Fewer Earthbound asteroids will hit home

July 16, 2003

Scientists report in Nature today that significantly fewer asteroids could hit the Earth's surface than previously reckoned.

Researchers from Imperial College London and the Russian Academy of Sciences have built a computer simulation that predicts whether asteroids with a diameter up to one kilometre (km) will explode in the atmosphere or hit the surface.

The results indicate that asteroids with a diameter greater than 200 metres (the length of two football pitches) will hit the surface approximately once every 160,000 years - way down on previous estimates of impacts every 2,500 years.

The findings also predict that many more asteroids blow up in the atmosphere than previous estimates, which means the hazard posed by impact-generated tidal waves or tsunamis is lower than previous predictions. The researchers suggest that proposals to extend monitoring of Near Earth Objects (NEO) to include much smaller objects should be reviewed.

Dr Phil Bland of Imperial's Department of Earth Science and Engineering and a Royal Society University Research Fellow, said:

"There is overwhelming evidence that impacts from space have caused catastrophes for life on Earth in the past, and will do so again.

"On the Moon it's easier to track the number, frequency and size of collisions because there is no atmosphere, so everything hits the surface. On Earth the atmosphere acts like a screen and geological activity erodes many craters too.

"Massive impacts of the type thought to have wiped out the dinosaurs leave an indelible print on the Earth but we have not been able to accurately document the effect of smaller impacts. Now, we have a handle on the size of 'rock' we really need to worry about and how well the Earth's atmosphere protects us."

When small asteroids hit the atmosphere the two forces collide like two objects smashing together, which often breaks the asteroid into fragments. Until now, scientists have relied on the 'pancake' model of asteroid impact to calculate whether the asteroid will explode in the atmosphere. This treats the cascade of fragments as a single continuous liquid that spreads out over a larger area - to form a 'pancake'. But a new model known as the 'separate fragment' (SF) model, which was developed by co-author of the study, Dr Natalya Artemieva of the Russian Academy of Science, has challenged this approach.

"While the pancake model can accurately predict the height from the Earth's surface at which the asteroid will break up, it doesn't give an accurate picture of how the asteroid will impact," explains Dr Bland. "The SF model tracks the individual forces acting on each fragment as it descends through the atmosphere."

To create a more accurate model of how asteroids interact with the atmosphere the researchers ran more than 1,000 simulations using both models. Objects made of either iron or stone, known as 'impactors', were used to reflect the composition of asteroids and experiments were run with varying diameters up to 1 km.

The researchers found the number of impacts for iron impactors were comparable using both models. For stone the pancake model significantly overestimated the survivability rate across the range used.

The SF simulations also allowed the researchers to define the different styles of fragmentation and impact rates for iron and stone, which correspond closely with crater records and meteorite data.

"Our data show that over most of the size range we investigated stony asteroids need to be 1,000 times bigger than the iron ones to make a similar sized crater. Much larger objects are disrupted in the atmosphere than previously thought.

"But we are not out of the woods yet," added Dr Bland "asteroids that fragment in the atmosphere still pose a significant threat to human life."

Dr Phil Bland is a member of the Meteorite and Impact Group that includes scientists from Imperial College London and the Natural History Museum.
-end-
Notes to editors

Publication: Nature (17 July 2003)

Title: "Efficient disruption of small steroids by Earth's atmosphere"

Authors: P.A Bland (1) and N.A Artemieva (2)

(1) Department of Earth Science and Engineering, Exhibition Road, Imperial College London, SW7 2AZ, Uk
(2) Institute for Dynamics of Geospheres, Russian Academy of Sciences, Leninsky Prospect 38/6 Moscow, 117939 Russia.

About Imperial College London

Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (10,000) and staff (5,000) of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions, which enhance the quality of life and the environment - underpinned by a dynamic enterprise culture.

Website: http://www.imperial.ac.uk

Imperial College London

Related Asteroid Articles from Brightsurf:

Asteroid's scars tell stories of its past
Asteroid Bennu, which was just sampled by NASA's OSIRIS-REx mission, only recently migrated into Earth's neighborhood, according to a detailed analysis of impact marks on boulders on its surface.

Asteroid Ryugu shaken by Hayabusa2's impactor
Professor ARAKAWA Masahiko (Graduate School of Science, Kobe University, Japan) and Hayabusa2 mission members discovered more than 200 boulders, which either newly appeared or moved as a result of the artificial impact crater created by the Japanese spacecraft's Small Carry-on Impactor.

Scientists peer inside an asteroid
New findings from NASA's OSIRIS-REx mission suggest that the interior of the asteroid Bennu could be weaker and less dense than its outer layers--like a crème-filled chocolate egg flying though space.

Designing better asteroid explorers
Recent NASA missions to asteroids have used robotic explorers to gather data about the early evolution of our Solar System, planet formation, and how life may have originated on Earth.

ATLAS telescope discovers first-of-its-kind asteroid
University of Hawai'i telescope discovers extraordinary asteroid with comet-like features that has researchers puzzled.

An iron-clad asteroid
Mineralogists from Jena and Japan discover a previously unknown phenomenon in soil samples from the asteroid 'Itokawa': the surface of the celestial body is covered with tiny hair-shaped iron crystals.

Asteroid impact enriches certain elements in seawater
University of Tsukuba researchers found two processes immediately after the end-Cretaceous asteroid impact that likely supplied chalcophile elements to the ocean, i.e., impact heating and acid rain.

Turbulent times revealed on Asteroid 4 Vesta
Planetary scientists at Curtin University have shed some light on the tumultuous early days of the largely preserved protoplanet Asteroid 4 Vesta, the second largest asteroid in our solar system.

In death of dinosaurs, it was all about the asteroid -- not volcanoes
Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, according to an international, Yale-led team of researchers.

Active asteroid unveils fireball identity
At around 1 a.m. local standard time on April 29, 2017, a fireball flew over Kyoto, Japan.

Read More: Asteroid News and Asteroid Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.