Frosty and fresh, fall begins tonight

Frost on colorful leaves, a sure sign that fall has arrived. Credit: Bob King

Lots of us have looked forward to the first day of fall after summer’s heat and humidity. I like the feel of a sweater on a night’s walk and the fire-hued trees that provide a pleasant distraction while sitting in traffic.

Two views of the sun’s travels along the celestial equator on the first day of fall. The left side shows the view from the equator where the sun passes overhead. The right shows the view from 50 degrees north latitude (S. Canada, Europe). At the north pole, the sun would follow a path along the horizon. Credit: Tau’olunga

The new season begins quietly tonight at 9:29 p.m. Central time. At that moment the sun drops into the southern sky like a penny in a piggy bank and fall officially begins. At the fall and spring equinoxes, the sun crosses the celestial equator, an imaginary extension of Earth’s equator into the sky. Picture the celestial equator as half of an imaginary hula hoop tilting up from the eastern horizon, crossing the southern sky and then arcing back down to the western horizon. The hoop’s other half continues below the horizon and beneath our feet, circling over the opposite hemisphere.

On the first day of autumn, the sun crosses the celestial equator moving south. The sun’s apparent motion across the sky over the year is caused by Earth’s revolution around the sun. Illustration: Bob King

If you live in parts of Kenya, Ecuador or Indonesia the celestial equator passes directly overhead. On the first day of spring and fall, it’s directly overhead at noon.

In mid-northern latitudes it cuts midway across the southern sky. On the first day of spring, the sun crosses this celestial borderline moving north. Seen from the northern hemisphere, the sun’s northward movement brings it higher and higher in the sky. Days lengthen and nights get shorter as we transition from spring to summer.

Tonight, the sun crosses the equator moving south along its yearly circuit of the sky. The southward-moving sun slides lower and lower in the coming days and weeks. We’ll watch daylight diminish at the expense of night as the northern hemisphere makes its transition from fall to winter.

Video to help picture Earth’s orbit around the sun and how its tilted axis causes different parts of the planet to receive different amounts of sunlight during the year. Variation in the amounts of daylight vs. night gives us the four seasons.

Seasons are caused by the 23.5 degree tilt of our planet’s axis. As Earth moves along its yearly orbit, the north-south position of the sun changes because of the changing orientation of our axis. When the north polar axis is pointed toward the sun, our star reaches its most northerly point in the sky and we experience long days and summer heat.

The first day of fall is special because Earth’s axis points neither toward nor away from the sun. Instead, we’re broadside to our star, and day and night are approximately equal across the planet.

The word equinox comes comes from the Latin words for equal and night because both day and night are approximately 12 hours long. Prior to September 22, days are longer; after the 22nd they get shorter. Shorter days are caused by the sun dropping farther south in the sky (lower altitude). The lower the sun, the less time it spends crossing the sky and the shorter the hours of daylight.

The sun in this sunrise photo is an illusion caused by the thick air at the horizon bending the real sun (still below the horizon) into view. Credit: Lyle Anderson; illustration: NOAA

Notice I didn’t say that day and night are exactly equal at the equinoxes. While it’s true that the center of the sun sets exactly 12 hours after it rises on the first day of fall, we determine sunrise at the first sighting of the sun, when its upper edge (not center) breaches the horizon. Similarly, sunset occurs when the last bit of sun disappears below the horizon. That adds about two minutes of extra daylight to the day.

We get another few minutes thanks to atmospheric refraction. That’s our atmosphere’s freaky ability to act like a prism and bend the sun’s rays upward into view when it’s still below the horizon. If you ever have the chance to see the sun directly on the horizon at sunset or sunrise, you’ll witness one of nature’s grandest illusions. The sun’s not really there. The air is thick enough across your sight line to “lift” the sun into view about two minutes before it rises for real.

MAVEN makes it safely to Mars!

This image shows an artist concept of NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission. Credit: NASA/Goddard Space Flight Center

After 10 months and over 422 million miles (771 million km) of travel, NASA’s Mars Atmosphere Volatile EvolutioN spacecraft settled safely into orbit around Mars Sunday evening at 9:24 p.m. Central Daylight Time. Engineers and scientists waited tensely as the onboard computers fired thrusters for 33 minutes to slow the craft enough so it could be captured by Mars’ gravity. The operation went smoothly.

