Rosetta’s Comet Meets Charlie Brown’s “Pig-Pen”

Anyone who’s ever read a Charlie Brown comic strip knows “Pig-Pen”, the lovable boy who walks around in a constant cloud of his own dirt and dust. Every time he sighs, dust rises in a little cloud around him. Why bother to bathe? There’s dignity in debris, which “Pig-Pen refers to as the “dust of countless ages”.  Comets shuffle around the Sun surrounded by a similar cloud of grime that’s as old as the Solar System itself.

Dust and gases released by the comet are so much fainter than sunlight reflected from the nucleus, they require special processing to see clearly. In this photo, many of the small, irregular specks may be cometary dust grains captured in a 4.3 second exposure. Credit:
Dust and gases released by the comet reflect so little light compared to the nucleus they require special processing to see clearly. In this photo, many of the small, irregular specks may be cometary dust grains captured in the 4.3 second exposure. Credit: ESA/Rosetta/NAVCAM

You’ve probably noticed little flecks and streaks in photos returned by the Rosetta spacecraft in the blackness of space surrounding comet 67P/Churyumov-Gerasimenko. After a recent year-end break, the Rosetta team has returned with new updates on the comet including a series of four images recently released as a mosaic. The pictures were processed to highlight surface features; the space around the nucleus is black in comparison. But if we take a closer look at what first appears void, we soon discover it’s not empty at all.

In photos taken January 3rd, the writer of ESA’s Rosetta blog notes that “some of the streaks and specks seen around the nucleus will likely be dust grains ejected from the comet, captured in the 4.3 second exposure time.”

At right is a streak that could either be a larger, fast-moving dust particle that trailed during the exposure or perhaps a cosmic ray hit. Credit:
At right is a streak that could either be a larger, fast-moving dust particle that trailed during the exposure or perhaps a cosmic ray hit. Credit: ESA/Rosetta/NAVCAM

Using an image-editing tool like Photoshop, we can hold back the glare of the nucleus and “open up” the shadows around the comet. Jets of dust released by vaporizing ice are the most obvious features to emerge. The soft, low-contrast plumes plow into the vacuum around the nucleus wrapping it in a silky cocoon of gas and dust – a tenuous atmosphere that reflects sunlight far more weakly than the comet itself.

The complete mosaic image of the comet taken on January 3rd and processed, like most of ESA's comet images, to highlight surface features. Credit: Rosetta/
The mosaic image of the comet taken on January 3rd and processed, like most of ESA’s comet images, to highlight surface features. Credit: ESA/Rosetta/NAVCAM

While staring at dust spots may not produce the same magical feelings as watching a sunrise, it’s fascinating nonetheless to contemplate what we’re seeing. If you’ve been struck by the beauty of a comet’s meteor-like head trailing a wispy tail, you’re looking at what countless individual grains of dust can do when sculpted by the master hand of the Sun. Perusing images of 67P, we see the process in its infancy as individual grains and small clots are released into space to be fashioned into something grander.

Image of the first dust grain captured by MIDAS. Credit:
Image of the first dust grain (center) captured by MIDAS. The bar at top left is 0.01 mm wide. Credit: Courtesy Mark Bentley

Rosetta’s Micro-Imaging Dust Analysis System or MIDAS measures the rate at which dust sweeps past the spacecraft and its size distribution. MIDAS catches dust grains by exposing a sticky target surface into space and waiting for a mote to drift by. It snatched its first one last November – a larger than expected mote measuring about 1/100 of a millimeter across with a complex shape and fluffy texture.

COSIMA catches first dust grains. Left: an image of the target plate (measuring 1 cm by 1 cm) on which the grains were collected; right: a section of the plate showing the state on 17 August (top) when no dust grains were visible and 24 August (bottom) when some large dust grains were detected. The plate is illuminated from the right by LEDs and the length of the shadows is proportional to the height of the dust grains. The resolution of the image is 14 microns per pixel. Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
COSIMA’s first dust grains. Left: an image of the target plate (measuring 1 cm by 1 cm) on which the grains were collected; right: a section of the plate showing it on August 17th (top) when no dust grains were visible and 24 August 24th (bottom) when two large dust grains were detected. The plate is illuminated from the right by LEDs, and the length of the shadows is proportional to the height of the dust grains.
Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/
BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

Analysis of the composition of another dust grain named “Boris” made by the COSIMA instrument has identified sodium and magnesium. Magnesium is no surprise as 95% of known minerals observed in comets resemble olivine and pyroxenes, common in meteorites and in the upper mantle of the Earth. Sodium has also been seen before in comas and tails, and originates in dust grains, but its mineral source remains uncertain.

