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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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