Quickie Questions - Solar System - Other

Date Answered Questioner (age, location) Question Answer
March 20, 2011frankI don't know what the "2012 riddle" is. I read that some people believe there will be a global transformation or catastrophe in 2012. Like many predictions, that one may or may not be true, but I find no scientific basis for believing it. Science is concerned with predictions that can be tested by experiment or observation.
May 10, 2010Shani (nj)is titan the largest moon in the solar system?Titan is the largest moon of the planet Saturn. Titan is the second largest moon in our Solar System. Jupiter's moon Ganymede is the only moon in our Solar System that is larger than Titan. Titan is larger than the planets Mercury and Pluto!
April 26, 2010isacc (florida)is their any other planet out thereWith the new clasification of Dwarf Planets, there a list of new planets that keeps growing. There are also extrasolar planets, or planets found orbint a different star than our sun.
April 26, 2010Luis (Florida)Why isn't Sedna listed as one of the dwarf planets?90377 Sedna is a trans-Neptunian object and a likely dwarf planet discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. Sedna currewntly is a dwarf planet candidate. Visit our web page New planetoid named Sedna discovered for more information.
April 22, 2010angela (ohio)why is it called the gas planetThe interior or rocky planets (Mercury, Venus, Earth, and Mars)are mostly made up of rock and metal. These planets are very heavy and move slowly. The giant, jovian or gas planets (Jupiter, Saturn, Uranus, and Neptune) are composed primarily of hydrogen and helium and generally have low densities, rapid rotation, deep atmospheres, rings and lots of satellites.
April 21, 2010Taylor (USA)Which takes the most amount of time? Earth rotates once or Earth revolves once or The moon revolves once or All take the same amount of time.Our planet Revolution Period about the Sun (Length of a Year) is 365 days 5 hrs, and its Rotation Period with respect to Sun (Length of Day) is 24 hrs. It takes the Moon the same amount of time, 27.322 days, to rotate around once as it does for the Moon to go around the Earth once.
April 20, 2010carol (south carilina)how many mercury's fit in one earth?The diameter of ou planet is 12 753 km (7,926 miles). The diameter of Mercury is 4 878 km (3,030 miles), or about three times smaller. So, for covering the face of Earth a little less than 3 mercuries would be lined end to end. Now, if we want to fit mercuries inside our planet, like marbles inside a bowl, then we will have to stretch the marbles in the bowl, or the mercuries in the earth, in three directions; up-down, in-out and left-right, or 3 x 3 x 3 = 9 (remember that it actually is less than 3 mercuries side by side, so the actual result is less than 9.)
March 30, 2010Albie (India)How did the Solar System Begin?How will it end?You can find the answer to your question in our page Solar System Formation.
March 25, 2010lou ()What is Ganymedes atmosphere made up of?Our web page Ganymede's Atmosphere discusses this topic.
March 25, 2010blake (australia)the distance between mercury and venus pleaseMercury’s orbit varies from 46 to 70 million km from the sun while Venus has a very circular orbit, averaging about 108 million km. So when Mercury and Venus are lined up on the same side of the sun, with Mercury at aphelion, they are just 38 million km apart.
March 24, 2010kimberly dasig (philippines)what are the other planetsMercury, Venus, Earth, and Mars are the interior planets. The giant planets are Jupiter, Saturn, Uranus and Neptune. The dwarf planets (so far) are Ceres, Pluto, Haumea, Makemake, and Eris. Abundant information on all of them can be found on our web page Our Solar System.
March 10, 2010kim (ks)what is the distance from earth to uranus in AU?Uranos mean distance to Earth is 21.084 AU. Our page How far is the Earth from the Sun, the Moon and all the other planets? explains how to calculate the actual distance from the other planets to the Earth.
March 5, 2010Madison (ME/USA)What is gravity like on all the other planets?The value of the planets' gravity at their surface is: Mercury: 3.7 m/s2 (0.38 x Earth's) Venus: 8.87 m/s2 (0.90 x Earth's) Mars: 3.7 m/s2 (0.37 x Earth's) Jupiter: 23.12 m/s2 (2.64 x Earth's) Saturn: 8.96 m/s2 (0.92 x Earth's) Uranus: 8.69 m/s2 (0.89 x Earth's) Neptune: 11 m/s2 (1.12 x Earth's) Pluto: 0.58 m/s2 (0.06 x Earth's)
March 5, 2010Amanda ( Australia)Are there Tectonic plates on other rock planets?There is no evidence for tectonic plate in Mercury and Venus. There is no final consensus about Mars. Some scientists believe that the patterns of magnetic striping observed in 1999 by the Mars Global Surveyor were a proof of tectonic plate, but other pointed to the lack of "magnetic reversal", a test used to see if they were formed by flipping polarities of a global magnetic field.
February 23, 2010eliglio (kansas)what is the average tempature between venus and the sunI am not sure what is your question about, so I will give you some numbers. Venus average temperature is 457oC (855oF). Temperature at Sun's surface is 5,500oC (9,932oF).
February 17, 2010Steve (Wisconsin,USA)I'm currently trying to understand celestial mechanics and what the various orbits look like visually,especially the moon. Where can I find some high quality graphic information showing all of the planetary relationships to the sun and each other,i.e. inclination,elliptical configurations, eccentricities,barycenters etc.Our website has many tools that could help with your interest. For example, the page Our Solar System links to each planet, and there you can find the orbital information of each one (click on "Planetary Facts"). The page Interactive Comet Animation is a useful tool to visualize the characteristics of orbits, and our page Orbital Data for the Planets & Dwarf Planets gives you all the orbital onformation in a table form.
