Blast From the Past

[This version revised: 11.22.00]

NASA Science News; Nov 7, 2000; News: "Much Ado about 2000 SG344" 

Astronomers at the Canada-France-Hawaii telescope, high atop the extinct volcano Mauna Kea, were looking for unusual near-Earth asteroids: those that had the same maximum orbital distance from the Sun as Earth.  They found a member of this rare species on September 29th and, based on brightness, initially figured it as a 30 to 70-meter asteroid.  Soon the object, given the rather dull tracking id of "2000 SG344,"  was put into the public "spotlight" when it was found to be in a very Earth-like 354 day solar orbit.  An orbit so close to our planet that, on November 3rd, the International Astronomical Union made the ominous proclamation that 2000 SG344's next meeting with Earth in 2030 might result in a collision!  

This caused alarm because the composition of 2000 SG344 is unknown: though a 30-meter carbonaceous chondrite would burn-up in the atmosphere, a 70-meter iron meteor could destroy a city.  But now new facts have come into play.  Sky survey images from May 1999 were found to contain the object.  Position measurements from those images were used to refine the orbit and determine there was no collision danger in 2030 -- but, pending a better orbit analysis, there was still a potential danger 30-years after that date.  With "doomsday" put off for other generations of scientists to deal with,  the object started getting more attention for another, most intriguing, reason.  According to Donald Yeomans, of the Jet Propulsion Laboratory's Near Earth Object program, "The orbit of SG344 is so Earth-like, it makes you wonder if came from our own planet."  You see, 2000 SG344 was last in our vicinity in 1971 -- around the time when large booster rockets were expended into space for the Apollo Moon-landing program. 

On the Saturn-V Apollo rockets the first and second stages, along with the various modules used to transport the astronauts, either burned-up, crashed, or landed on the Earth or Moon.  The prime-suspect in SG344's case is the S-IVB (third) stage of these rockets.  Most of these were crashed into the Moon for the benefit of seismic equipment left there, but the S-IVB of Apollo 12 wound up circling the Earth after the second Moon-launch of 1969.  The possibility exists that the Moon perturbed this stage into a solar orbit.  This theory is not just a historical curiosity: if true the object would no longer be considered a hazard to the Earth.  The 15-meter long, mostly hollow, booster would burn up in the atmosphere on collision with Earth. 

Attempts to resolve the identity of SG344  -- based on size derived from object brightness -- would require scientists to know how 30-years of exposure to space affects the reflectivity of an S-IVB.  Any answer would be somewhat speculative and the better bet would be to refine SG344's orbit  -- thus determining if it was ever in Earth orbit.  The "Holly Grail" would be to find a photographic image of the object from 1971. 

2000 SG344 takes a faster tack around the Sun than Earth.  So it is continually pulling away from us and will be beyond the "viewing horizon" by mid-2001.  But this speedy sail past our planet may be aptly so: for the Command Module of Apollo 12 was dubbed: the "Yankee Clipper."

Blasted in the Past

Space Telescope Science Institute; Nov. 9, 2000; Press Release: “Hubble Sees Bare Neutron Star Streaking Across Space”

NASA and F.M. Walter (SUNY Stony Brook)

In 1992 astronomers studying the X-ray region of the spectrum with the Roentgen Satellite detected a very bright X-ray source within 500 light-years of the Earth.  The data indicated it was a neutron star of only 12-miles diameter, but with a density 10-trillion times that of steel.  Designated "RX J185635-3754" it has now been imaged several times by the Hubble Space Telescope as a 26th magnitude blue object, with a surface temperature of 600-thousand degrees Kelvin, moving at 389,000 km-per-hour, and 200-light-years away -- and getting closer.  

Not much closer it turns out.  Hubble photos in 1996 and 1999 clearly show motion of 1/3-degree/year and confirm its trajectory will bring it no closer than 170-light-years in about 300,000-years.  While not as fleet as the the well-known Barnard's star -- whose relative motion transverses 10-arc-seconds per year -- this is still one of the fastest know stellar objects we know of.  And it is definitely an invaluable object of study as the closest neutron star to Earth.

