New Astrobites Post: Colors of Kuiper Belt Objects Reveal Their Histories

Another month, another post for Astrobites!

For today’s post, I wrote about a paper published by the Colors of the Outer Solar System Origins Survey team. They compiled a collection of 229 Kuiper Belt Objects (KBOs) that all have well-measured colors. By “color,” I mean that the astronomers obtained images of the KBOs in three different wavelength filters, and since the objects might not reflect the same amount of light in each filter, the difference between the three measurements gives an idea of the “color.” Just like how plants appear green because most of the light they reflect is green light.

There’s an additional complication, since the reflected light in question is the Sun’s light. The Sun inherently has its own color, and so colors of KBOs tend to be measured relative to the Sun’s color. Colors close to the Sun’s are referred to as “solar neutral” or “gray,” while redder KBOs are referred to as “red.” (There aren’t really any bluer-than-solar objects, though people sometimes confusingly refer to gray KBOs as blue instead, mostly to mean “not-red.” But the objects aren’t actually blue! Luckily the authors of this paper didn’t use that terminology).

What’s so special about color? It turns out that an object’s color corresponds to its composition, and its composition relates back to where in the early planetary disk the object formed. Furthermore, other properties about the object, such as its orbital inclination (how far the object swings out of the plane of the eight major planets), also tell us about the object’s history. Did it form closer to the Sun and get scattered out? Did it form farther out? Considering both inclination and color together could be a powerful constraint on where KBOs formed and how they got to where they are now!

I won’t spoil the punchline, though. You’ll have to go read the post!

New Astrobites Post: A Binary Jupiter Trojan Reveals the Solar System's Early History

Image is an artist’s rendition of Patroclus-Menoetious. Credit: W.M Keck Observatory/Lynette Cook

My latest post for Astrobites is now live!

In this post, I reviewed a paper that studied a peculiar binary asteroid system called (617) Patroclus-Menoetius that orbit around the Sun in a similar path as Jupiter (just 60 degrees behind Jupiter in its orbit). Binary systems contain two similarly-sized objects in orbit around a mutual center of mass (think more along the lines of Pluto and Charon, rather than the Earth and Moon). Binary asteroids are interesting because they’re likely some of the oldest relics in the Solar System. They probably formed when the cloud of “pebbles” that comprised the early planetesimal disk was still condensing and could easily form pairs of objects. Over time, though, encounters with other objects (like other asteroids or big planets) can disrupt binaries, causing them to collide or drift apart. The fact that Patroclus-Menoetius has survived the entirety of the Solar System’s lifetime can put some strong constraints on possible events in the Solar System’s history that would have otherwise disrupted the pair. The authors of the paper ran simulations of the early Solar System to figure out the conditions in which a binary pair like Patroclus-Menoetius could survive.

I won’t spoil the answer here, you’ll just have to go read the post! But what’s especially exciting is that NASA’s Lucy mission, due to launch in 2021, will visit this curious binary system in 2033. So we’ll soon know even more about this system and be able to place even stronger constraints on conditions in the early Solar System!