February 16, 2010mounila (Rwanda)my friends told me that the researchers have a new planet is it really true?
There is a recent created classification known as Dwarf Planets. New planets (in our solar system) are part of this group. Some of them are Ceres, Pluto, Haumea, Makemake, and Eris.
February 5, 2010Cynthia What is the size of our Solar System?There is no final answer to this question, because there are many ways to calculate the reach of the Solar System. One of the most common is to use the orbit of Pluto as the limit (which leaves out the Kuiper Belt and the Oort Cloud). So, we will use the average distance between the Sun and Pluto as the radius of the Solar System, which is 5,913,520,000 km, or 39.5 AU (Astronomical Unit).
February 5, 2010Jayla (Ohio)how far is Neptune from Uranus approximatelyThe closest approach between the two orbits is 9.80523772 AU (a little more than 911 million miles).
January 25, 2010Lory (Guam)What are the names of the planets and how many are there?Our web page Our Solar System responds your questions and offers much more information on the planets, moons, comets, etc.
January 25, 2010Lory Ngirailild (Guam)What are the names of the planets and how many are there?Our web page Our Solar System responds your questions and offers much more information on the planets, moons, comets, etc.
January 11, 2010Becca (UK)Whereabouts is the Solar System in our galaxy?Our Solar System is about 26 000 light-years from the center of the Milky Way Galaxy, which is about 80 000 to 120 000 light-years across and less than 7 000 light-years thick. The solar system is situated within a smaller spiral arm, called the Local or Orion Arm, which is a connection between the Sagittarius Arm and the Perseus Arm.
January 8, 2010yy (oklahoma)what color is eris's moonSee by yourself this picture of Dysnomia, the moon of Eris.
January 5, 2010Vaneh (pennsylvania)What is a Jovian planet?Jovian planets are also known as gas giants. There are four Jovian planets: Jupiter, Saturn, Uranus, and Neptune. They are the outer planets. The term Jovian came from Jupiter.
January 4, 2010Juri (I live in Japan)Which of comets,asteroid,or meteors have slightly elliptical orbits?Comets, as planets, have elliptical orbits.
January 4, 2010Jill (United States)How did all the planets(except mercury,) come to have an axial tilt. I need an exact explanation.I don't think there is an exact explanation. The most widely accepted theory is that during the formation of the Solar System objects of significant masses, probably protoplanets, collided with them, causing the tilt of the axis.
December 28, 2009Andrew (USA)Where is the position of the Sun in the elliptical orbits of each planet?The position of the Sun is always in ine of the focuses of the ellipse.
December 22, 2009Raymond (L.a)why is pluto not a plantetPluto is still a planet, although it is now clasified as a Dwarf Planet
December 22, 2009Julia (Nigeria)Is planet sedna still in existence and its statistics and its features.please help me, i couldnt get anything in the web? THANK YOU for your timeThere is no much information known about Sedna, it is way too far! Visit our web page Sedna for more information.
December 17, 2009Venetia (Florida)How many moons does the dwarf planet Eris have?Eris is a dwarf planet in our Solar System. Eris was one of the first three objects classified as a dwarf planet, along with Pluto and Ceres. Eris was first spotted in January 2005. Eris has a moon named Dysnomia.
October 27, 2009Aylla (massachussets)why is pluto not a planet anymore?PLuto was just reclasified as a dwarf planet, a recently defined grup. See our web page Dwarf Planets for more information.
October 27, 2009jahnavi (India)why are planets useful to us?The study of other planets offers information about the origin of the solar system, and of our own planet. This permits us better understand, and care for our beautiful Earth.
October 27, 2009yajna (Madhya Pradesh/ India)what is volcano& how it is formed?A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanoes form when hot material from below rises and leaks into the crust. This hot material, called magma, comes either from a melt of subducted crustal material, and which is light and buoyant after melting, or it may come from deeper in the interior of a planet and is light and buoyant because it is *very* hot.
October 16, 2009faiqah (johor)how long that the 9 planet do a complete circle[in minutes]Each planet complete a rotation about their own axis in: Mercury: 1407.6 hrs Venus: 5832 hrs Earth: 24 hrs Mars: 24.6 hrs Jupiter: 9.8 hrs Saturn: 10.67 hrs Uranus: 17.24 hrs Neptune: 17.24 hrs Pluto: 153.29 hrs Each hour is 60 minutes long, it is ver easy to calculate these periods in minutes!
October 13, 2009dominic (california)is the earths moon a planetNO, planets orbit around stars, moons orbit planets.
October 13, 2009CLA-OR (PHILLIPPINES)WHAT'S THE LATEST PLANET DISCOVERED?There have been several recent discovery of planets orbiting other stars. If you ask about new planets in our solar system, the latest discoverd are all Dwarf Planets: Eris, 2005 Makemake, 2005 Haumea, 2003 - 2005 Ceres, 1801
October 8, 2009srujan (india)why does the acceleration due to gravity changes from one planet to other planet?The acceleration of gravity is a direct result of the action of the gravitational field of a planet over objects nearby. The gravitational force is proportional to the product of the masses (in this case, the mass of the planet times the mass of the object) and inversely proportional to the square of the distance between them. Because the mass of the planets are different, their gravitational pull, and therefor their acceleration of gravity, are different.
September 30, 2009Philip (London, England)Why are the rings of Jupiter at the centre?

