The Sky is Waiting.
Rhea and friends…(Credit: Cassini/NASA/JPL).
Ahhhh, but to be a fly aboard a Saturn-circling mission… this weekend, I want to turn your attention to some fairly amazing imagery coming from NASA’s Cassini spacecraft in orbit about Saturn. Cassini has just completed a flyby of several moons, including Enceladus, returned some first ever images of the tiny moon Helene, and on January 11th, took the close-up of Rhea pictured above. [Read more...]
A classic of the early space age!
Before men landed on the Moon, we had to first crash land there successfully. This week, we dip back into the Astroguyz library to review the classic Journey Beyond Selene: Remarkable Expeditions Past Our Moon and to the Ends of the Solar System by Jeffery Kluger. We dug this gem up from our favorite Tucson haunt Bookman’s years ago. Selene tells the fascinating tale of the evolution of the unmanned space program. [Read more...]
Titan as imaged by Cassini in 2007. (Credit: NASA/ESA/Cassini).
It started with two papers… as of late, much good and bad science journalism has been committed to the mysteries of Saturn’s largest moon, Titan. A photochemical smog shrouded world, Titan is a dynamic place, and would easily qualify as a planet in its own right if it were in a solo orbit about the Sun. Titan has only begun giving up its secrets in the past decade; a close flyby of Voyager 1 in 1980 revealed an orange-brown disk devoid of detail. The arrival of the joint ESA-NASA Cassini Huygens mission has led to a wealth of data, as Cassini has performed a series of close mapping flybys of the moon and even deposited the successful Huygens probe on the surface in early 2005. Now, two papers from the Journal Icarus and the Journal of Astrophysical Research describe a curious anomaly; some process is consuming expected acetylene (HC2H) on the surface of Titan. Or something… but wait, let’s not got shouting, “Scientists find life on Titan!” We’re talking an indicator to a possible form of life. The studies site data gathered by Cassini’s infrared spectrometer and ion and neutral mass spectrometer as it swept by the moon. As a matter of fact, Cassini has just completed a 1,270 mile pass recently on June 5th. The process in question is the accumulation of hydrogen molecules high in the atmosphere and raining down to the lakes of methane and ethane coating the surface. Evidence supports the idea that Titan should be coated with organic molecules, not to be confused with full fledged life itself (old school media take note!). Clearly, something is sequestering the expected acetylene that should be forming… could it be methane-based life? Keep in mind, Titan is a cold place; daytime temps reach a balmy -290 degrees Fahrenheit. Perhaps there may be warmer, as of yet undiscovered pockets of geological activity, but the very idea of methane based life is very hypothetical. Such life forms would be vastly different than what we know here on Earth, and acetylene is on the short list of oxygen-metabolism substitutes. Mark Allen at NASA’s Astrobiology Institute points out that the lack of surface hydrogen and acetylene may have a non-biological cause; “Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed.” Other processes, such as bombardment by radiation or cosmic rays (remember Titan doesn’t have an ozone layer) or the chemical action of minerals could play a role.
So, what should the man on the street take away from this? That Titan is a fascinating and dynamic place, a place in our solar system where things are happening. Clearly, there is more to Titan’s methane- fueled hydrologic cycle than we currently understand, and a spacecraft such as the proposed Titan Survey mission that would put a dirigible-based probe in the atmosphere would go a long way towards solving the “Life on Titan” puzzle. For now, it’ll just have to go on our “Mars-Europa” short-list of interesting places to visit… but don’t believe the “Aliens found on Titan!” news hype just yet!
(Credit: NASA/ESA/Cassini).
The tiny shepherd world of Prometheus.
The moons of Saturn continue to astound. The count now stands at 61, and one by one, NASA’s Cassini orbiter is giving us a close up look at these unique worlds, some for the first time. Last year, Cassini passed within 36,000 miles of Prometheus just the day after Christmas. Discovered by Voyager 1 in 1980, this shepherd moon dips within the F-ring once every 15 hour orbit. This fact is apparent as the oblong cratered surface on the 74 mile long moon is coated with a fine layer of dust, giving it a smooth appearance. The constant “plowing” of these moons through Saturn’s rings cause the grooves that we see, and also confines the F-ring. These images are especially satisfying to Carolyn Porco, lead scientist of the Cassini research team who was also on hand for the tiny moon’s initial discovery by Voyager in 1980. It’s likely that we won’t get another look at this bizarre shepherd moon for some years to come!
