¶ Most people know about the Chicxulub impact that helped kill the dinosaurs (and 75% of all other plant and animal species as well), but growing evidence suggests that impacts over geologic history have shaped life on Earth in many other ways too. Recently, evidence based on an increase in the platinum and iridium content of sediment around the world (paper) has lent support for the Younger Dryas Impact Hypothesis, first suggested in 2007, which posits that an extraterrestrial impact 12,800 years ago caused a 1000 year ice age and the extinction of many large animal species along with a simultaneous decline in human populations. (Human hunting likely played a large part in megafauna extinctions as well, which is on-brand for us.) Further back, a newly confirmed impact 800,000 years ago may have cleared an expanse of jungle for human habitation. And even further back, 466 million years ago, the collision and breakup of a large asteroid in the belt between Mars and Jupiter created a dust cloud that showered the inner solar system, blocking sunlight and causing an ice age, the possible instigator of the Ordovician radiation, a rapid increase in biodiversity at the time (paper). This Ordovician meteor event remains the largest breakup in the last 3 billion years and is the source of almost a third of all the meteorites that still strike Earth today, almost half a billion years later. And finally, 4 billion years ago, the building blocks for life itself may well have been delivered to Earth on meteors and comets. (Much more controversially, it’s possible that muons from a supernova 2.6 million years ago could have wiped out large ocean animals, and that the Younger Dryas impactor could have been a supernova remnant.) |
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¶State of the asteroid union. As of 2020, our species has sent probes to 14 asteroids throughout the solar system, beginning with Galileo’s observation of Gaspra in 1991. Most have been near-Earth objects (NEOs), which can pose both an existential risk (see previous item), as well as a potential source of accessible in-space resources (here’s a fabulously detailed report, but also see the Etc. article from Casey Handmer below), including water, iron, cobalt, nickel, and platinum-group metals. For planetary defense, NASA announced the NEO Surveillance Mission last fall with the goal of launching an L1-located space telescope that observes in infrared to spot super dark NEOs as they are warmed by the sun. Recently, Hubble discovered that Eurybates—a Trojan asteroid scheduled to be visited by the upcoming 2022 Lucy mission (mission tour guide)—has a small "bonus" satellite that the mission will get to observe. Additionally, OSIRIS-REx just made its closest flyover (620 m) of its August sample gathering site on Bennu, and Hayabusa2 is currently returning to Earth to deliver bits of Ryugu this December. Other planned asteroid missions include NEA Scout (a CubeSat mission which will hitch a ride on Artemis I and then visit NEOs using a solar sail ✨⛵️), ASTER (Brazil's first planned, but perhaps unlikely, deep space mission), DART/Hera (shoot and then monitor an asteroid!), Psyche (cf. Issue 17), and China's proposed mission to Kamo'oalewa. 
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¶(Less impactful) News in brief. ESA and NASA’s Solar Orbiter is launching this Sunday—the mission will fly out of the ecliptic by slingshotting past Earth and Venus to study the Sun’s poles for the first time (see ars piece on the future of solar observation); Voyager 2 suffered a technical glitch; Rocket Lab launched some sort of small observation satellite for the NRO and again guided its booster intact through reentry into the ocean ahead of plans for mid-air capture; OneWeb plans to launch 34 satellites today on a Soyuz—they’re aiming for 648 in the final Internet service constellation; billionaire Yusaku Maezawa canceled his (we think highly misguided) personal lunar dating show due to "personal reasons" and apologized to the 27,722 women who applied; SpaceX may also want to build Starship and Super Heavy vehicles at a factory at the Port of Los Angeles—they would then be barged to Boca Chica or Florida for launch; another dramatic Starship SN1 test, this one using cryogenic liquid nitrogen filling a massive 9 m test tank, reached the 8.5 bar required for crewed flight, with approval for communications equipment for a 20km test flight requested from the FCC with a launch date NET March 16th; secretive Alameda, CA-based Astra (intro video) is planning a first orbital test on February 21—they had a failed suborbital flight test in Dec 2018; a Russian spy satellite (Kosmos 2542) is likely spying on a US spy satellite—the USA is known to observe other satellites as well through the Geosynchronous Space Situational Awareness Program (GSSAP). |
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¶Etc.- Earth’s plate tectonics may have been jump-started by meteor impacts (paper).
- A 70 km wide, 2.2 billion-year-old crater in Western Australia is now the oldest confirmed impact structure on Earth (paper) and may have shifted our planet out of a Snowpiercer-level massive global ice age at the time. Meanwhile, an even older impact crater has likely already been found in Greenland, created by an absolutely enormous 30 km wide impactor 3 billion years ago. The crater is currently 100 km wide but was once around 600 km wide. The algae and cyanobacteria of the time would have had quite the show.
- A proposal to use a 3D printer and S. oneidensis, a bacteria that can turn Martian regolith into magnetite, to make structures on Mars, and another proposal to do similarly with fungal mycelia. (Sort of related: Another bacteria, Metallosphaera sedula, likes to eat metallic meteorites—perhaps it’s similar to the first life on Earth, or even lends credence to lithopanspermia?)
- Check out these cell-like structures on the surface of the Sun, each roughly Texas-sized, captured by the Inouye Solar Telescope on Haleakala in Maui as it saw first light.
- Surprises from Asteroid Bennu, a video review of the OSIRIS-REx mission.
- ESA has asked amateur astronomers to help characterize a set of possible secondary targets for their upcoming Hera asteroid rendezvous mission.
- Finnish amateur photographers helped to discover a new form of aurora, nicknamed ‘dunes’.
- Asteroid 2003 YT1 has been determined to be the source of a bright (but harmless) fireball seen over Japan in 2017 (paper). If 2003 YT1 breaks apart completely (probably because of spinning too fast and flying apart due to the YORP effect), fragments could present danger to Earth—we’re probably good for a few million years, though.
- Two articles by Casey Handmer explain why (in his opinion) space-based solar power stations that beam energy to the ground don’t make sense, and why there is currently no commodity that would make sense to mine in space and sell on Earth (until we discover unobtanium, stroon, or spice). The comments are interesting too.
- Grains of interstellar dust found in an Australian meteorite are 5 billion or more years old (paper), now the oldest known material on Earth. They were expelled from dying stars long before the solar system formed.
- Figuring out where 2I/Borisov came from.
- SpaceX released a Rideshare Payload User’s Guide, in addition to announcing that smallsat operators can now book a rideshare berth online for as little as $1M, with just a $5,000 non-refundable deposit. Monthly launches are scheduled to start in July.
- A great visualizer for 3D satellite orbits and their 2D ground tracks from Jake Low.
- Rather than protecting the inner system from comets as previously posited, growing evidence suggests that Jupiter actively flings them toward us. (Can you really blame it?)
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