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Module 1 - The Solar System

Solar System Debris

Small Bodies or Solar System Debris

In addition to the major planets the solar system contains a large number of small bodies, which are officially referred to as, well, Small Bodies. Small bodies are primarily Asteroids and Comets. As we will see, they play an important role, primarily early in the history of the solar system. Since we are focussed on planetary processes in this course, we will only describe them briefly here. (Note: Dinosaurs would vigorously disagree with this seeming neglect. 65 million years ago an impact of a several mile wide asteroid created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico)

Asteroids like those at the top of the page are rocky bodies, most of which revolve around the sun in a position between the orbits of Mars and Jupiter (Asteroid Belt). Like the planets they revolve around the sun, but in shape and size they are more like satellites. The largest asteroid, 1 Ceres is 974 km in diameter. Overall the total mass of all asteroids is less than that of our moon. For more information, click here.

Small chunks of these rocky bodies entering our atmosphere provide us with meteorites, which are very important to our understanding of the formation of the solar system.
Any planetary surface in the solar system is a place one might find meteorites. Here is one on Mars:

Comets are a totally different class of objects, moving on elliptical orbits. Ice objects with minor amounts of rock fragments, they range in diameter from 1 to more than 10 km. Comets are thought to originate in the far outer reaches of the solar system, referred to as the Oort Cloud and the Kuiper Belt. On their path through the inner solar system, inside Mars orbit, their icy nuclei partially vaporize, forming large tails of gas and dust.
Arguably the most famous comet is Comet Halley, which returns to the inner solar system every ~76 years and can be traced back 239 BC. In 1986, an armada of five spacecraft from the USSR, Japan, and the European Community visited Comet Halley. ESA's craft Giotto approached within 540 km +/- 40 km of Halley's nucleus and obtained the best close-up photo.
This is that image:
As an illustration of how far space science has progressed, please contrast that image with the images from ESA's recent Rosetta mission to the lesser known comet 67P/Churyumov-Gerasimenko (alternatively check here). As part of that mission, the probe Philae also landed on the comet, though not totally successfully. Below is a picture of comet 67P/Churyumov-Gerasimenko from 177 miles away. The comet is 4.3 by 4.1 km.
Similar to Halley`s comet, this comet was also heating up and ejecting gases in violent outbursts. And here is an image of one of the outbursts:

ESA has now (June 2018) made the complete Rosetta Image Archive available to the public. You'll find link to images from Earth swing-bys to remarkable close-ups of the comet's surface. If you don't feel that you can spend hours browsing through thousands of images, take less than 3 min to watch the movie below. It's a compilation of the last few hours of Rosetta's decent to the comet. Information and links to download it in several formats can be found here.

Beyond the debris, mostly nothingness
The final component of the solar system is the Interplanetary medium. For the purposes of our course, it is essentially a vacuum and we will not mention it further.

