Saturn's moon Enceladus sprays its salty sea out into space. Those plumes are rich in phosphates. (NASA/JPL/SSI/J. Major)
Thanks to the Cassini mission we’ve known about the jets of icy brine spraying from the south pole of Saturn’s moon Enceladus for about 8 years now, but this week it was revealed at the 44th Lunar and Planetary Science Conference outside Houston, Texas that Enceladus’ jets very likely reach all the way down to the sea — a salty subsurface sea of liquid water that’s thought to lie beneath nearly 10 kilometers of ice.
Enceladus’ jets were first observed by the Cassini spacecraft in 2005. The jets constantly spray fine particles of ice into space which enter orbit around Saturn, creating the hazy, diffuse E ring in which Enceladus resides.
Emanating from deep fissures nicknamed “tiger stripes” that gouge the 512-km (318-mile) -wide moon’s south pole the icy jets — and the stripes — have been repeatedly investigated by Cassini, which has discovered that not only do the ice particles contain salts and organic compounds but also that the stripes are surprisingly warm, measuring at 180 Kelvin (minus 135 degrees Fahrenheit) — over twice as warm as most other regions of the moon.
Where the jets are getting their supply of liquid water has been a question scientists have puzzled over for years. Is friction caused by tidal stresses heating the insides of the stripes, which melts the ice and shoots it upwards? Or do the fissures actually extend all the way down through Enceladus’ crust to a subsurface ocean of liquid water, and through tidal pressure pull vapor and ice up to the surface?
“Baghdad Sulcus,” one of many tiger stripe fissures on Enceladus (NASA/JPL/SSI)
Researchers are now confident that the latter is the case.
In a presentation at the Lunar and Planetary Science Conference titled “How the Jets, Heat and Tidal Stresses across the South Polar Terrain of Enceladus Are Related” (see the PDF here) Cassini scientists note that the amount of heating due to tidal stress seen along Enceladus’ tiger stripes isn’t nearly enough to cause the full spectrum of heating observed, and the “hot spots” that have been seen don’t correlate with the type of heating caused by shear friction.
Instead, the researchers believe that heat energy is being carried upwards along with the pressurized water vapor from the subsurface sea, warming the areas around individual vents as well as serving to keep their channels open.
With 98 individual jets observed so far on Enceladus’ south polar terrain and surface heating corresponding to each one, this scenario, for lack of a better term… seems legit.
What this means is that not only does a moon of Saturn have a considerable subsurface ocean of liquid water with a heat source and Earthlike salinity (and also a bit of fizz) but also that it’s spraying that ocean, that potentially habitable environment, out into local space where it can be studied relatively easily — making Enceladus a very intriguing target for future exploration.
“To touch the jets of Enceladus is to touch the most accessible salty, organic-rich, extraterrestrial body of water and, hence, habitable zone, in our solar system.”
– Cassini imaging team leader Carolyn Porco et al.
Enceladus is actively spraying its habitable zone out into space (NASA/JPL/SSI)
Research notes via C. Porco, D. DiNino, F. Nimmo, CICLOPS, Space Science Institute at Boulder, CO, and Earth and Planetary Sciences at UC Santa Cruz, CA.
Top image: color-composite of Enceladus made from raw Cassini images acquired in 2010. The moon is lit by reflected light from Saturn while the jets are backlit by the Sun.
Find Arcturus easily by using the handle of the Big Dipper. This map shows the sky facing northeast around 9:30-10 p.m. local time in late March. Stellarium
Every star has a story but some are more curious than others. The star Arcturus has an electrifying story with a mysterious twist involving the 1933 World’s Fair.
If you step out on a clear night in mid-March and follow the curve of the Big Dipper’s handle toward the eastern horizon, you’ll come face to face with Arcturus, the 4th brightest star in the sky. Pale orange and fluttering in the low air like a candle in the breeze, Arcturus is a bellwether of spring. By late May it shines high in the south at the onset of night. For the moment, the star hunkers down in the east, sparking through tree branches and over neighborhood rooftops.
The name Arcturus comes from the ancient Greek word “arktos” for bear and means “Bear Watcher”. That’s easy to remember because he follows Ursa Major the Great Bear, the brightest part of which is the Big Dipper, across the spring sky.
