How to Hunt a Killer
Spring 2020 | By Laura J. Cole
All it would take is one ill-fated聽asteroid colliding with Earth to go聽from a bad day to the end of days.聽Such was the course of dinosaurs.
But unlike in the Mesozoic Era, today聽we have the tools to help us detect 鈥� and聽hopefully deflect 鈥� what 91吃瓜网 Professor聽and Director Yan聽Fernandez calls 鈥渃ivilization busters.鈥�
That鈥檚 where researchers at 91吃瓜网 and聽the 91吃瓜网-managed Arecibo Observatory聽in Puerto Rico come into play. Thanks to聽a $19 million grant from NASA, they鈥檙e聽working to characterize asteroids and聽comets so that governments and teams,聽such as NASA鈥檚 Planetary Defense聽Coordination Office, can make informed聽decisions on how to protect our planet.
鈥淵ou have to know what the asteroids聽are really like to have an effective聽mitigation strategy,鈥� Fernandez says.
For example, 鈥淚f you tried to blow up聽an asteroid that鈥檚 very porous with a聽nuclear device, the asteroid could end聽up just absorbing the blow rather than聽being dismantled completely,鈥� says Anne聽Virkki, planetary radar group lead at聽Arecibo, which is home to the largest, most聽sensitive radio telescope in the world.聽鈥淭hen you might end up with radioactive聽pieces of asteroid still hitting the Earth.鈥�
By collecting and analyzing data about聽each asteroid鈥檚 fundamental properties聽鈥� such as its mass, rotation, size and聽surface composition 鈥� scientists are聽not only making some pretty stellar聽discoveries about the more than 20,000聽space objects whirling past our precious聽home planet, but they鈥檙e providing vital聽information that can 鈥渕ean the difference聽between missing the Earth and hitting it,鈥澛燜ernandez says. Here鈥檚 how.
THE DANGER ZONE
NEOs
Near-Earth objects are asteroids, comets and聽meteoroids whose orbit is between Mars and聽the sun, posing a danger of collision.
460 Feet
鈥淣ASA would define a potentially聽hazardous asteroid as one that鈥檚 140 meters聽[or 460 feet] or more in diameter,鈥� Virkki聽says, which is slightly taller than the Great聽Pyramid of Giza.
4.5 Million Miles
Hazardous asteroids are also defined as聽鈥減assing the Earth closer than 19 lunar聽distances or 4.5 million miles,鈥� Virkki says.
1,000%
As a result of advances in science, the聽number of Great Pyramid-sized NEOs聽discovered soaring past our planet has聽increased by more than 1,000 percent聽since 2003.
955,656
Number of currently known asteroids
3,611
Number of currently known comets
WHY ARECIBO?
鈥淲e can do some serious analysis about what these asteroids are like without having to spend a bunch of money to send a spacecraft there.”Yan Fernandez
Radar telescopes, such as the one at Arecibo, emit radio waves from large antennas, which bounce off聽an asteroid and are reflected back, providing powerful data that helps scientists determine an asteroid鈥檚聽orbit, rotation, shape, size and surface composition. 鈥淎recibo鈥檚 radar is the most powerful in the world,聽which can transmit up to one megawatt of power,鈥� says Virkki. 鈥淎nd we also have the biggest antenna,聽about 305 meters [roughly 1,000 feet] across to collect the reflected signal.鈥�
WHAT TO LOOK FOR
1. Discovery and Orbit
While optical telescopes are still the best way to find聽NEOs and estimate their orbits, radar telescopes are聽powerful tools in improving orbital predictions.
2. Surface Composition
By bouncing radar signals off the surfaces of聽asteroids, Arecibo can provide valuable information聽about their physical characteristics. 鈥淩adar allows聽us to see up to one meter below the surface,鈥澛燰irkki says, which helps determine composition.聽鈥淔or example, some of the asteroids could be so聽fluffy that if you tried to hit one with a projectile聽or something to knock it off course or break it up,聽the projectile could just get sort of embedded in it聽instead,鈥� Fernandez says.
