spacecraft — which is still in operation today — was briefly connected through magnetism to Hyperion’s surface, receiving a surge of electrons. Cassini emerged from the encounter unharmed, even though team members estimate that it received the equivalent of a 200-volt shock from the moon. Charging events can hurt spacecraft, making this a valuable thing to know about for future missions.
“Our observations show that this is also an important effect at outer planet moons and that we need to take this into account when studying how these moons interact with their environment,” stated Geraint Jones of Mullard Space Science Laboratory (MSSL), University College London. He is a member of the Cassini Plasma Spectrometer (CAPS) team and one of the study’s supervisors.
CAPS is not in operation any more, since the instrument was turned off due to drawing excess current in 2012. But perhaps some of its past data, and observations from other Cassini instruments, can help unveil evidence of charging on other moons.
The tumbling motion of elongated Eros creates a changing brightness. (via transitofvenus.nl)
Previous research concerning some of Saturn’s moons, and the asteroid Eros, suggests that charged dust can move across the surface and perhaps even be able to sail into space against the force of gravity.
Several other instruments were used to gather data for this analysis, including Cassini’s magnetometer, magnetospheric imaging instrument, and radio and plasma wave science instrument.
You can read more about the research, which was led by Tom Nordheim, an MSSL doctoral candidate, in Geophysical Research Letters.
A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute
Could there be an ocean hidden somewhere in that Death Star-like picture? This is an image of Mimas, a moon of Saturn, and just yesterday (Oct. 15) newly released data from the Cassini spacecraft suggests there are big liquid reservoirs underneath its surface.
“The amount of the to-and-fro motion indicates that Mimas’ interior is not uniform. These wobbles can be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell,” said Cornell University in a press release. More flybys with the Cassini spacecraft will be required to learn more about what lies beneath.
You can read more about the study (led by Cornell astronomy research associate Radwan Tajeddine) in Science, where it was published. Below, learn more about other worlds in the Solar System that could host oceans under their surface.
Enceladus
Cassini images of Saturn’s moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. This image was taken looking more or less broadside at the “tiger stripe” fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb (edge) of the moon. This image was acquired on Nov. 27, 2005. Image Credit: NASA/JPL/Space Science Institute
After nearly a decade of speculation, this year the Cassini spacecraft returned gravity data suggesting Enceladus (another moon of Saturn) does have a large subsurface ocean near its south pole, if not a global ocean. If confirmed, that could help explain why scientists see water gushing out of fractures in that area. As this recent paper by Cassini scientists shows, Enceladus is a promising location for habitability.
Titan
A halo of light surrounds Saturn’s moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute
By the way, anyone noticed that we still haven’t even left Saturn’s system? Titan is usually high on astrobiology wish lists for researchers because its hydrocarbon chemistry could be precursors to how life evolved. What’s not talked about as much, though, is at least two research findings pointing to evidence of a hidden ocean. Evidence comes from Titan’s tidal flexing from interacting with Saturn — which is 10 times more than what would be expected with a solid core — and the way that it moves on its own axis as well as around Saturn.
Europa
Rendering showing the location and size of water vapor plumes coming from Europa’s south pole. Credit: NASA/ESA/L. Roth/SWRI/University of Cologne
That Minecraft-looking object floating beside Europa there is a rendering showing where water vapor erupted from the Jovian moon, spotted by the Hubble Space Telescope in 2013. We were lucky enough to have a close-up view of Europa in the 1990s and early 2000s courtesy of NASA’s Galileo spacecraft. What we know for sure is there’s thick ice on Europa. What’s underneath is not known, but there’s long been speculation that it could be a subsurface ocean that may have more water than our own planet.
