May 08 (NHK) - Japan's space agency says it has found that the asteroid Ryugu may have orbited between the Sun and Mercury in the distant past. That's different from its current orbit, which passes between Earth and Mars, but not between the Sun and Mercury.
The Japan Aerospace Exploration Agency, or JAXA, says it analyzed images of the asteroid taken by a camera on its probe Hayabusa2.
JAXA says much of the sand and rock on the surface of Ryugu turned red when exposed to heat of more than 600 degrees Celsius. It says such high temperatures are inconceivable even when the asteroid is at its closest point to the Sun in its current orbit.
JAXA says the sand and rock in a recent crater on Ryugu is blue, as it has not been heated to high temperatures. It says this is because the asteroid's orbit moved farther away from the Sun in the relatively recent past.
JAXA says these findings suggest that Ryugu's shortest distance from the Sun about 300,000 to 8 million years ago was roughly one-third to one-fifth the current one.
JAXA adds that Ryugu's orbit at the time may have passed between the Sun and Mercury before shifting to the present trajectory. Mercury is the closest planet to the Sun in our solar system.
JAXA says it remains unknown what caused the change in Ryugu's orbit, but that gravity could be one reason.
University of Tokyo Associate Professor Morota Tomokatsu, who conducted the analysis, says he thinks this is the first time a change in an asteroid's orbit has been studied geologically.
He says he is looking forward to examining sand and other particles to be brought back by Hayabusa2.
Hayabusa2 is now on its way back to Earth after completing its mission on Ryugu last November. The asteroid was about 300 million kilometers from Earth when the explorer reached it in 2018.
