Asteroid Vesta is 'last of a kind' rock. (Earth, solar, saturn)

[Baldrick]

An interesting article.

BBC News - Asteroid Vesta is 'last of a kind' rock

"Vesta is the only remaining example of the original objects that came together to form the rocky planets, like Earth and Mars, some 4.6 billion years ago.
This assessment is based on data from the Dawn probe which has been orbiting the second largest body in the asteroid belt for the past 10 months.
The findings from the Nasa mission are reported in Science magazine."

[Glitch]

Considering the vast amount of information that we do not know about our solar system, it is rather presumptuous to assume that Vesta is the "only remaining example."

[orogenicman]

Indeed, but I think the qualifier is "that came together to form the rocky planets". Ceres doesn't really count as one of these objects since it has already coalesced into a planetary body. In other words, it isn't a protoplanet like Vesta is. It is a dwarf planet more akin to Pluto. On the other hand, there are other objects in the solar system that are considered to be protoplanets. An object that is probably similar to Vesta is Phoebe, a moon of Saturn that, judging from its retrograde orbit, appears to be a captured Kuiper belt object. It has a similar composition and size, and likely is a relic of the birth of the solar system.

[Glitch]

Originally Posted by orogenicman

Indeed, but I think the qualifier is "that came together to form the rocky planets". Ceres doesn't really count as one of these objects since it has already coalesced into a planetary body. In other words, it isn't a protoplanet like Vesta is. It is a dwarf planet more akin to Pluto. On the other hand, there are other objects in the solar system that are considered to be protoplanets. An object that is probably similar to Vesta is Phoebe, a moon of Saturn that, judging from its retrograde orbit, appears to be a captured Kuiper belt object. It has a similar composition and size, and likely is a relic of the birth of the solar system.

While the Kuiper Belt objects formed at the same time as the rest of the solar system, there are chemically differences from the other planets and most other objects that formed within the solar system. For example, we have determined that our oceans could not have formed from Kuiper Belt objects, such as comets. The Deuterium levels in the Kuiper Belt objects is a lot more than what we find in our oceans. However, the Deuterium levels in the Asteroid Belt is an identical match to what we find in our oceans.

I agree with you that Phoebe is most likely a captured Kuiper Belt object, and it is also likely that Triton (one of Neptune's moons) also originated in the Kuiper Belt for the same reasons. Triton also orbits in a retrograde orbit, and as the same chemical composition as Pluto and other Kuiper Belt objects. It is considered an irregular moon, even though it is large enough to form a sphere, defying classification.

One of the places we have not explored in any depth, within our solar system, are the Greek (L4) and Trojan (L5) asteroids in Jupiter's Lagrange Points. Are they chemically the same as the objects in the Asteroid Belt, or the Kuiper Belt? Are they left over objects from the formation of the solar system, or are they captured objects from the Kuiper Belt?

Until those questions can be answered I do not think it is wise to proclaim Vesta as being the "only remaining example of the original objects that came together to form the rocky planets."