Fast-spinning asteroid tears itself to pieces

Top panel shows a wide-angle view of the main nucleus and smaller fragments embedded in a long dust trail.

Top panel shows a wide-angle view of the main nucleus of the crumbling asteroid P/2012 F5 and smaller fragments embedded in a long dust trail. Bottom panel shows a close-up view with the trail removed for a clearer view of the individual fragments. Credit: M. Drahus, W. Waniak (OAUJ) / W. M. Keck Observatory

A team of astronomers led by team led by Michal Drahus of the Jagiellonian University (Krakow, Poland) used one of the twin 10-meter (394-inch) telescopes of the W.M. Keck Observatory in Hawaii to study the strange behavior of four comet-like asteroids.

Most of the hundreds of thousands of known asteroids are made of rock and don’t develop fuzzy comas and tails the way similar-sized icy comets do. But since 2010, astronomers have uncovered a small number of oddball, “active asteroids” that mimic comets by releasing clouds of dust as they spin.

Artist illustration of the active asteroid P/2012 F5 trailing a tail of dust spun off due to its fast rotation. Credit: SINC

Artist illustration of the active asteroid P/2012 F5 trailing a tail of dust spun off due to its fast rotation. Credit: SINC

One of them, P/2012 F5 (Gibbs), located in the outer zone of the main asteroid belt, spins so fast, it’s literally falling apart. Using the Keck II telescope, Drahus and team discovered at least four fragments flung from the object.

We knew the asteroid was an active one because it had previously released a cloud of dust in a single, quick impulse back around July 1, 2011. Like a comet, the object looked slightly fuzzy and left a left a dust trail; this time around, P/2012 F5 took it to the next level and deposited a string of tiny asteroid satellites.

There are two theories on how otherwise quiet asteroids can suddenly explode to life — through a collision with another smaller asteroid or by “rotational disruption”, which is exactly what it sounds like.

Yorping the day away. Illustration showing how sunlight absorbed unevenly by an asteroid’s surface creates torque that can increase its spin rate. Illustration: Bob King

Yorping the day away. Illustration showing how sunlight absorbed unevenly by an asteroid’s surface and re-released as heat creates torque that can increase its spin rate. Illustration: Bob King

An asteroid can spin so fast that its weak gravity is overwhelmed by centrifugal force, the tendency of material to pull away from a rapidly spinning object. Centrifugal force can cause small objects like P/2012 F5 and its ilk to break apart. No surprisingly, the team measured F5’s rotation rate at just 3.24 hours, fast enough for it to theoretically explode.

So how do you spin up an asteroid until it shoots pieces of itself into space like some hell-bent disk golfer? Just add a little YORP. An acronym for Yarkovsky–O’Keefe–Radzievskii–Paddack effect, heating from the Sun can cause an asteroid’s tilt and rotation rate to change over time.

Sunlight shining on an asteroid warms the rock which releases the energy as heat, giving the object a tiny push. Assuming the asteroid is irregular in shape – and most are because they’re so small – some areas get hotter and give off more heat than others. The imbalance causes a torque on the asteroid, increasing its spin rate. Depending on the shape of the asteroid and variations in the reflectivity of its surface (some areas may be darker or lighter than others), those smidgeons of thrust can add up to twirl an asteroid to the breaking point.

And because many asteroids are little more than rubble piles, breaking up is easy to do.

This illustration shows one possible explanation for the disintegration of asteroid P/2013 R3. Sunlight absorbed unequally across the asteroid’s surface can spin up its rotation and cause it to fall apart. More details on how this happens below. Credit: NASA, ESA, D. Jewitt (UCLA), and A. Feild (STScI)

Sunlight absorbed unequally across the asteroid’s surface can spin up its rotation rate and cause it to fall apart. While it’s possible P/2012 F5 was struck by another object, this explanation best fits the observations. Credit: NASA, ESA, D. Jewitt (UCLA), and A. Feild (STScI)

“This is really cool because fast rotation has been suspected of catapulting dust and triggering fragmentation of some active asteroids and comets. But up until now we couldn’t fully test this hypothesis as we didn’t know how fast fragmented objects rotate,” Drahus said.

