11/06/2003
Big Rocks and Green Stuff
Phew! Hermes has been found again after 66 years in limbo. Its rediscovery rated less than half a page, an article by Govert Schilling, in the October 24 issue of Science but we can all breath a sigh of relief. Of course, the chances are that you didn’t even know Hermes has been lost since its discovery back in 1937 when German astronomer Karl Reinmuth discovered Hermes sailing by our earth only about twice as far away from us as our moon. Hermes was thought to be a rock, some called it a minor planet, roughly half a mile to a mile across. Hermes disappeared too quickly for its orbit to be nailed down precisely. Over the years, astronomers would wonder uneasily just where Hermes was and if it would return soon. There was concern that if it did return it might be much closer to Earth than during its 1937 visit.
Two years ago other German scientists, Lutz Schmadel and Joachim Schubart, took a closer look at some forgotten plates from 1937 and predicted that Hermes would return this year in October. Sure enough, a couple weeks ago, early on October 15, Brian Skiff of the Lowell Observatory Near-Earth Object Search Program in Arizona found a bit of new light on one of his images. Quickly, the image was dispatched to Timothy Spahr at the Minor Planet Center in Cambridge, Massachusetts. Spahr correlated the new object with some other very recent data he had received from the Lincoln Near Earth Asteroid Research project in New Mexico. In a remarkable example of a cross- country cooperative effort, before dawn on that same morning of October 15, James Young at the Table Mountain Observatory in California had confirmed the sighting.
The object was indeed Hermes. Events can move very rapidly in the astronomical community. Within a week of the new sighting, astronomers at the Arecibo Radio Telescope facility in Puerto Rico had weighed in with a new finding. They have evidence that Hermes may not be a single object, but two sizeable rocks in a tight orbit around each other, each rock somewhere between about 900 to 1300 feet across. Whatever the situation, we don’t have to worry. Earlier this week (on November 4), Hermes passed its closest to the earth on this trip, about nine times farther away than in 1937. And it looks like we don’t have to worry for the next hundred years. But Hermes is an erratic sort that has to be watched and future generations shouldn’t let it get lost again!
There was other space-related news, both good and bad, in the same issue of Science. The bad news had to do with the failure of a mission that was intended to study other objects flitting around in our celestial neighborhood, namely, comets. The mission was NASA’s Comet Nucleus Tour (CONTOUR), which was slated to visit at least two comets and analyze their compositions. CONTOUR was launched in July last year but contact was lost in August that year after firing a rocket engine to boost it out of orbit and head it toward the comet Encke. A NASA investigative report has just been released which cites the probable cause as being a failure of engineers to take into account the effects of hot gases emitted from the internally mounted rocket.
The likely cause of the loss of CONTOUR is that these hot gases resulted in actual melting of parts of the spacecraft. There’s speculation that budgetary constraints played a role in the lack of adequate engineering analysis of potential problems. This failure is added to the list of other doomed NASA missions, which include the Columbia disaster and the failures of two Mars probes to reach their objectives.
The good news is that one Mars mission continues to be a resounding success. The Mars Global Surveyor, which arrived at Mars in September 1997, has been chugging away in orbit around Mars ever since. Its current mission is to map the mineral composition of the entire surface of Mars. To identify the minerals, Surveyor employs an instrument known as a Thermal Emission Spectrometer (TES). The TES in essence measures the heat coming off the Mars surface. Actually, the heat is infrared radiation and the TES separates this infrared radiation into its various wavelengths or “colors”, much like a prism separates sunlight into the colors of the rainbow. The infrared “colors”, however, are not visible to our eyes. Different minerals can be identified by their distinct patterns, or spectra, of infrared radiation.
So far, about 3/4 of Mars’ surface has been mapped. According to the U. S. Geological Survey (USGS) Web site, literally hundreds of trillions of calculations have been performed on the data to obtain a detailed map of the minerals on Mars’ surface. The paper in Science is a collaborative effort of workers at USGS, Arizona State University and Goddard Space Flight Center and is titled “Discovery of Olivine in the Nili Fossae Region of Mars”.
Why the interest in olivine, a silicate containing magnesium and iron in various proportions? Well, for one reason, olivines are typically greenish in color and we know Mars as a red planet. This may sound trivial but the fact that there’s this green stuff on Mars is significant. Olivine is a mineral that here on earth is very prone to “weathering”. That is, in the presence of a warm and wet environment, olivines react to form a wide variety of other minerals that are not green in color. There’s been a lot of press given over the past few years concerning evidence on Mars that there has been massive flooding sometime in Mars’ history. Most researchers seem to agree that today there is a lot of water on Mars but it’s in the form of ice. And the temperature on Mars is way on the cold side.
What’s significant about the Nili Fossae region of Mars? Nili Fossae is a region associated with an impact zone dating back over 3 billion years ago. Some 30,000 square miles in this region are rich in olivine. If that olivine was exposed by the impact, it follows that there couldn’t have been a warm wet period in the region for over 3 billion years. Otherwise, the olivine would have weathered and no longer exist. This, if true, bodes poorly for the existence of any warm, wet weather on Mars and argues against the likelihood of any life forms of the type we’re familiar with.
Of course, there is the possibility that the olivine was not exposed until much more recently. In that case, we could only conclude that it was cold and dry since the more recent exposure. However, the authors of the Science paper point out that olivine has also been found extensively elsewhere on Mars, not just in this impact region. They would argue that Mars has been cold and dry for a long, long time. However, the door is still open and, hopefully, the two Mars landers scheduled to touch down in a few months will succeed in shedding more light on the question, “Is there or has there ever been life on Mars?”
Meanwhile, let’s keep our fingers crossed that there aren’t any large rocks such as Hermes headed our way. A visit to various Web sites such as a German site associated with Astroteam Aichfeld turned up lists of asteroids or rocks that have passed by us recently, some much closer than Hermes. We’re due later this month for the annual Leonid meteor shower, the debris from an old comet. This debris is more like dust than boulders so we shouldn’t have anything to worry about. But hey, I won’t sneer if you’re wearing a hard hat while watching those shooting stars!
Allen F. Bortrum
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