Subaru Telescope Detects the Mid-infrared Emission Band from Complex Organic Molecules in Comet 21P/Giacobini-Zinner

Figure 1: Comets are pristine remnants from the early Solar System. Comets are mostly made of ice and dust, but are also known to be rich in organic materials. If "complex" organic molecules like amino acids are enriched in comets and the meteoroids of cometary origin, the meteor showers might have delivered water and complex organic materials to the ancient Earth. (An artist's illustration. Credit: Kyoto Sangyo University)

Using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru Telescope, astronomers have detected an unidentified infrared emission band from comet 21P/Giacobini-Zinner (hereafter, comet 21P/G-Z) in addition to the thermal emissions from silicate and carbon grains. These unidentified infrared emissions are likely due to complex organic molecules, both aliphatic and aromatic hydrocarbons, contaminated by N- or O-atoms. Considering the properties of the dust and organic molecules, comet 21P/G-Z might have originated from the circumplanetary disk of a giant planet (like Jupiter or Saturn) where it was warmer than the typical comet-forming regions.

Comet 21P/G-Z is a Jupiter-family comet with an orbital period of about 6.6 years and is thought to be the parent body of the October Draconids meteor shower. Compared to other comets, this comet is peculiar in terms of its volatile content (depleted in carbon-chain molecules, NH₂, and highly volatile species) and the properties of its dust grains, and is categorized as "G-Z type" (~6% of surveyed comets). Based on previous studies, it was proposed that comet 21P/G-Z originated in a different region than other comets, but we didn’t have any information about the specific region in the protoplanetary disk. A negative trend of linear polarization in the optical wavelength region is also reported for the dust continuum of comet 21P/G-Z. It is suggested that this negative wavelength gradient of polarization might be explained by a higher content of organic materials in the dust grains of 21P/G-Z. If complex organic molecules like amino acids are enriched in comet 21P/G-Z and in the meteoroids of the October Draconids, this meteor shower might have delivered complex organic materials to the ancient Earth. However, complex high-molecular-weight organic molecules have never been detected clearly in comets, except in comet 67P/Churyumov-Gerasimenko by the in-situ measurements of the Rosetta spacecraft. How much and how complex of organic molecules are contained in comet 21P/G-Z is still an open question.

Figure 2: Comet 21P/Giacobini-Zinner observed in the optical on August 22, 2018

Credit: Michael Jaeger

A team of astronomers from the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA), Kyoto Sangyo University (KSU), National Astronomical Observatory of Japan (NAOJ), and Okayama University of Science (OUS) conducted mid-infrared spectroscopic and imaging observations of comet 21P/G-Z using COMICS on UT July 5, 2005 (when the comet was 1.04 au from the Sun, near its perihelion). The obtained spectrum of comet 21P/G-Z shows emission peaks of crystalline silicate grains, which are usually also seen in many other comets. In addition to these silicate features, the researchers found that the spectrum of comet 21P/G-Z exhibits unidentified infrared emission features, which could be attributed to a mixture of aliphatic and aromatic hydrocarbons (such as polycyclic aromatic hydrocarbons or hydrogenated amorphous carbons contaminated by N- or O-atoms).

Comet 21P/G-Z is enriched in complex organic molecules. The enrichment of complex organic molecules requires a warm temperature or high energetic particle environment around the comet in the early solar nebula. The presence of these complex organic molecules suggests that comet 21P/G-Z originated from a warmer region in the protoplanetary disk than the typical comet-forming region. Considering that the derived mass fraction of crystalline silicates in comet 21P/G-Z is typical of comets, we propose that the comet originated from the circumplanetary disk of a giant planet (like Jupiter or Saturn) where it was warmer than the typical comet-forming region (5–30 au from the Sun) and was suitable for the formation of complex organic molecules. Comets from circumplanetary disks might be enriched in complex organic molecules, similar to comet 21P/G-Z, and may have provided pre-biotic molecules to ancient Earth by direct impact or meteor showers.

