# How long will a ball of ice stay in orbit around Earth?

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How big would a ball of frozen water need to be to last one orbit? How would atmospheric drag effect the ball of water?

https://space.stackexchange.com/questions/32188/what-is-the-darkest-orbit-around-earth

Simply put. It all depends on the balance of an objects straight line speed orbiting the planet and gravity. The further away the object is from earth the slower the speed requirement for this balance is. Great question by the way.

## How long will a ball of ice stay in orbit around Earth? - Astronomy

Does Mars have ice on the inside or outside? How long does it take Mars to go round the sun?

What is the proof that life exists on Mars?
ARKA, AGE 12, KOLKATA, INDIA

Answer: One of the main bits of evidence that life has existed on Mars came from a meteorite that was found in the Antarctic. The meteorite came from Mars many years ago when a rock smashed into the surface and sent the rock flying off into space. Eventually it landed here on Earth.

Inside the rock we found tiny little things that are the result of some sort of very simple life. We do not know if life still exists on Mars but if it does it will be very simple life deep under the surface.

I have done a volcano/Olympus Mons project and I was wondering what the correct answer was for how many days there are in Mars in a year.

Answer: A Martian year is equal to 687 Earth Days. That makes the year on Mars about twice as long as a year on Earth.

I know a year on Mars lasts 687 Earth days but why does it last that long when its days are only 24 hours and 37 minutes?
RACHEL, AGE 12, TWICKENHAM

Answer: The length of a day is fixed by the time it takes a planet to spin once on its axis. The length of the year is the time it takes for the planet to go around the Sun. There is no real relationship between the two.

Why has Olympus Mons been able to 'grow' so much bigger then any volcano on earth?
SAL, AGE 12, YOKOHAMA, JAPAN

Answer: One of the main reasons volcanoes on Mars are bigger than ours here on Earth is that the gravity on Mars is less. Gravity is the force that holds us and everything else on the surface of the Earth.

If the gravity were stronger on Earth then we would all be pulled harder against the surface. The pull of gravity on Mars is weaker than it is on Earth so things are not pulled toward the surface so strongly. It’s because of this that Olympus Mons could grow so big.

Ice on Mars

How long does it take for a day in Mars?
FINLAY, AGED 8, TEMPLE EWELL

Answer: A day on Mars is 24 hours and 37 minutes, a little longer than a day on Earth.

Does Mars have ice on the inside or outside?
NICHOLAS, AGE 10, ALEXANDRA HILLS

Answer: When we look at Mars through a telescope we can see white spots on the top and bottom. They are actually areas where ice has formed around Mars' North and South pole.

How many moons does Mars have?
MATIAS, AGE 9

Answer: Mars, the fourth planet in the Solar System has two moons, Phobos and Deimos. Neither of them are as big as our Moon though.

How long does a year last on Mars?
NATHAN, AGE 13, BICESTER

Answer: One year on Mars is equal to 687 Earth days, making the Martian year nearly twice as long as ours.

Why do we never see Mars?
DANIEL, AGE 11, CRINGLEFORD

Answer: We do get to see Mars quite often. We will be able to see it again clearly in the evening sky later this year during the end of Summer 2005.

I know that Mars has an atmosphere, but, if air is put in it, will it stay in the planet, or is that a film fantasy?
JAVIER, MANCHESTER

Answer: Mars is only about half the size of the Earth and its gravity isn't as strong. If we did manage to make the atmosphere suitable for us to live there, we would have to ensure that it was kept topped up.

The gravity of Mars is not strong enough to hold on to an atmosphere that we would need to survive. It would be possible however to make special buildings that would stop the atmosphere from escaping which we could live in along with plants and animals.

 Mars is known as the red planet

A meteor was found on Earth that came from Mars. How do you know where it came from?
JESQ STUART, AGE 15

Answer: In the 1970s the Viking spacecraft landed on Mars. When it was there, it measured the types and mixture of gas in the atmosphere.

The meteorite that was found had tiny pockets of gas trapped inside it.

