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Tuesday, December 11, 2018

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A probe landed on a comet earlier this week. Photo: ESA/Rosetta/Philae/CIVA A probe landed on a comet earlier this week. Photo: ESA/Rosetta/Philae/CIVA

Probing a Comet 300 Million Miles Away

NASA engineer and SDSU alum Jordan Evans talks about the European Space Agency's historic landing of a probe on Comet 67P.
By Michael Price

The Curious Aztec takes you behind the scenes of scientific investigation and discovery taking place at San Diego State University.

Earlier this week, the European Space Agency made history when it landed the space probe Philae on the surface of comet 67P/Churyumov–Gerasimenko, some 317 million miles from Earth. Part of the agency’s Rosetta spacecraft mission, it marked the first time a probe has landed on a comet.

It was a mission 10 years in the making. Rosetta blasted off in 2004 from the Guiana Space Centre in French Guiana. While the Rosetta orbiter continues to circle the comet as it travels through space, the Philae probe will perform a number of analyses of the comet’s composition, amassing measurements that had until now been impossible to collect.

How long it will be able to carry out these analyses, however, is unclear. The probe landed in a shady spot of the comet’s surface, preventing its solar panels from harnessing energy from the sun. Without this energy, its batteries won’t last longer than a couple of days.

Whether or not mission controllers are able to relocate the probe to a more favorable location, the mission will be considered a success, showcasing an impressive feat of extreme engineering and demonstrating that such landings are indeed possible.

Astronomers and engineers at San Diego State University are intimately familiar with the colossal challenges, joys and sorrows of successfully navigating a spacecraft to a rendezvous with a celestial body. Numerous alumni have gone on to work at NASA’s Jet Propulsion Laboratory in Pasadena, California, including Jordan Evans, a former member of SDSU’s Rocket Project and a key player in NASA’s landing of the Mars rover Curiosity on the Red Planet in 2012.

We asked Evans to chime in on the significance of the Philae landing.

Why would a space agency want to visit a giant, dirty ice cube in space?

JE: Rosetta is one of those “Dare mighty things” kinds of missions. First and foremost, it was driven by the desire to answer some very important scientific questions about comets and their relationship to our solar system’s formation, as well as the presence of water on Earth. To answer those questions, this incredible engineering challenge was required.

Were the challenges similar to the ones you and your team faced when landing a rover on Mars?

JE: It is challenging for different reasons than Curiosity’s landing. Mars is tough because it has an atmosphere that is too thin to slow a lander down and too thick to be ignored. Landing on a comet is a challenge because it has such a weak gravity field. The weak gravity makes it difficult to “stick” to the surface.

Philae’s landing is certainly a stunning engineering achievement. When you couple that achievement with the science return we’ve already received from Rosetta, this is an undeniably important mission. In some ways, it’s like the Deep Impact mission where we hit an asteroid with a spacecraft while another spacecraft watched. The addition of the Philae lander pushes the complexity of the mission well beyond that, and presents engineering challenges that none of us have had to deal with before.

Now that Philae is there on Comet 67P, what will it be able to tell us?

JE: Philae has some wonderful scientific instruments onboard. Three of them came from our team here at NASA. The Rosetta mission will be able to give us a portrait of the nucleus of a comet for the first time. We’ve already learned a great deal about its shape and how the comet changes as it travels into the inner solar system.

We will also be able to understand the chemical composition of the comet and get a complete inventory of the chemicals, minerals, and isotopes present. It is hoped that this new information will inform our understanding of the origin of Comet 67P. Could this comet have witnessed the formation of our solar system? We may get compelling evidence to answer that question.

If Philae’s batteries die soon and we lose contact with the probe, how will that affect the mission?

JE: The fact that the team has been able to receive data from the lander has been tremendous for meeting the science objectives of the mission. The team has estimated that 90 percent or more of the science data has already been received. Of course it will be a disappointment to the team members once they lose contact, but that little machine has proven itself quite capable.

Philae landed, hopped around, and kept sending data. That makes it an overwhelming success from both an engineering and science standpoint. I expect people to be working with the Philae science data for many years to come.

Going forward, how will this affect future space missions?

JE: Missions like this produce a wealth of scientific information and tend to generate a new set of scientific questions that need answers. Developing spaceflight missions to answer those questions will follow. It’s almost a given that those missions will be challenging and push our engineering capabilities. Rosetta will be very helpful in moving us forward in our interaction with small bodies in our solar system.

The next mission to a small body, already in development, is NASA’s OSIRIS-REx, which will not only rendezvous with an asteroid and collect samples from it, but will return those samples to Earth.