An Observational Upper Limit on the Interstellar Number Density of Asteroids and Comets

Toni Engelhardt, Robert Jedicke, Peter Vereš, Alan Fitzsimmons, Larry Denneau, Ed Beshore, Bonnie Meinke

Research output: Contribution to journalArticlepeer-review

89 Scopus citations


We derived 90% confidence limits (CLs) on the interstellar number density (rIS CL) of interstellar objects (ISOs; comets and asteroids) as a function of the slope of their sizefrequency distribution (SFD) and limiting absolute magnitude. To account for gravitational focusing, we first generated a quasi-realistic ISO population to ∼750 au from the Sun and propagated it forward in time to generate a steady state population of ISOs with heliocentric distance <50 au. We then simulated the detection of the synthetic ISOs using pointing data for each image and average detection efficiencies for each of three contemporary solar system surveys-Pan-STARRS1, the Mt. Lemmon Survey, and the Catalina Sky Survey. These simulations allowed us to determine the surveys combined ISO detection efficiency under several different but realistic modes of identifying ISOs in the survey data. Some of the synthetic detected ISOs had eccentricities as small as 1.01, which is in the range of the largest eccentricities of several known comets. Our best CL of pISCL=1.4× 10-4 au-3implies that the expectation that extra-solar systems form like our solar system, eject planetesimals in the same way, and then distribute them throughout the Galaxy, is too simplistic, or that the SFD or behavior of ISOs as they pass through our solar system is far from expectation.

Original languageEnglish (US)
Article number133
JournalAstronomical Journal
Issue number3
StatePublished - Mar 2017


  • comets: general
  • minor planets, asteroids: general
  • planetary systems
  • protoplanetary disks

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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