MAVEN joins a fleet of other craft working at the Red Planet including Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter and the two rovers, Opportunity and Curiosity. On Wednesday, India’s Mars Orbiter Mission (MOM) will join the clan as it too brakes to settle into orbit.

“This was a very big day for MAVEN,” said David Mitchell, MAVEN project manager from NASA’s Goddard Space Flight Center, Greenbelt, Maryland. “We’re very excited to join the constellation of spacecraft in orbit at Mars and on the surface of the Red Planet. The commissioning phase (when the instruments will be checked and orbit slimmed from 35 to 4.5 hours) will keep the operations team busy for the next six weeks, and then we’ll begin, at last, the science phase of the mission. Congratulations to the team for a job well done today.”

Mars was once a much wetter and warmer planet (left) than it is today. Because it’s not protected by a planet-wide magnetic field like Earth, it’s thought that the sun and solar wind stripped away its atmosphere over time, leading to a cold, dry desert world (right). Credit: NASA

MAVEN’s primary mission will last one Earth year taking measurements of the composition, structure and escape of gases in Mars’ upper atmosphere and its interaction with the sun and solar wind. Without protection from a planet-wide magnetic field, it’s thought that the sun and solar wind have stripped molecules from the Martian atmosphere over time. MAVEN will dip into Mars’ atmosphere only 93 miles (150 km) above the surface to study how and what kinds of atoms are disappearing. Several deeper-dip missions will bring it to within 78 miles (125 km) altitude.

For more on MAVEN, check out the MAVEN website and this article in Universe Today.

Goodmorning moon / Tomorrow’s Titan flyby

Look east Monday morning around 6 a.m. to spot the goodmorning moon. Only 2.5% of the moon will be illuminated by the sun; the remainder by ghostly earthshine. Venus will be about a fist held at arm’s length to the moon’s lower left. Stellarium

Like a lot of parents, we read Goodnight Moon by Margaret Wise Brown to our kids to get them ready for bed at night. The calming words and repetition soothed child and adult alike at the end of the day.

Maybe a sequel titled “Goodmorning Moon” will be written someday about waking up to the smiling crescent in the east and getting ready for the day. Tomorrow morning we’ll see exactly that, a very thin moon, low in the eastern sky at dawn. Its delicate arc will surely make you stop and realize how much beauty nature puts on the plate for enjoyment and study every day.

Venus seekers can use the moon to make one last attempt to find the planet, now nestled very low in the east just a degree or two above the horizon 40 minutes before sunrise.

Animation showing clouds of methane moving over Ligeia Mare, a large sea of liquid methane near Titan’s north pole, between July 20 and 22, 2014 as Cassini departed the moon during the last flyby. Credit: NASA/JPL-Caltech/SSI

While we’re on the topic of planets, NASA’s Cassini spacecraft will make a close flyby of Saturn’s moon Titan tomorrow September 22nd. At 3,201 miles (5,150 km) across, Titan is the solar system’s second largest moon, only 79 miles smaller than Jupiter’s Ganymede. It’s also unique in having a very thick atmosphere – 1.5 times thicker than Earth’s – a feature usually found only on planets.

It’s still not known how Titan managed to hold onto all its air, which consists of primarily nitrogen mingled with methane and various other hydrocarbons that react in sunlight to create an orange smog that gives the moon its distinctive color. Several other moons such as Ganymede, Rhea and even our own moon have atmospheres, but they’re exceedingly thin compared to Titan’s.

In this photo taken by Cassini, Saturn’s airless, cratered moon Dione is juxtaposed with Titan. Titan appears smaller because it’s 600,000 miles farther away from the spacecraft’s perspective. To see beneath the clouds and map the surface, Cassini observes the moon in infrared light and with radar. Credit: NASA/JPL-Caltech

It’s thought that Titan maintains and replenishes its atmosphere through outgassing from its interior. The bitter cold temperatures at Saturn’s nearly billion mile distance from the sun along with Titan’s considerable gravitational pull undoubtedly help preserve and hang on to its air. Comet impacts may also contribute to the moon’s stockpile of ices and organic compounds.

