When Rocks Fall Like Rain

This map shows daytime (orange) and nighttime (blue) asteroid impacts over the past 20 years. The size of the dots reflect the amount of energy released. The largest impact occurred over the Russian town of Chelyabinsk (big orange dot in central Russia) and unleashed a 500-kiloton blast. Source: Nasa/JPL

556 asteroids struck Earth over the past 20 years according to a new report from Nasa’s Near Earth Object Program. Fortunately the constant rain of rocks and boulders striking our planet burn up in the atmosphere - unless it’s a big one like the Chelyabinsnk meteor. Learn how you can help the professionals protect our planet from asteroid threats.

Nasa used data from “US government sensors” - a euphemism for military and intelligence sensors - to map the location and size of the asteroid strikes. The map and its underlying statistics show that asteroid strikes are completely random - equally distributed in size, geography, and time. But the map only represents a fraction of the tons of material raining down from space every day.

Of the hundreds of tons of material entering Earth’s atmosphere, most consists of dust left behind by comets passing through the inner Solar System. These grains of dust produce the meteor showers that impress skywatchers. A small fraction of the material consists of pebble-sized objects large enough to produce fireballs - meteors as bright as Venus in the night sky. Even larger objects produce bolides - fireballs that explode under the crushing pressure of their passage through the atmosphere. 

The “government sensors” - presumably instruments looking for nuclear weapons testing - recorded these bolide explosions. The smallest of the bolides release the equivalent energy, but not the radiation, of a 5-kiloton nuclear weapon. The 20-meter Chelyabinsk meteor, the largest recorded event in the past 20 years, released the equivalent of a 500 kiloton blast. Fortunately it exploded high above the Russian city but still thousands were injured by shards of shattered window glass. 

The historical record shows that even larger objects have unleashed regional damage the equivalent of volcanoes - and even global devastation. Check out Canada's Earth Impact Database to see pictures of the 184 surviving impact craters. This is the reason why governments have tasked Nasa and other space agencies with finding and tracking asteroids larger enough to reach Earth’s surface. Nasa’s Near Earth Object Program, for example, is charged with finding all of the potentially hazardous objects larger than 140 meters across. Esa’s Space Situational Awareness Programme will complement Nasa’s by scanning for smaller objects as they approach Earth.

This image of Arizona's Barringer Meteorite Crater, the result of a 10 megaton impact, overlays imaging data from the Terra spacecraft on USGS elevation data. Image Credit: Nasa/GSFC/Meti/Ersdac/Jaros, and U.S./Japan Aster Science Team

Yet despite the massive resources space agencies and the world’s professional astronomers have at their disposal, they can’t do everything. Scientists can’t be everywhere and look at everything. The few dedicated asteroid observatories focus on discovering asteroids rather than making the dozens or hundreds of follow-on observations needed to calculate the asteroid’s orbit, size, and composition. 

That’s where amateurs come in. Whether you are an advanced amateur astronomer with thousands of dollars of equipment or just looking up at the night sky, you can play a role in monitoring the rain of dust and rocks falling on Earth.

Meteor and Fireball Reporting

You probably won't get the same view of meteor showers as astronaut Ron Garan had of the Perseids from the International Space Station. Source: Nasa

The easiest thing to do is report meteors and fireballs you see in the night sky. Pro-am organizations like the American Meteor Society and the International Meteor Organization compile these amateur reports into databases that scientists rely on for their research. Their websites provide tutorials for beginning and advanced observers alike.

Even easier is to use a smartphone app to report your observations. Nasa’s Meteoroid Environment Office produced the Meteor Counter app (iOS only) to collect reports of meteors of all sizes. Australian universities created the Fireballs in the Sky app (iOS and Android) to collect reports of the larger fireballs and bolides that might produce meteorites.