Astronomer Alex Gibbs discovered P/2012 F5 on March 22, 2012 with the Mount Lemmon 1.5 meter reflector in Arizona. It was initially classified as a comet, based on its fuzzy look, but two independent teams quickly showed that the dust was blasted out in a single pulse about a year before the discovery – something that doesn’t happen to comets, which continuously emit dust and other materials as the Sun vaporizes ice from their nuclei.

Gibb’s find and the other known active asteroids are all under 0.6 miles or one kilometer across. So tiny they’re incredibly faint. That’s why the biggest telescope on Earth was needed to dig down into the details and uncover the tale of an asteroids torn asunder by nothing more than sunlight.

Comet dust mimics stars, disorients Rosetta

This view of comet 67P/Churyumov-Gerasimenko was taken by Rosetta’s navigation camera on March 22, showing a cloud of dust and gas surrounding the nucleus. I've circled some of the troublesome dust Rosetta has recently been running into. Credit: ESA/Rosetta/NAVCAM

This view of comet 67P/Churyumov-Gerasimenko was taken by Rosetta’s navigation camera on March 22, and shows a cloud of dust and gas surrounding the nucleus. I’ve circled some of the troublesome dust particles Rosetta has recently been running into. Credit: ESA/Rosetta/NAVCAM

As Comet 67P/Churyumov-Gerasimenko heats up on its sunward journey, it’s becoming something of a hazard. All the lovely dust and water ice flying off the nucleus – the stuff that makes comets look hazy – have given mission planners and the Rosetta spacecraft a headache.

Rosetta ran into trouble on March 28 when the probe tore past the nucleus at a distance of only 8.7 miles (14 km). The spacecraft uses a set of cameras to fix on bright stars to determine its orientation in space. The trouble occurred when it was positioned over the larger of the two lobes of the comet.

Rosetta’s star trackers are marked in red in this illustration, and part of the high gain antenna can be seen in the background. The star trackers are used to automatically pinpoint the craft’s position and its orientation to Earth by using the known positions of stars. Credit: ESA/ATG medialab

Rosetta’s star trackers are marked in red in this illustration, and part of the high gain antenna can be seen in the background. The star trackers are used to automatically pinpoint the craft’s position and its orientation to Earth by using the known positions of stars. Credit: ESA/ATG medialab

Rosetta’s star trackers, which are supposed to find guide stars to monitor the spacecraft’s alignment with Earth and the Sun, mistook the bright, sunlit flecks of comet debris for stars, preventing the craft from getting a proper navigation fix. That triggered the craft to put itself into temporary safe mode, where science instruments and non-essential functions are shut down to prevent them from any damage.

If Rosetta knows how it’s oriented with respect to the stars, it can determine its orientation to the Earth and Sun. That’s critical because the probe needs to point its high-gain antenna at Earth in order to send data and receive communications. If the antenna drifts away from home base, communication with Rosetta could potentially be lost.

“Attempts were made to regain tracking capabilities, but there was too much background noise due to activity close to the comet nucleus: hundreds of ‘false stars’ were registered and it took almost 24 hours before tracking was properly re-established,” according to a blog posting on the European Space Agency’s Rosetta site.

In this specially processed image we see just how far dust extends from the nucleus (at lower left). The plume extends outward at least 15 miles. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

In this specially processed image taken April 2, dust extends from the 2.5-mile-wide nucleus (at lower left) up to and out of the frame – a distance of at least 15 miles. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Rosetta experienced similar trials during an even closer flyby of 3.7 miles (6 km) Feb. 14 but weathered the pelting without defaulting to safe mode.

Less serious but still concerning, the dust grains pushed against Rosetta’s two 46-foot-long (14 meter) solar arrays, causing drag on the spacecraft.

“Cross comparisons with other navigation mechanisms showed inconsistencies with the star trackers and some on board re-configurations occurred. While attempting to reconfigure those, the same error occurred again leading this time to an automatic safe mode on Sunday afternoon,” according to ESA.

The good news is that once mission control recovered the star trackers, the system auto-corrected and communications returned to full strength. All science operations are now back on line.

But it does bring up the question of what to do during future close flybys of the nucleus especially since the dust and vapor are only expected to thicken as 67P makes its closest approach to the Sun on Aug. 13. The good folks at ESA are right now re-accessing their options in light of Rosetta’s disorienting experiences.

