Earth probably shouldn't exist. 

That's because the orbits of the inner solar system planets — Mercury, Venus, Earth and Mars — are chaotic, and models have suggested that these inner planets should have crashed into each other by now. And yet, that hasn't happened.

New research published May 3 in the journal Physical Review X(opens in new tab) may finally explain why. 

Through a deep plunge into the models for planetary motion, the researchers discovered that the motions of the inner planets are constrained by certain parameters that act as a tether that inhibits the system's chaos. Besides providing a mathematical explanation for the apparent harmony in our solar system, the new study's insights may help scientists understand the trajectories of exoplanets surrounding other stars. 

Psychology Test and Assessment Modeling showcased in Nr. 4/2022 + 1/2023 the potentials and promises that machine learning and deep learning algorithms can bring about to improve the current assessment theory and practices in different assessment settings: low stakes and high-stakes. Hong Jiao, Qiwei He, and Lihua Yao edited the two special issues.