Skip to main content Accessibility help

Jupiter – friend or foe? II: the Centaurs

  • J. Horner (a1) and B.W. Jones (a1)


It has long been assumed that the planet Jupiter acts as a giant shield, significantly lowering the impact rate of minor bodies upon the Earth, and thus enabling the development and evolution of life in a collisional environment which is not overly hostile. In other words, it is thought that, thanks to Jupiter, mass extinctions have been sufficiently infrequent that the biosphere has been able to diversify and prosper. However, in the past, little work has been carried out to examine the validity of this idea. In the second of a series of papers, we examine the degree to which the impact risk resulting from objects on Centaur-like orbits is affected by the presence of a giant planet, in an attempt to fully understand the impact regime under which life on Earth has developed. The Centaurs are a population of ice-rich bodies which move on dynamically unstable orbits in the outer Solar system. The largest Centaurs known are several hundred kilometres in diameter, and it is certain that a great number of kilometre or sub-kilometre sized Centaurs still await discovery. These objects move on orbits which bring them closer to the Sun than Neptune, although they remain beyond the orbit of Jupiter at all times, and have their origins in the vast reservoir of debris known as the Edgeworth–Kuiper belt that extends beyond Neptune. Over time, the giant planets perturb the Centaurs, sending a significant fraction into the inner Solar System where they become visible as short-period comets. In this work, we obtain results which show that the presence of a giant planet can act to significantly change the impact rate of short-period comets on the Earth, and that such planets often actually increase the impact flux greatly over that which would be expected were a giant planet not present.


Corresponding author


Hide All
Babadzhanov, P.B., Wu, Z., Williams, I.P. & Hughes, D.W. (1991). The Leonids, Comet Biela and Biela's associated meteor stream. Mon. Not. R. Astron. Soc. 253, 6974.
Chambers, J.E. (1999). A hybrid symplectic integrator that permits close encounters between massive bodies. Mon. Not. R. Astron. Soc. 304, 793799.
Chapman, C.R. & Morrison, D. (1994). Impacts on the Earth by asteroids and comets: assessing the hazard. Nature 367, 3340.
Greaves, J.S. (2006). Persistent hazardous environments around stars older than the Sun. Int. J. Astrobiology 5, 187190.
Gomes, R., Levison, H.F., Tsiganis, K. & Morbidelli, A. (2005). Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets. Nature 435, 466469.
Horner, J., Evans, N.W. & Bailey, M.E. (2004). Simulations of the population of Centaurs – I. The bulk statistics. Mon. Not. R. Astron. Soc. 354, 798810.
Horner, J., Evans, N.W., Bailey, M.E. & Asher, D.J. (2003). The populations of comet-like bodies in the Solar system. Mon. Not. R. Astron. Soc. 343, 10571066.
Horner, J. & Jones, B.W. (2008). Jupiter – friend or foe? I: the asteroids. Int. J. Astrobiology 7(3–4), 251261.
Laasko, T., Rantala, J. & Kaasalainen, M. (2006). Gravitational scattering by giant planets. Astron. Astrophys. 456, 373378.
Levison, H.F. & Duncan, M.J. (1997). From the Kuiper Belt to Jupiter-family comets: the spatial distribution of ecliptic comets. Icarus 127, 1332.
Levison, H.F., Terrell, D., Wiegert, P.A., Dones, L. & Duncan, M.J. (2006). On the origin of the unusual orbit of comet 2P/Encke. Icarus 182, 161168.
Matese, J.J. & Lissauer, J.J. (2004). Perihelion evolution of observed new comets implies the dominance of the galactic tide in making Oort cloud comets discernable. Icarus 170, 508513.
Wetherill, G.W. (1994). Possible consequences of absence of Jupiters in planetary systems. Astrophys. Space Sci. 212, 2332.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

International Journal of Astrobiology
  • ISSN: 1473-5504
  • EISSN: 1475-3006
  • URL: /core/journals/international-journal-of-astrobiology
Please enter your name
Please enter a valid email address
Who would you like to send this to? *



Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed