"The good news made me so happy", Hayabusa2 project spokesperson Takashi Kubota said in a statement on the mission website.
They will also measure the surface temperature ahead of Hayabusa2's own landing late next month.
The rovers are collectively known as MINERVA-II1.
And about the "II" in the hoppers' name: The first Hayabusa mission, which was also operated by the Japan Aerospace Exploration Agency and arrived at the asteroid Itokawa in 2005, featured a hopper named MINERVA.
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In Japanese, Hayabusa means falcon, and Ryugu is the name of an undersea place where a dragon king lived. "This is just a real charm of deep space exploration".
An artist's impression of the MINERVA-II1 landers deployed by Japan's Hayabusa2 spacecraft.
Just knowing that two tiny robots are now hopping merrily around an asteroid with nearly no gravity makes our own world seem a little bit merrier. After the rovers were on their way, the spacecraft raised itself back up to its typical altitude of about 12.5 miles above the asteroid's surface (20 kilometers).
These samples will be sent to Earth for laboratory studies. The main Hayabusa 2 vessel should near the surface in October, when it will shoot a tantalum "bullet" into the asteroid so that it can catch particle samples and return them to Earth. A separate lander, MASCOT, will obtain the samples.
One of the principal concerns for deployment was Ryugu's rougher-than-expected surface, which is carpeted with boulders and has very few smooth patches.
Asteroids are essentially leftover building materials from the formation of the Solar System 4.6 billion years ago.