Scientists attempt to contact frozen Philae comet lander

You can see one of Philae's landing legs in this photo taken by the probe from the side of a cliff back in November. With more sunlight now flooding the site, there's hope we'll hear from Philae again. Credit: ESA/Rosetta/Philae/CIVA

You can see one of Philae’s landing legs in this photo taken by the probe from the side of a cliff back in November. With more sunlight now flooding the site, there’s hope we’ll hear from Philae again. Credit: ESA/Rosetta/Philae/CIVA

Remember Philae? The little lander has been sitting in a hole between cliffs on Comet 67P/Churyumov-Gerasimenko, but as George Harrison sang – Here Comes the Sun.

Philae (FEE-lay) bounced off the comet’s surface twice while attempting to touch down. On the first bounce, it rebounded at a speed of 15 inches per second, sending it sailing over half a mile above 67P’s surface. Had the lander exceeded 17 inches per second it would have escaped the comet’s gravity!

To get a feel for the alien beauty of Comet 67P, press play to take a flyover.

It finally came to rest on November 12, 2014 after a second bounce. Had the lander’s harpoons worked properly, it would have affixed itself upright on the surface on its first attempt.

After two bounces, Philae landed at an angle in a hole between cliffs on Comet 67P last November. Credit: ESA

After two bounces, Philae (in blue)  landed at an angle in a hole between cliffs on Comet 67P last November. Credit: ESA

Unfortunately, Philae landed in the shadows of cliffs with its solar panels steeped in shadow most of day. With too little sunlight to provide the energy to charge the lander’s batteries, the probe’s primary battery provided only 60 hours power before it shut down. Philae conducted as much data-gathering as it could and then powered down into hibernation mode on Nov. 15. No one’s heard from it since.

Comet 67P photographed with Rosetta's navigation camera on March 21. he image is lightly processed to bring out the details of the outflowing material. Copyright: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Comet 67P photographed with Rosetta’s navigation camera on March 21. The image is lightly processed to bring out the details of streams of dust, water and gas leaving the comet. Copyright: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

That might be the end of the story, but mission scientists are hopeful that as seasons change as 67P orbits the Sun (just like they do on Earth), sunlight will filter down between the steep hills at Philae’s location and provide the needed energy for the solar panels to power up the lander’s batteries.  The intensity of sunlight has also been increasing as 67P gets closer to the Sun. A few days of sunlight on the solar panels is all it would take to resume collecting data according to Philae landing manager Stephan Ulmanec.

Same as photo above but this version provides context photos for the close-up images below. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Same as photo above but this version provides context for the close-up photos featured below, which are newly-released but taken last fall. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Already the lander is receiving twice as much solar energy as it did last November. Optimistic mission managers recently switched on the communication unit on the Rosetta orbiter to call the lander.

Philae’s like a hibernating black bear during its winter sleep. Before the craft wakes up, its interior temperature has to “warm up” to -49° F (-45° C). Since the mean temperature of the comet’s nucleus is -94° F (-70° C), this bear will sleep a while longer.

The triple cheeseburger feature is a slabby outcropping with a 98-foot (30-meter) boulder perched on its edge. Credit: Same as photo above but this version provides context photos for the close-up images below. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

This slabby outcropping, which reminds me of  a triple cheeseburger, has a 98-foot (30-meter) boulder perched on its edge. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

At its landing site, named Abydos, after one of the oldest cities in ancient Egypt, only a little sunlight shines down each day. Once the solar panels can generate 5.5 watts – less than a typical night light uses – the probe will finally have enough power to begin the wake-up process.

Once the sleep is gone from its eyes, Philae’s next task is to switch on its receiver to listen for Rosetta’s signal. True two-way communication can’t begin until the panels can generate 19 watts of power. Once the link has been reestablished, Rosetta will send the good news back to Earth. For all we know, Philae’s back up in low-power mode but doesn’t have the energy yet for a two-way conversation.

