Mars’ potato-shaped moon Phobos will be receiving a fly-by of ESA’s Mars Express spacecraft this Sunday! Zipping by 28 feet above its surface, the spacecraft will be traveling too close and too fast for any photo ops, but the science collected from this fly-by will provide the most accurate details yet of the 27 x 22 x 18km moon’s gravitational field, which in turn, will enable us to better understand its internal structure.
"At just 45 km from the surface, our spacecraft is passing almost within touching distance of Phobos…we’ve been carrying out maneuvers every few months to put the spacecraft on track and, together with the ground stations that will be monitoring it on its close approach, we are ready to make some extremely accurate measurements at Phobos." stated Michael Denis, the Mars Express Operations Manager [source]
As the spacecraft nears Phobos, it will be pulled off course by the moon’s gravity, altering its velocity by a mere few centimeters per second. As these measurements are sent back as radio signals from Mars Express, Earthly scientists will then translate them to determine the mass and and density structure within the moon. This data will assist in addressing questions of origin pertaining to Phobos’ planetary sibling, Deimos, as well.
How does this work? Mars Express possesses a high-resolution stereo camera which has been taking photos of Phobos against the background star field in the previous weeks leading up to this 35 hour tracking sequence: before, during and after the close encounter with Phobos. In addition to researching obtained toward its gravitational field, Mars Express will take measurements on the influence of solar wind on the moon’s surface.
"By making close flybys of Phobos with Mars Express in this way, we can help to put constraints on the origin of these mysterious moons…Mars Express entered orbit around the Red Planet exactly ten years ago this week – this close flyby of Phobos is certainly an exciting way to celebrate!"
- Olivier Witasse, Mars Express Project Scientist at ESA [source]
Phobos’ relative size compared to the Alpes and town of Grenoble, France.
Not so lumpy now, eh?
Excerpts and information from the Phys.org article 'Mars Express heading towards daring flyby of Phobos'. For further details on this marvelous spacecraft, ESA put together a 10-year video montage of Mars Express highlights, providing insight into the sophisticated equipment on board, which you can accompany with the 90-minute replay of ESA’s Mars Express conference from June 2013, which highlights the key scientific discoveries of the mission along with a new mineral atlas created to chart the geological history of Mars.