### Abstract

We calculate the present-day impact flux on Mars and its variation over the martian year, using the current data on the orbital distribution of known Mars-crossing minor planets. We adapt the Öpik-Wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. We find that, at the current epoch, the Mars crossers have an axial distribution of the argument of perihelion, and the mean direction of their eccentricity vectors is nearly aligned with Mars' eccentricity vector. These previously neglected angular non-uniformities have the effect of depressing the mean annual impact flux by a factor of about 2 compared to the estimate based on a uniform random distribution of the angular elements of Mars-crossers; the amplitude of the seasonal variation of the impact flux is likewise depressed by a factor of about 4-5. We estimate that the flux of large impactors (of absolute magnitude H<. 16) within ±30° of Mars' aphelion is about three times larger than when the planet is near perihelion. Extrapolation of our results to a model population of meter-size Mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be 11-15, but if they track the orbital distribution of the large impactors, including their non-uniform angular elements, then this ratio would be about 3. Comparison of our results with the current dataset of fresh impact craters on Mars (detected with Mars-orbiting spacecraft) appears to rule out the uniform distribution of angular elements.

Original language | English (US) |
---|---|

Article number | 11703 |

Pages (from-to) | 140-153 |

Number of pages | 14 |

Journal | Icarus |

Volume | 262 |

DOIs | |

State | Published - Dec 1 2015 |

### Fingerprint

### Keywords

- Asteroids
- Asteroids, dynamics
- Cratering
- Mars
- Mars, surface

### ASJC Scopus subject areas

- Space and Planetary Science
- Astronomy and Astrophysics

### Cite this

*Icarus*,

*262*, 140-153. [11703]. https://doi.org/10.1016/j.icarus.2015.08.032

**The current impact flux on Mars and its seasonal variation.** / JeongAhn, Youngmin; Malhotra, Renu.

Research output: Contribution to journal › Article

*Icarus*, vol. 262, 11703, pp. 140-153. https://doi.org/10.1016/j.icarus.2015.08.032

}

TY - JOUR

T1 - The current impact flux on Mars and its seasonal variation

AU - JeongAhn, Youngmin

AU - Malhotra, Renu

PY - 2015/12/1

Y1 - 2015/12/1

N2 - We calculate the present-day impact flux on Mars and its variation over the martian year, using the current data on the orbital distribution of known Mars-crossing minor planets. We adapt the Öpik-Wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. We find that, at the current epoch, the Mars crossers have an axial distribution of the argument of perihelion, and the mean direction of their eccentricity vectors is nearly aligned with Mars' eccentricity vector. These previously neglected angular non-uniformities have the effect of depressing the mean annual impact flux by a factor of about 2 compared to the estimate based on a uniform random distribution of the angular elements of Mars-crossers; the amplitude of the seasonal variation of the impact flux is likewise depressed by a factor of about 4-5. We estimate that the flux of large impactors (of absolute magnitude H<. 16) within ±30° of Mars' aphelion is about three times larger than when the planet is near perihelion. Extrapolation of our results to a model population of meter-size Mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be 11-15, but if they track the orbital distribution of the large impactors, including their non-uniform angular elements, then this ratio would be about 3. Comparison of our results with the current dataset of fresh impact craters on Mars (detected with Mars-orbiting spacecraft) appears to rule out the uniform distribution of angular elements.

AB - We calculate the present-day impact flux on Mars and its variation over the martian year, using the current data on the orbital distribution of known Mars-crossing minor planets. We adapt the Öpik-Wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. We find that, at the current epoch, the Mars crossers have an axial distribution of the argument of perihelion, and the mean direction of their eccentricity vectors is nearly aligned with Mars' eccentricity vector. These previously neglected angular non-uniformities have the effect of depressing the mean annual impact flux by a factor of about 2 compared to the estimate based on a uniform random distribution of the angular elements of Mars-crossers; the amplitude of the seasonal variation of the impact flux is likewise depressed by a factor of about 4-5. We estimate that the flux of large impactors (of absolute magnitude H<. 16) within ±30° of Mars' aphelion is about three times larger than when the planet is near perihelion. Extrapolation of our results to a model population of meter-size Mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be 11-15, but if they track the orbital distribution of the large impactors, including their non-uniform angular elements, then this ratio would be about 3. Comparison of our results with the current dataset of fresh impact craters on Mars (detected with Mars-orbiting spacecraft) appears to rule out the uniform distribution of angular elements.

KW - Asteroids

KW - Asteroids, dynamics

KW - Cratering

KW - Mars

KW - Mars, surface

UR - http://www.scopus.com/inward/record.url?scp=84942083398&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84942083398&partnerID=8YFLogxK

U2 - 10.1016/j.icarus.2015.08.032

DO - 10.1016/j.icarus.2015.08.032

M3 - Article

AN - SCOPUS:84942083398

VL - 262

SP - 140

EP - 153

JO - Icarus

JF - Icarus

SN - 0019-1035

M1 - 11703

ER -