(Credit: NASA/ESA/STScI/AURA)
The scale of the enormous and thin Phoebe Ring as recently imaged by Spitzer.
Since its discovery by Giovanni Cassini in 1671, Saturn’s moon Iapetus has confounded astronomers. Even early on, observers knew something curious was going on with this far off moon; Iapetus varies in brightness between +10 & +12th magnitude as it orbits the ringed planet, nearly vanishing from sight for half its orbit! Late last year, NASA’s Cassini spacecraft and the Spitzer Space Infrared Telescope fingered the culprit; a tenuous outer ring of material now known as the Phoebe Ring that is raining down material on its surface. Like our own Moon, Iapetus is tidally locked in its 79 day orbit. As a consequence, the leading edge plows through this dusty stream of debris. This also causes sunlight to warm and sublimate icy material on the leading side, which streams and re-condenses on the trailing end. This nicely explains the sharply defined and complex boundary seen between the two hemispheres. Alas, no monolith as depicted in Clarke’s original 2001 novel adaptation. .. but perhaps a fine site one day for a cosmic ski resort!
(Credit: NASA/JPL/University of Arizona).
An amazing sight; sunlight reflected off the Kraken Mare caught by Cassini!
NASA’s Cassini spacecraft has revealed an elusive mystery on the surface of Titan; namely, why does the northern hemisphere of the large moon contain numerous lake basins, while in the south they’re relatively scarce? Now, scientists at Caltech working with JPL think they may have an answer. These lakes show up as bright (empty) and dark (filled) patches as the Cassini spacecraft pings them with its Synthetic Aperture Radar (SAR). Of course, on Titan, the hydrologic chemical of choice is liquid ethane and methane, and it is thought that some transport mechanism results in a net flow imbalance between the two hemispheres. Seasons on Titan last roughly 15 years as it dances around Saturn in its 29.5 year orbit about the Sun. But simple seasonal drainage of about a meter per year couldn’t empty the 100 meter-plus deep basins in a single season. This also doesn’t account for the overall disparity in number of basins seen, both filled and unfilled. Instead, scientists point towards the eccentricity of Saturn’s orbit as the possible cause. Saturn’s eccentricity is 0.055, or a little over 5% deviation from a perfect circle. This would make for periodic inequalities in the seasons, much like what occurs on Earth. For example, the perihelion of Earth actually occurs in northern hemisphere winter, somewhat ameliorating the severity of the seasons. But the variation of eccentricity coupled with the obliquity of the planetary spin axis and the precession of the equinoxes can vary over geologic time scales, causing variations in the climate. This is known as the Milankovitch cycle, and is thought to be a major contributing factor to the onset of Ice Ages. On Titan, a similar process is thought to occur, resulting in a net imbalance over thousands of years in the methane flow cycles between the two hemispheres. We may now simply be observing Titan during an epoch when seasonal methane pooling favors the northern hemisphere. Whatever the case, Titan is proving to be a fascinating and changing world deserving of further scrutiny.
The Moon as imaged during the 1999 Cassini flyby. (Credit: CASA/JPL/USGS).
Last year’s big news story was the announcement of water on the Moon. This evidence came from five separate sources, and spanned over a decades’ worth of data. This climaxed with the October 9th impact of the LCROSS spacecraft in the quest for a moisture laden plume. Now, a reanalysis of lunar samples returned by Apollo astronauts have turned up evidence of microscopic water beads imbedded in volcanic glass. This leads scientist Alberto Saal to suggest that the lunar interior may contain water in the order of 745 parts per million, a tiny but measureable amount.
The first whiff of water in the form of clay hydroxyls came from the Clementine and Lunar Prospector orbiters in the mid 90’s. Cassini imaged the Moon in the infrared on its way out to Saturn, but the water signature detected at the time was suspected to be due to spacecraft contamination. More recently, lunar water got a boost from NASA’s spectrometer aboard the Indian orbiter Chandrayaan 1 and observations by the Deep Impact spacecraft in its role of simulated exoplanet hunter… keep in mind, the amount of water being discussed is tiny; were talking maybe a liter per ton of lunar regolith near the poles, and half that amount at the equator! With the cancellation of Constellation, it’s to be seen if any of the proposed unmanned rovers will take up the hunt for lunar water over the next few years.