Along with an atmosphere come clouds, though of methane rather than the water vapor variety found on Earth. Temperatures at the surface hover just 90 degrees above absolute zero (-290º F, -179º C), chill enough for methane clouds to form and supply at least some of the precipitation to lakes of liquid ethane, methane and propane below.

This will be Cassini’s 9th flyby of Titan this year. During a flyby, the craft zips by the moon at high speed while keeping its instruments precisely pointed at the target using either its reaction wheels or thrusters, which spin the spacecraft to track the moon as it passes by. Thrusters are also used to keep Cassini from tumbling when it experiences drag while passing through Titan’s upper atmosphere during close flybys.

Descent through Titan’s atmosphere made by the Huygens probe on January 14, 2005

On Monday, Cassini will be traveling at 13,000 mph (21,000 km/hr) and come within 870 miles of Titan’s surface as it photographs seas and lakes – including Ligeia Mars shown above – around the north pole. Another instrument will observe Titan’s southern hemisphere atmosphere in ultraviolet light by observing the dimming of Alkaid, the star at the end of the Big Dipper’s handle as its light passes through the moon’s varied atmospheric layers.

Rosetta’s comet from 17.8 miles – forbidding yet inviting

Four image mosaic of comet 67P/Churyumov-Gerasimenko, using images taken on September 19th by Rosetta. Faint jets of vaporizing ice carrying dust and gas shoot upward from the comet’s ‘neck’.  Click for a jumbo version. Credit: ESA/Rosetta/NAVCAM

2.5 miles of rugged, icy, airless desert. Is there a more forbidding looking place in the solar system than Comet 67P/Churyumov-Gerasimenko? In this new close-up, composed of four separate images taken with Rosetta’s navigation camera on September 19, we take in the comet from a distance of only 17.8 miles (28.6 km).

Crop of the original photo mosaic showing a big boulder tilted on its side and casting a shadow.  Relatively smooth and rugged terrain are found side by side all over the comet. Credit: ESA/Rosetta/NAVCAM

Click to pull up the giant version on your screen and spend some time scrolling around the landscape. Layering and striations abound, especially in the center of the larger lobe (left). The top of the larger lobe and ‘neck’ between lobes display smoother terrain that looks as though softened either through below-surface melting and refreezing. Or maybe it’s just covered in dust.

A possible fissure across the comet’s neck. Credit: ESA/Rosetta/NAVCAM

Boulders are everywhere like sprinkles on a cupcake, but the most interesting feature to my eye is the apparent crack or fissure in 67P/C-G’s neck. No telling how deep it might be. Given that comets are easily breakable objects – sometimes crumbling to bits in the solar heat – we would expect to see cracks in its surface.

Toned up version of the Comet 67P/C-G showing active jets and spots and specks of possible dust in the vicinity. Click to enlarge. Credit: ESA/Rosetta/NAVCAM

A hint of the geyser-like jets are seen in the original photo, but I’ve lightened it further to make the near-comet environment easier to see. Recent measurements by Rosetta’s MIRO instrument reveals the comet losing water at a much faster rate than three months ago. Although the amount varies as the nucleus rotates, the maximum measured recently was 1.3 gallons (5 liters) per second with an average of a quarter-gallon (1 liter) per second.

The toned photo also shows lots of small flecks that might be noise in the camera detector, cosmic ray hits or sunlight reflecting off dust and ice lifting off the comet –  I can’t say.

Reconstructed color view of 67P/Churyumov-Gerasimenko showing how truly dark and coal-colored the comet is. Credit: ESA/Rosetta/MPS for OSIRIS team; MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA. Additional processing and copyright: Elisabetta Bonora and Marco Faccin (Alive Universe Images -

Finally, if you haven’t already seen it, I wanted to share a recent Astronomy Picture of the Day (APOD) photo of the comet taken in early September with Rosetta’s high resolution OSIRIS camera and reconstructed as a color image by Elisabetta Bonora and Marco Faccin. I’m not sure how they determined color shadings but the darkness of the comet is accurate.

Jupiter-moon conjunction / Space station expecting guests / Hello Mars!