Figure 3: Blackbody normalized mid-infrared spectra of comets. The spectrum of comet 21P/G-Z (black filled circles) is different from other comets, and exhibits unidentified infrared emission features. The features at ~8.2 microns, ~8.5 microns, and ~11.2 microns could be attributed to PAHs (or HACs) contaminated by N- or O-atoms, although part of the feature at ~11.2 microns comes from crystalline olivine. The feature at ~9.2 microns might originate from aliphatic hydrocarbons. (Credit: Ootsubo et al.). 

These results were published on November 18, 2019 in Icarus (Ootsubo et al., "Unidentified Infrared Emission Features in Mid-infrared Spectrum of Comet 21P/Giacobini-Zinner"). This research paper is also available as a preprint (Ootsubo et al., arXiv:1910.03485) on arxiv.org. This study is financially supported by MEXT Supported Program for the Strategic Research Foundation at Private Universities, 2014-2018 (No. S1411028). T.O. is supported by JSPS KAKENHI Grants-in-Aid for Scientific Research (C) JP17K05381 and (A) JP19H00725.

Link 

• Subaru Telescope Detects the Mid-infrared Emission Band from Complex Organic Molecules in Comet 21P/Giacobini-Zinner (Press Releases from ISAS/JAXA)

Source: Subaru Telescope

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Active pits on comet

Active pits on comet

Copyright; ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; 

graphic from J-B Vincent et al (2015). Hi-res image

Left: 18 pits have been identified in high-resolution OSIRIS images of Comet 67P/Churyumov–Gerasimenko’s northern hemisphere. The pits are named after the region they are found in, and some of them are active. The context image was taken on 3 August 2014 by the narrow-angle camera from a distance of 285 km; the image resolution is 5.3 m/pixel.  

Middle, top: close-up of the active pit named Seth_01 reveals small jets emanating from the interior walls of the pit. The close-up also shows the complex internal structure of the comet. The image is a section of an OSIRIS wide-angle camera image capture on 20 October 2014 from a distance of 7 km from the comet surface. Seth_01 measures about 220 m across.

Right, top: context image showing fine structure in the comet’s jets as seen from a distance of 28 km from the comet’s surface on 22 November 2014. The image was taken with the OSIRIS wide-angle camera and has a resolution is 2.8 m/pixel. In both images the contrast is deliberately stretched in order to see the details of the activity. The active pits in this study contribute a small fraction of the observed activity.

Left, bottom: how the pits may form through sinkhole collapse. 1. Heat causes subsurface ices to sublimate (blue arrows), forming a cavity (2). When the ceiling becomes too weak to support its own weight, it collapses, creating a deep, circular pit (3, red arrow). Newly exposed material in the pit walls sublimates, accounting for the observed activity (3, blue arrows).

Full story: Comet sinkholes generate jets

Source: ESA

Ice on Comet 67P/Churyumov-Gerasimenko

Ice on Comet 67P/Churyumov-Gerasimenko

Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Hi-Res JPG

Examples of six different bright patches identified on the surface of Comet 67P/Churyumov-Gerasimenko in OSIRIS narrow-angle camera images acquired in September 2014. The insets point to the broad regions in which they were discovered (not to specific locations). In total, 120 bright regions, including clusters of bright features, isolated features and individual boulders, were identified in images acquired during September 2014 when the spacecraft was between 20-50 km from the comet centre.

On the left hand side of the image a boulder with icy patches in Hatmehit (top) a cluster of icy features in Imhotep (middle) and a cluster in Khepry (bottom) is presented; on the right hand side a cluster in Anuket (top), a bright feature in Imhotep (middle) and a cluster close to the Khepry-Imhotep boundary (bottom) is shown.

The false colour images are red-green-blue composites assembled from monochrome images taken at different times and have been stretched and slightly saturated to emphasis the contrasts of colour such that dark terrains appear redder and bright regions appear significantly bluer compared with what the human eye would normally see. This imaging technique allows scientists to determine more about the nature of the material; in this case the bluer colour indicates the presence of ice.

Full story: Exposed water ice detected on comet’s surface

Source: ESA

Rosetta arrives at comet destination

Comet 67P/Churyumov-Gerasimenko by Rosetta’s OSIRIS narrow-angle camera on 3 August from a distance of 285 km. The image resolution is 5.3 metres/pixel. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

After a decade-long journey chasing its target, ESA’s Rosetta has today become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration. 

