Stunning Photo of Volcanic Lightning at Volcán de Colima in Mexico

by Nancy Atkinson on March 31, 2015

The Colima Volcano (Volcán de Colima) pictured on March 29, 2015 with lightning arcing through the ash plume. Credit and copyright: César Cantú.

The Colima volcano in Mexico is active again, and has been spewing out large plumes of ash nearly 3 kilometers into the air. Astrophotographer César Cantú captured this spectacular picture of lightning slicing through the cloud of ash.
How can lightning strike in an ash cloud? Through friction, particles of the ash can charge each other by rubbing against each other during the eruption. When the energy is discharged, it can create lightning bolts.

Also known as the “Fire volcano”, The Colima volcano is one of the most active volcanoes in Mexico, and is also called ‘Volcán de Fuego’ or ‘Fire volcano.’ It has erupted more than 40 times since the first documented eruption in 1576.
The latest news on this current eruption is that local authorities have put the volcano on a yellow alert, meaning the volcano is showing increased activity, and residents who live nearby should prepare for a possible evacuation.
Stay safe César, and thanks for sharing your image with Universe Today!

Take a Spin With NASA Cutting-edge Mars Landing Technology

March 26, 2015

This artist's concept shows the test vehicle for NASA's Low-Density Supersonic Decelerator (LDSD), designed to test landing technologies for future Mars missions.

Image Credit: 

NASA/JPL-Caltech

NASA's Low-Density Supersonic Decelerator (LDSD) project will be flying a rocket-powered, saucer-shaped test vehicle into near-space from the Navy's Pacific Missile Range Facility on Kauai, Hawaii, in June.
The public is invited to tune in to an hour-long live, interactive video broadcast from the gallery above a clean room at NASA's Jet Propulsion Laboratory in Pasadena, California, where this near-space experimental test vehicle is being prepared for shipment to Hawaii. During the broadcast, the 15-foot-wide, 7,000-pound vehicle is expected to be undergoing a "spin-table" test. The event will be streamed live on www.ustream.tv/NASAJPL2 on March 31, from 9 a.m. to 10 a.m. PDT. JPL's Gay Hill will host the program while LDSD team members will answer questions submitted to the Ustream chat box or via Twitter using the #AskNASA hashtag.
The LDSD crosscutting demonstration mission will test breakthrough technologies that will enable large payloads to be safely landed on the surface of Mars, or other planetary bodies with atmospheres, including Earth. The technologies will not only enable landing of larger payloads on Mars, but also allow access to much more of the planet's surface by enabling landings at higher-altitude sites.
More information about the LDSD space technology demonstration mission is online at:

/mission_pages/tdm/ldsd

Mars 'Marathon Valley' Overlook

This view from NASA's Mars Exploration Rover Opportunity shows part of "Marathon Valley," a destination on the western rim of Endeavour Crater, as seen from an overlook north of the valley.
The scene spans from east, at left, to southeast. It combines four pointings of the rover's panoramic camera (Pancam) on March 13, 2015, during the 3,958th Martian day, or sol, of Opportunity's work on Mars.
The rover team selected Marathon Valley as a science destination because observations of this location using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on NASA's Mars Reconnaissance Orbiter yielded evidence of clay minerals, a clue to ancient wet environments. By the time Opportunity explores Marathon Valley, the rover will have exceeded a total driving distance equivalent to an Olympic marathon. Opportunity has been exploring the Meridiani Planum region of Mars since January 2004.
This version of the image is presented in approximate true color by combining exposures taken through three of the Pancam's color filters at each of the four camera pointings, using filters centered on wavelengths of 753 nanometers (near-infrared), 535 nanometers (green) and 432 nanometers (violet).
Image Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

Amazing Views of Today’s Total Solar Eclipse From Earth… and Space

by David Dickinson on March 20, 2015

The view of today’s eclipse from low Earth orbit. Credit: ESA/Proba-2.

There’s an old Robert Heinlein saying that goes “climate is what you expect, weather is what you get,” And the weather certainly kept folks guessing right up until the start of today’s eclipse. And though much of the UK and tracks along the Faroe Islands were clouded out, folks who made the trek up to Svalbard were treated to a fine view of totality, while observers across Europe caught stages of the eclipse through its partial phases. Many more managed to capture glimpses of the eclipse thanks to our good friends over at Slooh and the Virtual Telescope project.
Here’s a quick sampling of images that have come our way thus far… we’ll be dropping in more as they become available from far flung corners of the globe and beyond:

Totality! Captured from the (thankfully sunny) Svalbard Islands. Credit and Copyright: Tony Hoffman.