Tomorrow morning September 20th the crescent moon will be lined up in conjunction with the planet Jupiter ahead of the Sickle of Leo. This view shows the sky a little more than an hour before sunrise. Stellarium

Getting a little extra sleep these September mornings? That benefit comes from later sunrises as we approach the fall equinox. I don’t know about you, but I sleep better in a darkened bedroom.

The rate of change has really picked up in the past few weeks with the sun now rising around 7 o’clock, a far cry from late June’s 5:15.

Later sunrises also mean a chance to catch an early morning sky event. Many of us are active around 6 a.m. prepping for work or getting your children ready for school. If you can find a few minutes to spare, tomorrow morning offers up two fine sights.

Look east in the brightening dawn and you’ll see a slender crescent moon in conjunction with the brightest of the planets, Jupiter. The two will just 5º apart meaning you’ll be able to squeeze three fingers held at arm’s length between them. Then, between 5:30-6:15 a.m. now through at least next week, the International Space Station (ISS) will be making regular passes across the northern sky from many locations across the U.S., Canada and Europe.

To find out exactly when and where to look, key in your zip code at Spaceweather’s Satellite Flybys site or select your city at Heavens Above. The ISS looks like the brightest “star” in the sky and travels from west to east. A typical complete pass takes about 5 minutes.

An earlier SpaceX Dragon capsule docking with the space station in March 2013. Astronauts will use the grapple arm to grab the capsule Monday morning Sept. 22 at around 6:30 a.m. CDT. Berthing begins around 8:45. Click to enlarge. Credit: NASA

The three current astronauts aboard the space station await the arrival of the other half of their crew next week. NASA astronaut Barry Wilmore, Soyuz Commander Alexander Samokutyaev and Flight Engineer Elena Serova will launch aboard their Soyuz spacecraft from the Baikonur Cosmodrome in Kazakhstan on Sept. 25 to begin a six-hour, four-orbit trek to the orbiting complex.

Before that, SpaceX’s unmanned Dragon ship will launch tomorrow morning Sept. 20 at 1:14 a.m. Central time to deliver cargo and crew supplies to the ISS early Monday morning Sept. 22nd.

Among the items are the first 3D printer in space, the ISS-RapidScat instrument to monitor ocean winds for climate research and weather forecasting and a commercial experiment designed to make a better golf club. The printer will allow astronauts to make their own tools and replacement parts that would otherwise cost a lot of money to ship up from Earth.

Fruit flies such as these spent one month aboard the International Space Station during an earlier study. More are on the way. Credit: NASA / Dominic Hart

20 female mice and 30 fruit flies will also go along for the ride. The mice will be housed in the new Rodent Research habitat, where they’ll be studied for the effects of spaceflight on the human body. In space, rodents don’t spend their time floating around. They’re very physically active but tend to hold onto the walls.

Fruit flies will be monitored for the effects of oxidative stress changes which happen in organisms ranging from fruit flies to humans. Oxidative stress involves a build up of harmful molecules inside cells that can cause cell damage, and it’s associated with infections and disease.

Artist view of India’s Mars orbiter at Mars. Arrival and orbit insertion is expected for Sept. 24. Credit: ISRO

There’s much more in the works for space mission news as Mars welcomes two new emissaries from Earth. NASA will insert the MAVEN spacecraft into orbit around Mars Sunday night, and India’s Mars Orbiter Mission (MOM) will arrive at the planet only three days later on Sept. 24.

The MAVEN mission will study Mars’ climate present and past as scientists try to figure out how the planet evolved from a warmer, wetter past to the current dry, cold desert. MOM is India’s first-ever mission to another planet. While primarily a demonstration and testing of that country’s technology, MOM will also photograph the Red Planet and study its mineral makeup from orbit.

Minor aurora alert tonight Sept. 18-19

The auroral oval has expanded south this evening (11:45 p.m. CDT) in response to favorable changes in the solar wind. Observers in northern Minnesota, Maine and other borderland states should be watchful for auroras overnight. Credit: NOAA

Observers in the northern U.S. and southern Canada should be alert for auroras tonight. The direction of the magnetic field has been mostly south for the past 8 hours, providing a nice linkage into Earth’s magnetic bubble. It’s cloudy in Duluth, Minn., but the Ovation oval plot (above) would indicate visible aurora low in the northern sky from northern Minnesota, Michigan’s Upper Peninsula and northern Maine around 11-11:30 p.m. CDT.