Asteroid Photo Bombs

The bright streak in this image is the asteroid 1999 AN10 discovered in 1999. Nasa scientists "precovered" the asteroid in this 1955 photographic image digitized by the Digital Sky Survey.  Source:  Nasa

The bright streak in this image is the asteroid 1999 AN10 discovered in 1999. Nasa scientists "precovered" the asteroid in this 1955 photographic image digitized by the Digital Sky Survey. Source: Nasa

Even when astronomers aren't studying asteroids, the objects drift through the picture frame all the time. Astronomers process the data out when "cleaning" their research, but the asteroid data is still there. When amateur and professionals astronomers use archived observations to find and track asteroids, it's called "precovery". Take a look at some of the precovery projects you can take part in: 

Near Earth Asteroid Precovery: The Spanish Virtual Observatory asks amateurs to search for signs of asteroids in images from the Sloan Digitized Sky Survey and the VISTA Hemisphere Survey.

Asteroid Zoo: Search for signs of asteroids in images from the Catalina Sky Survey. Organized by crowdsourcing service Zooniverse and asteroid mining company Planetary Resources, the project expects its amateur asteroid-spotters to find another 10,000 asteroids. [Check out my article about Asteroid Zoo]

Asteroid Data Hunter: If you’re a coder, then you can help Nasa by taking part in this programming challenge. The space agency wants to improve the efficiency of the algorithms that scan images for asteroids. By increasing the detection rate (and reducing the false positives) the space agency will be better able to conduct follow-up observations.

Asteroid Tracker: Another coding challenge from Nasa, this one asks programmers to help improve the radar systems that track asteroids passing close to Earth.

Observe Asteroids for Science

This 73-frame movie of asteroid 2012 DA14, discovered by amateur recipients of the Shoemaker Near Earth Object Grant, was generated from data obtained by NASA's Goldstone Solar System Radar on the night of Feb. 15 to 16, 2013. The observations were made as the asteroid was moving away from Earth. Image credit: NASA/JPL-Caltech & Asteroid and Comet Watch site

You can use your own telescope or an online telescope to make your own asteroid observations. Although professional observatories make almost all of the discoveries, amateurs play essential roles in the follow-up observations needed to fully document these objects. Calculating the size and shape of an asteroid as well as its orbit requires dozens - even hundreds - of observations. Repeat that for the hundreds of asteroids discovered every year. Most professional observatories can’t devote that much time given everything else they need to look at. Here are some programs that bring amateurs into the direct study of asteroids:

Minor Planet Center - The goto resource for professionals and amateurs alike, the International Astronomical Union’s Minor Planet Center collects all of the observations of asteroids, comets, and other small objects. Its database contains 118,000,000 observations of over 664,000 objects. Of the nearly 12,000 near-Earth objects in the database, more than 1,500 have potentially hazardous Earth-crossing orbits. The MPC accepts amateur contributions, but assumes you already know what you’re doing.

MinorPlanet.info - This site hosts several pro-am asteroid projects including the Collaborative Asteroid Lightcurve Link which coordinates the amateur lightcurve observations that let astronomers map asteroids’ shapes and other features. The site hosts observing guides and publishes professional and amateur research papers in its Minor Planet Bulletin.

Amateur Observers Program - The outreach program for many of Nasa’s asteroid missions hosts this introduction to asteroid observation. Tutorials walk you through beginner, intermediate, and advanced observation techniques. [Check out my article about the Amateur Observers Program.]

Target Asteroids Program - An outreach program of Nasa’s upcoming Osiris-Rex asteroid mission, Target Asteroids coordinates amateur observations of several near-Earth asteroids to better understand the objects’ size, rotation, and composition.

Lowell Amateur Research Initiative - The Lowell Observatory regularly conducts pro-am research projects. Right now Lari’s asteroid projects target objects in the outer Solar System, but previous projects have let amateurs help the Lowell observatory with follow-up observations of main belt and near-Earth asteroids.

Shoemaker Near-Earth Object Grant Program - The Planetary Society awards thousands of dollars in grants to amateur astronomers around the world to improve their asteroid observations. Originally developed to boost amateur discoveries, it now focuses on enhancing the amateur follow-up observations professionals depend on.