5 landing sites picked for daring comet touchdown

The approximate locations of four of the five landing sites are marked on these OSIRIS narrow-angle camera images taken on August 16 from a distance of about 62 miles (100 km). Click to enlarge. Credit: ESA

Five potential sites have been selected for what will be one of humanity’s most audacious undertakings – landing a spacecraft on a comet. Scientists will command the Rosetta spacecraft to ‘drop’ the washing-machine-sized lander called Philae onto comet 67P/Churyumov-Gerasimenko’s dusty surface on or about November 14.

Craggy crater walls and boulders of all sizes highlight this photo taken of Comet 67P/C-G on August 23, 2014. Credit: ESA

If mission controllers are feeling anxious, it’s no surprise.  Philae must land on the 2.5-mile-wide dirty iceball before heat from the sun makes it hazardous. Compared to a rocky asteroid, a comet’s practically alive with activity. The closer it gets to the sun, the faster its ices vaporize and the more dust the comet releases.

The last thing scientists want is to send the lander into a blizzard of dust and water ice crystals which could pose clear hazards to Philae and its suite of 10 instruments.

During the maneuver,  Rosetta and 67P/C-G will be 280 million miles (450 million km) from the sun, far enough (and cold enough) that the rate of vaporization and ‘geysering’ of water vapor from cracks in the comet’s surface will be low.

Model of a typical coma like 67P/C-G. Dust-laden ice boiled from the comet’s nucleus by the sun forms a head or coma and typically two tails, one of dust, which lags somewhat behind the comet, and one of fluorescing gases called the gas or ion tail which points directly opposite the sun. Credit: ESO / E. Slawik

An early landing also means scientists get a first-hand look at the surface ices and chemistry before solar heating changes the landscape, converting dirty ice into the vapor and dust that will expand the comet’s coma and flow into a tail. Scientists would like to sample and observe these goodies in as pristine a state as possible.

Comets, which have remained frozen in the far corners of the solar system since shortly after their formation, bear news from a distant and ancient era. Studying one in situ is like following a proverbial trail of breadcrumbs back to its beginning.

The five landing sites A, B, C, I and J. Credit: ESA

“The process of selecting a landing site is extremely complex and dynamic; as we get closer to the comet, we will see more and more details, which will influence the final decision on where and when we can land,” said Fred Jansen, Rosetta’s mission manager from the European Space Agency’s Science and Technology Center.

Rosetta’s lander will obtain the first images taken from a comet’s surface and will provide comprehensive analysis of the comet’s possible primordial composition by drilling into the surface. The tool can penetrate up to 10 inches deep.

Five candidate sites were identified on Comet 67P/Churyumov-Gerasimenko during the Landing Site Selection Group meeting held August 23-24, 2014. Credit: ESA

From an original 10 sites, lettered ‘A’ through ‘J’, the search has been narrowed to five. Three sites (B, I and J) are located on the smaller of the two lobes of the comet and two sites (A and C) are located on the larger lobe. Choosing the right one is a complex process based on several considerations:

* We need a location with at least six hours of daylight during the comet’s 12.4 hour rotation, both for good illumination of the surface for detailed photography and to provide power to Philae’s batteries via solar cells. But not too much sunlight, otherwise the probe could overheat.

* Flat terrain with as few boulders, cliffs and crevasses as possible for safety’s sake. While the boulders in the photos cry out for exploration, they’re too hazardous to approach. Mission controllers prefer safe and (somewhat) boring. Better than than losing the craft.

* An area where the lander can maintain regular communications with the Rosetta mother ship during its descent to the surface and after landing.

Artist’s view of the lander Philae touching down on the dusty-icy surface of comet 67P/C-G. Credit: ESA

“The five chosen sites offer us the best chance to land and study the composition, internal structure and activity of the comet with the ten lander experiments,” said Jean-Pierre Bibring, one of the lead lander scientists.