Is there more gravity at the centre in which case are people who live near the equator heavier than people in England!
The position of the rings is related with the centrifugal force (from Latin centrum "center" and fugere "to escape"), which represents the effects of the inertia related with the rotation. These forces are experienced as an outward force away from the center of rotation.
September 30, 2009Robert (Australia)Witch planet except the Earth was first discovered?Only three of the nine planets have official dicovery dates. They are Uranus, Neptune and Pluto. The rest of the planets are easily seen with the unaided eye, and have been known since ancient times.
September 14, 2009Bryce (Colorado)What is spin?Spin, in the context of the celestial bodies, is the continuous rotation of a planet or moon around its own axis.
August 20, 2009niranjan (india)why does planets rotateThe motions of the Sun, planets, and the rest of the solar system objects are primarily related to the original motion of the solar nebula from which the system was formed.
February 3, 2003Samantha (California, USA)What is the difference between moons and planets?

Planets orbit around the Sun. Moons orbit around a planet.

Some moons are actually as big as, or larger than, some planets. For example, Ganymede, one of the moons that orbits the giant planet Jupiter is larger than Mercury (one of the smallest planets).

January 30, 2003Chris (England)Who gave the planets in our solar system their symbols?The symbols that we use for each planet come from the Celtic people who once lived in the British Isles as well as other places in Europe.

November 22, 2002Wendy (England)Planet, star, moon, universe, galaxy, sun and solar system. Put in order starting with smallest first:The correct order (from smallest to largest) is moon, planet, sun/star (the sun is a star), solar system, galaxy, universe.

