Asteroids & Meteorites: The Hazards to Life 13 March 2018

Asteroids Apollo Trojans

Asteroid Belt as viewed from Above Over 100,000 objects greater than 10 km. now identified in the Main Belt Total mass less than 1% of moon’s mass Over 100 NEAs greater than 1 km. across are being tracked; probably part of a population of about 2000 Kirkwood gap (and others) occur in the belt where there are orbital resonances with Jupiter Asteroids classified by ‘spectral group

Kirkwood Gaps

S Asteroids (‘silicaceous’) 951 Gaspra 433 Eros (true color) Ida (and Dactyl) 19 x 12 x 11 km 33 x 13 x13 km 58 x 23 km (1km) Galileo flyby, 199 NEAR orbit/landing Galileo flyby, 1993 Grooves, curved near-Earth asteroid, member of Koronis depressions, ridges space weathering family, first ID of (Phobos-like) effects documented asteroid ‘moons’

C Asteroids (‘carbonaceous’) 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker Surface as dark as charcoal; typical outer belt asteroid

Ida and Dactyl

Itokawa

Hyabusa samples Itokawa

Hyabusa Returns June 2010

Steins 2008

Toutatis Model

Vesta, Ceres, Moon

Dawn Mission at Vesta

Vesta Craters

Asteroids Summary Solid objects mostly in a belt between Mars and Jupiter Small bodies much more common than larger ones Classes similar to meteorites: Stony (S), Carbonaceous (C), Metallic (M) Bodies and belts shaped by collisions, resonances with Jupiter Source of meteorites

Meteorites

Chondrite

Achondrite

Martian

Jackson Hole Fireball, August 10, 1972

Hoba Iron 3m x 2m x 1m; 60+ tons Found 1920, Namibia No crater, classified ataxite

Ordinary Chondrites (from S Asteroids?)

Three Views of Vesta Hubble image, model and color-shaded topography Largest member of V class of asteroids (vestoids) Spectral variations consistent with HED meteorites

Meteor showers Time exposure image, tracking stellar motion Stars stay still, meteorites make trails

The Peekskill (NY) Fireball

P Jenniskens et al. Nature 458, 485-488 (2009) Macroscopic features of the Almahata Sitta meteorite. P Jenniskens et al. Nature 458, 485-488 (2009)

Chondrites Rocky, inhomogeneous, contain round “chondrules” Microscope image

Iron meteorites: from core of differentiated asteroids

Stony-Iron meteorites - the prettiest Crystals of olivene (a rock mineral) embedded in iron From boundary between core and mantle of large asteroids?

Sutter’s Mill fell and found in 2012

The main points: Meteorites Each year the Earth sweeps up ~80,000 tons of extraterrestrial matter Some are identifiable pieces of the Moon, Mars, or Vesta; most are pieces of asteroids Meteorites were broken off their parent bodies 10’s to 100’s of million years ago (recently compared to age of Solar System) Oldest meteorites (chondrites) contain interstellar dust, tiny diamonds made in supernova explosions, organic molecules and amino acids (building blocks of life) Direct insight into pre-solar system matter, solar system formation

Asteroid Hazard: The Death of the Dinosaurs

Tunguska, Siberia, June 30, 1908 Black and white photos taken during field expedition in 1927; color photo taken in 1990

Potentially Hazardous Asteroid Threat Size-frequency diagram for impacting objects ~100 tons of meteroritic dust falls each day 50 m impactor once per 1000 yr (local effects) 500 m impactor once per million years (regional effects) 5 km. impactor once per 100 million years (global effects)

Plot of orbits of known potentially hazardous asteroids, with over 140 meters in size and passing within 7.6 million kilometers of Earth

Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid's potential to make threatening close approaches to the Earth. Specifically, all asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 au or less and an absolute magnitude (H) of 22.0 or less are considered PHAs. In other words, asteroids that can't get any closer to the Earth than 0.05 au (roughly 7,480,000 km or 4,650,000 mi) or are smaller than about 140 m (~500 ft) are not considered PHAs.

Potentially Hazardous Asteroids

While the chances of a major collision are not great in the near term, there is a high probability that one will happen eventually unless defensive actions are taken. Recent astronomical events—such as the Shoemaker-Levy 9 impacts on Jupiter and the 2013 Chelyabinsk meteor along with the growing number of objects on the Sentry Risk Table—have drawn renewed attention to such threats. NASA warns that the Earth is unprepared for such an event.

