Mars Express Makes Close Phobos Flyby
December 23, 2013

Mars Express To Make Nail-Biting Flyby Of Mars’ Moon Phobos

[ Watch The Video: Mars' Moon Phobos Seen From 360 Degrees ]

Brett Smith for - Your Universe Online

Scientists at the European Space Agency (ESA) are busy preparing for a December 29 fly-by of the Martian moon Phobos with the agency’s Mars Express craft.

On Monday, the ESA released a 360-degree animation of the Martian moon. The images were taken by the High Resolution Stereo Camera (HRSC) on ESA’s Mars Express at various times throughout the mission’s 10 years.

While the craft will pass the moon too quickly to capture usable images, it will be able to measure the moon’s gravitational field and possibly provide new details of its internal makeup.

The scientists said the fly-by could help solve the mystery of where the asymmetric moon came from, as well as the origin of Mars’ other moon, Deimos, which orbits the Red Planet at about three times the distance. The most popular theories assert that the two satellites are either asteroids ensnared by Mars’ gravity or that they originated from debris kicked up by giant impacts on Mars.

“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,” said Olivier Witasse, ESA’s Mars Express project scientist.

As the Mars Express passes Phobos, it is expected to be drawn slightly off course by the moon’s gravitational pull. While the course change will only be a few centimeters per second, the shift should be enough to be detected in the way the spacecraft’s signals are sent back to Earth. The ESA scientists will be looking to translate the signal changes into a way to determine the mass and density structure of the moon’s interior.

Previous fly-bys have indicated that Phobos could be between a quarter and a third empty space – meaning it is basically comprised of a large pile of loose rocks.

In addition to checking the moon’s gravity, the Mars Express is expected to take measurements of the solar wind’s influence on Phobos’ surface.

“At just (28 miles) from the surface, our spacecraft is passing almost within touching distance of Phobos,” said Michel Denis, Mars Express Operations Manager. “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.”

ESA scientists say the precise locations of both the spacecraft and the moon must be known in order to generate the most accurate calculations of the moon’s interior. To refine the positional data, the high-resolution stereo camera onboard the Mars Express has been taking images of Phobos set against the background star field.

The series measuring photos will continue in the week leading up to the fly-by and for some time afterward. The ESA will also be utilizing data from ground stations around the world to track the craft for the lead up to, during, and after the flyby: a total of 35 hours.

“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!” Witasse added.