Comet 67P/Churyumov–Gerasimenko and Rosetta now lie 405 million kilometres from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55 000 kilometres per hour. 

The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany it for over a year as they swing around the Sun and back out towards Jupiter again. 

Comets are considered to be primitive building blocks of the Solar System and may have helped to ‘seed’ Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through a comprehensive,in situstudy of the comet, Rosetta aims to unlock the secrets within. 

 Comet on 3 August 2014

The journey to the comet was not straightforward, however. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids Šteins and Lutetia, obtaining unprecedented views and scientific data on these two objects. 

“After ten years, five months and four days travelling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometres, we are delighted to announce finally ‘we are here’,” says Jean-Jacques Dordain, ESA’s Director General. 

“Europe’s Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start.” 

Today saw the last of a series of ten rendezvous manoeuvres that began in May to adjust Rosetta’s speed and trajectory gradually to match those of the comet. If any of these manoeuvres had failed, the mission would have been lost, and the spacecraft would simply have flown by the comet. 

“Today’s achievement is a result of a huge international endeavour spanning several decades,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration. 

“We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come.”

Comet activity on 2 August 2014

 

6 August 2014 - The comet began to reveal its personality while Rosetta was on its approach. Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet’s ‘coma’ – an extended envelope of gas and dust – became rapidly brighter and then died down again over the course of those six weeks. 

In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter, MIRO, suggested that the comet was emitting water vapour into space at about 300 millilitres per second.

Meanwhile, the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, measured the comet’s average temperature to be about –70ºC, indicating that the surface is predominantly dark and dusty rather than clean and icy. 

Then, stunning images taken from a distance of about 12 000 km began to reveal that the nucleus comprises two distinct segments joined by a ‘neck’, giving it a duck-like appearance. Subsequent images showed more and more detail – the most recent, highest-resolution image was downloaded from the spacecraft earlier today and will be available this afternoon.

“Our first clear views of the comet have given us plenty to think about,” says Matt Taylor, ESA’s Rosetta project scientist.

“Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects.”

Today, Rosetta is just 100 km from the comet’s surface, but it will edge closer still. Over the next six weeks, it will describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then at 50 km. 

At the same time, more of the suite of instruments will provide a detailed scientific study of the comet, scrutinising the surface for a target site for the Philae lander. 

Eventually, Rosetta will attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer. 

“Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land,” says Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager. 

 

Arriving at a comet

 

As many as five possible landing sites will be identified by late August, before the primary site is identified in mid-September. The final timeline for the sequence of events for deploying Philae – currently expected for 11 November – will be confirmed by the middle of October. 

“Over the next few months, in addition to characterising the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet,” says Matt. 

“After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behaviour from close quarters to give us a unique insight and realtime experience of how a comet works as it hurtles around the Sun.” 

Notes for Editors:

 

Rosetta woke up from deep space hibernation at 18:18 GMT on 20 January 2014, nine million kilometres from comet 67P/Churyumov–Gerasimenko. Following wake-up, the orbiter’s 11 science instruments and 10 lander instruments were reactivated and readied for science observations. Ten orbital correction manoeuvres were carried out between 7 May and 6 August, reducing the spacecraft’s velocity with respect to the comet from 775 m/s to 1 m/s, equivalent to walking pace. Each of these manoeuvres was critical: if any had failed, no rendezvous would have been possible. More information about these manoeuvres can be found on the Rosetta blog. 

The latest ‘arrival’ image will be presented in the science session of today’s ‘Rosetta comet rendezvous’ event at ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany, and in parallel will be published online on the ESA Portal. 

About the European Space Agency
 

The European Space Agency (ESA) is Europe’s gateway to space. It is an intergovernmental organisation, created in 1975, with the mission to shape the development of Europe’s space capability and ensure that investment in space delivers benefits to the citizens of Europe and the world. 

ESA has 20 Member States: Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland and the United Kingdom, of whom 18 are Member States of the EU. 

ESA has Cooperation Agreements with eight other Member States of the EU. Canada takes part in some ESA programmes under a Cooperation Agreement. 

ESA is also working with the EU on implementing the Galileo and Copernicus programmes. 

By coordinating the financial and intellectual resources of its members, ESA can undertake programmes and activities far beyond the scope of any single European country. 