Arcturus is 37 light years from Earth and classified as an orange giant star. It spans 25 times the sun’s diameter and shines 113 times more brightly.
It was another spring 80 years ago on May 27,1933, that the city of Chicago opened its Century of Progress Exposition as part of the World’s Fair highlighting progress in science and industry. 40 years prior in 1893 the city had hosted its first big fair, the World’s Columbian Exposition.
In the early 1930s astronomers estimated Arcturus’ distance at 40 light years. Edwin Frost, retired director of the Yerkes Observatory in Williams Bay, Wis., home to the world’s largest refracting telescope, hit upon the idea of using Arcturus to symbolically link both great fairs which were separated by a span of 40 years.
Poster from the Century of Progress Exposition also called the Chicago World’s Fair. Its theme was the significance of science and how it had bettered mankind. The event was celebrated on Chicago’s 100th anniversary. Credit: Wikipedia
At the time, the photocell, a device that produces an electric current when exposed to light, was all the rage. Clever entrepreneurs had figured out how to take advantage of light’s ability to knock electrons loose from atoms to open doors and count shoppers automatically. They’re still in wide use today from burglar alarms to toilets that magically flush when you step away.
Edwin Frost around the time he was director of Yerkes Observatory in Williams Bay, Wis. Credit: National Academy of Sciences
Technological innovation through scientific progress was the theme of the 1933 fair. What better way, thought Frost, to highlight the benefits of science and link both great events than by focusing the light of Arcturus onto a photocell and using the electric current generated to flip a switch that would turn on the lights at the fair’s opening.
Though we now know Arcturus is 37 light years away, at the time it was thought to be about 40. The light that left the star during the first world’s fair in 1893 would arrive just in time 40 years later to open the next. Arcturus was not only at the right distance but bright and easy to see during May at the fair’s opening. Could a more perfect marriage of poetry and science ever be arranged?
From left: Edwin B. Frost, Christian T. Elvey, staff, and Otto Struve, Yerkes director, examine a General Electric photoelectric relay and the photocell tube that will help activate the lights of the “Century of Progress,” thus opening the Chicago world fair of 1933. Courtesy Yerkes Observatory
On May 27, 1933 shortly before the appointed time, Century of Progress Fair president Rufus C. Dawes spoke to a crowd of some 30,000 people assembled in the courtyard at the Hall of Science:
“We recall the great Columbian Exposition of 1893. Never will its beauty be surpassed.
Never will there be held an exposition of more lasting value to this city. It was for Chicago a great triumph.”
Visitors throng the Hall of Science at the Chicago World’s Fair in 1933, site of the Arcturus lighting ceremony. Click to enlarge Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_027)
“We remind ourselves of that triumph tonight by taking rays of light that left the star Arcturus during the period of that exposition and which have traveled at the rate of 186,000 miles a second until at last they have reached us. We shall use these rays to put into operation the mysterious forces of electricity which will make light our grounds, decorate our buildings with brilliant colors, and move the machinery of the exposition.”
Above the speaker’s platform hung a large illuminated panel, the bottom half of which displayed a map of the eastern U.S. with the locations of the four observatories. The top half contained the instruments that completed the circuit from Arcturus to a searchlight in the Hall of Science.
When light beams from the star Arcturus were picked up by photoelectric tubes at four observatories, signals flashed on this display board on the rostrum of the Hall of Science to the show the audience. Click to enlarge. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_016)
At 9:15 p.m. each of the four observatories borrowed bits of Arcturus’ light, focused them onto their respective photocells and sent the electric current by Western Union telegraph lines to the Chicago fairgrounds.
In the book Fair Management – The Story of a Century of Progress, author Lenox Lohr described what happened next. One of the speakers, probably Philip Fox, director of Chicago’s Adler Planetarium, stepped to the podium to issue the final instructions :
“Harvard, are you ready?”
“Yes.”
A red glow ran across the map from Cambridge to Chicago.
“Is Allegheny ready?”
“Ready.”
“Illinois ready?”
“Yes.”
“Yerkes?”
“Let’s go.”
The switch was thrown, and a searchlight at the top of the Hall of Science shot a great white beam across the sky.”