Uncertainties in navigating the orbiter close to the comet mean that it’s only possible to specify any given landing zone in terms of an ellipse about four-tenths of a square mile (one square km). By September 14, the sites will be accessed and ranked and the best will be selected along with a backup.

For more on site selection, including profiles of each of the five, click HERE.


Quiet aurora tonight Aug. 27-28

A lquiet auroral arc topped by a faint pink band glowed softly in the northern sky tonight at 10:30 p.m.. The bright star at right is Capella in the constellation Auriga. Credit: Bob King

After Wednesday morning’s fine display, the current wave of magnetic activity is subsiding but not without leaving a tasty leftover. A low, quiet arc has hovered over the northern horizon all evening. Maybe it will take off again as the aurora did this morning, but the forecast indicates a gradual decline in activity overnight.

Map showing the extent of the auroral oval early this Thursday morning August 28. The arc in the photo above is the edge of the large, permanent oval of aurora centered on Earth’s geomagnetic pole. In this map, which is based on satellite data, you can see that the edge of the oval lies right at Minnesota’s northern border. Click to see the current oval. Credit: NOAA

If you live in in the northern U.S. away from city lights and enjoy the subtle side of nature, you’ll find tonight’s aurora suitable for contemplation.

Beautiful rays of aurora dapple the dawn sky

At 4:45 a.m. CDT this morning (Aug. 27) spectacular rays erupted from a low, bright green arc and paraded across the northern sky. Credit: Bob King

Maybe it’s because of the name aurora, which means ‘dawn’, but that’s exactly when the northern lights put on one great show this morning. With clouds constantly a bother this late summer, many of us have been thwarted in viewing all manner of conjunctions, comets and moonrises. Not this morning. I was determined to see Comet Oukaimeden near Orion just before dawn. And that’s exactly how I happened to be up to catch a surprisingly fine aurora.

A striking green arc perforated by many needle-like rays. Credit: Bob King

One of the keys to maximizing enjoyment of the aurora is to have a place you can get to with a low northern horizon. At least from mid-northern latitudes, lots of activity often occurs very low in the northern sky.

High speed electrons from the sun spiral down individual magnetic field lines in Earth’s magnetic bubble called the magnetosphere to create multiple parallel rays when they strike oxygen and nitrogen atoms in the upper atmosphere. Credit: Bob King

We were already primed for northern lights because of the NOAA space weather forecast, so when I looked out the window at 4 a.m., there they were.

I jumped in the car and sped to a country road not far from home. Arriving around 4:30 a.m. several pale green arcs snaked across the north, and within minutes they erupted with massive parallel rays. To the eye, the tall rays were colorless, but they loved the time exposure afforded them by the camera.

The pictures were taken using a 17mm lens at f/2.8, ISO 800 and exposure times around 15 seconds.

While I did get to see my comet in the nick of time, the northern lights made it more than worth my while. I hope you got to see them, too.

Jupiter (lower left next to the star Delta in Cancer) and Orion (upper right) sparkle in the dawn sky over Duluth, Minn. Wednesday morning. Credit: Bob King

The display continued deep into twilight and no doubt carried into darker skies farther west of my location. There’s still a possibility for minor auroras early tonight. I hope so. Two 4 a.m. stints in a row would kill me.

Aurora alert tonight Aug. 26-27 – updated

Painting by Etienne Trouvelot of a spectacular aurora observed on March 1, 1872.

North Americans skywatchers missed the last week’s aurora by the skin of our teeth. By nightfall, the whole display, enjoyed earlier from Scandinavia, went to heck. Maybe tonight will be different.

For the past few days NOAA space weather forecasters have been predicting a minor geomagnetic storm (Kp = 5) from incoming blasts of solar particles called coronal mass ejections that departed the sun on Aug. 22. ‘Minor’ often translates to an auroral arc (sometimes two) low in the northern sky pierced by occasional rays.

No great shakes, but if you live in the northern U.S. and southern Canada, be aware you might be visited by the green ghost. Activity should commence after sunset and peak between 1-4 a.m. CDT tomorrow morning Aug. 27.