The shadow of Titan as viewed by Cassini. (Credit: NASA/JPL/Space Science Institute).
Saturn is turning out to be a very electrified place. Last year, NASA’s Cassini orbiter spied a massive storm that broke the solar system record; beginning in January 2009, this storm raged on for 7 ½ months, the longest recorded. This marks the ninth storm on Saturn thus recorded; these behemoths tend to be around 1,900 miles in size. It’s been known since the initial Voyager flybys of the ringed world in the 1970’s that an ionization differential of x100 exists in favor of the daytime side of Saturn over its night side, but routine observations by Cassini are revealing what a turbulent world Saturn really is. Cassini utilizes its antennae aboard its Radio and Plasma Wave Science instrument to analyze the powerful radio emissions. Tantalizingly, the storms almost always originate in a region known as “Storm Alley” at latitude 35° south. The reason for this isn’t entirely clear. Scientists also took advantage of a passage of Cassini behind Saturn’s largest moon, Titan, to confirm the source of these radio emissions. Surely enough, when Titan occulted the body of Saturn, the emissions disappeared, only to return when Saturn came back into view. This was yet another proof that Saturn is still an active and mysterious place.
The wacky orbit of Iapetus. (Created in Starry Night & Paint).
As the majestic planet Saturn approaches opposition on March 21st, I’d like to turn your telescopic attention to one of the most bizarre moons in the solar system; Iapetus. It was way back when in the 17th century that Italian astronomer Giovanni Cassini noted that he could only see Iapetus when it was to the west of the ringed planet, but never to the east. He correctly deduced that Iapetus must not only be tidally locked, that is, holding one face towards Saturn, but must be correspondingly dark on one hemisphere and brighter on the other. In fact, Iapetus is known to vary from magnitude +10 to magnitude +12 over its 79 day orbit, a variation of 6 times in terms of brightness. the Cassini space probe has confirmed the duality of Iapetus, showing us a dark leading hemisphere with an albedo of 5% (think fresh asphalt) and a trailing hemisphere with an albedo of about 50% (think dirty snow). The third largest of the Saturnian moons, Iapetus is a “walnut shaped” world, with a large ridge running the equator of this twisted moon. Discovered by Cassini on New Year’s Eve 2004, no satisfactory explanation for the ridge is known, but the little world must have had a tumultuous history. [Read more...]
Sequence showing an evolving storm on Titan. (Credit: Gemini Obs/AURA/H. Roe/E. Schaller).
Think that this winter is brutal here on Earth? As February is about to set in, we here at Astroguyz invite you to contemplate the seasons on Titan, the largest moon of Saturn. At over 3,000 miles in diameter, Titan is larger than some planets, and possesses an opaque hydro carbon smog veil of an atmosphere. There, a balmy summer day might reach 290°F on the thermometer, and sunshine is a dim murk at best. Scientists have recently found out that this seemingly dismal world is in fact a dynamic place, and a world well worth further scrutiny. The Cassini spacescraft has already conducted fly-bys of the mysterious moon since its orbital insertion in 2004, and even deposited the Huygens probe, which still stands as the most distant soft landing of a manned spacecraft ever made. Now, scientists Emily Schaller of the University of Hawaii and Henry Roe of the Lowell Observatory have been successful in tracking storms in Titan’s turbulent atmosphere. Like Earth, Titan is one of the very few rocky worlds in the solar system that possesses a hydrological cycle and weather. On Titan, however, it rains liquid methane and pools of ammonia dot the surface of this bizarre world. Using the 3-meter Infra-red Telescope Facility, Schaller and Roe monitored Titan 138 nights over 2.2 years in the 2.1 micron range, using the much more sensitive Gemini North telescope also on Mauna Kea for follow up observations when things started to look interesting. Titan is a tough target to image; at its best, it presents a disk no more than 0.8” in diameter. The 2008 storm pictured about demonstrates that Titan is indeed a changing world, one that deserves further examination. Cassini has already performed another flyby of Titan earlier this month on January 12th as part of its mission extension.
The alien surface of Enceladus as seen during the Nov. 2nd pass. (Credit: NASA/JPL).
