VLT på sporet efter Rosettas komet
Den klare tågede klat midt på dette billede er en komet med navnet 67P/Churyumov-Gerasimenko, eller 67P/C-G blandt venner. Det er ikke en hvilkensomhelst komet; det er den komet, som ESAs rumsonde Rosetta nu kredser om mindre end 100 km fra kometens overflade [1]. Rosetta befinder sig dybt inde i kometens koma, så den eneste måde at se hele komet 67P/C-G på er med teleskoper fra Jorden.
Billedet er taget 11. august 2014 med et af de fire 8-meter teleskoper ved ESOs VLT (Very Large Telescope) i Chile. Det er sammensat af 40 individuelle optagelser; hver på 50 sekunder. I processen er baggrundsstjernerne fjernet, så vi får det bedst mulige kig på selve kometen. Rosetta er alt for lille til at kunne ses i denne forstørrelse. Den befinder sig indenfor den ene centrale pixel i billedet.
VLT er fire ens teleskoper, som både kan bruges sammen og individuelt. Dette billede er taget med FORS2-instrumentet (FOcal Reducer and low dispersion Spectrograph 2) på Antu, som er teleskop nummer 1. Antu betyder Solen på det oprindelige sprog mapuche i Chile.
FORS2 kan bruges på forskellige måder. I forbindelse med Rosettas opgave ved kometen bruges instrumentet til at bestemme kometens lysstyrke, størrelse og facon og komaens sammensætning.
Selvom 67P/C-G er svagtlysende, er den helt klart aktiv. Den har en coma af støv, som strækker sig omkring 19.000 km ud fra kernen. Komaen er asymmetrisk fordi støvet bliver blæst væk i retning modsat Solen - som befinder sig udenfor billedet forneden til højre. Kometen er også i gang med at danne den karakteriske komethale.
ESO og ESA samarbejder om at observere 67P/C-G fra Jorden samtidig med at Rosetta foretager målinger ved kometkernen. Cirka hver anden nat leverer VLT et billede. Ændringer i kometens klarhed bruges til at holde øje med kometens aktivitet, og resultaterne bliver sendt til Rosettaprojektet, så forskerne der bedre kan planlægge rumsondens bane omkring kometen.
Note
[1] Rosetta nåede en afstand på 100 kilometer fra 67P/C-Gs kerne den 6. august 2014, og siden er den kommet tættere på.
Link
Kilde:Colin Snodgrass/ESO/ESA
Om billedet
| Id: | potw1436a |
| Sprog: | da |
| Type: | Observation |
| Udgivelsesdato: | 8. september 2014 10:00 |
| Størrelse: | 954 x 614 px |
Om objektet
| Navn: | 67P/Churyumov-Gerasimenko |
| Type: | Solar System : Interplanetary Body : Comet |
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