ESA develops the launchers, spacecraft and ground facilities needed to keep Europe at the forefront of global space activities. 

Today, it launches satellites for Earth observation, navigation, telecommunications and astronomy, sends probes to the far reaches of the Solar System and cooperates in the human exploration of space. 

For further information, please contact:

ESA Media Relations Office
Tel: + 33 1 53 69 72 99
Email: media@esa.int
 
Markus Bauer
ESA Science and Robotic Exploration Communications Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int

Source: ESA

EPSC2013: Get ready for Rosetta's wake-up call with activity schedule for target comet

Comet 67P/Churyumov-Gerasimenko

Dust Coma

After a journey of almost ten years, the Rosetta mission has just a few months left to wait before beginning its rendezvous with a time capsule. Comet 67P/Churymov-Gerasimenko is a dirty snowball of ice and dust that preserves material from the formation of the Solar System 4.5 billion years ago. During 2014, the European Space Agency’s most ambitious mission to date will both start to orbit the comet’s nucleus and deploy a small laboratory of scientific instruments, Philae, to dock with the comet’s surface. To aid Rosetta in safely achieving its task, an international group of scientists back on Earth are using ground-based telescopes and computer models to understand the behaviour of the comet as it approaches the Sun and begins to form its tail. Their findings have been presented this week at the European Planetary Science Congress (EPSC) 2013 at University College London.

“For two or three orbits now, our community has been observing the comet to determine the shape of the nucleus, the angle at which it spins on its axis and how its activity varies as it orbits the Sun.   All of this information is vital for the planning of Rosetta’s orbit and Philae’s delivery,” said Jessica Agarwal of the Max Planck Institute for Solar System Research (MPS).

“At this meeting, we have discussed everything from the make-up of the surface layer of the nucleus to the dust production rates, size and velocity of the particles emitted, the way the comet interacts with the solar magnetic environment… There are a lot of things we need to know!” added Matt Taylor, ESA’s Project Scientist for the Rosetta Mission.

Jean-Baptiste Vincent (MPS) has used images and modelling to study the development of gas jets as the comet becomes active. “We need to understand the formation and evolution of dust coma structures at all scales: from tiny filaments only visible close to the surface of the nucleus, to large structures extending tens of thousands of kilometres in the coma. Comet 67P appears to behave in a very consistent way, at least over the last two orbits. The southern hemisphere is more active than the northern and there are three major active regions from where gas jets evolve, which can eject dust particles at around 50 kilometres per hour.” 

      

To safeguard the spacecraft during its long, cold journey through deep space, Rosetta was placed into hibernation in 2011. Research by a group led by Colin Snodgrass and Cecilia Tubiana of MPS suggests that 67P will start emitting gas and dust by March 2014, earlier than expected and just two months after the spacecraft receives its wakeup call on Monday 20 January 2014.

The scientists have based their predictions on 31 sets of images showing the comet at different points during its orbit. The images were recorded between 1995 and 2010 with telescopes including the Very Large Telescope (VLT) at the European Southern Observatory (ESO). By subtracting successive images to remove the starry background and making the comet stand out, they were able to study changes in brightness and hence the activity levels of the comet was at different points in its orbit.

"For the first time, we have a meaningful comparison of all data sets so that we can reconstruct the activity of the comet as it moves around the Sun," said Snodgrass. “The results were something of a surprise.”

Scientists had estimated that the comet would start to form is tail at distance of around 450 million kilometres from the Sun, when it would become warm enough for water ice to sublimate. Instead, it became active much further out -- at 650 million kilometres.

"Water will still be frozen solid at that distance from the Sun. Some other gas must be responsible for this earlier activity that we’ve observed," said Tubiana.