June 6, 2002Alexandra (Illinois, USA)What information can you give me on the planets' orbits? I have a huge math project due and I can't find anything!Here's a table of orbital data for the planets. I hope that helps!
May 18, 2001Miranda (15, USA)How would you relate the planets and space to geology?Geology has traditionally been thought of as the study of the history of the Earth and its life especially as recorded in rocks. But even Merriam-Webster has updated its definition of geology to include "a study of the solid matter of a celestial body." Many of the spacecraft sent to other planets have shed new light on the geology of these planets and their moons (what is the surface made of, what are rocks like on that planet or moon, are there plate tectonics, volcanoes, or a magnetic field on this body?).

Here are just a few of the pages we have that deal with planetary geology (where the fields of geology and space science merge!): Mars Interior and Surface, rocks explored by the Mars Pathfinder, Venus Interior and Surface, Volcanoes of the Solar System, and the Moon's geology.

April 24, 2001Allysa (11, Manitoba, Canada)I would like to know,if I am making a model of the solar system,what should I know?We actually have a solar system Model Builder guide that may help you!
March 7, 2001Jasmine (USA)What are the orbital speeds of the Planets??We just updated our orbital data page. You'll find the orbital speeds of the planets there!
February 19, 2001Pauline (Northern Ireland)What is an Elliptical orbit ?Kepler first figured out that the planets travel in elliptical orbits around the Sun and not circular orbits!
January 29, 2001Sparks (Canada)How many moons are in the solar system?Well, there have been lots of moon discoveries lately...but, as of this week, there are 78 known moons in the solar system.
December 22, 2000Meredith (Texas, USA)Is there a chance that astronauts will ever have the technology to travel to further planets or other galaxies???The International Space Station is actually being built with planet colonization in mind. Once we learn better how to live in space, we'll better know how to set up a colony on the Moon or Mars. So, yes, I think humans may very well end up on some other planets by the end of this century...other galaxies...that could be a while!
November 20, 2000Lauren (Georgia, USA)Of the nine planets,which number would earth be from the sun?It's the 3rd rock from the Sun!
October 31, 2000Jack (Massachusetts, USA)One word answer to the following question: An early stage in the formation of a planet is called?Is this for a crossword puzzle? answer: protoplanet
July 26, 2000unknown What, exactly, is the proto-planet hypothesis?As the solar system formed, the planets started as protoplanets. You can ready about this theory by clicking the protoplanets link.
June 30, 2000Jimmy (Singapore )If comets from afar can be attracted by Sun's gravity, and Pluto is also orbiting around the Sun, how come Mercury with its small size & density cannot be sucked towards by the Sun, considering its sheer size & stronger gravity?

Planets don't fall into the Sun because they exert a forward force that opposes the force of gravity from the Sun. Planets that are closer to the Sun (like Mercury) must move faster in order to stay in orbit.

You can recreate this experiment yourself. Take a ball with a string on it and twirl it around. Notice how fast you must twirl to keep the ball going around in a circle and not falling.

Now, make the string shorter, and you'll notice that you have to swing it around faster. Make the string longer, and you won't have to work as hard!

June 26, 2000Susan (California, USA )What is the cause of retrograde motion of the inferior planets?

Scientists don't know for sure. The current theory is that some large object crashed into the planets with retrograde motion: Venus, Uranus and Pluto. At one time, these planets most likely had "normal" motion. The collision would have forced them the other way.

June 16, 2000Alex Which is larger, Earth or Mars???The Earth (diameter 7,926 miles) is larger than Mars (diameter 4,217 miles).
June 1, 2000Maria (Florida, USA)What is the difference between a planet and a comet?

There are many differences between comets and planets. Comets tend to be much, much smaller than planets.

One of the biggest differences is type of orbit. Planets have a rather exact elliptical orbit, but comets don't. Although some, like Comet Halley, do have orbits that revolve around the Sun, others just fly through the solar system.

May 15, 2000Xavier (California, USA)Is there water in space?

Yes, if you include ice! The temperatures of space are too cold for liquid water. However, comets are made of ice, and there may be ice on some planets and moons.

February 9, 2000Charles (Louisiana, USA)Is our solar system in the same plane as our milky way galaxy? Are all solar systems in our galaxy in the same plane as our milky way galaxy?The plane of the solar system, called the Ecliptic which runs along the Zodiacal belt of constellations, is tilted about 60 degrees to the plane of the Milky Way.