Practicing solar eclipse observing safety… Credit and copyright: @johnmason1971

Though the live feed from the International Space Station was unavailable as the astros flirted with the Moon’s umbra, the crew did manage to get some quick shots of the eclipse from low Earth orbit:

They caught it! The eclipse captured from the International Space Station courtesy of @astrosamantha.

The umbra touches down at the start of the total solar eclipse as seen from the ISS. Credit: @Astrosamantha

And while the fake “eclipse seen from SPACE!!!” image made its predictable rounds, ESA’s solar observing Proba-2 spaccraft caught the eclipse from space for real:
No word yet if anyone caught the ‘money shot’ of the International Space Station transiting the Sun during the eclipse as seen from southern Spain.
UPDATE: Scratch that… Theirry Legault did indeed capture the ISS transiting the partially eclipsed Sun:
Awesome!

Totality from a balloon (!) over Svalbard. The team also has an exciting indiegogo project and hopes to make a film of the eclipse. Courtesy and Credit: @flyabloon/zero2infinity.

And while many observers and events were clouded out, many still noted the drop in ambient light levels.

Credit and Copyright: TheMagster3.

The Sun was relatively blank during the eclipse, with one lone sunspot group currently turned Earthward saving us from spotlessness.

Credit and copyright: @DavidBflower

As of this writing, more eclipse pics are still pouring in. Watch this space, as many eclipse chasers —especially those who traveled to distant Svalbard to witness totality in person — are still making their way in from the field and are no doubt hunting for stable internet connections as we speak.

Awaiting clear skies on the roof of the Anton Pannekoek Institute for Astronomy at the University of Amsterdam in the Netherlands. Credit and copyright: @Whereisyvette

And as always, the big question after every eclipse is: when’s the next one? Well, the next total solar occurs over Southeast Asia on March 9th, 2016, and the very next solar eclipse is a partial over South Africa on Sept 13 2015. And North America gets to see another total lunar eclipse in the ongoing tetrad in just two weeks on April 4th, 2015… and we’re well inside two years away now from the total solar eclipse spanning the continental united States on August 21st 2017!

An Iphone capture of the eclipse. Credit and copyright: @zubenelganubi

Let the first of two eclipse seasons for 2015 begin!
Read Dave Dickinson’s eclipse-fueled scifi tales Shadowfall and Exeligmos.
Update: although it was cloudy, Marco Langbroek did indeed catch the drop in light levels over the Netherlands:
And check out this amazing Vine of the dark umbra of the Moon crossing the North Atlantic courtesy of Meteosat-9:
Wowsa!
And sometimes, the simplest shots are the easiest to get out over social media immediately, be it at a rocket launch or during a solar eclipse:

A back of the camera shot of the eclipse as seen from northern Scotland. Credit: Edwin Quail.

There also been no word as of yet how Germany’s solar power grid fared during the eclipse, though it will be interesting to see what possible data was generated during the partial phases for future planning.

Partial phases of the solar eclipse today as seen from the United Kingdom. Credit and copyright: Sarah and Simon Fisher.

It was truly inspiring to see how many folks captured images and filled our feeds this morning with pictures of today’s eclipse.

The partial eclipse peeks out from behind the clouds over the Greek Embassy . Credit and copyright: clausdm @cldm_ish

Can’t wait til 2017? NASA’s New Horizons spacecraft is set give us a total solar eclipse from the edge of the solar system this July when it flies through the shadows of Pluto and its giant moon, Charon:

An artist’s concept of New Horizons in the shadow on Pluto. Credit: NASA/JPL.

Hey, maybe if we colonize Pluto by 2017 AD, we could witness said eclipses… in person, once every 6 days:
“Pluto One,” anyone?

Parallax in action: the view from Lahore Pakistan vs Slooh’s view shortly before totality. Credit: Roshaan.
Lahore Astronomical Society, Pakistan.

A 6% partial solar eclipse as seen from Israel. Credit and copyright: Gadi Eidelheit.