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A Piece of the Asteroid Vesta This meteorite is a sample of the crust of the asteroid Vesta, which is only the third solar system object beyond Earth where scientists have a laboratory sample (the other extraterrestrial samples are from Mars and the Moon). The meteorite is unique because it is made almost entirely of the mineral pyroxene, common in lava flows. The meteorite's mineral grain structure also indicates it was once molten, and its oxygen isotopes are unlike oxygen isotopes found for all other rocks of the Earth and Moon. The meteorite's chemical identity points to the asteroid Vesta because it has the same unique spectral signature of the mineral pyroxene. The meteorite also has the same pyroxene signature as other small asteroids, recently discovered near Vesta, that are considered "chips" blasted off Vesta's surface. This debris extends all the way to an "escape hatch" region in the asteroid belt called the Kirkwood gap. This region is swept free of asteroids because Jupiter's gravitational pull removes material from the main belt and hurls it onto a new orbit that crosses Earth's path around the Sun. The meteorite probably followed this route to Earth. It was torn off Vesta's surface as part of a larger fragment. Subsequent collisions broke apart the parent fragment and threw pieces toward the Kirkwood gap and onto a collision course toward Earth. The fragment's journey ended in 1960 when it fell in Western Australia. NASA's Hubble Space Telescope observations further confirm this scenario by revealing a giant impact basin on the 325-mile (525 km) diameter asteroid. The ancient impact was so powerful, it tore off a piece of the asteroid's crust, exposing a deeper mantle of rock. Most of the identified meteorites from Vesta are in the care of the Western Australian Museum. This 1.4 pound (631 gm) specimen comes from the New England Meteoritical Services. It is a complete specimen measuring 3.7 inch x 3.1 inch x 3.4 inch (9.6 cm x 8.1 cm x 8.7 cm) showing the fusion crust, evidence of the last stage in its journey to Earth. *Image Credit*: R. Kempton (New England Meteoritical Services)
Comet Trail and Tail This is an artist's concept of a comet dust trail and dust tail. The trail can only be seen in the light of radiated heat. The dust trail is made of particles that are the size of sand grains and pebbles. They are large enough that they are not affected much by the Sun's light and solar wind. The dust tail, on the other hand, is made of grains the size of cigarette-smoke particles. These grains are blown out of the dust coma near the comet nucleus by the Sun's light. *Image Credit*: K. Jobse, P. Jenniskens and NASA Ames Research Center
Dino Killer A large body of scientific evidence now exists that support the hypothesis that a major asteroid or comet impact occurred in the Caribbean region at the boundary of the Cretaceous and Tertiary periods in Earth's geologic history. Such an impact is suspected to be responsible for the mass extinction of many floral and faunal species, including the large dinosaurs, that marked the end of the Cretaceous period. Until now, the remains of such an impact crater have escaped detection. The geohydrological feature (Cenote Ring) of Northwestern Yucatan, was discovered through NASA Ames remote sensing technology and represents a prime candidate for the impact site of a global catastrophic event. *Image Credit*: Don Davis, NASA
Giotto at Halley
Martian Meteorite NASA's Mars Exploration Rover Opportunity has found an iron meteorite, the first meteorite of any type ever identified on another planet. The pitted, basketball-size object is mostly made of iron and nickel according to readings from spectrometers on the rover. Only a small fraction of the meteorites fallen on Earth are similarly metal-rich. Others are rockier. As an example, the meteorite that blasted the famous Meteor Crater in Arizona is similar in composition. "This is a huge surprise, though maybe it shouldn't have been," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science instruments on Opportunity and its twin, Spirit. The meteorite, dubbed "Heat Shield Rock," sits near debris of Opportunity's heat shield on the surface of Meridiani Planum, a cratered flatland that has been Opportunity's home since the robot landed on Mars nearly one year ago. "I never thought we would get to use our instruments on a rock from someplace other than Mars," Squyres said. "Think about where an iron meteorite comes from: a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle." Rover-team scientists are wondering whether some rocks that Opportunity has seen atop the ground surface are rocky meteorites. "Mars should be hit by a lot more rocky meteorites than iron meteorites," Squyres said. "We've been seeing lots of cobbles out on the plains, and this raises the possibility that some of them may in fact be meteorites. We may be investigating some of those in coming weeks. The key is not what we'll learn about meteorites -- we have lots of meteorites on Earth -- but what the meteorites can tell us about Meridiani Planum." The numbers of exposed meteorites could be an indication of whether the plain is gradually eroding away or being built up. NASA Chief Scientist Dr. Jim Garvin said, "Exploring meteorites is a vital part of NASA's scientific agenda, and discovering whether there are storehouses of them on Mars opens new research possibilities, including further incentives for robotic and then human-based sample-return missions. Mars continues to provide unexpected science 'gold,' and our rovers have proven the value of mobile exploration with this latest finding." Initial observation of Heat Shield Rock from a distance with Opportunity's miniature thermal emission spectrometer suggested a metallic composition and raised speculation last week that it was a meteorite. The rover drove close enough to use its Moessbauer and alpha particle X-ray spectrometers, confirming the meteorite identification over the weekend. Opportunity and Spirit successfully completed their primary three-month missions on Mars in April 2004. NASA has extended their missions twice because the rovers have remained in good condition to continue exploring Mars longer than anticipated. They have found geological evidence of past wet environmental conditions that might have "been hospitable to life. Opportunity has driven a total of 2.10 kilometers (1.30 miles). Minor mottling from dust has appeared in images from the rover's rear hazard-identification camera since Opportunity entered the area of its heat-shield debris, said Jim Erickson of NASA's Jet Propulsion Laboratory, Pasadena, Calif., rover project manager. The rover team plans to begin driving Opportunity south toward a circular feature called ""Vostok"" within about a week. Spirit has driven a total of 4.05 kilometers (2.52 miles). It has been making slow progress uphill toward a ridge on ""Husband Hill"" inside Gusev Crater. *Image Credit*: NASA
Comet 67P/Churyumov-Gerasimenko
Comet Halley
Rosetta's Comet From 177 Miles
The Asteroid Belt Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago. More likely, asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across, less than half the diameter of our Moon. The asteroid belt lies in the region between Mars and Jupiter. The Trojan asteroids lie in Jupiter's orbit, in two distinct regions in front of and behind the planet. *Image Credit*: Lunar and Planetary Institute