De weekend - Phobos

Au aparut in ultima vreme tot felul de zvonuri pe blogul lui David despre micuta luna a lui Marte. Si cum tot ne anunta Google ca azi aniversam 20 de ani de la lansarea lui Hubble am zis ca n-ar strica sa dedicam week-endul asta unui articol pe teme mai ... universale... :-)

Phobos este cel mai mare dintre cele două luni (sateliţi) ai lui Marte şi cel mai aproape de planetă. În termeni generali, Phobos este un bloc rocos de formă neregulată, de aproximativ 27 km lungime pe axul sau cel mai lung. Are o perioadă orbitală de 7 ore şi 39 minute. Suprafaţa sa prezintă un mare crater, care se numeşte Stickney; este rezultatul unei ciocniri cu alt obiect care putea sa distrugă acest satelit. Phobos a fost descoperit de astronomul american Asaph Hall, la 18 august 1877, în observatorul din Washington D.C., aproximativ la 09:14 GMT.

Pentru cei care se descurca mai usor in romana: Rusia va trimite viaţă către Phobos

Pentru ceilalti curiosi, avem site-ul agentiei spatiale europene: Phobos Fly-By 2010

Din care extragem cateva cateva citate interesante aparute in diverse articole din ultimele doua luni, cand cei de la ESA au tot experimetat cu radarele si s-au tot jucat scanand micuta luna ce le-a starnit curiozitatea:

Phobos flyby success

Something is not right about Phobos. It looks like a solid object but previous flybys have shown that it is not dense enough to be solid all the way through. Instead, it must be 25-35% porous. This has led planetary scientists to believe that it is little more than a ‘rubble pile’ circling Mars. Such a rubble pile would be composed of blocks both large and small resting together, with possibly large spaces between them where they do not fit easily together.

Last night’s flyby was close enough to give scientists their most exquisite data yet about the gravitational field of Phobos. Mars Express locked onto the radio signal from Earth at around 21:20 CET (20:20 UT). The radio frequency oscillators on the ground are 100 000 times more stable than those on the spacecraft, so for this experiment, which required the best precision possible, the signal was sent up to Mars Express and then returned by the spacecraft to the ground.

Radio science result from 2008 Phobos Flyby now accepted for publication

We report independent results from two subgroups of the Mars Express Radio Science (MaRS) team who independently analyzed Mars Express (MEX) radio tracking data for the purpose of determining consistently the gravitational attraction of the moon Phobos on the MEX spacecraft, and hence the mass of Phobos. New values for the gravitational parameter (GM=0.7127 ± 0.0021 x 10-³ km³/s²) and density of Phobos (1876 ± 20 kg/m³) provide meaningful new constraints on the corresponding range of the body's porosity (30% ± 5%), provide a basis for improved interpretation of the internal structure.

We conclude that the interior of Phobos likely contains large voids. When applied to various hypotheses bearing on the origin of Phobos, these results are inconsistent with the proposition that Phobos is a captured asteroid.

First look at the MARSIS radar data for Phobos

After the ground-processing of science data, it was found that the radar worked successfully during the flyby. The figure above shows echoes reflected by Phobos as the highest peak in the signal, clearly above the noise level. Scientific analysis of the results is still ongoing. The main quest is the determination of the origin of detected echoes: are they reflections from various surface features of Phobos, or have they been produced by the internal structure of the moon?

In the first phase of the data analysis, the main goal was to validate a new operative configuration of the onboard software and hardware. The scientific analysis of existing and future data will provide us with new and unique insights on the nature of Phobos’ interior.

P.S. Rog luati in considerare ceea ce spuneam AICI inainte de adaugarea unor eventuale comentarii. Va multumesc.