There is no physical reason why these two planes should be identical. Stars have their rotation axis pointed at random in space, and the plane of the solar systems that orbit them should also be oriented pretty much at random with respect to the Milky Way.

February 8, 2000Pat (Washington, USA)Why do only gas planets have rings?We actually don't know why only certain planets have rings. It may have something to do with the size of the planet, since only larger planets have them. Or, it might have something to do with their distance from the Sun: possibly being too near the Sun's gravity makes rings unstable.
January 11, 2000Katy (Florida, USA)which planet is spinning the fastest?Jupiter spins faster than any other planet. One day is 9 hours and 55 minutes long. Earth's is 24 hours! Saturn is not far behind Jupiter. A single day on Saturn takes a whopping 10 hours and 14 minutes.
January 11, 2000Amanda (Maryland, USA)Why do the planets have a maximum and minimum distance from the sun?The planetary orbits are in the shapes of ellipses, or ovals. That means, since the Sun is in the center, the planets will be farther away at the long end, and nearer on the side of the ellipse.
December 24, 1999Jason(Illinois, USA)When I was younger, I was taught a mnemonic device for remembering the order of the planets? Are you familiar with a good one?This is the one I learned when I was young: My Very Educated Mother Just Showed Us Nine Planets is one...Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. There are quite a few, this is just one...
November 20, 1999Jennifer (Utah, USA)What determines a planet and how do they decifer just an orbiting object in space?Conventionally, a planet is defined by three properties.
1) It must be orbiting a star.
2)It must not be a star or star-like object.
3)Its self-gravity must be enough to hold it in the general shape of a sphere.
Sometimes the line is not always exactly clear between what is a planet and what is not...hence the debate on whether or not Pluto is actually a planet (it is).
November 15, 1999Mary (California, USA)how many planets and moons have atmostspheres altogether?Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto all have atmospheres. Only five moons in the whole solar system have atmospheres (Europa, Io, Ganymede, Titan and Triton).
July 15, 1999Arturo (Germany)Why do all the planets in our solar system orbit around the sun in the same direction? Could planets in other solar systems orbit their sun's the other way around?All the planets orbit the Sun in the same direction (counter-clockwise as seen from above) because of the way the solar system formed. The cloud of gas which are solar system formed in began to rotate the planets simply formed within the same rotation as the cloud they came from. It is perfectly plausible that other planets rotate their stars the other way around since the orientation of stars and the rotation of their planets is random. In fact, the plane of the Ecliptic in our solar system is tilted about sixty degrees to the plane of the Milky Way.
June 3, 1999Chris (New Jersey, USA)When is Mercury visible?This page will tell you what appears in this week's sky....
May 13, 1999Carly(British Columbian, Canada)Why do scientists suspect a black hole just on the outer edges of the Solar System and what are the chances of it really being there?You can find the answer here.
May 12, 1999Codi(Oregon,USA)why isnt there gravity on other planets? Is there life on the other planets besides earth? Are you a real scientist and whats you name? Are you famous? Have you been on any other planet before? How old are you? Are you telling me the truth?Boy oh boy, you sure have a lot of questions! All planets have gravity. Some planets have more than others. Right now, we know that only Earth has life, although we are always look ing for others. Yes, I am a real scientist!(Although I just joined the Windows team recently) No, I'm not famous.... YET. I haven't been on any other planet- that I know of. I'm a lot older than you.... And of course I'm telling you the truth! Scientists don't lie!
January 19, 1999Morgan If we looked up at the sky from a different planet, what colors would we see and why would we see them?That would depend on what planet we were on. If we were on a planet with no atmosphere, we would see a perfectly black sky both at day and night. On Mercury, for example, which has a very little bit of atmosphere, we would be able to see stars and t he Sun, but the sky would be pitch black, even in the middle of the day. On Jupiter, the sky might be white because of suspended ice particles. On Mars, we know from pictures taken that the sky is red because of all the dust there.
January 12, 1999Victor Are planets of the solar system lying on a plane? Why is this?Yes, they are, more or less. The reason for this is that when the solar system formed, it was formed from a collapsing disk of spinning gases, with a bulge in the center which became the Sun.
November 30, 1998Rachelle What are the chances of a blackhole at the end of our solar system that is going to wipe us out. If so is this the reason some of the outer planets spin so fast? Is there a better chance of it being a blackhole or a planet x? Should we be worried? There is no black hole near our solar system (they are still only theoretical), and there is no Planet X. So, there is no reason to be worried about that!
November 19, 1998(Illinois, USA)Can trees grow on another planet?None of the planets in our solar system other than earth have the conditions necessary to support plant life (ex. oxygen, water, correct temperature, etc.)
September 1, 1998WendelWhat is the last and next time the planets of the solar system will all be in a line?All nine planets won't all be in a line (perfect alignment) in the predictable future. In 1982 there was a "grand alignment," which occurs every 176 years, with all nine planets on the same side of the sun. So the next grand alignment looks to be in 2158.
July 15, 1998Jim (North Carolina, USA)How was the age of the Sun determined? How about the Planets in general?The solar system is thought to be about 4.6 billion years old. Here's how scientists get that number.
June 22, 1998Sunshine (Michigan, USA)What keeps the planets in orbit?The Sun's gravity is what keeps the planets in orbit. Without gravity acting as the centripetal force (the pull toward the center of the Sun), the planets would move off in a st raight line into outer space!
June 19, 1998Nitisha (New Zealand)What are planets made from? What are the rings on some planets made from?The terrestial planets (Mercury, Venus, Earth and Mars) are composed mainly of rock and metal. The Jovian or gas planets (Jupiter, Saturn, Uranus, and Neptune) are made up of mainly Hydrogen and Helium gas. Pluto is made of both rock and ice.