The crowd went bananas. It was such a huge hit, nearby Elgin Observatory was pressed into operation to light the fair in similar fashion every night for the remainder of the season.
The Hall of Science area at the fair along with the Arcturus sign (far left) and a group of people creating a large star shape on a stage. Click for large version. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_017)
Harnessing a distant star for mankind’s benefit. We marvel at the 1933 fair promoters and astronomers for conceiving of this most ingenious way of linking past and present.
That would be the end of a wonderful story if it wasn’t for one Ralph Mansfield. Mansfield, a student at the time at the University of Chicago, worked as a guide at Chicago’s Alder Planetarium, which was also involved in the lighting ceremony. Before passing away in 2007, Mansfield shared the story of how he was the one to point the telescope at Arcturus and fire up the fairground lights.
The Adler Planetarium on Chicago’s Lake Michigan lakefront. Credit:Fritz Geller-Grimm
I learned this while reading an article by Nathan B. Myron, PhD on the topic in which Mansfield sought to set the record straight. In his version, then-director of the Adler Planetarium, Philip Fox. was apprehensive about cloudy skies, so he arranged for Mansfield to set up a telescope in the balcony of the Hall of Science. As Fox delivered opening remarks, Mansfield used the Dipper’s Handle to find Arcturus in a lucky break in the clouds, and at the key moment, fed its light to the photocell. The spotlight fired up and the day was saved.
So which is the true story?
“It’s a bit of a mystery,” said Richard Dreiser, public information officer for Yerkes Observatory. “No one really knows absolutely.”
His sentiments were echoed by Bruce Stephenson, current curator at the Adler Planetarium: “The truth as far as we can ascertain it today is not really known. These things happened long ago.”
Most historical accounts indicate that four observatories participated, but Mansfield’s story remains. Will the real version please stand up?
Before and after the GRAIL twins impacts on the Moon December 17, 2012. The LROC Narrow Angle Camera (NAC) directors were able to resolve the impact sites on February 28, 2013, revealing both to be about 5 meters in diameter. Upper panels show the area before the impact; lower panels after the impact. Arrows point to crater locations. LROC NAC observations M186085512R, M186078336L, M1116736474R and M1116736474L. Credit: NASA/GSFC/Arizona State University.
On December 17, 2012, the GRAIL mission came to an end, and the two washing machine-sized spacecraft performed a flying finale with a planned formation-flying double impact into the southern face of 2.5-kilometer- (1.5-mile-) tall mountain on a crater rim near the Moon’s north pole. The Lunar Reconnaissance Orbiter has now imaged the impact sites, which show evidence of the crashes.
But surprisingly, these impacts were not what was expected, says the LRO and GRAIL teams. The ejecta around both craters is dark. Usually, ejecta from craters is lighter in color – with a higher reflectance – than the regolith on surface.
“I expected the ejecta to be bright,” said LROC PI Mark Robinson at a press conference from the Lunar and Planetary Science Conference today, “because everybody knows impact rays on the Moon are bright. We are speculating it could be from hydrocarbons from the spacecraft.”
GRAIL A site seen before and after the impact event. Crater center is located at 75.609°N, 333.407°E/ Credit: NASA/GSFC/Arizona State University.
Typically ejecta from craters is brighter, since subsurface regolith tends to have a higher reflectance. The lunar regolith on the surface tends to be darker because of its exposure to the vacuum of space, cosmic radiation, solar wind bombardment, and micrometeorite impacts. Slowly over time, these processes tend to darken the surface soil.
Robinson said the hydrocarbons could have come from fuel left in the fuel lines (JPL estimated a quarter to half a kilogram of fuel may have remained in the spacecraft – so, not very much) or from the spacecraft itself, which is made out of carbon material.
GRAIL B site seen before and after impact event. Crater center is located at 75.651°N, 333.168°E. Credit: NASA/GSFC/Arizona State University.
Additionally, the impact craters’ shapes were not as expected. The impacts formed craters about 5 m (15 ft) in diameter, and there is little ejecta to the south – the direction from which the spacecraft were traveling. “The spacecraft came in at a 1 or 2 degree impact angle,” said Robinson, “so this not a normal impact, as all the ejecta went upstream in the direction of travel.”
