Free Astronomy Magazine January-February 2019

27 JANUARY-FEBRUARY 2019 SMALL BODIES (1999), the Yarkovsky effect has shifted its orbit by almost 6 km towards the Sun. This may seem a negligible quantity, but over the centuries, and with the possible ampli- fication made by gravitational perturba- tions, that modest amount could hide a real threat. It is worth ac- knowledging that, if an asteroid half a kilometer in diameter and 40 mil- lion tons of weight (like Bennu) should ever fall to Earth, it would release an energy comparable to 80,000 of the atomic bombs dropped on Hi- roshima, causing destruc- tion on a continental scale with heavy conse- quences for the whole planet. Experts at the Center for Near-Earth Object Stud- ies (CNEOS) at NASA’s Jet Propulsion Laboratory forecast that, in the sec- ond half of the next cen- so important to accurately know Bennu’s energy balance and to precisely trace its orbit by following the radio signals that OSIRIS-REx will send to our antennas for the next few years. Astronomers have cal- culated that, since Bennu was discovered T he Yarkovsky effect is the change in the orbit of an asteroid due to the thermal heat it releases. This effect can help scientists to study the orbits of various asteroids and even predict if any of them come dangerously close to our planet. [Alexandra Bolling, NRAO/AUI/NSF] Below, natural or induced emissions of heat or volatile elements from the surface of an aster- oid produce small variations in the orbital velocity that should not be underestimated. [ESA – Science Office]