This close-up image has been processed to emphasise the faint nebulosity above the horizon on the right, to show the 'peaks' on the horizon silhouetted against this nebulosity, and to see the deeper, darker shadows they're casting onto the nucleus. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

This close-up has been processed to emphasize the peaks projected against the comet’s hazy atmosphere on the right compared to the deeper, darker shadows they’re casting onto the nucleus. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Rosetta tried signaling the lander and listening for a response during a favorable alignment between starting March 12th and ending on the 20th. The next chance to hear a possible signal from the lander will be during the first half of April.

Before it went dark, Philae did a stellar job deploying its instruments and gathering as much information as it could about the comet’s alien surface and atmosphere. On its first touchdown attempt and also at its present site, the probe discovered a large amount of water ice beneath the dust-covered surface.

This photo captures some of the smooth Anubis region on the comet's larger lobe. the smooth portions of Anubis appear faulted or folded in some places, and scattered boulders may be the products of mass wasting. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

This photo captures some of the smooth Anubis region on the comet’s larger lobe. Some of the terrain appears faulted or folded, and scattered boulders may have dropped or rolled away from collapsed slopes and cliffs. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Attempts were made to drill into the crust, gather a sample of soil and deliver it to the lander’s ovens for analysis, but nothing was ever turned up. It’s thought that the lander’s cockeyed position prevented the drill from making contact with the surface. Another instrument, which banged the surface with a hammer, suggest that a veneer of dust 4-8 inches (10-20 cm) thick overlays a thick layer of ice. Organic molecules with carbon and hydrogen were found in the comet’s atmosphere, too.

Philae first touched down where you see the cross. After bouncing, it landed somewhere in the red oval. Scientists still don't know precisely where. Credit: ESA

Philae first touched down where you see the cross. After bouncing, it landed somewhere in the red oval. Scientists still don’t know precisely where. Credit: ESA

We’re eager to hear more from Philae, but the long winter of its discontent must first yield to what passes for spring on a comet.

Rosetta’s shadow darkens an unfamiliar landscape

Rosetta took this photo of Comet Churyumov-Gerasimenko from an altitude of just 3.7 miles (6 km) on Feb. 14. Details as small as 4-inches across are visible as is the spacecraft's shadow (bottom). Click to enlarge. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Rosetta took this photo of Comet Churyumov-Gerasimenko from an altitude of just 3.7 miles on Feb. 14. Details as small as 4-inches (11 cm) across are visible as is the spacecraft’s shadow (bottom). Click to enlarge. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Can you imagine how close Rosetta must be to comet 67P/C-G to see its own shadow? Try 19,500 feet. This photo was taken during its closest flyby yet on Valentine’s Day and reveals an exotic landscape of rock, ice and dust from an altitude of just 3.7 miles (6 km), about half the altitude of a typical jet.

Picture yourself looking out the window of a plane well before it reaches cruising altitude. While the landscape resembles the barren cliffs, canyons and hills of the southwestern U.S. it has its own unique platy cragginess. To the left, the rugged cliffs give way smoother, dust-covered terrain.

The OSIRIS narrow-angle camera image from the 14 February close flyby (bottom left) shown here in context with Navigation Camera images (top left, top right and bottom right). Credit: 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

The OSIRIS narrow-angle camera image from the February 14 close flyby (bottom left) is shown here in context with Navigation Camera images (top left, top right and bottom right) so you get a better idea of where on the comet the photo was made. Credit: 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

The shadow at bottom measures about 65 x 160 feet (20×50 meters), and the frame covers an area of just 750 feet square (250-m).

During the flyby, Rosetta passed through a unique observational geometry; for a short time, the Sun, spacecraft, and comet were exactly aligned. As seen from above, surface structures on the comet cast almost no shadows, allowing scientists to precisely measure the reflection properties of the materials, including determining the sizes of the mineral and ice grains.

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

Graphic showing 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

Coming back to the shadow, notice how fuzzy it is. Even though the Sun appeared only 0.2° across (0.5° from Earth) from Rosetta’s distance of 215.6 million miles at the time, it’s still not a point source. Only point sources of light create precisely sharp shadows identical in size to the objects that produce them. Rosetta’s shadow has a fuzzy, soft-edge “penumbra” that adds an additional 65 feet (20-m) to its size.