Cassini has completed another close reconnaissance pass of one of Saturn’s most intriguing moons; Enceladus. On November 2nd at 7:40 AM UTC, Cassini passed 62 miles above the icy surface of the south polar region, completing a carefully timed plunge through one of its liquid plumes. This was one of its most comprehensive passes of the moon out of the seven completed so far, enabling the spacecraft to utilize its array of infrared and ultraviolet detectors to analyze speed and particle size. Cassini itself is whizzing along at 5 miles per second. Sodium, water, and carbon dioxide have been detected in the out-gassing, tantalizing evidence that more complex organic chemistry may exist below the surface. Enceladus is heated from tidal flexing caused by Saturn’s gravity squeezing it like a rubber ball. Along with Jupiter’s moon, Europa, Enceladus has been proposed as deserving of future scrutiny as a possible abode of life. Enceladus is a tiny world, about 310 miles in diameter, or about 15% the diameter of our Moon. Two subsurface oceans in one solar system also poses the intriguing question; are environments like Enceladus and Europa more common throughout the universe than Earth? Cassini has phoned home after the recent pass and is reported in good health. Scientists are currently poring over the results; watch for another pass of Enceladus on April 28th of next year. What ever the outcome, Enceladus is proving to be a dynamic place, worthy of future study!
The tortured surface of Enceladus as seen earlier last year from Cassini. (Credit: NASA/JPL).
Move over Europa ; yet another moon may harbor a subsurface sea. Saturn’s moon Enceladus has been inching its way up the charts as of late as a candidate world for extraterrestrial life. Barely 300 miles in diameter, the tiny world is repeatedly flexed by Saturn’s gravity and an increased orbital eccentricity pumped up by the nearby moon Dione. This has caused the tiger-striped surface seen by the Cassini space probe, a surface that shows evidence of repeated fissuring and freezing that almost certainly covers a liquid interior. In fact, Cassini has caught several of the geysers in the act during four recent flybys of the moon. One flyby was close enough that Cassini actually flew through a geyser plume! Activity on Enceladus is now known to almost exclusively contribute to Saturn’s E ring…and recently, a much broader ring system has been revealed by the Spitzer space telescope. Sodium chloride has also been detected in the E ring, presumably from the interior of Enceladus…clearly, the Saturnian system is a dynamic place warranting more scrutiny. Let’s hope that NASA approves Cassini’s seven year mission extension!
Erlanger crater, a permenantly shadowed polar crater. (Credit: NASA/LRO).
In a stunning press conference on Thursday, NASA revealed conclusive proof for what has been suspected for decades; evidence for water-ice mixed into the lunar surface! The evidence comes from multiple sources over the past decade;
Lunar Prospector, which measured a “flux drop” with its neutron spectrometer during its operational phase of 1998-9.
The “M-cubed” instrument NASA sent aboard India’s Chandrayaan-1 measured tell tale infrared signatures during its recent lunar mission;
Cassini (yes, that Cassini!) and Deep Impact both measured signatures highly suggestive of water during their respective outbound passes. Cassini with the VIMS (the Visible Mapping Infrared Spectrometer) and Deep Impact in its extended EPOXY (Extrasolar Planet Observation and Deep Impact Extended Investigation) role.
Clementine, which operated in 1994 produced data that also backed up these findings.
Perhaps what was most astounding was the fact that water signatures were found not only at the poles, which has been long suspected, but in the lunar equatorial regions as well! Apparently, water exists in some degree at all latitudes… quantities quoted were of the magnitude of one quart per ton near the poles to a tablespoon per ton of lunar material at the equator. Keep in mind, much of this is mixed in as hydroxyl compound as well as lunar ice. Think a clay-like material. Scientists also pointed out that this is still “drier than the driest terrestrial desert…” clearly, future settlers will have to move tons of lunar regolith to exact a useable amount of H2O… another stunning mechanism discussed for the existence of equatorial water was the possibility of a pseudo “hydrological cycle” on the Moon! This would be driven by gravity, heating, and hydrogen ions from the solar winds bombarding the surface throughout the lunar day. The layer is perhaps a few millimeters thick. Three separate papers were published formalizing these findings yesterday. This will undoubtedly spur on lunar exploration, as well as put all eyes on the Moon for the LCROSS impact on October 9th!
Saturn's rings in darkness during the recent August 10th equinox. (Credit:NASA/JPL/Cassini Imaging Team).
