9. February 2015

Comet 67P/Churyu­mov-Gerasi­menko 'shed­ding its skin' in the heat of the south

Jet streams on Churyumov-Gerasimenko
Jet streams on Churyu­mov-Gerasi­menko
Image 1/2, Credit: ESA/Rosetta/NAVCAM - CC BY-SA IGO 3.0

Jet streams on Churyumov-Gerasimenko

A promi­nent jet, to­geth­er with gas an dust out­flows are vis­i­ble in this four-im­age mo­sa­ic, cre­at­ed from im­ages ac­quired by Roset­ta's Nav­i­ga­tion Cam­era NAV­CAM on 31 Jan­uary 2015. The comet’s ac­tiv­i­ty will in­crease as it ap­proach­es the Sun. Mod­el cal­cu­la­tions show that the north­ern sec­tion can ex­pect to lose a few me­tres of sur­face through­out the or­bit, while the south­ern part will lose up to 20 me­tres.
Mod­el cal­cu­la­tions for the ero­sion of 67P/Churyu­mov-Gerasi­menko
Image 2/2, Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/DLR .

Model calculations for the erosion of 67P/Churyumov-Gerasimenko

This im­age is based on a sur­face mod­el of comet Churyu­mov-Gerasi­menko and shows the pre­dict­ed ex­tent of ero­sion of cometary ma­te­ri­al. The left fig­ure shows the comet seen from the north; the cen­tre im­age shows the equa­to­ri­al plain and the right im­age shows the south­ern re­gion. The dif­fer­ent colours rep­re­sent the pre­dict­ed amount of ero­sion – the south­ern part of the comet could lose up to 20 me­tres of sur­face ma­te­ri­al dur­ing the or­bit.

Comet 67P/Churyumov-Gerasimenko could lose up to 20 metres of surface material from its previously unilluminated south side when it heats up, starting in May 2015. The increasing heat as the comet approaches the Sun will trigger this 'diet', during which gases and solid materials will be ejected into space. Horst Uwe Keller and Stefano Mottola from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), who have estimated the possible erosion of 67P using data acquired by the Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS), suggest that the northern hemisphere will lose much less mass. Their model reveals that, in its orbit around the Sun, the comet will lose a large part of its surface – particularly on its south side – during a brief but very intense 'summer'. "The comet sheds its surface almost constantly, revealing fresh material on its surface, which has not yet been aged by cosmic radiation," says Ekkehard Kührt, who leads the Rosetta mission science team at DLR.

Extreme seasons in the course of one orbit

It takes Comet 67P/Churyumov-Gerasimenko about six Earth years and five months to complete one orbit around the Sun. Its highly elliptical orbit takes it far away from the Sun for long periods of time. the next closest approach to the Sun (perihelion) will occur in August 2015. The inclination of comet's rotational axis – tilted 53 degrees with respect to its orbital plane – compared to just 23 degrees for Earth – means that the seasons in its two hemispheres are dramatically different. The northern hemisphere has a long, yet not particularly intense summer. The southern hemisphere summer will last for 10 months, but as it will occur during perihelion, it will be particularly severe. The Rosetta orbiter and its lander, Philae, will have an excellent view of the comet as it awakens and ejects gases and dust into space.

To estimate the loss of cometary material, the OSIRIS scientists used a surface model of the comet and divided it into 100,000 small triangles. It was necessary to consider the existence of shaded areas, for example in the craters, and that the rugged mountain walls reflect solar radiation onto nearby slopes, reinforcing it. "Our model calculation assumes that the water ice in the active regions is covered by a very porous, thin layer of dust," says Keller. In addition, the researchers assume in their simulation that about four times more dust than ice being ejected into space.

Twenty metres lost to space

"The result is that the southern side – not currently illuminated by the Sun and still new territory for the scientists – will lose up to 20 metres of its surface during this hot summer," says Mottola. "In the northern hemisphere, the outlook is quite different – only the peaks and cliffs will lose up to 10 metres." The current, particularly, active narrow region between the two comet lobes is calculated to be poorly lit during the overall orbit, and thus only moderately active generally.

The Philae lander will be able to take advantage of the summer; at its location near the equator, it may receive sufficient sunlight to 'wake up' from its current hibernation state. This might occur as early as March, but the probability that the Lander Control Center will resume contact and be able to send commands will be greatest in May.

The mission

Rosetta is a European Space Agency mission with contributions from its member states and NASA. The Rosetta lander, Philae, has been funded by a consortium led by DLR, the Max Planck Institute for Solar System Research (Max-Planck-Institut für Sonnensystemforschung; MPS), the French space agency (Centre National d'Études Spatiales; CNES) and the Italian space agency (Agenzia Spaziale Italiana; ASI).

Contact
  • Manuela Braun
    Ed­i­tor HR
    Ger­man Aerospace Cen­ter (DLR)
    Cen­tral HR Mar­ket­ing
    Telephone: +49 2203 601-3882
    Münchener Straße 20
    82234 Weßling
    Contact
  • Dr.rer.nat. Ekkehard Kührt
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search, As­ter­oids and Comets
    Telephone: +49 30 67055-514
    Fax: +49 30 67055-340
    Linder Höhe
    51147 Köln
    Contact
  • Dr. Horst Uwe Keller
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Linder Höhe
    51147 Köln
    Contact
  • Stefano Mottola
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Plan­e­tary Geodesy
    Rutherfordstraße 2
    12489 Berlin
    Contact

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