If you look again at the first image at the start of this blog, you’ll see a faintly bright halo around Rosetta’s shadow. This is primarily caused by the “opposition effect” or shadow hiding. Grains directly below Rosetta in line with the Sun cast no shadows and so appear brighter than other grains nearby casting very short shadows.

Did SOHO’s comet survive? The hunt is on!

Newly-named Comet C/2015 D1 (SOHO) will share the sky with Venus and Mars at dusk. For the next few nights it will be quite low and nearly impossible to see. Its situation improves over time as the comet moves rapidly northward into Pegasus and Andromeda. Tick marks show the comet's position each evening. Stars are shown to magnitude +6.5. Created with Chris Marriott's SkyMap software

Newly-named Comet C/2015 D1 (SOHO) will share the sky with Venus and Mars at dusk. For the next few nights it will be quite low and nearly impossible to see. Its situation improves over time as the comet moves rapidly northward into Pegasus and Andromeda. Tick marks show the comet’s position each evening. Stars are shown to magnitude +6.5. Created with Chris Marriott’s SkyMap software

There’s no telling whether anyone will yet see the “phoenix comet” that survived a close encounter with the Sun last week and continued to keep it together until it exited the coronagraph on the orbiting Solar and Heliospheric Observatory (SOHO).

The last we heard, SOHO-2875, now formally named C/2015 D1 (SOHO), still glowed around magnitude +4 on Feb. 21.

Now the hunt is on to see if enough of the comet remains after its perilous journey to make an appearance in evening twilight. After many position measurements from photos taken by SOHO, an orbit has been calculated that was just published today. Using those numbers, I made a map showing the comet’s nightly progress as it travels up from the western horizon not far from Venus and Mars through the constellations Pisces and Andromeda over the next couple weeks.

Don’t expect to see it tonight. It’s likely no brighter than the naked eye limit (magnitude +6) and swamped in the glow of twilight very low in the western sky. Still, by good fortune, it just happens to hover very close to the star Gamma in Pisces about 5° above the horizon near the end of dusk.Those with crystal clear skies and an open view to the west should give it a try.

The situation soon improves as SOHO’s northward movement carries it higher into a darker sky. It’s uncertain if the comet is a tight, dense ball or a ballooning bag of dust. Until the first observations come in, we won’t know how the comet’s fairing. Also keep in mind that the orbit is preliminary, meaning C/2015 D1 may not exactly follow the path shown. Do sweeps around the positions, moving left and right and up and down from each nightly spot.

I’m as eager as you to see our new visitor.

Moon meets Uranus next / Oddball comet update

Wow! What a fine photo from last night's conjunction. Venus, Mars and waxing crescent Moon over sculpture "Calling The Power" by Larry Bechtel at Vic Thomas Park. Credit: Terry Aldhizer

Wow! What a fine photo from last night’s conjunction. Venus, Mars and the waxing crescent Moon over the sculpture “Calling The Power” by Larry Bechtel at Vic Thomas Park in Roanoke, Virginia. Credit: Terry Aldhizer

Close-up of the moon, Venus, Mars gathering last night. The earthshine on the moon is amazing! Credit: Terry Aldhizer

Close-up of the moon, Venus, Mars gathering last night. The earthshine on the moon is amazing! Credit: Terry Aldhizer

We were  hopelessly cloudy for last night’s conjunction. You were luckier I hope. Don’t forget, tonight’s thicker crescent passes very close to the planet Uranus, occulting it from the far northeastern U.S. and southeastern Canada. Venus and Mars will also be in conjunction today and a smidge closer that they were yesterday evening.

Wide view of Uranus and the moon on tonight (Feb. 21)  as seen from the Midwest about an hour and a quarter after sunset. Source: Stellarium

For the Central Time Zone, Uranus will lie 0.5° west of the moon in twilight, 1° away the Mountain States and 1.5° for the West Coast. What a great opportunity to spot the 7th planet in binoculars. Not only that, but a simple time exposure with a tripod-mounted camera will easily show it. Wait till late twilight and try a range of exposures starting around 5 seconds at ISO 800 with the lens wide open to f/2.8 or 3.5.