Io
Jupiter’s volcanic moon Io , imaged by the Galileo spacecraft in 1997. Credit: NASA/JPL/University of Arizona
Still flying around Jupiter here, we now turn our attention to Io — a place that is often remarked upon because of its blotchy appearance as well as all of the volcanoes on its surface. A newer analysis of Galileo data in 2011 — looking at some of the lesser-understood magnetic field data signatures — led one research team to conclude there could be a magma ocean lurking underneath that violence.
Triton
A glimpse of Triton from the Voyager 2 spacecraft, which flew by the Neptunian moon in August 1989. Credit: NASA/JPL
Little is known about Triton because only one spacecraft whizzed by it — Voyager 2, which took a running pass through the Neptune system in August 1989. An Icarus paper two years ago speculated that the world could host a subsurface ocean, but more data is needed. The energy of Neptune (which captured Triton long ago) could have melted its interior through tidal heating, possibly creating water from the ice in its crust.
Charon
Hubble image of Pluto and some of its moons, Charon, Nix and Hydra. Image Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team
We don’t have any close-up pictures of this moon of Pluto yet, but just wait a year. The New Horizons spacecraft will zoom past Charon and the rest of the system in July 2015. In the meantime, however, findings based on a model came out this summer in Icarus suggesting Charon — despite being so far from the Sun — might have had a subsurface ocean in the past. Or even now. The key is its once eccentric orbit, which would have produced tidal heating while interacting with Pluto. The science team plans to look for cracks that could be indicative of “the structure of the moon’s interior and how easily it deforms, and how its orbit evolved,” stated Alyssa Rhoden of NASA’s Goddard Space Flight Center in Maryland, who led the research.
Looking to the future of space exploration, NASA and TopCoder have launched the "High Performance Fast Computing Challenge" to improve the performance of their Pleiades supercomputer. Credit: NASA/MSFC
TORONTO, CANADA – Could NASA’s new rocket bring a probe to sample the geysers of Saturn’s moon Enceladus, or ferry human explorers to the surface of Mars? Representatives of contractor Boeing think so.
They’ve put together some ideas for sending their Space Launch System to these far-flung destinations, which they presented at the International Astronautical Congress today (Oct. 1).
Bear in mind that the SLS hasn’t yet flown — it’s slated for 2018 if funding lasts and the schedule holds — and the destinations below are just in the conceptual stage. The gallery below summarizes some of the destinations SLS could visit. For more information, check out this brochure by Boeing.
Enceladus
Artist’s conception of the Cassini spacecraft flying amid geysers on Enceladus, a moon of Saturn. Credit: Karl Kofoed / NASA
The icy moon of Saturn is known as a hotspot for geysers; earlier this year, scientists found 101 gushers using data from the prolific Cassini probe. Using the SLS could bring a satellite there in four years, as opposed to about seven with rockets on the market today, according to Boeing. It also could carry a heavier spacecraft.
Europa
Artist’s conception of Europa’s surface, backdropped by planet Jupiter. Credit: NASA/JPL-Caltech
Europa is known to have a subterranean ocean, and it also is capable of spewing water plumes — as researchers using the Hubble Space Telescope discovered earlier this year. The SLS could get to Europa a lot faster than a launch with an Atlas, according to Boeing — it would only take two years to fly there directly as opposed to more than six years with the Atlas, which would need to fly by Venus first to pick up some speed.
Trojan asteroids
Artist’s diagram of Jupiter and some Trojan asteroids nearby the gas giant. Credit: NASA/JPL-Caltech
Trailing before and after Jupiter are more than a million asteroids that are called Trojans. This means any probe in the area would have no lack of targets to study, providing it had enough fuel on board. A mission profile from Boeing suggests the SLS could bring a spacecraft out there that could swing by a target at least half a dozen times.
Mars
Artist’s impression of astronauts exploring Mars. Credit: NASA/Pat Rawlings, SAIC
One of the largest challenges of getting to Mars is figuring out how to send all the life-support equipment and food that humans require — on top of the humans themselves! Since SLS is a heavy-lift rocket, Boeing is trying to position its rocket as the ideal one to get humans to Mars. But it remains to be seen what concept works best to get people out there.