A rather odd event is transpiring in the Saturnian system, one that only happens a couple of times in our lifetime; its rings are vanishing. Not really, of course; we are merely passing through the super-fine ring plane as viewed from the Earth. The exact date of the “crossing” as viewed from Earth is Friday, September 4th, when the 20 meter thick rings will be exactly edge on and vanish from all but the largest telescopes. Just a few weeks ago, Saturn passed equinox, when the rings were edge on to the Sun and hence, not illuminated across their 100,000+ km expanse. This happens every 14 to 15 years during the planet’s 29.7 year orbit. [Read more...]
Looking West from North America at Sunset on the 27th. (Credit: Starry Night).
Lots of happenings in this last week of February… the pick for the astro-event of the week was a toughie. I choose the Friday close conjunction/occultation of Venus and the Moon, as it’s one of the closest of the year! And it’s easily observed with the naked eye, and highly photogenic to boot! [Read more...]
A New Look: Three Faces of Titan.
Perhaps no world in the Solar System is as enigmatic as Titan. Until the last decade or so, what was known about this distant moon of Saturn could barely fill out a postcard, let alone a book. Titan Unveiled published by Princeton University Press is the first book solely dedicated to the moon, centering mostly on the phenomenally successful Cassini-Huygens mission to the ringed planet. [Read more...]
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Pictured is a Delta IV rocket launch from Cape Canaveral on November 21st, 2010. The image is a 20 second exposure taken at dusk, shot from about 100 miles west of the launch site. The launch placed a classified payload in orbit for the United States Air Force.
Difficult but not impossible to catch against the dawn or dusk sky, spotting an extreme crescent moon can be a challenge. The slender crescent pictured was shot 30 minutes before sunrise when the Moon was less than 20 hours away from New. A true feat of visual athletics to catch, a good pair of binoculars or a well aimed wide field telescopic view can help with the hunt.
The Sun is our nearest star, and goes through an 11-year cycle of activity. This image was taken via a properly filtered telescope, and shows the Sun as it appeared during its last maximum peak in 2003. This was during solar cycle #23, a period during which the Sun hurled several large flares Earthward. The next solar cycle is due to peak around 2013-14.
Located in the belt of the constellation Orion, Messier 42, also known as the Orion Nebula is one of the finest deep sky objects in the northern hemisphere sky. Just visible as a faint smudge to the naked eye on a clear dark night, the Orion Nebula is a sure star party favorite, as it shows tendrils of gas contrasted with bright stars. M42 is a large stellar nursery, a star forming region about 1,000 light years distant.
Orbiting the planet in Low Earth Orbit (LEO) every 90 minutes, many people fail to realize that you can see the International Space Station (ISS) from most of the planet on a near-weekly basis. In fact, the ISS has been known to make up to four visible passes over the same location in one night. The image pictured is from the Fourth of July, 2011 and is a 20 second exposure of a bright ISS pass.
Next to the Sun, the two brightest objects in the sky are the Moon and the planet Venus. In fact, when Venus is favorably placed next to the Moon, it might just be possible to spot the two in the daytime. Another intriguing effect known as earthshine or ashen light is also seen in the image on the night side of the Moon; this is caused by sunlight reflected back off of the Earth towards our only satellite.
A mosaic of three images taken during the total lunar eclipse of December 21st, 2010. The eclipse occurred the same day as the winter solstice. The curve and size of the Earth’s shadow is apparent in the image.
The Algonquin Indians had names for each of the seasonal Full Moons, many of which survive today. The Full Snow Moon pictured occurs in the month of December, when the first large winter storms coat the ground with snow. This Full Moon also tends to fall near the Winter Solstice, and thus rides high in the nightly sky opposite to the Sun on long winter nights.
Every rocket launch is unique, but twilight shuttle launches where by far the most impressive. The image pictured was of the April 5th, 2010 launch of Space Shuttle Discovery from the Kennedy Space Center at dawn. The exhaust plume caught the rising Sun overhead just right, and numerous noctilucent clouds persisted right up until sunrise. Unfortunately, space shuttle launches are now relegated to the pages of history.
18.02.11: A Titan(ic) Flyby.
Titan (Lower Left) paired with Saturn as seen from Cassini last year. (Credit: NASA/Cassini/JPL/The Space Science Institute).
Far out in the depths of the solar system, one of our most distant orbiting ambassadors is completing a flyby of the largest known moon. On Friday, February 18th at 11:04AM EST NASA’s Cassini orbiter will skim the Saturnian moon at a distance of just 2,270 miles above the enigmatic moon Titan. [Read more...]