Uranus in early twilight (left) just before its dramatic disappearance behind the earth-lit edge of the moon tonight Feb. 21 as seen from Portland, Maine. 36 minutes later Uranus emerges at the bright crescent’s edge. Both disappearance and reappearance occur in a dark enough sky to see in a small telescope. Source: Stellarium

Map showing where the occultation of Uranus by the moon will be visible. Between the white lines, it’ll be visible in a dark sky. Blue is twilight and the red dotted line is daytime. Uranus is too faint to see in the daytime sky. Click the map to get a list of disappearance and reappearance times for a variety of cities. Credit: IOTA/Occult

Most of the time the moon occults stars along its path since there are a lot more of those than planets. Because they’re so remote, stars are little more than points of light; as the moon moves over them they disappear with surprisingly suddenness. Since Uranus displays a real, measurable disk it will take a second or two to disappear behind the moon’s edge.

SOHO-8275 comet about 7 east of the Sun this morning at 9:06 a.m. (CST) this morning. Credit: NASA/ESA

SOHO-2875 comet about 7 east of the Sun this morning at 9:06 a.m. (CST) this morning. Credit: NASA/ESA

The little comet we discussed yesterday continues trekking away from the Sun after its searing encounter two days ago. SOHO-2875 still shows a short tail and hangs in there around magnitude +3.5. It reached the edge of the field of view of the Solar and Heliospheric Observatory’s C3 wide-field coronagraph this morning headed east-northeast.

Since the field of view of the coronagraph is 15°, the comet’s presently about 7° east of the Sun, too close to spot yet in twilight. Give it 4-5 more days and someone may see it in a telescope in evening twilight. As soon as an orbit becomes available I’ll put together a chart to help you find it.

New Fast-Moving Comet May Become Visible from Earth

SOHO-2875 seen SOHO's LASCO C3, wide-field coronograph called LASCO C3 at 11:02 a.m. (CST) today Feb. 20. It's already moved a good distance to the east-southeast of the Sun and still displays a short tail. Credit: NASA/ESA

SOHO-2875 seen SOHO’s LASCO C3, wide-field coronograph called LASCO C3 at 11:02 a.m. (CST) today Feb. 20. It’s already moved a good distance to the east-southeast of the Sun and still displays a short tail. Credit: NASA/ESA

A newly-discovered comet may soon make an appearance in the evening sky. Dubbed SOHO-2875, it was spotted in photos taken by the Solar and Heliospheric Observatory (SOHO) earlier this week. Astronomer Karl Battams, who maintains the Sungrazer Project website, originally thought this little comet would dissipate after its close brush with the Sun. To his and our delight, it’s now outperforming expectations. Given the comet’s rapid movement away from the Sun, we won’t have to wait long to find out whether it might be visible in a telescope.

Composite of Comet SOHO-2875 crossing the C2 coronagraph field yesterday. Credit: NASA/ESA/Barbara Thompson

Composite of Comet SOHO-2875 crossing the C2 coronagraph field yesterday. Credit: NASA/ESA/Barbara Thompson

Most sungrazing comets discovered by SOHO are members of the Kreutz family, a group of icy fragments left over from the breakup of a single much larger comet centuries ago. We know they’re all family by their similar orbits. The newcomer, SOHO’s 2,875th comet discovery, is a “non-group” comet or one that’s unrelated to the Kreutz family or any other comet club for that matter. According to Battams these mavericks appear several times a year.

Photo taken at 20:00 UT (2 pm. CST) Feb. 19 with the SOHO C2 coronagraph, a device that blocks the Sun, allowing a view of the area close by. A faint tail can be seen just below the comet's bright head. Credit: NASA/ESA

Photo taken at 20:00 UT (2 pm. CST) Feb. 19 with the SOHO C2 coronagraph, a device that blocks the Sun, allowing a view of the area close by. A faint tail can be seen just below the comet’s bright head. Credit: NASA/ESA

What’s unusual about #2,875 is how bright it is. At least for now, it appears to have survived the Sun’s heat and gravitational tides and is turning around to the east headed for the evening sky. I’m no expert but having looked at many SOHO photos over the years, I’d estimate the comet is presently about magnitude +2.5 and some 5° from the Sun. No one can say for sure whether it has what it takes to hang on, so don’t get your hopes up just yet.