IMAGES AND ANIMATIONS

Image of 67P/Churyumov-Gerasimenko acquired in February 2009, processed using a numerical filter. Structures visible in the image are signatures of regions of enhanced activity on the nucleus surface. Credit: J-B Vincent/MPS/GP Tozzi/L Lara/Z-Y Lin.  http://www.europlanet-eu.org/images/stories/epsc2013/rosetta_jets1.jpg

Image acquired between June 2008 and Feburary 2009. The location of the dust coma structures are enhanced by different filtering techniques ((1-3) adaptive Laplace-filtered images, (4) adaptive Laplace-filtered image with the structure geometry indicated by annotations and (5) dashed lines, (6) Larson-Sekanina filtered image). Credit: J-B Vincent/MPS/GP Tozzi/L Lara/Z-Y Lin.  http://www.europlanet-eu.org/images/stories/epsc2013/rosetta_67p-evolution.jpg

Dust coma of 67P at a distance of 187 million kilometres from the Sun, shortly before the comet’s closest approach. Image acquired on 18 Feb. 2009. The image (top left) is presented as processed through various numerical filters to enhance the visibility of the jets. J-B Vincent/MPS/GP Tozzi/L Lara/Z-Y Lin.  http://www.europlanet-eu.org/images/stories/epsc2013/rosetta_dust_coma.jpg

Movie showing modelled dust jets of comet 67P/C-G as they would be observed by the OSIRIS WAC camera on board Rosetta. Credit: J-B Vincent/MPS. http://www.mps.mpg.de/homes/vincent/COSSIM.html

Still from movie showing modelled dust jets of comet 67P/C-G as they would be observed by the OSIRIS WAC camera on board Rosetta. Credit: J-B Vincent/MPS

CONTACTS

Matt Taylor
Rosetta Project Scientist
ESTEC, European Space Agency
Noordwijk, Netherlands
Tel:+31 (0)71 565 8009
mtaylor@rssd.esa.int

Jessica Agarwal
Max-Planck-Institut für Sonnensystemforschung
Katlenburg-Lindau, Germany
agarwal@mps.mpg.de

Jean-Baptiste Vincent
Max-Planck-Institut für Sonnensystemforschung
Katlenburg-Lindau, Germany
vincent@mps.mpg.de

Colin Snodgrass
Max-Planck-Institut für Sonnensystemforschung
Katlenburg-Lindau, Germany
snodgrass@mps.mpg.de

Cecilia Tubiana
Max-Planck-Institut für Sonnensystemforschung
Katlenburg-Lindau, Germany
tubiana@mps.mpg.de

MEDIA CONTACTS

Anita Heward
EPSC 2013 Press Officer
anitaheward@btinternet.com
+44 (0)7756034243

Oli Usher
Communications Manager
MAPS Faculty, UCL
o.usher@ucl.ac.uk
+44 (0)20 7679 7964

NOTES FOR EDITORS

About the European Planetary Science Congress (EPSC)

EPSC is the major European meeting on planetary science. EPSC 2013 is taking place at University College London (UCL) from Sunday 8 September to Friday 13 September 2013. It is the first time that the Congress has been held in the UK. The 2013 programme includes around 75 sessions and workshops. Details of the Congress and a full schedule of EPSC 2013 scientific sessions and events can be found at the official website: http://www.epsc2013.eu/

EPSC 2013 is organised by Europlanet, UCL and Copernicus Meetings and the event is sponsored by the UK Space Agency, UCL, Astrium and the Science and Technology Facilities Council.

To celebrate EPSC coming to London, a ‘Festival of the Planets’ has been organised across the Capital in collaboration with partners including the Baker Street Irregular Astronomers, the Bloomsbury Theatre, the British Astronomical Association, the British Interplanetary Society, the Natural History Museum, the Open University, Queen Mary University of London, the Royal Astronomical Society, Royal Museums Greenwich and University College London. More information about the events can be found at:  http://www.europlanet-eu.org/epsc2013/outreach-activities

Follow #epsc2013 @epsc2013 @europlanetmedia on Twitter

About Europlanet

Europlanet is a network of planetary scientists, whose aim is to bring together the disparate European community so that Europe can play a leading role in space exploration. Europlanet’s activities complement the mission activities of the European Space Agency through field work at planetary-analogue terrains on Earth, laboratory measurements, computer modelling and observations from ground-based telescopes. Founded in 2002 and funded by the European Commission from 2005-2012, Europlanet has evolved into a community-based organisation that will carry on this work and plan for future missions and mission support. www.europlanet-eu.org

About UCL (University College London)

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.

UCL is among the world's top universities, as reflected by its performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.

UCL has nearly 27,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses – UCL Australia and UCL Qatar. Its annual income is more than £800 million.

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