“I was expecting to see skid marks, myself,” said GRAIL principal investigator Maria Zuber. She added that she was committed to using every bit of fuel to mapping the gravity field at as low an altitude as possible. “I was determined that we would not end the mission with unused fuel because that would have meant we could mapped it even lower.
LRO Wide Angle Camera (WAC) image of the GRAIL impact area on the south side of the unnamed massif. Credit: NASA/GSFC/ASU.
Robinson said he was skeptical that they could find the impact craters, since the team has yet to find the impact sites of the Apollo ascent stages, which should be much bigger than the GRAIL impacts.
“Finding the impact crater was like finding a needle in haystack,” Robinson said, “as the images are looking at an area that is about 8 km wide and 30 to 40 km tall, and we were looking for something that is a couple of pixels wide.”
Robinson said he spent hours looking for it with no luck, only to see it later when he was on a conference call and was just looking at it out of the corner of his eye.
“It was really fun to find the craters,” he said. LRO did take images in early January, but better images were taken on February 28, 2013.
While LRO’s camera was not able to image the actual impact since it occurred on the night-side of the Moon, the LAMP instrument (Lyman Alpha Mapping Project) on LRO was able to detect the plumes of the impacts.
Kurt Retherford, PI of LAMP said the UV spectrograph was pointed towards the limb of the Moon — and actually looking in the direction of the constellation Orion at the time of the GRAIL impact — to observe the gases coming out of the plumes. They did detect the two impact plumes which clearly showed an excess of emissions from hydrogen atoms. “We were excited to see this detection of atomic hydrogen coming from the impact sites,” Retherford said. “This is our first detection of native hydrogen atoms from the lunar environment.”
This video shows LRO as it flies over the north pole of the Moon, where it has a very good view of the GRAIL impact. The second part is the view from LRO through LAMP’s slit, showing the impact and the resulting plume. The orbits, impact locations, terrain, LAMP field of view, and starfield are accurately rendered.
Retherford said further studies from this will help in determining the processes of how the implantation of solar wind protons on the lunar surface could create the water and hydroxyl that has been recently detected on the lunar surface by other spacecraft and in studies of lunar rocks returned by the Apollo missions.
These radar images of asteroid 2013 ET were obtained when the asteroid was about 693,000 miles from Earth. The images span 1.3 hours or about 1/3 or the asteroid's rotation rate. Click to enlarge. Credit: NASA/JPL-Caltech/GSSR
Another space rock sat pretty for NASA’s big dish photographer. The 70-meter (230-feet) Goldstone antenna zinged radio waves at 2013 ET on March 10 when the asteroid flew by Earth at 2.9 lunar distances or about 693,000 miles (1.1 million km).
By studying the returned echoes, astronomers pieced together 18 images of a rugged, irregular-shaped object about 130 feet (40 m) across. Radar measurements of an asteroid’s distance and speed nail down its orbit with great accuracy, enabling scientists to predict whether or not it might become a danger to the planet at a future date.
The Goldstone dish dish, based in the Mojave Desert near Barstow, Cal. is used for radar mapping of planets, comets, asteroids and the moon. Credit: NASA
It’s also the only way outside of a sending a spacecraft to the object of seeing a small asteroid’s shape and surface features. Most optical telescopes cannot resolve asteroids as anything more than points of light.
By convention, radar images appear “lit” from above. That’s the side closest to the antenna. As you examine a radar image from top to bottom, distance from the antenna increases and the asteroid fades. If the equator of the asteroid faces the antenna, it will appear brightly illuminated at the top of the image. If the antenna faces one of the poles, the pole will be on top and lit up. It takes a bit of getting used to.
Nine radar images of near-Earth asteroid 2007 PA8 obtained between by NASA’s 230-foot-wide (70-meter) Deep Space Network antenna. The part of the asteroid closest to the antenna is at top. Credit: NASA/JPL-Caltech
The asteroid’s width in the images depends on the asteroid’s rotation rate and the antenna’s perspective. If the antenna stares directly down over the equator and the asteroid rotates rapidly, the images will be stretched from Doppler-shifting of the returned radar echo.
Radio waves are a form of light just like the familiar colors of the rainbow. If radio light is moving toward you, its waves bunch together more tightly and appear slightly bluer than if they were at rest. Astronomers call this a Doppler shift or blueshift. If they’re moving away, the light waves get stretched and become “redshifted”.