The March 20, 2015 solar eclipse taken from Malta with a PST solar telescope in H-alpha. Credit and copyright: Leonard Mercer.

New Binocular Nova Discovered in Sagittarius

Posted Yesterday

Looks like the Sagittarius Teapot’s got a new whistle. On March 15, John Seach of Chatsworth Island, NSW, Australia discovered a probable nova in the heart of the constellation using a DSLR camera and fast 50mm lens.

This view shows the sky facing south-southeast just before the start of dawn in mid-March from the central U.S. The nova’s located squarely in the Teapot constellation. Source: Stellarium

Checks revealed no bright asteroid or variable star at the location. At the time, the new object glowed at the naked eye limit of magnitude +6, but a more recent observation by Japanese amateur Koichi Itagaki puts the star at magnitude +5.3, indicating it’s still on the rise. 
A 5th magnitude nova’s not too difficult to spot with the naked eye from a dark sky, and binoculars will show it with ease. Make a morning of it by setting up your telescope for a look at Saturn and the nearby double star Graffias (Beta Scorpii), one of the prettiest, low-power doubles in the summer sky.

Close-in map of Sagittarius showing the nova’s location (R.A. 18h36m57s Decl. -28°55’42”) and neighboring stars with their magnitudes. For clarity, the decimal points are omitted from the magnitudes, which are from the Tycho catalog. Source: Stellarium

Nova means “new”, but novae aren’t fresh stars coming to life but an explosion occurring on the surface of an otherwise faint star no one’s taken notice of – until the blast causes it to brighten 50,000 to 100,000 times. A nova occurs in a close binary star system, where a small but extremely dense and massive (for its size) white dwarf siphons hydrogen gas from its closely orbiting companion. After swirling about in a disk around the dwarf, it’s funneled down to the star’s 150,000 F° surface where gravity compacts and heats the gas until detonates in a titanic thermonuclear explosion. Suddenly, a faint star that wasn’t on anyone’s radar vaults a dozen magnitudes to become a standout “new star”.

Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf pulls material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA

Regular nova observers may wonder why so many novae are discovered in the Sagittarius-Scorpius Milky Way region. There are so many more stars in the dense star clouds of the Milky Way, compared to say the Big Dipper or Canis Minor, that the odds go up of seeing a relatively rare event like a stellar explosion is likely to happen there than where the stars are scattered thinly.

A now-you-see-it-now-you-don’t animation showing the nova field before and after discovery. Credit: Ernesto Guido and Nick Howes

Given this galactic facts of life, that means most of will have to set our alarms to spot this nova. Sagittarius doesn’t rise high enough for a good view until the start of morning twilight. For the central U.S., that’s around 5:45-6 a.m.
Find a location with a clear view to the southeast and get oriented at the start of morning twilight or about 100 minutes before sunrise. Using the maps, locate Sagittarius below and to the east (left) of Scorpius. Once you’ve arrived, point your binoculars into the Teapot and star-hop to the nova’s location. I’ve included visual magnitudes of neighboring stars to help you estimate the nova’s brightness and track its changes in the coming days and weeks.
Whether it continues to brighten or soon begins to fade is anyone’s guess at this point. That only makes going out and seeing it yourself that much more enticing.

New photo of Nova Sagittarii. Note the “warm” color from hydrogen alpha emission. Credit: Erneso Guido and Nick Howes

UPDATE: A spectrum of the object was obtained with the Liverpool Telescope March 16 confirming that the “new star” is indeed a nova. Gas has been clocked moving away from the system at more than 6.2 million mph (10 million kph)!

NASA’s MMS Satellite Constellation Blasts to Orbit to Study Explosive Magnetic Reconnection

by Ken Kremer on March 13, 2015

A United Launch Alliance Atlas V rocket with NASA’s Magnetospheric Multiscale (MMS) spacecraft onboard launches from the Cape Canaveral Air Force Station Space Launch Complex 41, Thursday, March 12, 2015, Florida. Credit: Ken Kremer- kenkremer.com