Asteroid impact avoidance Asteroid impact avoidance comprises a number of methods by which near earth objects (NEO) could be diverted, preventing destructive impact events. A sufficiently large impact by an asteroid or other NEOs would cause, depending on its impact location, massive tsunamis, multiple firestorms and an impact winter caused by the sunlight-blocking effect of placing large quantities of pulverized rock dust, and other debris, into the stratosphere.

A collision between the Earth and an approximately 10-kilometer-wide object 66 million years ago is thought to have produced the Chicxulub Crater and the K-T extinction event, widely held responsible for the extinction of most dinosaurs.

Chicxulub, Yucatan penninsula, Mexico Gravity map of buried structure 180 miles across; 65 millions years old Identified in early 1990s with seismic data, after 10 year ‘search’

Toutatis

How Do We Mitigate the Hazard of Possible Asteroid Impacts? Efforts to mitigate the hazard of possible asteroid impacts with Earth include: asteroid deflection mission concept studies, impact effects studies, and emergency response planning. NASA’s NEO Observations Program is sponsoring several studies of techniques for impact mitigation. The European Union’s NEOShield Project is conducting a detailed analysis of “open questions relating to realistic options for preventing the collision of a NEO with the Earth.”

NEOShield is considering kinetic impactor options, blast deflection techniques, and gravity-tractor methods. Impact effects studies are ongoing at some of the Department of Energy’s national laboratories. Impact emergency response planning: NASA’s Near Earth Object Observations (NEOO) Program has participated in impact-response planning activities with the U.S. Air Force, the Defense Advanced Research Projects Agency, and the Federal Emergency Management Agency (FEMA). NASA and FEMA have formed a working group on impact emergency response planning. 

Asteroid Mining

Economics Currently, the quality of the ore and the consequent cost and mass of equipment required to extract it are unknown and can only be speculated. Some economic analyses indicate that the cost of returning asteroidal materials to Earth far outweighs their market value, and that asteroid mining will not attract private investment at current commodity prices and space transportation costs. Other studies suggest large profit by using solar power. Potential markets for materials can be identified and profit generated if extraction cost is brought down. For example, the delivery of multiple tons of water to low earth orbit for rocket fuel preparation for space tourism could generate a significant profit if space tourism itself proves profitable, which has not been proven

In 1997 it was speculated that a relatively small metallic asteroid with a diameter of 1.6 km (1 mi) contains more than US$20 trillion worth of industrial and precious metals. A comparatively small M-type asteroid with a mean diameter of 1 km (0.62 mi) could contain more than two billion metric tons of iron-nickel ore, or two to three times the world production of 2004. The asteroid 16 Psyche is believed to contain 1.7×1019 kg of nickel–iron, which could supply the world production requirement for several million years. A small portion of the extracted material would also be precious metals.

Not all mined materials from asteroids would be cost-effective, especially for the potential return of economic amounts of material to Earth. For potential return to Earth, platinum is considered very rare in terrestrial geologic formations and therefore is potentially worth bringing some quantity for terrestrial use. Nickel, on the other hand, is quite abundant and being mined in many terrestrial locations, so the high cost of asteroid mining may not make it economically viable

Financial feasibility Space ventures are high-risk, with long lead times and heavy capital investment, and that is no different for asteroid-mining projects. These types of ventures could be funded through private investment or through government investment. For a commercial venture it can be profitable as long as the revenue earned is greater than total costs (costs for extraction and costs for marketing).The costs involving an asteroid-mining venture have been estimated to be around US$100 billion. There are six categories of cost considered for an asteroid mining venture: Research and development costs Exploration and prospecting costs Construction and infrastructure development costs Operational and engineering costs Environmental costs Time cost

Summary: Asteroid Mining Due to the high launch and transportation costs of spaceflight, inaccurate identification of asteroids suitable for mining, and in-situ ore extraction challenges, terrestrial mining remains the only means of raw mineral acquisition today. If space program funding, either public or private, dramatically increases, this situation is likely to change in the future as resources on Earth are becoming increasingly scarce and the full potentials of asteroid mining are researched in greater detail.[However, it is yet uncertain whether asteroid mining will develop to attain the volume and composition needed in due time to fully compensate for dwindling terrestrial reserves.