Three views of asteroid 4179 Toutatis made in early Dec. 2012 by Goldstone. In all three, distance from the antenna increases from top to bottom and Doppler frequency increases toward the right, indicating Toutatis rotates from right to left, since that’s the side of the asteroid approaching the observer. Credit: NASA/JPL-Caltech
A slow-rotating asteroid will appear narrower to radar eyes, and if it doesn’t rotate at all, will show up as a “spike” of light. When the antenna happens to be point directly at a pole, the asteroid will appear to be rotating neither toward nor away from the observer and also look like a spike.
Most asteroids fall somewhere in between, and their radar portraits are close to their true shapes. Radar images show us surface textures, shape, size, rotation rate and surface features like craters. 2013 ET joins the ranks of numerous asteroids probed by radio waves from Earth as we try to grasp the complexity of our planetary neighborhood while hoping for we don’t stare down cosmic disaster anytime soon.
And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, sign up to be a host. Send an email to the above address.
Not even two and a half weeks after a memory glitch that sent NASA’s Curiosity rover into a safe mode on Feb. 27, the robotic Mars explorer once again went into standby status as the result of a software discrepancy — although mission engineers diagnosed the new problem quickly and anticipate having the rover out of safe mode in a couple of days.
“This is a very straightforward matter to deal with,” said Richard Cook, project manager for Curiosity at Jet Propulsion Laboratory in Pasadena. “We can just delete that file, which we don’t need anymore, and we know how to keep this from occurring in the future.”
“Curiosity initiated this automated fault-protection action, entering ‘safe mode’ at about 8 p.m. PDT (11 p.m. EDT) on March 16, while operating on the B-side computer, one of its two main computers that are redundant to each other. It did not switch to the A-side computer, which was restored last week and is available as a back-up if needed. The rover is stable, healthy and in communication with engineers.
“The safe-mode entry was triggered when a command file failed a size-check by the rover’s protective software. Engineers diagnosed a software bug that appended an unrelated file to the file being checked, causing the size mismatch.”
The rover is stable, healthy and in communication with engineers.
– NASA’s Jet Propulsion Laboratory
Once Curiosity is back online its investigation into the watery history of Gale crater will resume, but another hiatus — this one planned — will commence on April 4, when Mars will begin passing behind the Sun from Earth’s perspective. Mission engineers will refrain from sending commands to the rover during a four-week period to avoid data corruption from solar interference.
Keep up with the latest news from the MSL mission here.
Then again, there’s a certain personality on Twitter who claims a slightly different reason for these recent setbacks…
Aurora over Sweden on March 17, 2013. Credit: Chad Blakley/lightsoverlapland.com
Photographer Chad Blakley took this imagery yesterday of green aurorae over the Abisko National Park in Sweden. Fittingly, it was St. Patrick’s Day! Check out his website, in case you want to travel to see the aurora borealis – Blakley can take you on a tour!
Rock Target ‘Knorr’ Near Curiosity. Scientists used Curiosity's Mast Camera (Mastcam) to study spectral characteristics of the rock target called Knorr in the Yellowknife Bay area and determined that it possessed veins of hydrated minerals, including hydrated calcium sulfate. This self-portrait is a mosaic of images taken by Curiosity's Mars Hand Lens Imager (MAHLI) camera during Sol 177 (Feb. 3, 2013). Credit: NASA/JPL-Caltech/MSSS
The science team guiding NASA’s Curiosity Mars Science Lab (MSL) rover have demonstrated a new capability that significantly enhances the robots capability to scan her surroundings for signs of life giving water – from a distance. And the rover appears to have found that evidence for water at the Gale Crater landing site is also more widespread than prior indications.
The powerful Mastcam cameras peering from the rovers head can now also be used as a mineral-detecting and hydration-detecting tool to search 360 degrees around every spot she explores for the ingredients required for habitability and precursors to life.
Researchers announced the new findings today (March 18) at a news briefing at the Lunar and Planetary Science Conference in The Woodlands, Texas.
“Some iron-bearing rocks and minerals can be detected and mapped using the Mastcam’s near-infrared filters,” says Prof. Jim Bell, Mastcam co-investigator of Arizona State University, Tempe.
