New 'moon' found around Earth
There could be another one . . .
By Dr David Whitehouse
BBC News Online science editor
An amateur astronomer may have found
another moon of the Earth. Experts say it may have only just arrived.
Much uncertainty surrounds the mysterious object, designated J002E3. It could
be a passing chunk of rock captured by the Earth's gravity, or it could be a
discarded rocket casing coming back to our region of space.
It was discovered by Bill Yeung, from his observatory in Arizona, US, and
reported as a passing Near-Earth Object.
It was soon realised, however, that far from passing us, it was in fact in a
50-day orbit around the Earth.
Paul Chodas, of the American space agency's Jet Propulsion Laboratory in
California, says it must have just arrived or it would have been easily detected
long ago.
Calculations suggest it may have been captured earlier this year.
Moon or junk?
When he detected the object, Bill Yeung contacted the Minor Planet Center in
Massachusetts, the clearing house for such discoveries, which gave it the
designation J002E3 and posted it on their Near-Earth Object Confirmation webpage.
Soon, however, the object's motion suggested it was in an orbit around the
Earth. Its movements had all the hallmarks of being a spent rocket casing or
other piece of space junk.
But experts are not completely sure what exactly the object is.
Observations made by Tony Beresford in Australia indicate that the object's
position does not match any known piece of space junk.
Observations made in Europe have failed to see any variations in brightness
that might be expected from a slowly spinning metallic object.
Paul Chodas says the object must have arrived quite recently or else it would
have been easily detected by any of several automated sky surveys that
astronomers are conducting.
Its trajectory suggests that it may have been captured in April or May of
this year, but there is still some uncertainty about this.
If it is determined that J002E3 is natural it will become Earth's third
natural satellite.
Earth's second one is called Cruithne. It was discovered in 1986 and it takes
a convoluted horseshoe path around our planet as it is tossed about by the
Earth's and the Moon's gravity.
New Moon for Earth, or Space Junk?
AFP
Sep. 13 — An enigmatic object spotted in the night sky last week by an amateur astronomer has set experts wondering whether the Earth may have gained a new moon.
Others say the answer could be quite different, but almost as exciting. They believe it to be a piece of space history left over by the Apollo lunar pioneers, and that the Earth has now reclaimed it, saving it from the fiery embrace of the sun.
Bill Yeung, a keen astronomer who has a backyard observatory in Arizona, sparked the debate when he found the small object on September 3 and noted that it was on none of the lists of wanderers known to rove the solar system.
He reported his find to the Minor Planet Center, the clearing house for information about asteroids and comets.
It was categorized as a Near-Earth Object — a piece of space debris that flies past our planet as it pursues a lonely, elliptical path around our star — and designated J002E3.
But JOO2E3, located about 700,000 kilometers (450,000 miles) away, or twice the distance between the Earth and moon, turned out to be a puzzler.
Finer calculations determined it was not in orbit around the sun, but around the Earth, orbiting every 50 days. That meant one of two things. J002E3 was either a piece of space junk, part of a whirling mass of debris left from more than four decades of space flight, or a passing asteroid that had been snared by the Earth's gravity.
Early calculations by an Australian astronomer, Tony Beresford, and Czech astronomer Peter Kusnirak suggest that J002E3 may not be man-made. Its location does not match that of any known space junk and has never been spotted before, despite relentless scouring of the heavens by automatic scanners.
Nor does it show any of the variations in brightness that are typically given out by a spinning metallic object in space.
However, experts at NASA's Jet Propulsion Laboratory (JPL) believe it could be the third-stage booster of the mighty Saturn V rocket that propelled the Apollo 12 astronauts to the moon in November 1969. Measuring 58 feet (17.8 meters) long with a diameter of 22 feet (6.7 meters), the booster provided an all-important burn that set the three-man crew on their final lunar trajectory.
In a statement posted on the JPL's website Wednesday, Paul Chodas of the Near-Earth Object Program Office suggests the spent rocket body, if indeed this is what it is, was left in "a very distant" Earth orbit after it passed by the moon on November 18 1969.
JOO2E3 gradually fell into a heliocentric orbit, meaning an orbit around the sun, until in April this year it passed through the so-called L1 Lagrange Point, a location where the gravity of the Earth and sun approximately cancel each other out, said Chodas.
Plucked by the Earth's lingering gravitational tendrils, it was then gradually hauled back our way.
"JOO2E3 is the first known case of an object being captured by the Earth, although Jupiter has been known to capture comets via the same mechanism," Chodas wrote.
He calculated that the object has a one-in-five chance of smashing into the moon in 2003, as well as an approximately 3 percent chance of hitting the Earth, albeit without posing any significant threat to human life, within the next 10 years.
If J002E3 turns out to be a rock, it will be Earth's third companion. In addition to the moon, the Earth is orbited by a tiny asteroid called Cruithne, which was spotted by European astronomers in 1986 and named after Celtic tribes who came to Britain between about 880 and 500 B.C.
Cruithne, pronounced "Croo-een-ya," follows a strange horseshoe-shaped path around the solar system, pulled alternately by the sun and Earth. At its closest approach it only gets to within about 9 million miles (15 million kilometers) of our planet.
