I have read that the particles captured from that comet by the Stardust probe may reveal data about the composition of the early solar system as it has remained unchanged for about 4.5 billion years. Now, if that probe managed to collect a measurable amount of material from I presume a fairly short flyby, wouldn’t the mass lost over 4.5 billion years have weathered the entire comet away? I gather that a comet’s trail is visible as the sun’s heat evaporates it as it passes ‘nearby’. Or was the comet simply vast at birth?
Yes, it would, but the comet has not necessarily been in its present orbit for that length of time. Comets are thought to originate as Kuiper belt or Oort cloud objects that have been perturbed into a new orbit, either by collision with another object, or by passing something with enough gravity to alter their course significantly.