Bell explained that scientists used the filter wheels on the Mastcam cameras to run an experiment by taking measurements in different wavelength’s on a rock target called ‘Knorr’ in the Yellowknife Bay area were Curiosity is now exploring. The rover recently drilled into the John Klein outcrop of mudstone that is crisscrossed with bright veins.
Curiosity accomplished Historic 1st drilling into Martian rock at John Klein outcrop on Feb 8, 2013 (Sol 182), shown in this context mosaic view of the Yellowknife Bay basin taken on Jan. 26 (Sol 169) where the robot is currently working. The robotic arm is pressing down on the surface at John Klein outcrop of veined hydrated minerals – dramatically back dropped with her ultimate destination; Mount Sharp. Credit: NASA/JPL-Caltech/Ken Kremer (kenkremer.com)/Marco Di Lorenzo
Researchers found that near-infrared wavelengths on Mastcam can be used as a new analytical technique to detect the presence of some but not all types of hydrated minerals.
“Mastcam has some capability to search for hydrated minerals,” said Melissa Rice of the California Institute of Technology, Pasadena.
“The first use of the Mastcam 34 mm camera to find water was at the rock target called “Knorr.”
“With Mastcam, we see elevated hydration signals in the narrow veins that cut many of the rocks in this area. These bright veins contain hydrated minerals that are different from the clay minerals in the surrounding rock matrix.”
Mastcam thus serves as an early detective for water without having to drive up to every spot of interest, saving precious time and effort.
Hydration in Veins and Nodules at ‘Knorr’ rock in Yellowknife bay. At different locations on the surface of the same rock, scientists can use the Mast Camera (Mastcam) on Curiosity to measure the amount of reflected light at a series of different wavelengths to obtain spectral information about composition. The inset photograph shows two locations on a rock target called “Knorr,” where Mastcam spectral measurements were made: A light-toned vein and part of the host rock. The main graph shows the spectra recorded at those two points, with increasing wavelengths of visible light and near-infrared light from left to right, and with increasing intensity of reflectance from bottom to top. The bright vein shows greater reflectance through the range of wavelengths assessed. The shapes of the two curves also differ, especially where the vein spectrum dips in the near-infrared wavelengths. The range of wavelengths included in box-outlined portion of the vein spectrum is shown at the top of the group of reference spectra to the right. These reference spectra show how the dip in reflectance at those wavelengths in the vein material corresponds to dips in those wavelengths in several types of hydrated minerals — minerals that have molecules of water bound into their crystalline structure, including hydrated calcium-sulfates. Mastcam is not sensitive to all hydrated minerals, however, including many phyllosilicates. Credit: NASA/JPL-Caltech/MSSS/ASU
But Mastcam has some limits. “It is not sensitive to the hydrated phyllosilicates found in the drilling sample at John Klein” Rice explained.
“Mastcam can use the hydration mapping technique to look for targets related to water that correspond to hydrated minerals,” Rice added. “It’s a bonus in searching for water!”
The key finding of Curiosity thus far is that the fine-grained, sedimentary mudstone rock at the Yellowknife Bay basin possesses a significant amount of phyllosilicate clay minerals; indicating an environment where Martian microbes could once have thrived in the distant past.
“We have found a habitable environment which is so benign and supportive of life that probably if this water was around, and you had been on the planet, you would have been able to drink it,” said John Grotzinger, the chief scientist for the Curiosity Mars Science Laboratory mission at the California Institute of Technology in Pasadena, Calif.
Hydration Map, Based on Mastcam Spectra for ‘Knorr’ rock target shows coded map of the amount of mineral hydration indicated by a ratio of near-infrared reflectance intensities measured by Curiosity. The color scale on the right shows the assignment of colors for relative strength of the calculated signal for hydration. The map shows that the stronger signals for hydration are associated with pale veins and light-toned nodules in the rock. The Mastcam observations were conducted during Sol 133 (Dec. 20, 2012). The width of the area shown in the image is about 10 inches (25 centimeters). Credit: NASA/JPL-Caltech/MSSS/ASU
The Lunar X, captured by the author on June 8th, 2011.
This week offers observers a shot at capturing a fascinating but elusive lunar feature.
