By the end of this activity students will be able to:
- identify impact craters based on their features.
- describe reasons why evidence of impacts may change on various solar system bodies.
- create and use timelines that combine different scales.
Our solar system consists of the Sun, planets, and moons. But that’s not all! Asteroids are also important parts of the solar system. During this scavenger hunt, students will learn more about these objects, and explore what happens when they crash into planets.
By the end of this activity students will be able to:
Note: This activity has an “extra credit” portion on the third page (see "Wrap-Up" below).
During the field trip, students will be exploring the Academy’s specimens related to impacts on Earth and other large bodies in our Solar System. Before the field trip, introduce the concept of space rocks, impacts, and craters to your students. Encourage your students to brainstorm ideas about what can cause craters on Earth.
Teacher tip: Please do not use pictures of the moon or Barringer crater, since students will see these at the museum.
If you have chosen to do the “mini-meteors” activity, do so now by having your students try to duplicate the different craters they have looked at!
Space Rocks: Asteroid, Meteoroid, Meteor or Meteorite
In space, a large rocky body (larger than 10 meters in diameter) in orbit about the Sun is referred to as an asteroid. Whereas a much smaller particles (less than 10 meters in diameter) in orbit about the Sun are referred to as meteoroids. Once a meteoroid enters the Earth's atmosphere and vaporizes, it becomes a meteor (i.e., shooting star). If a small asteroid or large meteoroid survives its journey through the Earth's atmosphere and lands on the Earth's surface, it is then called a meteorite.
An impact crater is formed when an object like an asteroid or meteoroid crashes/collides into the surface of a larger solid object like a planet or satellite. To form a true impact crater, this object needs to be traveling extremely fast, many thousands of miles per hour! When a solid object crashes into something at these extreme speeds, it forms a crater regardless of how hard the object is. Smaller objects immediately vaporize and create an enormous shockwave through the ground that melts and recrystallizes rock. All that is left is a big hole in the ground and some reconfigured rocks. Sometimes the object is large enough for only part of the object to vaporize so that small pieces remain after impact.
Impacts on Earth
There is a relationship between the size of the object and the frequency of impact events. Small objects collide frequently with Earth’s atmosphere, disintegrating before reaching the ground. The larger objects that strike the Earth’s surface and leave impact craters happen less frequently. Asteroids with a 1 km (0.62 mi) diameter strike Earth every 500,000 years on average. Large collisions – with 5 km (3 mi) objects – happen approximately once every twenty million years. The last known impact of an object of 10 km (6 mi) or more in diameter was the dinosaur extinction event 66 million years ago.The Moon and its many impact craters
The California Academy of Sciences’ lunar sample (a piece of the Moon) was brought back from the Apollo 17 expedition in 1972. This was the last human mission to the Moon. This lunar sample was collected between the Sea of Tranquility and the Sea of Serenity. The sample was probably formed 3.7 billion year ago far below the lunar surface, then rose to the crust and solidified.
The moon has a lot more visible impact craters because it doesn't have an atmosphere to burn up smaller incoming space rocks. The moon also does not have liquid water or an active crust (with volcanoes and other forces) to change the surface and remove evidence of past impacts. The Moon once had large volcanic flows in the past that did cover up many of the bigger earlier impacts, but it has been without volcanism for around three billion years.
Why are impact craters hard to see on Planet Earth?
There are three processes that help Earth keep its surface with very little craters. The first is erosion. Erosion can break a crater down to virtually nothing. The second process is tectonics. Because of tectonics, the surface of Earth is recycled many times throughout its long history. As a result, very few rocks on Earth are as old as the rocks on the Moon. The third thing is volcanism. Volcanic flows can cover up impacts craters. This is a major way impact craters get covered up elsewhere in our solar system, but it is less important than the recycling of crust here on Earth. In addition to these three processes, the Earth’s surface is mostly covered in water, which affects the impact sites and may also hide evidence of an impact from human eyes.
Barringer Crater (also known as Meteor Crater)
Barringer crater is located outside Flagstaff Arizona. The meteoroid that created the 1219 meter wide (4,000 feet) Meteor Crater in Arizona was probably only about 50 meters (164 feet) in diameter. This really big for a rock falling from outer space, but still only a fraction of the size of the impact crater it created. Scientists estimate that this impact event occurred about 50,000 years ago—long before there were humans living in the area. This is a significant crater because it was the first crater proven to have been created by a space rock impact, not volcanism. Since then, numerous impact craters have been identified around the world, though Barringer Crater remains one of the most visually impressive.
Scientific and Engineering Practices
Disciplinary Core Ideas
5.a Students know some changes in the earth are due to slow processes, such as erosion, and some changes are due to rapid processes, such as landslides, volcanic eruptions, and earthquakes.
5.b Students know the solar system includes the planet Earth, the Moon, the Sun, eight other planets and their satellites, and smaller objects, such as asteroids and comets.
Earth and Life History
4.b Students know the history of life on Earth has been disrupted by major catastrophic events, such as major volcanic eruptions or the impacts of asteroids.
Harmon, Katherine (2011 May 16). Make Craters with Mini-Meteors. Scientific American. Retrieved August 18, 2016 from www.scientificamerican.com/article/make-craters-with-mini-meteors-bring-science-home/
NASA (2016 March 17). Why Is the Moon so Scarred with Craters?" NASA Space Place. Retrieved August 18, 2016 from http://spaceplace.nasa.gov/craters/en/
Smithsonian National Air and Space Museum. Impact Features. Exploring the Planets. Retrieved August 18, 2016 from https://airandspace.si.edu/exhibitions/exploring-the-planets/online/comparing-planets/impact.cfm
Elizabeth Howel (2013 February 19). Shoemaker-Levy 9: Comet’s Impact Left its Mark on Jupiter. Space.com. Retrieved August 29, 2016 from www.space.com/19855-shoemaker-levy-9.html
NASA: Jet Propulsion Laboratory (2014 November 14). New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population. NASA: Jet Propulsion Laboratory. Retrieved August 29, 2016 from www.jpl.nasa.gov/news/news.php?release=2014-397
NASA . Near Earth Object Program. NASA. Retrieved August 29, 2016 from neo.jpl.nasa.gov/faq/
Images of impact craters
Solar Views. Retrieved August 19, 2016 from http://solarviews.com/eng/tercrate.htm
Lunar and Planetary Institute. Retrieved August 19, 2016 from www.lpi.usra.edu/publications/slidesets/
Photo Journal. Jet Propulsion Laboratory. Retrieved August 19, 2016 from http://photojournal.jpl.nasa.gov/feature/impact