On checking the types and mixture of gasses in the pockets of gas, we found that it was exactly the same as the Viking spacecraft had measured on Mars.

How many days are in a year on Mars?
LIZ H, AGE 10

Answer: One year on Mars is equal to 780 Earth days.

How long does it take Mars to go round the sun?
ANASTASIA, AGE 9

Answer: Mars takes 687 days to go around the Sun. That's a little less than 2 years.

Wouldn't a thicker Martian atmosphere escape into space because of mars' weaker gravity?
SARISHA, AGE 14

Answer: Because Mars has about one third of the gravity that the Earth has then yes, a thicker Martian atmosphere would escape into space.

It would take many millions of years for this to happen but it is why Mars does not have a thick atmosphere today.

If we were to try to set-up a permanent home on Mars we would have to use some kind of building that would contain the atmosphere and stop it escaping into space.

What is Mars' distance from the sun, how many days does it take to complete one orbit and how many earth days does it take to rotate once on its axis?

Answer: Like all of the planets in the solar system, they all have an elliptical orbit around the Sun.

The shape of an elliptical orbit is similar to the shape of a squashed circle. Because of the elliptical orbit, the distance from Mars to the Sun varies over its year.

We can work out that on average, Mars is 228 million km away from the Sun and it takes a little under 687 Earth days to complete one orbit.

Spinning once on its axis takes Mars 24 hours, 37 minutes and 23 seconds.

### Do comets orbit the Sun?

Yes, comets do actually orbit the Sun like the planets and other objects within the Sun’s region of gravitational pull. However, comets typically have a more elongated, oval shaped orbit in comparison to the planets, which orbit the Sun in a more spherical manner.

### Comets vs Asteroids – What’s the difference?

Whilst comets are typically made of ice and rock, an asteroid is made up of primarily rock and metals. Comets originate further out in the solar system, whereas asteroids are located in the Asteroid belt, which lies between Mars and Jupiter.

### What is the name of the most famous comet?

The name of the most famous comet is called Halley’s comet. This comet is visible to the Earth every 75 years, with the last time being in 1986. Ancient recordings of this comet have been noted throughout the past thousands of years, within many different cultures from the Chinese to the Babylonians. It takes it’s name from English astronomer, Edmond Halley.

### What are the four parts of a comet?

When we’re examining a comet, we generally split the comet into four different parts. This is it’s nucleus at it’s center, it’s coma (the gas surrounding it), it’s gas tail and it’s dust tail – this is why you’ll see astronomers say that a comet has two tails, one of dust and one of gas.

### Where do comets come from?

Comets generally come from two different places. Some of them are located in the Kuiper belt, which is a ring around the Sun that is just past the planet Neptune. Other comets come from the Oort cloud, which is even further out than the Kuiper belt.

## Earth > Ask a Scientist About Our Environment > How did the ice age end?

I like how your question addresses both the past and the future of ice ages.

It turns out that we are most likely in an "ice age" now. So, in fact, the last ice age hasn't ended yet!

Scientists call this ice age the Pleistocene Ice Age. It has been going on since about 2.5 million years ago (and some think that it's actually part of an even longer ice age that started as many as 40 million years ago).

We are probably living in an ice age right now! But Earth's climate doesn't stay cold during the entire ice age.

The curious thing about ice ages is that the temperature of Earth's atmosphere doesn't stay cold the entire time. Instead, the climate flip-flops between what scientists call "glacial periods" and "interglacial periods."

Glacial periods last tens of thousands of years. Temperatures are much colder, and ice covers more of the planet.

On the other hand, interglacial periods last only a few thousand years and the climate conditions are similar to those on Earth today. We are in an interglacial period right now. It began at the end of the last glacial period, about 10,000 years ago.