* Update Friday, Sept. 19 — Minor storming is also possible tonight from higher latitudes in the U.S.


Hold my hand as we peer into the Bootes Void

The Big Dipper, the brightest part of the constellation Ursa Major the Great Bear, is followed down into the northwestern sky by twinkling orange Arcturus and the constellation Bootes, the Bear Guard. Stellarium

Most of us would consider Bootes the Bear Guard a spring constellation. That’s when it first appears in the eastern sky, following the tail of Ursa Major the Great Bear as the snow drifts recede. Come fall, Bootes (Boh-OH-tease) and its bright luminary Arcturus recline in the west within spitting distance of the Dipper.

Every evening I look up to check on the condition of the sky. Arcturus is either flashing happily or gone missing, hidden by clouds. Gazing up from Arcturus, it’s easy to trace out the remaining points of starlight that form the kite-like figure of Bootes. Like a kite let go, Bootes drifts away to the west as the night deepens.

The next clear night, follow the arc of the Dipper’s Handle to Arcturus and then work your way up and around to pick out the constellation’s fainter stars. If you now direct your gaze to a blank spot between Bootes and the end of the Dipper’s handle, you’ll be staring at the center of a remarkable nothingness, the Bootes Void.

Map of the Bootes Void showing it alongside other dense superclusters of galaxies. Credit: Richard Powell

Normally we talk about the presence of something in the sky in this blog, but today we’ll focus on absence. The Void, a roughly spherical realm of space 250 million light years in diameter, is virtually empty. Space is already empty enough. If the sun were shrunk down to the size of a grapefruit, the nearest star system, Alpha Centauri, would be 2,000 miles away. From there, it’s another 1,000 miles to the next closest, Barnard’s Star.

American astronomer Robert Kirschner discovered the void in 1981 as part of a survey to measure how fast distant galaxies were fleeing from one another as the fabric of space expands in the ever-widening wake of the Big Bang. Six years later, Kirschner and team turned up 8 galaxies in this vast volume of space centered 700 million light years from Earth. By the late ’90s only 60 galaxies were known, making the Void not as devoid of galaxies as originally thought.

Still, the wind blows through it like a ghost town. Considering that the average distance between galaxies in typically a few million light years, the Void should contain some 10,000 inhabitants. Where have they fled?

The Millenium Simulation will give you a feel for the large-scale structure of the universe. Enjoy the ride!

Galaxies are vast assemblages of stars, clusters, gas clouds and planets thousands of light years across. Their mass gives them considerable gravitational might, so they’re attracted to one another. Over the lifetime of the universe, galaxies congregate into strands, clumps and clusters. The surrounding space empties out like a parking lot at closing time and becomes a void.

The Bootes Void is no ordinary emptiness. It’s HUGE. Too big to have formed with the current lifetime of the universe say astronomers. That’s why it’s thought to have agglomerated from smaller voids that merged together to form one of the largest voids in the known universe, a so-called supervoid.

Millenium Simulation of the large-scale structure of the universe shows a sponge-like texture of filaments of galaxies threading empty voids of space. The galaxies – each too tiny to see individually at this huge scale – clump around invisible dark matter and each other. Credit: Millenium Simulation

Galaxy clumping has amazing consequences for the large-scale structure of the universe. Astronomers think the visible matter of the universe clustered around clumps of dark matter, which makes up 73% of all the ‘stuff’ out there, shortly after the Big Bang. Once galaxies formed, they continued their clustering ways up to the present day. Instead of a random distribution of matter across space, the universe looks like a sponge where hundreds of billions of galaxies swirl in filaments and nodes around the comparatively empty voids.

Funny how the biggest things in the universe can be so surprisingly close to home. Look up toward the Big Dipper and Arcturus in the western sky after sundown and think of where you are.

Follow Mars to Dschubba, whirling dervish of the night

Photo taken last night in late twilight at 8:30 p.m. looking southwest. With Mars nearby, finding our featured star Delta Scorpii is a snap. The two will be closest tomorrow night September 17th. A car zoomed by during the 20-second exposure. Credit: Bob King

Looked at Mars lately? If you haven’t I’m not surprised. It’s lost it’s luster since spring and rides the “low path” in Scorpius in the southwestern sky at dusk. From my home in the mid-northern latitudes, it now spends most of its brief nightly circuit hidden behind trees. But I encourage you to look for the Red Planet over the next few evenings. It’s passing very close to a fascinating star in the head of Scorpius the scorpion, Delta Scorpii.