We’ll be watching and waiting. I’ll have an update on SOHO-2875’s progress soon.

Sweet Valentine’s Day closeups of Rosetta’s Comet

Four image mosaic of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February at 14:15 GMT from a distance of 8.9 km from the surface. The image scale is 0.76 m/pixel and the mosaic measures 1.35×1.37 km across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image mosaic of Comet 67P/Churyumov-Gerasimenko taken on Feb. 14 at 8:15 a.m. (CST) from a distance of 5.5 miles from the surface. The view measures 0.8 miles across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe. Click for a large version. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

If you’ve ever wondered what it would be like to fly over a comet in a jet airplane, soak in these photos. This past Saturday, the Rosetta spacecraft swung within 3.7 miles (6 km) of the surface of Comet 67P/C-G. Pictures for the mosaic image (above) were taken from an altitude of just 29,000 feet, nearly 10,000 feet lower than a typical transatlantic flight.

It really is like looking out the plane window especially when you consider you’re viewing a chunk of landscape barely a mile across. You and I could walk across that mosaic in less than 20 minutes! Assuming no obstacles of course.

Cropped, close-in view of several raised circular structures near the center of the mosaic. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Cropped, close-in view of several raised circular structures near the center of the mosaic. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Closest approach occurred over the Imhotep region on the comet’s large lobe. What caught my eye was the long, layered mesa-like feature in the lower left of the frame. In the cropped version, you can make out the outlines of several raised, near-circular structures with smooth floors. Boulders, ranging in size from 12 feet (a few meters) to a 35 feet (10 meters) lie scattered across the whole surface of the comet. The big boulder near the top of the mosaic and seen up close below is named Cheops. It’s 148 feet or about 45 meters across.

Close-up view of the large, mesa-like formation photographed by Rosetta on Saturday from 29,000 feet. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Close-up, rotated view of the layered formation photographed by Rosetta on Saturday from 29,000 feet. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The big boulder Cheops casts a shadow at upper right. It's not far from what looks like a section of the comet's crust that's collapsed. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The big boulder Cheops (upper right) sits in its shadow. It’s not far from what looks like a collapsed area of the comet’s crust (left). Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

What appears to be a collapsed section of a cliff or wall. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

What appears to be a collapsed section of a cliff or wall. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Download the mosaic to your desktop and take a few minutes to explore it. You’ll find flows, depressions, more of of those circular features and a delightful assortment of boulders of all shapes and sizes. What are those things – dust-covered ice chunks?

Rosetta is now moving out for a far view of the comet and will reach a distance of about 158 miles (255 km) from the comet’s center tomorrow. Stop by in a day or two for new pictures of 67P’s atmosphere or coma. In the meantime you can download a zip file of the 16 individual frames comprising the mosaic here.

Glowing comets and deep fried ice cream

Comet 67P/C-G taken on February 6 from a distance of 77 miles (124 km) to the comet center. We see the comet’s small lobe on the left and larger lobe to the right. The image has been processed to bring out the details of the comet’s jetting activity. Exposure time was 6 seconds. Credits: ESA/Rosetta/NAVCAM

Everything’s glowing! This new photo from the Rosetta spacecraft was taken on Feb. 6 and processed to show jets active all over comet 67P. They’re brightest and most effervescent in the Hapi region, the name given to the neck of the comet, but take a look around the nucleus. You can see that the entire comet is swathed in a soft, nebulous halo of vaporizing ices and dust motes.

Some of the grainy white spots around the comet’s nucleus are background noise brought to the fore as a consequence of processing the images to see the jets more clearly, but some is actual comet stuff jetted into 67P’s coma like dried leaves from a leafblower.

Rosetta’s moved out from the comet temporarily as part of an orbit change that will see it fly just 3.7 miles (6 km) of its surface this Saturday. Photos from the flyby will be downlinked to Earth Sunday and Monday.

In other comet news, a team of astronomers have simulated what happens to a comet’s ices when it nears the Sun. It’s not what you’d expect.

Familiar ice like that on ponds, lakes and clinking as ice cubes in a glass are made of neatly ordered arrangements of water molecules. Amorphous ice is also made of water but its structure is disordered. Credit: Wikipedia

“A comet is like deep fried ice cream,” said Murthy Gudipati of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., corresponding author of a recent study appearing in The Journal of Physical Chemistry. “The crust is made of crystalline ice, while the interior is colder and more porous. The organics are like a final layer of chocolate on top.”

