Sun-grazing orbit of the unusual near-Earth object 2004 LG

¹ Institute of Astronomy, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague, Czech Republic
e-mail: vokrouhl@cesnet.cz
² Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, USA
e-mail: davidn@boulder.swri.edu

Received: 5 December 2011
Accepted: 9 March 2012

Abstract

Context. Near-Earth objects (NEOs) typically end their existence by falling into the Sun. Because the orbit evolution timescale is long, however, it is unlikely that we will witness such events or predict them happening in a foreseeable future.

Aims. We studied the orbital dynamics of NEOs to understand whether predictions of Sun impact are possible for individual bodies, and if so, whether special cases can be identified where the Sun impact is expected to happen in  ≲100 ky.

Methods. We identified an unusual NEO on a Sun-grazing orbit, 2004 LG, and numerically integrated its orbit to understand its dynamical history and future evolution.

Results. We found that the orbit of 2004 LG is strongly affected by the Kozai resonance. In about 9 ky from now, when the orbital eccentricity will reach the maximum value during its current Kozai cycle, 2004 LG has a greater than 25% probability of falling into the Sun. The probability of Sun impact is  >50% over the next 100 ky. 2004 LG was exposed to extreme solar radiation in the past and will be exposed to even more extreme solar radiation in the future. For example, we found that 2004 LG was approaching the Sun to within only  ≃5.6 solar radii some 3 ky ago, and its surface was baked at temperatures  ≃2500 K. Spectroscopic observations of 2004 LG would therefore be useful in characterizing the effects of extreme irradiation on NEOs’ surfaces. Our forward orbital integrations showed that 2004 LG will reach a very low orbital perihelion distance (<1.6 solar radii) at 9 ky from now, indicating its surface will be scorched at temperatures exceeding 4500 K while the interior will be exposed to strong solar tides and thermal stresses. The object will probably not maintain its physical integrity.