KENNEDY SPACE CENTER, FL – NASA’s constellation of state-of-the-art magnetospheric science satellites successfully rocketed to orbit late Thursday night, March 12, during a spectacular nighttime launch on a mission to unravel the mysteries of the process known as magnetic reconnection.
The $1.1 Billion Magnetospheric Multiscale (MMS) mission is comprised of four formation flying satellites blasted to Earth orbit atop a United Launch Alliance Atlas V rocket from Cape Canaveral Air Force Station, Florida, precisely on time at 10:44 p.m. EDT.
Magnetic reconnection is a little understood natural process whereby magnetic fields around Earth connect and disconnect while explosively releasing vast amounts of energy. It occurs throughout the universe.
NASA’s fleet of four MMS spacecraft will soon start the first mission devoted to studying the phenomenon called magnetic reconnection. Scientists believe that it is the catalyst for some of the most powerful explosions in our solar system.
The night launch of the venerable Atlas V booster turned night into day as the 195 foot tall rocket roared to life on the fiery fury of about a million and a half pounds of thrust, thrillinf spectators all around the Florida space coast and far beyond.

A United Launch Alliance Atlas V rocket with NASA’s Magnetospheric Multiscale (MMS) spacecraft onboard launches from the Cape Canaveral Air Force Station Space Launch Complex 41, Thursday, March 12, 2015, Florida. Credit: Ken Kremer- kenkremer.com

NASA’s four Magnetospheric Multiscale (MMS) spacecraft were stacked like pancakes on top of one another and encapsulated inside the rocket extended nose cone atop the Atlas V.
The venerable rocket continues to enjoy a 100% success rate. It launched in the Atlas V 421 configuration with a 4-meter diameter Extra Extended Payload Fairing along with two Aerojet Rocketdyne solid rocket motors attached to the Atlas booster first stage.
The two stage Atlas V delivered the MMS satellites to a highly elliptical orbit. They were then deployed from the rocket’s Centaur upper stage sequentially, in five-minute intervals beginning at 12:16 a.m. Friday, March 13. The last separation occurred at 12:31 a.m.
About 10 minutes later at 12:40 a.m., NASA scientists and engineers confirmed the health of all four spacecraft.
“I am speaking for the entire MMS team when I say we’re thrilled to see all four of our spacecraft have deployed and data indicates we have a healthy fleet,” said Craig Tooley, project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Artist’s concept of the MMS observatory fleet with rainbow magnetic lines. Image Credit: NASA

This marked ULA’s 3rd launch in 2015, the 53nd Atlas V mission and the fourth Atlas V 421 launch in the programs life.
Each of the identically instrumented spacecraft are about four feet tall and eleven feet wide.
The deployment and activation of all four spacecraft is absolutely essential to the success of the mission, said Jim Burch, principal investigator of the MMS instrument suite science team at Southwest Research Institute (SwRI) in San Antonio, Texas.
They will fly in a pyramid formation to conduct their science mission, spaced about 10 miles apart. That separation distance will vary over time during the two year primary mission.
NASA scientists and engineers will begin deploying multiple booms and antennas on the spacecraft in a few days, MMS mission scientist Glyn Collinson of NASA Goddard told Universe Today.
The deployment and calibration process will last about six months, Collinson explained. Science observations are expected to begin in September 2015.

Technicians work on NASA’s 20-foot-tall Magnetospheric Multiscale (MMS) mated quartet of stacked observatories in the cleanroom at NASA’s Goddard Space Flight Center in Greenbelt, Md., on May 12, 2014. Credit: Ken Kremer- kenkremer.com

“After a decade of planning and engineering, the science team is ready to go to work,” said Burch.
“We’ve never had this type of opportunity to study this fundamental process in such detail.”
The spacecraft will fly in a tight formation through regions of reconnection activity.
The instruments will conduct their science observations at rates100 times faster than any previous mission.
“MMS is a crucial next step in advancing the science of magnetic reconnection – and no mission has ever observed this fundamental process with such detail,” said Jeff Newmark, interim director for NASA’s Heliophysics Division at the agency’s Headquarters in Washington.
“The depth and detail of our knowledge is going to grow by leaps and bounds, in ways that no one can yet predict.”
MMS measurements should lead to significant improvements in models for yielding better predictions of space weather and thereby the resulting impacts for life here on Earth as well as for humans aboard the ISS and robotic satellite explorers in orbit and the heavens beyond.
The best place to study magnetic reconnection is ‘in situ’ in Earth’s magnetosphere. This will lead to better predictions of space weather phenomena.
Magnetic reconnection is also believed to help trigger the spectacular aurora known as the Northern or Southern lights.

