Interstellar Visitor Found to Be Unlike a Comet or an Asteroid
This is a little misleading because it presents the idea that there is a firm separation between &quot;comets&quot; and &quot;asteroids&quot;, each of which have very different properties. In reality we&#x27;ve discovered in recent decades that there is significant overlap. Pure comets were formed in the outer solar system beyond the frost line, and they are composed of a mixture of primarily chondritic grains and ices. As noted such bodies are not very structurally strong so if they approach the Sun too closely they will break up from the stress of gravity as well as from the intensity of off-gassing vaporizing gasses. On the other hand you have classic asteroids which are formed inside the frost line and are made up of either chondritic material, stone, or metal (depending on their histories). Such asteroids can be much stronger but they lack the ices which might off-gas during a close solar encounter.<p>Except, that dichotomy is a simplified fiction. The reality is that there are objects in the middle, sometimes called &quot;iceteroids&quot; which we&#x27;ve discovered over the years. These could be the cores of comets which have lost most of their ices or these could be objects with more complicated histories, such as asteroids which have accreted surface layers of ices through various processes.<p>So this is a mystery but it&#x27;s not some enormous mystery it&#x27;s a small mystery. The idea that an asteroid could have acquired a small amount of ices on its surface isn&#x27;t exactly world shattering news but because we don&#x27;t know the history of the object we don&#x27;t know the process by which it ended up with its observed properties.