Maybe we’ll get burned again. But you wouldn’t want me to keep this all to myself, would you?

* UPDATE 5:30 a.m. CDT: Big auroras lit up the northern sky this morning. Lots of arcs and long rays seen from Duluth, Minn. If you live in the northern third of the U.S. and it’s still dark, go out for a look.

What do stars sound like? Listen in

Singing stars – how astronomers turn starlight into sound

Fluttering, sizzling hiss, alien music. These are the sounds the stars make.

Animation showing an extrasolar planet passing in front of a star, causing its light to dim. By studying the light curve astronomers can determine planets sizes and other details. Credit: Transits of Extrasolar Planets Network

NASA’s Kepler space telescope observed 150,000 stars looking for telltale dips in their light that would indicate a planet cycling in front of a star. Knowing the distance and diameter of the star and the length of time the passing object dimmed the star’s light, astronomers can determine the planet’s size and mass.

Using the ‘transit method’, scientists have mined Kepler data to uncover 4,229 candidate extra-solar planets 981 of which are confirmed. Finding planets, which are typically much smaller than their host stars, is no easy business. Any noise in the data can hide the weak change in light caused by an orbiting object. But sometimes the noise itself can yield useful new information.

Solar granules, each about 900 miles across (1,500 km), bubble up from below, cool and sink back down. A typical granule lasts 8-20 minutes.

Star brightness is not constant, especially if you look closely over short intervals of time. Starspots (stellar versions of sunspots), flares and even the bubbles of heated gas called rising from the star’s hotter interior to the surface cause subtle changes in its brightness.

The last is called granulation and gives the sun’s surface a grainy or cellular texture. Plumes of rising gas are hot and bright but soon darken, cool and sink back down only to be re-heated and rise again. Seen in sped-up time, they cause a star to flicker.

In a recent paper that appeared in Nature, Fabien Bastienne of Vanderbilt University in Nashville and team analyzed the noise from the Kepler data and discovered that brightness changes under 8 hours directly relate to a sun-like star’s surface gravity. Smaller stars with higher surface gravity have less granulation than big ones with less gravity.

Turning sound into light and back again. How it’s done

Now here’s the beautiful thing. You can take these slight but continuous changes in a star’s brightness and convert them into sound. The accompanying video shows how an audio signal from a pocket radio, for instance, can be turned into light and then transformed back into sound using little more than an LED and solar cell.

With Kepler, the brightness variations were sped up and converted into sound, giving stars a ‘voice’. Starspots create the fluttery sounds, granulation the hiss. Small stars flutter a lot; red giants are big hissers.

Being a dwarf star in the grand scheme of things, the sun flutters much like the dwarf star in the video. To my ear, it sounds ominous, like background music for a dystopian sci-fi flick. Rotation speed also causes variations in sound.

Scientists use these curious hisses and flutters to help nail down a star’s size, mass and stage of its evolution. The more precisely we know those details, the more precisely we also know a transiting planet’s size and mass.

Motto of the story: Don’t throw away your garbage. There’s valuable data in there!

Sharing stars and making comets at Northwoods Starfest

7-year-old Madeline Chopp of Green Bay, Wis. laughs as she peeks into her dad Brian’s scope Friday evening. Credit: Bob King

Every August, the Chippewa Valley Astronomical Society (CVAS) holds a two-night star party at Hobbs Observatory near Fall Creek, Wisconsin. Tucked in a patch of forest between cornfields, Hobbs’ dark skies entice amateur astronomers across the Midwest to get their fill of nebulae, galaxies and comets otherwise lost in the glow of city lights.

Guest speakers, good food and great conversation liven up the mix and always make for an immensely satisfying weekend. Whenever you spend time with those who share your passion, you can’t help but come away energized.

Mike Brown, CVAS president, assembles his self-built, computer controlled 24-inch Dobsonian reflector Friday afternoon. He uses an iPad and tracking software to slew quickly to any object in the sky with a tap on the keypad. The club’s radio dish is seen in the background. Credit: Bob King

I attended Friday and set up my 15-inch (37-cm) reflector on the sandy flats among dozens of other telescopes. All types were represented – small to medium refractors, binoculars on homemade mounts and reflecting telescopes with mirrors up to 24-inches (61-cm) across. The club even operates a radio telescope.

Friday night I spoke on comets and the European Space Agency’s Rosetta Mission. Judging from the audience reaction, the ESA needs to fire up that high-resolution OSIRIS camera and shoot a lot more close-up, 3-D views of comet 67P C-G. Everyone loved the in-your-face realism of seeing the comet’s alien landscape in three dimensions.

Comet Hobbs is born during a comet-making demonstration at Northwoods Starfest Friday night. Notice the little ‘geysers’ of outgassing. Credit: Greg Furtman

After the talk, we gathered round a table to make a much smaller version of Rosetta’s comet in a bucket. I added water (comets are mostly water), molasses (sugar as organic molecules), dirt (dust embedded in cometary ices), ammonia, alcohol (methanol has been found in comets) and powdered charcoal (more carbon and to create a realistic black-coated ice ball) in a plastic bag and mixed it all together with a wooden spoon.

A real comet! 30-second time exposure of Comet Jacques at ISO 6400 with a 400 mm f/5.6 lens. Credit: Bob King

Then it was time for the crucial ingredient: dry ice. Three gloved handfuls of smoky white pellets went into the cosmic ‘stone soup’, the bag was closed and the mix crushed together into a well-packed snowball. Peeling back the plastic, a delightful mini-comet emerged replete with jets of vaporizing gas geysering from small cracks in the carbon-coated surface.

All new comets have names and this would be no exception, so we settled on Comet Hobbs, or more formally, C/2014 Q1 Hobbs. Sadly, this comet exists no more. A final observation revealed the fist-sized object had morphed into a petite puddle.

Mike Brown’s 24-inch reflector had a steady stream of customers at Northwoods Starfest this weekend. Mike treated folks to views of the globular cluster M13, Comet Jacques, the planetary nebula NGC 6210 and many others. Credit: Bob King

The night began overcast but soon turned partly cloudy. We had fun observing a real comet – C/2014 E2 Jacques – as it inched its way across Cassiopeia. The bright coma was very easy to see in 50mm binoculars. Mike Brown, CVAS president, generously shared time with anyone who wanted to see anything in his 24-inch reflector. In a big scope like that, even tiny objects like the planetary nebula NGC 6210 in Hercules invite many minutes of exploration.

Jon Dannehy of Arcadia, Wis. and Eric Norland of Duluth, Minn. have fun while standing around Eric’s homemade telescope Friday. Credit: Bob King

Another CVAS member, Greg Furtman, treated us to wide-field views of the comet and Veil Nebula in Cygnus with his homemade short-focus 6-inch (15-cm) reflector. At midnight, we welcomed the opportunity to rest our legs and recharge with the traditional ‘midnight snack’ in the campground’s dining cabin. Besides fruits, juices and chips, someone broke out a box of ice cream sandwiches. Deluxe!

Although I had to leave Saturday for work, Day 2 featured additional speakers, a swap meet, a dinner BBQ and l’m sure lots more great laughs and discussion. Nothing like hanging out with a bunch of crazy astronomers.

Comet Jacques zips through Cassiopeia – catch it this week!

Wow! Comet Jacques cuts between the Heart (right) and Soul Nebulae in Cassiopeia on August 19th. These clouds of fluorescing hydrogen gas are also known as IC 1845 and IC 1848. Click to enlarge. Credit: Michael Jaeger

Not many clear nights in my town lately – we had exactly one this week. I’m grateful because we finally got a peek at Comet Jacques, which recently climbed out of the morning sky into the familiar ‘W’ of Cassiopeia. That’s good news because it means you can spot Jacques now at nightfall instead of dawn.