The Moon
Artist’s impression of astronauts on the moon. This image was used to illustrate a landing concept of NASA’s now defunct Constellation program. Credit: John Frassanito and Associates / NASA
Boeing has an idea to bring a lander down to the Moon that could then lift off multiple times in search of other destinations. Such a concept would require a hefty amount of fuel and equipment. If it works, Boeing says the SLS could assist with plans for lunar mining and other exploration ideas.
Titan's thick haze. Image: NASA/JPL/Space Science Institute.
Is the surf up yet on Titan? As the moon of Saturn moves towards northern summer, scientists are trying to spot signs of the winds picking up. This weekend, the Cassini spacecraft plans a look at the the largest body of liquid on Titan, Kraken Mare, to see if there are any waves on this huge hydrocarbon sea.
Cassini will make the 105th flyby of Titan on Monday (Sept. 22) to probe the moon’s atmosphere, seas and even a crater. The spacecraft will examine “the seas and lakes of the northern polar area, including Kraken and Ligeia at resolution better than 3 miles (5 kilometers) per pixel,” the Cassini website stated.
Besides wet areas of Titan, Cassini will also look at dunes and the relatively fresh-looking Sinlap crater, where scientists hope to get a high-resolution image. Managers also plan a mosaic of Tsegihi — a bright zone south of the equator — and the darker dune-filled area of Fensal. The spacecraft additionally will examine aerosols and the transparency of hazes in Titan’s atmosphere.
Titan is of interest to scientists in part because its chemistry is a possible precursor to what made life possible. Earlier this week, Cassini transmitted several raw images of its view of Titan and Saturn right now — some of the latest pictures are below.
A raw image of Saturn’s moon Titan taken by the Cassini spacecraft Sept. 14, 2014. Credit: NASA/JPL/Space Science InstituteAtmospheric features on Saturn’s moon Titan appear to be faintly visible in this raw image taken by the Cassini spacecraft Sept. 10, 2014. Credit: NASA/JPL/Space Science InstituteA crescent Titan beckons the Cassini spacecraft (in Saturn’s system) in this image taken Aug. 24, 2014. Credit: NASA/JPL/Space Science InstituteA raw image of Saturn taken by the Cassini spacecraft Sept. 15, 2014. Credit: NASA/JPL/Space Science Institute
Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL).
It’s no joke… now is the time to begin searching the much-maligned (and mispronounced) planet Uranus as it reaches opposition in early October leading up to a very special celestial event.
Last month, we looked at the challenges of spying the solar system’s outermost ice giant world, Neptune. Currently located in the adjacent constellation Aquarius, Neptune is now 39 degrees from Uranus and widening. The two worlds had a close conjunction of just over one degree of separation in late 1993, and only long time observers of the distant worlds remember a time waaaay back in the early-1970s where the two worlds appeared farther apart than 2014 as seen from our Earthly vantage point.
Uranus rising to the east the evening of October 7th, just prior to the start of the October 8th lunar eclipse later the same evening. Created using Stellarium.
In 2014, opposition occurs at 21:00 Universal Time (UT)/5:00 PM EDT on October 7th. If this date sounds familiar, it’s because Full Moon and the second total lunar eclipse of 2014 and the ongoing lunar tetrad of eclipses occurs less than 24 hours afterwards. This puts Uranus extremely close to the eclipsed Moon, and a remote slice of the high Arctic will actually see the Moon occult (pass in front of) Uranus during totality. Such a coincidence is extremely rare: the last time the Moon occulted a naked eye planet during totality occurred back during Shakespearian times in 1591, when Saturn was covered by the eclipsed Moon. This close conjunction as seen from English soil possibly by the bard himself was mentioned in David Levy’s book and doctoral thesis The Sky in Early Modern English Literature, and a similar event involving Saturn occurs in 2344 AD.
