Asteroids may have delivered water to early Earth | Science News for Students

Asteroids may have delivered water to early Earth

Much of the space rocks’ water would not have boiled away on impact
Jun 1, 2018 — 6:45 am EST
asteroid impact

An asteroid impact can create glass and melted rock, which can trap water vapor. The finding boosts the idea that asteroids brought water to the early Earth.


View the video

Shooting small rocks from a high-speed cannon sounds like a school science project. In fact, it was a sophisticated science experiment. And the results showed how some asteroids could have brought water to the early Earth.

“We can’t bring an asteroid to Earth and crash it into the Earth. Bad things would happen,” says R. Terik Daly. “So we went into the lab and tried to recreate the event as best we can.” Daly is a planetary geologist at Johns Hopkins University in Baltimore, Md.

The solar system formed about 4.6 billion years ago. Earth developed fairly close to the sun. Here, it would have been too hot for water to condense out of its gas phase and form liquid water. Earth also was too small to hold onto much nearby gas anyway. So scientists think the pale blue dot may have received its water from elsewhere. How that might have happened, however, remains an open question.

Daly wanted to test whether Earth could have gotten its water from asteroids. His team’s new data indicate asteroids could have delivered up to 30 percent of their stored water to growing planets.

The group shared its findings April 25 in Science Advances.

How they learned that

Daly’s got his PhD in Earth and planetary sciences, last year, at Brown University in Providence, R.I. While there, he worked with planetary scientist Peter Schultz. Together, the two made marble-sized pellets of antigorite (An-TIG-or-ite). It resembles the type of rock that may have brought water to Earth billions of years ago.

To simulate a dry planetary surface, the team used a type of volcanic rock called pumice (PUMM-is). They baked it at 850° Celsius (1,562° Fahrenheit) for 90 minutes. Then they shot the antigorite pellets at this baked rock at the NASA Ames Vertical Gun Range in California. The pellets flew at about 5 kilometers (3.1 miles) per second. That speed is similar to that at which asteroids probably crashed into each other and nearby planets during the solar system’s early days, Daly says.

Computer programs have modeled what such impacts must have looked like. These computer models suggested that if an asteroid had been traveling faster than 3.1 kilometers per second, all of its water would vaporize upon impact. Early Earth lacked an atmosphere. So there, the water vapor should have been lost to space.

asteroid experiment
Scientists devised a high-speed impact in the lab that mimicked asteroids hitting a dry planet. The result: clumps of glass (top) and rocky conglomerate (bottom). The glass and rock trapped water vapor, perhaps supplying an explanation for how Earth got so wet.
R. Terik Daly

But the experiments by Daly and Schultz showed something different. Some water vapor released by the pellets’ impacts was captured within glass that was created from shocked rock. Water vapor also captured in conglomerates of “busted-up” rocks. These are called breccias (BREH-chee-uhs).

The next step, Daly says, will be working out how the water could escape from such rocks to create oceans and other bodies of water.

“I really like this work,” says Yang Liu. She is a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and was not involved in the study. “The experimental setup,” she observes, “is very clever.”

Liu studies water in material from the moon. One frequent question about her work is how the moon could have water at all. It lacks a thick atmosphere where vapor can accumulate. That means the moon should have had an even harder time than Earth did holding onto any impact-delivered water.

“This work demonstrates that this is feasible even for airless bodies” such as the moon, she says. The finding even suggests a way that future crewed missions might find water on the moon. To get the water we need, she says, perhaps researchers should look for rocks that melted when a meteorite hit them.

Daly’s interest in science didn’t start in college. He has been interested in it since he was a boy. In high school, he even took part in in two major science competitions. One was the Intel International Science and Engineering Fair. The other was the prestigious Science Talent Search (now sponsored by Regeneron). Both competitions are programs of the Society for Science & the Public (which also publishes this magazine).

This video shows a mineral pellet hitting a tray full of light and porous volcanic rock called pumice. Melted or shocked rocks fly out of the impact site. Those rocks trapped a surprising amount of water. The finding suggests asteroids could have left water behind after impacting Earth.
R. Terik Daly/Science News/YouTube

Power Words

(more about Power Words)

asteroid     A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

atmosphere     The envelope of gases surrounding Earth or another planet.

breccia      A type of rock made from sand or clay in which there are also sharp fragments of other minerals or some type of material.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

computer program     A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

condense     To become thicker and more dense. This could occur, for instance, when moisture evaporates out of a liquid. Condense can also mean to change from a gas or a vapor into a liquid. This could occur, for instance, when water molecules in the air join together to become droplets of water.

conglomerate     (in geology) A rough rock composed of rounded fragments generally greater than two millimeters in diameter stuck in finer sediment.

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

Intel International Science and Engineering Fair (Intel ISEF)     Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year now, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

meteorite     A lump of rock or metal from space that passes through Earth’s atmosphere and collides with the ground.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

moon     The natural satellite of any planet.

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.

PhD     (also known as a doctorate) A type of advanced degree offered by universities — typically after five or six years of study — for work that creates new knowledge. People qualify to begin this type of graduate study only after having first completed a college degree (a program that typically takes four years of study).

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

planetary science     The science of planets other than Earth.

pumice     A light-colored, porous rock flung from the lava of an erupting volcano. The rock tends to be relatively light-weight because the frothy lava had contained a large quantity of water and gases. These created little bubbles in lava, which broke open, then hardened. The material cooled so quickly that atoms in the liquid rock could not form crystals. Pumice is therefore a type of volcanic glass with an amorphous (irregular) structure.

Science Talent Search     An annual competition created and run by Society for Science & the Public. Begun in 1942, this event brings 40 research-oriented high school seniors to Washington, D.C. each year to showcase their research to the public and to compete for awards. Since spring 2016, this competition has been sponsored by Regeneron Pharmaceuticals.

simulate     To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.

solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

sophisticated     A term for something that is advanced, complex and/or elegant.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

vaporize     To convert from a liquid to a gas (or vapor) through the application of heat.

water vapor     Water in its gaseous state, capable of being suspended in the air.


  • MS-ESS2-2
  • MS-ETS1-3
  • HS-ESS1-2
  • HS-ESS1-6
  • HS-ETS1-2
  • HS-ETS1-4


Journal:​ ​​ R.T. Daly and P.H. Schultz. The delivery of water by impacts from planetary accretion to present. Science Advances. Published online April 25, 2018. doi:10.1126/sciadv.aar2632.