So Long, Space Junk
19 Sep 2002
(Source: Near Earth Object Program Office)
New Clues in the Continuing Detective Story of J002E3
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.