Lecture 22

Moon of Pluto?

In 1978 the American astronomer James W. Christy discovered that Pluto has a moon, named Charon. More recently, Pluto has been discovered to have four more moons, for a total of five. Charon's orbit is tilted at 61° to Pluto's orbit around the Sun. Charon orbits Pluto every 6.4 days, the same as Pluto's rotation.

Pluto From Earth

In 1989 Pluto was as close to the Earth as it had been for 248 years. (From 1979 to 1999 Pluto was inside Neptune's orbit.) Pluto's average distance from the Sun is 40 AU, but its eccentric orbit causes it to vary in distance from 30 AU to 50 AU. Pluto is now heading for its aphelion point. Pluto's orbit is tilted 17° to the ecliptic (no other planet is tilted more than 7°).

Mission to Asteroids?

NASA's Dawn spacecraft went into orbit around Vesta last year. In July of 2012 Dawn re-started its ion engine and started on a path that will had it travel on to a rendezvous with the dwarf planet Ceres where it went into orbit last year. Dawn is the first spacecraft to go into orbit around both a dwarf planet and an asteroid. Gaspra, an asteroid 19 X 12 X 11 km, was imaged by the Galileo spacecraft in 1990. Some asteroids like Gaspra have a reddish tint and are fairly bright. Others are dark like coal.

What we learned about Pluto thru missions

Scientists learned much more about Pluto in the summer of 2015 when NASA's Pluto Express spacecraft flew past Pluto and its moons. Since all of its instruments worked properly, this spacecraft sent back mankind's first detailed information on this planet and its moons. The new images of both Pluto and Charon were quite stunning and surprising.

Discovery of more moons of Pluto?

Several years ago, the Hubble Space Telescope (HST) was used to discover the second and third of Pluto's five moons. These are named Hydra and Nix. In June of 2011 the HST was also used to discover a fourth moon of Pluto. This moon is currently named Kerberos You may read a story about its discovery at http://www.nasa.gov/mission_pages/hubble/science/pluto-moon.html. Later a fifth moon, Styx, was also discovered.\

Atmosphere of Pluto

Stellar occultations indicated that Pluto has a methane atmosphere. At aphelion it is probably too cold for the methane to remain gaseous.

Orbits of Asteroids

The asteroids revolve around the Sun in a counterclockwise direction like the planets. Most asteroids orbit in or near the plane of the ecliptic. Most asteroids orbit the Sun at distances from 2.2 to 3.3 AU (between Mars and Jupiter) in what is called the asteroid belt.

Trojan Asteroids

There are two groups of asteroids which are located at Jupiter's distance from the Sun but which are either 60 degrees in front of or behind Jupiter's location at the vertices of equilateral triangles. tary scientists have long proposed that the Earth should have a few Trojan Asteroids just as Jupiter does, but until July of 2011 none had ever been found. Then, in late July of 2011, scientists announced the discovery of the first Trojan asteroid of the Earth.

Apollo Asteroids

some 50 asteroids with diameters larger than 1 km that have eccentric orbits that cross the Earth's orbit.

Extra Pluto Shit

A true-color image of Pluto taken by one of the cameras on NASA's Pluto Express spacecraft on July 14, 2015.The heart-shaped feature is thought to be a basin of several volatile ices. Enhanced-color images of both Pluto and Charon shown to the same scale. Pluto has many different types of terrain. The red area near Charon's pole might be escaped Methane from Pluto. Pluto Express image of haze layers in Pluto's atmosphere. Its upper atmosphere was unexpectedly discovered to be very cold. It is also losing much less nitrogen than experts had predicted.

Origin of asteroids

Astronomers originally thought the asteroids were due to an exploded planet, but there is no known mechanism for making a planet explode. Furthermore, even if all the asteroids were combined into one object, they would only form a body about 1,500 km in diameter, which would be much smaller than our Moon. Most likely the asteroids are primordial material that never formed into a planet because of Jupiter's gravitational influence.

TF is pluto?

A Former Moon of Neptune? Because Pluto is small and has an eccentric orbit, some theorize that it a former moon of Neptune that was somehow ejected. Charon's density of 1.2-1.3 g/cm3—or much less than Pluto's density of 1.87 g/cm3—points to its possible capture by Pluto, so it could have been captured after Pluto left Neptune. Alternatively, Charon might have been created in a collision of an object with Pluto, so we really do not know how Pluto and Charon originated. Several years ago an IAU resolution re-classified Pluto as a dwarf planet. A more recent IAU resolution also named Pluto as the first of a new class of objects known as plutinos, all of which have resonant orbits with Neptune.

How was Pluto Discovered?

An analysis of the orbital data of Uranus indicated that 98% of its orbital variation could be accounted for by the presence of Neptune; the remaining unexplained 2% variation led to the search for Planet X. In 1905 Percival Lowell initiated what would become a successful search for Planet X. Unfortunately, Lowell died in 1916 before Pluto was discovered. Clyde Tombaugh finally discovered Pluto at the Lowell Observatory in 1930. Tombaugh used a blink comparator to compare two photos of the sky taken a few days apart. A moving object such as a planet will appear to jump from one spot to another as the observer quickly changes views from the first photograph to the second. Pluto was discovered 6° from where Lowell had predicted it would be found. Pluto's mass, however, is too small to cause the irregularities that had been seen in Uranus's orbit. Later it was shown that these irregularities were not caused by another planet but were due to the use of an incorrect mass for Neptune. In conclusion, we now know that Pluto's discovery was an accident, although without Lowell's predictions, the search would not have been pursued so vigorously

Shit floatin through space?

Apart from the Sun (a large object) and the planets and larger moons (medium-sized objects), most of the other objects in the solar system can be classified as debris— an accumulation of rock fragments. Solar system debris comes in a number of forms, including asteroids, meteoroids, comets, and dust.

Distribution of Asteroids

Asteroids are not evenly distributed across the asteroid belt. At certain distances, for example, 2.5 and 3.28 AU, gaps appear which are related, respectively, to 1/3 and 1/2 of Jupiter's orbital period. These gaps, also called Kirkwood's Gaps, are due to synchronous tugs from Jupiter on the asteroids which used to be located there. Gaps in the asteroid belt also appear corresponding to 2/5 and 3/5 of Jupiter's orbital period. These are additional examples of what are known as Kirkwood's Gaps. They are caused by gravitational resonances of Jupiter and the original asteroids which were in those orbits.

Diameter and Density of Pluto

Pluto's atmosphere limited an accurate determination of its size, but the Pluto Express mission tells us its diameter is equal to 2,370 km. Charon's diameter is about 1,200 km. Pluto's mass is about 12 times Charon's, but only 1/5 of our Moon's. Pluto's density is equal to 1.869 gm/cm3.

Asteroids

Slightly more than 200 years after the first asteroid, Ceres, was discovered, by Giuseppe Piazzi in 1801, the orbits of some 5,000 asteroids have been accurately determined. Approximate orbits are known for thousands more. Ceres was discovered at 2.8 AU from the Sun because of the gap in Titius and Bode's Law there. Astronomers estimate that 10,000 asteroids have been captured on photographic surveys of the sky and more are being discovered constantly. Asteroids are also known as minor planets. Ceres, at 1,000 km (600 mi) in diameter, is the largest asteroid and makes up 30% of the mass of all asteroids. Recently another IAU resolution re-classified Ceres as a dwarf planet. Pallas and Vesta have diameters greater than 300 km. About 30 more asteroids have diameters between 200 and 300 km. About 100 are larger than 100 km. All the rest are under 100 km in diameter.