The little lander that could: the legacy of Philae

Tomasz Nowakowski

Philae, the little lander that was declared lost by the European Space Agency (ESA) earlier this year, has achieved a great deal despite its relatively short operational life on the surface of comet 67P/Churyumov-Gerasimenko. Future comet-landing missions will likely build upon the legacy that this small wayward probe has left behind.

The box-shaped lander was a part of ESA’s Rosetta mission which launched on March 2, 2004. Philae made history when it became the first lander to safely touch down on a comet on Nov. 12, 2014.

However, the lander fell silent three days later. Philae made contact again on June 13, 2015, and sent its ‘health’ data. According to ESA, contact with the ground team was established seven more times, but these remained erratic and unpredictable. The probe has remained silent since July 9, 2015, and the probability of re-establishing contact with Philae is currently almost zero.

The spacecraft is probably suffering from a lack of power as it is not receiving enough sunlight to warm itself up to be operational. Thus, it is in a state of permanent hibernation. There were hopes that Philae would wake up again when the comet moved closer to the Sun ahead of perihelion on Aug. 13, 2015. However, even with the improved thermal conditions, no further contacts were made.

“Unfortunately, chances to re-establish contact are very low. We are getting too far from the Sun again,” Stephan Ulamec, Philae project manager at the German Aerospace Center (DLR), told Astrowatch.net.

The last images of Philae will probably be acquired later this year when the Rosetta orbiter will image the lander during close flybys of the landing site on the comet.

“Rosetta is operational till September and we hope to receive informative images of the Lander from the Orbiter Camera,” Ulamec said.

The little probe was the first to land on a comet’s surface and carry out measurements there – it will likely not be the last. Despite its short life on the comet, Philae has managed to conduct many research studies and is leaving a rich legacy of scientific know-how that could come in handy in the future, when agencies prepare other missions to small icy worlds.

The lander conducted more than 60 hours of research with its instruments; it acquired images and was able to sense molecules and tried to hammer into the unexpectedly hard cometary surface.

“Philae was able to conduct the first-ever measurements from the surface of a comet. Some of the results include the indication that the comet surface is non-magnetic, high-resolution camera images from the surface material, analytical analyses and the detection of rich organic chemistry, measurements of the physical properties of the surface material and measurements of the internal structure by radar sounding,” Ulamec revealed.

The scientists studying the results provided by Philae agree that its measurements; for instance, offer a unique insight into the composition and, in particular, the water content and porosity of the cometary mantle. The researchers were also able to map out the global dust dispersed on the surface of 67P/Churyumov-Gerasimenko.

Even Philae’s landing event delivered crucial information that could be useful for future similar endeavors. The spacecraft failed to fire its harpoons that would have locked Philae onto the surface of the comet after its descent, bouncing from its initial touchdown point. It made contact with the comet four times during its additional flight across the small comet’s lobe.

“We learned, that the cometary surface, at least where Philae landed, was quite hard, and, thus, bouncing is more of a problem than e.g. sinking into the surface dust. Having a redundant system and, for example, a large primary battery has proven to be the right strategy,” Ulamec said.

As noted, Philae could set the path for future similar missions to explore comets. However, Ulamec admitted that much more could be achieved by sample return probes.

“The concept of Philae was good. Future missions will make use of newer technologies, allowing, for example, improved miniaturization of instruments or more powerful computers. The next big step in cometary science may become sample return. There is no way to perform in-situ analyses, as sophisticated as in laboratories on Earth,” he concluded.

Rosetta is an ESA mission with contributions from its member states as well as NASA. Rosetta’s Philae lander is provided by a consortium headed by DLR, the Max Planck Institute for Solar System Research (MPS), the French Space Agency (CNES), and the Italian Space Agency (ASI).

Video courtesy of ESA