Dennis Wingo
Sunday, September 27, 2009
It has been a few days now since the public revelations concerning the results from Cassini, Deep Impact, and the Brown University Moon Mineralology Mapper (mcubed) hosted on the Indian Chandryaan lunar orbiter. There has been much discussion and debate, some of it heated, between those who think that these revelations change the arguments of lunar versus Martian exploration by humans. Those on the lunar side think that this will greatly lower the cost and increase the viability of lunar development, and those who think that the Moon is still a wasteland that should be bypassed on the road to Mars. Amusingly, in the same Science issue, an article about how much more water that there is on Mars was included and was seized upon as "proof" that Mars is a more compelling target of exploration. However, in this argument between the two camps, it seems that the most important point is being missed. If, after 40 years of off and on again remote sensing that is just now finding the magnitude and extent of the water, what else have we not found?
The last mission to the Moon that landed was the Soviet Luna-24 mission of August 1976. It was a sample return mission. Prior to this, between the last Apollo landing in 1972, the only missions to the Moon were Soviet in origin (four of them). It is highly unfortunate that the data from these missions has never been fully disclosed as the Soviet rovers covered tens of kilometers worth of terrain over multiple lunar days. It will be very valuable to pore over that data to see if there is any surface confirmation of the lunar water found specifically by Cassini and Deep Impact. It was this checking of the archives of the Cassini data that provided some of the confirmation of the M3 data.
With this announcement and confirmation of water data it is probably necessary to go back and reexamine other data as well from the Apollo era. Dr. Larry Taylor from the University of Tennessee has reportedly taken a second look at the water data from the Apollo samples that was originally discarded as it was considered to be terrestrial contamination. What else in the existing archive should we reexamine?
One thing that has always been puzzling is the amount nanophase iron on the Moon. This iron is what contributes to the cohesiveness of lunar agglutinates. This iron is ubiquitous in the samples from Apollo and the Soviet Luna samples and has always been explained by heating and reduction of lunar regolith by micro impacts, but is this the case? With the amount of water and O-H hydroxyls found an alternate explanation can now be entertained. What if the nanophase iron is the result of the reduction of Fe-suboxides by solar wind hydrogen bombardment? What if the suboxides are the result of reduction of Fe-oxides? Any variation of this would also actually be extremely scientifically interesting as well as having implications for the amount of reduced iron on the Moon. It should be possible to use deep drill cores as a proxy for solar activity at a time scale of millions of years. The revelations from this week's Science articles can be the foundation for an explosion of new understanding of the Moon. What about new data?
First of all, the M3 instrument will provide a rich harvest of remote sensing data for years to come. The Brown University team created a marvelous instrument with very high resolution hyperspectral data that will provide surprises for years. We also currently have the Lunar Reconnaissance Orbiter (LRO), in orbit, the first serious imaging mission of the Moon since the Lunar Orbiter program of the 1960's. Our own project at NASA Ames will take the near side equatorial regions, imaged at comparable resolution to LRO and will develop a scientific product that will allow us to determine any changes to the area based upon 43 years of time between then and now. The missions of the Indians, Chinese, and Japanese can also provide remote sensing data that will improve our understanding of the Moon. However, no matter how many remote sensing missions we fly, it is time to get down into the regolith again, and in a serious manner.
We need to land landers and rovers in the polar regions of the Moon. It is amazing that in the entire space age there has been no landings in this scientifically interesting region of the Moon. These landers should carry experiments to allow them to sample the volatile concentrations to a depth below that possible from remote sensing missions (50 cm). These should be spread in the lunar north as well as the lunar southern regions. The Mars rovers have found multiple examples of metallic meteorites, that according to recent simulations by Melosh, et al, should also be extant on the lunar surface. Rovers and landers would help to further quantify the extent of lunar resources that can feed into the process for lunar exploration. Some in the Mars community will wail that this is taking resources from Mars exploration but since the United States has flown four landers (three successfully), plus the multibillion dollar MSL to Mars, this argument is really not tenable.
The lunar community, of which I am a part, has advocated for an increased tempo of scientific exploration for decades, which has been resisted by the Science Mission Directorate and its predecessors (few of the remote sensing missions to the Moon have been NASA science missions, including the current LRO). This resistance must end and a robust program of ground truth verification of remote sensing data be implemented. Today almost all remote sensing missions are calibrated from the Apollo data, which reduces its value in the non equatorial regions where differences may throw these calibrations off. Also, in the lunar highlands where the extent of iron is much less than in the Mare regions, different reduction products from solar wind hydrogen bombardment may be present. This may not be the case due to the energies involved, but we simply don't know what the state of the environment is in these regions.
We know far more about Mars as a planet than we know about the Moon. This is a condition that cannot be allowed to stand, and the revelations from the three papers in Science this week make this abundantly clear. The argument of the Mars advocates are all based upon the results of missions to the red planet over the past few decades, this lunar advocate just wonders how much more we would have learned about the Moon if a similar number of missions had flown there. Mars is a destination of romance, the moon of utility. At the end of the day, utility will triumph as without the utility of the riches in resources that the Moon brings, there will be no romance on Mars.
These missions do not have to be the multibillion dollar Mercedes missions that the current Mars programs enjoy, indeed studies by NASA and by private entities indicates that these missions can be quite cost effective. This is doubly so as there is a $30 million dollar prize being offered by Google. If NASA really wanted to do this in a cost effective manner a $100 million dollar prize for the first gram of water distilled from the regolith would get a lot of support. Science Mission Directorate missions to multiple locations, especially locations of potential lunar outposts, should become a priority.
The bottom line in all of this is that anyone who thinks that we know enough about the Moon, does not know enough about the Moon to give that opinion. At three days away, the Moon is far more accessible to science and exploration than Mars and the papers that came out in science this week simply indicate that the more that we learn about the Moon, the friendlier it is for science and exploration.