Scientists are still working to understand what causes ice ages. One important factor is the amount of light Earth receives from the Sun. The amount of sunlight that reaches Earth can vary quite a lot, mainly due to three factors:

## Orbits

An orbit is the path that an object makes around another body, such as the Earth, another planet, a moon or the Sun. Objects in an orbit are continuously being pulled towards the centre of the body they are orbiting, as they have not escaped its gravity. If the gravity were somehow switched off, they would continue to travel in a straight line and off into space. However, the combination of the forward motion of the satellite and the force of gravity makes the path of the satellite circle the planet, as can be seen in Figure 4.2, where a satellite is in orbit around a planet. This is similar to a toy yoyo on the end of a string. If the yoyo is swung around your head, it makes big circles. The string is like the gravity, holding the yoyo in an orbit around your head. If you let the string go, the yoyo would fly off. If the yoyo stops, it falls to the ground. The speed with which a satellite orbits an object is called the orbital velocity. A satellite will orbit at a distance where its speed balances the gravitational pull, and at the same

Satellite'3 Forward Motion

Satellite'3 Forward Motion

Figure 4.2 Forward Motion and Gravity Cause a Spacecraft to Stay in Orbit. Image courtesy NASA

Figure 4.2 Forward Motion and Gravity Cause a Spacecraft to Stay in Orbit. Image courtesy NASA

point in each orbit it will be at the same height above the Earth. As mentioned before, gravity diminishes with distance, and the further something is away from the body it is orbiting, the slower it must travel to remain in orbit. If the speed changes, the size or shape of the orbit will also change.

### Orbit Shape

Objects that repeatedly travel around a heavier body, such as a planet or star, have a closed orbit that they follow time and again. If the orbit is open the object just flies past the celestial body in an open curve and back off into space. Open orbits extend to infinity and are called hyperbolic. Hyperbolic orbits are used at the beginning of interplanetary missions by spacecraft that have enough speed to escape the gravitational pull of nearby planets or other objects, called the escape velocity. Most spacecraft and comets are in closed orbits around the Earth or the Sun, although some are in open orbits, such as Voyager 1 and 2.

In a circular orbit, the satellite will travel at the same speed wherever it is on its path, but orbits are not very often perfectly circular. The Earth's orbit around the Sun and the Moon's orbit around the Earth are both slightly squashed circles, called ellipses. An ellipse is a special type of oval shape. If a cone, like an ice cream cornet, is cut without cutting through the open end, the resulting shape will be an ellipse, as can be seen in Figure 4.3.

An ellipse can be drawn with the help of two drawing pins and a loop of string. Loop the string around the pins and put the pen inside the loop. Now pull the string taut, thus making a triangle. Move the pen around the drawing pins, while keeping the string taut. The resulting drawing will be an ellipse. Each pin is at a focus of the ellipse. The long axis of an ellipse is called the major axis, the shorter one, the minor axis. In a circle, both the major and minor axes are the same and are called the diameter, and both the foci are at the centre of the circle. Half of the major axis is called the semi-major axis. This is the equivalent of the radius in a circle. The length of the semi-major axis is used to describe the size of the ellipse. The properties of an elliptical orbit around the Earth are shown in Figure 4.4.

A circle is just a special type of ellipse and so for the purposes of orbits, it can usually be treated the same as an elliptical orbit. A satellite on an elliptical orbit around the Earth is said to be at apogee when it is furthest away from the centre of the Earth and perigee when it is closest to it. However, if something is orbiting the Sun it is said to be at aphelion when it is furthest away and at perihelion when it is closest. The generic terms for these are the apoapsis and the periapsis. For an orbit around Jupiter, they are apojove and perijove, around the Moon, apselene and periselene or apolune and perilune and around Saturn, apochron and perichron. How flat the ellipse looks is called its eccentricity and is described in more detail in Chapter 1 - "Introduction".

Figure 4.4 Properties of an Ellipse.

### Figure 4.4 Properties of an Ellipse.

In an elliptical orbit, a satellite travels faster when it is closer to the object it is orbiting, and slower when it is further away. Johannes Kepler discovered this change in speed in 1609, by using data about the planet Mars' motion about the Sun, provided by the Danish astronomer Tycho Brahe. It became the second of his three laws that are now known as Kepler's Laws of Planetary Motion.

The first law states that the orbit of each planet is an ellipse, with the Sun at a focus. This also applies to all objects orbiting a body. For example, the centre of the Earth is always at a focus of an elliptical orbit of an Earth-orbiting satellite.

Kepler's second law describes that a planet travels faster when it is nearer the Sun than when it is further away, although the wording of the law make it sounds quite complicated. The law is stated as "The line joining the planet to the Sun sweeps out equal areas in equal times." This can be seen in Figure 4.5. Each of the shaded segments is equal in area to each of the un-shaded areas and the time for a planet to move from one area to the next is the same, no matter where on its orbit it is. Therefore, when it is nearer the Sun, a planet travels faster than when it is further away. Again, this not only applies to planets, but to all objects orbiting another body.

Figure 4.5 Diagram Illustrating Kepler's Second Law.

The third law sounds even more complicated, but just describes the fact that the length of a planet's year, or orbital period, is related to the average distance it is from the Sun. The relationship is "The square of the period of a planet is proportional to the cube of its mean distance from the Sun".

Each orbit can be described by six orbital elements or orbital parameters. These define the size, shape and orientation of an orbit and are described in Appendix A - "Orbital Elements".

### Types of Orbit

Different types of orbit are used for different purposes, such as weather mapping, television broadcasts or manned space flight. All orbits around the Earth must circle the centre of the Earth and therefore they either follow the equator or cross it. The inclination of an orbit is the angle it makes when it crosses from the southern to the northern hemisphere. With improved technology and more advanced propulsion systems, it should eventually be possible to circle the globe above any line of latitude, although the amount of energy required may make it prohibitively expensive. If a spacecraft moves from west to east, it is said to be in a prograde orbit. This is the usual direction of rotation in our solar system. If it moves from east to west it is termed retrograde. Halley's comet has a retrograde orbit and Venus has a retrograde spin.

The exact position of a low Earth orbit has not been clearly defined, but it is usually considered to be between 100 and 1,000 kilometres above the surface of the Earth. This is the cheapest and easiest orbit to put a spacecraft into. It requires less energy to get a spacecraft into a LEO than a higher altitude orbit, in a similar same way that it takes less energy to throw a ball to a height of 20 metres than it does to 30 metres. The position of the LEO is between the Earth's atmosphere and the inner Van Allen radiation belt. The radiation belts are rings of energized charged particles that are trapped by the Earth's magnetic field, described in more detail in Chapter 1 - "Introduction". The International Space Station, the Hubble Space Telescope and the Iridium constellation of satellites are all in LEO.

Geosynchronous Earth Orbit (GEO)

If a satellite is in a geosynchronous Earth orbit it travels once around the Earth in the same time that it takes for the Earth to rotate once, called a sidereal day. Satellites in geosynchronous orbits include weather satellites, pictures from which are shown on the news each night, and relay satellites, which NASA uses to relay communications and data between spacecraft, such as the International Space Station or the Hubble Space Telescope and control centres on Earth. If a spacecraft is in a GEO and the orbit is circular and directly above the equator, as opposed to an inclined orbit, it is called a geostationary orbit (GSO). A satellite in GSO will appear to hover over one point on the Earth all the time. This means that a receiving dish on the Earth pointing at that satellite will not need to move or track the satellite across the sky. This is the type of orbit many satellite TV channels are broadcast from, and why home receiving dishes in the northern hemisphere face south and do not have to move. A group or constellation of geostationary satellites can see the Earth's entire surface between about 70° south and 70° north.

All geostationary orbits must be geosynchronous, however, not all geosynchronous orbits are geostationary. If a geosynchronous satellite is not positioned over the equator or it does not have a circular orbit, it will not appear stationary, but will appear to move across the sky. When viewed from the surface of the Earth, a satellite in a circular orbit inclined at an angle to the equator will appear to travel north and south, in a figure of eight pattern. A satellite in an elliptical orbit will trace a slanted figure of eight pattern.

To maintain a geostationary orbit, a satellite must be about 35,880 kilometres above mean sea level. If the satellite were any higher, it would circle the Earth slower than the Earth takes to rotate, any lower and it would orbit quicker than the Earth's rotation. This can be illustrated by the Moon and the International Space Station, both of which have almost circular orbits. The Moon is about 385,000 kilometres away from the Earth and takes 27.3 days to complete its orbit. This is called a sidereal month. The International Space Station, however, is only about 390 kilometres above the Earth and takes about 90 minutes to complete an orbit.

The idea of the geostationary orbit has been discussed since the early part of the 20th century. Konstantin Tsiolkovsky, Hermann Oberth and the Slovenian rocket engineer Herman Potoc-nik, who was also known as Herman Noordung, all wrote about them. However, the English author and inventor, Sir Arthur C. Clarke, is credited with the first description of the orbit for use as a global communication system. In October 1945 he published an article titled Extra-Terrestrial Relays He suggested that communications around the world would be possible via a network of three geostationary satellites spaced at equal intervals around the Earth's equator. This idea was proved in 1964 when NASA's Syn-com 3 became the first geostationary satellite, and broadcast live pictures of the Olympic games in Tokyo, Japan. The geostationary orbit is sometimes referred to as the Clarke Orbit or Clarke Belt.

As the geostationary orbit is only at one altitude above the Earth, the number of satellites that can occupy geostationary positions is limited. It is further limited by the possibility of interference between the different satellite communication channels used to provide data between the Earth and the satellite. Another disadvantage of geostationary orbits is that there is a long distance between the satellite and the ground. This either means that, compared to satellites in lower orbits, more power or larger antennas are required for communication and it also takes a long time for a signal transmitted from a satellite in GEO to reach the ground. This is why geostationary satellites are no longer used for most two way telephone calls. The main benefits of a geostationary orbit are that it remains stationary relative to the Earth's surface and it can be seen from about a third of the Earth's surface. It is therefore ideal for communications and television broadcasts, as it is not necessary to track the satellite and move the antenna. This makes the geostationary orbit one of the most popular orbits and every year a lot of money is spent getting satellites there.

### Polar Orbit

A polar orbit is where the satellite passes above or close to both the north and south poles of the Earth with each pass. As the Earth rotates below the satellite, the satellite will pass over a different region of the Earth with each cycle. Polar orbits are used to map the Earth and are also used by some weather satellites. These orbits are mainly at altitudes of about 1,000 kilometres, although some are as low as 200kilometres, and therefore the resolution of the images sent back is much higher than from geostationary satellites. These orbits are usually circular and therefore they keep almost the same height above the ground all the time. The amount or swath of the Earth seen by the satellite during each pass is dependant on the instruments on board and the altitude of the satellite. Most meteorological satellites can cover the whole globe in one day as they have a swath of about 3,300 kilometres.

### Sun Synchronous Orbit

A polar orbit that passes over the same part of the Earth at about the same local time each day is called Sun synchronous. This is useful in obtaining comparable data over a specific area. For example, air pollution over London, UK, at 9 a.m. will probably be very different to that at 9 p.m., due to variations in traffic movement at these times. To discover if the air pollution is improving or getting worse it is necessary to compare the quality at the same time each day. This could be achieved with a geosynchronous satellite, but most satellites in a Sun synchronous orbit are only about 600-800 kilometres above the Earth's surface and take about 95-100 minutes to circle the Earth.

### Medium and High Earth Orbits

At around an altitude of 1,000 kilometres up to a geosynchronous orbit, is the Medium Earth Orbit. This is particularly useful for constellations of satellites used for telecommunications.

An Earth orbit higher than a geosynchronous orbit is sometimes referred to as a High Earth Orbit.