As we might study the makeup of the dust Pig-Pen leaves in his wake to identify traces of earthly dirt, micro-organisms, pollen, pollution, and even recent volcanic eruptions, so we examine each mote that sprays Rosetta’s way, looking for clues to the origin of the planets and Solar System.

Rosetta’s Cloudy Comet Shroud Spotted From The Ground, While Spacecraft Picks Up Dust Grains

This picture shows it is possible to look at Rosetta’s comet from Earth, but what a lot of work it requires! The picture you see above is a composite of 40 separate images taken by the Very Large Telescope (removing the background stars).

Despite the fact that Rosetta is right next to Comet 67P/Churyumov–Gerasimenko, ground-based observatories are still useful because they provide the “big picture” on what the comet looks like and how it is behaving. It’s an observational challenge, however, as the comet is still more than 500 million kilometers (310 million miles) from the Sun and hard to see.

On top of that, the European Space Agency says the comet is sitting in a spot in the sky where it is difficult to see it generally, as the Milky Way’s prominent starry band is just behind. But what can be seen is spectacular.

“Although faint, the comet is clearly active, revealing a dusty coma extending at least 19 000 km [11,800 miles] from the nucleus,” ESA stated. “The comet’s dusty veil is not symmetrical as the dust is swept away from the Sun – located beyond the lower-right corner of the image – to begin forming a tail.”

And that dust is beginning to show up in Rosetta’s grain collector, as you can see below!

Rosetta's dust collector, Cometary Secondary Ion Mass Analyser (COSIMA), collected its first grains from Comet 67P/Churyumov–Gerasimenko in August 2014. This image shows before and after images of the collection. Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
Rosetta’s dust collector, Cometary Secondary Ion Mass Analyser (COSIMA), collected its first grains from Comet 67P/Churyumov–Gerasimenko in August 2014. This image shows before and after images of the collection. Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/
BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

Rosetta’s Cometary Secondary Ion Mass Analyser (COSIMA) picked up several dust grains in August, which you can see in the image, and are now looking at the target plate more closely to figure out more about the dust grains.

“Some will be selected for further analysis: the target plate will be moved to place each chosen grain under an ion gun which will then ablate the grain layer by layer. The material is then analyzed in a secondary ion mass spectrometer to determine its composition,” ESA stated.

All of these results were presented today (Sept. 8) at the European Planetary Science Congress 2014.

Coma Dust Collection Science starts for Rosetta at Comet 67P/Churyumov-Gerasimenko

With the historic arrival of the European Space Agency’s (ESA) Rosetta spacecraft at destination Comet 67P/Churyumov-Gerasimenko flawlessly accomplished on August 6, 2014 after a decade long journey, ground breaking up close science at this bizarre world has begun while the team diligently and simultaneously searches for a landing site for the attached Philae comet lander.

Rosetta started collecting cometary dust from the coma encircling the comet’s nucleus with the onboard COSIMA instrument on Sunday, August 10, 2014 as the spacecraft orbits around and ahead of the icy wanderer from a distance of approximately 100 kilometers (62 miles). See coma image below.

Hopes are high that unprecedented science discoveries await at this alien world described as a “Scientific Disneyland,” by Mark McCaughrean, senior scientific adviser to ESA’s Science Directorate, during ESA’s live arrival day webcast. “It’s just astonishing.”

COSIMA stands for Cometary Secondary Ion Mass Analyser and is one of Rosetta’s suite of 11 state-of-the-art science instruments with a combined mass of 165 kg.

Its purpose is to conduct the first “in situ” analysis of the grains of dust particles emitted from the comets nucleus and determine their physical and chemical characteristics, including whether they are organic or inorganic – in essence what is cometary dust material made of and how it differs from the surface composition.

COSIMA will collect the coma dust using 24 specially designed ‘target holders’ – the first of which was opened to study the comets environment on Aug. 10. Since the comet is not especially active right now, the team plans to keep the target holder open for at least a month and check the progress of any particle collections on a weekly basis.

COSISCOPE image of the first target taken on 19 July 2014 (before the exposure, on 10 August, for cometary dust collection). The 1x1 cm target consists of a gold plate covered with a thin layer (30 µm) of gold nanoparticles (“gold black”). Illumination is by two LEDs, from the right side in this case. The bright dots on the vertical strip on the right side are used for target identification and for defining the coordinate system. Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
COSISCOPE image of the first target taken on 19 July 2014 (before the exposure, on 10 August, for cometary dust collection). The 1×1 cm target consists of a gold plate covered with a thin layer (30 µm) of gold nanoparticles (“gold black”). Illumination is by two LEDs, from the right side in this case. The bright dots on the vertical strip on the right side are used for target identification and for defining the coordinate system. Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

In fact the team says the coma environment “is still comparable to a high-quality cleanroom”at this time.