But why study the Moon? It’s a question we occasionally receive as a backyard astronomer. There’s a sort of “been there, done that” mentality associated with our nearest natural neighbor in space. Keeping one face perpetually turned Earthward, the Moon goes through its 29.5 synodic period of phases looking roughly the same from one lunation to the next. Then there’s the issue of light pollution. Many deep sky imagers “pack it in” during the weeks surrounding the Full Moon, carefully stacking and processing images of wispy nebulae and dreaming of darker times ahead…
But fans of the Moon know better. Just think of life without the Moon. No eclipses. No nearby object in space to give greats such as Sir Isaac Newton insight into celestial mechanics 101. In fact, there’s a fair amount of evidence to suggest that life arose here in part because of our large Moon. The Moon stabilizes our rotational axis and produces a large tidal force on our planet. And as all students of lunar astronomy know, not all lunations are exactly equal.
A daytime capture of the Lunar X. (Photo by Author).
This week, we get a unique look at a feature embedded in the lunar highlands which demonstrates this fact. The Lunar X, also sometimes known as the Purbach cross or the Werner X reaches a decent apparition on March 19th at 11:40UT/7:40EDT favoring East Asia and Australia. This feature is actually the overlapping convergence of the rims of Blanchinus, La Caille and Purbach craters. The X-shaped feature reaches a favorable illumination about six hours before 1st Quarter phase and six hours after Last Quarter phase. It is pure magic watching the X catch the first rays of sunlight while the floor of the craters are still immersed in darkness. For about the span of an hour, the silver-white X will appear to float just beyond the lunar terminator.
Visibility of the Lunar X for the Remainder of 2013.
Lunation
Date
Time
Phase
Favors
1116
March 19th
11:40UT/7:40EDT
Waxing
East Asia/Australia
1116
April 3rd
3:20UT/23:20EDT*
Waning
Africa/Europe
1117
April 17th
23:47UT/19:47EDT
Waxing
Eastern North America
1117
May 2nd
16:19UT/12:19EDT
Waning
Central Pacific
1118
May 17th
10:51UT/6:51EDT
Waxing
East Asia/Australia
1118
June 1st
4:31UT/0:31EDT
Waning
Western Africa
1119
June 15th
21:21UT/17:21EDT
Waxing
South America
1119
June 30th
16:04UT/12:04EDT
Waning
Western Pacific
1120
July 15th
7:49UT/3:49EDT
Waxing
Australia
1120
July 30th
3:16UT/23:16EDT*
Waning
Africa/Western Europe
1121
August 13th
18:50UT/14:50EDT
Waxing
South Atlantic
1121
August 28th
14:27UT/10:27EDT
Waning
Central Pacific
1122
September 12th
9:50UT/5:50EDT
Waxing
East Asia/Australia
1122
September 27th
2:00UT/22:00EDT*
Waning
Middle East/East Africa
1123
October 11th
19:52UT/15:52EDT
Waxing
Atlantic Ocean
1123
October 26th
14:12UT/10:12EDT
Waning
Central Pacific
1124
November 10th
10:03UT/5:03EST
Waxing
East Asia/Australia
1124
November 25th
3:14UT/22:14EST*
Waning
Africa/Europe
1125
December 10th
00:57UT/19:57EST
Waxing
Western North America
1126
December 24th
17:07UT/12:07EST
Waning
Western Pacific
*Times marked in bold denote visibility in EDT/EST the evening prior.
Fun Factoid: All lunar apogees and perigees are not created equal either. The Moon also reaches another notable point tonight at 11:13PM EDT/ 3:13 UT as it arrives at its closest apogee (think “nearest far point”) in its elliptical orbit for 2013 at 404,261 kilometres distant. Lunar apogee varies from 404,000 to 406,700 kilometres, and the angular diameter of the Moon appears 29.3’ near apogee versus 34.1’ near perigee. The farthest and visually smallest Full Moon of 2013 occurs on December 17th.
The first sighting of the Lunar X feature remains a mystery, although modern descriptions of the curious feature date back to an observation made by Bill Busler in June 1974. As the Sun rises across the lunar highlands the feature loses contrast. By the time the Moon reaches Full, evidence of the Lunar X vanishes all together. With such a narrow window to catch the feature, many longitudes tend to miss out during successive lunations. Note that it is possible to catch the 1st and Last Quarter Moon in the daytime.
