ROMAP co-principal investigator Hans-Ulrich Auster from the Technische Universität Braunschweig, Germany, explains how the instrument will be used with RPC (on the Rosetta orbiter) to monitor Philae as it descends to the surface of comet 67P/Churyumov-Gerasimenko on 12 November – as well as looking out for any evidence of a ‘fossil’ magnetic field linked to the comet itself.

On 12 November, the magnetic field instruments on-board the Rosetta orbiter and lander will be assigned the task of monitoring Philae as it descends to the surface.

That’s possible because both the lander and the orbiter generate small magnetic fields of their own, due to the electronic circuits inside the spacecraft. These magnetic fields create perturbations in the data that the scientists normally remove in order to analyse the purely natural magnetic fields from the comet and the solar wind. However, on 12 November, these perturbations can be analysed to tell what is happening to the lander as it slowly drops towards the surface of 67P/C-G.

Once the lander has separated, the magnetic perturbation registered near the orbiter will decrease as Philae moves away. Later, when the lander deploys a boom arm for its ROMAP instrument, it will cause a brief variation in the perturbation. A similar variation may also be registered when the three landing legs spring into place.

The perturbations may prove too subtle for the RPC instruments, operating on Rosetta at some distance from Philae, but the ROMAP instrument on the lander will register the changes loud and clear.

We will be able tell what is happening on the lander by the changes in its magnetic field,” says ROMAP co-principal investigator Hans-Ulrich Auster.

These measurements will add to the overall picture of Philae’s progress to the surface of the comet.

Of course, the main focus of these instruments is on science. The comet should retain a memory of any magnetic field that was present in its environs 4.6 billion years ago when the Earth and the other planets were forming. For example, some theories of star and planet formation require a magnetic field to accelerate the growth of our Solar System, while others do not, and thus by measuring the ‘fossil’ field, Rosetta can hope to shed light on this epoch.

In the final few hundred metres of Philae’s descent, ROMAP will detect this magnetic fossil if it exists.

It’s a simple question, is it there: yes or no. We are just a few days away from knowing the answer to this,” says Auster.

After the landing, ROMAP will again play an operational role, by helping scientists determine the angle at which the lander has come to rest. This will be essential to help orient the lander so that as much light as possible falls onto its solar panels.

Although there are other ways in which this information will be monitored and returned to Earth, the contribution from RPC and ROMAP should prove very valuable.

We will do everything we can to help understand the overall state of Philae after landing,” says RPC principal investigator Karl-Heinz Glaßmeier, also from the Technische Universität Braunschweig, Germany.

After all, the more that can be done to keep the lander functioning, the more science will flow from the mission. And the more we will learn of our cosmic origins.


The contributing institutions to ROMAP are: Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Germany; Hungarian Academy of Sciences Centre for Energy Research, Hungary; and Space Research Institute Graz, Austria