### Highly Elliptical or Molniya Orbit

This type of orbit has an inclination of between 50° and 70°. It takes about 12 hours to complete one revolution. As a satellite travels faster at perigee and slows down at apogee, a satellite on this orbit swings by the Earth quickly, but then takes a long time over the higher altitude part of its orbit. The satellite is inserted into this orbit so that it will spend the greatest amount of time over a specific area of the Earth. For example, if communication is required in the arctic regions, a highly elliptical orbit communications satellite is launched whose orbit is configured so that is spends the bulk of its time above these latitudes. This type of orbit is also referred to as a Molniya orbit after the first Soviet communications satellites to use it.

### Parking and Graveyard Orbits

A parking orbit is a temporary orbit where a spacecraft may wait for the correct timing until other celestial bodies or satellites are in the correct alignment for rendezvous or interception missions. It can also be used to wait for the delivery of components, spacecraft or the rectification of a fault.

A graveyard orbit is where a spacecraft is intentionally left at the end of its working life so that it clears the way for other operational satellites and reduces the risk of collisions and the generation of more space debris. For satellites in geostationary orbits, the graveyard orbit is a few hundred kilometres above the operational orbit.

## Primary Source Connection

The following article was written by Mark Sappenfield, a staff writer for the Christian Science Monitor. Founded in 1908, the Christian Science Monitor is an international newspaper based in Boston, Massachusetts. The article describes the discovery of Xena, an icy world farther from the sun and larger than Pluto, and the resulting debate over what constitutes a planet by definition. In 2006, the International Astronomical Union (IAU) adopted a definition of the term “planet” that excluded Pluto, and Pluto's exact classification remains debated. The IAU has suggested that Pluto serves as the basis for a new classification called plutons—smaller planetary bodies with orbits farther from the sun than Neptune.

WHAT DEFINES A PLANET? NEW FINDS PUT THE ANSWER IN DOUBT

The discovery of an icy world beyond Pluto, and a moon circling it, points to an unforeseen diversity of objects.

WASHINGTON—the discovery of a tiny moon circling the most distant object seen in the solar system is further proof that the view of a tidy solar system with nine planets—enshrined in science-fair dioramas and school textbooks—is headed toward almost certain revision.

In July, astronomers announced the discovery of what they considered the 10th planet, an icy world that swings 9 billion miles away from the sun and is almost certainly larger than Pluto. This weekend, they declared this object, informally known as Xena, also has a most planetlike feature: a moon.

Whether Xena is in fact a planet will be the decision of the International Astronomical Union (IAU), which could instead begin a far more fundamental reexamination of what a planet is.

Whatever its final classification, though, Xena is but one in a series of new discoveries in the solar system that point to an unforeseen diversity of intriguing objects beyond the nine planets.

In the asteroid belt between Mars and Jupiter, for instance, scientists recently found the first “triple asteroid”—two asteroids orbiting a third.

In addition, they discovered that the largest known asteroid, Ceres, is probably a failed planet. It is not just a glob of rock. It is almost perfectly round, suggesting that it has a rocky core separated from an outer crust—like Earth. Only Jupiter's disruptive gravity prevented Ceres from accumulating more mass and becoming a planet.

Then again, Xena could redefine what a planet is. “It's going to reignite the planet debate,” says Marcos van Dam, who helped discover Xena's moon, Gabrielle.

The planet debate dates back to 1930 and the discovery of Pluto. Even then, Pluto was seen as an oddity—a tiny ball of ice wheeling among gas giants on an unusually elliptical orbit tilted far above and below the plane of the other eight planets. Yet in 1930, Pluto was unique, so it was deemed a planet.

Now, astronomers have found other worlds like Pluto in the Kuiper Belt—a band of frigid and far-flung objects beyond Neptune. Last year, they found Sedna, a curiously reddish body with its own moon. Now, with Xena, they have found a Kuiper Belt object larger than Pluto, and they could find scores more such “planets”—leading IAU to reconsider the term.

None of them, however, will probably be named after TV show characters, like Xena the Warrior Princess. Xena is technically named 2003 UB313 and will remain so until the IAU decides whether it is a planet. And IAU chooses the name itself.

Mark Sappenfield

sappenfield, mark. “what defines a planet? new finds put the answer in doubt.” christian science

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