Issue No. 71

Yesterday was Asteroid Day, so this issue may have a bias towards things fast and explosive... which really is most things in space.

The Orbital Index

Issue No. 71 | Jul 1, 2020

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Support for the Giant-impact Hypothesis. The Giant-impact hypothesis postulates that the Moon formed when a Mars-sized protoplanetary body named Theia crashed into Earth ~4.5 billion years ago. Until now, one problem with this theory was that oxygen isotopes found in Apollo-era lunar samples were more similar to those found on Earth than other Solar System bodies (paper). However, a recent analysis (paper) has shown differences in isotopic ratios depending on lunar rock type, with rocks from deeper inside the Moon appearing less Earth-like. Science Alert has more, saying, “This difference could be explained if only the outer surface of the Moon was pulverised and mixed during the impact, resulting in the similarity with Earth. But deep inside the Moon, the Theia chunk remained relatively intact, and its oxygen isotopes were left closer to their original state.

Didymoon gets a real name. The mini-moon orbiting asteroid Didymos (which unofficially is referred to as Didymos B—although we are fond of the even more unofficial Didymoon) has been christened Dimorphos. Dimorphos, which means “having two forms,” is the eventual target of the NASA/ESA planetary defense DART mission. The binary near-earth asteroid system was discovered in 2003 and its mini-moon is roughly the size of the Great Pyramid (which is big and would cost a lot to rebuild, apparently). DART will send a 650 kg primary spacecraft crashing into the 4.8 billion kg Dimorphos at 6.6 km/s in late 2022, with the 6U LICIACube, an  Italian-produced cubesat, trailing behind to record the impact. Due to its closeness to earth in 2022 (just 11 million km away, or 28x the lunar distance), the collision will also be observable with ground-based telescopes. A few years later, the ESA’s Hera will perform further reconnaissance to ascertain more precisely whether the impact changed the orbit of the mini-moon or the dynamics of the binary system, while also inspecting Didymos’ composition with an eye towards future mining. Hera will include two versatile cubesats as well.


(While this is 99.9% correct, here’s a slightly more complete version.)

News in brief. Virgin Galactic will work with NASA to develop a program to train private astronauts for missions to the ISS; as previously speculated, the May resignation of the former head of NASA human spaceflight Doug Loverro was due to evidence that Boeing was provided inside information related to NASA’s concerns about Boeing’s lunar lander bid; two ISS astronauts, including newly-arrived Bob Behnken, performed a spacewalk to replace batteries on the outside of the station (and dropped a handheld mirror which promptly became the newest piece of space debris); Space Adventures signed a deal for a Soyuz to fly two tourists to the ISS, one of whom may get to take a spacewalk; SpaceX tested SN7 to the breaking point to test a new alloy (and then patched it up and did it again), and NASA similarly tested their SLS liquid oxygen tank test article to failure; SpaceX launched a new GPS satellite and stuck the booster landing, which is becoming downright boring; SpaceShipTwo took another glide flight (likely its last before powered flight from the New Mexico spaceport); and, NASA renamed their Washington headquarters after their first black female engineer, Mary W. Jackson, one of the women depicted in Hidden Figures.
Mary W. Jackson at NASA Langley Research Center in 1977.

A mosaic of primary sample site Nightingale on Bennu, taken by OSIRIS-REx during a March flyover at 250 m. The mosaic is composed of 345 images and boasts a resolution is 4 mm per pixel. OSIRIS-REx will attempt to collect its first sample here on October 20th.

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