Paul Chodas and Steve Chesley
NASA’s Near-Earth Object Program Office

The precision of our orbit solution for the unusual Earth-orbiting
object J002E3 has improved considerably since last week, as
astronomers around the world have continued to track this
interesting body and provide measurements of its position.
Even though the object has been tracked for only 15 days and
traveled only about one sixth of the way around its orbit since
discovery, it is now possible to draw more precise conclusions
about its origin and future destinations.

While it was strongly suspected a week ago that J002E3 had been
captured by the Earth in April of this year, it was not known
how long the object had been orbiting the Sun prior to capture.
Additional observations have now confirmed that the object was
indeed captured from a solar orbit earlier this year, and they
have also made clear that it escaped the Earth-Moon system in
March 1971. The mechanics of the escape are much like those of
the capture in reverse: in both cases, the object passes slowly
through a portal separating the regions of space controlled by
the Earth and Sun. The portal is located at the L1 Lagrange
point, about 1.5 million kilometers from Earth on a line
towards the Sun.

The timing of the object’s escape is consistent with our
theory that this object is the Apollo 12 S-IVB third stage,
which was left in a distant Earth orbit after it was launched
on November 14, 1969 and passed the Moon four days later. We
theorize that the spent rocket orbited the Earth chaotically for
15 months before finding the exit pathway through the L1 portal.
The excellent match between the intrinsic brightness of J002E3
and that expected for a rocket stage of the S-IVB’s size also
supports this theory. The other four S-IVB stages still flying
(those from Apollos 8 through 11) have been dismissed as
suspects because they entered solar orbit much earlier than
March 1971.

Other possibilities for the true identity of J002E3 have been
suggested. The object could be one of the Spacecraft-Lunar
Module Adapter panels which enclosed the Lunar Module during
Apollo launches. Or, the object might be a rocket stage from
an unmanned lunar probe from that era. None of these, however,
were launched at the right time or are known to have entered
the sort of distant orbit from which escape is possible.
Furthermore, these alternative candidates seem too small to
explain the current brightness of J002E3. We conclude that the
Apollo 12 S-IVB stage is the most likely identity of the object.

Our improved orbital knowledge for J002E3 is also allowing
more precise predictions for its future motion. The likelihood
that the object will impact the Moon next year has decreased
to less than one percent. This new conclusion follows from
the fact that the range of possible motion in 2003 is now more
tightly constrained and barely intersects the Moon. The
possibility of collision with the Earth has also decreased,
down to well less than one percent. (Even if it should hit our
planet, the object is too small to be considered hazardous.)
It now appears likely that the object will escape back into
solar orbit in June 2003 after its brief six-orbit visit to
our planet. In 30 years time the Earth may once again capture
J002E3 for another brief tour around its home planet.