A 1st Quarter Moon with the Lunar X (inset). (Photo by Author).
Compounding the dilemma is the fact that the lighting angle for each lunation isn’t precisely the same. This is primarily because of two rocking motions of the Moon known as libration and nutation. Due to these effects, we actually see 59% of the lunar surface. We had to wait for the advent of the Space Age and the flight of the Soviet spacecraft Luna 3 in 1959 to pass the Moon and look back and image its far side for the first time.
We actually managed to grab the Lunar X during a recent Virtual Star Party this past February. Note that another fine example of lunar pareidolia lies along the terminator roughly at the same time as the Lunar X approaches favorable illumination. The Lunar V sits near the center of the lunar disk near 1st and Last Quarter as well and is visible right around the same time. Formed by the confluence of two distinct ridges situated between the Mare Vaporum and Sinus Medii, it is possible to image both the Lunar X and the Lunar V simultaneously!
A simultaneous capture of the Lunar X & the Lunar V features. (Photo by Author).
This also brings up the interesting possibility of more “Lunar letters” awaiting discovery by keen-eyed amateur observers… could a visual “Lunar alphabet be constructed similar to the one built by Galaxy Zoo using galactic structures? Obviously, the Moon has no shortage of “O’s,” but perhaps “R” and “Q” would be a bit more problematic. Let us know what you see!
-Thanks to Ed Kotapish for providing us with the calculations for the visibility of the Lunar X for 2013.
Comet PANSTARRS above a farm near Alto, Michigan. Credit: Kevin's Stuff on Flickr.
Comet C/2011 L4 (PanSTARRS) keeps getting easier to see, and over the weekend, we were inundated with images and videos from astrophotographers around the world. NASA says that solar heating from the comet’s close pass of the Sun last week has caused the comet to glow brighter than a first magnitude star. Bright twilight sharply reduces visibility, but it is still an easy target for binoculars and small telescopes 1 and 2 hours after sunset. And as of March 15th, people reported they can see the comet with the unaided eye.
Photographer Fred Kamphues took this timelapse from the Leiden Observatory in The Netherlands, the oldest astronomical observatory in the world still active today. Kamphues notes that astronomer Jan Hendrik Oort of Leiden Observatory discovered the origin of comets in 1950. The observatory is used today by student astronomers to learn observing.
Comet C/2011 L4 (PANSTARRS) taken on March 16 from Mount Faito (Naples, Italy). Credit and copyright: Ernesto Guido & Antonio CatapanoSpecial filters and a negative image to try and ‘tease out the structure of the tail,’ says photographer David G. Strange.Comet PANSTARRS over Tallinn, Estonia on March 16, 2013. Credit and copyright: Karthikeyan VJComet PANSTARRS over the San Gabriel mountains on 3/12/2013 above Pasadena,CA, 3-4 miles from Mt.Wilson. Shot with a with Canon 60D. Credit and copyright: Henry Levenson.Comet PANSTARRS, shot from near Keene, Ontario, Canada, on March 16, 2013, using a Canon 50D (modified) with Canon 200mm lens; 4 sec. exp.; f/4.5; 640 ISO. Credit and copyright: Rick Stankiewicz, Peterborough Astronomical Association (PAA) [/caption
This video, above, from UT reader Brent (a.k.a. HelloBozos) in Florida shows this compilation of views of the Sun and the comet. “At 2:08 in the video, a bird flies in front of the camera,” Brent said via email, “This was all done off the side the road, on 3-16-13 8pm-8:30pm.”
[caption id="attachment_100801" align="aligncenter" width="580"] Comet PANSTARRS over Arizona on March 16, 2013. Credit and copyright: Chris Schur
This image is from Chris Schur in Arizona. He says, “Note the fan tail appearing! Also the tail is really starting to curve in the images. Very easy to see naked eye, and so was the yellow color in binoculars when it gets lower.”
Comet PANSTARRS on March 17, 2013. Credit and copyright: Andrei Juravle.Comet PanSTARRS (C/2011 L4) taken near Koprivnica (Koprivni?ki Bregi), Croatia. Credit and copyright: Vedran Matica.