NASA MMS spacecraft fly in a pyramid pattern to capture the 3-D structure of the reconnection sites encountered. Credit: NASA

MMS is a Solar Terrestrial Probes Program, or STP, mission within NASA’s Heliophysics Division. The probes were built, integrated and tested at NASA Goddard which is responsible for overall mission management and operations.

First Attempt to Contact Hibernating Philae Lander Will Be March 12

by Nancy Atkinson on March 10, 2015

Artist rendition of the Philae lander on Comet 67P/Churyumov-Gerasimenko. Credit: DLR.

Where is the Philae lander and will it wake up again? Those are the questions the team at the DLR Lander Control Center will be trying to answer starting this week. Thursday, March 12 provides the first possibility to receive a signal from Rosetta’s lander, sitting somewhere on Comet 67P/Churyumov-Gerasimenko.
“It could be that the lander has already woken up from its winter sleep 500 million kilometers away, but does not yet have sufficient power to inform the team on Earth,” said Koen Geurts from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt) in a blog post today.

The animated image below provides strong evidence that Philae touched down for the first time almost precisely where intended. The animation comprises images recorded by Rosetta’s navigation camera as the orbiter flew over the (intended) Philae landing site on November 12th. The dark area is probably dust raised by the craft on touchdown. The boulder to the right of the circle is seen in detail in the photo below. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The lander has been sleeping in a shaded spot on the comet’s surface after its dramatic touchdown (actually, three touchdowns) four months ago on Nov. 12, 2014 when it flew, landed, bounced and then repeated that process for more than two hours across the surface. Scientists estimated it could have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in a spot that –- at that time — didn’t get much sunlight. The solar-powered lander quickly ran out of power, just hours after landing.
The team admits they would be very lucky if a signal were to be received from Philae at the first opportunity, which is 05:00 CET on March 12, 2015 (midnight on March 11 EDT) when the communication unit on the Rosetta orbiter will be switched on to call the lander.
While the comet is coming ever-closer to the Sun, Philae needs to receive enough solar energy to activate a few systems before it can wake up and begin communicating.
“Philae currently receives about twice as much solar energy as it did in November last year,” said Lander Project Manager Stephan Ulamec from DLR. “Comet 67P/Churyumov-Gerasimenko and its companion, Philae, are now only 300 million kilometers from the Sun. It will probably still be too cold for the lander to wake up, but it is worth trying. The prospects will improve with each passing day.”
The team did give a caveat that several conditions must be met for Philae to wake up and start operating again. By no means is it a given that Philae will awake.
First, the interior of the lander must be at least at minus 45 degrees Celsius before Philae can wake up from its winter sleep. In addition, the lander must be able to generate at least 5.5 watts using its solar panels to wake up. The temperatures are significantly lower in the shadowed region where it sits (named Abydos, even though the exact location has not been identified) than at the originally planned landing location.
While hibernating, the lander has been gathering and storing as much power as possible to heat up and Geurts said that as soon as Philae ‘realizes’ that it is receiving more than 5.5 watts of power and its internal temperature is above minus 45 degrees Celsius, it will turn on, heat up further and attempt to charge its battery.
Then, once awakened, Philae will switch on its receiver every 30 minutes and listens for a signal from the Rosetta orbiter. This, too, can be performed in a very low power state, but Philae needs a total of 19 watts to begin operating and allow two-way communication.

Mars Loses an Ocean But Gains the Potential for Life

by Bob King on March 6, 2015

NASA scientists have determined that a primitive ocean on Mars held more water than Earth’s Arctic Ocean and that the Red Planet has lost 87 percent of that water to space. Water would have covered 20% of the globe about 3 billion years ago. Credit: NASA/GSFC

It’s hard to believe it now looking at Mars’ dusty, dessicated landscape that it once possessed a vast ocean. A recent NASA study of the Red Planet using the world’s most powerful infrared telescopes clearly indicate a planet that sustained a body of water larger than the Earth’s Arctic Ocean.
If spread evenly across the Martian globe, it would have covered the entire surface to a depth of about 450 feet (137 meters). More likely, the water pooled into the low-lying plains that cover much of Mars’ northern hemisphere. In some places, it would have been nearly a mile (1.6 km) deep. 