The rings of planets seem to be made of water ice chunks and then some rocky pieces with icy coverings.

June 16, 1998Lauren (California, USA)What does planet mean?Planet comes from the Greek word for wanderer or to wander.
June 16, 1998Jenessa (California, USA)How/why can tiny (i.e.postage stamp size ) debris travel through outter space at a such high rate of speed? What would happen if one of these postage stamps hit the Space Shuttle?Even small specks of paint travel at speeds of about 17,500 miles/hour. The space shuttle is hit by orbiting bits of paint or ice particles from earlier missions. These impacts with such minute particles cause minimal damage (scratching the surface of the shuttle, causing small dents), but enough so that the International Space Station will have a bumper to absorb stray particles.

Each time the shuttle does go into orbit, it runs a one in a million chance that it will be hit by a trackable piece of space debris (those objects that are greater than eight inches in diameter). A crash with s uch an object would cause an explosion many times that of a hand grenade. The explosion could be fatal to any astronauts onboard.

June 8, 1998Jim (North Carolina, USA)I would like to know how Astronomers know how far things are away from us and how big things are. For that matter how was the sizes of our own planets in our own Solar System determined as well as their distance?The method for determining distances to objects actually depends on how far away the object is. Distances to planets were first well-determined by Copernicus using simple observations of the positions of the planets. Relatively nearby objects beyond the solar system will appear to shift position relative to distant objects as the Earth moves from one side of the Sun to the other. This effect is called parallax, and you experience it everyday. Parallax gives reliable distances to stars up to about 1 00 parsecs. But 100 pc isn't very far, little more than the solar neighborhood. Distances to galaxies can be determined via Cepheid variable stars, and many other methods.

Once distances are known, it's not hard to get sizes. Suppose you hold a quarter at arm's length, and then have someone take that quarter 100 yds away. Obviously the quarter appears smaller, though it's real size hasn't changed. If yo u know how big it appears and how far away it is, you can work backwards and figure out how large the quarter really is. Astronomers can measure how big something appears to be on the sky, and if they can figure out it's distance, they can calcul ate how big it really is.

