During its descent and dice roll, MASCOT saw 2 distinct types of rocks, distributed roughly equally around Ryugu's surface. One type is comparatively brighter (remember, Ryugu is very, very dark) and has smooth faces and sharp edges, while the other type is darker with cauliflower-like, crumbly surfaces. The rocks MASCOT imaged during its second night were of the cauliflower variety, and appear to include small grains that are rich in calcium and aluminum. That makes the rocks reminiscent of a rare type of meteorite called carbonaceous chondrites. (Specifically, for meteorite fans: they are most similar to CI2 chondrites like the Tagish Lake meteorite.) These rocks are about 4.5 billion years old—practically the age of the solar system. They've never been melted by volcanic processes or impacts from other objects, though they’ve been warm enough for liquid water to change their chemistry.

Okay, so Ryugu has 2 types of rocks, and some were formed during the birth of our solar system. Where did Ryugu come from? Here's what Ralf Jaumann, head of the MASCOT science team and lead author of the new paper, says about this:

"Ryugu could have been formed following the collision of two bodies made of different materials. As a result, it would have broken up, before the fragments came together under the influence of gravity to form a new body made up of the two different types of rock. Alternatively, Ryugu could be the remnant of a single body whose inner zones had different temperature and pressure conditions, thus resulting in the formation of two types of rock."

Another interesting MASCOT finding is that there's no regolith or dust in these images, just rocks. The unexpected rockiness of Ryugu (and likewise of Bennu, seen by the OSIRIS-REx mission) has been an important finding. In theory, there should be regolith on Ryugu for the same reason it's everywhere on the Moon: continual micrometeorite bombardment.

Jaumann speculates that the micrometeorite dust either escapes into space thanks to Ryugu's weak gravity, or settles into cavities beneath the surface. As Emily Lakdawlla reported in a post on Ryugu's initial science results, the asteroid is basically a rubble pile riddled with gaps and pockets. It has a density of just 1.2 grams per cubic centimeter—barely denser than water ice. Since it’s made of rocky material with a density of about 3 grams per cubic centimeter, that means it has to have a lot of empty space.

All this means Ryugu is extremely fragile, which has some implications for planetary defense. Ryugu is a C-type (chondrite) asteroid; roughly 75% of known asteroids are C-type. If a Ryugu-like asteroid were to come hurtling towards Earth, blowing it up might be the worst thing we could do, writes Jaumann:

"In the event that it was impacted with great force, the entire asteroid, weighing approximately half-a-billion tonnes, would break up into numerous fragments. Then, many individual parts weighing several tonnes would impact Earth."

Fortunately, there's a reason that carbonaceous chondrite meteorites—possibly made from the same type of rock that MASCOT saw on night 2—are rare. They're so porous and fragile, they burn up in Earth’s atmosphere. That was a finding from a paper on MASCOT's radiometer published in July.

But just how big of a C-type asteroid chunk can Earth’s atmosphere handle? The scientists behind the radiometer paper say that "...further research is necessary to determine the maximum asteroid size for which this atmospheric protection is effective." Sounds like we better keep working on our planetary defense efforts!