Comets, which formed in the bitter cold of the outer solar system, are probably composed of amorphous ice, a form of water ice where the H20 molecules are randomly arranged instead of packed into neat lattices like those that make up the more familiar crystalline ice we use to chill our sodas.

Researchers at NASA’s Jet Propulsion Laboratory use a cryostat instrument, nicknamed “Himalaya,” to study the icy conditions under which comets form. Image credit: NASA/JPL-Caltech

First, the team flash-froze water vapor infused with carbon compounds called polycyclic aromatic hydrocarbons (PAHs) at -405° F to preserve the disorderly states of the water molecules and create amorphous ice. Then, using a cryostat instrument nicknamed “Himalaya”, they gradually raised the temperature of the mixture from -405° F to -190° F (-243° C to -123° C).

The PAHS stuck together and were expelled by the ice as it crystallized. With the carbon compounds now gone, the water molecules moved into the empty spaces linking up to form more compact crystalline ice.

That rings true when it comes to the Rosetta mission’s Philae lander which hit 67P/C-G with a big bounce proving it had a hard surface. Some of the dust seen around 67P might well have been “squeezed” out when amorphous ice transformed into the crystalline variety.

Similar to the fried ice cream pictured here, comets have cold, icy interiors surrounded by a crust of organics expelled when amorphous ice warms to become crystalline ice. Credit: Wikipedia

“What we saw in the lab — a crystalline comet crust with organics on top — matches what has been suggested from observations in space,” said Gudipati. Deep fried ice cream is really the perfect analogy, because the interior of the comets should still be very cold and contain the more porous, amorphous ice.”

Rosetta sees fascinating changes in Comet 67P

A new jet issues from a fissure in the rugged, dusty surface of Rosetta’s comet. Credit: ESO/Rosetta/Navcam; processed by Elisabetta Bonora & Marco Faccin

It only makes sense. Sunlight heats a comet and causes ice to vaporize. This leads to changes in the appearance of surface features. For instance, the Sun’s heat can eat away at the ice on sunward-facing cliffs, hollowing them out and eventually causing them to collapse in heaps of shards. Solar heating can also warm the ice that’s beneath the surface. When it becomes a vapor, it pushes against the ice above, cracking it and releasing sprays of gas and dust as jets.

Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I’ve labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam

Recent photos taken by the Rosetta spacecraft reveal possible changes on the surface of 67P/Churyumov-Gerasimenko that are fascinating to see and contemplate. In a recent entry of the Rosetta blog, the writer makes mention of horseshoe-shaped features in the smooth neck region of the comet called “Hapi”. An earlier image from Jan. 8 may show subtle changes in the region compared to a more recent image from Jan. 22. We’ll get to those in a minute, but there may be examples of more vivid changes.

Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month’s time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam

I did some digging around and found what appears to be variations in terrain between photos of the same Hapi region on Dec. 9 and Jan.8. Naturally, we have to be careful when comparing photos taken under different lighting conditions and viewing geometry. Rarely does one view precisely match another. That has to be taken into account when deciding whether a change in a feature is real or due to change in lighting or perspective.

Side by side comparison of the two image from Dec. 9, 2014 (left) and Jan. 8, 2015. Credit: ESA/Rosetta/Navcam

But take a look at those cracks in the December image that appear to be missing in January’s. The change, if real, is dramatic. If they did disappear, how? Are they buried in dust released by jets that later drifted back down to the surface?

Comparison of Jan. 22 and Jan. 9 photos of the “horseshoes” or depressions in 67P’s Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam

Now back to those horseshoe features. Again, the viewing angles are somewhat different, but I can’t see any notable changes in the scene. Perhaps you can. While comets are expected to change, it’s exciting when it seems to be happening right before your eyes.

Four-image mosaic shows the overall view of the comet on January 22 photographed 17.4 miles (28 km) from its center. The larger of the two lobes is at left; Hapi is the smooth region at the transition between the lobes. Credit: ESA/Rosetta/Navcam