Let’s call these three MNRAS issues “October,” an arbitrary line:
Volume 533, Issue 4, October
Rodríguez Rodríguez, J. Díez Alonso, E. Iglesias Álvarez, S. et al. Light-curve analysis and shape models of NEAs 7335, 7822, 154244, and 159402 Pg 4160 stae2046
Kokou, P. Detection of fireballs in the Lightning Imager data
Pg 4450 stae2061
Volume 534, Issue 1, October
Abhijnanam Bora, C. Singh Kushvah, B. Chandra Mouli, G. et al. Temporal trends in asteroid behaviour: a machine learning and N-body integration approach Pg 415 stae2083
Li, Z. Qiao, D. Li, X. et al. Investigating temporary capture in the Sun–Jupiter three-body system via Lagrangian coherent structures Pg 902 stae2122
Volume 534, Issue 2, October
Cheng, B. Baoyin, H. Structural stability of China’s asteroid mission target 2016 HO3 and its possible structure Pg 1376 stae1744
As I’ve noted, there are tens of thousands of NEOs (Near-Earth Objects). Whatever you’re looking for, one of that population will fit the criterion. The issue is sifting through the data, including some NEOs that haven’t been characterized yet- incomplete data. Rodríguez et al. get us one step towards that completion. Four more such bodies are no longer dots of light in the sky.
Speaking of dots of light, fireballs are bigger meteors- the “shooting stars” you may see at night are roughly the size of sand, maybe fine pebbles. Going by meteor showers (numerous, clustered meteors likely pieces from a common parent), we can trace back lots of meteors to a comet as their parent body. Fireballs are brighter, larger grains, and beyond a certain point are unlikely to be of cometary parentage. Comet material (we assume…) never had a chance to sinter from dust/sand/pebbles into macroscopic bodies. To some extent (poorly defined…) we assume fireballs are the death spasms of asteroid bits as they hit Earth’s atmosphere. Our weather satellites now include instruments like Lightning Imager, which stares at the Earth, trying to put numbers on rainclouds. Well, it turns out instruments like these are good for plenty of atmospheric phenomenon, like stuff hitting that atmosphere. Kokou agrees.
AI, AI, AI… can’t open the news these days without seeing something about AI (whether it’s actually appropriate, or seguewayed anyway). Astronomy is not much of an exception, but I’ll give Abhijnanam et al. some credit. The research group is trying to study the dynamics of small bodies, as the planets and the Sun perturb them fore and back. After enough perturbations, a small body may actually jump orbits. (This is all aside from being perturbed into collision, with a planet, with each other, with the Sun, or being perturbed clear out of the Solar System- ejection.) The “AI” angle here is marking the bounds of true NEO members, vs. mere planet-crossers, vs. Main-Belters, etc. with no human labor in the database.
Some of those “planet crossers” are Trojans- bodies captured into commensurate orbits at the leading (L4, stuck orbiting 60 degrees ahead of a planet) or trailing (L5, stuck 60 degrees behind) Lagrange points. In the cases of Jupiter (a MASSIVE planet, and thus capturing lots with its huge gravity), the Jupiter Trojans are a very important clue to the early Solar System. Very important. Some Jupiter Trojans may actually have been captured by the planet since, oh, close to the birth of the Solar System itself. Others may be recent captures. Which is which? We can’t tell yet by looking, but dynamical considerations give us some hint on odds and likelihoods, and therefore relative numbers.
If the Trojans are important enough to merit a launch, would an Earth Trojan also be considered worthy? Either way, the Chinese are going to launch one- the energetic cost (delta V, a measure of the spacecraft acceleration and thus the fuel usage) is rather small, and the mission rather lightweight and low-cost. Still, does the Earth Trojan (2016 HO3) tell us something, of NEOs in general, or of something specific? This Trojan is small, but small objects include fast rotators. We have never sent a mission to a fast rotator, though the Hayabusa2 extended mission (now “Hayabusa2#”) will- barring a failure- eventually reach one, 1998 KY26. Fast rotators must be held together with mechanical strength, since their spin is too fast- a body held together by gravity alone would fling apart. Gathering more data on these (including comparing two fast rotators) tells us more than simple pictures can- it would tell us what’s going on inside these rocks.