Churyumov-Gerasimenko

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67P / Churyumov-Gerasimenko [i]
Comet 67P on 19 September 2014 NavCam mosaic.jpg
Comet from the spacecraft Rosetta seen from
Properties of the orbit ( animation )
Epoch:  November 20, 2014 ( JD 2,456,981.5)
Orbit type short-term
Numerical eccentricity 0.6410
Perihelion 1.2432 AU
Aphelion 5.6824 AU
Major semi-axis 3.4628 AU
Sidereal period 6.44 a
Inclination of the orbit plane 7.0402 °
Perihelion August 13, 2015
Orbital velocity in the perihelion 33.51 km / s
Physical properties of the core
Dimensions approx. 4 km × 3.5 km × 3.5 km
Dimensions ≈ 10 13 kg
Medium density 0.533 g / cm³
Rotation period 12.7614 h
history
Explorer Klym Churyumov ,

Svetlana Gerasimenko

Date of discovery 11th September 1969
Older name 1969 IV
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

Tschurjumow-Gerassimenko (German), official name 67P / Churyumov-Gerasimenko (English transcription from Russian Чурюмов-Герасименко ), often called Tschuri ( English Chury ) by researchers and since mid-2014 also by the media , is a short- period comet . It is the first comet to be accompanied by a spacecraft (2014-2016, Rosetta ) and the first to be dropped by a lander (November 12, 2014, Philae ). The results of the mission are surprising in many ways, especially the irregular shape, the high average density and the varied surface structures: rock-hard ice with a high mineral content, almost entirely covered with gravel and loose, partly polymeric organic material.

discovery

The comet was discovered in 1969 at the Institute for Astrophysics of Alma-Ata by Klym Churyumov when he was examining a photographic plate that had been exposed by Svetlana Gerassimenko on September 11, 1969 for the purpose of researching the comet Comas Solà . She found a comet-like object on the edge of the plate and assumed that it was Comas Solà. Upon her return to Kiev , all photographic plates were carefully examined. On October 22nd it was discovered that the object could not be the comet in question because its position deviated from the expected one by more than 1.8 ° . Closer inspection revealed a faint image of Comas Solà in the right place, proving that the object Churyumov recognized was a newly discovered comet.

Orbit

Tschuryumow-Gerassimenko belongs to the Jupiter family of short-period comets and shares the fate of being either thrown out of the solar system or towards the sun or hitting the giant planet itself due to orbital disturbances within historical periods of time. When the originally long-period comet came under Jupiter's control is unknown, as the uncertainty of the course of the orbit increases sharply with each close encounter. In 1840 the perihelion distance of its orbit changed from about four AU (too cold for a visible coma ) to three AU and slowly to 2.77 AU by 1959. The 1959 encounter lowered perihelion to 1.29 AU, which is now 1.24 AU.

Observation with Hubble

Reconstruction based on observations from the Hubble Space Telescope in 2003

In preparation for the Rosetta mission , 61 images of the comet were taken over 21 hours on March 11 and 12, 2003 with the Hubble Space Telescope . The result was a period of rotation of about 12 hours and an elongated, irregular shape with diameters of about 3 km and 5 km, respectively. Previously, a diameter of up to 6 km was feared, which would have made a soft landing on the comet difficult. It is about three times larger than the original, no longer achievable Rosetta mission goal 46P / Wirtanen .

Observation with Rosetta

Increasing activity at the end of February 2015

The unusual shape of the comet - images from the OSIRIS camera on the right - may mean that it is composed of two bodies that collided at low speed 4.5 billion years ago, or that the loss of mass was concentrated in the “neck region”. The shape of the comet is reminiscent of a bath duck - even in scientific publications reference is made to the “body”, “head” and “neck” of the comet. For more precise location information, 19 regions are defined and named in ancient Egypt, mostly after deities.

Region
named
after		 noticeably
times
Mafdet rocky
Bastet
Selqet
Hathor
Anuket
Chepre
Aker
Atum
Apis
Hapi smooth
Imhotep
Anubis
Ma'at
covered with dust
Ash
Babi
Hatmehit great
sink
Groove
Aton
Seth holey,
brittle
With an albedo of around 0.05, the comet would appear as black as charcoal to the human eye. The contrast of the images is lightened so that the brightest pixels are white. NAVCAM-Mosaic from the end of September 2014 from a distance of 28.5 km.
Representation of the different shapes of the surface
Rugged landscape
Surroundings of the "Cheops rock" (stereo recording)

