Asteroids and Comets

Notes compiled by

Paul Woodward

Astronomy DepartmentUniversity of Minnesota

3. Asteroids and Comets

a) These are the most numerous objects in the solar system.

b) Asteroids are small, rocky bodies and are located mainly in the asteroid belt between the orbits of Mars and Jupiter.

c) Asteroids orbit the sun in the same direction as the planets.

d) Asteroid orbits lie close to the plane of the planets’ orbits, although they are usually a bit tilted.

e) Some asteroids have quite eccentric orbits compared to the nearly circular orbits of the planets.

f) The largest asteroids are only a few hundred km in radius.

Kuiper Belt and Oort Cloud

Histogram of number of asteroids as a function of orbital period.Note the absence of asteroids with orbital periods that are resonant with that of Jupiter. The positions of the Trojan asteroids near the

sun-Jupiter Lagrangian points are also shown.

Ida, an S-Type Asteroid

Asteroid Ida with Satellite

Artist’s conception of a 10 mile by 3 mile asteroid striking the Yucatan Peninsula.

Kara-kul CraterTajikistan; <5 million years old, 52 km diameter

Impact nature recently confirmed from shock features found in local breccias

Sudbury Crater, 1.8 billion yr., 200 km diameter 31,000 cubic kilometers of impact melt (Chicxulub has about 18,000 )

This is the second-largest impact basin on earth.It is thought to have resulted from a comet impact 1.8 billion years ago.

Sudbury Crater, 1.8 billion yr., 200 km diameter 31,000 cubic kilometers of impact melt (Chicxulub has about 18,000 )

Sierra Madera Crater, Ft. Stockton Texas<100 million years old, 13 km diameter

Both impact structures are about 35 million years old, with diameters near 100 km. These crater events could have been

responsible for the extinctions found near the Eocene-Oligocene boundary layer when 20% of the subgenera became

extinct (compared to 80% at KT boundary).

Popigai crater in Siberia

Chesapeake Bay Crater, US

Comet Siding Spring shoots past Mars on Sunday, 10/19/2014.

This is a photo taken from the earth, but NASA has lots of stuff on or orbiting Mars that can outdo this photo for sure.

Comet Siding Spring shoots past Mars on Sunday, 10/19/2014.The comet passes at about 1/3 of the distance between the earth and

the Moon. The comet’s orbital period is thought to be about a million years. It is likely to be made of primordial material.

Comet Siding SpringHubble Space Telescope

image.

On the next slide:10.20.2014

First Resolved Image of a Long-Period Comet's Nucleus

These images were taken of comet C/2013 A1 Siding Spring by NASA's Mars Reconnaissance Orbiter on Oct. 19, 2014, during the comet's close flyby of Mars and the spacecraft. Comet Siding Spring is on its first trip this close to the sun from the Oort Cloud at the outer fringe of the solar system. This is the first resolved imaging

of the nucleus of a long-period comet.The High Resolution Imaging Science Experiment (HiRISE) camera on Mars

Reconnaissance Orbiter acquired images of this comet from a minimum distance of about 86,000 miles (138,000 kilometers), yielding a scale of about 150 yards (138

meters) per pixel. Telescopic observers had modeled the size of the nucleus as about half a mile, or one kilometer, wide. However, the best HiRISE images show only two to three pixels across the brightest feature, probably the nucleus, suggesting a

size less than half that estimate.This composite image shows two versions of each of two of the best HiRISE images

of the comet. Shown at top are images with the full dynamic range, showing the nucleus and bright coma near the nucleus. Shown at bottom are versions where the fainter outer coma is brightened, saturating the inner region. The images at left and

right were taken about nine minutes apart.

Comet Siding Spring shoots past Mars on Sunday, 10/19/2014.These images (short exposes top & longer on bottom) were taken by

the Mars Reconnaissance Orbiter upon the comet’s closest approach to Mars on 10/19/2014.

Comet Siding Spring shoots past Mars on Sunday, 10/19/2014.This is another one of those great artist’s concepts. The comet passes

at about 1/3 of the distance between the earth and the Moon.

3. Asteroids and Comets, continued

a) Comets are small, icy bodies.

b) Comets spend most of their time well beyond the orbit of Pluto.

c) The orbits of comets in the Oort cloud are completely random, with no pattern to their directions, inclinations, or eccentricities.

A comet’s tail points away from the sun, regardless of the comet’s direction of motion. Nearest to the sun, the tail is largest.

An artist’s concept of the appearance of the surface of a comet’s nucleus

Halley’s Comet, 1910

Halley’s Cometand

Saguaro Cacti1986

Dennis Mammana

Giotto’s “Suicide” Plunge into Halley’s Head

Comet Halley’s nucleus from within

600 km

The nucleus is 14.9 ×8.2 km.

March 13, 1986

(European Space Agency)

Comet Wild 2, very close up

Comet Wild 2, very close up

The following slide in this lecture set are only for the curious student.We will not cover them in class.

After Giotto, ESA did much better with its Rosetta mission to

Comet Churyumov-Gerasimenko.

The spacecraft accompanied the

comet on its trip past the sun, observing its

activity close up, sent a lander (Philae) and

ultimately crashed on the comet.

Comet Churyumov-Gerasimenko nucleus

from Rosetta spacecraft

(European Space Agency)

Comet Churyumov-Gerasimenko nucleus from Rosetta spacecraft.Separate outburst of gas were recorded, and it proved possible to trace these to their

origins at surface features.

Gas and dust from the comet were analyzed, and conclusions are that the earth’s atmosphere could have been brought to it by comets, but the earth’s ocean has a different amount of deuterium than this comet’s water and therefore was most likely not brought to

the earth by comets.

Comet Churyumov-Gerasimenko nucleus from Rosetta spacecraft.Separate outburst of gas were recorded, and it proved possible to trace these to their origins

at surface features.

Many simple molecular building blocks of life were found among the molecules discovered on this comet.

Further research will try to sort out which must have been in the solar nebula before its collapse and which might have formed later.

The European Space Agency’s Rosetta probe visits a comet in 2014Rosetta sent a lander, Philae, onto this comet while it was still far from the sun.

The European Space Agency’s Rosetta probe visits a comet in 2014Rosetta sent a lander, Philae, onto this comet while it was still far from the sun.

The European Space Agency’s Rosetta probe visits a comet in 2014Rosetta sent a lander, Philae, onto this comet while it was still far from the sun.