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Starts With A Bang

Why Earth Isn’t A Technologically Mature Planet Just Yet

The presence of comets and asteroids helps create the zodiacal dust that we see, but also presents the greatest existential threat to our species from space, carrying along with it the potential of a catastrophic collision similar or even worse than the one that caused our last great mass extinction 65 million years ago. (SWRI/SETI INSTITUTE (ANDREW BLANCHARD, DAVID NESVORNY AND PETER JENNISKENS))

And the one step we can take to show extraterrestrials we’re figuring it out.


Every year, Earth’s meteor showers accomplish two important tasks.

This composite photograph shows a large number of Geminid meteors captured during the night of the peak in December a few years back. Dark skies and lots of patience are key to enjoying a meteor shower, and December’s Geminids may be the best meteor shower not only of the year, but of the century. (J.C. CASADO/TIERRA Y ESTRELLAS/© STARRYEARTH/INSTITUTO DE ASTROFÍSICA DE CANARIAS)

One is illuminating our skies, streaking through our atmosphere with brief, brilliant flashes.

A view of many meteors striking Earth over a long period of time, shown all at once, from the ground (left) and space (right). The faster, larger, and more numerous the cometary fragments striking Earth’s atmosphere are, the more spectacular the ensuing meteor shower is. (ASTRONOMICAL AND GEOPHYSICAL OBSERVATORY, COMENIUS UNIVERSITY (L); NASA (FROM SPACE), VIA WIKIMEDIA COMMONS USER SVDMOLEN (R))

The second reminds us that our ultimate demise is certain without preparation.

A planetoid colliding with Earth, analogous (but larger and slower-moving) than an impact between Swift-Tuttle and Earth would be. The asteroid that wiped out the dinosaurs had just 1/28th the energy that being hit by Comet Swift-Tuttle would carry, and that impact was enough to wipe out 75% of all species on Earth. (NASA / DON DAVIS)

The rocky, icy fragments that create meteor showers routinely cross Earth’s orbit.

Although, for many comets or asteroids, there is a higher density of debris associated with the location of the main body, over enough time, the debris will get smeared out along the orbit to such a sufficient degree that the meteor shower can become very consistent year-to-year. The Leonids have not yet reached that stage, and as such, they still peak roughly every 33.25 years. (GEHRZ, R. D., REACH, W. T., WOODWARD, C. E., AND KELLEY, M. S., 2006)

These large masses, multiple kilometers across, contain comparable energies to the Chicxulub impactor.

The size distribution of asteroids is closely related to the size distribution and frequency distribution of meteors that strike Earth. However, there are additional strikes that also occur, and they cannot be explained by our asteroid belt alone. (MARCO COLOMBO, DENSITYDESIGN RESEARCH LAB)

Most megafaunal species were wiped out 65 million years ago; a comparable catastrophe would ensue today.

The Cretaceous-Paleogene boundary layer is very distinct in sedimentary rock, but it’s the thin layer of ash, and its elemental composition, that teaches us about the extraterrestrial origin of the impactor that caused the mass extinction event. Earth has hundreds of meters worth of sedimentary rock covering its surface practically everywhere, with limestone making up about 10% of the sedimentary rock in total. (JAMES VAN GUNDY)

Gravitational perturbations from other masses, like planets, are statistically random.

The idea of a gravitational slingshot, or gravity assist, is to have a spacecraft approach a planet orbiting the Sun that it is not bound to. Depending on the orientation of the spacecraft’s relative trajectory, it will either receive a speed boost or a de-boost with respect to the Sun, compensated for by the energy lost or gained (respectively) by the planet orbiting the Sun. This occurs, naturally and in an uncontrolled fashion, for all asteroids and comets that pass close by another planet. (WIKIMEDIA COMMONS USER ZEIMUSU)

Today’s near-miss could portend tomorrow’s extinction event.