The comet rotates around its first main axis of inertia . The dimensions and especially the volume are smaller than assumed from the Hubble photos. The mass was  corrected upwards from Doppler measurements of Rosetta's flight path by a factor of three to (9982 ± 3) · 10 9 kg. The density is (533 ± 6) kg / m³, roughly like pine wood. These measurements at a distance of 10 to 100 km also resulted in a homogeneous mass distribution, i.e. no rocks or larger cavities. Rather, the comet consists entirely of porous, dusty ice. The porosity is 72 to 74%, the mass ratio of dust to ice 4: 1 (2: 1 by volume). Spectrally resolved images in the visible and in the thermal IR (VIRTIS instrument) showed that the surface is ice-free and covered by organic material, but no signs of nitrogen compounds. Thermal radiation at 0.5 mm and 1.6 mm wavelength (MIRO instrument) provides the temperature just below the surface. Their variation with the rotation suggests a heat penetration coefficient of 10 to 50 J · K −1 · m −2 · s −1/2 and thus loose, heat-insulating material. The same microwave spectrometer also showed water outgassing, mainly from the neck of the comet, which increased from 0.3 to 1.2 kg / s between the beginning of June and the end of August 2014.

Mass spectrometry (ROSINA instrument) showed the composition of the outgassing: predominantly water and carbon dioxide as well as the more volatile carbon monoxide. The outgassing shows a high variability in density and composition with the rotation of the comet. For the first time, molecular nitrogen could also be found in a cometary coma. The N 2 / CO ratio of (5.70 ± 0.66) · 10 −3 is a factor of 20 to 30 lower than assumed for the protoplanetary nebula, which suggests that the temperature at which the cometary material condensed, was at most 30 K. Finally, the D / H isotope ratio is about three times as high as in terrestrial oceans - the variability of this size was already known from other comets.

Rosetta also demonstrated molecular oxygen. In 2017, its origin was shown in the California Institute of Technology . The outgassing water is ionized by losing an electron due to radiation from the sun. The resulting H 2 O + ion is accelerated by the solar wind to such an extent that it hits the comet. As a result of the impact, not only does the ion disintegrate, but molecular oxygen is also created from silicates and iron oxides on the surface using the Eley-Rideal mechanism .

Photos show jets that sometimes start suddenly and last for hours to days. They consist of dust, of which the roughly micrometer-sized fraction is mainly visible - finer dust does not scatter light effectively, the number density drops sharply towards larger particles . Jets were known from previous comet missions . It was clear that the dust was driven by gas jets, but not how these are so collimated. One of the competing hypothetical mechanisms - slow outgassing creates cavities under the relatively solid, ice-free crust, which collapses, revealing fresh, ice-bearing surfaces - has now been confirmed: several deep pits were photographed in areas from which jets emanated.

Exploration using the Philae Lander

Representation of the lander Philae on the comet's surface

For details on the lander, its instrumentation and the course of the landing, see Philae .

The main aim of the research was to analyze the four billion year old material that makes up the comet. Among other things, the question of the origin of the terrestrial water should be examined for its isotopic composition using various physical-chemical measurements . Furthermore, the comet ice should be based on organic compounds such as B. Amino acids are examined in order to possibly come closer to the answer to the question of the origin of life .

To do this, Rosetta dropped the Philae lander onto the comet on November 12, 2014 . The lander ricocheted off the designated landing site, which is called " Agilkia " based on a Nile island and came to rest after two long, very slow hops at an inconvenient place called "Abydos" and in an inconvenient location. In the 63 hours until the lander's primary batteries were depleted, a series of experiments were automatically performed, data collected, and transmitted to Earth via Rosetta. The data comes from Agilkia, Abydos and - in teamwork with Rosetta - from the inside of the comet's head. A first series of scientific publications appeared in Science in July 2015 :

During the descent and hopping, optical and infrared images were taken and probed with radar and magnetometers . The magnetic field measurements showed that the comet is not magnetized, i.e. at the time of its formation there was not a sufficiently strong field to align the possibly magnetized particles.

The images from the ROLIS descent camera show that Agilkia is covered by a layer of regolith up to 2 m thick with grains of centimeters up to 5 m large blocks. The close-ups are rough up to the resolution limit of 1 cm per pixel, i.e. without a deposited layer of sand or dust, which is probably the result of movements of the material. Shapes that are reminiscent of wind drifts are interpreted as a result of erosion caused by falling particles.

At Abydos, the panorama camera CIVA (in IR and visible light) was used and showed broken-rocky structures with varying reflectivity and inclusions (in water ice) of different grain sizes. The MUPUS experiment used a thermal probe to determine the coefficient of thermal penetration . The value of 85 ± 35 J · K −1 · m −2 · s −1/2 and the only partial penetration of the temperature sensor into the surprisingly solid material - compressive strength greater than 2 MPa - indicates dirty ice with a proportion of 30 to 65 % fine pores.