Comet C/2014 E2 Jacques cruises through the W of Cassiopeia the next few nights. The view shows the sky facing northeast at nightfall in late August around 9:30 p.m. Click for a detailed map showing the comet’s position nightly through early September. Stellarium

Through a pair of 8x40s two nights ago, the comet was a faint, fuzzy patch next to the lower left star of the ‘W’. Jacques is currently making its closest approach to Earth; on August 28 it will pass us at 52.4 million miles (84 million km). While that’s a fair distance, its relative proximity causes it to move relatively quickly across the sky. Currently the comet’s puffing along at a couple degrees a day. Those with telescopes can easily see it shift position against the background stars within an hour.

Small telescopes will reveal Jacques’ largish diffuse coma and bright core. The core is where the icy nucleus hides behind a shroud of dust and gas vaporized by the heat of the sun. No one knows its exact size – thanks to all that dust – but it’s probably a mile or two across, typical of many comets.

36 pictures of Comet Jacques taken on August 17th combined into a movie show its motion and changes in its gas tail caused by interaction with the solar wind, a stream of subatomic particles blowing from the sun. Click to enlarge. Credit: Gianluca Masi

Larger scopes 8-inches and up will show varying amounts of the comet’s long, faint ion or gas tail that points to the southwest and a hint of green color in the coma from fluorescing gases.

Even though Jacques has been traveling away from the sun since closest approach on July 2, its brightness will remain nearly constant at magnitude +7 through early September because it’s ‘in the neighborhood’.

Try to spot it the next clear night. From a dark sky, the comet’s easy in binoculars and any telescope will show it. Moonlight won’t get in the way until early next month.

Know your planet and eat it too

A Jupiter cake made by Rhiannon, who writes the Cakecrumbs blog, shows the giant planet’s layered atmosphere and interior in a fun and realistic way. Click for recipe. Credit: Rhiannon

I had no idea Jupiter had a mud cake core surrounded by almond butter cake and enveloped with a blue-tinted vanilla Madeira sponge. Topped off with vanilla buttercream and marshmallow icing, it’s the first planet that’s ever made my mouth water.

The Great Red Spot inspired Rhiannon to pick Jupiter for her cake. The iconic feature is instantly recognizable. She used ivory, brown and maroon edible ink to dry brush the Spot and other atmospheric features like belts and vortices on the outer layer of marshmallow fondant (icing). Credit: Rhiannon /cakecrumbs.me

Rhiannon, who writes the Cakecrumbs blog, had two passions as a child, animals and the solar system. A self-taught cook and cake decorator, she recently created what she calls her “Jupiter Structural Layer Cake” based on current knowledge of the planet’s atmosphere and interior.

Why Jupiter? It wouldn’t surprise you to know that the Great Red Spot – that huge storm more than twice the size of Earth that’s been whirling around up there the past few hundred years – has always been one of her favorite outer space personalities.

Jupiter concentric layer cake tutorial

Painting on the Red Spot and many other atmospheric details, all based on photos of the planet over many years, took 8 hours, just 2 hours shy of one complete rotation of the real Jupiter. That’s dedication.

You’ll have to watch the video to appreciate the details (three baking steps were required), but to create the sphere, she joined two cake hemispheres with buttercream.

The non-cake Jupiter spans nearly 87,000 miles across and is striped with jet-stream like belts of ammonia ice clouds. Earth is shown for comparison. Credit: NASA

Rhiannon cautions that her cake is “totally not to scale”, but she’s got the details down. Jupiter’s marshmallow cream atmosphere is mostly hydrogen and helium with clouds made of ammonia ice and even water ice further down. All those lovely yellows, reds and oranges so lovingly applied with tiny brushstrokes of food coloring are likely trace amounts of compounds of sulfur, carbon and phosphorus in real life.