Three of the best infrared observatories in the world were used to study normal to heavy water abundances in Mars atmosphere, especially the polar caps, to create a global map of the planet’s water content and infer an ancient ocean. Credit: NASA/ GSFC

Now here’s the good part. Before taking flight molecule-by-molecule into space, waves lapped the desert shores for more than 1.5 billion years – longer than the time life needed to develop on Earth. By implication, life had enough time to get kickstarted on Mars, too.

A hydrogen atom is made up of one proton and one electron, but its heavy form, called deuterium, also contains a neutron. HDO or heavy water is rare compared to normal drinking water, but being heavier, more likely to stick around when the lighter form vaporizes into space. Credit: NASA/GFSC

Using the three most powerful infrared telescopes on Earth – the W. M. Keck Observatory in Hawaii, the ESO’s Very Large Telescope and NASA’s Infrared Telescope Facility – scientists at NASA’s Goddard Space Flight Center studied water molecules in the Martian atmosphere. The maps they created show the distribution and amount of two types of water – the normal H2O version we use in our coffee and HDO or heavy water, rare on Earth but not so much on Mars as it turns out.

Maps showing the distribution of H20 and HDO (heavy water) across the planet made with the trio of infrared telescopes. Credit: NASA/GSFC

In heavy water, one of the hydrogen atoms contains a neutron in addition to its lone proton, forming an isotope of hydrogen called deuterium. Because deuterium is more massive than regular hydrogen, heavy water really is heavier than normal water just as its name implies. The new “water maps” showed how the ratio of normal to heavy water varied across the planet according to location and season. Remarkably, the new data show the polar caps, where much of Mars’ current-day water is concentrated, are highly enriched in deuterium.

It’s thought that the decay of Mars’ once-global magnetic field, the solar wind stripped away much of the planet’s early, thicker atmosphere, allowing solar UV light to break water molecules apart. Lighter hydrogen exited into space, concentrating the heavier form. Some of the hydrogen may also departed due to the planet’s weak gravity. Credit: NASA/GSFC

On Earth, the ratio of deuterium to normal hydrogen in water is 1 to 3,200, but at the Mars polar caps it’s 1 to 400.  Normal, lighter hydrogen is slowly lost to space once a small planet has lost its protective atmosphere envelope, concentrating the heavier form of hydrogen. Once scientists knew the deuterium to normal hydrogen ratio, they could directly determine how much water Mars must have had when it was young. The answer is A LOT!

Goddard scientists estimate that only 13% of Mars’ original water reserves are still around today, concentrated in the icy polar caps. The rest took off for space. Credit: NASA/GSFC

Only 13% of the original water remains on the planet, locked up primarily in the polar regions, while 87% of the original ocean has been lost to space. The most likely place for the ocean would have been the northern plains, a vast, low-elevation region ideal for cupping huge quantities of water. Mars would have been a much more earth-like planet back then with a thicker atmosphere, providing the necessary pressure, and warmer climate to sustain the ocean below.

Mars at the present time has little to no liquid water on its cold, desert-like surface. Long ago, the Sun almost certainly saw its reflection from wave-rippled lakes and a northern ocean. Credit: NASA/GSFC

What’s most exciting about the findings is that Mars would have stayed wet much longer than originally thought. We know from measurements made by the Curiosity Rover that water flowed on the planet for 1.5 billion years after its formation. But the new study shows that the Mars sloshed with the stuff much longer. Given that the first evidence for life on Earth goes back to 3.5 billion years ago – just a billion years after the planet’s formation – Mars may have had time enough for the evolution of life.
So while we might bemoan the loss of so wonderful a thing as an ocean, we’re left with the tantalizing possibility that it was around long enough to give rise to that most precious of the universe’s creations – life.
To quote Charles Darwin: “… from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Illustration showing Mars evolving from a wet world to the present-day where liquid water can’t pond on its surface without vaporizing directly into the planet’s thin air. As Mars lost its atmosphere over billions of years, the remaining water, cooled and condensed to form the north and south polar caps. Credit: NASA/GSFC

Rosetta blog: Comet flyby: OSIRIS catches glimpse of Rosetta’s shadow

Posted Yesterday

Images from the OSIRIS scientific imaging camera taken during the close flyby on 14 February have now been downlinked to Earth, revealing the surface of Comet 67P/C-G in unprecedented detail, and including the shadow of the spacecraft encircled in a wreath of light.