A significantly higher porosity of 75 to 85% for the interior of the comet was provided by the fluoroscopy of the comet's head with radio waves (90 MHz) while Rosetta flew around the comet ( bistatic radar , travel time, absorption, small-angle scattering, CONSERT experiment). The mineral / ice volume ratio was only uncertainly recorded by these measurements, 0.4 to 2.6. The spatial variation is small above the resolution limit of a few tens of meters.

COSAC and Ptolemy are mass spectrometer experiments for volatile and higher molecular compounds. Their measurements were made 25 and 20 minutes after the first contact with the ground, i.e. at an altitude of about one kilometer. COSAC worked in the more sensitive sniffing mode, i.e. without previous separation methods (e.g. in enantiomers ). Among the 16 compounds identified were oxygen and nitrogen compounds, but no sulfur compounds. Four of the compounds, methyl isocyanate , acetone , propionaldehyde and acetamide , had not previously been detected in comets, but their occurrence is not surprising.

With Ptolemy, a mass spectrum of grains that had fallen on the lander could be obtained. The material was fragmented in the mass spectrometer . Regular distances of 14 and 16 in m / z indicate -CH 2 - or -O- as a structural element of polymers. Aromatics and sulfur compounds are not found, nitrogen compounds in small quantities.

With regard to the origin of Churyumov-Gerasimenko, researchers suspected either a collision between two separate bodies or a particularly intense erosion at the location of the comet, which then developed into a “neck”. The analysis of the high-resolution comet images of the OSIRIS camera from Rosetta, which were taken between August 6, 2014 and March 17, 2015, provided a decisive gain in knowledge in this regard. As a result, two comets probably collided in the still young solar system and formed the double body visible today, whereby the measured low density and the well-preserved layered structures of both parts of the comet indicate that the collision must have been very gentle and at low speeds. This also provides important clues about the physical state of the early solar system about 4.5 billion years ago.

Rosetta Ground Observation Workshop

In June 2016, 40 research partners met in Styria to compare earth-based and space-based observations and to improve research methods.

dust

In September 2016, based on in-situ measurements by an atomic force microscope (MIDAS), grain sizes of 1 to a few tens of micrometers were reported.

Public exhibition

From 9 May to 12 September 2018 was in the NHM Vienna the special exhibition "comet. The Mission Rosetta ”, created by the German Aerospace Center (DLR) in cooperation with the Max Planck Society and made available free of charge. An approximately 4 m high model by Tschuri was set up. Austria's contribution to the mission is shown in particular in Vienna, for example with the MIDAS (Micro-Imaging Dust Analysis System) instrument or the thermal insulation of the probe.

