Scientists detect mysterious force pushing asteroid toward Earth—and suspect hidden comet
Researchers tracking a near-Earth asteroid found it accelerating in ways gravity alone cannot explain. The leading theory: invisible water vapor ejecting from the rock's surface, like a comet. The discovery matters for predicting asteroid trajectories and understanding which space rocks pose collision risks.
Originaltitel: (523599) 2003 RM: The Asteroid that Wanted to be a Comet
Asteroiden (523599) 2003 RM uppvisar en oregelbunden bana som inte kan förklaras av enbart gravitationskrafter — en upptäckt relevant för utvecklingen av beräkningsmodeller för små himlakroppar. Forskare vid JPL och partnerinstitutioner analyserade omfattande observationer från 2003 till 2018 och identifierade en transvers acceleration motsvarande cirka 10²³ vattenmolekyler per sekund vid perihel. Denna magnitud överskrider de krafter som orsakas av Yarkovsky-effekten eller solstrålningstryck, vilket pekar mot kometsisk utgasning. Djupa infraröda observationer från Very Large Telescope bekräftade ingen uppenbar dammproduktion, men vattensublimering kan förklara accelerationen inom observationsosäkerheten. Asteroiden härstammar sannolikt från huvudbältet snarare än från Jupiters familjekometer. För material- och rymdteknikföretag understriker resultatet betydelsen av förbättrade banföreskrifningar för mindre himlakroppar och vikten av infraröd övervakning vid asteroidkarakterisering.
<p>We report a statistically significant detection of nongravitational acceleration on the subkilometer near-Earth asteroid (523599) 2003 RM. Due to its orbit, 2003 RM experiences favorable observing apparitions every 5 yr. Thus, since its discovery, 2003 RM has been extensively tracked with ground-based optical facilities in 2003, 2008, 2013, and 2018. We find that the observed plane-of-sky positions cannot be explained with a purely gravity-driven trajectory. Including a transverse nongravitational acceleration allows us to match all observational data, but its magnitude is inconsistent with perturbations typical of asteroids such as the Yarkovsky effect or solar radiation pressure. After ruling out that the orbital deviations are due to a close approach or collision with another asteroid, we hypothesize that this anomalous acceleration is caused by unseen cometary outgassing. A detailed search for evidence of cometary activity with archival and deep observations from the Panoramic Survey Telescope and Rapid Response System and the Very Large Telescope does not reveal any detectable dust production. However, the best-fitting H2O sublimation model allows for brightening due to activity consistent with the scatter of the data. We estimate the production rate required for H2O outgassing to power the acceleration and find that, assuming a diameter of 300 m, 2003 RM would require Q(H2O) similar to 10(23) molec s(-1) at perihelion. We investigate the recent dynamical history of 2003 RM and find that the object most likely originated in the mid-to-outer main belt (similar to 86% probability) as opposed to from the Jupiter-family comet region (similar to 11% probability). Further observations, especially in the infrared, could shed light on the nature of this anomalous acceleration.</p>