Comet Lander Working, But Not Optimal

Rosetta’s Philae lander hopped twice before landing in the shade in a tilted position, but the instruments are working.

The Rosetta team’s second day Media Briefing was a mix of celebration and guarded optimism, after analysis showed good news and bad news.

The good news was that the lander touched down in a near perfect position as planned.  The bad news was that the surface was harder than expected, causing the lander to undergo a two-hour bounce, landing some distance away.  A third bounce put Philae into the shadow of a rocky cliff, where its solar panels will only be able to receive about a third of the solar power it needs to run its instruments for the nominal mission.  It also appears that one of the legs is pointing up, not on the ground.

Because of the precarious orientation and reduced power budget, mission planners are having to think hard about what scientific instruments to run.  Lead lander scientist Jean-Pierre Bibring believes it may be possible, after initial standalone science data is received, to run a mechanical operation that might right the lander or make it hop to a more sunlit place.  Scientists would love to be able to run the drill and sample collection instruments, so that analysis of the comet’s chemistry could be performed, but it is too risky in Philae’s current orientation.  If the solar panels cannot get more sunlight, science planners will have to prioritize what can be done with the limited power on board.  The BBC News posted a good summary of the mission status, with the latest pictures.

Comets are known to have very low density.  Philae settled down on at a gentle speed of about 2 km/hr.  Scientists expected it would simply rest on fine dust.  Dr. Holger Sierks, manager of the OSIRIS (remote imaging) camera expressed surprise at bouncing off hard ground:

The rebound of the lander is an indication of a higher strength material that was a surprise to us. So with this picture of dust falling back to the surface in high porosity layers, I would think we failed to explain the rebounds.  But we have seen the variety of surfaces there—this snowfield of soft stuff—and we have seen this rocky-like (but no rock) stuff, which is perhaps higher-strength material.  We also see stuff shining through the dust layer, where the dust is wiped away, following the gravity field, and exposing the higher strength material, and this is something that we could consider be the reason for the rebound.

The first images show a series of terrains, from a rocky “cliff” on one side to smooth plains on the other.  Despite the less-than-optimal final landing position, the team was elated and as enthusiastic as could be after many hours of work without sleep.  Even under worst-case scenarios, Philae has already made history.  When its power lapses, the Rosetta orbiter is still in good shape to fulfill another two years of science collection.  Things could get exciting as the comet approaches perihelion next year, its volatiles sublimating into a long tail.

Comet 67P/Churyumov–Gerasimenko joins the few bodies in the solar system whose surfaces have been studied by man-made landers with scientific instruments: Venus, Mars, the moon, and Titan.  Jupiter has no surface, but Galileo sent a probe into the clouds, and then went in itself at the end of its life.  Stardust collected material from a comet, and Deep Impact drove a probe into another comet.  All the other space missions have flown by objects, or orbited them from a distance.  There’s nothing like “ground truth.”

Update 11/14/14: Science Magazine posted a status report.  The battery’s lifetime is running out, but the Rosetta team is getting some science from the Philae lander, and considering rescue options.  The drill is being tried for sample analysis.  Even if the battery fails by Saturday, Philae has already achieved a major historical success.

It’s to be expected that problems will occur in first-time explorations like this.  The Rosetta teams deserve immense credit for succeeding in this high-risk, high-reward endeavor that began with its launch 10 years ago (and years of planning beforehand).  We hope enough good science will be salvageable to help us understand comets better, because it will undoubtedly take many years to follow up this mission with another like it.

What looks like rocky crust may be as flimsy as meringue.  The new data will need to be integrated with findings from Giotto, Stardust, and Deep Impact to present a unified picture of comets.  As with just about everything else in the solar system, what has been learned so far went contrary to earlier theories.

It’s worth re-emphasizing that creationists are enthusiastically supportive of scientific discovery; the only problems arise from materialistic interpretations of science data.  It was good to hear a complete absence of speculation at this press conference about the origin of life and the origin of Earth.  BBC reporter Jonathan Amos, though, couldn’t resist: comets “could have ‘seeded’ the Earth with the chemistry needed to help kick-start biology,” he said.  Just the facts—that’s good for everyone.