the probe met the planet every two years ...

English translation: Physical explanation

09:55 Jan 17, 2008
English language (monolingual) [PRO]
Science - Astronomy & Space / Mercury exploration
English term or phrase: the probe met the planet every two years ...
I am translating a text dealing with Mercury exploration and the probe Mariner 10. I do not understand the following sentence, which is the caption of this image

http://photojournal.jpl.nasa.gov/jpegMod/PIA03104_modest.jpg

"This image mosaic was compiled during Mariner 10's final flyby. Because the probe met the planet every two Mercury years, the same areas were illuminated on each flyby."

I don't catch the connection between "meet every two years" and "illuminated areas".

Thank you
Stéphanie Soudais
France
Local time: 19:55
Selected answer:Physical explanation
Explanation:
For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and keeping the same face directed towards the Sun at all times, in the same way that the same side of the Moon always faces the Earth. However, radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun...
http://www.answers.com/Mercury?cat=technology&gwp=13

This means that the rotation of mercury is extremely slow; if the probe spends a couple of terrestrial hours or days in the vicinity of Mercury, the illuminated area will hardly change. Since the rotation and revolution of the planet show a perfect combined periodicity with a 2-year period, the probe will see the same when it returns 2 years later. If the probe approached the planet every year, it would see two different areas illuminated.
Selected response from:

Attila Piróth
France
Local time: 19:55
Grading comment
Thank you all !
4 KudoZ points were awarded for this answer



SUMMARY OF ALL EXPLANATIONS PROVIDED
5 +5Physical explanation
Attila Piróth
4la sonde approchait la planète tous les deux ans (à intervalles de...)
Pierre Gehenne
4la sonde ayant croisé la planète tous les deux ans...
David BUICK


Discussion entries: 1





  

Answers


8 mins   confidence: Answerer confidence 4/5Answerer confidence 4/5
la sonde approchait la planète tous les deux ans (à intervalles de...)


Explanation:
La sonde Mariner 10 a pris ses photos à deux ans d'intervalle et donc dans les mêmes conditions d'éclairement, ce qui a permis de composer la mosaïque d'images présentée.

Pierre Gehenne
France
Local time: 19:55
Native speaker of: Native in FrenchFrench
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9 mins   confidence: Answerer confidence 4/5Answerer confidence 4/5
la sonde ayant croisé la planète tous les deux ans...


Explanation:
(NB: deux ans *mercuriens*)

La sonde croise mercure à la même époque chaque fois, donc c'était toujours la même face qui était exposée (je suppose!)

Example sentence(s):
  • La sonde ROSETTA dont la trajectoire a croisé la planète Mars a fourni des bonnes images,

    Reference: http://www.astrosurf.com/saf/news/SAF2007/MANIF/COMMISSIONS/...
David BUICK
Local time: 19:55
Native speaker of: Native in EnglishEnglish
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22 mins   confidence: Answerer confidence 5/5 peer agreement (net): +5
Physical explanation


Explanation:
For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and keeping the same face directed towards the Sun at all times, in the same way that the same side of the Moon always faces the Earth. However, radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun...
http://www.answers.com/Mercury?cat=technology&gwp=13

This means that the rotation of mercury is extremely slow; if the probe spends a couple of terrestrial hours or days in the vicinity of Mercury, the illuminated area will hardly change. Since the rotation and revolution of the planet show a perfect combined periodicity with a 2-year period, the probe will see the same when it returns 2 years later. If the probe approached the planet every year, it would see two different areas illuminated.

Attila Piróth
France
Local time: 19:55
Works in field
Native speaker of: Native in HungarianHungarian
PRO pts in category: 4
Grading comment
Thank you all !

Peer comments on this answer (and responses from the answerer)
agree  Gert Sass (M.A.): Confirms my immediate assumption and makes much sense.
32 mins

agree  Ken Cox: nicely done
37 mins

agree  Deborah Workman: Yes, and as per Jonathan MacKerron's comment, too.
13 hrs

agree  ErichEko ⟹⭐
15 hrs

agree  Alexandra Tussing
18 hrs
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