Minor Planets Disrupt Earth’s Orbit

Observations of Ceres by NASA’s Hubble Space Telescope. Credit: NASA, ESA, J.-Y. Li (University of Maryland) and G. Bacon (STScI)

Numerical simulations of the long-term evolution of the orbits of minor planets Ceres and Vesta, which are the largest bodies in the asteroid belt between Mars and Jupiter, have found that close encounters among these bodies lead to strong chaotic behavior of their orbits, as well as of the Earth’s eccentricity. This means that the Earth’s past orbit cannot be reconstructed beyond 60 million years. Studying the interactions between the Earth and the solar system environment can help astrobiologists understand the conditions that make Earth habitable for life, and the future that could be in store for our planet’s biosphere.

Ceres is 6,000 times less massive than the Earth and almost 80 times less massive than our Moon. Vesta is almost four times less massive than Ceres. These two minor bodies, long thought to peacefully orbit in the asteroid belt, are found to affect their large neighbors and, in particular, the Earth in a way that had not been anticipated. This is showed in the new astronomical computations by Jacques Laskar from Paris Observatory and his colleagues, and published in the journal Astronomy & Astrophysics.

NASA’s Dawn mission will visit two of the first bodies formed in our solar system: the “dwarf planet” Ceres and the massive asteroid Vesta. Credit: NASA

Although small, Ceres and Vesta gravitationally interact together and with the other planets of the Solar System. Because of these interactions, they are continuously pulled or pushed slightly out of their initial orbit. Calculations show that, after some time, these effects do not average out. Consequently, the bodies leave their initial orbits and, more importantly, their orbits are chaotic, meaning that we cannot predict their positions.

The two bodies also have a significant probability of impacting each other, estimated at 0.2% per billion year.

Last but not least, Ceres and Vesta gravitationally interact with the Earth, whose orbit also becomes unpredictable after only 60 million years. This means that the Earth’s eccentricity, which affects the large climatic variations on its surface, cannot be traced back more than 60 million years ago. This is indeed bad news for Paleoclimate studies.

This unexpected discovery comes at a time when both objects are the targets of the NASA/Dawn mission. The Dawn probe will encounter Ceres in February 2015. Dawn’s flyby of Vesta occurred on Saturday, July 16, 2011.