Protoplanetary Phlegm

Originally it was thought that the moon was a captured protoplanet that had been so attracted by Earth’s gravitational well it decided to stick around for a few hundred million years. Then, theory evolved and changed, so the moon became the aftereffects of a massive collision between early Earth and some other huge body. Planets form from collisions of smaller things slamming together around a star.

Spitzer, the last of NASA’s Great Observatories mission, has retrieved images containing evidence that such collisions are taking place in the Pleiades star cluster located in Taurus on the night sky. When planets form from dusty discs around new stars, one of two things can happen. The dust can clump together and smash into neighboring clumps and stick, or they can crumble into itty bitty pieces and try to start the clumping process over again.

The amount of dust that Spitzer is imaging, however, is said to have been caused by something much bigger than little clumps of rocks floating around. According to calculations made by the researching team, only crashing planetoids could leave behind the trail that is being seen. An analysis from the emission lines coming from the dust led scientists to conclude that the ring around the star HD 23514 in the Pleiades is indeed second generation, or the dust had formed something massive at one time and had been smashed apart subsequently.

One of the reasons scientists think this disk is not primordial is because the stars are so old. The Pleiades star cluster is on the order of 100 million years old, which is more than enough time to clear its neighborhood of any dust and debris. The remaining particles in the star’s area must be something too heavy to be blown away by stellar winds and radiation.
This is not the first ring that has been found around a star where the dust is not of primordial make up. The same team that monitored HD 23514 also discovered a ring of second generation particles orbiting around a solar like star. This was in fact what led them to look at the Pleiades star system and find a dust ring around one of their stars.

Such star systems are crucial to learning about how our own solar system formed. Terrestrial planets and the cores of gas giants formed from massive collisions of protoplanets just like the ones that are being postulated in the systems above. If we can learn about planetary formation by studying stars such as HD 23514, then we might learn more about other solar systems that are forming, and why our own solar system seems to be a minority, containing terrestrial planets rather than gas giants.