3. Size, Shape and Rotation
Radar images can also help reconstruct an asteroid鈥檚聽size, shape and rotation with a level of detail that聽can otherwise only be obtained by a spacecraft.聽鈥淔or example, in 2018, we were observing a very聽rare type of binary asteroid called equal mass聽binary, where you have two pretty much equally聽sized lobes orbiting each other,鈥� Virkki says.
4. Density and Mass
How do you weigh something that you can鈥檛 get聽close enough to touch? 鈥淢ass and density were聽very difficult problems to solve in planetary聽science for a very long time,鈥� says Fernandez.聽鈥淚t鈥檚 really hard to figure out the mass of things聽unless you use tricks, right?鈥� That鈥檚 where moons聽can help. According to NASA, nearly 400 asteroids聽have a small companion moon, and its orbit can聽help determine the mass of the primary body.聽鈥淚f you can figure out the shape and volume聽of the asteroid, that gets you density,鈥澛燜ernandez says.
IDENTIFIED FLYING OBJECTS
ASTEROID: Apophis
Discovered: June 19, 2004
Size: 1,100 feet wide
When it was initially discovered, scientists calculated that the asteroid聽Apophis had a 2.7 percent chance of hitting Earth. 鈥淎recibo鈥檚 radar was able聽to show that though its orbit is going to go very close to Earth, it isn鈥檛 going聽to hit us,鈥� Virkki says. 鈥淚nstead, we can prepare our telescopes to observe聽it when it goes by.鈥� Which it will, when on April 13, 2029, it will become the聽closest asteroid of its size to fly by Earth 鈥� at about 19,400 miles away.
METEOROID: Chelyabinsk
Size: 66 feet
While scientists are able to discover many asteroids and comets, there聽are some that slip by undetected. Such was the case with the Chelyabinsk聽meteoroid that entered Earth鈥檚 atmosphere over Russia on February 15, 2013,聽injuring at least 1,200 people from the shockwave. Scientists believe it is聽a fragment of an asteroid that gained speed when it was ejected from the聽asteroid belt between Mars and Jupiter. 鈥淚 think it was pretty porous 鈥斅爄t just broke in the atmosphere when it got low enough,鈥� Virkki says.
COMET: 679/Churyumov-Gerasimenko
Discovered:聽Oct. 22, 1969
Last visited by: Rosetta spacecraft in 2014-16
Size: 2.5 miles wide
鈥淪ome asteroids can look like comets, some comets like asteroids,鈥� Fernandez聽says. 鈥淚n the old days, scientists believed that comets and asteroids were聽totally separate things, but in the last 20 to 30 years, we鈥檝e discovered聽there鈥檚 really a continuum.鈥� For example, the rubber duck-shaped comet 67P/聽Churyumov-Gerasimenko looks like an asteroid in that it consists of two lobes聽attached by a narrow neck, which is known as a 鈥渃ontact binary.鈥� Prior to聽images of it taken in 2014, no one had seen a comet look quite like that.
DID YOU KNOW?
91吃瓜网 researchers are also part of NASA鈥檚 OSIRIS-REx mission, which has sent a spacecraft to take a sample of the asteroid Bennu. One of the team鈥檚聽recent discoveries found the asteroid is shooting out plumes of dust 鈥� a phenomenon never witnessed before 鈥� which indicates the asteroid is聽active.
Some asteroids and comets are light enough to float. 鈥淲e all intuitively think that rocks are going to sink in the water, but some asteroids聽and comets are actually less dense than water,鈥� Fernandez says.
聽Arecibo鈥檚 location in Puerto Rico provides optimal celestial viewing. 鈥淏eing this close to the equator helps us see objects on the ecliptic plane聽better,鈥� Virkki says.
Asteroids can impact their own orbit. By absorbing sunlight and re-emitting that energy as heat, asteroids get a small propulsion, which 鈥渁cts as a mini thruster that can slowly change the聽asteroid鈥檚 direction,鈥� Fernandez says.
Water is more prevalent in the solar system than previously believed. This discovery could help propel space exploration further.