Delta, also known by its Arabic name, Dschubba (JOOB-a), normally shines at magnitude 2.3, a tad fainter Beta Scorpii (2.6) directly above it. But on June 26, 2000, amateur astronomer Sebastian Otero of Buenos Aires noticed something peculiar. He’d been making brightness estimates that night of stars that are constant or don’t vary in brightness.

Mars will be very near Delta in the head of Scorpius not far from similarly colored Antares tonight. The pair will be closest tomorrow night (September 17) at just a half-degree apart. Delta is an unusual variable star that’s been in outburst since 2000. Stellarium

To his surprise, when he selected Delta, he found it brighter than normal. After alerting others to confirm his result, observers around the world watched as the star slowly rose in light until peaking at magnitude 1.6 in 2003. Yes, three years later.

I got in on the fun, too, watching Dschubba outshine every star in its constellation except the brightest, Antares. The change in the appearance of the scorpion’s head was striking. It still is. While the star has fluctuated in brightness since Otero’s discovery, it remains unusually bright; current estimates place it around magnitude 1.8. And now Mars will take you right to it.

Delta Scorpii likely resembles VFTS-102 (illustrated here), the fastest rotating star found to date. It goes round at 1 million mph or 100 times faster than the sun. The incredible speed has flattened the star into an egg shape and spun off a disk of material in the star’s equatorial plane like Delta. Credit: NASA

Delta’s an amazing star despite its unremarkable appearance. Nearly 15  times more massive than the sun and located about 470 light years from Earth, it’s blazing surface shines at least 14,000 times brighter than the home star. If those aren’t superlatives enough, this star rotates at least 112 miles per second, 90 times the sun’s rate.

Studies reveal the star is disrobing right in front of our eyes, flinging mass from its equator as it spins at breakneck speed. The material accumulates in a disk around the star and is responsible for the rise in brightness and appearance of bright lines of emission in the star’s rainbow spectrum.

Dschubba has three companion stars in orbit about it. One, a cooler, fainter star with a period of 10.8 years, may be connected with the Delta’s outburst in 2000 and a second peak in brightness in 2011. Perhaps its revolution about the primary star stirs the great beast to release extra material every 11 years.

While Delta Scorpii lays low this time of year, you can still follow it into October and then watch with anticipation when it returns to the morning sky in winter. If you’d like a chart with magnitudes to estimate its brightness, click over to the AAVSO and key in Delta Sco in the “Create a finder chart” window.

Site ‘J’ it is! Comet lander readies for November touchdown

The primary landing site for the Rosetta lander Philae will be on the comet’s head in an area that’s both safe and shows interesting activity. Site J was chosen from the original “Top 5″. Credit: ESA/Rosetta/MPS for Osiris team/UPD/LAM/IAA/SSO/INTA/UPD/DASP/IDA

Site J it is! European Space Agency scientists have selected a safe but intriguing region on 67P/Churyumov-Gerasimenko for humanity’s first-ever soft landing on a comet. Site C, located on the larger ‘body’ of the comet, was selected as backup.

Close-up of Philae’s primary landing site J, which is located on the ‘head’ of Comet 67P/Churyumov–Gerasimenko. The image was taken by Rosetta’s OSIRIS narrow-angle camera on August 20, 2014 from a distance of about 42 miles. Click to enlarge. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Choosing a landing site hasn’t been easy. Safety was a prime concern. Site J appears to have relatively few boulders and receives sufficient daily sunlight to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase. The majority of slopes there are sloped less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. The J Site also allows the probe to be in regular communication with the orbiter as it passes overhead during each orbit of the comet.

Close-up of Site C,  Philae’s backup landing site.

“As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging,” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

Since the descent to the comet is passive in the comet’s low gravity field – like dropping a piece of paper – it’s only possible to predict the landing point to within about 1,000 feet (~300 meters). Descent time to the surface is estimated at 7 hours. Landing has to happen by November before 67P/C-G becomes too active spewing dust and gas as it draws ever nearer the sun.