Close-up view of a 228 x 228 m region on the Imhotep region on Comet 67P/Churyumov-Gerasimenko, as seen by the OSIRIS Narrow Angle Camera during Rosetta’s flyby at 12:39 UT on 14 February 2015. The image was taken six kilometres above the comet’s surface, and the image resolution is just 11 cm/pixel. Rosetta’s fuzzy shadow, measuring approximately 20 x 50 metres, is seen at the bottom of the image.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

This OSIRIS shape model is marked with the position of the narrow-angle camera field of view taken during the 14 February flyby. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The image released today shows an area near the edge of the comet’s “belly” close to the Imhotep-Ash regional boundary, where a mesh of steep slopes separates smooth-looking terrains from a craggier area. The image was taken from a distance of 6 km from the comet’s surface and has a resolution of 11 cm/pixel. It covers an area of 228 x 228 m.
To better identify the exact region on the comet, in the graphic below we compare the new OSIRIS narrow-angle camera image with a wider view of the comet, along with the NAVCAM image taken at 14:15 UT,  noting that there are uncertainties in the distance to the surface and change in perspective between the images. Indeed, while the match on the smooth-looking region at the bottom of the NAC image in the displayed orientation is good, it is harder to match the upper half because of the lack of shadows in the NAC image, and because the geometry/viewing perspective has changed between the images. This means that the NAC image would have to be distorted and “draped” over the surface to fit the NAVCAM properly. To better understand the relationship of the images, you can download a short movie that fades through the images here.

The OSIRIS narrow-angle camera image from the close flyby shown here in context with a NAVCAM image. Note the region outlined in the upper left is approximate due to the change in perspective.
Credits: NAVCAM: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0;
OSIRIS: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

During the flyby, Rosetta not only passed closer by the comet than ever before, but also passed through a unique observational geometry: for a short time the Sun, spacecraft, and comet were exactly aligned. In this geometry, surface structures cast almost no shadows, and therefore the reflection properties of the surface material can be discerned.
“Images taken from this viewpoint are of high scientific value,” says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “This kind of view is key for the study of grain sizes.”
As a side effect of this exceptional observational geometry, Rosetta’s shadow can be seen cast on the surface of Comet 67P/C-G as a fuzzy rectangular-shaped dark spot surrounded by a bright halo-like region.

Graphic to illustrate the difference between how a sharp shadow is generated by a point source (left) and a fuzzy shadow by a diffuse source (right). Credits: Spacecraft: ESA/ATG medialab. Comet background: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The shadow is fuzzy and somewhat larger than Rosetta itself, measuring approximately 20 x 50 metres. If the Sun were a point source, the shadow would be sharp and almost exactly the same size as Rosetta (approximately 2 x 32 m). However, even at 347 million km from 67P/C-G on 14 February, the Sun appeared as a disc about 0.2 degrees across (about 2.3 times smaller than on Earth), resulting in a fuzzy “penumbra” around the spacecraft’s shadow on the surface. In this scenario and with Rosetta 6 km above the surface, the penumbra effect adds roughly 20 metres to the spacecraft’s dimensions, and which is cast onto the tilted surface of the comet.
If you were standing on the surface with Rosetta high above you, there would be no place in the shadow where the entire Sun would be blocked from view, which explains why there is no fully dark core to the shadow.
Rosetta is not the first spacecraft to capture its own shadow in this way. In 2005, JAXA’s Hayabusa spacecraft captured its shadow on asteroid Itokawa. However, because Hayabusa was only a few tens of metres above the surface, the penumbral effect was much less, resulting in a sharper and darker shadow of the spacecraft.
Also, the comet surface surrounding Rosetta’s shadow on Comet 67P/C-G appears significantly brighter than the rest of the surface seen in the image. Scientists refer to this effect as the ‘opposition surge’ and it is commonly observed when highly-structured regolith surfaces on planets and moons are illuminated directly behind the observer. For example, astronauts on the lunar surface saw the effect surrounding their own shadows. The primary cause of opposition surge is ‘shadow hiding’. When the Sun is directly behind the observer, the shadows cast by small grains disappear from the perspective of the observer, hidden behind the grains themselves, leading to a pronounced increase in brightness. There may also be a contribution from coherent backscatter due to the retro-reflective properties of small dust grains.

Source: Rosetta blog