Ideas:

Perhaps the people of Easter Island had heard about the planet Saturn having rings, which sometimes could be seen (though not with the naked eye) protruding out on either side of the planet.

If so, then it is not certain that they also had got the idea correct: Saturn being encircled by these rings. Maybe they thought one ring was on one side and another on the other side of the planet.

To the left of the glyph above we have:

which I guess can be translated into something like "the brilliant planet, black as earth and forecasting the weather', in which case then a possible continuation could describe Saturn's rings.