Volume 3 Issue 4, April 2019

Japanese and US missions returning samples from the carbon-rich asteroids Ryugu and Bennu are the latest steps in probing our Solar System’s smallest bodies, near and far, for clues to our own origins and directions for our future exploration.

After the return of Hayabusa from asteroid Itokawa in 2010, the Japanese space agency JAXA developed a plan to investigate how our planet became habitable. The Hayabusa2 spacecraft mission to the asteroid Ryugu is just one part of this exploration that aims to track water and organics throughout our Solar System.

On 27 June 2018 the Hayabusa2 spacecraft arrived at the carbonaceous asteroid Ryugu — a top-shaped asteroid with a very dark surface and many boulders. After a careful search for a safe and flat landing site, the first touchdown successfully took place on 22 February 2019.

The new generation of sample return missions from small bodies will deliver to us fresh witnesses from the early Solar System. In-depth laboratory analysis of retrieved samples will allow us to look in unprecedented detail at the formation and evolution of organic materials in asteroids.

In 1951, three separate research groups established radio astronomy as a contender to the dominance of optical astronomy. Using the interstellar 21-cm line, they provided a method to look deeper into our own Galaxy and back in time to the birth of all galaxies.

Using a pair of modest telescopes, Arimatsu et al. have observed an occultation event that purports to have been caused by a kilometre-sized Kuiper belt object (KBO). KBOs of this order of magnitude in size have not been detected before, but are likely to represent the most populous size of object in the Kuiper belt.

The initial abundance of ²⁶Al in a planetary system determines the surface environment of its solid planets. High levels of ²⁶Al will dehydrate planetesimals and produce water-poor worlds similar to the terrestrial planets in our Solar System; sub-solar levels of ²⁶Al will preferentially generate ocean planets.

An outburst from young star V883 Ori has vaporized much of the ice inventory of its protoplanetary disk, uniquely revealing a rich organic chemistry involving several complex molecules.

Using precise distances to more than 1,300 classical Cepheids, Chen et al. have traced the warp of the Milky Way’s stellar disk to beyond 20 kpc. The Galaxy’s warp likely arose due to the torques exerted by its massive inner disk.

The iodine–xenon record in meteorites can be used to probe late-time processes within the Solar System, during the dissipation of its debris disk. Most primitive meteorites were processed and heated by impacts during this ~50 Myr period, rather than by the decay of ²⁶Al.

Signatures of phyllosilicate-like hydrated minerals are widespread on Bennu’s surface, indicating significant aqueous alteration. The lack of spatial variations in the spectra down to the scale of ~100 m indicates both a relatively uniform particle size distribution and a lack of compositional segregation, possibly due to surficial redistribution processes.

Bennu’s surface presents evidence of a variety of particle sizes, from fine regolith to metre-sized boulders. Its moderate thermal inertia suggests that the boulders are very porous or blanketed by thin dust. Bennu’s boulders exhibit high albedo variations, indicating different origins and/or ages.

Bennu’s surface has experienced continuous changes, mostly induced by its accelerating spin rate, which could have resulted in a collapse of its interior in the past. This scenario is also supported by the heterogeneity of Bennu’s internal mass distribution.

The OSIRIS-REx mission has reached its target, asteroid Bennu, and is engaging in reconnaissance and early science observations in preparation for sample collection. Principal investigator team Heather Enos and Dante Lauretta provide an overview.