The footprint of the October 8th occultation of Uranus. Credit: Occult 4.1.
We’re also in a cycle of occultations of Uranus in 2014, as the speedy Moon slides in front of the slow moving world every lunation until December 2015. Oppositions of Uranus — actually pronounced “YOOR-un-us” so as not to rhyme with a bodily orifice — currently occur in the month of September and move forward across our calendar by about 4 days a year.
Uranus (lower left) near the limb of the gibbous Moon of September 11th, 2014. Credit: Roger Hutchinson.
This year sees Uranus in the astronomical constellation Pisces just south of the March equinoctial point. Uranus is moving towards and will pass within a degree of the +5.7 magnitude star 96 Piscium in late October through early November. Shining at magnitude +5.7 through the opposition season, Uranus presents a disk 3.7” in size at the telescope. You can get a positive ID on the planet by patiently sweeping the field of view: Uranus is the tiny blue-green “dot” that, unlike a star, refuses to come into a pinpoint focus.
The apparent path of Uranus from September 2014 through January 2015 across the constellation Pisces. The inset shows the tilt and orbit of its major moons across a 2′ field of view. Created by the author using Starry Night Education software.
Uranus also presents us with one of the key mysteries of the solar system. Namely, what’s up with its 97.8 degree rotational tilt? Clearly, the world sustained a major blow sometime in the solar system’s early history. In 2014, we’re viewing the world at about a 28 degree tilt and widening. This will continue until we’re looking straight at the south pole of Uranus in early 2030s. Of course, “south” and “north” are pretty arbitrary when you’re knocked back over 90 degrees on your axis! And while we enjoy the September Equinox next week on September 23rd, the last equinox for any would-be “Uranians” occurred on December 16th, 2007. This put the orbit of its moons edge-on from our point of view from 2006-2009 for only the third time since discovery of the planet in 1781. This won’t occur again until around 2049. Uranus also passed aphelion in 2009, which means it’s still at the farther end of its 19.1 to 17.3 astronomical unit (A.U.) range from the Sun in its 84 year orbit.
The moons of Uranus and Neptune as imaged during the 2011 opposition season. Credit: Rolf Wahl Olsen, used with permission.
And as often as Uranus ends up as the butt (bad pun) of many a scatological punch line, we can at least be glad that the world didn’t get named Georgium Sidus (Latin for “George’s Star”) after William Herschel’s benefactor, King George the III. Yes, this was a serious proposal (!). Herschel initially thought he’d found a comet upon spying Uranus, until he realized its slow motion implied a large object orbiting far out in the solar system.
A replica of the reflecting telescope that Herschel used to discover Uranus. Credit: Alun Salt/Wikimedia Commons image under a Creative Commons Attribution Share-Alike 2.0 license.
Spurious sightings of Uranus actually crop up on star maps prior to Herschel’s time, and in theory, it hovers juuusst above naked eye visibility near opposition as seen from a dark sky site… can you pick out Uranus without optical assistance during totality next month? Hershel and Lassell also made claims of spotting early ring systems around both Uranus and Neptune, though the true discovery of a tenuous ring system of Uranus was made by the Kuiper Airborne Observatory (a forerunner of SOFIA) during an occultation of a background star in 1977.
A corkscrew chart for the moons of Uranus through October. Credit: Ed Kotapish/Rings PDS node.
Looking for something more? Owners of large light buckets can capture and even image (see above) 5 of the 27 known moons of Uranus. We charted the orbital elongations for favorable apparitions through October 2014 (to the left). Check out last year’s chart for magnitudes, periods, and maximum separations for each respective moon. An occulting bar eyepiece may help you in your quest to cut down the ‘glare’ of nearby Uranus.
