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

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.

Supercatastrophic Disruption of Asteroids in the Context of SOHO Comet, Fireball, and Meteor Observations

“…This highly-inclined orbit together with a Tisserand parameter with respect to Jupiter of 2.7 suggests that this body may in fact be a dynamically highly evolved comet, though no activity from it has yet been reported. The past extremely-low perihelion distance was previously noted by Vokrouhlický & Nesvorný (2012), who computed that the surface of the asteroid could have reached 2500K. They assessed the effects of the denser solar wind, circumsolar dust and the Yarkovsky effect on the orbit of 2004 LG and found them to be negligible, so there is no obvious dynamical mechanism (unless the object does at times exhibit cometary outgassing) which would have prevented it reaching a very low perihelion distance.…”

Asteroid Thermophysical Modeling

“…However, dynamical simulations show that a much larger fraction of asteroids had small perihelion distances for some time, hence experiencing episodes of strong heating in their past (Marchi et al, 2009). For instance, the asteroid 2004 LG was approaching the Sun to within only ∼5.6 solar radii some 3 ky ago, and its surface was baked at temperatures of 2500 K (Vokrouhlický and Nesvorný, 2012).…”

Surface Properties of Near-Sun Asteroids

“…Nine of the objects we attempted to observe were predicted to be within our FOVs and above our detection limit but were not recovered, most likely due to the very large uncertainty in their orbits. We also observed NEA 2004 LG, which previously spent 2500 yr with a perihelion distance less than 0.076 au, the disruption limit of Granvik et al (2016), experiencing extreme temperatures of ∼2500 K at the surface (Vokrouhlický & Nesvorný 2012;Wiegert et al 2020).…”

“…Formerly low-q asteroid 2004 LG, which spent 2500 yr with q < 0.076 au (Vokrouhlický & Nesvorný 2012;Wiegert et al 2020), does not exhibit any unusual colors compared to the near-Sun population and other NEAs, though we would suspect otherwise after being in an extreme environment, within the catastrophic disruption limit determined by Granvik et al (2016). Object 2004 LG may not be an S-or Q-type and therefore experiences near-Sun properties differently.…”