Below the clouds, Jupiter just gets weird. Its atmosphere reaches down for thousands of miles. In December 1995, NASA’s Galileo spacecraft released an Entry Probe toward the planet. As the craft descended into the maelstrom of Jovian clouds, it transmitted data back to the orbiter for just 58 minutes. At a depth of 373 miles (600 km), transmissions stopped as the machine was presumably crushed by the extreme atmospheric pressure. Pressures at the base of Jupiter’s atmosphere are 4 million times what we experience on Earth.

Cutaway showing both the cloudtops and the interior of Jupiter. About 75% of the planet’s weight is taken up by fluid metallic hydrogen. Jupiter’s composition is very similar to the sun’s, and like the sun, it’s very hot in the center, but not hot enough to ignite hydrogen and burn as a star.

It only gets more intense as you approach the core. At a certain depth, airy hydrogen is compressed by the vast amount of material above it into liquid molecular hydrogen (the blue cake layer). Below that we arrive at a truly exotic form of matter, liquid metallic hydrogen (white cake).

Under the extreme pressures and heat near the core, ordinary hydrogen gets squeezed so tightly, its electrons depart and move about just like they do in metals. And just as metals conduct electricity, so too this bizarre hydrogen cousin. If you could somehow touch it – impossible because it can’t be created on Earth – it would resemble liquid mercury.

Don’t care for Jupiter? How about a slice of Earth? This is one of Rhiannon’s earlier cakes. The slice shows the crust, mantle (red), outer core (yellow) and inner core. Credit: Rhiannon / cakecrumbs.me

Jupiter’s intense magnetic field is thought to arise from the rapid spinning of this electric liquid. Deeper down, we meet a putative core of rock (mud cake), something like the Earth in composition, but 10-15 times more massive.

Have you had enough cake yet?


Brief aurora Weds. Aug. 20-21 – maybe more overnight?

A low arc and dim green rays were topped by a red border in this photo taken around 11 p.m. CDT Wednesday night Aug. 20. Details: ISO 3200, f/2.8, 20mm lens. Credit: Bob King

Scandinavians were the lucky ones yesterday when auroras broke out during their nighttime. Here in the U.S. it was still afternoon. Auroras are mighty scarce in sunshine.

Tonight to my surprise, we had a brief display around 11 p.m. CDT.  An arc rose above Boulder Lake north of Duluth, Minn., where a group of naturalists and I spent the night at the telescope under a starry sky. At the sight of a few needle-thin rays, one in our group jumped in a canoe and paddled out into the lake for a better view.

More rays taken a few minutes after the first photo. The display was fairly quiet and reached to about 10 degrees above the northern horizon. Credit: Bob King

Not 15 minutes after it began, the arc and rays faded away, leaving only a faint, diffuse glow until fog settled in around midnight. The Kp index rose slightly during the evening, and the ACE satellite plot has shown a southward pointing Bz or solar magnetic field in Earth’s vicinity for many hours. This is often a good indicator of auroral activity on the way.

The show was subtle but no one was disappointed. Auroras are always welcome around here.

Aurora alert tonight Aug. 19-20 for northern U.S.

“Unbelievable,” says Reid Wiseman on seeing a spectacular auroral display from a window on the International Space Station this evening. This photo was tweeted out at 6 p.m. CDT. Credit: NASA/Reid Wiseman

The astronauts are seeing it from the space station. You and I just might too. A G2 moderate auroral storm kicked up this afternoon and early evening, and according to NOAA space weather experts, is expected to continue into the night.

Another shot of the aurora from orbit. “Never in my wildest dreams did I imagine this,” said Wiseman.

A coronal mass ejection (CME) caused by a filament or plume of hydrogen gas ejected a few days ago caused the sudden surge. The Kp index, a reliable indicator of magnetic activity in Earth’s upper atmosphere hit 6 earlier this evening. Should it ‘stick’ there, skywatchers in Canada and across the northern U.S. stand a good chance of seeing auroras tonight. Look to the north at the onset of night. I’ll keep you posted.

* Update 11 p.m. CDT: The Kp has plummeted to 2! That’s not good. It’s always possible that activity will shoot up again overnight. If you’re out tonight, take a look before going to bed.