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Scope on the Skies

Preparing for Cosmic Collisions

Science Scope—January 2020 (Volume 43, Issue 5)

By Bob Riddle

The following information is based on simulations done by various space organizations. An asteroid is not expected to enter the Earth’s  atmosphere as described below.  

In 2009 scientists initially calculated that the orbit of an asteroid they discovered would travel around the Sun until reaching the Earth’s orbit in 2019 or so. Since the discovery of the asteroid, astronomers realized that this asteroid fits within the potentially hazardous asteroid (PHA) category, meaning there was a good chance that it would intersect the Earth’s orbit. The same calculations showed that the Earth will be at that same point in its orbit, thus putting the asteroid on a possible collision course with our planet. 

Four years after its discovery, the asteroid was still too far away for an accurate determination of its size and mass based on the asteroid’s brightness, known as its absolute magnitude. At that time, however, estimates put its absolute magnitude at around 20, which suggested the asteroid could be up to 0.5 km (1,700 ft.) in size. If the asteroid were to enter our atmosphere, astronomers thought it would break apart explosively above the ground and not reach the surface, much like the 1908 Tunguska explosion (see Resources) or the Chelyabinsk Meteor in 2013 (see Resources). But the greatest questions and cause for concern are where on Earth would this impact occur, what damage would there be, and is there anything that could be done to avert this potential disaster?

In 2010, NASA and other space programs, including Russia, China, India, Japan, and Europe, launched a series of probes on a two-year voyage to the asteroid. The probes were designed to send back data about the asteroid. As a group, the four probes were placed in trajectory paths that would have them collide with the asteroid to alter the asteroid’s path to avoid Earth. During the asteroid approach, the probes nudged the asteroid off its current trajectory and useful data were collected. How much of a change the nudge made was determined a few months later as scientists were able to more accurately calculate the trajectory of the asteroid. 

When the asteroid was a few months from Earth, it became more certain that the asteroid’s orbital path would take it across Earth’s orbit. The probes did not provide enough force to alter the path. What is uncertain is the location of where the asteroid would enter the atmosphere and over or on what part of the Earth the asteroid would explosively break apart. Calculations initially create what is known as “risk corridor,” the area of the Earth where the event may occur (Figure 1). In this situation, the risk corridor wraps about halfway around the globe. The asteroid is expected to explode in the atmosphere and not form an impact crater. Nonetheless, the effect of this will be devastating to the surface below. Anything within the risk corridor is a potential site for the impact. As time passed, the accuracy of the risk corridor steadily increased until scientists were confident of the event site. 

Figure 1
Initial calculations show the simulated Risk Corridor

As the date for the asteroid collision gets closer, calculations are finalized to the degree that not only is the date and time of atmospheric entry known, but also the location on the Earth above which the asteroid will explode is known. Based on estimates, the asteroid will explode between 6 km to 12 km (4 mi to 7 mi) above the Earth over a city in Bangladesh (see Figure 2).

Figure 2
The estimated damage “footprint” 
For Students
  1. Read about the close flyby of asteroid Apophis in 2019 and how scientists planned for it (see Resources).
  2. This column was based in part on a simulated asteroid impact scenario. For a more detailed chronology of the events including maps and NASA websites read the “2015 PDC Hypothetical Asteroid Impact Scenario” (see Resources). 
  3. Use the online Impact Earth or the Impact Earth Effects simulator (see Resources) to model simulated impacts by varying the “impact parameters.”

Alan Hills Meteorite—

Asteroid 2008 TC3—

Asteroid Apophis—

Asteroid Watch—

Best Asteroid, Comet, and Meteorite Books—

Buzz Aldrin—

Buzz Aldrin’s Rocket Experience Video—

Calculating the age of solar system objects—

Center for NEO Studies (CNEOS)—

Dwarf planet Eris—


Glossary-Potential Hazardous Asteroids (PHA)—

Hypothetical Asteroid Impact Scenario—

Impact Earth Simulator—

Earth Impacts Effects Program—

Killer Asteroids—

La Criolla Meteorite—

Lorton Meteorite—

Lost City Meteorite—

Mars Meteorite EETA 79001—

Minor planet center—

Penumbral Lunar Eclipse—

Potential Hazardous Asteroid—

Power of the Chelyabinsk Meteor 2013—

Quadrantids Meteor Shower—

Quadrantids Meteor Shower—

Tagish Lake Meteorite Shower—

Tunguska Explosion 1908— 

Vigarano Meteorite—




Moon at apogee: 404,600 km (251,407 mi.)


First quarter Moon


Quadrantids meteor shower

Lost city meteorite (1970)


The Sun is at perihelion: 147,084,626 km (91,394,150 mi.)


La Criolla meteorite (1985)


Moon at ascending node


Mercury at superior conjunction

Penumbral lunar eclipse

Full Moon


Waning gibbous Moon near M-44, the Beehive Open Star Cluster


Saturn conjunction

Moon at perigee: 366,000 km (227,422 mi.)

Discovery of Mars meteorite EETA 79001 (1980)


Last quarter Moon

Last quarter Moon near Spica

Mars passes Antares over the next week


Lorton meteorite (2010)

Tagish Lake meteorite shower (2000)


Waning crescent Moon near Mars and Antares

Buzz Aldrin’s birthday


Moon at descending node

Thin waning crescent Moon near Jupiter

Vigarano Meteorite (1910)


New Moon

Discovery of Mars meteorite Dhofar 019 (2000)


Chinese New Year


Thin waxing crescent Moon, west of Venus


Thin waxing crescent Moon, east of Venus


Moon at apogee: 405,400 km (251,904 mi.)


Waxing crescent Moon near Uranus




First quarter Moon


Waxing gibbous Moon near Aldebaran


Moon at ascending node


Waxing gibbous Moon near Gemini Twins


Moon near Beehive Open Star Cluster


Full Moon

Moon near Regulus


Mercury at eastern elongation (18°E)

Moon at perigee: 360,463 km (223,981 mi.)


Last quarter Moon

Galileo Day


Waning crescent Moon near Mars

Moon at descending node

Neagari meteorite hits a car in Japan (1995)


Waning crescent Moon near Jupiter


Waning crescent Moon near Saturn


New Moon


Mercury at inferior conjunction


Moon at apogee: 406,276 km (252,448 mi.)


Waxing crescent Moon near Venus


Leap Day

Visible Planets

Mercury will move from superior conjunction, on the opposite side of the Sun, to become more visible as an evening planet at sunset local time, until mid-February when it moves into inferior conjunction, between the Earth and the Sun.

Venus will be visible over the western horizon at sunset.

Mars will rise before sunrise local time and will be visible over the eastern horizon.

Jupiter will slowly become more visible over the eastern horizon in the pre-dawn skies.

Saturn will be at solar conjunction, on the opposite side of the Sun, and will not be visible again until later next month as it becomes more visible over the eastern horizon in the pre-dawn skies.

Quadrantids Meteor Shower will reach its peak on the morning of January 4. This annual meteor shower will occur the last week of December through mid-January. It is a somewhat unusual meteor shower because the meteoroids entering our atmosphere come from Asteroid 2003 EH1 rather than from the debris left behind by a comet. It is thought that the asteroid may be the remnants of a comet that is no longer active as it orbits the Sun in 5.52 years.

Astronomy Middle School

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