April 16, 1998Freddy (New York, U.S.A.) How was it proven that the Sun is the center of our Universe?Well, as far as I've heard, the Sun is not at the center of the universe. In fact, the Sun is not even the center of our Milky Way galaxy. The center of the Milky Way is found by looking in the direction of the constellation Sagittarius. Sagittarius is a summer constellation in the northern hemisphere, so you should be able to look that way soon!
April 3, 1998Eric (Rhode Island, U.S.A.) How do planets get their rings?We don't really know where the planetary rings come from. They are probably pieces from collisions between the planets and stray asteroids. Perhaps too they are leftover pieces of material that never got together to become moons. These pieces of ma terial are held in orbit by the planet's gravity.
March 24, 1998Ann (Michigan, USA) Can planets be considered 'stars'??Stars give off energy. Since our planets simply reflect the energy of the Sun they are not considered to be stars.
March 17, 1998L (Australia) What is the role of planetismals in planet formation ?Planetismals were the smaller, comet-sized objects out of which the planets were formed. As solid material began to condense out of the solar nebula, they swept together to form boulders. They could stick together because they were a little warm & soft, kind of like "silly-putty". Eventually a larger group of planetismals would crash together and form the core of a planet. the remaining Planetismals would then crash onto the large planet-sized object which was building up. Near the end of this pr ocess, planetismals would create craters on the surface. Some of these craters can still be seen today on the moon & some planets like Mercury which have not experienced surface change since those days.
March 4, 1998Glenn (Wisconsin, USA) Is it true that there is a molten planet before Mercury? If there is, could you send me a picture?No, Mercury is the planet closest to the Sun.
March 3, 1998Linda (North Carolina, USA) What is the 'entire'(estimated) mass of the Kuiper Belt by itself and what is the 'entire' (estimated) mass of the hypothetical Oort Cloud? How could you do an experiment to prove that that these objects to prove that they would effect the orbits of Uranus and Neptune?We don't really know the masses of either object. However, the mass of the Kuiper belt is probably close to the mass of Jupiter, say 2x10^27 kg. The Oort belt is estimated to be in the range of 1.5x10^25 kg. Astronomers don't do experiments to see if these objects would affect the orbits of the planets. They look for any tiny irregularities in the predicted orbits of the planets. These irregularities mean that possibly there is some object like the Kuiper Belt or the Oort Cloud that has a strong gravitational pull which is altering the path of the planet.
February 11, 1998Mark (Holland)I've heard that in the year 2000 all seven planets will be on a row. Is there any danger that the gravities of the seven planets is so much that they will start to attract each other ? Or is there anything to worry about?On May 5, 2000, Mercury, Venus, Mars, Jupiter and Saturn will all be within 16 degrees of the sun. They will not really be in a line, but they will all appear close together. Since they will be so close, many astronomers are calling this occurence a Grand Conjunction. There is definitely no danger of their gravity affecting us. There have been many conjunctions in the past, none of which have had a noticable effect on the Earth. And the planets are too still too far away from each other to effect each other's orbits.
January 29, 1998Cheryl (Alberta, Canada)Does our solar system have a name, or is it just called 'The Solar System'? If it does have its own name, what is it?Our Solar System is just called the "Solar System." 'Solar' means "of the Sun", which is the central part of the entire group of planets, moons, and space debris that make our Solar System.
January 28, 1998Katya and Cynthia (Illinois, USA)How big does an object that is circling a planet have to be to be considered a moon? Can big rocks within the rings of Saturn or Jupiter be called 'moons'?As far as I know, there is not a lower limit on the size of a moon. In other words, moons come in all shapes and sizes! Ganymede, the largest moon of Jupiter, is 3,166 miles (5,276 kilometers) in diameter w hich is larger than the planets Mercury and Pluto! One of the Saturn's smallest moons is Helene which is only 10 miles across!
I do know that for a moon to be officially added to the list of satellites, there must be at least 2 photographs of it, it must have a predictable orbit and it must not be a part of a ring system.
January 13, 1998Dirk (Wisconsin, USA)How are the densities of the other planets in the solar system determined?Density is the mass of an objecty divided by its volume. Scientists determine the mass of planets by looking at properties such as their pull on nearby objects. They also look at what the planets are made of, using data gathered by the space probes. Using this information, and knowing how big the planets are, they can use the above formula and find the densities of the planets.
January 5, 1998Jackson (Melbourne, Australia)Why do planets spin as they orbit the sun?The planets have been spinning since the beginning of the solar system, when they were formed. Since they are already spinning, they will continue until something stops them. This is called the conservation of linear momentum.
December 8, 1997DavidWill we be able to live on other planets?Probably. Mars is the most likely planet humans will try to colonize first since it is more similar to Earth than any of the other planets. NASA plans to send a manned mission to the Red Planet by the year 2020. See Audrey's question below for link s to other questions about inhabiting Mars.

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