Web links

Commons : Churyumov-Gerasimenko  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ Comet where spacecraft landed makes closest approach to sun. August 13, 2015, accessed November 28, 2015 .
  2. ↑ IAU MPC ( Memento of the original from November 4, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed August 10, 2014 @1@ 2Template: Webachiv / IABot / scully.cfa.harvard.edu
  3. ↑ There were previously only landings on six other celestial bodies: the Moon , Venus , Mars , Titan , Eros and Itokawa ; Hand, Eric: Comet Breakthrough of the Year + People's choice. Science , December 19, 2014, accessed January 2, 2015 .
  4. ↑ ESA: Rosetta's target: comet 67P / Churyumov-Gerasimenko . November 8, 2014.
  5. ↑ ESA: Hubble provides assistance for the Rosetta comet mission , September 8, 2003
  6. ↑ Holger Sierks et al .: On the nucleus structure and activity of comet 67P / Churyumov-Gerasimenko. In: Science 347, 2015, doi: 10.1126 / science.aaa1044 .
  7. ↑ M. Jutzi, E. Asphaug: The shape and structure of cometary nuclei as a result of low-velocity accretion. In: Science 348, 2015, S 1355-1358, doi: 10.1126 / science.aaa4747 .
  8. ↑ Emily Lakdawalla: Unseen latitudes of comet Churyumov-Gerasimenko - revealed! The Planetary Society , May 15, 2015.
  9. ↑ NAVCAM'S SHADES OF GRAY , rosetta blog on October 17, 2014
  10. ↑ a b M. Pätzold et al .: A homogeneous nucleus for comet 67P / Churyumov-Gerasimenko from its gravity field. In: nature 530, 2016, pp. 63–65 doi: 10.1038 / nature16535 .
  11. ^ Fabrizio Capaccioni et al .: The organic-rich surface of comet 67P / Churyumov-Gerasimenko as seen by VIRTIS / Rosetta. In: Science 347, 2015, doi: 10.1126 / science.aaa0628 .
  12. ↑ Samuel Gulkis et al .: Subsurface properties and early activity of comet 67P / Churyumov-Gerasimenko. In: Science 347, 2015, doi: 10.1126 / science.aaa0709 .
  13. ^ Myrtha Hässig et al .: Time variability and heterogeneity in the coma of 67P / Churyumov-Gerasimenko. In: Science 347, 2015, doi: 10.1126 / science.aaa0276 .
  14. ↑ Martin Rubin et al .: Molecular nitrogen in comet 67P / Churyumov-Gerasimenko indicates a low formation temperature Science 10 April. In: Science 348, 2015, doi: 10.1126 / science.aaa6100 .
  15. ↑ K. Altwegg et al .: 67P / Churyumov-Gerasimenko, a Jupiter family comet with a high D / H ratio. In: Science 347, 2015, doi: 10.1126 / science.1261952 .
  16. ↑ A. Bieler et al .: Abundant molecular oxygen in the coma of comet 67P / Churyumov – Gerasimenko, 2015, Nature 526, 678–681
  17. ↑ Yunxi Yao, Konstantinos P. Giapis: Dynamic molecular oxygen production in cometary comae, Nature Communications 8, 2017, 15298
  18. ↑ HU Keller et al .: Collimation of cometary dust jets and filaments . Planetary and Space Science 42, 1994, pp. 367-382, doi: 10.1016 / 0032-0633 (94) 90126-0 .
  19. ↑ Jean-Baptiste Vincent et al .: Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse . Nature 523, 2015 doi: 10.1038 / nature14564 .
  20. ↑ Comet Research - Has Philae Been Damaged?
  21. ↑ Philae has fallen silent - All scientific data transferred. from November 15, 2014 Neue Zürcher Zeitung. Accessed June 17, 2015
  22. ↑ J.-P. Bibring et al .: Philae's First Days on the Comet - Introduction to Special Issue. In: Science 349, 2015, p. 493, doi: 10.1126 / science.aac5116 .
  23. ↑ Hans-Ulrich Auster et al .: The nonmagnetic nucleus of comet 67P / Churyumov-Gerasimenko . doi: 10.1126 / science.aaa5102 .
  24. ^ S. Mottola et al .: The structure of the regolith on 67P / Churyumov-Gerasimenko from ROLIS descent imaging . doi: 10.1126 / science.aab0232 .
  25. ↑ J.-P. Bibring et al .: 67P / Churyumov-Gerasimenko surface properties as derived from CIVA panoramic images . doi: 10.1126 / science.aab0671 .
  26. ↑ T. Spohn et al .: Thermal and mechanical properties of the near-surface layers of comet 67P / Churyumov-Gerasimenko . doi: 10.1126 / science.aab0464 .
  27. ↑ Wlodek Kofman et al .: Properties of the 67P / Churyumov-Gerasimenko interior revealed by CONSERT radar . doi: 10.1126 / science.aab0639 .
  28. ^ Fred Goesmann et al .: Organic compounds on comet 67P / Churyumov-Gerasimenko revealed by COSAC mass spectrometry . doi: 10.1126 / science.aab0689 .
  29. ^ IP Wright et al .: CHO-bearing organic compounds at the surface of 67P / Churyumov-Gerasimenko revealed by Ptolemy . doi: 10.1126 / science.aab0673 .
  30. ↑ Elizabeth Gibney: How the rubber-duck comet got its shape: Two pieces of rock became one, but the details are still up for debate . On: nature.com/news of August 7, 2015, doi: 10.1038 / nature.2015.18150 .
  31. ↑ H. Rickman, S. Marchi, MF A'Hearn et al. a .: Comet 67P / Churyumov-Gerasimenko: Constraints on its origin from OSIRIS observations . On: arxiv.org from May 26, 2015 for publication in Astronomy & Astrophysics.
  32. ↑ Stefan Oldenburg: Rosetta Mission: Noble Gases on Comet Tschurjumow-Gerasimenko . On: Spektrum.de/news from September 28, 2015.
  33. ↑ MC De Sanctis1, F. Capaccioni1, M. Ciarniello1 and a .: The diurnal cycle of water ice on comet 67P / Churyumov-Gerasimenko. In: Nature. 525, September 24, 2015, pp. 500–503, doi: 10.1038 / nature14869 .
  34. ↑ http://steiermark.orf.at/news/stories/2781255/ Komet "Tschuri": data analyzed in Styria, orf.at, June 20, 2016, accessed June 20, 2016.
  35. ↑ Comet dust under the microscope science.orf.at, August 31, 2016, accessed September 3, 2016.
  36. ↑ Aggregate dust particles at comet 67P / Churyumov – Gerasimenko Nature, September 1, 2016, accessed September 3, 2016.
  37. ↑ comets. the mission rosetta. nhm-wien.ac.at, May 9, 2018, accessed June 30, 2018.
  38. ↑ Museum shows meter-high comet replica orf.at, May 10, 2018, accessed June 30, 2018.