But everyone expects that to change radically as Rosetta continues escorting Comet 67P as it loops around the sun, getting closer and warming the surface every day and until reaching perihelion in August 2015.

COSIMA is managed by the Max Planck Institute for Solar System Research (Max-Planck-Institut für Sonnensystemforschung ) in Katlenburg-Lindau, Germany, with Principal Investigator Martin Hilchenbach.

There are also substantial contributions from the Institut d’Astrophysique Spatiale in France, Finnish Meteorological Institute, Osterreichisches Forschungszentrum Seibersdorf and more.

The target holders measure about one square centimeter and were developed by the Universität der Bundeswehr in Germany.

Each of these targets measures one square centimeter and is comprised of a gold plate covered with a thin 30 µm layer of gold nanoparticles (“gold black”) which the team says should “decelerate and capture cometary dust particles impacting with velocities of ~100 m/s.”

The target will be illuminated by a pair of LED’s to find the dust particles. The particles will be analyzed by COSIMA’s built in mass spectrometer after being located on the target holder by the French supplied COSISCOPE microscopic camera and ionized by a beam of indium ions.

Photo of the COSIMA (Cometary Secondary Ion Mass Analyser) instrument on Rosetta.  Credit: Max Planck Institute for Solar System Research/ESA
Photo of the COSIMA (Cometary Secondary Ion Mass Analyser) instrument on Rosetta. Credit: Max Planck Institute for Solar System Research/ESA

The team expects any grains found on the first target to be analyzed by mid-September 2014.

“COSIMA uses the method of Secondary Ion Mass Spectrometry. They will be fired at with a beam of Indium ions. This will spark individual ions (we say secondary ions) from their surfaces, which will then be analysed with COSIMA’s mass spectrometer,” according to a description from the COSIMA team.

The mass spec has the capability to analyze the elemental composition in an atomic mass range of 1 to 4000 atomic mass units, determine isotopic abundances of some key elements, characterize organic components and functional groups, and conduct mineralic and petrographic characterization of the inorganic phases, all of which will inform as as never before about solar system chemistry.

Comets are leftover remnants from the formation of the solar system. Scientists believe they delivered a vast quantity of water to Earth. They may have also seeded Earth with organic molecules – the building blocks of life as we know it.

Any finding of organic molecules and their identification by COSIMA will be a major discovery for Rosetta and ESA and inform us about the origin of life on Earth.

Data obtained so far from Rosetta’s VIRTIS instrument indicates the comets surface is too hot to be covered in ice and must instead have a dark, dusty crust.

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.

Ken Kremer

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Read my Rosetta series here:

What’s Ahead for Rosetta – ‘Finding a Landing Strip’ on Bizarre Comet 67P/Churyumov-Gerasimenko

Rosetta Arrives at ‘Scientific Disneyland’ for Ambitious Study of Comet 67P/Churyumov-Gerasimenko after 10 Year Voyage

Rosetta on Final Approach to Historic Comet Rendezvous – Watch Live Here

Rosetta Probe Swoops Closer to Comet Destination than ISS is to Earth and Reveals Exquisite Views

Rosetta Orbiter less than 500 Kilometers from Comet 67P Following Penultimate Trajectory Burn

Rosetta Closing in on Comet 67P/Churyumov-Gerasimenko after Decade Long Chase

ESA’s Rosetta Spacecraft nears final approach to Comet 67P/Churyumov-Gerasimenko in late July 2014. This collage of imagery from Rosetta combines Navcam camera images at right taken nearing final approach from July 25 (3000 km distant) to July 31, 2014 (1327 km distant), with OSIRIS wide angle camera image at left of comet’s expanding coma cloud on July 25. Images to scale and contrast enhanced to show further detail. Credit: ESA/Rosetta/NAVCAM/OSIRIS/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA   Collage/Processing: Marco Di Lorenzo/Ken Kremer
ESA’s Rosetta Spacecraft nears final approach to Comet 67P/Churyumov-Gerasimenko in late July 2014. This collage of imagery from Rosetta combines Navcam camera images at right taken nearing final approach from July 25 (3000 km distant) to July 31, 2014 (1327 km distant), with OSIRIS wide angle camera image at left of comet’s expanding coma cloud on July 25. Images to scale and contrast enhanced to show further detail. Credit: ESA/Rosetta/NAVCAM/OSIRIS/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA Collage/Processing: Marco Di Lorenzo/Ken Kremer