Last Thursday, Maria T. Zuber, a professor of geophysics and planetary science at the Massachusetts Institute of Technology, spoke at the College for the first of her five-college lecture series. Zuber’s lecture, “Expedition to an Asteroid: The Near Earth Asteroid Rendezvous Mission,” told the story of an unexpected success. Her lecture centered on the body of information that she and a group of scientists gathered from an asteroid landing performed by a spacecraft that they never expected to land anywhere.
The spacecraft, a Shoemaker research probe launched in 1997, was initially aimed at one particular asteroid named Eros (after the goddess of love) 433. In its first attempt to land on Eros 433 the Shoemaker spacecraft failed and missed its target. Luckily, the probe’s trajectory allowed Zuber and her team to attempt a second rendezvous. But in this case, just enough fuel was left in the craft’s tanks to allow the team to bring the spacecraft back to Earth’s orbit. From this secure position, the team was able to redirect the spacecraft towards Eros 433. In the second attempt, the spacecraft made it to Eros and entered its orbit. Zuber explained that this was really only one of the three stages of studying a cosmic body. This first one, having a spacecraft in the body’s orbit, allows scientists to take a preliminary look. The second stage is to map the body, and the third to actually land on it. The Shoemaker probe was initially intended only to collect preliminary data on Eros 433, which would be used in developing concepts for future missions.
However, after the probe was safely orbiting Eros 433, the team began considering the possibility of further, more in-depth research. After collecting data from Eros’ orbit, the team decided that it was a feasible possibility that the spacecraft could land on Eros’ surface, even though the spacecraft was not built for such an activity and lacked landing gear. It took the team three years to convince the National Aeronautics and Space Administration (NASA) to allow them to land the spacecraft. NASA’s reluctance at accepting this impromptu landing was caused by the high probability that it would end in a crash, which would not cause any harm, since the spacecraft had already served its purpose, but would nevertheless produce bad publicity for the beleaguered agency.
However, despite projections to the contrary, the spacecraft was successfully programmed to descend to the surface, and upon landing continued to send data back to Earth. No one expected that the spacecraft’s landing, which used the vehicle’s two solar panels and a corner of the superstructure as landing gear, would succeed. Again, luck was on the team’s side. One of the main reasons that the spacecraft survived the asteroid landing with its instruments and internal components intact was that it landed in a “pond,” which is what smooth areas on asteroid surfaces are called. The spacecraft would have almost certainly been destroyed had the spacecraft landed on a rockier surface.
Zuber and her team have learned a great deal about Eros 433 and asteroids in general from the landing. Among the most interesting information gathered was the composition of the asteroid. Eros is part of a group of asteroids called Ordinary Chrondites, which is the most common composition of meteorites. The interesting aspect of this class of asteroids is that their composition is very similar to that of our sun.
The landing also allowed the scientist to learn that most of Eros 433 is solid rock, unlike some meteorite classes that are composed of an aggregate of rocks, dust and ice rubble, individual rocks packed closely together. This information also opposes the idea of blowing up an asteroid headed for Earth. As seen in Eros 433, blowing a meteorite on its way to Earth would only cause many solid rock formations to impact instead of only one. Zuber explained that fear of meteorite impact on Earth is a “practical, but low probability reason to study asteroids.” She said that it was a good idea to have a plan, just like there is a plan for nuclear warfare, but that the likelihood of an asteroid impacting Earth is very low.
She went on to explain that if an asteroid was on its way to Earth scientists would know by as much as one hundred years before it became a threat to us. Even then she said all it would take to change the asteroids’ course would be a “nudge” which could be achieved by “mundane” effects such “asteroid sails.”
Zuber’s lecture was enlightening, in that it explained why the universe is not to be feared, but marveled for all that is out there. Eros 433 is only one type of the numerous cosmic bodies and so much was learned from it in an expedition that was not intended.
Zuber’s team may be finished with the Shoemaker spacecraft currently resting on Eros’ surface. Although it is turned off right now, since the side the spacecraft’s location is not receiving sunlight, the team will attempt to reactivate it in late October. Zuber is pessimistic about the spacecraft turning on again. She said that it has been “too cold and too long” for the spacecraft that was not designed to survive such harsh and dynamic conditions. She summed up the experience of the unanticipated landing on Eros: “Sometimes you can surprise yourself.” If the spacecraft does turn back on it will once again, beat the odds and surprise the team behind it.