The comet that gives rise to the Perseid meteor shower, Comet Swift-Tuttle, was photographed during its last pass into the inner Solar System in 1992. This comet, which gives rise to the Perseid meteor shower, also displayed a spectacular green coma. (NASA, OF COMET SWIFT-TUTTLE)

The parent body of August’s Perseids, Comet Swift-Tuttle, is the single most dangerous object known to humanity.

The orbit of Comet Swift-Tuttle (purple) from the years 1850–2150. The next close approach to Earth (blue) will occur in 2126. Also shown, for scale and orbital period comparisons, are the orbits of Jupiter (green), Saturn (red), and Uranus (orange). Comet Swift-Tuttle is in a 1:11 orbital resonance with Jupiter. (PHOENIX7777/WIKIMEDIA COMMONS; DATA: HORIZONS, JPL, NASA)

A direct impact — threatened in 4479 — would deliver over ~25 times the energy of the Chicxulub impact.

The crater left by the asteroid that wiped out the dinosaurs is located in the Yucatán Peninsula. It is called Chicxulub after a nearby town. Part of the crater is offshore and part of it is on land. The crater is buried beneath many layers of rock and sediment. A 2016 mission led by the International Ocean Discovery Program extracted rock cores from the offshore portion of the crater. (THE UNIVERSITY OF TEXAS AT AUSTIN/JACKSON SCHOOL OF GEOSCIENCES/ GOOGLE MAP)

But a proverbial ounce of prevention could protect our planet indefinitely.

This view of the Halloween Asteroid, 2015 TB145, clearly showcases its rotating craters, which give it a skull-like appearance. It made another close pass by Earth during November of 2018, and will likely continue to threaten our planet, like many potentially hazardous asteroids, for some time until a gravitational perturbation changes its trajectory, or a collision occurs. (ARECIBO OBSERVATORY)

Near-Earth asteroids and Earth-crossing comets all represent potential hazards.

Long-term predictions of well-characterized orbits can be extracted, portending a near-Earth encounter with a potentially hazardous object in March of 2880. Close encounters with bodies, such as Jupiter or Neptune, can perturb these orbits, potentially leading to a collision with Earth someday. (NASA / JPL)

By shepherding them into stable, non-hazardous orbits, we can eliminate the risk to Earth.

The animation depicts a mapping of the positions of known near-Earth objects (NEOs) at points in time over the past 20 years, and finishes with a map of all known asteroids as of January 2018. In order to accurately know the orbital characteristics of an asteroid (or any near-Earth object), its position and velocity must be measured at many different points over time. (NASA/JPL-CALTECH)

Asteroid and comet tracking, plus redirection technologies, could secure humanity’s safety from large-scale impacts.

The NEXIS Ion Thruster, at Jet Propulsion Laboratories, is a prototype for a long-term thruster that could move large-mass objects over very long timescales. Once a potentially hazardous object is identified, attaching a thruster and activating it could shepherd a hazardous object into a safe, stable orbit. (NASA / JPL)

Perhaps all technologically “mature” planets clear this species-threatening hazard from their orbits.

This time lapse animated photograph shows asteroid 3200 Phaethon, tracked from Riga, Latvia, in 2017. This is the parent body of the Geminid meteor shower: an asteroid just 5.8 km in diameter, approximately the size of the asteroid that catastrophically struck Earth some 65 million years ago. (INGVARS TOMSONS / C.C.A.-S.A.-4.0)

Detecting this non-natural property in exoplanetary systems could indicate intelligent, technologically advanced aliens.

Intelligent aliens, if they exist in the galaxy or the Universe, might be detectable from a variety of signals: electromagnetic, from planet modification, or because they’re spacefaring. Although we haven’t found any evidence for an inhabited alien planet so far, looking for a solar system without planet-crossing asteroids or comets could be the “smoking gun” of extraterrestrial intelligence. (RYAN SOMMA / FLICKR)

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.

Starts With A Bang is written by Ethan Siegel, Ph.D., author of Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.


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