The Mars Express probe is only about 45 kilometers of Phobos ... - RTVE

JAVIER PEDREIRA ‘WICHO’

This past weekend the Mars Express, the European Space Agency, departed from his usual routine of exploring Mars, if the word routine fits when talking about a space mission, much as this probe lead and ten years in orbit around Mars, to take advantage he would spend only 45 kilometers of Phobos, the planet larger, and devote all their attention moon.

This meeting is not entirely accidental, since in recent months responsible for mission gone slightly adjusting the orbit of Mars Express to promote this event , which exceeds 67 km obtained in March 2010 , as a result of these adjustments has been another very close approximation on 21 December, only 500 miles, and another will occur next January 4, 2014

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No instruments

But apart from the extraordinary proximity of the probe and the moon, this event is unusual because none of the instruments on board was used to obtain information about Phobos, Mars Express but itself because the relative velocities and the crossing angle was virtually certain that no image quality is not obtained.

To do what was done was measure acceleration due to gravity probe Phobos taking advantage of the Doppler effect produced on the radio signal that is received on Earth from this. This is the same effect that makes the sound of a car engine change tone as towards or away from anyone who hears it.

detect this shift in the radio signal from the Mars Express is a extremely delicate, and for this task which made the European Space Agency was ordered to probe not transmit any data for the signal to be as constant as possible, so that what is received on Earth was only a carrier like when a radio station no one speaks for a moment or hard wedge planned advertising or music, nothing that would interfere.

So is facilitated the task of detecting the changes caused by the gravitational pull of Phobos.

In addition, the ESA was continuously listening to the signal from the Mars Express for 35 hours to measure changes before and after closest approach, which required coordinating follow from ESA station in New Norcia in Australia with stations NASA Robledo de Chavela in Spain and Goldstone in California and again New Norcia so that there were no interruptions, something that is usually not necessary, as the Mars Express is capable of storing data for transmission to Earth when not in contact with any monitoring station.

Objective met

Preliminary data indicate that indeed has been possible to detect the acceleration caused by Phobos on Mars Express , so now is analyzed to see how the irregular shape of Phobos, measuring approximately 27x22x18 kilometers has influenced the speed of the probe.

This data, once crossed with the images already obtained on 21 December and with those obtained on 4 January, which in turn will allow more accurately calculate the orbit of Phobos to compare their position with that of the stars that are seen in the images, will enable scientists to better estimate the mass of the Moon and internal distribution as previous approaches have allowed to estimate that between a third and a quarter of its interior is empty space.

With this information scientists can define a little more plausible theories about the origin of Phobos and Deimos, which the two most popular are that either are asteroids captured by Mars’ gravity, or that are ejected from the surface by an impact this material.