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28th November 2015

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Detectability of planetesimal impacts on giant exoplanets →

This interesting recent paper by Laura Flagg, Alycia J. Weinberger, and Keith Matthews (the preprint is available at Detectability of Planetesimal Impacts on Giant Exoplanets and as a PDF) notes that…

“In today’s Solar System, planetesimals infrequently hit planets; although, in the past, such impacts were much more common. The cratering rates on the Moon and Mars indicate that the impact rates were high prior to ∼800 Myr after the formation of the Solar System, perhaps ending in a ‘Late Heavy Bombardment.’ Today, a comet larger than 1 km in diameter impacts Jupiter only every few hundred years.”

Planetesimals only infrequently hit planets in our planetary system, but in so far as we are able to look at the almost countless planetary systems in our universe, an event that this rare here will be amply represented elsewhere. Scientific methods and instruments that make it possible for us to study exoplanetary systems not only will reveal interesting new properties, but will also greatly increase the frequency with which we can view events that are known but rare in our own planetary system.

When I noticed this paper I immediately thought of the studies of supernovae in other galaxies that revealed to us that the universe is accelerating in its expansion. In our galaxy, supernovae are infrequent on a human time scale. Tycho Brahe (1572) and Kepler (1604) saw supernovae with the naked eye before the invention of modern scientific instruments; hundreds of years later SN1987A was observed in Large Magellanic Cloud where we were able to observe it with a variety of scientific instruments, including neutrino detectors buried deep in the Earth, which registered the neutrino flux from the core collapse.

When we look out into the universe, supernovae go from being rare events on a human time scale to being common events. This is the spatial equivalent to what Carl Sagan pointed out in terms of time:

“On the landscapes of other planets where the records of the past have been preserved, there is abundant evidence of major catastrophes. It is all a matter of time scale. An event that would be unthinkable in a hundred years may be inevitable in a hundred million.” (Carl Sagan, Cosmos, Chapter IV, “Heaven and Hell”) 

Similarly, an event that would be unthinkable within our solar system may be inevitable when we look out among the billions of planetary systems within our own galaxy.

As our ability to image and to study exoplanets improves, we will no doubt face a cornucopia of data, making once rare events commonplace to us. This is, in a sense, a function of the way in which cosmology is the principle of plenitude teaching by example. The deeper we peer into the universe, the more we will see, and there is almost nothing we can imagine that will not be exemplified in some planetary system somewhere in the cosmos.

Tagged: astronomyastrophysicsexoplanetsplanetary systemsscienceLaura FlaggAlycia J. WeinbergerKeith Matthews