The asteroid 1998 KY26 was observed with radar by Steve Ostro 28 years ago as of this weekend: https://echo.jpl.nasa.gov/asteroids/ostro+1999_ky26_science.pdf .

Steve gave me a 3D print of the shape model he produced. It was suspiciously symmetric, which turned out to be because the period measurement was off by a factor of 2.

An 800-Million-Year-Old Impact Shower on the Terrestrial Planets from the Breakup of the Eulalia Parent Body

William F. Bottke, David Vokrouhlick\'y, Melissa Dykhuis, Nicolle Zellner
https://arxiv.org/abs/2606.05036 https://arxiv.org/pdf/2606.05036 https://arxiv.org/html/2606.05036

arXiv:2606.05036v1 Announce Type: new
Abstract: Multiple studies have proposed a substantial surge in large lunar impacts approximately $800$ million years ago (Ma). Some are based on analyses of the ages of large lunar craters, such as the $93$ km Copernicus crater. Others focus on the age distributions of impact glasses returned by lunar missions. A key challenge has been identifying and testing a plausible source for this putative impact spike. Here we use collisional and dynamical models to link this event to the formation of the Eulalia asteroid family, whose primitive carbonaceous chondrite-like parent body disrupted $\sim 800$ Ma near the 3:1 mean motion resonance with Jupiter (J3:1). Our simulations indicate that approximately three-quarters of the family's fragments eventually entered the J3:1 over a $\sim 150$-million year interval. While some fragments were injected into the resonance immediately after the disruption, others migrated more gradually via non-gravitational (Yarkovsky) thermal forces. Once in the J3:1, the fragments were dynamically transported into the planet-crossing region, leading to an elevated rate of bombardment on the Moon and terrestrial planets. Our results demonstrate that the Eulalia breakup can plausibly account for the observed lunar craters formed near $800$ Ma. Intriguingly, this event may also have had widespread repercussions across the inner Solar System. On Earth, its timing coincides with significant shifts in the biosphere, possibly linked to large impacts. On Mars, these impacts might have triggered a pulse of volcanic activity. Together, they showcase how certain catastrophic collisions in the main belt can have far-reaching consequences for the history of the terrestrial planets.

toXiv_bot_toot

I need to share the joy. To quote the v. wholesome comments section: "this is the musical equivalent of all the dishes simultaneously falling out of your cupboard and landing perfectly stacked. I cannot look away."

https://www.youtube.com/watch?v=0Ssi-9wS1so

Nereid as a Regular Satellite of Neptune

Matthew Belyakov, M. Ryleigh Davis, Ian Wong, Konstantin Batygin, Michael E. Brown
https://arxiv.org/abs/2606.02818 https://arxiv.org/pdf/2606.02818 https://arxiv.org/html/2606.02818

arXiv:2606.02818v1 Announce Type: new
Abstract: Nereid, Neptune's third largest moon, is considered to be a captured irregular satellite due to its highly eccentric orbit. However, among irregular satellites, Nereid is an outlier: it is the largest, the closest to its host planet, and the most eccentric. We present James Webb Space Telescope near-infrared spectroscopy of Nereid that demonstrates that its composition is inconsistent with its suggested captured origin. We then simulate Nereid's early orbital history subsequent to Triton's capture to demonstrate a plausible dynamical pathway for a regular satellite formed in-situ around Neptune to evolve to Nereid's present-day orbit. Based upon the available spectroscopic and dynamical evidence, we propose that Nereid is not a body captured from the Kuiper belt, but rather the sole surviving intact regular satellite of Neptune.

toXiv_bot_toot

Today I was given this fabulous rock specimen from the Lewisian Complex in Iona.

We have a grey banded garnet-gneiss on the left side of the image. This banding is truncated by the dark rock on the right, indicating that the dark rock must have been intruded after the banding had formed.

Then both rocks have been heated, and the grey banded rock has partially melted, forming a granitic melt which has then intruded into the dark rock.

More in Alt txt.

#Iona #Lewisian #GranuliteFacies