¶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. |
|
¶Papers- Two papers about the Chicxulub impact which wiped out the dinosaurs 66 million years ago find that the approximately 100 million megaton explosion (10 billion Hiroshimas) melted a portion of the Earth’s crust and created a magma chamber nine times larger than the Yellowstone caldera which lasted for 2 million years (paper) and that the estimated impact angle of 60 degrees maximized its climate-altering destruction (paper), which wiped out 75% of life on Earth.
- Data from Gaia (paper) suggest that the Sagittarius dwarf galaxy which orbits the Milky Way has crashed through our galaxy’s disc 3+ times in the last 6 billion years. These collisions may have helped form the Milky Way’s spiral arms (paper), and ripples from a collision 4.7 billion years ago may also have caused a burst of star formation that resulted in the formation of our Sun and solar system. (Stars very rarely actually collide in galactic collisions, since galaxies are mostly empty space.) Related: Gaia just issued their second data release with 1.7 billion stars. Also, an upcoming merger with the Magellanic Clouds is already causing new star formation in the Milky Way.
- The recent SN2016aps supernova is the brightest supernova ever observed. It was 10x more powerful than a normal supernova and was likely the result of a “pulsational pair instability” in which two massive stars merge before exploding. This explosion emitted “six times the total amount of energy the Sun will emit over its entire seven-billion-year lifespan” in just two years. For this to occur, a star must get so hot that high energy photons in the core convert directly into electron/positron pairs (through E = mc2), which, unlike photons, don’t help support the star’s structure, and… BOOM. (Here’s a pdf with way more than you want to know about exactly why it goes boom.)
- The earliest evidence of a human dying from a meteorite fall (paper) comes from Sulaymaniyah, Iraq, on August 22, 1888. In that event, a bright light with a smoke trail was seen flying towards a village called “Dilaver” part of the Sulaymaniyah city-state of the Ottoman Empire after which “it continued to rain meteorites for many minutes. Some surviving fragments hit two men, killed one and paralyzed another.”
|
|
| ¶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. |  |
|
|
