Both 2011 JY31 and 2014 OS393 appeared slightly elongated in the images compared to a nearby star. So the team fit the shapes with a two-body model: two asteroids in a tight orbit. Even though the individual rocks weren't resolved, the modeling showed that two bodies were better able to explain the elongation, as well as the brightness seen. The model for 2011 JY31 had two 50-km-wide objects nearly 200 km apart, while for 2014 OS393, the model had slightly smaller bodies (30 km across) that orbited each other 150 km apart.
The tight-orbiting twins would have formed in situ, and — like twin-lobed Arrokoth seen up close by New Horizons in early 2019 — support a formation model in which gentle, low-velocity collisions among small objects, or “pebbles”, produce denser pebble-filled clouds that then collapse into larger planetesimals, as either contact binaries (like Arrokoth) or tight twins (like the other two asteroids).
David Dickinson
Impressive how data from the New Horizons missions is still delivering scientific insights. It also supports proposals for more probes in the outer solar system, orbiting the cold giants and surveying the Kuiper Belt. Maybe this would finally settle the question whether a large ‘Planet Nine’ is orbiting the Sun somewhere in the far reaches of the system.
I have high hopes for another recently launched mission, Lucy, which will explore Jupiter’s Trojan asteroids over the next decade. I love how its final purpose is to serve as a time capsule for future solar system explorers – or alien visitors, if they ever manage to arrive.
After the final flyby in 2033, Lucy may be granted a mission extension, but will otherwise remain in a stable, 6-year orbit between the two Trojan camps. Knowing this, mission planners attached a plaque to Lucy, which includes 20 samples of poetry and quotations from luminaries including Martin Luther King Jr., Carl Sagan, and the Beatles. The plaque also shows the orbital configuration of the planets of solar system at launch, plus the path of Lucy, and the geological position of the continents of the Earth at the time of launch for any would-be spacecraft salvagers, thousands or millions of years in the future.
David Dickinson
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