Simplify the following text for a Grade 10 native English-speaking person.
Original: Although Cruithne 's orbit is not thought to be stable over the long term , calculations by Wiegert and Innanen showed that it has probably been synchronized with Earth 's orbit for a long time .
Simplified: Although Cruithne 's orbit is not thought to be stable over the long term , calculations showed that it has probably been synchronized with Earth 's orbit for a long time .