"The scientific importance of this object lies in the fact that the neutron star is isolated," says Frederick M. Walter of the State University of New York at Stony Brook, NY. "It appears to be hot, not because it is accreting hydrogen gas as it moves through space, but because it is still young and cooling off. Since we know its approximate age, we can test how fast neutron stars cool off. Because this is the closest and brightest of the few known isolated neutron stars, it is the easiest to study and is an excellent test bed for nuclear astrophysical theories."  Studies of this star were presented at the 2000 meeting of the American Astronomical Society's High Energy Astrophysics Division in Honolulu.

Current theory is that 1-million years ago, in a region that is now part of the constellation Scorpius,  the large member of a binary system went super nova.  The core of the star collapsed into this neutron star and started its journey toward us.  The smaller companion also started moving away and is suspect of being the naked-eye star known as Zeta Ophiuchus.  This is surmised because Zeta Ophiuchus and the neutron star were in the same location 1-million years ago. 

Moon to Be "Power King?"

Space.com; Nov 9, 2000; Business: "Moonlighting: Power Schemes Discussed at Conference"

A three-day meeting of the Space Resources Round Table, hosted by the Colorado School of Mines, raises the possibility of large solar "power plots" on the Moon created by robot crawlers.  Already tested on Earth, using simulated lunar soil, the lunar crawlers would scoop up the top layer of lunar regolith and process the silicon, iron, and other materials in the soil into silicon-based solar cells. 

Advantage would be taken of abundant solar energy to power the crawlers so they can melt, evaporate, and deposit refined silicon, electrodes, and coatings onto a substrate by using solar heat and the natural vacuum of the Moon.  The result is a  functional solar cell.  The process would not create the most efficient solar-cells, but what the process lacks in quality it makes up in quantity.  

Roving across the lunar surface as they processed material, the crawlers would leave a trail of 200kW solar cells for every 180-kg of lunar soil processed.  Eventually multi-megawatt plants could be built on the Moon this way.  This would achieve the goal of self-sufficiency in powering facilities on the Moon and in orbit.  The slow-moving robotic crawler is still in the design phase and could be used on Mars with some modifications.  

The facilities powered by the on-site cells would include scientific equipment,  bases, and factories to extract oxygen and fuel from the local environment.  The possibility of beaming energy back to Earth, via a "Lunar Light and Power Company," was also discussed.  

Proponents of a return to the Moon point to the commercialization prospects of the lunar powered crawlers.  "The only way we’re going back to the Moon is for commercial reasons. Something big has to come along to replace all the Cold War reasons that drove us to the Moon in the first place. The Cold War is over," G. Jeffrey Taylor, a lunar and planetary scientist at the University of Hawaii in Honolulu said, "and now it’s going to have to be commercialization. It has to be."

Pluto on the Edge

SpaceDaily.com; Oct. 24, 2000; Space Science: "Astronomers Discover Apparent Outer 'Edge' to the Solar System"

Evidence was presented at the recent division of Planetary Sciences meeting in Pasadena that there are no large objects beyond the orbit of Pluto.  This was the conclusion reached after Lynne Allen and Gary Bernstein, of the University of Michigan, and Renu Malhotra of the University of Arizona Lunar and Planetary Laboratory, searched areas of the sky looking for objects as small as 160-km in diameter at a disance of 65-AU.  This work was done with advanced equipment at the Cerro Tololo Inter-American Observatory high in the Chilean Andes.  

Images in 1998 and 1999 discovered 24 new objects, but none further out than about 50-AU -- the extreme edge of Pluto's orbit.  In total there are now 300 such "Kuiper Belt Objects" -- all within 55 AU of the Sun.  This is compelling evidence that the solar system has an "edge" in the vicinity of Pluto's orbit.  Speculation is that something happened in the past to strip away planet-building material beyond this border.

While comets and some Kuiper Belt Objects have orbits that carry them beyond Pluto, these are thought to have been formed within the bounding orbit of Pluto and perturbed by the outer planets to move outside this boundary.  Continuing surveys are being made to determine facts concerning our solar system and its history.