See it in 3D! You can roam Philae’s primary landing site with all its ridges and valleys if you have a pair of red-blue 3D glasses. Click to enlarge. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

“There’s no time to lose, but now that we’re closer to the comet, continued science and mapping operations will help us improve the analysis of the primary and backup landing sites,” says ESA Rosetta flight director Andrea Accomazzo.

Site J offers scientists a place to analyze 67P/C-G’s ice and dust and study the ice vaporization processes that make comets such special critters.
During the descent, Philae will take photos and observe the comet’s dusty-gassy environment. Once it gently drops to the surface at the equivalent of a walking pace, it will fix itself to the comet’s crust using a harpoon-like device and ice screws in the landing legs. It will then shoot a 360-degree panorama of its surroundings.
Next comes an analysis of the plasma and magnetic environment, and the surface and subsurface temperature. The lander will employ a drill to collect samples from beneath the surface and analyze them inside its onboard lab. The interior structure of the comet will also be explored by sending radio waves through the surface towards Rosetta.
Source: Rosetta blog, ESA

Philae snaps photo of Rosetta orbiting comet / New mosaic may show ice particles

The Philae lander, stowed aboard Rosetta, took this photo of the side of the mothership and one of its 46-foot (14-m) long solar arrays with comet 67P/Churyumov-Gerasimenko in the background. Two images with different exposure times were combined to capture the bright, 2.5-mile-wide comet and dimmer hardware. Click to enlarge. Credit: ESA/Rosetta/Philae/CIVA

Seeing this makes me feel like I’m in orbit. What a nice perspective with the comet in the frame. It was taken by the Comet Infrared and Visible Analyzer (CIVA) on September 7th and shows part of the spacecraft and one of its solar arrays from a distance of about 31 miles (50 km) from the comet.

CIVA is several instruments in one. CIVA-P consists of seven cameras – five regular cameras and one dual-instrument stereo camera – that will take a 360º panorama of the landing site once it’s safely on the surface of the comet. A section of the panorama will be shot in stereo.  Landing is scheduled for November 11th.

Artist’s impression of Rosetta’s lander Philae (front view) on the surface of the comet. Philae will be deployed to 67P/C-G in November where it will make in situ observations of the comet surface, including drilling 9 inches (23 cm) into the surface to gather a sample for analysis in its on board laboratory. Copyright: ESA/ATG medialab

CIVA-M has a miniaturized visible light microscope and a coupled infrared spectrometer (an instrument used to measure light in the infrared part of the spectrum) that will be used to study a drilled sample from the comet’s crust. CIVA-M is designed to identify organic materials in the soil.

Four-image navigation camera mosaic of Comet 67P/Churyumov-Gerasimenko, using photos taken on September 10 when Rosetta was just 17.3 miles from the comet. Click for a giant version. Copyright: ESA/Rosetta/NAVCAM

Stephan Ulamec, Philae lander manager, will announce the primary and backup landing sites for the washing-machine-sized probe at a presentation tomorrow morning at ESA Headquarters in Paris. The challenges and scientific expectations of the sites will be presented and shared with the media. We’ll have photos and the latest information here when it arrives.

In this cropped version, a bright, reflective spot is visible. It doesn’t show in images taken before this one (although the shadow does, so it’s unrelated). It’s either a camera artifact or something reflective like a fleck of ice or dust that passed by in the foreground. Credit: ESA/Rosetta/NAVCAM

In the meantime, have fun exploring the huge mosaic of 67P/C-G snapped from just 17.3 miles (27.8 km) away. In the cropped closeup, there’s an interesting bright spot that may either be an artifact or a something reflective (ice?) in the foreground. Take a look at the image below, which I’ve lightened up to show the comet’s neck in reflected sunlight and a speckling of either “noise” from cosmic ray hits or a mix of noise and reflections from bright ice and dust particles released by the comet.

In this lightened up view of the comet, we can the neck area dimly illuminated by sunlight reflecting from the comet’s larger lobe. Small streaks and specks – cosmic ray hits, detector noise or dust and ice or some combination – are visible too. I’ve circled a few of the larger ones. Credit: ESA/Rosetta/NAVCAM