When will we return to Uranus? Thus far, humanity has explored the world up close exactly once, when Voyager 2 passed by in 1986. A possible “Uranus Probe” (perhaps, Uranus Orbiter is a better term) similar to Cassini has been an on- and off- proposal over the years, though it’d be a tough sell in the current era of ever dwindling budgets. Plutonium, a mandatory power source for deep space missions, is also in short supply. Such a mission might take up to a decade to enter orbit around Uranus, and would represent the farthest orbital reconnaissance of a world in our solar system. Speedy New Horizons is just whizzing by Pluto next July.
All great thoughts to ponder as you scour the skies for Uranus in the coming weeks!
A map of Saturn's F ring from 2006 shows one of the few bright, extended clumps (indicated by a green box) seen during six years of observation by Cassini. Image credit: NASA/JPL-Caltech/SSI
Nothing stands still. Everything evolves. So why shouldn’t Saturn’s kookie, clumpy F ring put on a new face from time to time?
A recent NASA-funded study compared the F ring’s appearance in six years of observations by the Cassini mission to its appearance during the Saturn flybys of NASA’s Voyager mission, 30 years earlier.
A kink in part of Saturn’s F ring. While the ring is held together by the shepherd moons Prometheus and Pandora, which orbit just inside and outside the ring, embedded moonlets are believed responsible for the kinks and clumps. The rings is several hundred kilometers wide. Credit: NASA
While the F ring has always displayed clumps of icy matter, the study team found that the number of bright clumps has nose-dived since the Voyager space probes saw them routinely during their brief flybys 30 years ago. Cassini spied only two of the features during a six-year period.
Scientists have long suspected that moonlets up to 3 miles (5 km) wide hiding in the F ring are responsible for its uneven texture. Kinks and knots appear and disappear within months compared to the years of observation needed changes in many of the other rings.
Saturn’s F ring is extremely narrow compared to the historic A, B and C rings. It measures just a few hundred kilometers across. Credit: NASA/Cassini
“Saturn’s F ring looks fundamentally different from the time of Voyager to the Cassini era,” said Robert French of the SETI Institute in Mountain View, California, who led the study along with SETI Principal Investigator Mark Showalter. “It makes for an irresistible mystery for us to investigate.”
A 2007 artist impression of small boulder-like chunks of ice that comprise Saturn’s rings. The largest are about 10-12 feet across.They clump together to form elongated, curved aggregates, continually forming and dispersing. Credit: NASA/JPL/Univ. of Colorado
Because the moonlets lie close to the ring and cross through it every orbit, the research team hypothesizes that the clumps are created when they crash into and pulverize smaller ring particles during each pass. They suspect that the decline in the number of exceptionally bright kinks and the clumps echoes a decline in the number of moonlets available to do the job.
So what happened between Voyager and Cassini? Blame it on Prometheus. The F ring circles Saturn at a delicate point called the Roche Limit. Any moons orbiting closer than the limit would be torn apart by Saturn’s gravitational force.
The culprit? Prometheus measures 74 miles (119 km) across and orbits the inner edge of Saturn’s F ring. Credit: NASA
“Material at this distance from Saturn can’t decide whether it wants to remain as a ring or coalesce to form a moon,” said French. “Prometheus orbits just inside the F ring, and adds to the pandemonium by stirring up the ring particles, sometimes leading to the creation of moonlets, and sometimes leading to their destruction.”
Every 17 years the orbit of Prometheus aligns with the orbit of the F ring in a way that enhances its gravitational influence. The researchers think the alignment spurs the creation of lots of extra moonlets which then go crashing into the ring, creating bright clumps of material as they smash themselves to bits against other ring material.
Sounds like a terrifying version of carnival bumper cars. In this scenario, the number of moonlets would gradually drop off until another favorable Prometheus alignment.
The Voyagers encounters with Saturn occurred a few years after the 1975 alignment between Prometheus and the F ring, and Cassini was present for the 2009 alignment. Assuming Prometheus has been “working” to build new moons since 2009, we should see the F ring light up once again with bright clumps in the next couple years.
